Alterations in maternal corticosteroid levels influence fetal urine and lung liquid production.

Abstract

This study was designed to test the hypotheses that disruption of maternal adrenal secretion in late pregnancy requires fetal adaptations in order to maintain fetal blood volume and fetal viability. Pregnant ewes were adrenalectomized at approximately 112 days, and cortisol and aldosterone were replaced to either normal pregnant levels (with 1 mg/kg per day of cortisol and 3 microg/kg per day of aldosterone) or normal nonpregnant levels of aldosterone or cortisol (0.5 mg/kg per day of cortisol or 1.5 microg/kg per day of aldosterone). Fetal blood volume, blood pressure, lung liquid production, urine production, free water clearance, and glomerular filtration rate were measured at 130 days. In a separate group, fetal organ blood flow was measured. Fetal blood volume was not significantly decreased by disruption of maternal corticosteroid secretion. However fetal urine production and free water clearance were reduced in fetuses of low cortisol or low aldosterone ewes. Fetal lung liquid secretion was also significantly reduced in the low aldosterone group. The glomerular filtration rate was reduced in fetuses of all adrenalectomized ewes, regardless of replacement dose. Fetal blood pressure was significantly reduced in the fetuses of low aldosterone ewes; blood flow to several fetal organs was increased in this group, indicating that decreased vascular resistance may contribute to the relative hypotension. Alterations in maternal adrenal corticosteroid levels resulted in fetal adaptation to maintain fetal blood volume despite relative maternal hypovolemia. These adaptations occurred at the expense of fetal urine and lung liquid production.