Age and gender effects on insulin secretion and glucose sensitivity of the endocrine pancreas

Glucose-stimulated insulin secretion was evaluated in whole perfused pancreases and islets of Langerhans (90 to 110 microns diam) isolated from female and male Fischer 344 (F344) rats aged 6, 12, and 26 mo. Total glucose-stimulated (11.1 mmol/l) insulin release of whole perfused pancreases from male rats did not differ among age groups. In contrast, insulin secretion of 26-mo-old female rats was significantly greater than 6- and 12-mo-old female rats. Insulin secretion by islets of Langerhans incubated in glucose concentrations of 11.1, 16.7, and 22.2 mmol/l was greater in male rats compared with age-matched female animals at all three ages, and was greater in 6-vs. 26-mo-old male rats. Insulin secretion of female rats revealed some significant differences among the age groups, although no clear pattern was evident. Sensitivity of the islets to glucose was estimated from the rate of glucose oxidation. At incubation medium glucose concentrations of 11.1 mmol/l or higher, no effect of gender was observed, although the glucose oxidation rate of islets from male 26-mo-old rats was greater than that of islets from gender-matched 6-mo-old rats. These data indicate that in both the whole perfused pancreas and isolated islets of Langerhans, glucose-stimulated insulin secretion is not significantly altered with age or gender in the F344 rat. However, it appears that maintenance of insulin secretory capacity by aging male rats is achieved by enhancement of beta-cell sensitivity to glucose.