PubMed1987
In winter, hibernating mammals enter a long phase of lethargy which is characterized by low body temperature, depressed metabolism and minimal release of metabolic substrates from endogenous fuel stores. Periodically, they spontaneously warm themselves to regain the euthermic state. These arousals are, by contrast, times of high release and consumption of endogenous substrates. Insulin and glucagon may contribute to the control of both contrasting metabolic periods. The secretion and metabolic effects of these two hormones were investigated in two hibernators: the hedgehog (Erinaceus europaeus) and the edible dormouse (Glis glis). During lethargy, blood glucose, insulin and glucagon concentrations were low. In vivo and in vitro studies showed that the secretion of both hormones was markedly depressed by low temperatures. Insulin secretion was not stimulated by glucose, although glucagon secretion remained reactive to arginine. Blood glucose was not regulated by insulin but pharmacological doses of glucagon increased blood glucose concentrations. The tissues were found to be highly insulin-resistant, preventing the fall of blood glucose and consequently limiting the depletion of glucidic substrates during the long periods of starvation. During arousal, blood glucose, insulin and glucagon levels increased at the end of rewarming while glucose turnover gradually increased above a body temperature of 15 degrees C. The effects of glucagon and insulin on glucose metabolism increased markedly beyond this stage. Thus the metabolic effect of both hormones are temperature-dependent. Insulin and glucagon allow an increase in glucose availability for the active metabolic processes which occur during arousal.