ADRENAL AND GONADAL-FUNCTION IN HYPOTHYROID ADULT MALE-RATS

The functional relationship between thyroid, adrenal and gonadal hormo nes was investigated using adult male rats. Hypothyroidism was produce d by the administration of 4-methyl-2-thiouracil (thiouracil) in the d rinking water for 2 weeks. Plasma concentrations of TSH dramatically i ncreased, whereas plasma concentrations of tri-iodothyronine and thyro xine decreased in thiouracil-treated rats as compared with euthyroid r ats. Hypothyroidism increased basal levels of plasma ACTH and pituitar y content of ACTH. The pituitary responsiveness to CRH for ACTH releas e markedly increased, whereas the adrenal responsiveness to ACTH for c orticosterone release decreased. These results indicated that hypothyr oidism causes adrenal dysfunction in adult male rats. Pituitary conten ts of LH and prolactin decreased in hypothyroid rats as compared with euthyroid rats. In addition, hypothyroidism lowered pituitary LH respo nsiveness to LHRH. Testicular responsiveness to human chorionic gonado trophin for testosterone release, however, was not different between e uthyroid and hypothyroid animals. These results indicated that hypothy roidism causes adrenal dysfunction and results in hypersecretion of AC TH from the pituitary gland. Adrenal dysfunction may contribute to the inhibition of LHRH secretion from the hypothalamus, possibly mediated by excess CRH.