Sonia Rawal, Han-Hung Huang, Lesya Novikova, Tyler Hamedi, Irina V Smirnova and Lisa Stehno-Bittel
Exercise and physical activity improve the glycemic control in people with type 2 diabetes (T2D). It is known that activity improves muscle utilization of glucose, and that exercise can spare islets if initiated prior to the onset of diabetes. However, any effect of exercise on pancreatic islet function after the diagnosis of overt diabetes is unknown. The aim of the study was to investigate the effects of exercise training on pancreatic islets in a rodent model of overt T2D. 12-week old male Zucker Diabetic Fatty (ZDF) rats and control lean rats were divided into 4 groups: sedentary control exercised control, sedentary diabetic and exercised diabetic. Exercised rats were trained with moderate intensity running on a treadmill for 7 weeks. Assessment of plasma insulin levels, islet cell composition (relative proportion of α, β and δ cells), islet density, insulin content and islet core diameter was conducted at the end of the study. Diabetes in ZDF rats lead to high HbA1c and BGLs, which was not reversed by exercise. Diabetes caused destruction of the islet structure and significant loss of β-cells, with an increased proportion of α- and δ-cells. Exercise improved islets morphology in the diabetic group, while islet density and islet cell composition were not affected by exercise. Increased insulin immunostaining of the pancreatic islets was identified in the diabetic animals after exercise. Although exercise did not affect the diabetes-induced decrease in the proportion of islet β cells, there appeared to be an improvement in the islet architecture and in β-cell insulin content.