Changes in plasma glucagon levels to stressful environmental temperatures.

Effects of temperature stimuli on plasma glucagon levels were studied in fasted (18 hr) and shorn rats. Plasma glucagon levels rose significantly on exposures to both cold (-5 degrees C, 60 min) (p less than 0.001) and heat (36 degrees C, 60 min) (p less than 0.001) from that in control rats at 25 degrees C. Cold stimulus increased blood FFA level (p less than 0.001) and both cold and heat stimuli increased blood glycerol levels (p less than 0.05-0.001). FFA/glycerol molar ratio decreased to a similar extent on both cold and heat exposures (p less than 0.02-0.01). It was noted that plasma glucagon, blood FFA and glycerol levels increased significantly more in cold-exposed rats (p less than 0.001) than in heat-exposed ones. There were positive relations of plasma glucagon levels to blood FFA and glycerol levels (p less than 0.001), while an inverse relation of plasma glucagon level to FFA/glycerol molar ratio was observed in all experimental rats (p less than 0.05). Cold exposure reduced blood glucose level (p less than 0.001), while heat exposure did not affect it. Cold-induced increases of plasma glucagon and blood FFA levels were diminished significantly in cold-acclimated rats as compared with those in controls (p less than 0.05-0.001). Blood glycerol increased and FFA/glycerol molar ratio decreased to a similar extent on cold exposure in both control and cold-acclimated rats. Correlation between plasma glucagon and FFA/glycerol molar ratio was inversely significant in controls, but not significant in cold-acclimated rats. Blood glucose level was not altered on cold exposure in cold-acclimated rats. It was concluded that acute exposures to temperature stimuli, especially to cold, stimulate glucagon release, accompanied by increased utilization and mobilization of FFA and glucose, and plasma glucagon response to cold is diminished due to cold acclimation.