Responses of fetal sheep to reduced maternal renal blood flow and maternal hypertension

Abstract

In 16 chronically catheterized fetal sheep the effects of reducing and restoring maternal renal blood flow (RBF) and thus inducing and reversing hypertension were studied in uninephrectomized pregnant ewes; controls were 3 fetuses that were carried by uninephrectomized ewes in which RBF was not reduced and that did not become hypertensive. Within 24-72 h of maternal RBF reduction, fetal arterial PO2 had fallen (P < 0.001) and PCO2 had increased (P < 0.025); fetal arterial pressure also increased (P < 0.005). These effects persisted, despite restoration of maternal RBF and reversal of maternal hypertension. Within 24-72 h of reduction of maternal RBF, fetal urine flow had increased (P < 0.005), and it remained elevated over the first 3 h after RBF was restored; 24-72 h later it was lower (P < 0.025) and returned to control levels. The excretion of sodium, potassium, and chloride showed a similar increase when maternal RBF was reduced (P < 0.001), with return to control values 24-72 h after RBF had been restored. Fetal glomerular filtration rate did not change; thus the natriuresis and diuresis that occurred were due to reduced tubular solute and water reabsorption (P < 0.025). These changes in fetal renal function may be related, in part, to changes in fetal PO2 and PCO2, but they are most likely due to reduced maternal renal function due to the restriction in maternal RBF, inasmuch as they were reversed when RBF was restored.