In order to obtain direct informations on the mechanisms of transepithelial urate transport in the rat kidney, renal clearance study, tissue analysis study and methods of tracer (2-14C-urate) microinjection into tubular lumen and peritubular capillary were performed. Futhermore, thin layer chromatogm raphic analysis were performed to clarify whether or not 2-14C-urate injected was metabolized. Results obtained from these studies are summerized as follows. 1) Fractional excretion rate of filtered urate was below 1.0 under hydropenic state, indicating net tubular reabsorption of urate. 2) Reabsorption of urate was found to occur primarily in the proximal comvoluted tubule, partly in the Henle's loop, and negligibly both in the distal tubule and collecting tubule. 3) The lack of conversion of radioactive urate to allantoin in the tubular lumen after microinjection indicated that the obtained values of reabsorptive fluxes were neither overestimated nor underes-timated. 4) Unidirectional secretary flux of 2-14C urate from the peritubular capillary into tubular lumen was also found, although the secretion sites along the nephron was not clarified. 5) Mannitol diuresis resulted inn an increment in fractional excretion rate of filtered orate inn accordance with decrement in the unidirectional reabsorptive flux of 2-14C-urate across the proximal tubule and Henle's loop.
