Transplacental transfer of aldosterone and its effects on renal function in the fetal lamb

Seven chronically catheterized fetal lambs between 100 and 130 days gestation (term, 140 to 145 days) and five unborn lambs were infused with d-aldosterone monoacetate, 100 microgram/kg bolus, and 100 microgram/kg over 60 min. Fetal lamb plasma aldosterone levels increased from a mean and S.E. baseline of 4.5 +/- 0.3 microgram/dl to greater than 100 microgram/dl. Maternal plasma aldosterone concentrations increased from 10.2 +/- 0.8 to 26.2 +/- 2.4 microgram/dl after 15 min (P less than 0.05) of the infusion. Amniotic fluid levels increased from 13.3 +/- 0.8 to 23.8 +/- 2.3 microgram/dl (P less than 0.05) after 15 min of infusion. There was no change in plasma renin activity levels in the fetus or pregnant ewe. Urine sodium excretion decreased from 0.87 +/- 0.09 to 0.34 total mEq (P less than 0.05), and urine potassium increased from 0.25 +/- 0.06 to 0.38 +/- 0.07 total mEq (P less than 0.05) between 60 and 90 min after the start of the infusion in the fetal lamb. There was no change in creatinine clearance or urinary sodium and potassium excretion in the newborn lamb. These data show that aldosterone crosses the placenta during the last trimester in the fetal lamb and can control sodium and potassium transport in the distal renal tubule. Lack of distal tubular responsiveness to aldosterone in the newborn is not due to maturational factors.