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

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Abstract
The renin-angiotensin-aldosterone system was studied in 50 healthy children aged 4-16 yr under normal Na and K 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 Na excretion; r = -0.40, P < 0.01. This relationship remained significant when the daily urinary Na excretion was corrected for 1.73 m2 body surface area (BSA); r = -0.40, P < 0.01. Using multivariance analysis, plotting the plasma renin activity against the 2 combined parameters (24 h urinary Na excretion and age), no improvement was obtained (r = 0.38, P > 0.05). During childhood, Na rather than age apparently 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 2 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 Na excretion nor 24 h urinary K excretion improved the multiple correlation coefficient with plasma aldosterone when added to plasma renin activity and age.