The feminisation of gonadotrophin responses in intact male transsexuals

Abolition of endocrine dimorphism in hyperthyroid males? An argument for the positive feedback effect of hyperoestrogenaemia on LH secretion

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.

Luteinizing hormone surge in adult female rats after androgen priming

The effects of androgens alone and in combination with oestrogens on luteinizing hormone secretion in adult female rats were studied after 1, 2 and 4 months of priming. Each adult female rat was implanted with a Silastic capsule filled with testosterone or dihydrotestosterone alone or together with another similar capsule of oestradiol. An oestrogen challenge test was carried out in each rat after priming. Blood samples were collected before androgen priming. During the oestrogen challenge test, blood samples were collected before (0 h or day 0) and at 12, 24, 36 and 48 h after the intramuscular injection of 50 μg oestradiol vaierate for rats primed for 1 month, or daily for 5 days (days 1 to 5) for other rats. An oestrogen challenge test was also performed in two groups of untreated male and female rats which served as controls. The results indicated that long-term androgen priming had resulted in the attenuation or total blockade of the luteinizing hormone surge which normally occurs during an oestrogen challenge test in adult female rats. This suggests that androgens may be important modulators of the luteinizing hormone surge mechanism in rats. Furthermore, the fact that the luteinizing hormone surge can be blocked by androgen priming in adult female rats suggests that the sexual dimorphic response to oestrogen feedback is not immutably imprinted in the hypothalamic-pituitary axis as was originally proposed.

The LH surge in humans: its mechanism and sex difference

There is a sex difference in the response to an estrogen challenge test in humans, but, unlike with rats, this sex difference is not permanently imprinted in the central nervous system. Estrogen is not only the important ovarian signal to trigger off the LH surge, but it also probably plays an important role in activating the positive estrogen feedback mechanism in humans. For an LH surge to occur, amplification of the hypothalamic signal (enhanced secretion of GnRH) as well as sensitization of the pituitary responsiveness to GnRH are required. It is unlikely that androgens per se are responsible for suppressing the positive estrogen feedback in humans and the possible role of another gonadal factor other than androgens remains speculative. The LH surge is a neuroendocrine phenomenon involved primarily in the process of ovulation and it is not correlated to sexual identity and orientation. Furthermore, how the hypothalamic-pituitary axis (HPA) responds to the estrogen challenge can be accounted for purely by its exposure to a different steroid milieu without reference to gender identity or sexual orientation of the subject.

Changes in gonadotropin regulation in both behavioral and phenotypic disturbances of sexual differentiation in men

Determinations of gonadotropins and testosterone were performed in 22 men with hypospadias (H), seven male-to-female transsexuals (T) and in 16 normal men (N), all of similar age. The response of serum FSH and LH to GnRH was determined in six subjects in each group. Oligospermia was found in five of 13 patients with H. All patients with transsexualism revealed normospermia. Both the patients with H and with T had significantly higher mean serum concentrations of LH than the normals (H: 16.96 +/- 13.83 mIU/ml; T: 15.30 +/- 6.50 mIU/ml; vs 5.73 +/- 3.66 mIU/ml in N). Also, an exaggerated response of LH to GnRH was found in both H and T. No negative correlations were demonstrated between serum LH and testosterone in either the H or the T. Rather, higher mean serum LH occurred together with higher mean serum testosterone in severe H. A significant elevation of basal serum FSH was found in H (H: 7.24 +/- 2.14 mIU/ml vs N: 4.84 +/- 1.65 mIU/ml), which might be related to underlying gonadal injury. No increase of serum basal FSH concentration was found in T patients, but the FSH response to GnRH was higher than in N. It is concluded that hypospadias, a phenotypic disturbance of sexual differentiation, represents a less-specific change in the gonadotropin regulation, while male transsexualism reveals hypergonadotropism with a specifically increased evocability of gonadotropins not coexisting with signs of gonadal injury.