Abolition of endocrine dimorphism in hyperthyroid males? An argument for the positive feedback effect of...

Our aim was (i) to investigate the hypothalamo-hypophyseal-gonadal axis in hyperthyroid Indian males, (ii) to rule out the modulatory role of adrenal steroids on it and (iii) to determine if the simultaneous rise in oestradiol and luteinising hormone (LH) in hyperthyroid males is due to a positive feedback action of oestradiol on pituitary LH release. Age- and BMI-matched men were divided into two groups, I, euthyroid subjects (n = 17) and II, hyperthyroid patients (n = 12) on the basis of their thyroid hormone levels. Serum levels of thyroid-stimulating hormone, triiodothyronine, thyroxine, LH, follicle-stimulating hormone (FSH), prolactin, E(2), T, P(4), sex hormone binding globulin and dehydroepiandrosterone sulphate (DHEAS) were assayed. Mean levels of T and E(2) were approximately two times higher in group II in comparison with group I. DHEAS levels were similar in both groups ruling out any adrenal involvement. Mean serum LH level was 2.6 folds higher in group II in comparison with group I. Mean serum levels of FSH were higher in group II, it was marginally nonsignificant. On the basis of these and previous observations, we hypothesise that endocrinological dimorphism in human male and female is not rigid; a sustained rise in serum oestradiol probably induces a positive feedback action on pituitary leading to elevated gonadotrophin levels.