Glucagon-insulin balance in genetically lean or fat chickens.

Circulating levels of insulin, glucagon, glucose and non-esterified fatty acids (NEFA) were compared in genetically lean (LL) or fat (FL) lines of chickens between 5 and 6 weeks of age. FL birds exhibited lower levels of plasma glucose and higher levels of NEFA when fasted or fed; however no genotypic differences were found for insulin or glucagon. Oral glucose tolerance test induced higher insulin concentrations in FL chickens with faster glucose tolerance whereas glucagon was similar between genotypes. Refeeding led to lower plasma glucose and insulin in FL chickens but similar levels of glucagon in both lines. Exogenous insulin (0.25 or 0.50 U/kg) had less hypoglycemic effects but induced higher levels of glucagon in fasted LL chickens at 0.50 U. The insulin to glucagon ratio cannot explain differences in fattening between genotypes. Lipolysis is slightly higher in FL chickens. A difference between the 2 genotypes for their glucose-insulin balance is probably the main mechanism involved.