Oviduct binding ability of porcine spermatozoa develops in the epididymis and can be advanced by incubation with caudal fluid

Abstract

The sperm reservoir is formed when spermatozoa bind to the epithelium of the utero-tubal junction and caudal isthmus of the oviduct. It is an important mechanism that helps synchronize the meeting of gametes by regulating untimely capacitation and polyspermic fertilisation. This study investigated the influence of epididymal maturation and caudal fluid on the ability of spermatozoa to bind to oviduct epithelium using a model porcine oviduct explant assay. Spermatozoa from the rete testis, middle caput (E2-E3), middle corpus (E6) and cauda (E8) of Large White or Large White x Landrace boars at 10-14 months of age were diluted in modified Androhep solution and incubated with porcine oviduct explants. Results reported in this study support our hypothesis that testicular spermatozoa need to pass through the regions of the epididymis in order to acquire the ability to bind to the oviduct. There was a sequential increase in the number of spermatozoa that bound to oviduct explants from the rete testis to caudal epididymis. Binding of caudal spermatozoa to isthmic explants was the highest (15.0 ± 1.2 spermatozoa per 1.25 mm2; mean ± standard error of the mean; P ≤ 0.05) and lowest by spermatozoa from the rete testis (2.0 ± 0.3 per 1.25 mm2), and higher to isthmus from sows compared to gilts (35.8 ± 6.7 per 1.25 mm2 vs. 14.8 ± 3.0 per 1.25 mm2; P ≤ 0.05). Binding of ejaculated spermatozoa to porcine isthmus was higher than for caudal spermatozoa (26.3 ± 1.4 per 1.25 mm2 vs. 15.0 ± 0.8 per 1.25 mm2; P ≤ 0.05), and higher to porcine than to bovine isthmus (26.3 ± 2.3 per 1.25 mm2 vs. 18.8 ± 1.9 per 1.25 mm2; P ≤ 0.05). Incubation of spermatozoa from the caput and corpus in caudal fluid increased the ability of spermatozoa to bind to oviduct epithelium (P ≤ 0.05). In conclusion, the capacity of testicular spermatozoa to bind to oviduct epithelium increases during their maturation in the epididymis, and can be advanced by components of the caudal fluid.