The magnitude of the influence of endogenous adrenal steroids upon renal excretion of electrolytes has been assessed by observing the changes on administering spironolactone, which blocks, at least in part, the effect of steroids upon the kidney. The findings indicate that endogenous steroids exert a sodium-retaining effect in subjects asleep at night, recumbent or standing in the afternoon, and ambulant and perhaps also recumbent in the morning. Endogenous steroids also promote chloride reabsorption, but the changes are usually smaller. Changes in excretion of potassium and hydrion have been less convincingly demonstrated, but it is believed that sodium reabsorption is by ion exchange for potassium and hydrion, as well as in association with chloride.
If the subject maintains the recumbent posture for 5 hr. from midday, the influence—and probably the production—of endogenous steroids declines steadily, but it is maintained if he stands. The contribution of steroids to the altered renal behaviour on changing posture has been assessed; the low sodium excretion on standing is in part due to a non-adrenal, presumably haemodynamic factor, and in part to aldosterone secretion; and on standing there is a modest but significant fall in potassium excretion due to the non-adrenal factor.