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.