VASCULAR EFFECTS OF 17-BETA-ESTRADIOL IN MALE SPRAGUE-DAWLEY RATS

Bolus intravenous injection of 100 mu g/kg 17 beta-estradiol significa ntly decreased the presser responses to norepinephrine (NE; 0.3 mu g/k g) at the fourth, fifth, and sixth hour in anesthetized male Sprague-D awley rats. At doses of 10(-6) to 3 x 10(-5) M, 17 beta-estradiol rela xed the sustained phase of contraction in male Sprague-Dawley rat tail artery helical strips precontracted in vitro by [Arg(8)]vasopressin ( AVP), KCl, or NE. The effect was dose dependent. At doses of 3 x 10(-6 ) to 3 x 10(-5) M, it also decreased the initial phase of tension gene ration and extracellular Ca2+-dependent vasoconstriction induced by NE , AVP, or KCl in a dose-dependent manner in male Sprague-Dawley rat ta il artery helical strips. 17 beta-Estradiol (2 x 10(-8) to 2 x 10(-6) M) decreased the voltage-dependent inward Ca2+ current and the intrace llular free Ca2+ concentration ([Ca2+](i)) increment induced by 15 mM KCl in a dose-dependent manner (3.6 x 10(-8) to 3.6 x 10(-6) M) in vas cular smooth muscle cells (VSMC) isolated from male Sprague-Dawley rat tail arteries. We suggest that, at pharmacological doses, estrogen ha s a direct vasodilating effect on the rat tail artery that is mediated by its inhibitory effect on Ca2+ influx through voltage-dependent Ca2 + channels. The inhibitory effect of estrogen on the presser responses to NE or AVP may be correlated with its modulation of VSMC [Ca2+](i) through its actions on membrane Ca2+ channels.