Lithium and the antidiuretic hormone.

The effect of lithium on the urine concentrating response to antidiuretic hormone (ADH) and the excretion of ADH has been studied in rats and man. The maximum urine osmolarity following 18 h dehydration and Pitressin (5 u) was decreased in three out of four patients during lithium treatment compared to their response to the same test in the absence of lithium. In a fifth patient, tested only during lithium treatment, the urine remained hypotonic to plasma throughout this test. Lithium increased the excretion of ADH in non-polyuric patients from 9-22 mu/24 h in the absence of lithium to 36-202 mu/24 - during lithium treatment. In four patients with lithium-induced polyuria, a diuretic acting on the distal tubules, clorexolone, reduced the polyuria. Lithium increased urine volume and the excretion of ADH in four rats receiving lithium in their diet. The response to exogenous ADH was decreased during lithium administration.