Autonomic modulation of ovine fetal responses to atrial natriuretic factor infusion

The aim of this study was to determine whether the autonomic nervous system modulates the cardiovascular, endocrine, and/or urinary responses to atrial natriuretic factor (ANF) infusion in the fetus. We infused ANF intravenously for 30 min into chronically catheterized, late-gestation sheep fetuses with autonomic blockade and compared the responses to those in autonomically intact fetuses. During the infusions, plasma ANF concentration increased similarly in the blocked and intact fetuses. Arterial pressure decreased by 2 mmHg in both groups, but the decrease occurred earlier in the blocked fetuses. Heart rate was significantly decreased by an average of 15 beats/min in the blocked compared with the intact fetuses. Plasma protein concentration decreased in the blocked fetuses compared with a rise in the intact fetuses. In the blocked fetuses, the restoration of blood volume to normal during the postinfusion period occurred earlier. In the blocked animals, low doses of ANF produced a diuresis, whereas high doses did not increase urine flow; the opposite responses occurred in the intact group. Plasma arginine vasopressin (AVP) concentration increased during the infusion only in the blocked animals. The fetal venous pressure, plasma renin activity, and norepinephrine responses were similar in both groups. These data suggest that the autonomic nervous system may play a role in modulating the fetal arterial pressure, heart rate, blood volume, plasma protein concentration, AVP, and urine flow responses to ANF. Thus the autonomic nervous system appears to significantly modulate multiple responses to ANF in the late-gestation ovine fetus.