Streptozotocin diabetic male albino rats were observed to exhibit faulty conversion of tryptophan into niacin. Streptozotocin-injected rats, kept on niacin-deficient diet and given a dose of L-tryptophan (intraperitoneal or oral) excreted comparatively less quantities of niacin and N1-methylnicotinamide in urine than the control nondiabetic rats. Rats continued to show this effect for at least three months after streptozotocin injection. Dietary intake was found to have no influence on the excretory pattern. Streptozotocin diabetic rats were also observed to excrete greater amounts of xanthurenic acid and other tryptophan metabolites on tryptophan administration as compared to the nondiabetic rats.

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