On the LH response to oestrogen and LH-RH in transsexual men.

In male rats, androgen deficiency during a critical period of sexual brain differentiation was shown to give rise to a predominantly female-differentiated brain. Such animals displayed "homosexual behaviour", i.e., they were sexually attracted preferentially to partners of the same sex. In addition, they exhibited a sex-specific evocability of a positive oestrogen feedback effect. A positive oestrogen feedback effect on LH secretion was also induced in homosexual transsexual men, in contrast to hetero- or bisexual transsexual men. Thus in homosexual transsexual men, an intravenous injection of 20 mg Presomen (Premarin) produced a significant decrease of serum LH levels followed by a significant increase above the initial LH values. In hetero- or bisexual transsexual men, by contrast, intravenous oestrogen administration, while producing a significant decrease of serum LH levels, was not followed by an increase above the initial LH values. A positive oestrogen feedback effect on LH secretion was also found in homosexual non-transsexual men, in contrast to heterosexual men. These findings suggest that transsexual as well as non-transsexual homosexual men possess a predominantly female-differentiated brain which may be based, at least in part, on androgen deficiency during sexual differentiation of the central nervous system. Homosexual transsexual men also showed an increased LH and FSH response to LH-RH as compared to hetero- or bisexual transsexual men.