Transtubular potassium concentration gradient in preterm neonates

To determine the postnatal changes in mineralocorticoid action on the corti cal distal nephron in preterm neonates. we evaluated the transtubular potas sium gradient (TTKG) and its relationship to other renal and non-renal para meters in 16 preterm neonates during the first 5 weeks of life. Preterm neo nates were divided into two groups according to their gestational age: the first group (group A, n=9) had a gestational age less than 30 weeks and the second group (group B, n=7) had a gestational age over 30 weeks. TTKG in b oth groups increased significantly with postnatal age, and TTKG in group A was significantly lower than that in group B (P=0.0003; two-way repeated an alysis of variance). TTKG in group A was significantly lower during the 2 w eeks of postnatal life than that in full-term neonates [TTKG during Ist wee k (mean+/-SD) 3.73+/-1.32, P<0.00001; during 2nd week 7.77+/-3.60, P=0.0096 versus full-term neonates (n=19); 11.56+/-3.23]. TTKG in group B was signi ficantly lower only during the Ist week of life (6.55+/-2.71, P=0.0013) com pared with full-term neonates. Plasma aldosterone concentration did not cor relate with TTKG value. Stepwise regression analysis showed that postnatal age, cortical lumen sodium concentration (CLNa), and clinical condition req uiring the use of mechanical ventilation were independent variables that co rrelated significantly with TTKG. We postulate that the low TTKG level in p reterm neonates might reflect the prematurity of renal function (early post natal age, CLNa) and the condition(s), relating to immaturity, such as the use of mechanical ventilation.