Effect of a restricted diet on the in vitro glucose-induced insulin release of aging rats

Comparison of the effects of 20 days and 15 months of calorie restriction on male Fischer 344 rats

The aim of this study was to compare, in 19-month-old male Fischer 344 rats, the influence of brief (20 days) and prolonged (approximately 15 months) calorie restriction (CR; consuming approximately 60% of ad libitum, AL, intake) on circulating levels of glucose, insulin, C-peptide, and free fatty acids (FFA); age-matched AL rats were also studied. In the prolonged CR group, there was an approximately 85% decline in fat pad masses (epididymal and retroperitoneal) compared to AL and brief CR rats (these latter groups did not differ significantly). Compared to AL levels, glucose was 15% lower with prolonged CR (p < 0.05) while the brief CR values tended to be lower (10%) than AL; the CR groups did not differ significantly. Plasma FFA levels were significantly (p < 0.05) greater (85-106%) in the brief CR group compared to each of the other groups. Plasma insulin concentrations for the CR groups were lower (p < 0.05; approximately 50-60%) than AL levels. Plasma concentrations of C-peptide (an indicator of insulin secretion) were also lower for each CR group vs AL levels, and a high correlation was found between plasma insulin and C-peptide concentrations (r2 = 0.90; p < 0.001). The C-peptide/insulin ratios for the CR groups were similar, and the value of each CR group exceeded that for the AL rats. These results demonstrate that: the CR-induced reduction in plasma insulin is attributable in large part to reduced insulin secretion; these decreases in insulin secretion and concentration are essentially undiminished when brief CR is initiated rather late in life, and the reductions are independent of substantial reductions in body fat.

Impaired second phase insulin response of diabetes-prone C57BL/6J mouse islets

The C57BL/6J mouse develops obesity and diabetes in response to a high-fat, high-simple carbohydrate diet. To determine the dynamics of glucose-induced insulin release in this animal model of NIDDM, we studied the acute insulin response to glucose of perifused islets in C57BL/6J (diabetes-prone) and A/J (diabetes-resistant) mice fed a normal control diet and of others fed a diabetogenic diet. The insulin response of normal C57BL/6J islets was almost monophasic, with a deficiency in the second phase during high glucose stimulation when compared to that of A/J control islets. The defect in C57BL/6J mice was exaggerated in animals fed a diabetogenic diet. It is suggested that a latent deficiency of second phase insulin release may contribute to the development of the diet-induced syndrome in this model.

Impaired insulin release in aging rats: metabolic and ionic events

We investigated the effect of aging on glucose uptake, glucose-induced O2 consumption, glucose-induced 45Ca movements, and calmodulin content to elucidate age-related impairment of glucose-induced insulin release in pancreatic islets of Wistar rats. Intact pancreatic islets from old (24-month-old) rats showed impaired glucose-induced insulin release; glucose uptake and O2 consumption were lower in old than in young (2-month-old) or adult (12-month-old) rats. Moreover, 45Ca uptake and calmodulin content were decreased in pancreatic islets from older rats, which explained the impairment in glucose-induced insulin release in aging. No major differences between the 3 age groups in glucose-induced 45Ca efflux in pancreatic islets were observed.