Function of the renin-angiotensin-aldosterone system in relation to electrolyte balance in the small-for-date neonate.

To assess the influences of intrauterine growth retardation on the electrolyte status and the activity of renin-angiotensin-aldosterone system of newborn infants, sodium and potassium balance, as well as plasma renin activity, plasma aldosterone concentration and urinary aldosterone excretion were determined simultaneously in a group of healthy growth retarded and healthy normally grown neonates. It was observed that intake, urinary excretion and retention rate of sodium and potassium as well as the plasma sodium and potassium levels were essentially the same in the two groups. Similarly, no significant difference was found in plasma renin activity, plasma aldosterone level and urinary aldosterone excretion between the neonates whose birth weight was small or appropriate for gestational age. It is concluded that intrauterine growth retardation has no significant influence on the electrolyte status and the activity of the renin--angiotensin--aldosterone system, suggesting that in the regulation of these functions gestational factors are mainly involved.