Levels of insulin, corticosterone, T3, T4 and insulin sensitivity in fat and lean chickens.

The late generations of fat (FL) and lean (LL) chickens were compared. In the fasted state, plasma glucose was lower in FL chickens, whereas insulin, T3, T4 and corticosterone were unchanged. In the fed state, plasma insulin and T4 were increased in FL chickens whereas glucose, T3 and corticosterone were unchanged. During ad libitum refeeding both plasma glucose and insulin, and to a lesser degree T3, were lower and T4 higher in FL chickens whereas corticosterone remained unchanged between lines. The low glucose and insulin levels observed in FL during refeeding, which were not observed in the F4 generation, were also found after force-feeding. In contrast, during oral glucose tolerance test, as in previous generations, a better glucose tolerance, higher plasma insulin and slightly higher free fatty acid levels were found in FL chickens. The hypoglycemic effect of exogenous insulin was very similar (and poor) in both lines in the fed state and was higher in FL than in LL chickens in the fasted state. From the present and previous studies, a change in the glucose-insulin balance and possibly, in T3, could account for the differences in fattening of both lines.