Abstract
Summary
1. L-Triiodothyronine (TRIT) injected into thyroidectomized rats at a dose level equivalent to 0.5 mg L-thyroxine/kg body weight/day is capable of stimulating the oxygen consumption of liver, diaphragm, heart and salivary gland preparations to the same extent as 2 mg of L-thyroxine. 2. Neither 0.5 nor 2 mg TRIT injected/kg/day altered the metabolic rates of tissues found unaffected by 2 mg of L-thyroxine, including brain, spleen, testis, seminal vesicle, prostate, ovary, uterus, thymus, lymph node and gastric smooth muscle. 3. Even if thyroxine is converted to TRIT before exerting its effect on the metabolic rate the failure of these tissues to respond to thyroxine does not seem referable to any possible inability to carry out this deiodination.
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