T4 AND T3 RELEASE FROM THE PERFUSED CANINE THYROID ISOLATED IN SITU

Abstract

ABSTRACT A method for once-through perfusion of the canine thyroid isolated in situ is described. The perfusion medium was a modified Krebs Ringer buffer with 4 % dextran added. In 4 control experiments the T4 and T3 concentrations in effluent were stable or slightly falling during 3 h perfusion. There were no significant alterations in the T4/T3 ratio in the effluent during these experiments. A 10-min infusion of bovine TSH (1 mU/ml) caused an increase in the release of T4 and T3 after 15–25 min. The T4/T3 ratio in the effluent was significantly reduced after TSH stimulation. However, the ratio returned to pre-stimulation values while the hormone release was still very high. T4 and T3 content of the contralateral thyroid was determined after homogenation and hydrolysis with pronase. The T4/T3 ratio in the homogenate was twice as high as the T4/T3 ratio in the effluent during control perfusion. Thus there was a preferential secretion of T3 from the perfused canine thyroid and this was increased after TSH stimulation.