1. When changes in urine flow rate were induced by vasopressin administration in eight subjects, urate excretion decreased by a mean of 14% and was positively correlated with urine flow rate (r = 0·88, p < 0·01). The effect of vasopressin on urate excretion was not influenced by prior changes in extracellular fluid volume.
2. Mannitol administration in a dose sufficient to prevent vasopressin-induced alterations in urine flow rate blocked the effect of vasopressin on urate excretion.
3. Alterations in urate excretion produced by changes in extracellular fluid volume could be distinguished from the urate-retaining effect of vasopressin-mediated decrease in urine flow. Urate retention after vasopressin was entirely attributed to a decrease in pyrazinamide-suppressible urate excretion, consistent with either decreased secretion or enhanced post-secretory reabsorption of urate.
4. Since diminished urine flow rate in the distal part of the nephron is more likely to lead to enhanced reabsorption of urate, these results provide additional evidence for urate reabsorption in the distal part of the nephron.