INHIBITION OF SHIVERING THERMOGENESIS BY CENTRALLY APPLIED GLUCAGON IN MUSCOVY DUCKLINGS

Glucagon has marked thermogenic and lipolytic effects in birds but cou ld also be involved in the central modulation of neural activity on th e basis of the recently discovered glucagon receptors in several areas of the brain in ducklings. The aim of this work was to investigate th e possible role of these receptors in the modulation of thermogenic pr ocesses. Glucagon was infused into the lateral ventricle of the brain in ducklings after an acute cold exposure (4 degrees C, 2 h) or at the rmoneutrality (25 degrees C). Electromyographic (EMG) data were simult aneously recorded with electrodes implanted in the gastrocnemius muscl e. Glucagon (10(-4) M) was infused at a rate of 8 mu l/min. When acute ly exposed to cold, ducklings increased their metabolic rate by shiver ing thermogenesis. A significant decrease in shivering activity was el icited after 5 min of glucagon infusion. After 16 +/- 2 min of glucago n infusion, shivering was completely inhibited, corresponding to a tot al dose of 36 +/- 4 mu g/kg. The suppression of shivering was accompan ied by a diminution of metabolic rate (5.3 +/- 0.3 vs. 8.5 +/- 0.2 W/k g, P < 0.05). The values of metabolic rate obtained at 4 degrees C aft er glucagon infusion were not significantly different from those measu red at 25 degrees C before glucagon infusion (6.4 +/- 0.3 W/kg, P > 0. 05). The infusion of the same dose of glucagon did not induce any chan ge in EMG activity and resting metabolic rate at 25 degrees C. These f indings suggest that glucagon infused into the brain has no thermogeni c effect but could be involved in the central control of somatic motri city. Although the origin and the mechanisms of action of the endogeno us peptide still remain unknown, glucagon might have a role in the dev elopment of non shivering thermogenesis during prolonged cold exposure via an inhibition of shivering in birds.