The effect of extremely high sodium intake on plasma renin activity, plasma aldosterone concentration, and urinary excretion of aldosterone metabolites.

The effect of sodium intake on aldosterone production was examined in eight healthy men whose urinary sodium excretion approached their dietary sodium intake at levels of 10, 300, 800 and 1500 mEq sodium/day. Aldosterone secretion was estimated from the excretion rate of two aldosterone metabolites: Thaldo and aldosterone-18-glucuronide. Maximal suppression of aldosterone secretion appeared to have been reached when sodium intake was 800 mEq/day, since no further decrease in aldosteron metabolite excretion rates was observed at 1500 mEq/day dietary sodium. Both plasma renin activity and plasma aldosterone concentration were suppressed and approached or were below the detection limits of the respective radioimmunoassays when sodium intake reached 800 and 1500 mEq/day. Body weight and blood pressure significantly increased at each increment of sodium intake. Our findings show that when sodium intake is extremely high, aldosterone secretion does not decrease to zero but continues at a rate we estimate to be 10 to 30 microgram/day. We suggest that this nonsuppressible secretion of aldosterone may have contributed to the observed increases in weight and blood pressure.