Fat and lean chickens: prefattening period and in vivo sensitivity to insulin, atropine, and propranolol.

Fat (FL) or lean (LL) chickens have been obtained by divergent selection. In previous studies, FL chickens were consistently hypoglycemic (slightly) and had high plasma levels of insulin in response to glucose or refeeding from 5 to 8 wk of age. In these, at 12-13 days of age before any difference in fattening can be demonstrated, FL chickens exhibit a better glucose tolerance pattern and enhanced glucose-induced insulin levels but normal insulin levels during refeeding. Plasma levels of alpha-NH2 nonprotein nitrogen, uric acid, free fatty acids, and potassium were neither consistent nor significantly different between lines. Atropine, at high dose, blocked the absorption of glucose and at low dose had no major effect on glucose-induced insulin release in either line. At 8 wk, sensitivity to and disappearance of exogenous insulin were normal in FL birds. Propranolol slightly decreased plasma glucose and inhibited the hypokalemic effect of exogenous insulin to the same extent in both lines. Cerebrospinal fluid glucose level and liver glycogen content were similar in both lines in the fasting or the fed state, but liver glycogen was restored faster after refeeding in the FL, at least in older birds.