Human uterine luminal fluid volumes and prolactin levels in normal menstrual cycles

Human uterine luminal fluid has not been well characterized. Prolactin is produced in vitro by decidualized human endometrium and is secreted in vivo into the uterine luminal fluid of cynomolgus monkeys. Uterine luminal fluid prolactin has not been demonstrated in vivo in human beings. To study cyclic uterine luminal fluid volumes and prolactin levels, uterine luminal fluid was aspirated 8 to 13 times each during a single menstrual cycle in six ovulatory women. No anesthesia was used. Seventy of 75 (93%) attempts were successful; there were no complications. Serum estradiol, progesterone, luteinizing hormone, and prolactin levels were assayed every 1 to 3 days. Uterine luminal fluid volume and prolactin were normalized to the luteinizing hormone peak (day 0). Uterine luminal fluid volumes were relatively constant until the early luteal phase, when they then decreased. Uterine luminal fluid prolactin was detectable in all samples. Mean values were stable until day +3 or +4, after which they rose to a peak at day +9 or +10. This study establishes that (1) frequent uterine luminal fluid sampling is possible; (2) uterine luminal fluid volume decreases in the luteal phase; (3) uterine luminal fluid prolactin is detectable in vivo in women and its concentration increases in the luteal phase; and (4) cyclic human uterine luminal fluid prolactin levels differ from those in cynomolgus monkeys and from those anticipated from human in vitro studies.