Seasonal changes in pancreatic insulin and glucagon in the little brown bat (Myotis lucifugus)

Seasonal changes in pancreatic insulin and glucagon were investigated in the little brown bat (Myotis lucifugus). Pancreatic protein content increased 21% from the nonhibernating state in June compared to the nonhibernating or early hibernating state in late October, and then decreased 50% between October and the months of deep hibernation. The content of insulin and glucagon increased from June to October, and both hormones further increased during hibernation, when a fall in pancreatic protein content occurred. The concentration of both insulin and glucagon increased from October to February. Of note, the insulin concentration progressively increased during deep hibernation from February to April, whereas the glucagon concentration remained constantly elevated throughout this time interval. The persistent elevation of pancreatic glucagon during hibernation may be related to its role in counterregulation and carbohydrate homeostasis during fasting. The elevation of pancreatic insulin, and its further increase during hibernation, is less clear but may be hypothesized to provide a rapidly releasable storage pool required for immediate secretion during arousal, possibly to prevent a hyperosmolar state.