EFFECTS OF THYROIDECTOMY OR THIOURACIL TREATMENT ON COPULATORY-BEHAVIOR IN ADULT MALE RATS

Male copulatory behavior and the function of the hypothalamo-hypophysi al-gonadal axis in hypothyroid male rats were investigated in the pres ent study. Hypothyroidism was induced by thyroidectomy or thiouracil. In male copulatory behavior test, intromission latencies in hypothyroi d rats were significantly longer than those in euthyroid rats and ejac ulation frequencies were reduced in hypothyroid male rats compared to control rats without reduction of plasma concentrations of testosteron e. These changes in copulatory behavior in hypethyroid male rats were restored to control levels by administration of T4 (5 mu g/rat). Hypot hyroidism decreased adrenal weights, and basal and peak concentrations of corticosterone during diurnal variation, whereas it increased peak concentrations of ACTH in adult male rats. These results indicate tha t hypothyroidism causes adrenal dysfunction directly and results in hy persecretion of ACTH. The adrenal disturbance observed in hypothyroid rats may affect male copulatory behavior.