Effect of sodium restriction on urinary excretion of cortisol and its metabolites in humans.

The adrenal gland is involved in the control of urinary sodium excretion mainly via the secretion of the mineralocorticoid aldosterone. Although under certain conditions glucocorticoid seem to be also involved in the regulation of sodium homeostasis, there are contradictory reports on the relationship between cortisol secretion and sodium intake. Given recent findings linking regulation of physiological activity of steroids to the activity of specific enzymatic pathways, we have examined changes in urinary excretion of cortisol and its metabolites in eight healthy volunteers on a low sodium diet. Urinary steroids were measured with specific radioimmunoassays after extraction and chromatography (F and E) or after dilution (THF and THE). Excretion of cortisol (124 +/-41 nmol/day) was significantly lower on Day 2 (86 +/- 27 nmol/day, p < 0.01) and Day 7 (85 +/- 25 nmol/day, p < 0.01) of sodium restriction. On the same samples calculated ratios of THF/F (55 +/- 15; 61 +/- 22; 68 +/- 21) and E/F (2.5 +/- 0.6; 2.8 +/- 1.4; 3.0 +/- 1.3) reflecting the activity of 5 beta-reductase and 11 beta-hydroxysteroid dehydrogenase, respectively, showed significant increases in the former on both Days 2 and 7 and for the latter only on Day 7. This study supports the notion that sodium restriction decreases urinary cortisol excretion and provides evidence that increased activity of 5 beta-reductase and lowered metabolism by 11 beta-HSD are presumably the mechanisms of this decrease.