Effects of l-Methyl-2-mercaptoimidazole and Perchlorate on the Insulin-Mediated Enhancement of131I Incorporation Into Iodoamino Acids by Fetal Thyroid Glands in Organ Culture

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Abstract
The effect of insulin was studied on 1131 uptake and its corporation into protein-bound MIT [monoiodotyrosine], DIT [diiodotyrosine], and T [thyro-xine], by thyroid glands excised from fetuses of 20 or 21-day-pregnant rats and cultured for 3 days. Insulin enhanced the incorporation of 1131 into protein-bound MIT and DIT. Labeled thyroxine was not detected in the explants 6 hr after the addition of 1131 to the basal medium, but did appear when insulin was added to the medium. Insulin also enhanced the 1131 uptake and its incorporation into iodoamino acids by glands that were pretreated with sodium perchlorate so as to destroy their iodide-concentrating ability. However, insulin did not alter the 1131-iodide recoveries in the glandspretreated with Tapazole. It is suggested that insulin increased the incorporation of 1131 into protein-bound iodotyrosines and thyroxine by stimulating some step or steps subsequent to iodide transport.

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