Glucose tolerance, plasma insulin and immunoreactive glucagon in chickens selected for high and low body weight.

Relationships among glucose tolerance, plasma insulin and plasma glucagon were examined in chicks developed through selection for high (HW) and low (LW) body weight at 56 d of age and F1 crosses (HL) obtained from HW males mated to LW females. At 21, 42, 63 and 84 d of age, chicks from each population were intubated with glucose (2 g/kg body wt) following a 24-h fast. Blood was collected at 20-min intervals up to 100 min postadministration. At all ages, the LW chicks were better able to clear glucose from their blood than were their HW counterparts, and the HL chicks exhibited intermediate responses. Impaired glucose tolerance in the HWs and HLs was not associated with insulin insufficiency; the HWs and HLs, in comparison to the LWs, exhibited higher plasma concentrations of insulin at 42 and 63 d of age and plasma insulin levels did not differ significantly among populations at 21 or 84 d of age. Plasma immunoreactive glucagon responses to glucose intubation were inconsistent at the different ages; however, concentrations were consistently higher in the HWs and HLs than in the LWs. It was concluded that excessive fat deposition in chickens selected for rapid growth is associated with increased concentrations of insulin and glucagon in plasma and perhaps insulin resistance.