Studies on goitrogenic action of minocycline and related compounds.

Abstract

In an attempt to study the mechanism of action of minocycline and related compounds on thyroid activity, 9 chemically related compounds were administered to male and female rats fed a low or high iodine diet, to rats treated with thyroxine (T4) and to thyroidectomized, T4 maintained rats. Administration of minocycline produced a large goiter with high radioiodine uptake, the effect being more apparent in rats fed a relatively high iodine diet. Among the 9 compounds tested, minocycline, tetracycline phosphate (TC-phosphate), metacycline and doxycycline were goitrogenic in rats fed a low iodine diet, although goitrogenic activity varied greatly from compound to compound. In contrast, chlortetracycline hydrochloride (C1-TC-HC1) and demethyl chlortetracycline hydrochloride (demethyl C1-TC-HC1) reduced thyroid size under similar condition. Minocycline administration reduced thyroidal T4 and triiodothyronine (T3) and lowered plasma PBI, without affecting MIT/DIT. In sharp contrast with methylthiouracil, minocyc...