Change in endocrine pancreatic function in short-term diet restriction.

Long-term diet restriction can retard the aging process. Lower sustained plasma glucose levels may be one of the key factors for prolongation of life. The purpose of this study was to determine the effects of short-term diet restriction on the endocrine pancreas in rats. One hundred 5-wk-old male Sprague-Dawley rats were fed ad libitum for 1 wk, and then 10 rats (5 fed, 5 fasted for 24 h) were killed. The remaining 90 rats were divided into two groups, either fed ad libitum or maintained on a restricted food intake (60% of control/day). At regular intervals after the start of food restriction, rats from each group were killed, and plasma and the pancreas were collected for measurements of glucose, insulin, and glucagon concentration and content. At the end of the study, isolated pancreatic perfusions were performed to examine dynamic insulin response to glucose. Throughout the study, plasma glucose and insulin levels were lower in fed rats from the diet-restricted group than in fed rats from the normally fed group. Furthermore, there were no differences in plasma glucose or insulin levels between fed and fasted rats in the diet-restricted group. Pancreatic perfusion showed that the second phase of insulin release was significantly lower in rats from the diet-restricted group than in rats from the normally fed group. Decreased content of spermine in the pancreas of the diet-restricted rats may correlate with a decreased second phase of insulin release. These findings may partly explain why lowered plasma insulin levels are observed in diet-restricted rats.