ESTRADIOL EFFECTS ON PLASMA-RENIN ACTIVITY AND ALDOSTERONE IN CHRONICALLY CATHETERIZED CASTRATED SHEEP

The administration of 17-beta estradiol to human, and all the animals species tested, results in blood volume expansion. This effect has bee n postulated to be mediated through an increase in the circulating lev els of aldosterone. We infused 17-beta estradiol (30 mu g/kg/day) into 5 chronically-castrated ewes over a 3-week period, and determined the plasma concentrations of 17-beta estradiol, PRA, and aldosterone at w eekly intervals. By the end of the third week, 17-beta estradiol plasm a concentration had increased 150-fold, while PRA increased 2-fold; al dosterone decreased 40% from baseline values. Thus, during a period in which we have previously observed blood volume expansion, there was a dissociation between the levels of 17-beta estradiol and aldosterone. These findings question the theory that the estradiol-mediated blood volume increase observed during pregnancy is secondary to an increase in the circulating aldosterone levels.