Aldosterone metabolism in pregnant ewes and fetal and newborn lambs.

Twenty primiparous Limousine ewes whose fetuses had been chronically catheterized in utero on day 120 of gestation were used. Plasma aldosterone levels were measured by radioimmunoassay during the last 15 days of gestation both in dams and fetuses, and during the first neonatal week in lambs. Aldosterone metabolic clearance rates in dams, fetuses and newborns were determined by continuous infusion of [1, 2, 6, 7-3H]-aldosterone. The highest plasma aldosterone levels were observed in dams on days 130 and 142 of gestation, and in fetuses on days 135 and 140. No correlation was observed between plasma aldosterone and electrolyte levels in the mother, fetus or newborn. Aldosterone metabolic clearance rate decreased between days 142 and 145 in dams and at birth in fetuses of both sexes. No aldosterone transfer could be demonstrated either from dam to fetus or vice-versa.