Iodothyronine secretion from perfused dog thyroid lobes after prolonged thyrotropin treatment in vivo.

Abstract

In previous studies we found that a considerable part of the T3 and rT3 secreted from perfused dog thyroid lobes originates from T4 deiodinated during secretion. In the present study, we investigated the influence of prolonged TSH pretreatment in vivo on these processes. Six mongrel dogs were treated with 0.2 IU/kg bovine TSH, sc, every 12 h for 7 days before thyroid perfusion, while 6 dogs received saline. Serum T4, T3, and rT3 were considerably increased by TSH treatment, the concentrations being highest during the early part of the stimulation period. The thyroid weight of TSH-treated dogs was nearly double that of the controls, while the absolute iodothyronine content was approximately half that of the controls. The T4 concentration in effluent perfusate from the TSH-pretreated thyroid lobes was 8 times higher than that from control lobes.This was, however, significantly lower than the response to an acute infusion of 100 μU/ml TSH (19 times) seen in a large series of experiments in untreated dogs. Th...