AJP - Heart Watch the video to learn how APS reaches out to developing nations.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Heart Circ Physiol 289: H1542-H1550, 2005. First published June 3, 2005; doi:10.1152/ajpheart.01024.2004
0363-6135/05 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
289/4/H1542    most recent
01024.2004v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (4)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Li, M.
Right arrow Articles by Stallone, J. N.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Li, M.
Right arrow Articles by Stallone, J. N.

Estrogen potentiates vasopressin-induced contraction of female rat aorta by enhancing cyclooxygenase-2 and thromboxane function

Min Li1 and John N. Stallone1,2

1Department of Veterinary Physiology and Pharmacology, and 2Michael E. DeBakey Institute for Comparative Cardiovascular Science, College of Veterinary Medicine, Texas A&M University, College Station, Texas

Submitted 7 October 2004 ; accepted in final form 1 June 2005


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
To determine the roles of estrogen and constrictor prostanoids in vasopressin (VP)-induced contraction of female rat aorta, vascular reactivity to VP was determined in thoracic aortas of intact, ovariectomized, and ovariectomized + estrogen-replaced female rats in the presence of indomethacin (Indo), NS-398, SQ-29,548, or vehicle control. The effects of estrogen on vascular reactivity to the thromboxane A2 analog U-46619 were also examined. Maximal contractile response to VP in intact female rats (5,567 ± 276 mg/mg of aortic ring wt) was markedly attenuated by ovariectomy (2,485 ± 394 mg; P < 0.001) and restored by estrogen replacement with 17{beta}-estradiol (5,059 ± 194 mg; P > 0.1). Indo and NS-398 significantly attenuated maximal responses to VP in intact female rats to a similar extent [3,176 ± 179 (P < 0.0001) and 3,258 ± 152 mg (P < 0.0001), respectively]. Ovariectomy abolished and estrogen replacement restored the inhibitory effects of Indo, NS-398, and SQ-29,548. Contractile responses of rat aorta to U-46619 were significantly greater (P < 0.0001) in females (5,040 ± 238 mg) than in males (3,679 ± 96 mg). Ovariectomy markedly attenuated (3,923 ± 84 mg; P < 0.01) and estrogen replacement restored (5,024 ± 155 mg; P > 0.1) responses to U-46619 in female aortas. These data reveal that estrogen is an important regulator of the contractile responses of female rat aorta to VP, which appears to potentiate both cyclooxygenase-2 and constrictor prostanoid function in the vascular wall.

arginine vasopressin; constrictor prostanoids; indomethacin; NS-398; SQ-29,548; U-46619; vascular reactivity; vasoconstriction

VASOPRESSIN (VP) IS AN EXTREMELY potent vasoconstrictor that functions in the short- and long-term control of blood pressure during hypovolemic states such as hemorrhage or dehydration (34, 47). Previous studies revealed that a marked sexual dimorphism exists in the vascular reactivity of the rat to VP. Contractile responses of female rat aorta to VP are three- to fourfold greater than those of male aorta (19, 51, 52, 54), and similar sex differences exist in the reactivity of rat mesenteric vasculature to VP (1, 53, 56). The presence of gonadal steroid hormone receptors in both endothelium (2, 13, 14) and vascular smooth muscle (VSM; Refs. 2, 25, 37, 39, 42) of the vascular wall suggests that female gonadal steroid hormones may influence VSM and/or endothelial functions and thereby mediate sex differences in vascular reactivity to VP and other vasoconstrictors. Previous studies also established that VP-stimulated release of nitric oxide (NO) is much greater in male rat aorta and is responsible for the markedly attenuated responsiveness to VP compared with females (51, 52). Interestingly, even in the presence of NO synthase (NOS) inhibition, contractile responses of rat aorta to VP are still significantly higher in females, and the cyclooxygenase (COX) inhibitor indomethacin (Indo) attenuates contractile responses to both VP (51) and the {alpha}-adrenergic agonist phenylephrine (PE; Ref. 19) in female but not male aorta. These data suggest that constrictor products of COX may contribute to the enhanced vascular reactivity of female rat aorta to both VP and PE.

In the present investigation, the effects of estrogen on the contractile responses of thoracic aorta to VP were examined in intact, ovariectomized, and ovariectomized + estrogen-replaced female Sprague-Dawley rats. The role of COX products, especially thromboxane A2 (TxA2), in modulating vascular reactivity to VP was determined by the use of COX pathway inhibitors. The role of estrogen in modulating constrictor prostanoid function was further examined by determining vascular reactivity to the TxA2 analog U-46619 in thoracic aortas of male and female rats.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animals

Age-matched (14–18-wk old) female and male Sprague-Dawley rats (Harlan; Houston, TX) were used in all studies. The rats were housed in vivarium facilities at the College of Veterinary Medicine (Laboratory Animal Resources and Research facility) with controlled temperature (22–24°C), relative humidity (~50%), and lighting (12:12-h light-dark cycle). The animals were segregated by sex and housed in pairs in standard plastic laboratory rat cages. Tap water and standard laboratory rat chow (Harlan; Indianapolis, IN) or an alfalfa- and soy-free diet (7% corn oil diet; Harlan TekLad) was provided ad libitum. This latter special diet is free of phytoestrogens, which are often present in commonly used standard laboratory rat chow (45, 46) and have been reported to confound the effects of ovariectomy on vascular reactivity to VP (19). All experiments were reviewed and approved by the Texas A&M University Laboratory Animal Care Committee.

Animal Preparations

Animals were randomly separated into four experimental groups: males, intact females (Int-F), ovariectomized females (Ovx-F), and ovariectomized + estrogen-replaced females (Ovx+ER-F). Because previous studies established that contractile responses of female rat aorta to VP or PE do not differ with phase of the estrous cycle (54), female rats were studied without regard to estrous cycle status. For each experimental group, sample sizes of 5–9 rats were used to account for known levels of statistical variability in vascular experiments in vitro. Bilateral ovariectomy of female rats was performed at 4–5 wk of age using standard methods. Half of the Ovx-F rats received estrogen replacement therapy (ERT) beginning at 8–9 wk of age for 21–28 days using 17{beta}-estradiol (two 0.05 mg, 60-day release pellets). Previous studies have shown that this dose produces physiological plasma levels of 17{beta}-estradiol in Ovx-F rats (61).

Preparation of Isolated Thoracic Aortas

Animals were killed by rapid decapitation in accordance with American Veterinary Medical Association guidelines (3). Trunk blood was collected at the time of decapitation for radioimmunoassay (RIA) of plasma 17{beta}-estradiol (see RIA of plasma estradiol). The thoracic aorta was rapidly but gently removed to avoid stretching or damaging the endothelium and was placed in chilled (4°C), gassed (95% O2-5% CO2) Krebs-Henseleit bicarbonate solution (KHB). The KHB was composed of (in mM): 118.0 NaCl, 25.0 NaHCO3, 10.0 glucose, 4.74 KCl, 2.5 CaCl2, 1.18 MgSO4, and 1.18 KH2PO4 (pH 7.40; osmolality, 292 ± 1 mosmol/kgH2O). The aorta was cleaned of all adipose and connective tissue, and the mid-thoracic region was cut into rings (3 mm long). Aortic rings were studied either with the endothelium intact (Endo+) or denuded (Endo–), which was accomplished by gently passing a frayed nylon string through the lumen (51). The rings were carefully mounted on two 25-gauge stainless steel wires; the upper one was attached to a force-displacement transducer (model FT-03D; Grass Instruments; Quincy, MA) for measurement of isometric tension, and the lower one was attached to a stationary stainless steel rod and micrometer that allowed for adjustment of passive tension in the aortic rings. The transducers were connected to a polygraph (model 2600S; Gould; Cleveland, OH) to provide a continuous record of contractile tension.

Isometric Tension Studies

Immediately after being mounted, aortic rings were immersed in water-jacketed organ baths filled with 15.0 ml of warmed (37°C) KHB and continuously gassed with 95% O2-5% CO2. Passive tension was then gradually (over a 30-min period) increased to 2.50 g, which is the optimal tension for male aortas and both intact and ovariectomized female aortas as established in previous studies (51, 52, 54). The rings were allowed to equilibrate for 90 min, and the KHB was replaced with fresh gassed and warmed KHB every 20 min. Passive tension was adjusted to maintain 2.50 g throughout the equilibration and experimental periods. After the equilibration period, the aortic rings were stabilized by two successive near-maximal contractions with PE (10–6 M final concentration). After each contraction reached a stable plateau tension, the endothelium-dependent vasodilator acetylcholine (ACh) was added to the baths (10–7 M) for assessment of functional integrity of the endothelium. The baths were rinsed twice, and the aortas were allowed to reequilibrate in fresh KHB for 30–45 min before further experimentation.

Experimental Protocols

Effects of prostanoid pathway inhibitors. The effects of constrictor prostanoid pathway inhibitors on vascular reactivity to VP were examined by obtaining cumulative concentration responses to VP (10–11 to 10–6 M) in Endo+ aortic rings from Int-F rats in the presence of the following: 1) the nonselective COX inhibitor Indo (10 µM); 2) the COX-2-selective inhibitor NS-398 (NS; 10 µM); 3) the PGH2/TxA2 receptor antagonist SQ-29,548 (SQ; 1 µM); or 4) vehicle control (0.13% DMSO). Duplicate or triplicate rings prepared from each aorta were pretreated with inhibitors or vehicle 20 min before the concentration responses to VP were obtained. To examine whether the effects of the COX-2-selective inhibitor were agent specific, cumulative concentration responses to VP were also obtained in the presence of a second, chemically dissimilar COX-2-selective inhibitor, niflumic acid (NA; 10 µM).

Effects of estrogen on prostanoid pathway function. To determine the effects of estrogen on vascular reactivity and constrictor prostanoid function in female rat aortas, cumulative concentration responses to VP (10–11 to 10–6 M) were obtained in Endo+ aortic rings prepared from Ovx-F and Ovx+ER-F rats. Duplicate or triplicate rings from each aorta were pretreated with Indo (10 µM), NS (10 µM), or vehicle control.

Male-female differences in vascular reactivity to U-46619 and effects of estrogen. To determine male-female differences in vascular reactivity to TxA2 and the effects of estrogen on vascular reactivity to TxA2 in female rat aorta, cumulative concentration responses to the TxA2 analog U-46619 (1 x10–11 M to 3 x 10–6 M) were obtained in paired Endo+ and Endo– aortic rings obtained from male, Int-F, Ovx-F, and Ovx+ER-F rats.

RIA of plasma estradiol. Trunk blood samples (~5–6 ml) were collected from rats at the time of decapitation into 13x 100-mm glass culture tubes coated with 150 U of sodium heparin. Blood samples were centrifuged (10,000 g for 5 min), and the resultant plasma was separated and stored at –70°C until RIA for plasma 17{beta}-estradiol levels was performed. Estradiol concentrations were measured in unextracted plasma in duplicate using a double-antibody RIA (Diagnostic Products; Los Angeles, CA) validated for measurements of rat plasma (61). The limit of detection of this assay is ~2.0 pg/ml in this laboratory.

Chemical Reagents and Drugs

The following reagents and drugs were used: 17{beta}-estradiol (Innovative Research of America; Sarasota, FL), U-46619 (9,11-dideoxy-9{alpha},11{alpha}-methanoepoxy prostaglandin F2{alpha}), NS, and NA (Cayman Chemical; Ann Arbor, Michigan), arginine VP (Bachem; Torrance, CA), PE hydrochloride, ACh chloride, and Indo (Sigma Chemical; St. Louis, MO). Stock solutions of all drugs were prepared fresh daily except for VP (which was diluted daily from aliquots of 1 x 10–3 M stock solution stored at –70°C) and NS (which was diluted daily from 1 mg/ml stock solution stored at –20°C).

Data Analysis

All data are expressed as means ± SE; n indicates the number of animals studied. Contractile responses to VP and U-46619 were normalized by dry weight of the aortic rings and are expressed as milligrams of contractile force per milligram of ring weight. The concentration of VP or U-46619 that produced 50% of the maximal response (EC50) was calculated individually from the log concentration-response curve of each aortic ring, and these values are reported as the mean ± SE for the particular experimental group. U-46619 data groups were analyzed by sex (male vs. female) and by experimental treatment (e.g., Endo+ vs. Endo–) using two-way ANOVA to detect significant differences among the treatment groups and subsequently by pair-wise Student's t-tests to distinguish significant differences between any two means of the data groups. VP data groups were analyzed by sex (Int-F vs. Ovx-F vs. Ovx+ER-F) and by experimental treatment (control vs. Indo vs. NS) using two-way ANOVA and Student's t-tests as described. U-46619 and VP data groups involving the effects of ovariectomy were analyzed by sex alone (Int-F vs. Ovx-F vs. Ovx+ER-F) using one-way ANOVA and Student's t-tests as described. Differences between any two means were accepted as significant if P < 0.05.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Effects of Ovariectomy and Estrogen Replacement on Vascular Reactivity to VP

Plasma 17{beta}-estradiol concentrations are summarized in Table 1. Compared with Int-F rats, ovariectomy reduced plasma estradiol concentration by 97% (P < 0.05), whereas 17{beta}-estradiol replacement restored the plasma concentration to levels similar to those of Int-F rats (P > 0.05). Plasma estradiol concentration of male rats was similar to that of Ovx-F rats (P > 0.05).


View this table:
[in this window]
[in a new window]
  		Table 1. Plasma 17{beta}-estradiol concentrations of male and female Sprague-Dawley rats

 
In rats fed the phytoestrogen-free diet, ovariectomy attenuated contractile responses to VP throughout the concentration-response curve; in contrast, ERT restored the contractile responses to VP (Fig. 1). Maximal contractile responses to VP were reduced 55% by ovariectomy (P < 0.001) and were fully restored by ERT compared with Int-F rats (P > 0.1; Table 2). Sensitivity to VP (EC50) was not altered by ovariectomy (P > 0.1), although ERT produced a slight but significant increase in sensitivity to VP compared with ovariectomized rats (P < 0.01; Table 2). In preliminary experiments, reactivity to VP in aortas obtained from Ovx-F rats fed the standard (phytoestrogen-containing) laboratory rat chow did not differ from that of Int-F rats (P > 0.05; data not shown).



View larger version (19K):
[in this window]
[in a new window]
  		Fig. 1. Concentration-response curves for arginine vasopressin (VP) in endothelium-intact aortic rings from intact female (Int-F), ovariectomized female (Ovx-F), and ovariectomized + estrogen-replaced female (Ovx+ER-F) Sprague-Dawley rats. Data points represent means ± SE (n, no. of animals). Veh, vehicle control. Statistically significant differences exist in Int-F vs. Ovx-F (0.0002 ≤ *P ≤ 0.005) and in Ovx+ER-F vs. Ovx-F (*P < 0.0001) at both maximal (1 x 10–6 M) and middle (1 x 10–8 M) concentrations of VP. No differences exist in Int-F vs. Ovx+ER-F (P ≥ 0.1).

 

View this table:
[in this window]
[in a new window]
  		Table 2. EC50 values and corresponding maximal contractile responses to arginine VP in thoracic aortas of female Sprague-Dawley rats pretreated with indomethacin, NS-398, or vehicle control

 
Effects of Ovariectomy and Estrogen Replacement on Prostanoid Pathway Inhibitors

In Int-F rat aortas, VP produced concentration-dependent contractions with a maximal response of 5,567 ± 276 mg/mg of ring wt and an EC50 of 8.0 ± 1.2 nM (Fig. 2A; Table 2). Both the nonselective COX inhibitor Indo and the COX-2-selective inhibitor NS significantly attenuated contractile responses to VP at middle and higher concentrations (Fig. 2A; Table 2). The maximal contractile responses were reduced by 43 (P < 0.001) and 41% (P < 0.001) by Indo and NS, respectively, compared with the control group. Sensitivity (EC50) of the female aortas to VP was unchanged after pretreatment with either Indo (P = 0.165) or NS (P = 0.180; Table 2) compared with the control group. The chemically dissimilar COX-2-selective inhibitor NA produced attenuating effects on the contractile responses to VP that were qualitatively and quantitatively similar to those of NS (P > 0.05), thereby reducing maximal response to VP by 47% (P < 0.001; data not shown).



View larger version (25K):
[in this window]
[in a new window]
  		Fig. 2. Concentration-response curves for arginine VP in endothelium-intact aortic rings prepared in triplicate from Sprague-Dawley Int-F (A), Ovx-F (B), or Ovx+ER-F (C) rats in the presence of indomethacin (Indo, 10 µM), NS-398 (NS, 10 µM), or Veh. Statistically significant differences exist in A in Veh vs. Indo (0.0001 ≤ *P ≤ 0.048) and Veh vs. NS (0.0001 ≤ #P ≤ 0.009) at both maximal (1 x 10–6 M) and middle (1 x 10–8 M) concentrations of VP and in C in Veh vs. Indo (0.0002 ≤ *P ≤ 0.0003) and Veh vs. NS (#P < 0.0001) at both maximal and middle concentrations of VP. No statistically significant differences exist in B in Veh vs. Indo (P ≥ 0.088), in Veh vs. NS (P ≥ 0.160), or in Indo vs. NS (P ≥ 0.521) at both maximal and middle concentrations of VP.

 
In rats fed the phytoestrogen-free diet, ovariectomy attenuated contractile responses to VP throughout the concentration-response curve and abolished the attenuating effects of Indo and NS (Fig. 2B; Table 2). In contrast, ERT fully restored the contractile responses to VP and the attenuating effects of Indo and NS (Fig. 2C; Table 2). Maximal contractile responses to VP were reduced 55% by ovariectomy (P < 0.001) and restored by ERT compared with Int-F rats (P > 0.1; Table 2). In Int-F rats, the differences in maximal contractile responses among control, Indo–, and NS-treated aortas were highly significant (P < 0.001; Table 2); in contrast, in Ovx-F rats, maximal contractile responses of control, Indo-, and NS-treated aortas did not differ significantly (P > 0.05; Table 2). With ERT, significant differences in maximal contractile responses among control, Indo-, and NS-treated aortas were fully restored (P < 0.001; Table 2). Sensitivity to VP (EC50) in Int-F, Ovx-F, and Ovx+ER-F rats did not differ significantly among control, Indo-, or NS-treated aortas (P > 0.1; Table 2) with the exception of control aortas from Ovx+ER-F rats, which exhibited a slight but significant increase in sensitivity to VP (P < 0.031; Table 2). In preliminary experiments, reactivity to VP in aortas obtained from Ovx-F rats fed the standard (phytoestrogen-containing) laboratory rat chow did not differ from that of Int-F rats (P > 0.05; data not shown), and the inhibitory effects of Indo and NS were not abolished by ovariectomy.

In rats fed the phytoestrogen-free diet, ovariectomy attenuated contractile responses to VP throughout the concentration-response curve and abolished the attenuating effects of SQ (Fig. 3). In contrast, in Ovx+ER-F rats, ERT fully restored the contractile responses to VP and the effect of SQ to attenuate contractile responses to VP (Fig. 3). Maximal contractile responses to VP were reduced 51% by ovariectomy (2,485 ± 394 mg; P < 0.001) compared with ERT in Ovx+ER-F rats (5,058 ± 193 mg). In Ovx-F rats, maximal contractile responses of control (2,485 ± 394 mg) and SQ-treated (1,721 ± 172 mg) aortas did not differ (P > 0.05); in contrast, in Ovx+ER-F rats, maximal contractile responses of control (5,058 ± 193 mg) aortas were reduced by 31% in SQ-treated aortas (3,471 ± 206 mg; P < 0.001). Sensitivity to VP (EC50) in Ovx-F rats did not differ significantly between control (9.19 ± 1.51 nM) and SQ-treated (7.26 ± 0.80 nM) aortas (P > 0.1). In Ovx+ER-F rats, ERT increased sensitivity to VP slightly in control aortas (4.90 ± 0.40 nM), and this was unchanged in SQ-treated aortas (4.77 ± 0.53 nM; P > 0.10).



View larger version (22K):
[in this window]
[in a new window]
  		Fig. 3. Concentration-response curves for arginine VP in endothelium-intact aortic rings prepared in duplicate from Ovx-F and Ovx+ER-F Sprague-Dawley rats in the presence of SQ-29,548 (SQ, 1 µM) or Veh. Statistically significant differences exist in Ovx+ER-F for SQ vs. Veh (0.0001 ≤ *P ≤ 0.001) at both maximal (1 x 10–6 M) and middle (1 x 10–8 M) concentrations of VP. No statistically significant differences exist in Ovx-F for SQ vs. Veh (P ≥ 0.100) at both maximal and middle concentrations of VP.

 
Male-Female Differences in Vascular Reactivity to U-46619 and Effects of Ovariectomy and Estrogen

Contractile responses of Endo+ aortic rings to U-46619 were significantly higher in females than in males in the upper half of the concentration-response curve (Fig. 4). The maximal contractile response of Endo+ aortic rings was significantly higher in female than in male rat aortas (P < 0.0001; Fig. 4; Table 3). Deletion of the endothelium potentiated the contractile responses of both female and male rat aortas to a similar extent; thus contractile responses of Endo– females were significantly greater than those of Endo– males (P < 0.0001; Fig. 4; Table 3). Sensitivity (EC50) to U-46619 in Endo+ aortic rings was slightly but significantly higher in males than in females (P < 0.029). Deletion of the endothelium increased the sensitivity of both female and male aortas to a similar extent (~40–50%; Table 3).



View larger version (22K):
[in this window]
[in a new window]
  		Fig. 4. Concentration-response curves for U-46619 in endothelium-intact (Endo+) and endothelium-denuded (Endo–) aortic rings from Int-F and male Sprague-Dawley rats. Statistically significant differences exist in female Endo+ vs. male Endo+ (*P < 0.001) and in female Endo– vs. male Endo– (#P < 0.001) at both maximal (3 x 10–6 M) and middle (1 x 10–7 M) concentrations of U-46619. Statistically significant differences exist in female Endo+ vs. female Endo– (P = 0.012) and in male Endo+ vs. male Endo– (P = 0.008) at middle concentrations of U-46619. No statistically significant differences exist in female Endo+ vs. female Endo– (P ≥ 0.111) or in male Endo+ vs. male Endo– (P ≥ 0.051) at maximal concentrations of U-46619.

 

View this table:
[in this window]
[in a new window]
  		Table 3. EC50 values and corresponding maximal contractile responses to thromboxane A2 analog U-46619 in paired endothelium-intact and endothelium-denuded thoracic aortic rings of Sprague-Dawley rats

 
In rats fed the phytoestrogen-free diet, ovariectomy noticeably attenuated contractile responses of female Endo+ aortic rings to U-46619 at middle and higher concentrations. Maximal response of Ovx-F rat aortas to U-46619 was attenuated by 22% (P < 0.01) compared with Int-F rat aortas (Fig. 5; Table 3). Estrogen replacement restored contractile responses to U-46619 in Endo+ aortic rings to levels similar to those of Int-F rat aortas (Fig. 5; Table 3). Ovariectomy had no effect on sensitivity of Endo+ aortic rings to U-46619 (P > 0.1; Table 3). Interestingly, in preliminary experiments in which female rats were fed standard (phytoestrogen-containing) laboratory rat chow, ovariectomy had no significant effect on reactivity of female Endo+ aortic rings to U-46619 (P > 0.05).



View larger version (19K):
[in this window]
[in a new window]
  		Fig. 5. Concentration-response curves for U-46619 in Endo+ aortic rings from Int-F, Ovx-F, and Ovx+ER-F Sprague-Dawley rats. Statistically significant differences exist in Int-F vs. Ovx-F (0.001 ≤ *P ≤ 0.002) and in Ovx+ER-F vs. Ovx-F (0.0001 ≤ #P ≤ 0.031) at both maximal (3 x 10–6 M) and middle (1 x 10–7 M) concentrations of U-46619. No statistically significant differences exist in Int-F vs. Ovx+ER-F (0.307 ≤ P ≤ 0.963) at either maximal or middle concentrations of U-46619.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
In the present investigation, the roles of estrogen and constrictor prostanoids in the contractile responses of rat aorta to VP were determined in female Sprague-Dawley rats. The results reveal that endogenous estrogen is an important regulator of the contractile responses of female rat aorta to VP, which appears to potentiate both COX-2 and constrictor prostanoid function in the vascular wall.

Effects of Prostanoid Pathway Inhibitors

To determine the role of constrictor prostanoid function in VP-induced contraction of female rat aorta, the effects of COX inhibitors were examined. The nonselective COX inhibitor Indo significantly attenuated the contractile responses of female rat aorta to VP by 43%. Interestingly, the chemically dissimilar COX-2-selective inhibitors NS and NA both attenuated contractile responses to VP to a similar extent as Indo (41 and 47%, respectively), which strongly suggests that COX-2 but not COX-1 contributes to the constrictor prostanoid-mediated potentiation of contractile responses of female rat aorta to VP.

Previous studies established that the contractile responses of rat aorta to VP are three- to fourfold higher in females than in males (51, 54). Similar sex differences in the vascular reactivity to VP have been observed in mesenteric arterioles of anesthetized rats (1) and in isolated perfused rat mesenteric vasculature (53, 56). Previous studies also demonstrated that VP-stimulated release of NO is much greater in male rat aorta and is responsible for the markedly attenuated responses to VP compared with female aorta (51, 52). Interestingly, even in the presence of NOS inhibition, contractile responses to VP are still higher in females, and several studies have revealed that this remaining sex difference in reactivity to VP involves enhanced constrictor prostanoid function in the female vascular wall (19, 51). The nonselective COX inhibitor Indo and the PGH2/TxA2 receptor antagonist SQ both attenuated contractile responses of female but not male rat aorta to VP and the {alpha}-adrenergic agonist PE to the same extent (19), which demonstrated that constrictor prostanoids play a significant role in potentiating the contractile responses of the female but not the male systemic vasculature to VP and PE. However, these studies did not examine the underlying mechanism in detail. Thus the present study is the first to establish the involvement of a constitutive form of COX-2 in the constrictor prostanoid-mediated potentiation of the contractile responses of the systemic vasculature in female rat aorta to VP.

COX-1 and -2 are enzyme isoforms that are encoded by different genes (30, 31). COX-1 is the constitutive isoform present in many cells and is a housekeeping enzyme (50, 65). Conversely, COX-2 is an inducible isoform activated by inflammatory agents (28, 40); however, COX-2 is also constitutively expressed in some tissues such as kidney and aorta (38, 40, 64) and may play a role in regulating normal renal function and blood flow. The present study provides clear functional evidence that a constitutive form of COX-2 is, in fact, involved in the regulation of systemic vascular function in female rats.

Effects of Estrogen on Constrictor Prostanoid Pathway Function in Female Aorta

To determine the role of estrogen in the regulation of the constrictor prostanoid pathway in female rat aorta, the effects of ovariectomy and ERT on vascular reactivity to VP and prostanoid function were determined. Plasma 17{beta}-estradiol levels of Int-F and Ovx-F rats measured in the present study are consistent with previous findings (49, 61). Plasma concentrations of 17{beta}-estradiol were attenuated drastically in Ovx-F rats and did not differ from those of male rats. ERT restored plasma estradiol levels to concentrations that did not differ from those of Int-F rats.

Ovariectomy markedly attenuated contractile responses to VP in Endo+ female rat aorta and abolished the inhibitory effects of the COX inhibitors Indo and NS as well as the PGH2/TXA2 receptor antagonist SQ. In contrast, long-term (3–4 wk) ERT in Ovx-F rats with 17{beta}-estradiol completely restored contractile responses to VP and the inhibitory effects of Indo, NS, and SQ. These results reveal that constrictor prostanoid-mediated potentiation of the contractile responses of female rat aorta is strongly dependent upon the action of estradiol on the vascular wall. Estrogen receptors have been identified in both endothelium (2, 13, 14) and VSM (2, 37, 39); thus the potentiating effect of estrogen on the contractile responses to VP in female aorta may involve actions on endothelium and/or VSM.

In the present study, pharmacological blockade of the prostanoid pathway at the levels of COX and the PGH2/TxA2 receptor strongly suggests that the potentiating effect of estrogen involves upregulation of COX-2 and the subsequent constrictor prostanoid pathway, which thereby regulates both the release of and vascular reactivity to constrictor prostanoids in the vascular wall. Numerous studies support the idea that estrogen enhances vascular prostanoid production. For example, pretreatment of isolated, blood-perfused lungs of juvenile female sheep with estradiol enhances the production of prostaglandins (57). Similarly, in isolated rat lung, COX activity varies during the course of the estrous cycle and peaks during the estrogen surge at proestrus, and this is coincident with maximal release of PGI2 and TxA2 at proestrus (4). Furthermore, estrogen treatment enhances TxA2 production in rat endothelial cells (66) and PGI2 production in both rat VSM cells (11) and ovine fetal pulmonary artery endothelial cells (48). The results of the present study are consistent with these previous findings and further reveal that estrogen potentiates the contractile responses to VP in female rat aorta by enhancing the activity of COX-2. This effect of estrogen also appears to involve the subsequent enhancement of the constrictor prostanoid pathway as suggested by the effects of ovariectomy and ERT on constrictor prostanoid function in past (19) and present studies. Indeed, preliminary studies reveal that VP-stimulated release of TxA2 by rat aorta is dramatically reduced by ovariectomy but is restored by ERT (33). In a previous study, removal of the endothelium attenuated the contractile responses to VP to a similar extent as either Indo or SQ and abolished the attenuating effects of Indo and SQ, which suggests the involvement of endothelium-derived constrictor prostanoids (19). Additional studies are necessary to elucidate the mechanism underlying estrogen-mediated increases in VP-stimulated constrictor prostanoid release and the origin of their production in female rat aorta.

The present study also demonstrates that estrogen not only enhances the activity of COX-2 but also potentiates reactivity of female aorta to the constrictor prostanoid TxA2. Thus contractile responses of female rat aorta to the stable TxA2 analog U-46619 were significantly higher in females than in males. Furthermore, ovariectomy abolished and ERT restored the contractile responses of female aorta to U-46619. The present findings are consistent with those reported for the isolated rat pulmonary vasculature (16), which both reveal that estrogen potentiates the contractile effects of the constrictor prostanoid TxA2 on the vasculature. The underlying mechanisms may include: 1) estrogen-induced increases in the density of PGH2/TxA2 receptors in rat VSM cells; 2) U-46619-stimulated release of vasoactive substance(s) from the vascular endothelium, which may be enhanced by estrogen; or 3) estrogen modulation of downstream signal transduction mechanisms involved in TxA2-stimulated VSM constriction. A previous study of cultured rat aortic VSM cells reported that the number of TxA2 binding sites per cell is higher in females than in males (36), but reactivity of the TxA2 receptors in female aorta was not assessed. Thus it is possible that the greater contractile responses to U-46619 in females in the present study, especially in Endo– aortic rings, involve enhancement of PGH2/TxA2 receptor expression by estrogen in female aortic VSM cells. Indeed, preliminary studies suggest that estrogen upregulates expression of PGH2/TxA2 receptors in female aortic VSM cells (32). Concentration-response curves with paired Endo+ and Endo– aortic rings suggest that deletion of the endothelium increases contractile responses to U-46619 in both males and females; however, the increases were not significantly different in either group. The increase in contractile responses to U-46619 after removal of the endothelium may be due to the loss of endothelial vasodilators, especially NO; however, this mechanism does not appear to contribute to sex differences in the responses of rat aorta to U-46619. Thus sex differences in U-46619-induced release of vasoactive factors from endothelium are not likely to be involved in the observed sex differences in reactivity to U-46619. Studies with human omental arteries also showed that neither inhibition of NOS by N{omega}-nitro-L-arginine nor removal of the endothelium affected contractile responses to U-46619 (59). Finally, estrogen may potentiate downstream signal transduction mechanisms involved in the TxA2-induced VSM contraction; in particular, the activity of VSM phospholipase C or inositol 1,4,5-trisphosphate are likely sites of regulation by estrogen that would enhance TxA2-induced contraction.

The greater contractile responses of female aorta to VP also may be due to the upregulation of VP receptors in VSM cells by estrogen. In the present study, ovariectomy reduced the maximal contractile response to VP by 55%, which was greater than the effects of Indo or NS (43 and 41%, respectively) in Int-F rat aortas; thus it is possible that ovariectomy not only decreased constrictor prostanoid function but also reduced the expression of VP binding sites in aortic VSM cells. Estrogen significantly increases the expression of VP V1{alpha} receptor mRNA in the preoptic area of young ovariectomized rats (20). Similarly, estrogen increases VP V1 receptor expression in rabbit myometrium and rat mesenteric arterioles (35, 56). In the latter study, upregulation of VP V1 receptors was correlated with an increase in the vasoconstrictor responses to VP in the isolated, perfused mesenteric vascular bed. Estradiol also increased the maximal response to VP and the density of VP binding sites in the mesenteric vasculature of male rats (56). This evidence suggests that it is possible, indeed likely, that ovariectomy not only decreased constrictor prostanoid function but also reduced the expression of VP binding sites in female aortic VSM cells.

Although most studies reveal that long-term treatment with estrogen enhances reactivity to VP or U-46619, not all studies agree with these findings. For example, long-term estrogen replacement of ovariectomized rats has been reported to be without effect on reactivity of resistance-sized mesenteric arteries to either VP or U-46619 (68). The reason(s) for these differences is uncertain but may involve differences in the blood vessels studied and/or the dose of ERT employed.

Although rat aorta is a large conduit vessel not involved in regulation of peripheral resistance, the ovarian steroid-dependent constrictor prostanoid mechanism identified in rat aorta in present and past (19) studies appears to be quite relevant to the regulation of systemic arterial blood pressure. Preliminary studies reveal that intravenous infusion of the PGH2/TxA2 receptor antagonist SQ into conscious normotensive rats reduces mean arterial blood pressure (MAP) by 15% in females but has no effect in males; even more striking, infusion of this antagonist into aortic coarctation-hypertensive rats reduces MAP by 34% in females but only 15% in males (5). Taken together, these data suggest that the estrogen-dependent constrictor prostanoid mechanism in the vascular wall may play an important role in the regulation of vascular tone in females but not in males in both normal and pathophysiological states.

The findings of the present study are consistent with the extensive epidemiological data that reveal the existence of a prominent sexual dimorphism in the incidences of primary vascular diseases that involve excessive vasoconstriction. Primary pulmonary hypertension (21, 63), migraine headache (41), and Raynaud's disease (6, 9, 22, 62) all occur in premenopausal women at rates as much as fourfold higher than in men. Furthermore, an association has been reported between Raynaud's disease and these other afflictions, which suggests that a common mechanism of vasospasm may be involved (8a). Elevated vascular production of TxA2 may be the common mediator of vasospasm in these diseases. The production of this constrictor prostanoid is increased in patients with Raynaud's disease (44), migraine headache (29), and pulmonary hypertension (12). Animal studies also revealed the relationship of TxA2 and the development of these diseases (10, 17). Furthermore, the thromboxane synthase inhibitors CGS-13080 and dazoxiben have been successfully used for treatment of primary pulmonary hypertension and Raynaud's disease (8, 43).

The higher incidences of primary vascular diseases in premenopausal women suggest that estrogen and/or other ovarian steroids may be involved in the pathogenesis of primary vascular diseases in women. Indeed, the recent Heart and Estrogen-Progestin Replacement Study (HERS) reported no overall benefit of ERT, and untoward cardiovascular events including venous thrombosis actually increased significantly in the first year of the study (23, 24, 26). Similar deleterious effects of ERT on the incidences of coronary artery disease, stroke, and venous thrombosis were also reported in the more recent Women's Health Initiative (WHI) studies (67). Furthermore, oral contraceptive use in young women is also associated with an increased risk of thrombosis (7, 15) and acute myocardial infarction (27). The influence of estrogen on constrictor prostanoid function, as established in the present study, may contribute to these deleterious effects of estrogen on the vasculature. Indeed, postmenopausal women undergoing ERT have elevated urinary levels of both TxA2 and prostacyclin (18, 60). Similarly, preliminary studies in rat aorta suggest that estrogen upregulates the release of TxA2, and that this effect of estrogen involves increased expression of message for COX-2, TxA2 synthase, and TxA2 VSM receptor (33, 55). These findings raise the intriguing possibility that the deleterious effects of estrogen on the vascular wall and/or thrombosis that are suggested by both the Heart and Estrogen-Progestin Replacement Study (23, 24, 26) and the more recent Women's Health Initiative studies (67) may involve the potentiating effects of estrogen on TxA2 and the constrictor prostanoid pathway.

In conclusion, the present study is the first to establish that estrogen potentiates the contractile responses of female rat aorta to VP, and that this effect of estrogen appears to involve the enhancement of both COX-2 and constrictor prostanoid function in the vascular wall. The mechanisms underlying the effects of estrogen on COX-2 and the constrictor prostanoid pathway are presently being investigated in our laboratory.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This study was supported by National Heart, Lung, and Blood Institute Grant HL-47432 and by an American Heart Association-Texas Affiliate Grant In Aid (both to J. N. Stallone).


   ACKNOWLEDGMENTS
 
The authors gratefully acknowledge the technical assistance of Feng Xu.

Present Address of Min Li: Dept. of Anesthesiology and Critical Care Medicine, Johns Hopkins University, School of Medicine, 600 Wolfe St., Baltimore, MD 21287.


   FOOTNOTES
 

Address for reprint requests and other correspondence: J. N. Stallone, Dept. of Veterinary Physiology and Pharmacology, College of Veterinary Medicine, Texas A&M Univ., College Station, TX 77843-4466 (e-Mail: JStallone{at}cvm.tamu.edu)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Altura BM. Sex and estrogens and responsiveness of terminal arterioles to neurohypophyseal hormones and catecholamines. J Pharmacol Exp Ther 193: 403–412, 1975.[Abstract/Free Full Text]
  2. Andersson C, Lydrup ML, Ferno M, Idvall I, Gustafsson J, and Nilsson BO. Immunocytochemical demonstration of oestrogen receptor beta in blood vessels of the female rat. J Endocrinol 169: 241–247, 2001.[Abstract]
  3. AVMA Panel on Euthanasia. American Veterinary Medical Association. 2000 Report of the AVMA Panel on Euthanasia. J Am Vet Med Assoc 218: 669–696, 2001.[CrossRef][ISI][Medline]
  4. Bakhle YS and Zakrzewski JT. Effects of the oestrous cycle on the metabolism of arachidonic acid in rat isolated lung. J Physiol 326: 411–423, 1982.[Abstract/Free Full Text]
  5. Baltzer W and Stallone JN. Aortic coarctation-induced hypertension is greater in females vs. males and is more constrictor prostanoid dependent (Abstract). FASEB J 16: A81, 2002.
  6. Bartelink ML, van de Lisdonk E, van den Hoogen H, Wollersheim H, and van Weel C. Migraine in family practice: prevalence and influence of sex hormonal status. Fam Med 25: 331–336, 1993.[Medline]
  7. Beaumont V, Lemort N, Lorenzelli L, and Beaumont JL. Vascular thrombosis and oral contraceptives—a risk correlated study. J Med 12: 51–61, 1981.[CrossRef][ISI][Medline]
  8. Belch JJ, Cormie J, Newman P, McLaren M, Barbenel J, Capell H, Leiberman P, Forbes CD, and Prentice CR. Dazoxiben, a thromboxane synthetase inhibitor, in the treatment of Raynaud's syndrome: a double-blind trial. Br J Clin Pharmacol 15 Suppl 1: 113S–116S, 1983.
  9. Berkow R(Editor). The Merck Manual of Diagnosis and Therapy (15th ed.). Rahway, NJ: Merck Sharp & Dohme Research Laboratories, 1987, p. 563–564.
  10. Brand FN, Larson MG, Kannel WB, and McGuirk JM. The occurrence of Raynaud's phenomenon in a general population: the Framingham study. Vasc Med 2: 296–301, 1997.[Medline]
  11. Buzzard CJ, Pfister SI, and Campbell WB. Endothelium-dependent contractions in rabbit pulmonary artery are mediated by thromboxane A2. Circ Res 72: 1023–1034, 1993.[Abstract/Free Full Text]
  12. Chang WC, Nakao J, Murota S, and Tai HH. Induction of fatty acid cyclooxygenase in rat aortic smooth muscle cells by estradiol. Prostaglandins Leukot Med 10: 33–37, 1983.[CrossRef][ISI][Medline]
  13. Christman BW, McPherson CD, Newman JH, King GA, Bernard GR, Groves BM, and Loyd JE. An imbalance between the excretion of thromboxane and prostacyclin metabolites in pulmonary hypertension. N Engl J Med 327: 70–75, 1992.[Abstract]
  14. Cid MC, Schnaper HW, and Kleinman HK. Estrogens and the vascular endothelium. Ann NY Acad Sci 966: 143–157, 2002.[Abstract/Free Full Text]
  15. Colburn P and Buonassisi V. Estrogen-binding sites in endothelial cell cultures. Science 201: 817–819, 1978.[Abstract/Free Full Text]
  16. De Oliveira EM, Gibertoni RM, Campos O, da Costa OF, Goldenberg J, Cutait D, and do A Baruzzi AC. Severe pulmonary thromboembolism caused by contraceptives in adolescents. Arq Bras Cardiol 65: 427–430, 1995.[Medline]
  17. Farhat MY and Ramwell PW. Estradiol potentiates the vasopressor response of the isolated perfused rat lung to the thromboxane mimic U-46619. J Pharmacol Exp Ther 261: 686–691, 1992.[Abstract/Free Full Text]
  18. Fike CD, Kaplowitz MR, and Pfister SL. Arachidonic acid metabolites and an early stage of pulmonary hypertension in chronically hypoxic newborn pigs. Am J Physiol Lung Cell Mol Physiol 284: L316–L323, 2003.[Abstract/Free Full Text]
  19. Foidart JM, Dombrowitz N, and de Lignieres B. Urinary excretion of prostacyclin and thromboxane metabolites in postmenopausal women treated with percutaneous estradiol (Oestrogel) or conjugated estrogens (Premarin). In: Physiological Hormone Replacement Therapy, edited by Dusitsin N and Notelovitz M. Carnfurth, UK: Parthenon, 1990.
  20. Fulton CT and Stallone JN. Sexual dimorphism in prostanoid-potentiated vascular contraction: roles of endothelium and ovarian steroids. Am J Physiol Heart Circ Physiol 283: H2062–H2073, 2002.[Abstract/Free Full Text]
  21. Funabashi T, Shinohara K, Mitsushima D, and Kimura F. Estrogen increases arginine-vasopressin V1a receptor mRNA in the preoptic area of young but not of middle-aged female rats. Neurosci Lett 285: 205–208, 2000.[CrossRef][ISI][Medline]
  22. Gaine SP and Rubin LJ. Primary pulmonary hypertension. Lancet 352: 719–725, 1998.[CrossRef][ISI][Medline]
  23. Grisanti JM. Raynaud's phenomenon. Am Fam Physician 41: 134–142, 1990.[ISI][Medline]
  24. Herrington DM. The HERS trial results: paradigms lost? Heart and Estrogen/Progestin Replacement Study. Ann Intern Med 131: 463–466, 1999.[Abstract/Free Full Text]
  25. Herrington DM, Reboussin DM, Brosnihan KB, Sharp PC, Shumaker SA, Snyder TE, Furberg CD, Kowalchuk GJ, Stuckey TD, Rogers WJ, Givens DH, and Waters D. Effects of estrogen replacement on the progression of coronary-artery atherosclerosis. N Engl J Med 343: 522–529, 2000.[Abstract/Free Full Text]
  26. Horwitz KB and Horwitz LD. Canine vascular tissues are targets for androgens, estrogens, progestins, and glucocorticoids. J Clin Invest 69: 750–758, 1982.[ISI][Medline]
  27. Huley S, Grady D, Bush T, Furbeg C, Herrington D, Riggs B, and Vittinghoff E. Randomized trial of estrogen plus progestin for secondary prevention of coronary heart disease in postmenopausal women. JAMA 280: 605–613, 1998.[Abstract/Free Full Text]
  28. Jick H, Dinan B, Herman R, and Rothman KJ. Myocardial infarction and other vascular diseases in young women. JAMA 240: 2548–2552, 1978.[Abstract]
  29. Kam PC and See AU. Cyclo-oxygenase isoenzymes: physiological and pharmacological role. Anaesthesia 55: 442–449, 2000.[CrossRef][ISI][Medline]
  30. Kitano A, Shimomura T, Takeshima T, and Takahashi K. Increased 11-dehydrothromboxane B2 in migraine: platelet hyperfunction in patients with migraine during headache-free period. Headache 34: 515–518, 1994.[CrossRef][ISI][Medline]
  31. Kosaka T, Miyata A, Ihara H, Hara S, Sugimoto T, Takeda O, Takahashi E, and Tanabe T. Characterization of the human gene (PTGS2) encoding prostaglandin-endoperoxide synthase 2. Eur J Biochem 221: 889–897, 1994.[ISI][Medline]
  32. Kraemer SA, Meade EA, and DeWitt DJ. Prostaglandin endoperoxide synthase gene structure: identification of the transcriptional start site and 5'-flanking regulatory sequences. Arch Biochem Biophys 293: 391–400, 1992.[CrossRef][ISI][Medline]
  33. Li M, Kuo L, and Stallone JN. Estrogen enhances contractile responses of rat aorta by upregulating expression of cyclooxygenase-2 and thromboxane synthase (Abstract). Circulation 106: II-211, 2002.
  34. Li M and Stallone JN. Sex dimorphism in constrictor prostanoid-potentiated contraction involves greater release of and reactivity to thromboxane in female than in male rat aorta (Abstract). FASEB J 15: A1127, 2001.
  35. Liard JF. Vasopressin in cardiovascular control: role of circulating vasopressin. Clin Sci (Lond) 67: 473–481, 1984.[Medline]
  36. Maggi M, Fantoni G, Peri A, Giannini S, Brandi ML, Orlando C, and Serio M. Steroid modulation of oxytocin/vasopressin receptors in the uterus. J Steroid Biochem Mol Biol 40: 481–491, 1991.[CrossRef][ISI][Medline]
  37. Matsuda K, Mathur RS, Ullian ME, and Halushka PV. Sex steroid regulation of thromboxane A2 receptors in cultured rat aortic smooth muscle cells. Prostaglandins 49: 183–196, 1995.[CrossRef][ISI][Medline]
  38. Nakao J, Chang WC, Murota SI, and Orimo H. Estradiol-binding sites in rat aortic smooth muscle cells in culture. Atherosclerosis 38: 75–80, 1981.[CrossRef][ISI][Medline]
  39. Okamoto T and Hino O. Expression of cyclooxygenase-1 and -2 mRNA in rat tissues: tissue-specific difference in the expression of the basal level of mRNA. Int J Mol Med 6: 455–457, 2000.[ISI][Medline]
  40. Orimo A, Inoue S, Ikegami A, Hosoi T, Akishita M, Ouchi Y, Muramatsu M, and Orimo H. Vascular smooth muscle cells as target for estrogen. Biochem Biophys Res Commun 195: 730–736, 1993.[CrossRef][ISI][Medline]
  41. Parente L and Perretti M. Advances in the pathophysiology of constitutive and inducible cyclooxygenases: two enzymes in the spotlight. Biochem Pharmacol 65: 153–159, 2003.[CrossRef][ISI][Medline]
  42. Rasmussen BK, Jensen R, Schroll M, and Olesen J. Epidemiology of headache in a general population—a prevalence study. J Clin Epidemiol 44: 1147–1157, 1991.[CrossRef][ISI][Medline]
  43. Register TC and Adams MR. Coronary artery and cultured aortic smooth muscle cells express mRNA for both the classical estrogen receptor and the newly described estrogen receptor beta. J Steroid Biochem Mol Biol 64: 187–191, 1988.
  44. Rich S, Hart K, Kieras K, and Brunddage B. Thromboxane synthase inhibition in primary pulmonary hypertension. Chest 91: 356–360, 1987.[Abstract/Free Full Text]
  45. Sakamoto K, Houya I, Inoue K, Tanaka M, Suzuki T, Sakamoto Y, and Matsuo H. An imbalance in plasma prostanoids in patients with Raynaud's phenomenon and pulmonary vasospasm. Eur Respir J 13: 137–144, 1999.[Abstract]
  46. Setchell KDR. Phytoestrogens: the biochemistry, physiology, and implications for human health of soy isoflavones. Am J Clin Nutr 68 Suppl: 1333S–1334S, 1998.
  47. Setchell KDR and Cassidy A. Dietary isoflavones: biological effects and relevance to human health. Am J Nutr 129 Suppl: 758S–767S, 1999.
  48. Share L. Role of vasopressin in cardiovascular regulation. Physiol Rev 68: 1248–1284, 1988.[Free Full Text]
  49. Sherman TS, Chambliss KL, Gibson LL, Pace MC, Mendelsohn ME, Pfister SL, and Shaul PW. Estrogen acutely activates prostacyclin synthesis in ovine fetal pulmonary artery endothelium. Am J Respir Cell Mol Biol 26: 610–616, 2002.[Abstract/Free Full Text]
  50. Smith MS, Freeman ME, and Neill JD. The control of progesterone secretion during the estrous cycle and early pseudopregnancy in the rat: prolactin, gonadotropin and steroid levels associated with rescue of the corpus luteum of pseudopregnancy. Endocrinology 96: 219–226, 1975.[Abstract]
  51. Smith WL and DeWitt DL. Prostaglandin endoperoxide H synthases (cyclooxygenase)-1 and -2. Adv Immunol 62: 167–215, 1996.[ISI][Medline]
  52. Stallone JN. Role of endothelium in sexual dimorphism in vasopressin-induced contraction of rat aorta. Am J Physiol Heart Circ Physiol 265: H2073–H2080, 1993.[Abstract/Free Full Text]
  53. Stallone JN. Sex differences in nitric oxide-mediated attenuation of vascular reactivity to vasopressin are abolished by gonadectomy. Eur J Pharmacol 259: 273–283, 1994.[ISI][Medline]
  54. Stallone JN. Mesenteric vascular responses to vasopressin during development of DOCA-salt hypertension in male and female rats. Am J Physiol Regul Integr Comp Physiol 268: R40–R49, 1995.[Abstract/Free Full Text]
  55. Stallone JN, Crofton JT, and Share L. Sexual dimorphism in vasopressin-induced contraction of rat aorta. Am J Physiol Heart Circ Physiol 260: H453–H458, 1991.[Abstract/Free Full Text]
  56. Stallone JN and Li M. Constrictor prostanoid-potentiated contraction of female rat aorta involves estrogen-dependent upregulation of cyclooxygenase-2 function (Abstract). FASEB J 15: LB-16, 2001.
  57. St-Louis J, Parent A, Lariviere R, and Schiffrin EL. Vasopressin responses and receptors in the mesenteric vasculature of estrogen-treated rats. Am J Physiol Heart Circ Physiol 251: H885–H889, 1986.[Abstract/Free Full Text]
  58. Sylvester JT, Gordon JB, Malamet RL, and Wetzel RC. Prostaglandins and estradiol-induced attenuation of hypoxic pulmonary vasoconstriction. Chest 88 Suppl 4: 252S–254S, 1985.[Abstract/Free Full Text]
  59. Vedernikov YP, Belfort MA, Saade GR, and Garfield RE. Inhibition of cyclooxygenase but not nitric oxide synthase influences effects on the human omental artery of the thromboxane A2 mimetic U46619 and 17{beta}-estradiol. Am J Obstet Gynecol 185: 182–189, 2001.[CrossRef][ISI][Medline]
  60. Viinikka L, Orpana A, Puolakka J, Pyorala T, and Ylikorkala O. Different effects of oral and transdermal hormonal replacement on prostacyclin and thromboxane A2. Obstet Gynecol 89: 104–107, 1997.[Abstract]
  61. Voss MR, Stallone JN, Li M, Cornelussen RN, Knuefermann P, and Knowlton AA. Gender differences in the expression of heat shock proteins: the effect of estrogen. Am J Physiol Heart Circ Physiol 285: H687–H692, 2003.[Abstract/Free Full Text]
  62. Voulgari PV, Alamanos Y, Papazisi D, Christou K, Papanikolaou C, and Drosos AA. Prevalence of Raynaud's phenomenon in a healthy Greek population. Ann Rheum Dis 59: 206–210, 2000.[Abstract/Free Full Text]
  63. Wagenvoort CA and Wagenvoort N. Primary pulmonary hypertension: a pathologic study of the lung vessels in 156 clinically diagnosed cases. Circulation 42: 1163–1184, 1970.[Abstract/Free Full Text]
  64. Wallace JL. Distribution and expression of cyclooxygenase (COX) isoenzymes, their physiological roles, and the categorization of nonsteroidal anti-inflammatory drugs (NSAIDs). Am J Med 107: 11S–17S, 1999.[CrossRef][Medline]
  65. Wang LH, Hajibeigi A, Xu XM, Loose-Mitchell D, and Wu KK. Characterization of the promoter of human prostaglandin H synthase-1 gene. Biochem Biophys Res Commun 190: 406–411, 1993.[CrossRef][ISI][Medline]
  66. Witter FR and DiBlasi MC. Effect of steroid hormones on arachidonic acid metabolites of endothelial cells. Obstet Gynecol 63: 747–751, 1984.[Abstract/Free Full Text]
  67. Writing Group for Women's Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women. JAMA 288: 321–333, 2002.[Abstract/Free Full Text]
  68. Zhang Y and Davidge ST. Effect of estrogen replacement on vasoconstrictor responses in rat mesenteric arteries. Hypertension 34: 1117–1122, 1999.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
M. P. Kunert, M. R. Dwinell, I. Drenjancevic Peric, and J. H. Lombard
Sex-specific differences in chromosome-dependent regulation of vascular reactivity in female consomic rat strains from a SS x BN cross
Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2008; 295(2): R516 - R527.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
M. Li, L. Kuo, and J. N. Stallone
Estrogen potentiates constrictor prostanoid function in female rat aorta by upregulation of cyclooxygenase-2 and thromboxane pathway expression
Am J Physiol Heart Circ Physiol, June 1, 2008; 294(6): H2444 - H2455.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
M. M. Sellers and J. N. Stallone
Sympathy for the devil: the role of thromboxane in the regulation of vascular tone and blood pressure
Am J Physiol Heart Circ Physiol, May 1, 2008; 294(5): H1978 - H1986.
[Abstract] [Full Text] [PDF]

Home page
 Physiol. GenomicsHome page
K. L. Hamilton, L. Lin, Y. Wang, and A. A. Knowlton
Effect of ovariectomy on cardiac gene expression: inflammation and changes in SOCS gene expression
Physiol Genomics, January 17, 2008; 32(2): 254 - 263.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
C. J. Mark, R. Tatchum-Talom, D. S. Martin, and K. M. Eyster
Effects of estrogens and selective estrogen receptor modulators on vascular reactivity in the perfused mesenteric vascular bed
Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2007; 293(5): R1969 - R1975.
[Abstract] [Full Text] [PDF]