THE EFFECTS OF VARIOUS GOITROGENS ON THE DETERMINATION OF THE RELATIVE POTENCY OF THYROID BY THE GOITRE PREVENTION ASSAY

Abstract

ABSTRACT It is well known that thiouracil and its derivatives not only block the synthesis of thyroid hormones but also alter the peripheral metabolism of thyroxine and triiodothyronine. Other goitrogens such as thiourea, thiocyanate and perchlorate do not have this extra-thyroidal effect. Hence the measurement of endogenous thyroid function namely »thyroxine secretion rate« as determined by the goitre-prevention response is affected by thiouracil but not presumably by the other goitrogens. The purpose of the present study was to see what effect different goitrogens had on the estimation of the relative potency of thyroid powder by the goitre prevention assay. The biological activities of pork and beef thyroid samples relative to a house standard were determined in a series of bioassays which used various goitrogens. Assays employing either thiouracil, thiourea, aminotriazole or perchlorate led to statistically equivalent potency estimates and indicated that the pork thyroid was significantly more active than the beef thyroid on the basis of the total iodine content. However, the slope of the log dose-response lines were significantly affected by the different goitrogens. When the relative potencies of pork and beef thyroid were computed on the basis of the triiodothyronine content, the three preparations had equivalent activity for each of the goitrogens. Thiocyanate proved to be toxic at the dose level employed and a valid assay was not possible.