RENAL MECHANISMS IN COINCIDENT ADDISON's DISEASE AND DIABETES INSIPIDUS: EFFECTS OF VASOPRESSIN AND HYDROCORTISONE*

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Abstract
A case of coincident cryptogenic diabetes insipidus and Addison''s disease which responded to appropriate replacement therapy is described. Cortisone and hydrocortisone increased water exchange and restored to normal the diuretic response to a water load; hydrocortisone increased the mean level and decreased the variability of endogenous creatinine clearance. Effect on water diuresis persisted longer than could be attributed to a direct action of the steroid hormone on renal tubules. Clearance studies in osmotic diuresis and hydropenia showed that hydrocortisone increased renal plasma flow, glomerular filtration rate, and free water clearance. The small increase in the latter function is attributed to an indirect rather than to a direct action of the steroid on the specific tubular mechanism of water reabsorption. The defective water excretion caused by adrenocortical insufficiency is interpreted as a sequel to diminished glomerular filtration. Since the increase in free water clearance during steroidal therapy is too small to account for the observed large increase in water exchange, the latter is related to stimulation of thirst.