Plasma beta-endorphin, pain thresholds and anxiety levels across the human menstrual cycle.

ABSTRACT

PIP: 9 mormally cycling women and 7 other women employing oral contraceptives (OCs) were tested during 5 phases (menstrual, follicular, ovulatory, luteal, and premenstrual) of their menstrual cycle. An anxiety inventory was administered and pain detection and pain thresholds in response to electric shock and the cold pressor task were determined. Venipunctures were also performed and the plasma of normally menstruating women later assayed for beta-endorphin. Analyses revealed that the variance but the not mean levels in peripheral beta-endorphin levels differed significantly (p0.01) across the menstrual cycle with the greatest amount of variance found during the ovulatory phase and the least during the luteal. The high variance during the period around ovulation was due to several subjects having extremely elevated beta-endorphin levels; this may have resulted from the occurrence of ovulation. Furthermore, a significant positive correlation between anxiety levels and beta-endorphin levels was found only during the menstrual phase. The absence of findings concerning cyclic variation in pain thresholds is contrary to earlier reports and indicates that such a phenomenon may be dependent on the paradigm employed.