ACUTE EFFECT OF 17-BETA-ESTRADIOL ON RABBIT CORONARY-ARTERY CONTRACTILE RESPONSES TO ENDOTHELIN-1

We assessed the acute effect of 17-beta-estradiol on coronary artery constrictor responses to endothelin-1. 17-beta-Estradiol significantly shifted endothelin-1, calcium, or BAY K 8644 concentration-dependent contraction curves to the right in endothelium-denuded coronary arteries isolated from nonpregnant female rabbits. The -log 50% effective dose (ED50) of calcium in high KCl medium (100 mM) was 3.8 +/- 0.11 in control and 3.2 +/- 0.1 and 2.8 +/- 0.12 after incubation with 17-beta-estradiol (1 and 10-mu-M, respectively). The -log ED50 of BAY K 8644 (KCl 15 mM) was 7.8 +/- 0.1 in control and 7.4 +/- 0.08 and 7.2 +/- 0.05 in the presence of 17-beta-estradiol (1 and 10-mu-M, respectively). The -log ED50 of endothelin-1 was 9.2 +/- 0.08 in control and 8.8 +/- 0.1, 8.4 +/- 0.07, and 8.1 +/- 0.12 after incubation with 17-beta-estradiol (3, 10, and 30-mu-M, respectively). Similar results were obtained from coronary arteries of male rabbits. These increases of -log ED50 values were significant (P < 0.05 or 0.01). 17-beta-Estradiol and verapamil induced dose-dependent relaxation in both endothelium-intact or -denuded coronary arteries submaximally precontracted by endothelin-1. N(G)-monomethyl-L-arginine had no effect on relaxation induced by 17-beta-estradiol, whereas it eliminated relaxation induced by acetylcholine in rings with an intact endothelium. These data suggest that 17-beta-estradiol attenuates the rabbit coronary artery contraction induced by endothelin-1 via an endothelium-independent mechanism, possibly by affecting calcium influx.