Quantitation of renal uric acid synthesis in the chicken.

The contribution of uric acid synthesized in the kidney (nephrogenic uric acid) to the total uric acid excreted in the urine was studied in the chicken by use of the isotope-dilution technique. In the non-fasted chicken the urine-to-plasma specific activity ratio (SAR) of [14C]uric acid was 0.83, suggesting that a minimum of 17% of the uric acid excreted in the urine is synthesized in the kidney. During allopurinol infusion into the renal portal circulation of one kidney the SAR increased to 0.99, indicating that the renal synthesis of uric acid was almost completely inhibited and that the SAR is a valid indicator of the contribution of nephrogenic uric acid excreted into the urine without first entering the circulation. Chickens fasted for 18 h showed a lower rate of renal synthesis of uric acid. Hypoxanthine infusion into the systemic circulation increased the rate of renal synthesis of uric acid in both fasted and nonfasted chickens, suggesting that circulating precursor levels may in part regulate the renal synthesis of uric acid.