Endocrine and metabolic responses of intact and hypophysectomized turkey poults given a daily injection of chicken growth hormone.

Abstract

Female turkey poults were hypophysectomized at 4-5 weeks of age. Beginning at 6 weeks of age, 20 hypophysectomized and 20 intact birds received a daily intramuscular injection of natural chicken growth hormone (cGH, 100 micrograms/kg body weight) or vehicle for 12 days. Blood samples were taken from each bird just before injection and 4 hr post-injection at 6 and 12 days of treatment. Hypophysectomy reduced the growth rate of turkey poults to 75% of that of intact controls, significantly reduced carcass protein and ash percentages, and significantly lower plasma concentrations of GH, insulin-like growth factor-I, triiodothyronine, thyroxine, insulin, glucose, triglycerides, and non-esterified fatty acids. Hypophysectomy was without effect on liver GH receptor binding activity, but increased liver 5'-monodeiodinase activity. Daily cGH injection had no effect on the average daily gain of either hypophysectomized or intact poults when compared to vehicle-injected controls over 12 days of treatment. Daily cGH administration increased plasma insulin-like growth factor-I levels in intact and hypophysectomized turkeys, and increased plasma triiodothyronine, insulin, glucose, and triglyceride concentrations in hypophysectomized birds, but not in intact birds. Responses of young turkeys to hypophysectomy and GH replacement were consistent with the known metabolic role of GH in other species, but the influence of GH on growth appears to be of less importance in poultry than in mammals.