Renal hemodynamics and functional changes during the transition from fetal to newborn life in sheep

Abstract

The effects of delivery on renal function and renal hemodynamics were studied in conscious and chronically instrumented fetal sheep. Each fetus was studied 1 h before delivery and 1, 4, and 24 h following delivery by cesarean section. Delivery was not associated with significant changes in plasma renin activity, plasma angiotensin II, plasma aldosterone, and plasma arginine vasopressin concentrations when determined 1 h after birth. On the other hand, the transition from fetal to newborn life was accompanied by significant increases in plasma epinephrine and norepinephrine concentrations. No significant changes in renal blood flow velocity or in renal vascular resistance were observed during the transition from fetal to newborn life; percent changes in renal blood flow velocity and renal vascular resistance values were respectively 15.4 ± 11 and -2.4 ± 1.0% at 1 h, 4.0 ± 8.0 and 5.8 ± 9.1% at 4 h, and 3.2 ± 8.0 and 9.7 ± 13% at 24 h. No significant changes in urinary flow rate, urine osmolality, free water clearance, and osmolar clearance were observed in the first 24 h following delivery. On the other hand, glomerular filtration rate increased 3-fold from 3.3 ± 0.4 ml/min in fetuses to 10.1 ± 1.2 ml/min in newborn lambs at 24 h of age. This rise in glomerular filtration rate was associated with significant decreases in urinary sodium excretion (UNaV) (from 36 ± 7 to 13 ± 3 utEq/min) and fractional excretion of sodium (FEN») (from 7.6 ± 0.9 to 1.1 ± 0.3%). In summary, present results demonstrate that transition from fetal to newborn life is associated with a rapid rise in glomerular filtration rate and an important decrease in urinary sodium excretion and fractional excretion of sodium. These changes seem to be independent of changes in renal blood flow velocity, renal vascular resistance, and blood pressure. © 1986 International Pediatric Research Foundation, Inc.