Uric acid excretion by the pig kidney.

The handling of uric acid by the pig kidney has been investigated during continuous urate infusion in unrestrained, unanesthetized animals. Urate-to-inulin clearance rates in excess of 1 were found under all experimental conditions, demonstrating only net secretion by the pig kidney. The demonstration of a secretory maximum was precluded owing to a progressive reduction in the GFR associated with high rates of urate infusion. Urate clearance was independent of urine flow rate up to 10 ml/min. The administration of probenecid inhibited urate secretion, but urate-to-inulin clearance ratios below unity were not observed. Pyrazinamide or pyrazinoic acid, at doses which either inhibited secretion or promoted uricosuria in other species, did not alter urate excretion in the pig. Probenecid together with pyrazinamide exerted the same inhibitory effect on urate secretion as probenecid alone. Pyrazinoic acid was reabsorbed at all infusion rates. It is concluded that the pig kidney eliminates uric acid by filtration and secretion only.