Improved cold tolerance in glucagon-treated rats

In glucagon-treated rats (50 μg/100g, twice a day, 4 wks, sc) (GTR), the weights of liver and interscapular brown adipose tissue (BAT), and the level of plasma glucagon increased as compared with those in the vehicle-treated controls (VC). Mitochondria of BAT were markedly developed in size and cristae. Cold tolerance as assessed by the rate of fall in colonic temperature at ?5 °C was improved. Elevations of colonic temperatures by noradrenaline (40 μg/100g, im) were significantly enhanced in GTR. After cold exposure, blood free fatty acids (FFA) and plasma glucagon levels increased, but blood glucose and β-hydroxybutyrate levels were not changed in VC. Both blood FFA and β-hydroxybutyrate levels increased and blood glucose level decreased, but plasma glucagon levels was not affected by cold exposure in GTR. These results suggest that glucagon is involved in cold acclimation by means of enhanced nonshivering thermogenesis, possibly due to an activation of BAT as well as increased production and utilization of ketone bodies in the liver.