No abstract

Plasma renin activity (PRA) and plasma aldosterone concentrations (PAC) were determined in fifty normal newborns during the first 72 h of life. PRA was elevated in all cases and tends to increase from the first (6.79 +/- 0.69SE ng/ml/h) to the third day of life (8.24 +/- 0.96SE ng/ml/h). PAC was also elevated and rose from 24.06 +/- 3.23SE ng/dl on the first day to 39.20 +/- 4.25SE ng/dl on the third day. No significant correlation was observed between PRA and PAC. Serum sodium was within the normal range, whereas serum potassium was slightly elevated during the first 48 h of life. The physiological significance of the high levels of PRA and PAC in newborns is not clear at present. Many factors may be involved in the increased activation of the renin-angiotensin-aldosterone system: low blood pressure, hypersensitivity of the macula densa to catecholamines, relative insensitivity of the immature kidney to aldosterone, hyperkalaemia and other control mechanisms for aldosterone secretion all of which probably operate simultaneously during the first days of life.