Experimental Studies on the Hypothalamic Control of the Thyroid Gland

Abstract

Relationship between the hypothalamus and the pituitary-thyroidal system was investigated with respect to TRF, extracted from the anterior hypothalamus and urine, and the following results were obtained.
(1) Consecutive intramuscular and single intravenous injections of the hypothalamic or the urinary extract elevated the blood level of TSH and PBI. The active principle accelerated the release of I¹³¹ from the thyroid.
(2) Resection of the pituitary stalk induced hypofunction of the pituitary-thyroid system. TRF, if given in such operated cases, not only inhibited the hypofunction but rather stimulated this system.
(3) When TRF was given to cases in which thyroidal function was depressed by hypophysectomy, any thyrotrophic effect was observed. It was thus indicated that TRF exerts its effect on the thyroid only through the mediation of TSH, namely, TRF is an accelerator of TSH release.
(4) When the anterior hypothalamus was stimulated, the release of I¹³¹ from the thyroid was remarkably accelaerated only in bilaterally adrenalectomized rats.
(5) When lesion was given in the anterior hypothalamus, extending from the supraoptic nuclei to to the suprachiasmatic nuclei basally and rostrally, remarkable hypofunction of the thyroid was induced. Thus the above mentioned site is considered to be the regulatory center for the thyroid. In this case, goitrogenic action of MTU was inhibited, but the administration of TRF exerted evident metabolic and goitrogenic action, giving stimulation to the pituitary-thyroid system.
(6) The administration of TRF in a minute and a small dose elevated only the T/S level, but in a medium and a large dose it exerted both goitrogenic and thyrotrophic action. Namely it is considered that there are not two factors-growth factor and metabolic factor-in TSH, but only one thyroid-controlling factor (TRF) is present.