Capacitation in vitro of bovine spermatozoa by oviduct epithelial cell monolayer conditioned medium

The effect of the active capacitating factor secreted from oviduct epithelial cell monolayers (OECM) in different environments on in vitro fertilization was evaluated. Capacitation was determined as the ability of sperm to fertilize bovine oocytes in vitro. When the mTALP was supplemented with glucose during conditioning, the sperm penetration rate was significantly reduced (P < 0.05) compared to the control (7% +/- 1 vs. 30% +/- 4). The percentages of sperm penetrated oocytes were higher following insemination in the OECM-conditioned medium derived from the early stage (48% +/- 7) of the estrous cycle than in the OECM-conditioned medium derived from either mid (35% +/- 2) or late stages (28% +/- 3) of the estrous cycle. When the medium was supplemented with 0.1 or 0.5 microgram/ml estradiol-17 beta during medium conditioning, sperm penetration rates increased (P < 0.05) compared to the control group (55% +/- 4 vs. 40% +/- 3 and 54% +/- 2 vs. 41% +/- 3, respectively). In addition, the percentages of penetrated oocytes significantly decreased (P < 0.05) following insemination when the OECM-conditioned medium was added to 0.01%, 0.05%, and 0.1% ethanol compared to the control (25% +/- 4, 19% +/- 2, 18% +/- 3, and 45% +/- 3, respectively). Sperm penetration rates significantly (P < 0.01) decreased when the OECM-conditioned medium was heated to 100 degrees C for 5 min (10% +/- 1 vs. 40% +/- 3). These results suggest that the active capacitating factor was secreted by the OECM and that this capacitating factor in the OECM-conditioned medium was inhibited by the presence of glucose. This factor was found to be heat-sensitive and its action was affected by ethanol. The OECM derived from the three phases of the estrous cycle as well as the presence of estradiol-17 beta influenced the capacity of the OECM to secrete this capacitating factor in vitro.