Insulin response in rats acutely exposed to cold.

To examine the role of insulin during shivering thermogenesis, rats (unacclimatized) were exposed to 4 degrees C for 24 h and compared with control rats kept at 25 degrees C. Cold exposure lowered plasma insulin levels by one half, despite unchanged plasma glucose concentrations. Adrenodemedullation 2 weeks prior to cold exposure partially restored the ability of cold rats' plasma insulin levels to respond to a glucose load, unless it was accompanied by a subcutaneous injection of epinephrine. When additional normal rats were cold stressed and injected immediately after exposure with an alpha-adrenergic blocking agent (phentolamine), an intravenous glucose challenge caused a mean peak insulin value that was 50% higher than that of untreated controls, while the glucose level was less elevated. The results suggest that cold depresses blood insulin levels through activation of the sympathetic adrenal system, an effect most likely mediated by alpha-adrenergic inhibition of the pancreatic insulin response.