β-Endorphin levels in the follicular fluid of human oocytes fertilized in vitro

This study was carried out in order to investigate the relationship between β-endorphin (β-ep) levels in plasma and follicular fluid and fertilization rates of oocytes from women undergoing treatment on our in vitro fertilization and embryo transfer program. Nine women suffering from severe tubal damage, with regular menstrual cycles, were studied. Follicular growth was induced with clomiphene citrate, combined with human menopausal gonadotropins. Analysis of follicular fluids and plasma showed no significant difference in β-ep levels. The larger follicles (> 2 ml volume) had significantly higher β-ep levels than smaller follicles (< 2 ml volume; p < 0.001); however, there was no significant difference in the fertilization rates of their oocytes.