Plasma renin activity during ovine pregnancy.

Chronic intravascular catheterization in maternal, fetal, and neonatal sheep was utilized to assess basal plasma renin activity (PRA) and changes in PRA in response to furosemide. Maternal PRA increased from base-line levels during the last trimester of pregnancy and remained elevated for 12 wk postpartum. Fetal basal levels of PRA were variable but usually greater than maternal levels. Intravenous administration of furosemide to pregnant ewes resulted in a prompt and significant increase in maternal PRA with inconsistent changes in fetal PRA. Fetal and neonatal animals with low basal levels showed a significant increase in PRA; maternal PRA did not change. Animals with higher basal levels did not respond to the stimulus, perhaps reflecting a maximum renin secretory rate. These data are consistent with the conclusions that fetal renin originated predominantly from the fetal kidney, that fetal PRA receives no significant contribution from the maternal circulation, and that renin does not cross the ovine placenta.