Effect of glucagon on thermogenesis in the pigeon

The effects of glucagon injection on temperature regulation and some metabolic parameters were studied in the pigeon. Glucagon (100 microng/kg) always inhibited shivering and caused a fall in the oxygen consumption and body temperature of the unanesthetized pigeon at + 6 degrees C. At + 34 degrees C, the same dose of glucagon had no effect on these parameters. At 22 degrees C, glucagon produced an elevation in plasma free fatty acid (FFA) and blood glucose levels. The rise in FFA at 22 degrees C coincided with the suppression of shivering at 6 degrees C. The glucagon-mediated rise in plasma FFA, but not glucose level, was potentiated by cold ambient temperature. Adrenergic blocking agents given prior to glucagon did not abolish its effects. Phentolamine even prolonged the absence and accelerated the suppression of shivering. A dissociation in the mechanisms by which catecholamines and glucagon suppress shivering is suggested. Although mobilizing energy reserves, glucagon does not seem to be calorigenic in the pigeon at this dose. The interpretation of the changes in plasma FFA levels is discussed in relation to fuel consumption during shivering.