Effect of isoproterenol on renal uric acid excretion in rats

Effect of isoproterenol on renal uric acid excretion was examined in oxonate-loaded and oxonate-nonloaded rats, using a clearance technique. Oxonate loading was performed by continuous infusion into the femoral vein. Isoproterenol (50 micrograms/kg, i.v.) induced antidiuresis and hyperuricemia accompanied with decreases in urinary excretion rate of uric acid, uric acid clearance, inulin clearance, and uric acid clearance/inulin clearance ratio in oxonate-nonloaded rats. These effects of isoproterenol were inhibited by propranolol (1 mg/kg, i.v.). Very similar results were obtained in oxonate-loaded rats; i.e., systemic blood pressure decreased synchronously with uric acid excretion by isoproterenol. In contrast, phenylephrine (100 micrograms/kg, i.v.) induced hypertensive, diuretic and slightly uricosuric results. In allopurinol-pretreated and oxonate-loaded rats, isoproterenol also decreased renal uric acid excretion and showed a less potent hyperuricemic effect than that observed in the animals not pretreated with allopurinol. In addition, in rats with ligated renal vessels, the hyperuricemic effect of isoproterenol was completely inhibited by allopurinol. These results suggest that isoproterenol-induced hyperuricemia is related not only to the stimulation of uric acid production, but also to the depression of renal uric acid excretion.