Temporal dynamics of ram sperm binding and survival during 48-h coculture with oviducal epithelial cells

Following insemination, ram spermatozoa bind to oviducal epithelial cells (OEC) in vivo and remain viable for several hours before fertilisation. In the present study, we investigated whether OEC monolayers reproduce this effect in vitro, performing an analysis of ram sperm binding and survival over an extended (48 h) period at 39 degrees C. We wanted to determine whether the reproductive cycle phase and/or oviducal region would influence ram sperm binding and survival in coculture with OEC and whether reproductive and non-reproductive epithelial cells bound and maintained the viability of ram spermatozoa equivalently. Oviducts were separated into groups based on their ovarian state (follicular or luteal) and then divided into two parts (isthmus and ampulla) for OEC isolation. Sheep kidney epithelial cells (Madin-Darby ovine kidney; MDOK) were purchased commercially. Reproductive cycle phase, but not oviducal region, affected sperm binding to OEC. Although more spermatozoa bound to luteal OEC than to follicular OEC at 1 h, at 24 h follicular OEC had bound more spermatozoa than luteal OEC. Generally, spermatozoa that were bound to OEC and MDOK had enhanced viability at each of the time points investigated (1, 6, 24 and 48 h), but the viability of the OEC-bound spermatozoa was greater than that of the MDOK-bound spermatozoa at 48 h. In conclusion, ram sperm-epithelial cell interactions are temporal, dynamic and depend on the origin of the epithelial cells.