A new, spontaneously diabetic syndrome has been recognized in nonobese outbred Wistar rats of both sexes. The age at detection of first glycosuria has varied from 48 to 120 days, with a mean of 67 days. Eighteen rats have been studied, 14 untreated and four during and after cessation of insulin treatment. The affected animals have demonstrated a spectrum of severity, with hyperglycemia (252–732 mg./dl.), hypoinsulinemia (0–1 ng./ml.), and hyperketonemia. The severely ketotic rats, with total blood ketone body levels between 6 and 13 mM, showed rapid loss in weight and dehydration over one to six days. The moderately ketotic (1–5 mM) declined gradually in weight over 15 days, with marked polyuria and glycosuria. The stable rats, with ketonemia less than 1 mM, sustained their weights, polyuria, and glycosuria for longer than 40 days.

A relative or absolute increase in plasma immunoreactive glucagon and elevated levels of free fatty acids and branched-chain amino acids were observed in relation to the severity of the syndrome. Intraperitoneal arginine or tolbutamide elicited no insulin response, but the glucagon response to arginine was exaggerated. Pancreatic insulin content was markedly diminished and glucagon content was normal or moderately decreased. Light-microscopic examination of pancreases of ketotic animals at the end stage of the disease showed islets to be very small and rare, consisting virtually of non-β cells. In stable and earlier ketotic rats, the islets were small, with reduction in β-cell number and a striking inflammatory cell infiltration. Surviving β cells showed variable degranulation. This model of spontaneous diabetes in nonobese rats displays insulin deficiency, glucagon excess, and ketosis, with a dramatic inflammatory lesion during active β-cell destruction.

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