Relationship between Maturity, Electrolyte Balance and the Function of the Renin-Angiotensin-Aldosterone System in Newborn Infants

Abstract

Simultaneous measurement of plasma renin activity (PRA), plasma aldosterone concentration (PA) and urinary aldosterone excretion (UAE) was made using the RIA method along with determination of Na and K balance in 1-week-old neonates with gestational age of 30–41 weeks (mean 35.9 weeks) and birth weight of 1,160–4,670 g (mean 2,680 g). It was demonstrated that PRA decreased from the value of 36.3 ± 6.3 ng/ml/h (mean ± SE) to a level of 10.2 ± 2.1 ng/ml/h (p < 0.001), PA did not change and UAE increased from 3.3 ± 0.8 to 7.8 ± 1.4 μg/day (p < 0.01) as the gestational age advanced from 30–32 to 39–41 weeks. There was no correlation between either PRA and PA or PA and UAE. PRA showed a significant positive correlation with urinary Na excretion (p < 0.001) and plasma K concentration (p < 0.05), but it was negatively related to Na balance (p < 0.001). Significant negative correlations were found between UAE and urinary Na excretion (p < 0.05), urinary Na/K ratio (p < 0.01) and plasma K concentration (p < 0.05); however, UAE positively correlated with Na balance (p < 0.01). It is concluded that, in response to renal salt wasting and to the subsequent negative salt balance, premature infants can augment their PRA above values found for full-term infants. Their adrenals, however, failed to respond adequately to this stimulation.

Sodium and potassium balances and plasma aldosterone levels in newborn calves

“…as well as in human neonates (Beitins et al, 1972 ;Dillon et al, 1976 ;Tochigi et al, 1976 ;Sparano et al, 1978 ;Sulyok et al, 1979 Plasma sodium levels decreased from 144 + 2 mM at birth to 139 + 1 mM (P < 0.05) on day 6 to 137 ± 1 mM (P < 0.05) on day 7 ( fig. 11.…”

Ontogeny of flow-stimulated potassium secretion in rabbit cortical collecting duct: functional and molecular aspects

“…NEWBORN HUMANS AND animals maintain a state of positive K balance, as is appropriate for growth, unlike their adult counterparts who are in net zero K balance (49). It is now well established that the neonatal kidney contributes to this K retention.…”

“…It is now well established that the neonatal kidney contributes to this K retention. Clearance studies provide abundant evidence for a low rate of urinary K excretion early in life (39,49). In response to exogenous K loading, infants, like adults, can excrete K at a rate that exceeds its filtration (55), indicating the capacity for net tubular secretion.…”

Electrolyte balance, mode of delivery and plasma aldosterone levels in newborn lambs

“…On the contrary the regulation of plasma aldosterone concentration is still poorly understood in newborn mammals. No relationship has been demonstrated between the RA system and aldosterone concentration in human neonates (Dillon et al, 1976 ;Sulyok et al, 1979b The ability of the adrenal cortex to secrete aldosterone has been the subject of several investigations in foetal lambs (Alexander et al, 1968 ;Wintour et al, 1975). Aldosterone transfer from mother to foetus is not significant, and more than 80 % of the aldosterone in foetal blood is of foetal origin in sodium-replete sheep (Moncaup et al, 1980 ;Wintour et al, 1980).…”

“…Their adrenal glands however fail to respond adequately to this stimulation (Sulyok et al, 1979a). Plasma aldosterone concentration measured between 24 and 48 h after birth in premature and fullterm infants is significantly altered by the duration of pregnancy (Godard et al, 1979 ;Sulyok et al, 1979a) and cannot be correlated with renal Na excretion or urinary Na/K ratio (Sulyok et al, 1979b). …”