Plasma Estrogens, Progestins and Spinnbarkeit Characteristics during Selected Portions of the Menstrual Cycle of the Cynomolgus Monkey (Macaca fascicularis)

Cynomolgus monkeys (Macaca fascicularis) were examined daily for menstrual cycle associated changes. Plasma estrogens and progestins were measured by competitive protein binding analyses while cervical mucus specimens were assessed for quantity, appearance, ferning and spinnbarkeit. Cyclic bleeding was monitored by daily vaginal swab or by observation of waste pans for blood. Vaginal swabbing was the superior procedure establishing menstrual cycle length at 31.5 ± 1.3 days with a range of 20–46 days. Visual examination of waste troughs produced cycles ranging from 20 to 133 days with an average of 42 ± 8.5 days. Between days 6–10, plasma estrogens averaged 183 ± 52 pg/ml. On days 11–12, significant increases ranging from 680 to 850 pg/ml were recorded in ovulatory cycles. During days 13–16 and 18–20, estrogen levels were not statistically different from early proliferative phase determinations. On day 17, a marked depression of estrogen levels occurred; possibly related to the development of a functional corpus luteum. Plasma progestin rose steadily from days 13–18 in ovulatory cycles but never exceeded 5 ng/ml in anovulatory animals. Spinnbarkeit was the most reliable cervical mucus parameter for detection of approaching ovulation even though individual variation was marked. Diminished spinnbarkeit was noted in anovulatory animals. Ovulation could be anticipated if plasma estrogen increased markedly on days 11–13. Laparotomy confirmed that total progestin was meaningful in determining if ovulation had occurred. Cervical mucus monitoring used in conjunction with progestin data could also detect the occurrence of ovulation.