Fetal atrial natriuretic factor and arginine vasopressin responses to hyperosmolality and hypervolemia

Atrial natriuretic factor (ANF) is a class of diuretic and natriuretic peptides secreted by mammalian cardiac atria. Although basal plasma ANF levels in the ovine fetus are elevated relative to the adult, fetal secretion of ANF increases in response to intravascular isotonic saline infusion. Recent in vitro and in vivo studies indicate that ANF secretion also may be stimulated by increased plasma osmolality and/or sodium concentration. The present studies were conducted to determine if volume expansion associated with increased plasma osmolality would further augment ANF secretion in the ovine fetus. In response to successive 30-min intravenous infusions of 3% saline at 0.5 and 1.0 ml/kg/min fetal plasma ANF significantly increased from a basal level of 98 +/- 31 pg/ml to a peak of 439 +/- 42 pg/ml (p less than 0.05). During a 30-min postinfusion recovery period, fetal plasma ANF significantly decreased from peak values to 224 +/- 10 pg/ml (p less than 0.05), although remaining above basal levels. Fetal plasma osmolality significantly increased from 300 +/- 2 mosmol to 325 +/- 3 mosmol (p less than 0.05) whereas fetal plasma arginine vasopressin increased from 1.9 +/- 0.4 to 10.9 +/- 7.0 pg/ml (p less than 0.05) at the conclusion of the 3% saline infusion. During the saline infusion a significant increase in fetal heart rate and decrease in fetal hematocrit were noted. Fetal blood pressure and maternal plasma ANF and arginine vasopressin concentrations remained unchanged. Despite the potential stimulatory effects of hyperosmolality, increased plasma arginine vasopressin, and intravascular volume expansion, the increase in fetal plasma ANF in the present study did not exceed that induced by isotonic saline alone.(ABSTRACT TRUNCATED AT 250 WORDS)