Structure and function changes in the endocrine pancreas of aging rats with reference to the modulating effects of exercise and caloric restriction

Abstract

The current study was conducted to determine if physical activity and/or weight control could influence the age-related decrease in beta cell insulin response noted in earlier studies. As such, virgin, male Sprague-Dawley rats were maintained in our facility for 1 yr on three differential experimental programs: in the first groups, control rats lived under standard laboratory conditions; the second group of rats ran several miles a day in exercise wheels; and the third group was given a calorie-restricted diet designed to keep the rats weight-matched with the exercising rats. The results showed that the 12-mo-old sedentary control rats weighed an average of 800 g. From the time these rats were 4 mo old, they were significantly hyperinsulinemic, with mean (±SEM) serum insulin levels of 55±6 μU/ml compared with their base-line levels at 1 1/2 mo of 20±3 μU/ml. Morphological studies on the pancreas of these rats at the end of the year revealed enlarged, multilobulated, fibrotic islets. After collagenase digestion, the most normal-appearing islets from the 12-mo-old controls were used for insulin secretion studies, these islets showed significantly reduced glucose-induced insulin release (0.83 μU insulin/min per volume islet) compared with islets from young rats (1.80 μU insulin/min per volume islet). In contrast, 12-mo-old exercised or calorie-restricted rats weighed ~500 g and did not show the changes in serum insulin levels or pancreas pathology exhibited by the sedentary control animals. However, islets from the calorie-restricted group functioned in vitro no better than islets from the sedentary control group. Islets from the exercised rats were somewhat improved in this regard. In summary, we believe, exercise and weight control diminishes the animals' need for insulin - resulting in youthful-appearing islets after a year's time. However, these regimes do not appear able to correct the beta cell decline in function previously described.