Changes in plasma glucagon levels to stressful environmental temperatures.

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Abstract
Effects of temperature stimuli on plasma glucagon levels were studied in fasted (18 h) and shorn rats. Plasma glucagon levels rose significantly on exposures to both cold (-5.degree. C, 60 min) (P < 0.001) and heat (36.degree. C, 60 min) (P < 0.001) from that in control rats at 25.degree. C. Cold stimulus increased blood FFA [free fatty acid] level (P < 0.001), and both cold and heat stimuli increased blood glycerol levels (P < 0.05-0.001). FFA/glycerol molar ratio decreased to a similar extent on both cold and heat exposures (P < 0.02-0.01). Plasma glucagon, blood FFA and glycerol levels increased significantly more in cold-exposed rats (P < 0.001) than in heat-exposed ones. There were positive relations of plasma glucagon levels to blood FFA and glycerol levels (P < 0.001), while an inverse relation of plasma glucagon level to FFA/glycerol molar ratio was observed in all experimental rats (P < 0.005). Cold exposure reduced blood glucose level (P < 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 < 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. 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.