Figure 8. Episodic secretion of LH (top) and progesterone (bottom) during the luteal phase of a woman. Abbreviations: LH, luteinizing hormone: P, progesterone E2, estradiol; LH + 8, LH surge plus 8 days. (From Filicori M, Butler JP, Crowley WF Jr. Neuroendocrine regulation of the corpus luteum in the human. J Clin Invest. 73:1638 1984.