Selective sperm binding to pig oviductal epithelium in vitro

The sperm reservoir in the caudal isthmus of the oviduct of a number of spe cies is created by binding of spermatozoa to oviductal epithelium. The sper m reservoir fulfills a number of functions such as control of sperm transpo rt, maintenance of sperm viability and modulation of capacitation. The init ial capacities of ejaculated and epididymal boar spermatozoa to bind to ovi ductal epithelium were investigated using a modified pig oviductal explant assay. The number of spermatozoa that bound to 0.01 mm(2) of explant surfac e was used as the parameter of binding capacity. Binding of spermatozoa to oviductal epithelial explants was dependent in a linear manner on the numbe r of spermatozoa added (P less than or equal to 0.05). No difference was fo und in initial sperm binding between isthmic and ampullar explants. There w as no effect of the stage of the oestrous cycle or the reproductive status of the female donor. There was a significant effect (P less than or equal t o 0.05) of the individual boar on the binding index. The binding index corr elated negatively with the percentage of spermatozoa with cytoplasmic dropl ets and the percentage of morphologically abnormal spermatozoa (P less than or equal to 0.05). Epididymal spermatozoa showed significantly lower initi al binding capability than did ejaculated spermatozoa from the same boars ( P less than or equal to 0.05); therefore, components of seminal plasma may play a role in the binding process. The individual differences revealed by this study and their relation to morphology and contact of spermatozoa with seminal fluid indicate a selective function of sperm-oviduct binding.