The objective of this study was to determine whether coculture of stallion spermatozoa and mare oviductal (uterine tubal) epithelial cells induced sperm cell capacitation in vitro. Capacitation as determined by zona binding and chlortetracycline staining of the sperm cells was compared for stallion spermatozoa: (1) incubated with medium alone (negative control), (2) treated with calcium ionophore A23187 (positive control) or (3) cultured with mare oviductal epithelial cells (OEC) for 4 h. Chlortetracycline staining patterns of sperm cells bound to the zonae were used to group spermatozoa as uncapacitated, capacitated or acrosome reacted. The zonae and attached spermatozoa were stained for evaluation after initial binding (pulse) and after 1 h of co-incubation (chase). More sperm cells in the ionophore and OEC treatments bound to the zonae at both the pulse and chase than in control medium (P < 0.001). More bound sperm cells were capacitated at the pulse, and acrosome reacted at the chase, for the ionophore and co-culture groups than for the controls (P < 0.001). Staining patterns for sperm cells not bound to the zona pellucida in each of the treatments differed (P < 0.05) from the population of sperm cells that bound to the zona pellucida. There was a higher percentage of capacitated spermatozoa and a lower percentage of acrosome-reacted spermatozoa bound to the zonae at the pulse than were represented in the treatment suspensions of sperm cells. The co-culture treatment resulted in a higher (P < 0.05) proportion of sperm cells in suspension with the capacitated staining pattern and a lower (P < 0.05) proportion with the uncapacitated pattern than those in the ionophore treatment.
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