The renin-angiotensin-aldosterone system has hitherto been investigated extensively in adults, but little information has been reported with regards to children, partly because large quantities of blood were needed for measuring the system's components and sampling difficulties were encountered in young children.Recently, some simple radioimmunoassays were developed and it became easier to measure plasma aldosterone concentrations (PA) and plasma renin activity (PRA) in children. In this study, PA and PRA were determined by using radioimmunoassay, and electrolytes of plasma and erythrocyte were measured by flame photometer and an atomic absorption photospectrometer. In addition, in order to clarify the causes of high PA and PRA levels in neonates, the relationships between oral sodium intake on one hand and PA and PRA on the other were also examined.The subjects were 418 children, aged from the first day of little to fifteen years, and 8 adults, who were in convalescence from acute infectious diseases without evidence of circulatory or renal diseases. They were on free diets and kept at rest in a supine position as a rule. Venous blood samples were taken during the one-hour period from 8 A.M. to 9 A.M. PA was measured by ALDOK-Kit (CIS), and PRA was measured by Renin-Riakit (Dinabot).The child subjects were divided into 10 groups according to age difference, and the eleventh group of adults served as a control : I) 0-6 days, II) 7-27 days, III) 1-2 months, IV) 3-5 months, V) 6-11 months, VI) 1-2 years, VII) 3-5 years, VIII) 6-8 years, IX) 9-11 years, X) 12-45 years, XI) adults.The results were as follows : A. The mean values of PA and PRA for each group : 1) PA (ng/dl) : I) 62.66 ± 48.54, II) 52.19 ± 23.49, III) 38.16 ± 20.95, IV) 29.91 ± 19.01, V) 17.37 ± 9.63, VI) 14.20 ± 7.56, VII) 11.43 ± 6.51, VIII) 9.72 ± 4.46, IX) 9.62 ± 4.59, X) 7.44 ± 2.23, XI) 8.47 ± 1.37.2) PRA (ng/ml/hr) : I) 8.83 ± 8.67, II) 7.40 ± 3.74, III) 5.70 ± 2.97, IV) 3.54 ± 1.96, V) 2.58 ± 1.41, VI) 2.11 ± 1.14, VII) 1.76 ± 0.99, VIII) 1.37 ± 0.61, IX) 1.28 ± 0.55, X) 0.91 ± 0.42, XI) 1.01 ± 0.14.B. 1) PA and PRA had similar patterns; in group I, the values were about 7-8 times as high as those of group XI and ranged widely. Then, they rapidly decreased with increasing age, the rate growing mild in group VI and after, and group X showed no significant difference from group XI.2) A significant positive correlation was found between PA and PRA (r=0.5374, P<0.001, N=357).3) No significant correlation was noted between PA and plasma sodium in any group.4) A significant positive correlation was found between PA and plasma potassium in all groups except the neonatal period.5) A significant negative correlation between PA and plasma magnesium was found in all groups, especially in the neonatal period.6) There was no significant correlation between either of PA and PRA and the ratio of plasma electrolyte to erythrocyte electrolyte.7) In children under six months, there was a significant negative correlation between both PA (r=-0.4601, P<0.001, N=77) and PRA (r=-0.3043, P<0.01, N=81) and oral sodium intake (mEq/M2 /day).8) A significant negative correlation was found between oral sodium intake and the ratio of PA to PRA (r=-0.4601, P<0.001, N=52) in the neonatal period.These findings suggest that oral sodium intake is one of the causes of high PA and PRA levels in newborns and infants, and that in the neonatal period, markedly low sodium intake increases the sensitivity of angiotensin II receptor in the adrenal cortex to the renin substance.
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