Responsiveness of plasma catecholamines to intracerebroventricular injection of glucagon in Muscovy ducklings

Summary.

Recent investigations have demonstrated a modulatory action of glucagon on shivering via the central nervous system in ducklings. The aim of this study was to investigate the effects of intracerebroventricular injection (i.c.v.) of glucagon on metabolic rates (MR) and plasma catecholamines in control ducklings (TN) and in ducklings exhibiting nonshivering thermogenesis after chronic glucagon treatment: (GT). At thermoneutrality (25°C, Ta), i.c.v. injection of glucagon had no thermogenic effects in TN and GT ducklings. At cold (+4°C, Ta), i.c.v. glucagon injection elicited a concomitant decrease of plasma norepinephrine (NE) and MR in TN ducklings, whereas in GT ducklings, the plasma catecholamines and the MR remained unchanged. These results indicate that glucagon treatment rendered the catecholaminergic system of GT ducklings insensitive to cold or i.c.v. glucagon injection.