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.