Beta-endorphin levels in the preovulatory follicles and the outcome of in vitro fertilization.

The level of immunoreactive beta-endorphin-like (IR-beta-EP) material(s) was determined in follicular fluid samples obtained from patients treated for in vitro fertilization (IVF). Follicles containing morphologically mature oocytes had slightly lower concentrations of IR-beta-EP. The total IR-beta-EP content was similar in follicles with oocytes at different degrees of maturity. A smaller amount of IR-beta-EP in the follicle fluid was associated with a greater developmental potential of the oocytes, which formed embryos that reached the three- to six-cell stage at 40-44 hr after insemination (r = -0.35, P less than 0.026). A higher IR-beta-EP content was seen in fluid samples containing oocytes that remained uncleaved after fertilization (P less than 0.05 by Duncan's multiple-range test).