SODIUM, POTASSIUM AND AGE: POSSIBLE DETERMINANTS OF PLASMA RENIN ACTIVITY AND ALDOSTERONE DURING CHILDHOOD (AGE 4–16)

The renin‐angiotensin‐aldosterone system was studied in fifty healthy children aged 4–16 years under normal sodium and potassium intake. The plasma renin activity (PRA) and plasma aldosterone (PA) decreased with age: r =−0·30, P < 0·05 for plasma renin activity and r =−0·33, P < 0·05 for plasma aldosterone. Significant negative correlation was obtained between plasma renin activity and the 24‐h urinary sodium excretion; r =−0·40, P < 0·01. This relationship remained significant when the daily urinary sodium excretion was corrected for 1·73 m² body surface area (BSA); r =−0·40, P < 0·01. Using the multivariance analysis, plotting the plasma renin activity against the two combined parameters (24‐h urinary sodium excretion and age), no improvement was obtained (r = 0·38, P > 0·05). This finding suggests that during childhood, sodium rather than age has a major modulatory role on plasma renin activity. With advancing age the plasma aldosterone showed a significant positive correlation coefficient with plasma renin activity (r = 0·29, P < 0·05). Multivariance analysis between plasma aldosterone and the two combined parameters, plasma renin activity and age, significantly improved the correlation coefficient (r = 0·42, P < 0·05) suggesting that both plasma renin activity and age play a dominant modulatory role in the control of plasma aldosterone during childhood. Neither 24‐h urinary sodium excretion, nor 24‐h urinary potassium excretion, improved the multiple correlation coefficient with plasma aldosterone when added to plasma renin activity and age.