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

Abstract.

Physiological studies have shown that glucagon is a potential mediator of nonshivering thermogenesis (NST) in birds. The present work was undertaken in order to investigate whether the observed thermogenesis results from a direct action of glucagon on avian thermoregulatory mechanisms or in fact requires the participation of other agents such as catecholamines. Our experiments were performed using cold-acclimated (CA) ducklings which developed muscle NST. A comparison was made with thermoneutral (TN) ducklings of the same age. Our principal results showed that: (1) at ambient temperature (25°C), circulating norepinephrine (NE) was markedly decreased in CA ducklings (–42%), while circulating epinephrine (E) did not undergo any consistent change; (2) in CA and TN ducklings, an intraperitoneal injection of glucagon (360 µg.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 less 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 activity during cold acclimation could be associated with adaptive changes leading to NST.