IN VITROSTUDIES OF THE INTACT THYROID GLAND*

Abstract

In order to circumvent possible in vivo influence of peripheral utilization and excretion of thyroid hormone with regard to the physiological states of the thyroid, in vitro studies were undertaken on the effect of thyroxine and of thyrotropic hormone (TSH) on the functional activity of the intact isolated gland. Radioiodide (I131) was employed in determining thyroid functional activity. Thyroxine has been found to exert in vivo an inhibitory effect on the thyroid by inhibiting the release of TSH from the hypophysis. In vitro, thyroxine apparently does not exert any influence on the release of inorganic and organic iodine from the gland. The results of the in vitro studies on the thyroid, using TSH and I131 under various experimental conditions, indicate that the primary effect of TSH is to induce a release of hormone from the gland. Continuous stimulation of the thyroid by repeated TSH administration over a period of 2 to 3 days was found to result in an increased content of inorganic and organic radioiodine in the gland.