Testicular dysfunction in men with primary hypothyroidism; reversal of hypogonadotrophic hypogonadism with replacement thyroxine

OBJECTIVE Primary hypothyroidism can cause disturbances in normal gonadal f unction. The aim of this study was to investigate the relationship in men b etween hypogonadism and primary hypothyroidism and the extent to which free and total testosterone levels rose after introduction of replacement thyro xine. DESIGN Paired study of patients in a hypothyroid and thyroxine treated stat e. PATIENTS Ten men with primary hypothyroidism. MEASUREMENTS Free and total testosterone, gonadotrophin and prolactin level s before and after thyroxine replacement therapy. RESULTS Low free testosterone levels (161 +/- 62 pmol/l) demonstrated at th e time the men were hypothyroid rose significantly with the commencement of thyroxine replacement (315 +/- 141 pmol/l; P < 0.001). Gonadotrophin level s were not elevated consistent with hypogonadotrophic hypogonadism. Hyperpr olactinaemia, which can occur in primary hypothyroidism and cause hypogonad otrophic hypogonadism, was not present in the majority of these patients. H owever a reduction in prolactin level was evident with thyroxine replacemen t and a rise in free testosterone levels. CONCLUSION This suggests an effect of hypothyroidism on gonadotrophin secre tion at the level of the hypothalamus-pituitary, either directly or through modulation of prolactin secretion. Low free testosterone may also be a con tributing factor to some of the symptoms and signs of hypothyroidism in men .