Effects of Cold Exposure on Insulin and Glucagon Secretion in Sheep

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Abstract
The effects of cold exposure on the secretion of insulin and glucagon were examined using five adult sheep. Endocrine responses were studied in a warm environment and after cold exposure (0 C) from 4–19 days. Compared to levels at room temperature, basal plasma glucose levels were elevated during cold exposure, but basal levels of plasma insulin and glucagon were unchanged. Cold exposure significantly decreased the early insulin response to a primed iv infusion of glucose. Plasma glucose and glucagon levels during glucose infusion were unaffected by cold exposure. The decrease in plasma glucose after iv insulin injection (0.2 U/kg BW) was greater during cold exposure than at room temperature. Butyrate injection (0.625 mmol/kg, iv) resulted in a significantly lower secretion of both insulin and glucagon in the cold than in the warm environment. The glucagon response to arginine infusion (0.5 g/kg over 30 min, iv) was elevated by cold exposure, whereas the insulin response to arginine tended to be reduced. Propranolol infusion (20 μg/kg-min, iv) caused a slight inhibition of insulin secretion in the cold environment, but did not affect glucagon levels in either the cold or warm environment. Phentolamine infusion (20 μg/kg-min, iv) inhibited glucagon secretion, particularly in the cold environment, and caused a markedly greater stimulation of insulin secretion in the cold. It is concluded that cold exposure insufficient to cause hypothermia decreases insulin secretion in response to a variety of stimuli. Effects of cold on glucagon secretion depend upon the stimulating agent used.