The biological action of substances related to thyroxine. 11. Acetic acid analogues of thyroxine and tri-iodothyronine

Abstract

The metabolism of Il31-labeled acetic acid analogues of thyroxine and tri-iodothyronine was compared in the rat with that of the corresponding iodothyronines. Since the urinary radioactivity was shown to consist almost exclusively of I- the urinary excretion could be regarded as a measure of the extent of deiodination in all 4 cases. The acetic acid analogues underwent much less deiodination than did the iodothyronines. The overall rate of excretion of tetraiodothyroacetic acid was markedly less than that of any of the other compounds. Both acetic acid analogues increased the rate of O2 consumption of mice, but no effect was observed until 10 hr. after administration. The duration of this effect was about the same in each case. The antithyroxine compound, butyl 4-hydroxy-3,4-diiodobenzoate, reduced the degree of deiodination of both acetic acid analogues, but did not diminish the increase in the 02 consumption produced by these substances in mice.