Assessment of human sperm functional changes after in-vitro coincubation with cells retrieved from the human female reproductive tract.

Human spermatozoa must undergo functional changes prior to fertilization; however, the site of this physiological event is still unclear. To evaluate the influence of the female reproductive tract on sperm fertilizing capacity, fertile sperm samples were coincubated with endometrial, oviductal, granulosa and cumulus cells, follicular fluid and maternal serum. Sperm penetration into the zona-free hamster ova and motion parameters were measured daily for 72 h. Compared to control samples, endometrial and oviductal cell cultures did not alter sperm fertilizing capacity or their movement characteristics. Sperm coincubated with follicular fluid, granulosa or cumulus cells exhibited a significantly higher ability to penetrate zona-free hamster ova for up to 48 h. Sperm motility increased at 4 h in the presence of follicular fluid and serum. At 24 h sperm velocity and amplitude of lateral head displacement significantly declined in sperm samples exposed to serum, and velocity also declined in follicular fluid and with coincubation using ovarian follicle cells. Sperm motility and velocity decreased at 48 h in the presence of serum, follicular fluid, cumulus or granulosa cells. Our findings may suggest that specific secretory factors produced in the human pre-ovulatory ovarian follicle enhance human sperm fertilizing capacity.