The effects of overeating on insulin secretion in normal mice

This study was performed to examine the effect of overeating on in vivo and in vitro insulin secretion in normal mice. Six week old male CRJ-ICR mice were maintained on a cookie and chocolate mashed diet (C.C. diet) until 30 weeks of age; control mice received an ordinary mouse chow. The mice on the C.C. diet (C.C. mice) consumed 125-130% of the daily caloric intake of control mice throughout the study. C.C. mice developed mild hyperglycemia with relative obesity from 16 weeks of age. Fed blood glucose levels at 30 weeks of age for C.C. mice were 158.3 +/- 6.7 mg/dl as opposed to 127.2 +/- 3.1 mg/dl for controls (p less than 0.01). In experimental mice at 18 weeks of age, plasma insulin response after intraperitoneal glucose load (2 mg/g BW) and insulin secretion at 30 mM glucose from the perfused pancreas were similar to those in control mice. However, at 30 weeks of age, insulin secretion at 30 mM glucose from perfused pancreas in C.C. mice was significantly suppressed compared with that of control mice (p less than 0.02). Conversely, in vivo insulin secretory response to intraperitoneal glucose load was significantly increased in C.C. mice (p less than 0.05). There were no differences in insulin secretion at 15 mM glucose from perfused pancreas. These results indicate that impairment of beta-cell secretory capacity develops in impaired glucose tolerant mice with obesity, while in vivo studies show a high insulin response to glucose. This alteration of beta-cell function may be the initial change during the development of the hyperglycemia-induced defect in insulin secretion.