[Intrathyroid deiodination of thyroxine: the effect of thyrotropic hormone and denervation of the thyroid].

Intrathyroid transformation of thyroxin (T4) into triiodothyronine (T3) and the role of thyrotropic hormone and denervation in this process were studied with in vivo blood perfusion of dog thyroid gland in situ and at 37 degrees C. Both labelled 125I-T4 (200,000 imp/min) and nonlabeled T4 (1000 ng) were administrated in the arteries of thyroid lobules in situ and in a constant-temperature cabinet. Enhanced excretion of triiodothyronine (both labeled and nonlabeled) observed two hours after the injection in the thyroid blood output was suggested as an evidence of denervation-independent deiodination occurring in the thyroid tissue. Without T4 load the proportion of T3 in the thyroid venous blood was significantly increasing under the thyroid denervation thus attesting inhibitory effect of nervous impulse on T4 deiodination in the thyroid gland. TTH being administrated into thyroid arteries in a dose of 20 I.U. produced a pronounced elevation of T4 thyroid conversion in T3 which was less manifest in the process of denervation thus evidencing the high sensitivity of the process to TTH.