THE EFFECT OF MATERNAL DIETARY Na+ AND ECF ON FETAL PLASMA RENIN ACTIVITY (PRA)

Abstract

The effect of changes in maternal ECF and dietary Na+ intake on fetal PRA and urine Na+ was measured in 43 near-term fetal lambs. Fetal and maternal blood and urine Na+, K+, Osm and PRA was measured in 12 fetuses after a maternal intake of “normal” sheep chow. Similar studies were made in 12 fetuses after a maternal low Na+ diet and in 19 fetuses after a maternal diet supplemented with 10 gm Na+ plus daily IM DOCA.These data demonstrate that control fetal PRA is higher than that in the ewe. Maternal low Na+ intake resulted in a significant increase in PRA and a decrease in UNa in the fetus as well as the ewe. Simultaneous measurement of uterine vein renin revealed no maternal - fetus gradient. Ewes on a low Na+ diet for 3 days subsequently expanded for 3 days with DOCA and added salt, resulted in a decrease in fetal as well as maternal PRA. These data indicate that fetal renin activity is fetal in origin and is in part responsive to maternal changes in ECF and dietary Na+. This response might serve to protect the fetus from exaggerated changes in maternal body composition.