Hemorrhage-induced reductions in plasma atrial natriuretic factor in the ovine fetus

To investigate the effects of blood volume reduction on fetal plasma atrial natriuretic factor concentrations, chronically catheterized ovine fetuses at 109 to 138 days' gestation were subjected either to withdrawal of two consecutive blood samples or to a moderate hemorrhage. In fetuses from which two blood samples of 3.5 ml each (approximately 1% of fetal blood volume) were withdrawn under basal conditions at 15- to 30-minute intervals, plasma atrial natriuretic factor concentrations in the second sample decreased by 17 ± 7 pg/ml from 178 ± 8 pg/ml in the first sample (p < 0.02). If the fetal blood removed during the first sample was replaced with an equal volume of maternal blood, plasma atrial natriuretic factor concentrations did not change significantly. In these same samples, plasma arginine vasopressin and angiotensin II concentrations were unchanged between the two samples regardless of whether volume was replaced. In fetuses subjected to hemorrhages of 21% ± 2% over 10 minutes without blood replacement, plasma atrial natriuretic factor concentration at 1.5 hours after hemorrhage was suppressed by 42 ± 10 pg/ml from basal level of 139 ± 9 pg/ml (p < 0.05). Plasma atrial natriuretic factor returned to control levels by 5.5 hours after hemorrhage as blood volume returned to normal. Thus in the ovine fetus a reduction in blood volume results in a decrease in plasma atrial natriuretic factor concentrations. Also, atrial natriuretic factor appears to be more sensitive to changes in blood volume than other vasoactive hormones studied.