Spermatozoa binding to oviduct cells: The influence of the endocrine milieu on the effectiveness of the binding test.

This study evaluates the effect of endocrine environments on the ability of sperm to bind to bovine oviduct epithelial cells (BOEC) cultured in vitro. In Experiment 1, reproductive tracts from slaughterhouse (n = 12) were classified based on the presence of a dominant follicle (DF ≥ 10 mm; high estradiol [E2], low progesterone [P4]) or a corpus luteum (CL; high P4). In Experiment 2, 10 Bos indicus cows were hormonally synchronized and slaughtered either in the pre-ovulatory phase (8-d-old DF, n = 5) or in diestrus (14-d-old CL, n = 5). Oviductal isthmus spheroids were categorized based on their laterality relative to the ovarian structure: DF-Ipsi, DF-Contra, CL-Ipsi, and CL-Contra. Sperm binding was assessed at 0.5, 12, and 24 h after incubation with 1 × 105 motile sperm/mL. Statistical analyses were performed by SAS 9.4 (P ≤ 0.05). In Experiment 1, P4 concentrations in follicular fluid (FF) were higher in CL-Ipsi compared to all other groups. In Experiment 2, CL-Ipsi also exhibited higher P4 concentrations than DF-Contra. Also, cows with 14-d-old CL had greater concentrations of P4 than cows with 8-d-old DF. Estradiol concentrations differed only in Experiment 2, with greater values in DF-Ipsi compared to other groups. In both experiments, morphometric analysis showed greater epithelial and muscular thickness in cows with high E2, and sperm binding was consistently lower in CL-Ipsi across all incubation times, with the most pronounced differences observed at 12 and 24 h. In conclusion, the endocrine milieu affected the capacity of sperm to bind to BOEC. Therefore, the best in vitro model to evaluate sperm binding as a strategy for fertility assessment is using the oviduct from tracts with DF and without functional CL.