1082 OXYTOCIN INDUCED NATRIURESIS IN NEWBORN DOGS

Abstract

Newborns have an attenuated natriuretic response to salt loading, due to the inability of the newborn kidney to adequately reduce tubular sodium reabsorption. When newborn dogs were saline loaded (2 ml/min/kg for 15′ then 0.5 ml/min/kg for 2 hours), fractional sodium excretion (FENa) averaged less than 2% compared to similarly saline loaded adults who had FENa more than 6% (p<.01). Saline loaded hypophysectomized (HPx) adult dogs (n=11), however, had FENa of only 1.3%, similar to the intact puppy. When given 8mU oxytocin (oxy) IV, these HPx saline loaded dogs increased FENa to 5.9%, (p<.01) similar to intact saline expanded adult controls. Growth hormone, ACTH & ADH had no such effect. Oxy infusion to 7 saline expanded puppies resulted in a 5.9% increase of FENa, similar to the expanded HPx adult. However, oxy produced <1% increase in ≥ from 7 nonexpanded intact puppies and 3 HPx adult dogs. In both saline expanded and non expanded puppies, oxy produced no consistent effect on K excretion, GFR & blood pressure, but did increase chloride and osmolar excretion. Oxy had no effect in the intact adult dog. The results suggest that a) oxy is essential for an appropriate natriuretic response to saline loading b) The natriuretic effect of oxy occurs only during saline loading and c) a lack of oxy may be responsible for the attenuated natriuretic response to saline loading in the newborn.