COMPARISON OF THE EFFECTS OF VARIOUS GOITROGENS ON THE BIOSYNTHESIS OF THYROID HORMONES IN VITRO

Abstract

The effect of various goitrogens on in vitro biosynthesis of thyroid hormones was studied. The compounds in decreasing order of relative activity to completely inhibit DIT formation were 1-methyl-2-mercaptoimidazole (MIA), thiouracil (TU); propylthiouracil PTU) and goitrin; thiourea and methylthiouracil (MTU). Those in decreasing order of relative activity to completely inhibit MIT formation were MIA; PTU, MTU, TU and thiourea; goitrin. Of the compounds tested MIA was thus the most potent inhibitor of the rat thyroid gland in vitro. The conversion of monoiodo-tyrosine to diiodotyrosine was more sensitive to every goitrogen than the iodination of tyrosine to form monoiodotyrosine. The modes of action of these antithyroid drugs seemed to be approximately the same, except for goitrin, which showed very weak inhibition of MIT formation. Progoitrin, the precursor of goitrin, did not seem to possess any anti-thyroid activity.