Beta endorphin in serum and follicular fluid of PCOS- and non-PCOS women

Purpose To compare the concentrations of beta endorphin in serum and follicular fluid (FF) of PCOS- and non-PCOS women. Secondarily, to investigate associations between beta endorphin and other parameters. Methods Fifty-nine women undergoing in vitro fertilization (IVF) were included in the study. Sixteen were stratified to the PCOS group using the Rotterdam criteria. The remaining 43 women served as controls. Follicular fluid was collected during oocyte retrieval and peripheral blood sampling was performed on the same day. Beta endorphin concentrations in serum and follicular fluid, serum levels of insulin, glucose, LH, estradiol and progesterone were measured. Additionally, testosterone was measured before starting the stimulation protocol. Results There was no difference in beta endorphin levels between PCOS- and non-PCOS women. The concentration of the peptide was higher in serum than in FF, likely due to collection of FF after ovulation induction and corresponding to the early luteal phase. We found a significant correlation between the number of mature Metaphase II (MII) oocytes retrieved and beta endorphin concentration in FF. In women with biochemical hyperandrogenemia, beta endorphin levels in FF correlated with testosterone levels. Conclusion Beta Endorphin concentrations in serum and FF do not differ between PCOS- and non PCOS-women undergoing IVF. However, together with sex hormones, beta endorphin might play a key role in oocyte maturation.