Expression of an uncoupling protein gene homolog in chickens.

An avian uncoupling protein (UCP) gene homolog was recently sequenced from skeletal muscle and was proposed to have a role in thermogenesis in chickens, ducks and hummingbirds. Since mammalian UCP 2 and UCP 3 also appear to have functions associated with energy and substrate partitioning and body weight regulation, the purpose of this study was to further characterize chicken UCP under conditions of nutritional stress and/or leptin administration. Male 3-week-old chickens were starved for 24 or 48 h and then half of each group was refed for an additional 24 h. In a follow-up experiment, chickens were fed or starved for 48 h with or without leptin administration. Feed deprivation increased UCP mRNA expression in skeletal muscle by up to 260% (P<0.001), and in a time-dependent manner in pectoralis muscle. Refeeding for 24 h normalized muscle UCP mRNA levels. Leptin administration had no effect on muscle UCP. Chicken muscle UCP mRNA levels were highly correlated with plasma triglyceride and non-esterified fatty acid (NEFA) concentrations, and with circulating levels of insulin, insulin-like growth factor (IGF)-I and IGF-II. These results suggest that, as in mammals, avian UCP is up-regulated during feed deprivation and is highly correlated with increased fatty acid oxidation and flux into skeletal muscle.