Testicular function in hyperthyroidism.

Testicular function was assessed in nine men aged 17 to 35 years and seven men aged 36 to 46 years with Graves' disease. Levels of total testosterone, estradiol, sex hormone binding globulin, luteinizing hormone, and follicle stimulating hormone, and gonadotropin responses to gonadotropin releasing hormone were significantly greater than these levels and responses in age-matched controls. Although the percentage of free testosterone was lower than control values in the hyperthyroid men, calculated levels of free testosterone were not different from normal. Lower than normal percentages of free estradiol values resulted in higher than normal calculated free estradiol levels. As a result, the free testosterone/free estradiol ratio in the men with Graves' disease was lower than normal. Although mean sperm densities in the hyperthyroid men were not different from control values, the percent forward progressive motility of sperm from these men was significantly lower than control values. The hormonal and seminal abnormalities corrected when the patients became euthyroid after radioiodine therapy. The results of this study indicate that hyperthyroid men may have abnormalities in their hypothalamic-pituitary-testicular axes.