Levels of serum reproductive hormones throughout the menstrual cycle in healthy women receiving twice-daily injections of saline or kisspeptin-54. A, Comparison of cycle length in individual healthy women undergoing twice-daily sc bolus injections of saline or kisspeptin-54 (KP54) between menstrual days 7 and 14 of the study protocol. B–D, Levels of serum LH (B), FSH (C), and estradiol (D) during the menstrual cycle in healthy women undergoing twice-daily sc bolus injections of saline or kisspeptin-54 between menstrual days 7 and 14. E, Comparison of peak serum LH in individual healthy women undergoing twice-daily sc bolus injections of saline or kisspeptin-54 between menstrual days 7 and 14 of the study protocol. F and G, Levels of serum progesterone (F) and comparison of menstrual day of onset of the luteal phase (G) in individual healthy women undergoing twice-daily sc bolus injections of saline or kisspeptin-54 between menstrual days 7 and 14 of the study protocol. The luteal phase of the menstrual cycle was defined as beginning when serum progesterone was elevated >10 nmol/L. Data are presented as mean ± SEM. *, P < .05; **, P < .01.