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Plasma concentrations of beta-endorphin in trained eumenorrheic and amenorrheic women
V J Harber1, J R Sutton, J D MacDougall
1Department of Reproductive Biology, McMaster University, Hamilton, Ontario, Canada. vharber@per.ualberta.ca
Objective:
To characterize the pattern of plasma beta-endorphin throughout the normal menstrual cycle and test the hypothesis that beta-endorphin concentrations are elevated in trained women with amenorrhea compared with trained and sedentary eumenorrheic women.
Design:
Cohort analytic study.
Setting:
Academic research environment.
Participants:
Healthy female volunteers: 10 eumenorrheic sedentary, 11 eumenorrheic trained, and 11 amenorrheic trained women.
Interventions:
Blood samples were collected three times per week for either one complete menstrual cycle (eumenorrheic sedentary and trained subjects) or for a 4-week period (amenorrheic trained subjects).
Main Outcome Measure:
Plasma beta-endorphin concentrations.
Results:
beta-Endorphin levels varied considerably across the sampling period and were not associated with menstrual status, gonadotropin, or gonadal steroid concentrations. Average beta-endorphin levels were not different between the follicular and luteal phases for menstruating subjects, but were greater in the eumenorrheic athletes. Compared with eumenorrheic sedentary subjects, plasma beta-endorphin levels were higher in the athletic groups, regardless of menstrual status.
Conclusion:
There were no cycle-related beta-endorphin changes. Eumenorrheic and amenorrheic athletes have higher beta-endorphin concentrations that may reflect adaptations to intense training and not exercise-associated amenorrhea.