Abstract
The thyroid gland inhibition which follows administration of excess thyroid hormone (TH) is a classic illustration of feedback control of pituitary thyrotropic hormone (TSH) secretion. Recent experiments demonstrating that thyroxine inhibits thyroidal iodide trapping and release rate more completely than does hypophysectomy suggest that there may be pituitary factors other than TSH which influence thyroid gland activity. This problem has been studied in rats by comparing the effects of thyroxine treatment with the effects of TSH deficiency induced in 2 different ways: by hypophysectomy, which gives, in addition, deficiency of other tropic hormones; and by treatment with anti-TSH antibody, which produces selective interference only with thyrotropic stimulation. In normal rats, the thyroidal 13lI release rate was reduced to the same degree by TH, by hypophysectomy and by anti-TSH. As measured by the distribution of iodinated amino acids in thyroid homogenates 24 hr after 131I injection, hormonogenesis was s...
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