Effects of thyroid hormones on weights of individual muscles in forelimbs, body stem, and hind legs of chickens

The effects of thyroid hormones on the increases in weights of individual muscles in forelimbs, body stem, and hind legs were studied using surgically thyroidectomized chickens. Male chicks (White Leghorn, Hisex strain) were divided into the following 4 experimental groups: sham operation, T4 (L-thyroxine) injection, autotransplantation and thyroidectomy. Thyroidectomy were carried out at 10 - 1l days of age and the ectomized glands were immediately autotransplantated into the hypodermis of anterior pectoral region. The glands were removed again at 27 - 28 days of age except the autotransplantation group and a half of the re-ectomized birds were injected with equivalent amount of T4 to normal secretion rate (1.0 - 1.5 mug/100g bwt/day) intraperitoneally from 3l to 70 days of age. Muscular weights in each of forelimbs, body stem, and hind legs, and weights of main individual muscles from these body parts were determined at 71 - 74 days of age. As the results, the weights of individual muscles from forelimbs, body stem, and hind legs showed significantly lower values in the thyroidectomy group compared with other3 experimental groups, leading to the reduction in muscular weights in each of these body parts. On the other hand, there were no differences in relative weights (percentage to the muscle weight of body part in which the individual muscle was situated) of 15 out of l7 individual muscles among the experimental groups including thyroidectomy group. However, the relative weights of M. pectoralis profundus in forelimbs and M. quadriceps femoris in hind legs were lowered significantly in thyroidectomy group compared to other 3 groups. These two muscles of thyroidectomy group showed the highest values in decrease rates of muscular weight to the autotransplantation group as a control