Sodium loading raises urinary cortisol in man.

It has been suggested that cortisol secretion is modified by sodium intake. We therefore studied the pituitary-adrenal axis by measuring diurnal rhythms of ACTH and cortisol levels in serum of 10 normal control subjects after 4 days of low sodium diet (intake 40 mEq/day) and after 6 days of high sodium diet (intake 320 mEq/day). Urinary excretion of aldosterone-18-glucuronide and free cortisol were determined at the end of each diet. Urinary aldosterone excretion declined from 17.9 +/- 2.6 to 2.8 +/- 1.1 microgram/day and urinary cortisol increased from 26.2 +/- 6.2 to 36.8 +/- 13.8 micrograms/day during low and high sodium intake. In contrast, plasma ACTH and serum cortisol measured every two hours for a 24-h period were similar both during low and high sodium intake. The results suggest an altered handling of cortisol by the kidney during high salt intake.