Plasma concentrations of β-endorphin in trained eumenorrheic and amenorrheic women

Abstract

Objective: To characterize the pattern of plasma β-endorphin throughout the normal menstrual cycle and test the hypothesis that β-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 β-endorphin concentrations. Results: β-Endorphin levels varied considerably across the sampling period and were not associated with menstrual status, gonadotropin, or gonadal steroid concentrations. Average β-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 β-endorphin levels were higher in the athletic groups, regardless of menstrual status. Conclusion: There were no cycle-related β-endorphin changes. Eumenorrheic and amenorrheic athletes have higher β-endorphin concentrations that may reflect adaptations to intense training and not exercise-associated amenorrhea.