No abstract

ABSTRACT. We have previously demonstrated that systemic atrial natriuretic factor (ANF) infusion induced a renal vasoconstrictor response in fetal and newborn sheep. The present study was designed to test the hypothesis that the fetal and neonatal renal vasculatures do, in fact, vasodilate in response to ANF but that this effect is negated by vasoconstrictor compensatory mechanisms when ANF is infused systemically. To test this hypothesis, the renal hemodynamic response to intrarenal infusion of ANF was studied in chronically instrumented fetal (125-135 d of gestation; term 145 d) and newborn (8-15 d) sheep. Intrarenal infusion of ANF (0.125 to 4.0 pg/kg of body wt in fetuses and 0.25 to 8.0 pg/kg in newborns) had no significant effect on mean arterial blood pressure and heart rate. (5, 7) suggest that the cardiovascular, renal hemodynamic, and possibly renal function responses to continuous intravenous infusion of ANF change during maturation. It has been found that the natriuresis and chloruresis produced by systemic infusion of ANF is of greater magnitude in adult than in fetal sheep (3). Systemic ANF infusion decreases arterial blood pressure and increases heart rate in newborn and adult sheep (3). In fetal sheep, ANF produces either a decrease (7) or no change (3, 5) in arterial blood pressure associated with either a rise (5, 7) or no change (3) in heart rate. It has also been demonstrated that systemic ANF infusion decreases RBF and increases RVR in fetal and newborn animals but decreases RVR in adult sheep (3).No studies have demonstrated if this renal vasoconstrictor response to systemic ANF infusion is particular to the renal vasculature of developing animals or is secondary to compensatory mechanisms. The present study was designed to evaluate the renal hemodynamic response to direct intrarenal infusion of ANF in conscious and chronically instrumented fetal and newborn sheep and to test the hypothesis that ANF does relax the renal vasculature during renal maturation. MATERIALS A N D METHODSAnimal preparation and surgical procedures. Fetuses of eight pregnant sheep of Dorset and Suffolk mixed breeding (3.27 f 0.1 1 kg) were studied at 125-135 d of gestation (term being 145 d). Gestational ages were based on the induced ovulation technique as previously described (8).Ewes were fasted for 24 h before surgery. General anesthesia of the ewe and fetal surgery were performed as previously described (9). Briefly, the ewe was anesthetized with a mixture of 1% halothane, 33% oxygen and 66% nitrous oxide. The uterus was opened and polyethylene catheters (outer diameter, 1.27 mm; inner diameter, 0.86 mm) were inserted in both femoral veins and arteries. A catheter was also secured in the amniotic cavity for intrauterine pressure recording. The left kidney of the fetus was exposed through a left flank incision. A Doppler flow probe was secured around the renal artery with care being taken It has been demonstrated that ANF can be synthesized, stored to not interfere with renal innervation. Thereafter, a nonobstruc...