Luteinizing hormone (LH) is a glycoprotein gonadotropin released by gonadotrophs in the anterior pituitary under control of gonadotropin-releasing hormone. It participates in ovulation and formation of the corpus luteum, and promotes testosterone production in the testis. The hormone's output is regulated within interacting pituitary and gonadal feedback pathways.[ref]
Anatomy and Physiology 2e by J. Gordon Betts and others. Section 17.3: Luteinizing Hormone and the pituitary hormone summary
The shape of a LH surge can be investigated by measuring several signals through time. In 1983, J. D. Hoff and colleagues studied five women with hormone measurements every two hours for five consecutive days around midcycle. They compared estradiol, progesterone and gonadotropin trajectories, finding an abrupt onset of the LH and follicle-stimulating hormone surges in temporal association with the estradiol peak.[ref]
Hormonal dynamics at midcycle: a reevaluation by J. D. Hoff and others. Abstract: sampling schedule, surge onset and the associated ovarian hormone changes
The report included a doubling of LH within a two-hour interval at surge onset. Such a change illustrates why sampling frequency matters: coarse measurements can blur an abrupt transition or shift the apparent ordering of events. The study describes a measured cohort pattern; it does not turn one isolated hormone measurement into a complete account of the cycle.
The relation to GnRH can also be probed by paired portal and peripheral blood plasma measurements. The hypophyseal portal system makes those two locations physiologically different: one carries the hypothalamic input, while the other records the pituitary's released output.
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