The Role of Aldosterone on the Development of Renal Tubular Reabsorption in Low Birth Weight Infants

ABSTRACT

PURPOSE: To determine the postnatal changes in aldosterone action on the renal tubular reabsorption in low birth weight(LBW) infants, we assessed the relation of the aldosterone concentrations to renal parameters during the first 10 days of life. METHODS: Twenty LBW infants were evaluated and their gestational ages ranged from 32.4 to 39.3 weeks and their birth weights ranged from 1,440 to 2,500 g. Estimated glomerular filtration rate, fractional excretion of sodium(FENa) and potassium(FEK), and plasma aldosterone concentrations were analyzed according to the postnatal age and the conceptional age(CA). RESULTS: Glomerular functions were improved after birth and were correlated with CA. FENa and FEK decreased after birth and correlated with CA. Plasma aldosterone concentrations increased to 318.6 +/- 147.2 ng/dL at 48 hours and then decreased to 162.0 +/- 72.2 ng/dL at 10 days after birth. Plasma aldosterone concentrations of infants less than 38th week of CA were higher than that of infants more than 38th week. There was a significant negative correlation coefficient between plasma aldosterone concentrations and FENa in infants more than 34th week of CA, but not in that of less than 34th week. CONCLUSIONS: LBW infants have higher plasma aldosterone concentrations, but a poor correlation between plasma aldosterone concentration and urinary sodium excretion for the first few days of life and in lower chronologic aged infants. These results show that the renal tubule reabsorption of sodium is less responsive to plasma aldosterone in these infants and, therefore, the careful management of fluid and electrolyte balance is mandatory.