Effects of fasting on beta-cell function, body fat, islet volume, and total pancreatic insulin content

The effect of 24 to 48 hours of fasting on beta-cell function, islet area, islet number, and total pancreatic insulin content was examined in mice. Estimation of total body fat mass was based on the known relationship between weight of the gonadal fat pad and percentage of total body fat. The body fat decreased by 31% after 24 hours and 68% after 48 hours (P = 0.003) of fasting. Glucose-stimulated insulin release from the isolated, perfused mouse pancreas decreased by 50% and 76% after 24 and 48 hours, respectively, without affecting the dynamic pattern of insulin secretion. The fall in secreted amount of insulin was closely related to the decrease in the body fat (P = 0.002). The islet area was determined by planimetric quantitation of the perfusion-stained pancreatic islets and was related to the total pancreatic insulin content. Neither islet area nor islet number changed significantly during the fasting periods, whereas a higher pancreatic insulin content was found in mice fasted for 24 hours. A close connection existed between total pancreatic insulin content and islet area (P = 0.003). Our data suggest that the decrement in body fat induced by fasting is synchronized with a progressive loss of the capability of the pancreatic beta cells to release insulin.