INFLUENCE OF OESTROGENS ON TSH-THYROID RELATIONSHIP

SUMMARY 1. Oestradiol benzoate in a dosage range of 10-1000 μg. administered daily for a week to castrated male rats enhances the thyroid weight and increases the uptake of radioactive iodine by the thyroid. There is, however, no clear-cut quantitative relation between dosage of oestrogens and effect on the thyroid. 2. In hypophysectomized rats oestrogens enhance the action of T. S. H. on thyroid weight and radioactive iodine uptake, though, in the absence of T. S. H., they have by themselves no »thyrotrophic« action. The enhancement increases with increasing doses of oestrogens. 3. It is concluded that oestrogens influence the thyroid in two ways, viz. by diminishing the release of T. S. H. by the hypophysis and by sensitizing the thyroid to the effect of T. S. H. 4. The abovementioned conclusion is supported by control experiments, performed in order to eliminate possible objections: a. The transformation of inorganic iodides into organically bound iodine is not inhibited by oestrogens. b. Although oestrogens cause a slight diminution of the urinary iodine excretion, we were able to show that this could not be the only factor responsible for the observed increase in radioiodine uptake in the thyroid. c. Even in vitro isolated thyroids from oestrogen treated rats show a larger uptake of radioiodine from the medium.