Estrogen affects vascular tone differently according to vasoactive substances in ovariectomized Sprague-Dawley rat

The favorable effects of estrogen on cardiovascular diseases can be explained by several mechanisms such as changes in serum lipid profiles and thrombogenecity. Estrogen also affects the vascular tone, but there has been no report in which the effect of estrogen was tested comprehensively for several vasoactive substances, especially after long-term administration. Two weeks after bilateral ovariectomy in 8-week old female Sprague-Dawley rats, placebo or 17 beta-estradiol (E2) pellets (0.5 mg; released over 3 weeks) were implanted subcutaneously. Two weeks after pellet implantation, organ chamber experiments were performed using aortae. Compared with control, E2-treated vessels showed impaired endothelium-dependent relaxation to acetylcholine. E2 enhanced the contraction to norepinephrine and U46619 and had no effect on endothelin-1-induced contraction. In contrast, the contraction to angiotensin (AT)-II was inhibited by E2. Northern blot analysis for AT1 receptor expression using cultured aortic smooth muscle cells showed no difference between control and E2-treated cells, suggesting that AT1 receptor downregulation is not the likely mechanism. These results suggest that E2 affects the vascular tone variably according to vasoactive substances.

Effect of Estrogen Replacement on Vascular Responsiveness in Ovariectomized Spontaneously Hypertensive Rat

BACKGROUND: Although postmenopausal estrogen replacement therapy is known to reduce cardiovascular mortality, the mechanism is not clear yet. Furthermore, the effect of estrogen on vascular tonus is reportedly variable according to the animal models, vascular beds and agonists used. MATERIALS AND METHOD: Bilateral ovariectomies were performed in 12 week-old, 18 spontaneously hypertensive rats (SHR) and 18 normotensive Wistar-Kyoto rats (WKY). Rats were divided into three groups according to the dose of 17beta-estradiol (E 2 ) pellets implanted subcutaneously two weeks after ovariectomy: control (no implantation), low-dose (0.5 mg) and high-dose (5 mg) E 2 replacement group. Two weeks after pellet implantation, organ bath experiments were performed using descending thoracic aortae. For endothelium-dependent relaxation, acetylcholine (10(-9) -3x10(-6) M) was cumulatively added into the vessels precontracted with 10(-7) M norepinephrine (NE). For vasoconstrictor responses, cumulative concentration-contraction curves were constructed in quiescent vessels using NE (10(-9) -10(-5) M), U46619 (10(-9) -3x10(-6) M), endothelin-1 (10(-10) -10(-7) M). In addition, contraction to angiotensin II (10(-7) M) was also obtained. Serum 17beta-estradiol levels were measured by radioimmunoassay. Blood pressure was measured by tail-cuff method in some SHRs before ovariectomy and after placebo/E 2 replacement. RESULTS: Endothelium-dependent relaxation to acetylcholine was impaired in WKY treated with 5 mg E 2 (pIC 50 : control vs 5mg E 2 : 7.75+/-0.13 vs 7.27+/-0.16: n=6: p<0.05). No significant effect was noted in SHR. Contraction to angiotensin II was inhibited by low-dose E 2 in WKY and high-dose E 2 in SHR (% of the contraction to 60 mM KCl: WKY: control vs 0.5 mg E 2 : 39+/-5 vs 25+/-2: SHR: control vs 5 mg E 2 : 34+/-4 vs 22+/-2: n=6 and p<0.05 in WKY and SHR). In contrast, NE-induced contraction was enhanced by E 2 replacement (both low- and high-dose) in WKY and SHR (WKY: control vs 0.5 mg E 2 vs 5 mg E 2 : AUC: 280+/-24 vs 387+/-26 vs 374+/-25: maximal contraction: 137+/-8 vs 166+/-8 vs 162+/-3: pD 2 : 7.63+/-0.11 vs 8.17+/-0.13 vs 8.13+/-0.13: SHR: control vs 0.5 mg E 2 vs 5 mg E 2 : AUC: 265+/-17 vs 349+/-16 vs 406+/-19: maximal contraction: 152+/-6 vs 181+/-9 vs 203+/-16: pD 2 : 7.45+/-0.13 vs 7.91+/-0.08 vs 8.04+/-0.04: n=6 and p<0.05 between control and treated groups in WKY and SHR for all parameters). Contraction to U46619 was enhanced by E 2 replacement in SHR (control vs 0.5 mg E 2 : AUC: 478+/-30 vs 574+/-23: maximal contraction: 181+/-9 vs 230+/-10: n=6: p<0.05 for both parameters). Maximal contractile response to endothelin-1 was also enhanced in SHR (control vs 0.5 mg E 2 vs 5 mg E 2 : maximal contraction: 165+/-7 vs 189+/-7 vs 199+/-8: n=6 and p<0.05 between control and treated groups) but not in WKY. Blood pressure was not different between placebo and E 2- treated SHR (171+/-2 vs 174+/-4 mmHg). CONCLUSION: In WKY, chronic high-dose estrogen replacement impairs endothelium-dependent relaxation to acetylcholine.: low-dose estrogen replacement does not affect endothelium-dependent relaxation in SHR and WKY. Estrogen replacement enhances the contraction to most of the contractile agonists tested except angiotensin II in both WKY and SHR. These results suggest that estrogen replacement affect the vascular tonus differently according to the vasoactive substances and/or hormones without significant effect on blood pressure.

Pathophysiological Role of Endothelin-1 and Clinical Usefulness of Endothelin Antagonists

No abstract available.

Pathophysiological Role of Endothelin-1 and Clinical Usefulness of Endothelin Antagonists

No abstract available.

Effect of Endothelin Antagonists on Myocardial Infarct Size after Coronary Artery Occlusion and Reperfusion in Rat

BACKGROUND: Although experimental and clinical evidences suggest that endothelin-1(ET-1) may play a pathophysiological role in ischemic heart disease, it is still controversial whether ET-1 produced during myocardial ischemia and reperfusion affects the extent of necrotic myocardium. This study was performed to investigate the role of ET-1 and the effect of ET antagonists in infarct size determination. METHODS: Male Wistar rats(260-400g) were anesthetized with pentobarbital(i.p. 50mg/kg) and ventilation was assisted via tracheostomy tube. The heart was exposed by midline incision and the left anterior descending coronary artery was ligated with 6-0 silk suture. The ligature was released after 1 hour and reperfusion was performed for 2 hours. In the first set of experiment, FRI139317(ET-A antagonist) was given as bolus i.v.(3mg/kg) 10 minutes before reperfusion, followed by continuous infusion(total 24mg/kg) throughout reperfusion. In the other protocol, bosentan(ET-A/ET-B antagonist ; 10mg/kg) was given 10 minutes before coronary occlusion as i.v. bolus. At the end of reperfusion, the heart was excised and stained with Evans blue dye(1% w/v) and triphenyltetrazolium chloride(TTC;1%) to distinguish infarct region(not stained by TTC and Evans blue), ischemic but viable myocardium(stained brick-red by TTC but not stained by Evans blue) and nonischemic myocardium(dyed by Evans blue). These three regions of myocardium were separated and weighed for analysis. Infarct size(in percent) was expressed as the ratio of infarct region to ischemic myocardium(i.e. infarct region plus ischemic but viable myocardium). RESULTS: In the first protocol, infarct region was 57.0 +/-3.8% of the ischemic myocardium in control(n=9) and 58.9+/-4.9% in FR139317 group(n=7) ; The difference was not significant statistically. Likewise, ET-A/ET-B antagonist bosentan given before coronary occlusion did not reduce infarct size significantly ; the ratio was 74.2+/-3.2% in control(n=7) and 69.5+/-2.0% in bosentan group(n=7). CONCLUSIONS: ET-A antagonist FR139317, given throughout reperfusion, did not reduce myocardial infarct size in rat. Bosentan(ET-A/ET-B antagonist) given just before coronary occlusion as i.v. bolus also did not reduce myocardial infarct size in rat.