Insulin secretion in sheep exposed to cold.

1. Cold exposure caused a marked decrease in insulin response to intravenous injection of glucose, with a sharply declining response over the first 4 days of cold exposure followed by a constant low response up to 13 days of the experimental cold period. 2. The glucose-induced insulin response was unaffected by concomitant infusion of phentolamine in the warm environment. In contrast, the low response of insulin secretion to glucose during cold exposure was so augmented by concomitant infusion of phentolamine as to exceed the response observed in the warm environment. 3. Intravenous infusion of phentolamine caused an increase in the concentration of plasma insulin in the cold but not in the warm environment. 4. Adrenaline completely abolished the insulin response to glucose in the warm environment. 5. Exposure to cold environment brought about an increase in urinary excretion of adrenaline and noradrenaline and in heart rate, but rectal temperature was unchanged. 6. It is concluded that cold exposure insufficient to cause hypothermia produces a marked decrease in insulin secretion by the pancreas of sheep, mediated through adrenergic alpha-receptors stimulated by augmented sympatho-adrenomedullary activity.