While it is believed that the mammalian distal nephron is not involved in uric acid transport, this has not been directly evaluated. Nevertheless, some studies are consistent with significant distal nephron transport. 2. As uric acid transport in man may be similar to the rat, undirectional uric acid permeability was evaluated by perfusion of the isolated rat papillary collecting duct. 3. Uric acid permeability was 0.61 +/- 0.04 micron/s, which was similar to sodium permeability (0.66 +/- 0.05 micron/s) but was less than chloride permeability (0.93 +/- 0.07 micron/s) and markedly less than water permeability (4.81 +/- 0.21 micron/s). Uric acid permeability was not changed following the addition of a maximal antidiuretic concentration of arginine vasopressin (200 microU/mL), nor was it changed by altering the uric acid concentration in the perfusate and bath. 4. These results demonstrate that the papillary collecting duct is permeable to uric acid. The coefficient of transport is sufficiently low and insensitive to arginine vasopressin and uric acid concentrations to suggest that any transport that occurs is probably passive and only of minor physiological significance.
