EFFECT OF SOME THYROXINE ANALOGUES ON HYPOTHYROID TADPOLES

Abstract

ABSTRACT Using a new tadpole assay for thyroid hormone which has previously been described, the activities of some thyroxine analogues have been investigated. Apart from the usual immersion technique, microinjection was also used for administration of drugs. Diiodotyrosine was found to have no effect. Diiodothyronine only had a small effect. This compound as well as triprop, triac and tetrac gave dose response curves quite unlike those of triiodothyronine and thyroxine, so that an estimation of the relative activity could hardly be made. The implications of this finding is discussed. D-thyroxine was found to be 7 times less active than L-thyroxine. Triiodothyronine which in previous immersion experiments was found to be about 9 times as active as thyroxine was in injection experiments about 5 times as active as thyroxine. None of the fatty acid derivatives investigated was more active than thyroxine if given by injection. Contamination with small amounts of these derivatives in the test material therefore does not invalidate the results obtained by the present method.