Mechanism of Action of TSH Studied by Organ Culture of Fetal Rat Thyroid Gland. ∗

Abstract

Summary

Thyroid glands excised from fetuses of 21-day pregnant rats were cultured for 3 days in the absence and presence of TSH. The 6-hour ¹³¹I uptake as well as the incorporation of the isotope into proteinbound iodotyrosines and thyroxine were higher in the presence of TSH. Under similar conditions TSH failed to influence the 6-hour ¹⁴C incorporation of [¹⁴C]leucine into protein. Puromycin blocked almost completely the 6-hour incorporation of leucine carbon into protein by the fetal glands cultured in the presence and absence of TSH, but did not abolish the TSH-induced increase in the incorporation of ¹³¹I into protein-bound iodotyrosines and thyroxine. It seems therefore that TSH stimulation is not dependent on increased synthesis of protein, Treatment with sodium perchlorate affected the ability of the explants to concentrate iodide with little effect on total PB¹³¹I; however, the disposition of ¹³¹I within the lobes is strongly altered. In the presence or absence of TSH, pretreatment with perchlorate provoked approximately the same effect. Although TSH had an influence on the ¹³¹I recoveries in the glands treated with Tapazole, it is suggested that the effect of TSH on organ culture of embryonic thyroid glands is not dependent only on the stimulation of iodide concentrating ability of the explants.