Involvement of the catecholaminergic system in glucagon-induced thermogenesis in Muscovy ducklings (Cairina moschata)

Physiological studies have shown that glucagon is a potential mediator of n onshivering thermogenesis (NST) in birds. The present work was undertaken i n order to investigate whether the observed thermogenesis results from a di rect action of glucagon on avian thermoregulatory mechanisms or in fact req uires the participation of other agents such as catecholamines. Our experim ents were performed using cold-acclimated (CA) ducklings which developed mu scle NST. A comparison was made with thermoneutral (TN) ducklings of the sa me age. Our principal results showed that: (1) at ambient temperature (25 d egreesC), circulating norepinephrine (NE) was markedly decreased in CA duck lings (-42%), while circulating epinephrine (E) did not undergo any consist ent change; (2) in CA and TN ducklings, an intraperitoneal injection of glu cagon (360 mug.kg(-1)) was followed after 10 min by prominent lipolysis and a large increase in circulating NE (4- to 6-fold) and E (14- to 17-fold), which was sustained for at least 1 h. The elevation of circulating NE was l ess pronounced in CA ducklings. The thermogenic action of glucagon in birds is probably indirect and involves at least the mobilization of lipids and sympatho-adrenal stimulation. The changes in peripheral noradrenergic activ ity during cold acclimation could be associated with adaptive changes leadi ng to NST.