EFFECT OF ATRIAL-NATRIURETIC-FACTOR ON RELEASE OF ARGININE-VASOPRESSIN AND RENIN IN FETAL LAMBS

The purpose of this study was to determine the effect of increased pla sma atrial natriuretic factor (ANF) concentrations on the arginine vas opressin (AVP) and renin response to arterial hypotension in fetal she ep. Lamb fetuses at 123-133 days of gestation were infused intravascul arly with 0.9% NaCl and ANF at 25 ng.kg(-1).min(-1) (low dose) or NaCl and ANF at 250 ng.kg(-1).min(-1) (high dose) for 115 min. After 45 mi n, sodium nitroprusside was infused for 10 min to yield a 25% decrease in mean arterial blood pressure. ANF infusions resulted in plasma con centrations of 150-200 and 500-800 pg/ml in the low-dose and high-dose groups, respectively. In both the low-dose and high-dose ANF groups, AVP and renin concentrations increased in response to hypotension. In the low-dose ANF group, there was no difference in this response betwe en ANF and control lambs. Compared with controls, a high dose of ANF r esulted in an elevated basal level of AVP (1.6 +/- 0.04 vs. 12.3 +/- 6 .7 pg/ml) and an 11-fold increase of AVP at 10 min of hypotension (12. 2 +/- 5.6 vs. 134.9 +/- 36.1 pg/ml). Basal and stimulated renin concen trations were unchanged by the high-dose ANF infusion. This study demo nstrates that in the fetal lamb, ANF concentrations of 500-800 pg/ml a ugment the basal and stimulated release of AVP but do not affect the r enin response.