T4 and T3 release from the perfused canine thyroid isolated in situ.

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 of the T4 and T3 concentratios 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 ration 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 determatio in the homogenate was twice as high as the T4(3 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.