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 292: H1770-H1776, 2007. First published December 1, 2006; doi:10.1152/ajpheart.01011.2005
0363-6135/07 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
292/4/H1770    most recent
01011.2005v1
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 Web of Science
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 Web of Science (6)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Xue, B.
Right arrow Articles by Hay, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Xue, B.
Right arrow Articles by Hay, M.

Estrogen receptor-{alpha} mediates estrogen protection from angiotensin II-induced hypertension in conscious female mice

Baojian Xue,2 Jaya Pamidimukkala,3 Dennis B. Lubahn,4 and Meredith Hay1,2

Departments of 1Physiology and Biophysics and 2Psychology, University of Iowa; Iowa City, Iowa; and 3Dalton Cardiovascular Research Center and 4University of Missouri Center for Phytonutrient and Phytochemical Studies, University of Missouri-Columbia, Columbia, Missouri

Submitted 22 September 2005 ; accepted in final form 22 November 2006


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
It has been shown that the female sex hormones have a protective role in the development of angiotensin II (ANG II)-induced hypertension. The present study tested the hypotheses that 1) the estrogen receptor-{alpha} (ER{alpha}) is involved in the protective effects of estrogen against ANG II-induced hypertension and 2) central ERs are involved. Blood pressure (BP) was measured in female mice with the use of telemetry implants. ANG II (800 ng·kg–1·min–1) was administered subcutaneously via an osmotic pump. Baseline BP in the intact, ovariectomized (OVX) wild-type (WT) and ER{alpha} knockout (ER{alpha}KO) mice was similar; however, the increase in BP induced by ANG II was greater in OVX WT (23.0 ± 1.0 mmHg) and ER{alpha}KO mice (23.8 ± 2.5 mmHg) than in intact WT mice (10.1 ± 4.5 mmHg). In OVX WT mice, central infusion of 17beta-estradiol (E2; 30 µg·kg–1·day–1) attenuated the pressor effect of ANG II (7.0 ± 0.4 mmHg), and this protective effect of E2 was prevented by coadministration of ICI-182,780 (ICI; 1.5 µg·kg–1·day–1, 18.8 ± 1.5 mmHg), a nonselective ER antagonist. Furthermore, central, but not peripheral, infusions of ICI augmented the pressor effects of ANG II in intact WT mice (17.8 ± 4.2 mmHg). In contrast, the pressor effect of ANG II was unchanged in either central E2-treated OVX ER{alpha}KO mice (19.0 ± 1.1 mmHg) or central ICI-treated intact ER{alpha}KO mice (19.6 ± 1.6 mmHg). Lastly, ganglionic blockade on day 7 after ANG II infusions resulted in a greater reduction in BP in OVX WT, central ER antagonist-treated intact WT, central E2 + ICI-treated OVX WT, ER{alpha}KO, and central E2- or ICI-treated ER{alpha}KO mice compared with that in intact WT mice given just ANG II. Together, these data indicate that ER{alpha}, especially central expression of the ER, mediates the protective effects of estrogen against ANG II-induced hypertension.

cardiovascular disease; sex hormone

THERE IS CONSIDERABLE EVIDENCE from studies in both human and animal models that estrogen modulates cardiovascular physiology and function (22). In a number of experimental models of hypertension, it has been shown that ovariectomy exacerbates and estrogen replacement attenuates the course of hypertension (7, 12, 14, 25). Recent studies from our laboratory have also shown that increases in blood pressure (BP) induced by chronic infusion of angiotensin II (ANG II) are less in wild-type (WT) female mice than in WT male mice. Ovariectomy augments ANG II-induced hypertension in females, suggesting that the female sex hormones protect against the development of ANG II-induced hypertension (42). However, the mechanisms underlying the protective effect of estrogen in the development of ANG II-induced hypertension remain uncertain.

ANG II is an important factor in many forms of both clinical and experimental hypertension. Acutely, systemic ANG II infusion increases BP by its peripheral vasoconstrictor effect. Chronically, ANG II-induced increase in BP is attributed in part to centrally mediated activation of the sympathetic nervous system (6, 32). Moreover, it has been shown that ANG II increases sympathetic nervous system activity and BP and resets baroreflex function via actions on circumventricular organs (CVOs), such as subfornical organ (SFO) and area postrema (AP) (1, 3, 4, 10, 11, 13, 41). Previous studies from our laboratory have shown that, in rats, estrogen opposes ANG II-mediated increases in neuronal activity and intracellular calcium in AP (19, 26). In mice, estrogen attenuates ANG II-induced increases in cellular reactive oxygen species (ROS), a key signaling intermediate in ANG II-stimulated activation of the central nervous system neurons (45), in both AP and SFO (27, 43). Taken together, these results implicate that estrogen may interact with ANG II in CVOs to antagonize the centrally mediated effects of ANG II on sympathetic nervous activity, BP, and baroreflex function.

Physiologically relevant concentrations of estrogen have both rapid and the long-term positive cardiovascular effects that are mediated by ERs, including ER{alpha} and ERbeta (23). A crucial role for ER{alpha} in the protection against vascular injury, activation of endothelial nitric oxide synthase, and antiatherosclerotic effects have been amply documented (15, 29). Genetic deletion of ERbeta results in the development of hypertension in middle-aged female and male mice due to multiple abnormalities of ion channel function in blood vessels (44). However, very little is known about the ERs involved in mediating the cardioprotective effects of estrogen on the central nervous system. We have previously reported that in female mice lacking ER{alpha}, ANG II resets cardiac baroreflex function similarly to that seen in males (28). The present study tested the hypotheses that 1) the ER{alpha} is involved in the protective effects of estrogen against ANG II-induced hypertension and 2) central ERs are involved.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animals

All experiments were performed in female mice. ER{alpha} knockout (ER{alpha}KO) mice were obtained by mating mice of C57BL/6J background that were heterozygous for the ER{alpha} gene disruption as described previously (20). Briefly, the ER{alpha}KO mouse is generated by disrupting the reading frame of the ER{alpha} gene NH2-terminal domain with a neomycin expression construct. This yields a small expression of incomplete ER{alpha} transcript expression but no fully functional {alpha}-subtype receptors (5). After mice were genotyped, only homozygous ER{alpha}KO (ER{alpha}–/–) females and homozygous (ER{alpha}+/+) wild-type (WT) females were used in these experiments. All the mice were obtained from a breeding colony maintained in the animal care facility at the University of Missouri. The mice were 12–16 wk old and had an average weight of 24–29 g. Mice were housed in standard polypropylene cages placed in a temperature- and humidity-controlled facility. The mice were maintained on a 12-h:12-h light-dark cycle (6:00 AM to 6:00 PM) and were fed soy-based Purina chow 5001 lab chow (PMI feeds, St. Louis, MO). The mice were divided into nine groups: intact WT, intact WT with peripheral ER antagonist ICI-182,780 (ICI) infusion, intact WT with central ICI, ovariectomized (OVX) WT, OVX WT with central 17beta-estradiol (E2), OVX WT with central E2 + ICI, intact ER{alpha}KO, intact ER{alpha}KO with central ICI, and OVX ER{alpha}KO with central E2 females. All procedures were approved by the University of Missouri and the University of Iowa Animal Care and Use Committees.

Surgical Procedures

Ovariectomy. Ten days before implantation of the BP transmitters, bilateral ovariectomy was performed in female mice anesthetized with a mixture of ketamine (100 mg/kg) and xylazine (10 mg/kg). Briefly, a single 1- to 2-cm dorsal midline incision was made in the skin and underlying muscles. The ovaries were isolated, tied-off with sterile suture, and removed, and the incisions were closed.

Telemetry probe implantation. Implantable mouse BP transmitters (TA11PA-C20, Data Sciences International, St. Paul, MN) were used to directly measure arterial pressure in individual animals. The mice were anesthetized with a ketamine-xylazine mixture. The carotid artery of the mouse was accessed with a ventral midline incision. The left carotid artery was isolated with fine-tipped vessel dilation forceps. Two occlusion sutures were placed beneath the artery. The elevated artery was punctured with a catheter introducer, and the telemetry catheter was inserted into the vessel. The catheter tip was advanced into the thoracic aorta so that ~3 mm of the thin-walled tip section could reside in the aorta. The sutures were tied and secured with tissue adhesive. Through the same ventral incision, a subcutaneous tunnel was formed across the right pectoral area and was enlarged to form a pocket along the right flank. The body of the transmitter was slipped into the pocket and secured with tissue adhesive. The ventral incision was then closed with suture.

Chronic intracerebroventricular cannula implantation. After baseline BP and heart rate (HR) recordings were made, the mice were again anesthetized with a ketamine-xylazine mixture, and the intracerebroventricular cannula with osmotic pump (ALZET Brain Infusion Kits, Alzet) was implanted into the right lateral ventricle (coordinates: 0.3 mm caudal, 1.0 mm lateral to bregma, and 3.0 mm below the skull surface) for chronic infusion of E2 (30 µg·kg–1·day–1), ICI (1.5 µg·kg–1·day–1), a nonselective ER antagonist, or E2 + ICI. In a separate group, osmotic pumps containing the same dose of ICI were implanted subcutaneously to determine the effect of peripheral blockade of ERs on ANG II-induced hypertension, which also served as the control for the effect of central infusion of ERs antagonist. At the end of the experiment, the animals were euthanized and perfused. The accuracy of the lateral ventricle cannula implantation was verified histologically.

Osmotic pump implantation. The mice were anesthetized with inhalational isoflurane to allow the implantation of osmotic pumps. Osmotic pumps (model 1002, Alzet) containing ANG II (Sigma Chemical) at a concentration sufficient to allow an infusion rate of 800 ng·kg–1·min–1 were implanted subcutaneously on the left side of the back.

Fluorescent immunohistochemistry. The WT and ER{alpha}KO mice were anesthetized deeply and perfused intracardially with phosphate-buffered saline (PBS) followed by 2% paraformaldehyde. The brains were removed, postfixed in 2% paraformaldehyde for 1 h, and then cryoprotected for 2 days in 30% sucrose at 4°C. Frozen 20-µm coronal slices were cut with a cryostat. Brain sections were washed with PBS and then blocked with 10% donkey serum (Jackson, PA) in PBS containing 0.2% Triton X-100 at 25°C for 1 h. Sections were then incubated with a rabbit anti-ER{alpha} antibody (1:400, Santa Cruz) in 10% donkey normal serum with 0.2% Triton X-100 for 72 h at 4°C. After being thoroughly washed with PBS, sections were incubated with rhodamine red-X-conjugated AffiniPure donkey anti-rabbit IgG (1:50, Jackson) in PBS for 24 h at 4°C. Sections were then washed, transferred to slides, air dried, and mounted with Mowioil. Fluorescence was then identified using a confocal microscope.

Experimental Protocol

Measurement of BP and HR. All mice were allowed 10 days of recovery from transmitter implantation surgery before any measurements were made. This time interval is necessary for the mice to regain their circadian BP and HR rhythm (2). Thereafter, BP and HR were telemetrically recorded and stored with the Dataquest ART data acquisition system (Data Sciences International).

To determine the effects of ANG II alone on BP and HR in WT and ER{alpha}KO mice, the osmotic pumps with ANG II were implanted subcutaneously in animals after 5 days of baseline recording.

To determine the effects of E2, ICI, or E2 + ICI on ANG II-induced hypertension in WT and ER{alpha}KO mice, the intracerebroventricular cannula with osmotic pump was implanted into the right lateral ventricle for chronic infusion of E2, ICI, or E2 + ICI for 14 days. On day 7, the osmotic pumps with ANG II were implanted subcutaneously.

Evaluation of response of BP to autonomic blockade. BP levels in female mice were also measured in the presence of the ganglionic blocker hexamethonium (30 mg/kg ip). The ganglionic blockade was repeated two times in each animal, during baseline and on day 7 during infusion of ANG II. On the day of the experiment, the mice were allowed to stabilize for at least 60 min, after which BP was recorded 20 min before hexamethonium injection and for 20 min after the treatment.

Data Analysis

Mean arterial pressure (MAP) and HR collected for 5 and 7 consecutive days before and during ANG II pump implantation, respectively, were plotted as mean values. All data are expressed as means ± SE. Statistical analyses of the effects of blockade of ERs or ER{alpha}KO on BP before and after ANG II infusion were performed with two-way ANOVA for repeated measures (Sigma Stat, version 2.06). Post hoc analysis was performed with Fisher least significant difference multiple comparison test where appropriate. One-way ANOVA was used for comparing changes in BP. Statistical significance was accepted at P < 0.05.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
The mice exhibited circadian organization of MAP and HR both before and during infusion of ANG II. ANG II infusion elicited increases in daytime and nighttime BPs. Consequently, all data were expressed as values averaged from daytime and nighttime measurements.

The Anatomical Placement of the Intracerebroventricular Cannula and ER{alpha} Expression in CVOs

Figure 1A is a photomicrograph that illustrates the anatomical placement of the intracerebroventricular cannula within the lateral ventricle.


Figure 1
View larger version (35K):
[in this window]
[in a new window]

  		Fig. 1. Photomicrograph illustrates brain cannula track that extended through the cortex into the lateral ventricle (LV, A). B and C: estrogen receptor-{alpha} (ER{alpha}) immunoreactivity in subfornical organ (SFO) in wild-type (WT) and ER{alpha} knockout (ER{alpha}KO) mice. 3V, 3rd ventricle.

 
Figure 1, B and C, shows ER{alpha} immunoreactivity in the SFO, a CVO in the lateral ventricle adjacent to where the cannula was implanted, in WT and ER{alpha}KO mice, respectively. The ER{alpha} expression presented in the SFO neurons of WT mice but not in the SFO neurons of ER{alpha}KO mice.

Baseline BP and HR in Conscious Mice

Baseline values for BP were comparable in all groups, which included WT females (102.4 ± 1.1 mmHg, n = 7), intact WT females with peripheral infusion of ICI (103.2 ± 2.1 mmHg, n = 5), intact WT females with central infusion of ICI (105.1 ± 3.2 mmHg, n = 6), and OVX WT (99.2 ± 0.9 mmHg, n = 5), OVX WT with central E2 (102 ± 0.8 mmHg, n = 5), OVX WT with central E2 + ICI (100.1 ± 1.8 mmHg, n = 5), intact ER{alpha}KO (106.1 ± 1.6 mmHg, n = 6), intact ER{alpha}KO with central ICI (101.1 ± 1.6 mmHg, n = 4), and OVX ER{alpha}KO with central E2 (102.0 ± 2.1 mmHg, n = 4) females. However, baseline HR was significantly higher in intact WT mice (630.1 ± 7.9 beats/min, P < 0.05) than in OVX WT (577.3 ± 27.7 beats/min) and ER{alpha}KO mice (576.4 ± 14.4 beats/min).

Effects of ANG II on MAP and HR in Intact WT, OVX WT, and ER{alpha}KO Mice

Averaged daily MAP, HR, and increases in MAP during infusion of ANG II in WT, OVX WT, and ER{alpha}KO mice are shown in Fig. 2A. Seven days of ANG II (800 ng·kg–1·min–1) infusion resulted in a 23.0 ± 1.0-mmHg (P < 0.05) and 23.8 ± 2.5-mmHg (P < 0.05) increase in MAP in OVX WT and ER{alpha}KO mice versus a 9.2 ± 1.5-mmHg increase in intact WT mice (Fig. 2B). Moreover, unlike intact WT mice (630.1 ± 7.9 to 596.2 ± 9.3 beats/min, P < 0.05), the increase in BP with ANG II did not result in the expected decrease in HR in OVX WT (577.3 ± 27.7 to 562.8 ± 9.3 beats/min) and ER{alpha}KO mice (576.4 ± 14.4 to 574.7 ± 7.8 beats/min) (Fig. 2C).


Figure 2
View larger version (14K):
[in this window]
[in a new window]

  		Fig. 2. Daily measurement of mean arterial pressures (MAPs, A) and heart rates (HRs, C) before and during infusion of angiotension II (ANG II) in intact, ovariectomized (OVX) WT and ER{alpha}KO female mice. B: averaged increases in MAP induced by ANG II infusion in intact, OVX WT and ER{alpha}KO female mice. C, control day. Control days are followed by 7 days of ANG II infusion. *P < 0.05 compared with baseline; #P < 0.05 compared with intact WT females.

 
Effects of Lateral Ventricle Infusion of E2 or E2 + ICI on ANG II-Induced Hypertension in OVX WT and ER{alpha}KO Females

Baseline MAP in OVX females was unaltered during central infusion of either E2 (30 µg·kg–1·day–1, WT 102 ± 0.8 to 99.6 ± 0.4 mmHg; ER{alpha}KO 102 ± 2.2 to 103.2 ± 2.3 mmHg) or E2 + ICI (1.5 µg·kg–1·day–1, WT 100.1 ± 1.8 to 100.5 ± 2.5 mmHg). In OVX WT mice, central E2 significantly inhibited the increases in MAP induced by ANG II ({Delta}MAP, 7.0 ± 0.4 mmHg, P < 0.05) compared with that seen in OVX mice with ANG II alone ({Delta}MAP, 23.0 ± 1.0 mmHg). Concurrent administration of ICI prevented this protective effect of E2 ({Delta}MAP, 18.8 ± 1.5 mmHg). In contrast, the pressor effect of ANG II was unchanged in central E2-treated OVX ER{alpha}KO mice ({Delta}MAP, 19.0 ± 1.1 mmHg) (Fig. 3, A and B). ANG II infusion did not change HR in either central E2-treated or central E2 + ICI-treated OVX mice (Fig. 3C).


Figure 3
View larger version (18K):
[in this window]
[in a new window]

  		Fig. 3. Daily measurement of MAPs (A) and HRs (C) before and during infusion of ANG II in central 17beta-estradiol (E2) or E2 + ICI-182,780 (ICI)-treated OVX WT and ER{alpha}KO female mice. B: averaged increases in MAP induced by ANG II infusion in all groups of female mice. Control days are followed by 14 days of E2 or E2 + ICI and 7 days of ANG II infusion. *P < 0.05 compared with baseline; #P < 0.05 compared with OVX WT females given just central E2.

 
Effects of Central and Peripheral Infusion of ICI on ANG II-Induced Hypertension in Intact WT and ER{alpha}KO Mice

Neither central or peripheral infusions of ERs antagonist had an effect on baseline MAP in conscious mice. Seven days of ANG II infusion resulted in a 17.8 ± 4.2-mmHg (P < 0.05) increase in MAP in WT mice treated with central infusions of ICI (1.5 µg·kg–1·day–1) versus a 10.1 ± 4.9 mmHg increase in mice treated with peripherally administrated antagonist. In contrast, central infusion of ICI had no effect on ANG II-induced increases in BP in ER{alpha}KO mice (19.6 ± 1.6 mmHg) (Fig. 4, A and B). As shown in Fig. 4C, ANG II infusion produced a significant decrease in HR in peripheral ICI-treated mice (636.7 ± 27.1 to 590.6 ± 12.4 beats/min, P < 0.05) but not in central ICI-treated (616.7 ± 15.3 to 613.9 ± 9.2 beats/min) and central ICI-treated ER{alpha}KO (584.4 ± 3.5 to 573.1 ± 2.7 beats/min) mice.


Figure 4
View larger version (19K):
[in this window]
[in a new window]

  		Fig. 4. Daily measurement of MAPs (A) and HRs (C) before and during infusion of ANG II in peripheral and central ICI-treated intact WT and ER{alpha}KO female mice. B: averaged increases in MAP induced by ANG II infusion in all of ICI-treated female mice. Control days are followed by 14 days of ICI and 7 days of ANG II infusion. *P < 0.05 compared with baseline; #P < 0.05 compared with WT females with peripheral ICI treatment.

 
Effects of Autonomic Blockade on BP

Figure 5 shows decreases in BP with acute ganglionic blockade in all group of female mice. The hexamethonium-induced decreases in BP were comparable in all groups before infusion of ANG II. Following seven days of ANG II infusion, acute hexamethonium injection resulted in a 53.8 ± 3.0, 56.6 ± 3.6, 58.4 ± 4.3, 60.1 ± 5.2, 59.1 ± 2.8, and 57.4 ± 3.5 mmHg decrease in BP in central ICI-treated intact WT, central ICI-treated intact ER{alpha}KO, OVX WT, central E2 + ICI-treated OVX WT, intact ER{alpha}KO, and central E2-treated OVX ER{alpha}KO mice, respectively. All of these groups showed significantly greater decreases in BP following hexamethonium relative to that seen in the WT females given just ANG II (36.6 ± 6.6 mmHg, P < 0.05).


Figure 5
View larger version (31K):
[in this window]
[in a new window]

  		Fig. 5. Decreases in MAP in response to ganglionic blockade with hexamethonium before and on day 7 after infusion of ANG II in all groups of female mice (A–C). Peri, peripheral; Cent, central. *P < 0.05 compared with control; #P < 0.05 compared with intact WT mice given just ANG II.

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The main findings of this study are 1) ER{alpha} is required for the protective effects of estrogen against ANG II-induced hypertension, 2) central ERs are involved in protection against ANG II-induced hypertension, and 3) the augmented effects of ANG II on BP in ER{alpha}KO females and females centrally treated with estrogen antagonist involve an increase in sympathetic outflow.

We have previously reported that the removal of ovaries, the main source of circulating estrogen in females, appears to facilitate the development of ANG II-dependent hypertension, suggesting that estrogen has a protective role in the development of ANG II-induced hypertension (42). The present study further addresses whether central estrogen and its receptors mediate the protective effects of estrogen. We found that in OVX female WT mice, central infusion of E2 attenuated the pressor effect of ANG II and that this attenuated effect of E2 was prevented by coadministration of ICI. Furthermore, in intact WT females, central, but not peripheral, administration of the ER antagonist ICI augmented increases in BP by ANG II. These observations suggest that it is central ERs, not peripheral ERs, that mediate the protective effects of estrogen in this hypertension model.

The chronic phase of ANG II-induced hypertension is associated with the increase in sympathetic nerve activity and blunting of baroreflex HR response (6, 8, 9, 21, 31, 33, 40). Estrogen in general is also known to facilitate baroreflex function in rats. Saleh et al. (35–37) have shown that central administration of estrogen decreases sympathetic activity and increases parasympathetic activity. Moreover, central injection of ER antagonist ICI blocked increases in vagal nerve activity and decreases in renal nerve activity induced by bolus injection of estrogen (iv), indicating that peripheral-administered estrogen modulates baseline autonomic tone via the activation of central ERs (38). We have previously shown that ganglionic blockade produces less reduction in BP in female mice compared with that in male mice during ANG II infusion and that reflex bradycardic responses are blunted in males but not in females during ANG II infusion, which may be indicative of females being able to buffer the increases in BP better than in males through a reduced activation of sympathetic nervous system and maintenance of the baroreflex sensitivity (42). The present study confirms and extends this previous study by showing that the increases in BP with ANG II did not result in the expected decrease in HR in either central ERs antagonist-treated WT or ER{alpha}KO mice. In addition, ganaglionic blockade produced greater reduction in BP in the ER{alpha}KO mice, suggesting that central ERs, especially ER{alpha}, play an important role in buffering ANG II-induced central resetting of baroreflexes and increase in sympathetic nervous system activity, which contributes to attenuated increase in BP during ANG II infusion in females.

Both ER{alpha} and ERbeta have been shown to be involved in the regulation of cardiovascular function (15, 22, 23, 29, 44). Because of homologous regions in the genes for ER{alpha} and ERbeta (17, 18, 24, 30, 39), to date there is no selective ERbeta antagonist commercially available. However, the observation of distinct biological functions for ER{alpha} and ERbeta in genetic mice lacking ER{alpha}, ERbeta, or both represents a novel tool to dissect the ligand-dependent function of ER{alpha} and ERbeta (29, 44). In the present study, the intent for studying ANG II-induced hypertension in ER{alpha}KO mice was to further address the role of ER{alpha} in mediating protective effects of estrogen in this mouse model. It has been shown that intact ER{alpha}KO females have high levels of estrogen and testosterone (28). However, it has been also shown in the same study that, in the ER{alpha}KO mice, responses to ANG II remain the same irrespective of the estrogen levels. Baroreflex responses to ANG II in OVX ER{alpha}KO mice, which eliminate the high levels of estrogen and testosterone, were identical to responses in intact ER{alpha}KO mice. In addition, estrogen replacement in these OVX ER{alpha}KO mice had no effect on ANG II-mediated baroreflex responses (28). In the present study, ANG II-mediated increases in BP in OVX WT mice ({Delta}23 ± 1 mmHg) and in intact ER{alpha}KO mice ({Delta}23.8 ± 2.5 mmHg) are very similar. Central ICI or E2 infusion has no influence on the pressor effect of ANG II in intact ER{alpha}KO or OVX ER{alpha}KO mice, respectively. These results indicate that reducing estrogen levels or total knockout of ER{alpha} has similar effects on ANG II-dependent hypertension. Taken together, we interpret the data as suggestive of a predominant role for ER{alpha} in mediating effects of estrogen in this mouse model with no significant compensation from other pathways.

Although the central mechanisms by which estrogen acts to produce protective effects are not known, there is increasing evidence indicating that the effects of estrogen could be attributed in part to modulation of the renin-angiotensin system. It has been established that the central effect of ANG II, the main component of the renin-angiotensin system, is mediated predominantly by ANG II type 1 (AT1) receptor subtype in CVOs, such as SFO and AP (9, 40). Kisly et al. (16) reported that estrogen treatment decreases SFO AT1 receptor binding as well as hypothalamic AT1 receptor mRNA, suggesting that the genomic regulation of central ANG II receptor by estrogen may underlie the BP changes observed in females. Another potential mechanism may involve estrogen regulation of ANG II-induced ROS, a key signaling intermediate in ANG II-stimulated activation of the central nervous system neurons (45). Preliminary studies from our laboratory indicated that estrogen inhibits an ANG II-induced increase in cellular ROS in SFO and AP living slices and that these inhibitory effects of estrogen are blocked by ICI (27, 43). These results are in good agreement with the morphological evidence obtained by us and others that shows high densities of ER{alpha} in CVOs and colocalization of ER and AT1 receptor in the SFO (34). Therefore, it is reasonable to hypothesize that blockade of central ERs may cause increases in AT1 receptor expression and binding, and ROS production, leading to an enhanced biological effect of ANG II that could in part serve as an explanation for the augmented increase in BP induced by ANG II.

In summary, the present study demonstrated that ER{alpha}, especially the central expression of the ER, mediates the protective effect of estrogen in the development of ANG II-induced hypertension in female mice.


   GRANTS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported by National Heart, Lung, and Blood Institute Grant HL-62261 and American Heart Association Grant 0325515Z.


   FOOTNOTES
 

Address for reprint requests and other correspondence: B. Xue, Dept. of Psychology, Univ. of Iowa, 11 Seashore Hall E, Iowa City, IA 52242 (e-mail: baojian-xue{at}uiowa.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
 METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. Bishop VS, Hay M. Involvement of the area postrema in the regulation of sympathetic outflow to the cardiovascular system. In: Frontiers in Neuroendocrinology. New York: Raven, 1993, p. 57–75.
  2. Butz GM, Davisson RL. Long-term telemetric measurement of cardiovascular parameters in awake mice: a physiological genomics tool. Physiol Genomics 5: 89–97, 2001.[Abstract/Free Full Text]
  3. Collister JP, Hendel MD. Chronic effects of angiotensin II and AT1 receptor antagonists in subfornical organ-lesioned rats. Clin Exp Pharmacol Physiol 32: 462–466, 2005.[CrossRef][Web of Science][Medline]
  4. Cottrell TG, Ferguson AV. Sensory circumventricular organs: central roles in integrated autonomic regulation. Regul Pept 117: 11–23, 2004.[CrossRef][Web of Science][Medline]
  5. Couse JF, Curtis SW, Washburn TF, Lindzey J, Golding TS, Lubahn DB, Smithies O, Korach KS. Analysis of transcription and estrogen insensitivity in the female mouse after targeted disruption of the estrogen receptor gene. Mol Endocrinol 9: 1441–1454, 1995.[Abstract/Free Full Text]
  6. Cox BF, Bishop VS. Neural and humoral mechanisms of angiotensin-dependent hypertension. Am J Physiol Heart Circ Physiol 261: H1284–H1291, 1991.[Abstract/Free Full Text]
  7. Crofton JT, Share L. Gonadal hormones modulate deoxycorticosterone-salt hypertension in male and female rats. Hypertension 29: 494–499, 1997.[Abstract/Free Full Text]
  8. Ferrario CM. Neurogenic actions of angiotensin II. Hypertension 5: 73–79, 1983.
  9. Gorbea-Opplinger VJ, Fink GD. Cerebroventicular injection of angiotensin II antagonist: effects on blood pressure responses to central and systemic angiotensin II. J Pharmacol Exp Ther 273: 611–616, 1995.[Abstract/Free Full Text]
  10. Hasser EM, Cunningham JT, Sullivan MJ, Curtis KS, Blaine EH, Hay M. Area postrema and sympathetic nervous system effects of vasopressin and angiotensin II. Clin Exp Pharmacol Physiol 27: 432–436, 2000.[CrossRef][Web of Science][Medline]
  11. Hay M. Subcellular mechanisms of area postrema activation. Clin Exp Pharmacol Physiol 28: 551–557, 2001.[CrossRef][Web of Science][Medline]
  12. Haywood JR, Hinojosa-Laborde C. Sexual dimorphism of sodium-sensitive renal-wrap hypertension. Hypertension 30: 667–671, 1997.[Abstract/Free Full Text]
  13. Hendel MD, Collister JP. Contribution of the subfornical organ to angiotensin II-induced hypertension. Am J Physiol Heart Circ Physiol 288: H680–H685, 2005.[Abstract/Free Full Text]
  14. Hinojosa-Laborde C, Lange DL, Haywood JR. Role of female sex hormones in the development and reversal of Dahl hypertension. Hypertension 35: 484–489, 2000.[Abstract/Free Full Text]
  15. Huang A, Kaley G. Gender-specific regulation of cardiovascular function: estrogen as key player. Microcirculation 11: 9–38, 2004.[CrossRef][Web of Science][Medline]
  16. Kisley LR, Sakai RR, Fluharty SJ. Estrogen decreases hypothalamic angiotensin II AT1 receptor binding and mRNA in the female rat. Brain Res 844: 34–42, 1999.[CrossRef][Web of Science][Medline]
  17. Kuiper GG, Shughrue PJ, Merchenthaler I, Gustafsson JA. The estrogen receptor beta subtype: a novel mediator of estrogen action in neuroendocrine systems. Front Neuroendocrinol 19: 253–286, 1998.[CrossRef][Web of Science][Medline]
  18. Laflamme N, Nappi RE, Drolet G, Labrie C, Rivest S. Expression and neuroprptidergic characterization of estrogen receptor (ER{alpha} and ERbeta) throughout the rat brain: anatomical evidence of distinct role of each subtype. J Neurobiol 36: 357–378, 1998.[CrossRef][Web of Science][Medline]
  19. Li ZC, Hay M. 17beta-Estradiol modulation of area postrema potassium currents. J Neurophysiol 84: 1385–1391, 2000.[Abstract/Free Full Text]
  20. Lubahn DB, Moyer JS, Golding TS, Couse JF, Korach KS, Smithies O. Alteration of reproductive function but not prenatal sexual development after insertional disruption of the mouse estrogen receptor gene. Proc Natl Acad Sci USA 90: 11162–11166, 1993.[Abstract/Free Full Text]
  21. Matsukawa S, Reid IA. Role of area postrema in the modulation of baroreflex control of heart rate by angiotensin II. Circ Res 67: 1462–1473, 1990.[Abstract/Free Full Text]
  22. Mendelsohn ME. Protective of effects of estrogen on the cardiovascular system. Am J Cardiol 89: 12E–18E, 2002.[Web of Science][Medline]
  23. Mendelsohn ME, Kara RH. Molecular and cellular basis of cardiovascular gender differences. Science 38: 1583–1587, 2005.
  24. Mitra SW, Hoskin E, Yudkovitz J, Pear L, Wilkinson HA, Hayashi S, Pfaff DW, Ogawa S, Rohrer SP, Schaeffer JM, McEwen BS, Alves SE. Immunolocalization of estrogen receptor beta in the mouse brain: comparison with estrogen receptor alpha. Endocrinology 144: 2055–1067, 2003.[Abstract/Free Full Text]
  25. Ouchi Y, Share L, Crofton JT, Iitake K, Books DP. Sex differences in development of deoxycorticosterone-salt hypertension. Hypertension 9: 172–177, 1987.[Abstract/Free Full Text]
  26. Pamidimukkala J, Hay M. 17beta-Estradiol inhibits angiotensin II activation of area postrema neurons. Am J Physiol Heart Circ Physiol 285: H1515–H1520, 2003.[Abstract/Free Full Text]
  27. Pamidimukkala J, Xue B, Hay M. Role of ROS in angiotensin II-activation of area postrema (AP) neurons and systemic hypertension (Abstract). FASEB J LB501: A103, 12004.
  28. Pamidimukkala J, Xue B, Newton LG, Lubahn DB, Hay M. Estrogen receptor-{alpha} mediates estrogen facilitation of baroreflex heart rate responses in conscious mice. Am J Physiol Heart Circ Physiol 288: H1063–H1070, 2005.[Abstract/Free Full Text]
  29. Pare G, Krust A, Karas RH, Dupont S, Aronovitz M, Chambon P, Mendelsohn ME. Estrogen receptor {alpha} mediates the protective effects of estrogen against vascular injury. Circ Res 90: 1087–1092, 2002.[Abstract/Free Full Text]
  30. Pettersson K, Gustafsson JA. Role of estrogen receptor beta in estrogen action. Annu Rev Physiol 63: 165–192, 2001.[CrossRef][Web of Science][Medline]
  31. Potter EK, Reid IA. Intravertebral angiotensin II inhibits cardiac vagal efferent activity in dogs. Neuroendocrinology 40: 493–496, 1985.[Web of Science][Medline]
  32. Reid IA. Interactions between ANG II, sympathetic nervous system, and baroreceptor reflexes in regulation of blood pressure. Am J Physiol Endocrinol Metab 262: E763–E778, 1992.[Abstract/Free Full Text]
  33. Reid I, Kumagai K. Angiotensin II exerts differential actions on renal nerve activity and heart rate. Hypertension 24: 451–456, 1994.[Abstract/Free Full Text]
  34. Rosas-Arellano MP, Solano-Flores LP, Ciriello J. Co-localization of estrogen and angiotensin receptors within subfornical organ neurons. Brain Res 837: 254–262, 1999.[CrossRef][Web of Science][Medline]
  35. Saleh MC, Connell BJ, Saleh TM. Autonomic and cardiovascular reflex responses to central estrogen injection in ovariectomized female rats. Brain Res 879: 105–114, 2000.[CrossRef][Web of Science][Medline]
  36. Saleh MC, Connell BJ, Saleh TM. Medullary and intrathecal injections of 17beta-estradiol in male rats. Brain Res 867: 200–209, 2000.[CrossRef][Web of Science][Medline]
  37. Saleh TM, Connell BJ. Centrally mediated effect of 17beta-estradiol on parasympathetic tone in male rats. Am J Physiol Regul Integr Comp Physiol 176: R474–R481, 1999.
  38. Saleh TM, Connell BJ. 17beta-Estradiol modulates baroreflex sensitivity and autonomic tone of female rats. J Auton Nerv Syst 80: 148–161, 2000.[CrossRef][Web of Science][Medline]
  39. Shughrue PJ, Lane MV, Merchenthaler I. Comparative distribution of estrogen receptor-{alpha}, and -beta mRNA in the rat central nervous system. J Comp Neurol 388: 507–525, 1997.[CrossRef][Web of Science][Medline]
  40. Wong J, Chou L, Reid IA. Role of AT1 receptors in the resetting of the baroreflex control of heart rate by angiotensin II in rabbits. J Clin Invest 91: 1516–1520, 1993.[Web of Science][Medline]
  41. Xue B, Gole H, Pamidimukkala J, Hay M. Role of the area postrema in angiotensin II modulation of baroreflex control of heart rate in conscious mice. Am J Physiol Heart Circ Physiol 284: H1003–H1007, 2003.[Abstract/Free Full Text]
  42. Xue B, Pamidimukkala J, Hay M. Sex differences in the development of angiotensin II-induced hypertension in conscious mice. Am J Physiol Heart Circ Physiol 288: H2177–H2184, 2005.[Abstract/Free Full Text]
  43. Zhao Y, Pamidimukkala J, Hay M. Angiotensin II evoked increases in reactive oxygen species in subfornical organ neurons in the living brain slice (Abstract). FASEB J 699.2: A1291, 2005.
  44. Zhu Y, Bian Z, Lu P, Karas RH, Bao L, Cox D, Hodgin J, Shaul PW, Thoren P, Smithies O, Gustafsson JA, Mendelsohn MA. Abnormal vascular function and hypertension in mice deficient in estrogen receptor beta. Science 295: 505–508, 2002.[Abstract/Free Full Text]
  45. Zimmerman MC, Lazartigues E, Lang JA, Sinnayah P, Ahmad IM, Spitz DR, Davisson RL. Superoxide mediates the actions of angiotensin II in the central nervous system. Circ Res 91: 1038–1045, 2002.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
B. Xue, D. Badaue-Passos Jr, F. Guo, C. E. Gomez-Sanchez, M. Hay, and A. K. Johnson
Sex differences and central protective effect of 17{beta}-estradiol in the development of aldosterone/NaCl-induced hypertension
Am J Physiol Heart Circ Physiol, May 1, 2009; 296(5): H1577 - H1585.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
G. Wang, T. A. Milner, R. C. Speth, A. C. Gore, D. Wu, C. Iadecola, and J. P. Pierce
Sex differences in angiotensin signaling in bulbospinal neurons in the rat rostral ventrolateral medulla
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2008; 295(4): R1149 - R1157.
[Abstract] [Full Text] [PDF]

Home page
 HypertensionHome page
A. K. Sampson, K. M. Moritz, E. S. Jones, R. L. Flower, R. E. Widdop, and K. M. Denton
Enhanced Angiotensin II Type 2 Receptor Mechanisms Mediate Decreases in Arterial Pressure Attributable to Chronic Low-Dose Angiotensin II in Female Rats
Hypertension, October 1, 2008; 52(4): 666 - 671.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
B. Xue, Y. Zhao, A. K. Johnson, and M. Hay
Central estrogen inhibition of angiotensin II-induced hypertension in male mice and the role of reactive oxygen species
Am J Physiol Heart Circ Physiol, September 1, 2008; 295(3): H1025 - H1032.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
J. C. Sullivan
Sex and the renin-angiotensin system: inequality between the sexes in response to RAS stimulation and inhibition
Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2008; 294(4): R1220 - R1226.
[Abstract] [Full Text] [PDF]

Home page
 HypertensionHome page
J. C. Sartori-Valinotti, R. Iliescu, L. L. Yanes, W. Dorsett-Martin, and J. F. Reckelhoff
Sex Differences in the Pressor Response to Angiotensin II When the Endogenous Renin-Angiotensin System Is Blocked
Hypertension, April 1, 2008; 51(4): 1170 - 1176.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
H. Girouard, A. Lessard, C. Capone, T. A. Milner, and C. Iadecola
The neurovascular dysfunction induced by angiotensin II in the mouse neocortex is sexually dimorphic
Am J Physiol Heart Circ Physiol, January 1, 2008; 294(1): H156 - H163.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Cell Physiol.Home page
E. Mendez-Bolaina, J. Sanchez-Gonzalez, I. Ramirez-Sanchez, E. Ocharan-Hernandez, M. Nunez-Sanchez, E. Meaney-Mendiolea, A. Meaney, J. Asbun-Bojalil, A. Miliar-Garcia, I. Olivares-Corichi, et al.
Effect of caveolin-1 scaffolding peptide and 17 -estradiol on intracellular Ca2+ kinetics evoked by angiotensin II in human vascular smooth muscle cells
Am J Physiol Cell Physiol, December 1, 2007; 293(6): C1953 - C1961.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
292/4/H1770    most recent
01011.2005v1
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 Web of Science
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 Web of Science (6)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Xue, B.
Right arrow Articles by Hay, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Xue, B.
Right arrow Articles by Hay, M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2007 by the American Physiological Society.