In vivo and in vitro effects of adrenaline on conversion of thyroxine to triiodothyronine and to reverse-triiodothyronine in dog liver and heart.

Infusion of adrenaline in healthy dogs in a dose simulating spontaneous release of the catecholamine during experimental myocardial infarction produced a significant decrease in the conversion of thyroxine (T4) to triiodothyronine (T3) and a moderate increase in the conversion of T4 to reverse-triiodothyronine (rT3). Similar changes in deiodination of T4 to T3 and to rT3 were also observed when adrenaline was added in vitro to liver and heart homogenates. These results are consistent with a direct effect of adrenaline on T4 deiodination as degradation of exogenous T4, T3 and rT3 was only slightly increased under the experimental condition employed. The present study suggests that increased tissue exposure to adrenaline might contribute to the hormonal changes seen in at least some case of the 'low T3 syndrome'.