Tubular secretion of urate in the dog

Abstract

Clearance studies under appropriate conditions of urate loading and osmotic diuresis yielded C_urate/GFR ratios > 1.10 in both Dalmatian and non-Dalmatian dogs, indicating tubular secretion of urate. In the purebred Dalmatian, stop-flow studies (U/P_urate: U/P_creatinine ratios) localized peak net urate secretion to the proximal segment, with a second, lesser peak in the distal segment. Both peaks were abolished by probenecid and, in massive dosage, by PAH, yielding ratios < 1. In the mongrel dog, stop-flow studies showed maximal net tubular reabsorption of urate in the proximal segment, peak net tubular secretion of urate in the distal segment. Proximal urate secretion was not demonstrated but may have been masked by preponderant urate reabsorption. It is suggested that, as in man, renal regulation of urate excretion in the dog involves glomerular filtration, tubular reabsorption (deficient but still demonstrable in the Dalmatian) and tubular secretion (ordinarily masked by preponderant reabsorption in the non-Dalmatian). Both reabsorption and secretion of urate in the dog appear to be effected largely by ‘active’ processes.