Effect of chicken growth hormone, triiodothyronine and hypophysectomy in growing domestic fowl.

Hypophysectomy in growing chicks was followed by reduced body and skeletal (shank-toe length) growth. In addition decreases were observed in tibia length and weight (although the proximal growth plate often contained more cartilage and was less uniform in its thickness), the plasma concentrations of immunoreactive-Somatomedin C (IR-SmC) and free fatty acids and weight for the heart, liver, pectoralis, thymus, and bursa Fabricus. The effect of triiodothyronine (T3) and purified chicken growth hormone (GH) on body and other growth was examined in hypophysectomized chicks. Body and skeletal growth (as estimated by respectively the increases in body weight and shank toe length in 24 days) were increased by the administration of T3 (either as injections or in the diet). T3 also increased tibia weight and length and returned the proximal growth plate thickness to that found in intact controls. Similarly T3 administration was followed by increases in the weights of the heart, liver, thymus, and bursa Fabricus. However plasma concentrations of IR-SmC were unaffected by T3 treatment. Chicken GH at a dose of 100 micrograms/kg stimulated aspects of growth somewhat with injections of chicken GH being followed by a slight increase in tibia length and a substantial increase in thymus weight. Chicken GH also increased plasma concentrations of IR-SmC and free fatty acids. Combination T3 and chicken GH treatment did not cause greater growth than observed with T3 alone. An exception to this being the greater weight of the bursa Fabricus in the chicks receiving T3 and GH than T3 alone. Intact male chicks which received injections of chicken GH (10 micrograms) between 1 and 14 day old had slightly greater body weight at 31, 38 and 44 days old relative to vehicle injected chicks.