INFLUENCE OF THIOURACIL-INDUCED HYPOTHYROIDISM ON ADRENAL AND GONADALFUNCTIONS IN ADULT FEMALE RATS

The effect of hypothyroidism on adrenals and gonads in adult female ra ts was investigated throughout the estrous cycle. Hypothyroidism was i nduced by administration of 4-Methyl-2-thiouracil (Thiouracil) in the drinking water. The weight of ovaries and adrenals, and the plasma lev els of corticosterone decreased in hypothyroid rats as compared with e uthyroid rats throughout the estrous cycle. Hypothyroidism resulted in decreased concentrations of plasma LH on the day of diestrus and proe strus, whereas the plasma concentrations of prolactin and progesterone increased as compared with euthyroid rats. The weight of uteri and pl asma concentrations of estradiol decreased during the day of diestrus and proestrus in hypothyroid rats as compared with euthyroid rats. To further clarify the dysfunction of hypothalamo-hypophysial-adrenal axi s in hypothyroid rats, animals were stressed by immobilization for 3 h r. In hypothyroid rats, a marked increase in plasma levels of ACTH in response to immobilization stress was observed compared to euthyroid c ontrol, whereas increases in plasma concentrations of corticosterone w ere much smaller in hypothyroid than euthyroid rats. These results cle arly indicate that hypothyroidism causes both gonadal and adrenal dist urbances in adult female rats. The increased concentrations of plasma progesterone may be due to hypersecretion of prolactin during the day of proestrus and estrus, which in turn result in disruption of the est rous cycle.