A subpopulation of morphologically normal, motile spermatozoa attach to equine oviductal epithelial cell monolayers

Attachment of spermatozoa to oviductal epithelial cells (OEC) may be a prefertilization event in some species. We tested the hypothesis that spermatozoa that attach to equine OEC monolayers are a selected subpopulation of the initial inseminate, containing a higher proportion of morphologically normal, motile cells than the inseminate. Washed stallion spermatozoa were cocultured with monolayers of OEC or monolayers of Vero cells, and controls were incubated in wells coated with basement membrane extract (Matrigel [Mgel]) or in plastic (uncoated) wells. Unattached spermatozoa were removed by rinsing at 0.5 h of coculture. Spermatozoa that attached and subsequently released were collected at 3 h. Total cell numbers and percentages of motile, viable, and morphologically normal spermatozoa were counted in the initial inseminate, in plastic control wells, and in the coculture supernatants after incubation. The percentages of motile and morphologically normal spermatozoa attached to OEC, Mgel control wells, and Vero cell cocultures were measured in situ after 0.5 and 3 h of incubation. Populations of spermatozoa that attached to either OEC or Mgel had higher motility and those attached to OEC contained a higher percentage of normal spermatozoa than the inseminate. Compared to the inseminate, populations that did not attach had similar viability and contained a similar percentage of normal spermatozoa, but had lower motility. Spermatozoal populations released (at 3 h) were similar in percentage of normal morphology to those that were attached, but exhibited reduced motility and viability when compared to the inseminate. We noted no difference in motility or morphology between populations of spermatozoa attached to OEC and those attached to Vero cell monolayers. These results suggest that attached spermatozoa represent a selected population of normal, motile cells. Furthermore, the findings indicate that some morphologically normal spermatozoa are released over time.