Studies on the Effect of Thyrotropin on Human Thyroid Function*

Time-response and dose-response relationships between a single intramuscular injection of thyroid-stimulating hormone (TSH) and its effect on thyroid function were studied in human subjects without thyroid disease. The effect of TSH on thyroidal accumulation of radioiodine was demonstrable after a latent period of eight to ten hours. It reached its maximum after eighteen to twenty-four hours, decreased to pre-TSH values after five to six days, fell to levels significantly below the pre-TSH values from the eighth to eighteenth days after injection of TSH, and then returned to the original level. The rate of release of thyroid hormone had already started to increase within the first ninety minutes after injection of TSH, and did not return to the pre-TSH rate for at least twenty-four hours. The effect of TSH on the radioiodineaccumulating capacity of the thyroid increased continuously with mounting doses from 0.003 to 0.025 USP unit per Kg. of body weight, but no additional rise was obtained after a further increase of the dose of TSH. The rate of thyroid hormone release, however, also increased continuously with mounting doses of TSH above 0.025 unit per Kg.