AJP - Heart Watch the video to see 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 288: H1931-H1936, 2005. First published December 2, 2004; doi:10.1152/ajpheart.00931.2004
0363-6135/05 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
288/4/H1931    most recent
00931.2004v1
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 ISI 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 ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Colantuoni, A.
Right arrow Articles by Iervasi, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Colantuoni, A.
Right arrow Articles by Iervasi, G.

Effects of tetraiodothyronine and triiodothyronine on hamster cheek pouch microcirculation

A. Colantuoni,1 P. L. Marchiafava,2 D. Lapi,2 F. S. Forini,3 and G. Iervasi3

1Department of Neuroscience, "Federico II" University Medical School, Naples; 2Department of Physiology and Biochemistry, University of Pisa; 3Consiglio Nazionale delle Ricerche Institute of Clinical Physiology, Pisa, Italy

Submitted 7 September 2004 ; accepted in final form 29 November 2004


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
The aim of the present study was to assess the effects of topically applied triiodothyronine (T3) and thyroxine (T4) on the arterioles of hamster cheek pouch microcirculation in vivo. Microvessels were visualized using a fluorescent microscopy technique. Topical application of T3 (3.08, 30.8, 61.5, 307, 615, and 6,150 nM/l) consistently induced dose-dependent dilation of arterioles within 2.0 ± 0.5 min of administration. The application of T4 (150, 257, 514, and 5,140 nM/l) caused different dose-dependent effects: dilation at the three lower doses within 16 ± 2 min and rhythmic diameter changes at the highest dose. Aging of hamsters did not alter the arteriolar responses to T3 and T4. T3-induced dilation was countered by the inhibition of nitric oxide synthase with NG-nitro-L-arginine-methyl ester or NG-nitro-L-arginine. Iopanoic acid (IPA), which inhibits types I and II 5'-deiodinase, abolished the dilation elicited by 514 nM T4 but did not affect T3-dependent dilation. 6-Propyl-2-thiouracil (PTU), which inhibits type I 5'-deiodinase only, did not affect the dilation induced by T4. IPA and PTU did not impair arteriolar dilation induced by acetylcholine or sodium nitroprusside. These results indicate that T3 induces arteriolar dilation, likely through nitric oxide release. The local conversion of T4 to T3 appears to be crucial for the dilation induced by T4.

microcirculation; vasodilation; arterioles; nitric oxide; NG-nitro-L-arginine methyl ester; NG-nitro-L-arginine; iopanoic acid; 6-propyl-2-thiouracil; thyroid hormones

THE THYROID GLAND synthesizes and releases the thyroid hormones (THs) mainly as tetraiodothyronine (thyroxine, T4) (15). Most of the biologically active triiodothyronine (T3) derives from the conversion of T4 by 5' monodeiodination (types I and II 5'-deiodinase) in peripheral tissues (17, 19). Type I 5'-deiodinase has a primary role in maintaining circulating T3 levels, whereas type II 5'-deiodinase regulates the intracellular concentration of T3 (12, 18). The direct effects of the THs are triggered by their binding to nuclear receptors (3). Recently, T3 and T4 have been shown to stimulate extranuclear sites. A number of nongenomic effects of T3 have also been identified, including ion fluxes at the level of the plasma membrane (11).

Both THs markedly affect the peripheral vascular tone (10). However, the mechanisms by which they influence the peripheral vasculature have not been fully explained. Their vasodilating effects have been related to the local formation of vasodilatory substances due to metabolic activity, oxygen consumption, and heat production. Furthermore, it has been shown that both THs directly interact with vascular smooth muscle (VSM) cells of isolated rabbit mesenteric artery, causing dilation; in particular, T4 has a greater inhibitory effect than T3 on VSM contraction (9). In vitro studies have also demonstrated that exposure to T3 of VSM cells isolated from the rat aorta caused these cells to relax rapidly. T4 did not compete for the binding sites of T3. This effect was independent of cAMP and nitric oxide (NO) formation (14). Indeed, primary cultures of vascular endothelial cells exposed to T3 show no NO production, indicating that T3 interacts directly with VSM to cause relaxation. However, it has been reported in rat skeletal muscle resistance arteries (diameter: ~100 µm) that T3 is more effective than T4 in inducing vasodilation (13). This dilation appears to have both endothelium-dependent and -independent components, because T3 dilation was attenuated by NG-nitro-L-arginine, indomethacin, and glibenclamide.

By contrast, in rat mesenteric resistance vessels, Zwaveling and colleagues (29) have observed that T4 is more potent than T3 in inducing vascular relaxation. This effect was impaired by NG-nitro-L-arginine methylester (L-NAME); moreover, as vascular relaxation was observed at supraphysiological concentrations (100 times the basal level), the authors concluded that the direct effects of the THs are not relevant for the in vivo situation. Recently, direct effects of the THs have been described in rat coronary arteries within a few seconds of administration, suggesting a nongenomic mechanism of action of the hormone (23). All data indicate that the peripheral vasculature may represent a physiological target for the THs. By contrast, the THs have not yet been proved to affect in vivo microcirculation.

The present study was designed to assess the effects of T3 and T4 on the arterioles of hamster cheek pouch microcirculation, a widely used experimental model (7, 6). We hypothesize that T3 might induce its predominant vasodilatory effect through NO release. Moreover, T4 dilatory effect might be related to local conversion of T4 into T3. Therefore, we evaluated the arteriolar responses to T3 and T4 administration after inhibition of NO synthase (NOS) by L-NAME or NG-nitro-L-arginine (L-NNA). Furthermore, we topically applied the hormones on the cheek pouch after inhibition of types I and II 5'-deiodinase by iopanoic acid (IPA) or inhibition of type I 5'-deiodinase by 6-propyl-2-thiouracil (PTU) (12).


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Male Syrian hamsters weighing 80–100 g (Charles River) were randomly assigned to 10 groups. Control hamsters (n = 10) received topically the vehicles or DMSO and were compared with the animals from the other nine groups that received topically T3 or T4 alone or preceded by other substances, as described below. Group A (n = 50) received topically T3 (at the doses of 3.08, 30.8, 61.5, 307, 615, and 6,150 nM/l delivered for 2 min) or T4 (150, 257, 514, and 5,140 nM/l delivered for 2 min). T3 and T4 were dissolved in a solution containing methanol-ammonia (99:1); 1 µg/µl of T3 and T4 from this stock solution was finally added to Ringer solution to obtain the appropriate concentration with adjusted pH. Group B (n = 8) was administered 1 mM topical L-NAME (n = 5) or 1 mM topical D-NAME, an isomer of NAME (n = 3), 15 min before receiving T3, 615 nM/l delivered for 2 min. Group C (n = 5) was administered 1 mM topical L-NNA 15 min before receiving T3, 615 nM/l delivered for 2 min. Group D (n = 5) was administered 1 mM topical L-NAME 15 min before receiving T4, 5,140 nM/l delivered for 2 min. Group E (n = 5) was administered 1 mM topical L-NNA 15 min before receiving T4, 5,140 nM/l delivered for 2 min. Group F (n = 5) was given topically 1 mM L-arginine and 1 mM L-NAME 15 min before receiving T3, 615 nM/l delivered for 2 min. Group G (n = 5) was given topically 1 mM L-arginine and 1 mM L-NNA 15 min before receiving T3, 615 nM/l delivered for 2 min. Group H was administered 0.4 mM topical IPA 15 min before receiving T3, 615 nM/l delivered for 2 min (n = 5), or T4, 514 nM/l delivered for 2 min (n = 5), or T4, 5,140 nM/l delivered for 2 min (n = 5); 0.3 ml of DMSO was added to the solution of IPA. Group I (n = 5) received topically 2 mM PTU 20 min before T4, 514 nM/ delivered for 2 min. Group J (n = 30) was given topically 1 µM ACh (n = 5) or 1 µM sodium nitroprusside (NT) (n = 5), or 0.4 mM IPA 15 min before ACh (n = 5) or NT (n = 5), or 2 mM PTU 20 min before ACh (n = 5) or NT (n = 5). Each dose of the THs was used in only one animal. The drugs were obtained from Sigma (St. Louis, MO).

A reverse-phase HPLC technique was used for purification and separation of iodothyronines to assess contaminant T4 or T3. Briefly, chomatography was performed by a 10-µm C18 silica gel column (3 x 300 mm); mobile phase was methanol-water (55:45) with a flow rate of 1.2 ml/min at a pressure of 2,800 psi (2). Radiolabeled T4 and T3 were added to measure recovery and to identify the iodothyronine of interest (i.e., T4 and T3) after extraction and HPLC separation.

Fifteen aged male hamsters, weighing 150–160 g (18–20 mo old), served as aged (AG) control (n = 5) or were given topically T3, 615 nM/l delivered for 2 min (n = 5), or T4, 514 nM/l delivered for 2 min (n = 5), to determine the effects of THs also in aged hamsters.

The hamsters were caged, fed, and killed in accordance with the principles for research involving animals and human being and the institutional rules for the care and handling of experimental animals.

The cheek pouches were surgically prepared as reported previously (4). Anesthesia was induced with a pentobarbital sodium injection (Nembutal, 5 mg/100 g body wt ip) (Abbott, Chicago, IL). The animals were tracheotomized; the right carotid artery and femoral vein were cannulated to measure blood pressure and to administer additional anesthesia and the fluorescent tracer. The cheek pouch was gently everted and fixed to a special stage of the microscope; a thin black blade was inserted through a small incision between the upper and lower layers of the pouch to visualize microcirculation of the superior layer. The membrane was suffused (4 ml/min) with Ringer solution (in mM: 137 NaCl, 4.7 KCl, 1.2 MgSO4, 2.0 CaCl2, and 18.0 NaHCO3) at 36 ± 0.5°C containing 5% CO2-95% N2 adjusted to pH 7.35. The animal was warmed with a heating pad, and the rectal temperature was measured by a thermocouple wire.

Observations were made with a fluorescent microscope (Leitz Orthoplan) fitted with a long-working objective [x4, numerical aperture (NA) 0.14; x20, NA 0.25; x32, NA 0.60], a x10 eyepiece, and a filter block (Ploemopak, Leitz). Epi-illumination was provided by a 100-W mercury lamp fitted with the appropriate filters for fluorescein isothiocyanate bound to dextran (molecular mass 150 K, 50 mg/100 g body wt iv as 5% wt/vol solution in 5 min) (Sigma) and a heat filter (Leitz KG1). The area of interest was televised with a Dage MTI 300 digital low-light level camera and observed on a Sony PVM 122 CE monitor. Video images were videotaped and microvascular measurements made off-line using a computer-assisted imaging software system (MIP Image, CNR Institute of Clinical Physiology, Pisa, Italy).

Vessel diameter was measured with a computer-assisted method on analog-digital converted video-recorded images. To avoid bias due to single operator measurements, two independent "blinded" operators measured the vessel diameters. Their measurements overlapped in all cases. Mean arterial blood pressure (Viggo-Spectramed P10E2 transducer, Oxnard, CA, connected to a catheter in the carotid artery) and heart rate were monitored with a Gould Windowgraf recorder (model 13-6615-10S, Gould, OH). All data were recorded and stored in a computer.

The arteriolar vessels in each preparation were classified according to a centrifugal ordering scheme from the largest (A1) to the smallest (A4) arterioles. In each animal, two A2, two A3, and two A4 arterioles were studied under baseline conditions and after application of the THs alone or preceded by the drugs. These substances were applied switching from one to another reservoir filled with the drugs for 2 min. The time to maximum dilation and the time to baseline diameter recovery were evaluated starting from the end of drug application. The video images of the microvascular networks were recorded for 20 min during baseline observation and for up to 45 min after drug administration. To reduce the effects of epi-illumination on microvessels, the recordings were performed for 20 s/min under baseline conditions and for 30 s/min when the observation lasted more than 10 min after drug administration. At the end of the observation, dilation to topical ACh (1 x 10–6 M) and constriction to phenylephrine (PE) (5 x 10–6 M) were randomly assessed to explore vessel reactivity.

All values are means ± SD. An SPSS+ statistical package was used for analysis of statistical significance. Data were tested for normal distribution using the Kolmogorov-Smirnov test. Parametric (paired and unpaired Student's t-test, ANOVA, and Scheffé's post hoc test) and nonparametric tests (Wilcoxon test, Friedman test, Mann-Whitney U-test, and Kruskal-Wallis test) were applied where appropriate. Statistical significance was set at P < 0.05.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The arterioles of cheek pouch microvascular networks, from the largest A2 to the smallest A4, were studied in control and AG control hamsters. The baseline diameters were not significantly different in the two groups (diameter: A2, 23.3 ± 1.6 µm; A3, and 13.9 ± 1.2 µm; A4, 7.5 ± 1.0 µm in control group vs. AG group: A2, 23.5 ± 1.5 µm; A3, 13.7 ± 1.4 µm; and A4, 7.7 ± 0.8 µm). Pilot studies indicated that the lowest effective doses inducing vasodilation were 3.08 nM (T3) and 150 nM (T4) because lower concentrations of the hormones (1.54, 1.84, 2.15, 2.46 nM T3 and 50, 75, 100, 125 nM T4) caused no vessel response. We used different doses in the range 3.08–6,150 nM for T3 and 150–5,140 nM for T4. We report in Fig. 1 and in Table 1 the arteriolar responses to the lowest effective and higher doses that are comprised in the plasmatic ranges of hamster THs (15, 20).



View larger version (16K):
[in this window]
[in a new window]
  		Fig. 1. Dose-dependent arteriolar (A2, A3, and A4) relaxation induced by triiodothyronine (T3). Percent changes were evaluated by the ratio of maximum diameters before and after T3. All diameter variations were statistically significant, *P < 0.01. Each entry = 10 arterioles studied in 5 animals.

 

View this table:
[in this window]
[in a new window]
  		Table 1. Averages of maximum diameters of A2, A3, and A4 arterioles under baseline conditions and after application of T4

 
T3 induced a dose-dependent dilation of all arterioles. The percent changes of A2, A3, and A4 arteriole diameter after T3 topical administration (semilog plot) are reported in Fig. 1. Vessel diameter increased significantly (P < 0.01) with all doses. Time to maximum dilation was 2.0 ± 0.5, 1.8 ± 0.6, 1.8 ± 0.5, 4.5 ± 1.0, 5.5 ± 0.7, and 2.5 ± 0.8 min for the corresponding dose of T3, respectively, 3.08, 30.8, 61.5, 307, 615, and 6,150 nM/l. Effect duration was also dose dependent and lasted 5.0 ± 1.0, 18.0 ± 2.5, 22.0 ± 3.0, 28.0 ± 3.0, 33.0 ± 1.0, and 36.0 ± 1.0 min according to the dose, as above reported.

T4 also caused dose-dependent responses (Table 1). The lowest dose-induced arteriolar dilation, 16.0 ± 2.0 min from administration, lasting 4.5 ± 1.0 min; a typical response is reported in Fig. 2. Arteriolar dilation was also observed for the doses 257 and 514 nM within 15.0 ± 1.0 and 14.0 ± 0.8 min of injection, respectively. Maximum of dilation was detected just at the beginning and lasted 16.0 ± 2.0 and 20.0 ± 3.0 min, respectively. The highest dose of T4 caused rhythmic diameter changes within 5.0 ± 1.0 min of application that lasted up to 20.0 ± 2.0 min from administration.



View larger version (50K):
[in this window]
[in a new window]
  		Fig. 2. Arteriolar dilation induced by lowest concentration (150 nM/l) of tetraiodothyronine (T4). Left, baseline; right, 16 min after T4 application. Bar: 10 µm.

 
Inhibition of NOS by L-NAME or L-NNA prevented the vasodilatory action of T3 (Table 2). L-Arginine but not D-arginine was able to reverse the effects of both inhibitors (Table 2), whereas D-NAME did not influence the dilation induced by T3 (data not shown). L-NAME did not affect the rhythmic changes in diameter induced by the highest dose of T4.


View this table:
[in this window]
[in a new window]
  		Table 2. Averages of maximum diameters of A2, A3 and A4 arterioles under baseline conditions, after L-NAME or L-NNA, and after T3 application

 
IPA, which inhibits both type I and type II 5'-deiodinase, the enzyme that transforms the prohormone T4 into biologically active T3, did not interfere with the dilation elicited by T3 (Table 3). By contrast, it abolished the effect induced by the dilating dose of T4 (514 nM). IPA did not interfere with the effects of the highest dose of T4 (5,140 nM) that were characterized by rhythmic changes in diameter.


View this table:
[in this window]
[in a new window]
  		Table 3. Averages of maximum diameters of A2, A3, and A4 arterioles under baseline conditions and after application of IPA and T3, or IPA and T4, or PTU and T4

 
Topical application of PTU, the specific inhibitor of type I 5'-deiodinase, 20 min before 514 nM T4 did not affect the dilation induced by the hormone (Table 3). The increase in arteriole diameter was observed within 16.0 ± 2.0 min of T4 administration.

In each animal, at the end of the experimental protocol, the vessels retained vascular tone because the arterioles dilated to ACh (A2: +13.0 ± 1.5% of baseline; A3: +19.0 ± 2.0%; and A4: +25.0 ± 1.9%) and constricted after PE (A2: –12.0 ± 1.2% of baseline; A3: –15.0 ± 1.9%; and A4: –19.0 ± 1.8%).

Topical application of IPA, PTU, the vehicles, and DMSO did not modify arteriolar diameter. Topically applied IPA or PTU did not interfere with arteriolar dilation induced by ACh or NT (Fig. 3). The arteriolar responses to THs did not appear to be related to the age of animals. In AG hamsters the arteriolar diameter changed significantly after application of 615 nM T3 (A2: 25.1 ± 1.2 µm vs. 22.3 ± 1.3 µm; A3: 17.8 ± 1.1 µm vs. 13.1 ± 1.0 µm; A4: 10.2 ± 1.0 µm vs. 7.2 ± 0.9 µm; P < 0.01; n = 5 animals) and 514 nM T4 (A2: 25.6 ± 1.1 µm vs. 23.8 ± 1.2 µm; A3: 18.1 ± 1.0 µm vs. 14.0 ± 0.9 µm; A4: 10.6 ± 1.0 µm vs. 7.8 ± 0.8 µm; P < 0.01; n = 5 animals).



View larger version (14K):
[in this window]
[in a new window]
  		Fig. 3. Averages of maximum diameters of A2, A3, and A4 arterioles (left) under baseline conditions (B) and after acetylcholine (ACh) or iopanoic acid + ACh (IPA + ACh) or 6-propyl-2-thiouracil + ACh (PTU + ACh) (right) under baseline conditions (B) and after sodium nitroprusside (NT) or IPA plus NT (IPA + NT) or 6-propyl-2-thiouracil plus NT (PTU + NT) or after application of vehicles.

 
Topical application of T3 and T4 did not cause significant changes in heart rate (HR) or mean arterial blood pressure (MAP). At the dosages of 615 nM T3 and 514 nM T4 HR and MAP were 283 ± 9 beats/min and 106 ± 7 mmHg, 284 ± 8 beats/min and 107 ± 9 mmHg, respectively, compared with 280 ± 9 beats/min and 109 ± 7 mmHg under baseline conditions.

L-NAME (HR: 278 ± 9 beats/min; MAP: 110 ± 6 mmHg), L-NNA (HR: 277 ± 8 beats/min; MAP: 111 ± 7 mmHg), IPA (HR: 282 ± 8 beats/min; MAP: 107 ± 6 mmHg), PTU (HR: 280 ± 10 beats/min; MAP: 109 ± 7 mmHg), and DMSO (HR: 279 ± 9 beats/min; MAP: 109 ± 8 mmHg) did not significantly affect the systemic parameters.


   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
Administration of the THs induced microvascular responses in the in vivo model of hamster cheek pouch microcirculation used in this study. T3 caused a dose-dependent dilation of the arterioles within few minutes of its application. Such quick response suggests a nongenomic mechanism of action triggered by the hormone. In addition, arteriolar relaxation was abolished by NOS inhibition, indicating a correlation between T3-induced dilation and NOS activation. Therefore, these results support our suggestion that NO is the main factor in T3-induced arteriolar dilation.

The present findings are in agreement with previous observations of a nongenomic mechanism of action of T3 and T4 (23), even though the vessels investigated in that work were different. The data indicating that NO mediates T3-induced arteriolar dilation are partially supported by the observations that T3-induced dilation is attenuated by NOS inhibition in rat skeletal muscle resistance arterioles (13). However, previous results indicate that vascular endothelial cells exposed to T3 do not release nitrate nor show increased cGMP content (14). These discrepancies with our results may be ascribed to differences in the experimental procedure, namely between the study of primary cultures of rat aortic endothelial or VSM cells and the present in vivo model of microcirculation. It is reasonable to suppose that in vitro conditions do not allow one to observe the integrated response of the peripheral microcirculation. It is worth noting that a previous research (1) showed that skin muscle arterioles respond differently to NOS inhibition, pointing to different properties of endothelial and VSM cells in different sized arterioles.

Interestingly, the present results demonstrate that the lower doses of T4 (150 mM) determined dilation of the arterioles after its application. Time to dilation was significantly different for T4 and T3. The effect of T4 was abolished by the inhibition of 5'-deiodinase activity (types I and II) by IPA, because 514 nM T4 did not cause dilation after IPA. The concentration 5,140 nM T4 after IPA, however, determined rhythmic changes in arteriolar diameter. We did not test lower doses of T4 after IPA because the highest dilatory dose of T4 (514 nM) was ineffective. Therefore, these results support the hypothesis that local conversion of T4 into T3 is crucial for dilation induced by THs. Indeed, PTU, an inhibitor of type I 5'-deiodinase, did not interfere with the dilation induced by T4. We did not try to assess the effects of different doses of T4 after PTU because there was no change in the vessel response to T4 after local application of PTU. T4 may thus cause an increase in arteriolar diameter after type II 5'-deiodinase-mediated local conversion to T3. This finding argues for the presence of type II 5'-deiodinase in vascular smooth muscle cells, as recently shown in cultured coronary artery and aortic smooth muscle cells (12). This enzyme thus appears to play a physiological role in the regulation of the vascular tone and arteriolar dilation induced by T3.

Our data indicate that the highest dose of T4 (5,140 nM) did not cause significant arteriolar dilation but induced rhythmic changes in diameter. Such effect may be related to the inhibition of 5'-deiodinase activity by high T4 concentrations. The inhibition of 5'-deiodinase by supraphysiological doses of T4 has been reported previously in smooth muscle cell preparations (12). Moreover, 5'-deiodinase blockade by IPA does not appear to affect the rhythmic changes in diameter caused by 5,140 nM T4. However, further studies are required to clarify this important issue.

The opposite effects of T4, dilation at lower doses and vasomotion at higher doses, are in agreement with previous observations, indicating increase in sarcoplasmic reticulum ATPase activity at lower doses and decrease of this activity at higher concentrations of T4 (20). Therefore, T4 appears to differently modulate responses of target cells, according to the doses.

It has been reported that pentobarbital anesthesia reduces plasma T4 level in rats. These effects appear within 60–90 min of pentobarbital administration and have been described only for T4 (15). In our model, we did not measure serum T4 and T3 concentrations. However, the experiments lasted up to 60–120 min according to the protocol, but there were no significant changes in the diameter of control hamster arterioles up to 60–120 min of observation.

In this study, we used hamster upper physiological range doses of T3 and T4 (16, 21). However, it is worth noting that lower doses of THs were used by Kemperer and co-workers (13, 14) to reduce the systemic vascular resistance and to increase coronary blood flow in clinical pathophysiological conditions. In our model, the morphological and functional properties of the cheek pouch membrane, where a thick epithelial layer effectively opposes the diffusion of substances, dictated the utilization of relatively high doses of THs to cause vessel response. The same approach has previously been tried using this model with substances such as bradykinin (5).

Altogether, our findings show marked effects of the THs in the in vivo microvasculature that implicate a modulation of the NO system, which has a role in maintaining the microvascular tone.

Our data support previous studies indicating that T4 affects the NO system because subcutaneous injection of T4 for 3 days suppressed the contraction of aortic rings induced by norepinephrine (NE); L-NNA, an inhibitor of NOS, enhanced the NE-induced contraction of aortic rings in T4-treated rats more than in control ones (8).

It is difficult to derive indications on endogenous thyroid hormone function in humans from the present experimental data. However, recent results indicate that in human hypothyroidism there is a reduction in NO availability (26). Moreover, clinical hypothyroidism and hyperthyroidism are accompanied by changes in systolic-diastolic index, indicating variations in arterial compliance (7). Furthermore, clinical hypothyroidism is characterized by an increase in the time to peak flow during postocclusion reactive hyperemia, likely due to decrease in dilation capacity of arterioles giving origin to the nailfold capillaries (19).

The effects of THs were not influenced by ageing of animals, at least for the single dose used in this study. Furthermore, we did not observe differences in the response of single animals. However, these preliminary results need to be confirmed by experiments carried out on a large number of animals with different doses of THs.

In conclusion, our results indicate that microcirculation is a physiological target for THs. The effects of T3 on the in vivo microcirculation appear to be mostly mediated by NO through a nongenomic mechanism of action. The effects of T4 appear to be mediated by local conversion to T3 when the concentration is in the physiological range. Higher doses of T4 are able to induce vessel responses characterized by vessel diameter changes with no evident dilation.


   FOOTNOTES
 

Address for reprint requests and other correspondence: A. Colantuoni, Dept. of Neuroscience, "Federico II" Univ. Medical School, Via S. Pansini, 5 80131 Naples, Italy (E-mail: colantuo{at}unina.it)

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
 REFERENCES
 

  1. Bertuglia S, Colantuoni A, and Intaglietta M. Effects of L-NMMA and indomethacin on arteriolar vasomotion in skeletal muscle microcirculation of conscious and anesthetized hamsters. Microvasc Res 48: 68–85, 1994.[CrossRef][ISI][Medline]
  2. Bianchi R, Molea N, Cazzuola F, Fusani L, Lotti M, Bertelli P, Ferdeghini M, and Mariani G. High-perfomance liquid chromatographic separation of iodoaminoacids for tracer studies of thyroid hormones in vivo. J Chromatogr 3: 297393–297398, 1984.
  3. Brent GA. The molecular basis of thyroid hormone action. N Engl J Med 331: 847–854, 1994.[Free Full Text]
  4. Colantuoni A, Berardi PG, and Orefice G. Increased permeability of the microcirculation to high molecular weight dextran in experimental diabetes, shown by intravital microfluorimetry. J Nucl Med Allied Sci 23: 49–54, 1979.[ISI][Medline]
  5. Daffonchio L, Novellini R, and Bertuglia S. Protective effect of ketoprofen lysine salt on interleukin-1beta and bradykinin induced inflammatory changes in hamster cheek pouch microcirculation. Inflamm Res 51: 223–228, 2002.[CrossRef][ISI][Medline]
  6. Duling BR. The preparation and use of the hamster cheek pouch for studies of the microcirculation. Microvasc Res 5: 423–429, 1973.[CrossRef][ISI][Medline]
  7. Dyszkiewicz A and Kucharz EJ. Photoplethysmographic evaluation of microcirculation in patients with overt and latent hyperthyroidism or hypothyroidism. Pol Arch Med Wewn 104: 339–343, 2000.[Medline]
  8. Fulton GP and Lutz BR. The use of hamster cheek pouch and cinephotomicrography for research on the microcirculation and tumor growth and for teaching purposes. Boston Med Quart 8: 1–7, 1957.
  9. Honda H, Iwata T, Mochizuki T, and Kogo H. Changes in vascular reactivity by acute hyperthyroidism in isolated rat aortae. Gen Pharmacol 34: 429–434, 2000.[CrossRef][ISI][Medline]
  10. Ishikawa T, Chijiwa T, Hagiwara M, Mamiya S, and Hidaka H. Thyroid hormones directly interact with vascular smooth muscle strips. Mol Pharmacol 35: 760–765, 1989.[Abstract]
  11. Klein I and Ojamaa K. Thyroid hormone and the cardiovascular system. N Engl J Med 344: 501–509, 2001.[Free Full Text]
  12. Klein I and Ojamaa K. Thyroid hormone. Targeting the vascular smooth muscle cell. Circ Res 88: 260–261, 2001.[Free Full Text]
  13. Klemperer JD, Klein I, Gomez M, Herlm RE, Berman K, Ojamaa K, Thomas SJ, and Krieger K. Thyroid hormone treatment after coronary-artery bypass surgery. N Engl J Med 333: 1562–1563, 1995.[Free Full Text]
  14. Klemperer JD, Zelano J, Herlm RE, Berman K, Ojamaa K, Klein I, Isom OW, and Krieger K. Triiodothyronine improves left ventricular function without oxygen wasting effects after global hypothermic ischemia. J Thorac Cardiovasc Surg 109: 457–465, 1995.[Abstract/Free Full Text]
  15. Langer P, Foldes O, Brozmanova H, and Gschwendtova K. Studies on the effects of pentobarbiturate, ether and heparin on plasma thyroxine level in rats. Endokrinologie 76: 309–314, 1980.[ISI][Medline]
  16. Mizuma H, Murakami M, and Mori M. Thyroid hormone activation in human vascular smooth muscle cells: expression of type II iodothyronine deiodinase. Circ Res 88: 313–318, 2001.[Abstract/Free Full Text]
  17. Ojamaa K, Klemperer JD, and Klein I. Acute effects of thyroid hormone on vascular smooth muscle. Thyroid 6: 505–512, 1996.[ISI][Medline]
  18. Park KW, Dai HB, Ojamaa K, Lowestain E, Klein I, and Sellke FW. The direct vasomotor effect of thyroid hormones on rat skeletal muscle resistance arteries. Anesth Analg 85: 734–738, 1997.[Abstract]
  19. Pazos-Moura CC, Moura EG, Breitenbach MM, and Bouskela E. Nailfold capillaroscopy in hypothyroidism and hyperthyroidism: blood flow velocity during rest and postocclusive reactive hyperemia. Angiology 49: 471–476, 1998.[ISI][Medline]
  20. Pilo A, Iervasi G, Vitek F, Ferdeghini M, Cazzuola F, and Bianchi R. Thyroidal and peripheral production of 3,5,3'-triiodothyronine in humans by multicompartmental analysis. Am J Physiol Endocrinol Metab 258: E715–E726, 1990.[Abstract/Free Full Text]
  21. Rosler B. Thyroxine and triiodothyronine protein complexes in serum Mesocricetus auratus and gerbillus pyramidum. Acta Biol Med Ger 18: 597–606, 1967.[ISI][Medline]
  22. Sabatino L, Iervasi G, Ferrazzi P, Francesconi D, and Chopra IJ. A study of iodothyronine 5'-monodeiodinase activities in normal and pathological tissues in man and their comparison with activities in rat tissues. Life Sci 68: 191–202, 2000.[CrossRef][ISI][Medline]
  23. Sabatino L, Chopra IJ, Tanavoli S, Iacconi P, and Iervasi G. A radioimmunoassay for type I iodothyronine 5'-monodeiodinase in human tissues. Thyroid 11: 733–739, 2001.[CrossRef][ISI][Medline]
  24. St Germain DL and Galton VA. The deiodinase family of selenoproteins. Thyroid 7: 665–668, 1997.
  25. Suko J. The calcium pump of cardiac sarcoplasmic reticulum: functional alterations at different levels of thyroid state in rabbits. J Physiol 228: 563–582, 1973.[Abstract/Free Full Text]
  26. Taddei S, Caraccio N, Virdis A, Dardano A, Versari D, Ghiadoni L, Salvetti A, Ferrannini E, and Monzani F. Impaired endothelium-dependent vasodilation in subclinical hypothyroidism: beneficial effect of levothyroxine therapy. J Clin Endocrinol Metab 88: 3731–3737, 2003.[Abstract/Free Full Text]
  27. Vriend J. Influence of the pineal gland and circadian rhythms in circulating levels of thyroid. hormones of male hamsters. J Pineal Res 1: 15–22, 1984.[ISI][Medline]
  28. Yoneda K, Takasu N, Higa S, Oshiro C, Oshiro Y, Shimabukuro M, and Asahi T. Direct effects of thyroid hormones on rat coronary artery: nongenomic effects of triiodothyronine and thyroxine. Thyroid 8: 609–613, 1998.[ISI][Medline]
  29. Zwaveling J, Pfaffendorf M, and van Zwieten PA. The direct effects of thyroid hormones on rat mesenteric resistance arteries. Fundam Clin Pharmacol 11: 41–46, 1997.[ISI][Medline]




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
288/4/H1931    most recent
00931.2004v1
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 ISI 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 ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Colantuoni, A.
Right arrow Articles by Iervasi, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Colantuoni, A.
Right arrow Articles by Iervasi, G.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2005 by the American Physiological Society.