Plasma renin concentration, activity and substrate in normal children.

Plasma renin concentration (PRC), activity (PRA) and substrate concentration (PRSC) were measured in 27 males and 31 female children aged 3 days to 14.5 years (median age 10 months). No sex difference between the three parameters was found and the data were therefore combined for boys and girls. Logarithmic transformation were used for all parameters. PRC, PRA and PRSC were significantly higher in children than in adults and were negatively correlated by age or body surface area. As expected, PRA was strongly positively correlated to PRC (r = 0.98, P less than 0.001) and to PRSC ( r = 0.55, P less than 0.001). From the second order partial correlation coefficients it is concluded that PRSC and PRC in children decrease with age or body surface area, and that PRA consequently also decreases. A negative feed-back regulatory mechanism between PRSC and PRC is suggested. Because of the decline in PRSC during childhood, it is recommended to measure PRC instead of PRA and to use age related reference values.