ABSTRACT
Glucagon is known to be a central modulator of neural activity and a peripheral thermogenic effect. The purpose of this study was to better understand the role of glucagon in the control of heat production, shivering and particularly as a mediator of nonshivering thermogenesis (NST) in ducklings. In order to study the mechanism of NST, an intracerebroventricular (i.c.v.) injection of glucagon (10(-7) M) in to thermoneutral (TN), chronically glucagon treated (GT) and cold acclimatized (CA) ducklings exposed to acute cold (4 degrees C) or a thermoneutrality (25 degrees C), was performed. At 25 degrees C ambient temperature (Ta), the metabolic rate (MR) remained unchanged after glucagon injection. At 4 degrees C Ta i.c.v. glucagon injection, no significant change in MR was observed in GT and CA ducklings during 160 min of cold exposure, whereas there was 63% decrease in MR in (TN) ducklings (5.02 +/- 0.1 2 vs 7.91 +/- 0.1 4 W/kg(-1) p < 0.05). Shivering activity was completely suppressed in TN and GT ducklings after glucagon administration. The NST was estimated to be 3.26 W/kg. This findings suggest that glucagon administered into the brain has no thermogenic effect but could be involved in the central control of somatic motricity, and here we demonstrated for the first time, of our knowledge, that central glucagon have a role in the development of nonshivering thermogenesis during prolonged cold via an inhibition of shivering in birds.
