Studies on Hyperuricemia in Gout by Inosine loading Test

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As a simple method for analysing urate metabolism abreviation in hyperuricemia of gouty patients, inosine loading test has been investigated.<BR>Eight hundred mg of inosine was injected intravenously into 282 patients with gout and 32 controls (normal subjects and non gouty patients with normal renal function). Urine samples for 60 min. before and after the injection, respectively, and blood samples immediately before and 60 min. after the injection were collected, respectively. Serum uric acid level (Sua), urinary urate excretion (Uua), and creatinine clearance (Ccr), were determined and uric acid clearance (Cua), and clearance ratio (R=Cua /Ccr), were calcurated before and after the injection, respectively.<BR>Serial determination of Sua after the injection of inosine revealed that Sua began to be immediately elevated and reached to a plateau level in 20-30 min. after the injection. The increments at the plateau level of Sua were approximately 2.0 mg/d1 which suggested that the urate pool was enlarged approximately 500 mg in size by the injection. Only 1.8% of inosine injected was detectable in urine collected for 120 min. after the injection. These findings suggested that inoshin injected intravenously was rapidly converted to urate without significant loss of oxypurine and the injection was resulted in a stoichiometric expansion of the urate pool. The elevation of Sua resulted in a parallel increase of Uua with Sua. Therefore, Cua was not changed significantly by the injection. Increments of Sua of gouty patients were exactly the same to that of the control, but increments of Uua in gouty patients were significantly lower than those of the control. Among patients with gout, the increments of Uua in patients of underexcretion type were significantly less than those in patients of overproduction type.<BR>In patients under allopurinol treatment, few increase of Sua and Uua were observed by the inosine loading but in patients under benzbromarone treatment the increment of Sua by inosine loading was significantly lower than that of the control. However, the increments of Uua in patients under the benzbromarone treatment were significantly higher than those of the control, which reflecting action mechanism of the urate production inhibitor and the uricosuric agents, respectively.<BR>These findings indicates that the inosine loading test is a valuable method for estimating urate excretion and also for urate production such as for evaluation of efficacy of allopurinol.

Studies on Hyperuricemia in Gout by Inosine loading Test

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