[Effects of sex steroid hormones on vascular reactivity to angiotensin II in castrated rat].

The vascular reactivity to exogenous angiotensin-II (A-II) was blunt in castrated rats treated with estrogen alone or with estrogen plus progesterone. To study the effect of the steroids on vascular reaction to A-II, the plasma renin activity (PRA), plasma aldosterone concentration (PAC) and prostanoids concentration were determined in castrated rats treated with sex steroid hormones. In castrated rats treated with estradiol benzoate, PRA and 6-keto PGF1 alpha were significantly higher than those of untreated rats. On the other hand, PAC in castrated rat treated with progesterone was significantly higher than that in untreated rats. And no significant difference in mean arterial pressure under anesthesia was found between the castrated rats and hormone-treated rats. These findings suggest that rats treated with estradiol benzoate alone or with estradiol benzoate plus progesterone remain in a normotensive state in spite of high PRA, as a compensatory mechanism of decreased vascular reactivity and a vasodilatory prostaglandin may be involved in the regulation of vascular reactivity to A-II in rats treated with estradiol benzoate or with estradiol benzoate plus progesterone.