Sodium potassium adenosine triphosphatase activity in preterm and term infants and its possible role in sodium homeostasis during maturation

AIM—To investigate sodium (NA+) potassium (K+) adenosine triphosphatase (ATPase) activity in newborn infants at different gestational ages, to elucidate the mechanism underlying poor renal sodium conservation in preterm infants. METHODS—Fifty three healthy newborn infants, gestational age 30-42 weeks, were studied. Umbilical cord red blood cell Na+ K+ATPase activity, plasma renin activity, and plasma aldosterone activities were measured in all of them. Red blood cell Na+ K+ATPase activity was re-examined in eight preterm infants, one and two weeks after birth. Total and ouabain sensitive ATPase activity was measured spectrophotometrically using a method that couples ATP hydrolysis with NADH oxidation. RESULTS—Red blood cell Na+ K+ATPase activity was significantly lower (p