The effect of physical training on insulin secretion of rat pancreatic islets.

Rats were either physically trained by a 12-wk swimming program or were freely eating or weight matched, sedentary controls. Islets of Langerhans were isolated and incubated in various glucose concentrations. Within the range of physiological glucose concentrations the rate of insulin release from islets of trained rats was lower than that from islets of sedentary controls. The DNA content of the islets was similar in the different groups. The demonstrated decreased glucose sensitivity of the insulin secretory mechanism within the beta-cells of trained rats may partly explain the finding of lower plasma insulin concentrations during intravenous glucose tolerance test in these rats compared with sedentary rats. Epididymal fat pads of trained rats were smaller than those of weight matched controls which in turn were smaller than those of freely eating controls, these differences being due to differences in fat cell size. The lower glucose sensitivity of the beta-cells in trained rats was probably not a consequence of the low body weight and small fat depots in these rats