Secretion of testicular steroids and gonadotrophins in hypothyroidism.

Inconsistent alterations in gonadal steroidogenesis and pituitary functions have been reported in hypothyroid males. We have compared the lipid and endocrine profiles of the euthyroid and hypothyroid [thyroid-stimulating hormone (TSH) >100 mIU l(-1)] males. Hypothyroidism was found to be associated with an increase in the circulating level of total cholesterol and LDL-cholesterol (LDL-C) and a reduction in the levels of progesterone and testosterone, without any change in the serum levels of oestradiol and gonadotrophins. The failure of gonadotrophins to rise could be accounted by a normal level of serum oestradiol in the hypothyroid male. A mild hyperprolactinaemia was also noted in the hypothyroid patients. The reduction in serum testosterone level could be explained by (i) a reduced uptake of LDL-C by the Leydig cells and thereby a reduction in the synthesis of progesterone and consequentially testosterone, (ii) a further reduction in the rate of conversion of progesterone to testosterone, (iii) a higher rate of conversion of testosterone to oestradiol, (iv) a decrease in serum triiodothyronine and (v) hyperprolactinaemia. Rise in TSH needs to be investigated as a cause of the suppression of gonadal steroidogenesis.