Factors affecting urate reabsorption in the rat kidney.

1. Urate transport in the rat appears to be saturable. However, affinity of the transport system for urate is very low and transport far from saturated at physiological plasma concentrations. 2. Since increase of the nonionized fraction of uric acid by a factor of five failed to increase urate reabsorption, transport cannot be due to nonionic diffusion but rather involves ionized urate. 3. Increases in luminal flow rate markedly depress urate reabsorption in the loop of Henle, which results in wash out of medullary urate.