Two daily glucagon injections induce nonshivering thermogenesis in Muscovy ducklings

In 6-wk-old chronically glucagon-treated (GT) ducklings, the calorigenic effect of intraperitoneal test injection of glucagon was measured at 25 and 4 degrees C ambient temperature (Ta). At 25 degrees C Ta, the increase in metabolic rate (MR) due to test injection of glucagon (360 micrograms/kg) reached 5.3 W/kg (i.e., 98% above the saline control value) in GT ducklings and only 1.7 W/kg (i.e., 29% above the control value) in control (TN) ducklings. After the injection, GT ducklings developed a hyperthermia, reaching 2.4 degrees C, accompanied by intense panting, whereas thermal body temperature did not change in TN ducklings. At 4 degrees C Ta for the same dose of glucagon, no significant change in MR was observed in GT ducklings during 180 min of exposure, whereas a 25% decrease in MR occurred in the same conditions in TN ducklings. In the cold, glucagon injection inhibited shivering in both groups of ducklings but thermogenesis was not suppressed in GT ducklings, showing a true nonshivering thermogenesis in these birds. This nonshivering thermogenesis was estimated to be 3 W/kg (i.e., 55% above resting MR). Such changes produced by chronic glucagon treatment resemble the artificial cold acclimation of rats chronically treated by norepinephrine.