Urate reabsorption in proximal convoluted tubule of the rat kidney

Urate reabsorption was examined in the rat utilizing clearance and in vivo microperfusion techniques. In control rats, the fractional excretion of urate averaged 12.5 +/- 1.3% of the filtered load, with 60-70% of perfused urate reabsorbed at 2 mm of perfused tubule length (urate efflux). Increasing the perfusion concentration of urate to 6, 12, and 25 mg/100 ml did not alter the fractional rate of reabsorption. The acute administration of chlorothiazide resulted in a fall in GFR and Curate such that the fractional excretion was unchanged from controls and averaged 13.3 +/- 2.0%, without an associated change in urate reabsorption from proximal perfusates despite the presence of significant inhibition of sodium and water reabsorption. By contrast, the chronic administration of chlorothiazide accompanied by a low-sodium diet resulted in a significantly lower fractions excretion rate of urate of 7.95 +/- 0.5% and a significant increase in reabsorption of sodium and water as well as urate from microperfusates, In control rats receiving an infusion of 5% mannitol in isotonic saline, urate secretion was demonstrated by the urinary precession of [2-14C]urate from [methoxy-3H]inulin following placement of these isotopes on the surface of the kidney. The additional infusion of chlorothiazide did not alter this pattern of isotope recovery in the urine.