Effect of urine flow rate on uric acid excretion in man

The effect of alteration in rate of urine flow on renal excretion of uric acid was studied with 29 clearance studies in 12 subjects. Uric acid excretion was found to increase with increase in urine flow. The relative contributions of changes in reabsorption and secretion to the observed increment in urate excretion were estimated by measuring the decrement in urate excretion produced by pyrazinamide, an inhibitor of renal tubular secretion. On the basis of these studies, the increment in uric acid excretion occurring during increased urine flow was attributed almost entirely to enhanced tubular secretion of urate as long as substantial extracellular fluid volume expansion was avoided. Extracellular fluid volume expansion was associated with decreased tubular reabsorption of urate. Since stimulation of the tubular transport system for urate by water ingestion is considered unlikely, this study was interpreted as consistent with the existence of a second, postsecretory distal tubular reabsorptive site for urate. Variation in urine flow rate must be taken into account in the interpretation of studies of renal handling of uric acid in man.