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 been postulated to be mediated through an increase in the circulating levels of aldosterone. We infused 17-beta estradiol (30 micrograms/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 weekly intervals. By the end of the third week, 17-beta estradiol plasma concentration had increased 150-fold, while PRA increased 2-fold; aldosterone 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.