Age versus urinary sodium for judging renin, aldosterone, and catecholamine levels: studies in normal subjects and patients essential hypertension

Abstract

The relative influence of sodium balance and age on plasma renin activity (PRA), aldosterone (PA), norepinephrine (NE), and epinephrine (E) levels, and urinary NR or E measured in an outpatient setting was evaluated in 90 normal subjects and 79 patients with benign essential hypertension. Ranges, of age (17 to 76 yr) and urinary sodium excretion (U(Na)) (51 to 241 mEq/24 hr) were comparable. In normal subjects, supine or upright PRA and supine plasma E correlated (P < 0.05) inversely and supine plasma PNE or NE excretion correlated positively with age, but not with U(Na); the upright plasma NE correlated closer with age than it did with U(Na). Supine PA correlated with both age and U(Na); upright PA did so only with U(Na). Based on significant relationships with either age or U(Na), dynamic normal ranges with 95% confidence limits could be established. Hypertensive patients exhibited also age-related decreases in PRA and PA and increases in NE; PRA and PA did not correlate with U(Na). Consideration of age revealed low or high PRA in 10 and 7%, respectively; these abnormalities occurred more commonly with moderate-severe (>160/105 mm Hg) than with mild hypertension and were associated with parallel variations in age-adjusted plasma NE. Nevertheless, plasma NE was within the normal range, except for slightly low upright values in 15% of patients. PA related to age or U(Na) was increased in 25% of patients while supine, but it was usually normal in the upright position. These findings demonstrate that without profound sodium depletion, age may be more important than sodium excretion as a frame of reference for judging both renin and norepinephrine measurements; both factors should be considered for interpretation of PA. On this basis, one fourth of patients with essential hypertension have mild hyperaldosteronism while maintaining the supine position. Low renin hypertension is much less common than previously suggested and may be related to low adrenergic activity.