Effect of macromolecules from oviductal conditioned medium on bovine sperm motion and capacitation

The effect of macromolecules from oviductal conditioned medium (CM) on sperm motility and capacitation was studied. Sperm pooled from three bulls was incubated in either luteal isthmic CM, luteal ampullary CM, estrual isthmic CM, estrual ampullary CM, or control medium (no CM) for 4 h. Sperm capacitation and motility were assessed at 10 min and 4 h. Estrual isthmic CM capacitated significantly more spermatozoa at 4 h than estrual ampullary CM or control medium. CM also affected lateral head movement (ALH) and beat cross-frequency (BCF) of sperm. In a second experiment, the glycosaminoglycan (GAG) content of the different types of oviductal CM was quantified. Estrual isthmic CM contained more GAG than estrual ampullary CM. Among luteal samples, no difference in GAG concentration between the isthmic and ampullary CM was found. Heat treatment (100 degrees C) of oviductal CM before coincubation with sperm significantly reduced, but did not eliminate, the capacitating ability. Because heat treatment denatures proteins and decreases the capacitating ability of certain GAG, we concluded that the capacitating effect of estrual isthmic CM may be associated with proteins, GAG, and proteoglycans in the CM. Isthmic secretions may play a major role during in vivo sperm capacitation, given that bovine spermatozoa may reside in the oviduct isthmus for up to 18 h before fertilization.