EFFECT OF THYROXINE ON THE WEIGHT AND COMPOSITION OF MUSCLE, PELT AND OTHER TISSUES IN YOUNG HYPOPHYSECTOMIZED RATS

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Abstract
Administration of thyroxine, 2.5 [mu]g daily, doubled the body weight gain in male rats hypophysectomized at weaning. The carcass protein gain as the result of thyroxine therapy was 3 g/rat. The increment in body fat was proportional to that in body weight. Some tissues were considerably more responsive than others to thyroxine injections. The proportion of thigh muscle protein to body weight was increased 20% and that of the total pelt (skin and hair) protein increased 2*5%. The pelt protein increment accounted for 30% of the total protein gain in the treated animals. Determination of various N fractions in muscle and pelt indicated that all fractions were proportionally increased, with the exception of muscle collagen which was decreased. The heart/body weight ratio in thyroxine-treated rats was also increased whereas the proportion of hind-leg bone and of head weight to body weight were decreased. With the exception of thymus, which was doubled in weight, there was no effect of thyroxine on the weight of the endocrine glands or the accessory sexual tissue. Thyroxine had no effect on the weight of the levator ani muscle in hypophysectomized rats.