Fetal cardiovascular, endocrine, and fluid responses to atrial natriuretic factor infusion

The purpose of this study was to determine the effects of atrial natriuretic factor (ANF) in the fetus and to explore the interactions among the fetal cardiovascular, endocrine, and fluid responses to ANF. In 12 chronically catheterized fetal sheep at 130 ± 1 (SE) days gestation, ANF was infused intravenously for 30 min at 14-300 ng · min^-1 · kg^-1. Fetal arterial plasma ANF concentration increased by 174 to 5,410 pg/ml from a preinfusion value of 163 ± 13 pg/ml. The clearance of ANF from the circulation was 122 ± 28 ml · min^-1 · kg^-1 and the half-life was 0.46 ± 0.07 min. When plasma ANF was > 2,000 pg/ml, fetal arterial pressure decreased, venous pressure increased transiently, and heart rate was unchanged. Plasma arginine vasopressin (AVP) concentration and plasma renin activity (PRA) increased with high ANF concentrations, while norepinephrine concentrations were unaffected. Fetal blood volume decreased in all fetuses, and urine flow increased significantly but not in every fetus. Blood and urine osmolalities did not change. On terminating the infusion, venous pressure and urine flow decreased below control, while blood volume and arterial pressure remained reduced. Plasma AVP concentration increased further, and this was accompanied by an increase in urine osmolality. Thus the most consistent effect of ANF in the fetus was a reduction in blood volume, which was independent of urine flow changes. Other cardiovascular, endocrine, and fluid responses to ANF as well as interactions among them appeared to occur largely at supraphysiological concentrations and may be secondary to the changes in blood volume. These observations suggest that there may be little interaction among the fetal cardiovascular, endocrine, and fluid responses to physiological amounts of ANF and that the fetus may be less responsive to ANF than the adult.