Sodium potassium adenosine triphosphatase activity in preterm and term infants and its possible role in sodium homeostasis during maturation.
OBJECTIVE
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<0.01) in preterm babies with a gestational age below 35 weeks, compared with those with aged 35 weeks and above: 2.3 (0.8) and 6.7 (1.3) nmol NADH/minute/mg protein, respectively. There was no correlation between gestational age, Na(+) K(+)ATPase, plasma renin activity and aldosterone values either in the preterm or term babies. Two weeks after birth, irrespective of gestational age, the enzyme activity of the preterm babies increased to values similar to those observed in the term neonates at birth.


CONCLUSIONS
The differences in sodium homeostasis between term and preterm babies are modulated via changes in Na(+) K(+)ATPase activity.
Bistritzer
T
T
Department of Paediatrics, Assaf Hroheh Medical Center, Zerifin 70300, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel.
Berkovitch
M
M
Rappoport
M J
MJ
Evans
S
S
Arieli
S
S
Goldberg
M
M
Tavori
I
I
Aladjem
M
M
D005865:Gestational Age; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood / Q000378:metabolism*
D000254:Sodium-Potassium-Exchanging ATPase