1. The renal response to a single slow intravenous injection of diazoxide has been studied in three patients with vasopressin-deficient diabetes insipidus, one patient with nephrogenic diabetes insipidus and three normal subjects.
2. In all patients there was a fall in urinary volume, free water clearance and sodium excretion. This effect was maximal 3–4 h after the injection. Potassium excretion was unchanged. In only one experiment was there a fall in blood pressure. There was no correlation between these changes in renal function and changes in creatinine clearance.
3. The renal effect of diazoxide on the diuresis of diabetes insipidus therefore resembles that of thiazide diuretics, with the important difference that the antidiuresis is associated with sodium retention rather than natriuresis. It is postulated that diazoxide induces increased proximal tubular reabsorption of sodium and water, as an indirect result of its peripheral vasodilator action, and that this explains both the similarities and the differences between the action of this drug and the thiazide diuretics in diabetes insipidus.