Studies on the Stimulation of Thyroidal Inorganic127Iodide Releasein Vitroby Thyrotropin

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Abstract
When beef thyroid slices were incubated with thyrotropin (TSH), inorganic 127iodide accumulated in a rectilinear fashion for up to 8 hr of incubation, whereas little change was noted in controls. An oxygen atmosphere was essential for this effect. The log-dose response curve was biphasic, with hormone concentrations ranging from 0.01 to 100 mU/ml incubation medium. Maximum increases in stable iodide were achieved at 1 mU/ml TSH levels. Thiourea and/or perchlorate did not alter this biphasic response. TSH inhibited the protein binding of added radioiodide after 5 hr of incubation, although slice uptake was not impaired. Again the dose response was biphasic, with 1 mU/ml concentrations appearing to be most effective. In shorter incubations, however, the larger TSH doses increased radioiodine organification. Deiodination per se, as measured by the accumulation of radioiodide from diiodotyrosine- 131I in the presence of an excess of added carrier diiodotyrosine, was not stimulated by TSH. These data indicate that TSH concentration and/or incubation time markedly alter stable iodide accumulation and radioiodine organification. It is further concluded that the observed accumulation of inorganic 127iodide is a result of TSH-augmented proteolysis of thyroglobulin. (Endocrinology74: 395, 1964)