Interaction of equine spermatozoa with oviduct epithelial cell explants is affected by estrous cycle and anatomic origin of explant.

This research investigates how horse sperm attaches to the internal lining of female reproductive organs and the effect of menstrual cycle stages and anatomic location of the cells these sperms attach to. Additionally, the influence of hormones on this process was evaluated.

Methodology and Approach

• The researchers used co-culture methods to investigate how equine (horse) sperm interacted with its own female reproductive tract lining cells (oviductal epithelium).
• Fresh sperm samples from stallions were prepared and then incubated with cells obtained from two regions of the female reproductive tract (isthmus and ampulla) at three different stages of the menstrual cycle: follicular, postovulatory, and diestrous.
• These test groups were also treated with two types of sex hormones (estradiol and progesterone) and a control for comparison.
• The researchers then evaluated the motility (movement capability) of the sperm and the total number of sperm that had successfully adhered to the cells at three different time intervals: half an hour, 24 hours, and 48 hours after the start of incubation.

Research Findings

• It was observed that the sperm attached to the cellular lining of the oviduct through their frontal part (rostral acrosomal region), and this attachment could occur with both types of cells found in the oviduct lining: ciliated and non-ciliated.
• Neither the application of sex hormones (estrogen and progesterone) nor the anatomic location of the female reproductive cells (ampulla and isthmus) influenced the movement of the sperm or the total number of sperm that attached to the cells.
• But, the stage of the menstrual cycle did have an effect on sperm movement. Sperm that attached to cells from the follicular stage of the cycle had a higher movement capability than those attached to cells from postovulatory or diestrous stages.
• The number of successfully attached sperm was influenced by various factors, including the stage of the menstrual cycle, the anatomical origin of the cells, the duration of incubation, and the combination of all three factors.
• The largest number of sperm adhered to cells were from the isthmus region, and cells from the follicular and postovulatory stages, as compared to the diestrous stage.

Implications and Conclusions

• These observations confirm the existence of a sperm reservoir within the isthmus region of the mare’s oviduct, which is where the largest number of sperm were found attached.
• The findings also imply that the stage of the menstrual cycle may play a significant role in regulating both the movement capability and the successful attachment of sperm to the oviduct lining.