Calorigenic and Antigoitrogenic Actions of L-Triiodothyronine and L-Thyroxine in Thyroidectomized and Intact Rats.

Abstract

Antigoitrogenic tests in rats showed L-triiodothyronine to be about 3.5 times as active as L-thyroxine on a molar basis. In addition, in thyroidectomized rats, the L-triiodothyronine had a more potent calorigenic effect than L-thyroxine; in this case, the molar potency ratio was not less than 3.5:1. When the response was in the hyperthyroid range, the ratio was even greater than 3.5:1. Calorigenic tests in normal, intact rats showed a somewhat different effect in that both the triiodothyronine at a 1:1 molar dosage ratio and the triiodothyronine at 1:3.5 molar dosage ratio (triiodothyronine: thyroxine) produced changes not too far different from that obtained with the thyroxine.