THE ROLE OF EPINEPHRINE AND NOREPINEPHRINE ON GLUCAGON-INDUCED THERMOGENESIS DUCKLING (CARINA MOSCHATA): A HPLC STUDY

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 the catecholamines. We focused our study on the effects of central glucagon on plasma catecholamine and heart rate on cold acclimated (CA) ducklings in cold environment. Our results showed that cold exposure (4 degrees C) induced an increase of circulating norepinephrine (NE) in thermoneutral (TN) and CA (42 % and 43 % respectively), while epinephrine (E) decreased only in TN (-45%). After glucagon injection, we found that circulating E increase in TN and CA (280%, 516% respectively), whereas NE concentrations decreased only in TN ducklings (-23%). Injection of glucagon causes a decrease in heart rate in TN duckling whereas it has no effect on CA ducklings. The large increase in E levels in CA and TN ducklings may be due to a massive release of adrenal catecholamine in response to the conditions below.