Effect of Thyrotropic Hormone on Turnover Rate

A thyrotropic preparation was subcutaneously administered to guinea pigs once daily for four days. On the fifth day the hormone-treated as well as the control guinea pigs received intraperitoneally a trace dose of radioiodine. Larger amounts of appeared in the hyperactive than in the normal animals in addition, the former contained about twice as 

Time after administration, hr. Weight of glands, mg. Per Cent of administered recovered in whole thyroid gland Per cent of total thyroic found as 

The plasma of the hormone-treated animals contained larger amounts of organically bound labeled iodine than did the plasma of the control animals, which is just what we should expect (132). After twenty hours about 80% of the plasma iodine in the animals treated with thyrotropic preparation was present as tliyroxine. This observation also suggests that the end product of iodine synthc.sis i.s thyroxine and l)eautifully demonstrates the role of thyrotropic hormone in providing thyroxine to the circulation. Hypophysectomy (c/. 35) is followed by a reduced uptake of radioiodine by the thyroid gland (115). 

Recovery of Trace Dose op Labeled Iodine in Thyroid and Plasma OF Guinea Pigs (132) 

Experimental con(iition Time, hr. Per cent of radioiodine re covered in thyroid gland as Per cent of radioiodine recovered in 20 ml. plasma as  

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