Fig. 2

Legend, menstrual cycle hormone peaks and molecular effects: The sequence of hormone peaks for ovulatory menstrual cycles. Estrogen levels peak first, increasing expression of relaxin receptors in the body and increasing global synthesis of MMPs. The drop in estrogen triggers ovulation, and the remains of that ovarian follicle form the corpus luteum. As a temporary endocrine body, the corpus luteum secretes progesterone to prepare the endometrium for pregnancy and to sustain itself. It also synthesizes and releases relaxin, which binds receptors to activate MMPs recently upregulated by estrogen while also suppressing transcription of de novo collagen. Relaxin is active during the luteal phase, chiefly CD21-24