Changes in sperm ultrastructure and localisation in the porcine oviduct around ovulation

Changes in the morphology and localisation of spermatozoa in the utero-tubal junction (UTJ) and three equal segments of the isthmus (lower, middle and upper isthmus) within ± 8 h of ovulation were studied with scanning and transmission electron microscopy. Spermatozoa were located at specific sites within the UTJ-isthmic environment. Two sperm subpopulations were evident, one with epithelial contact and one without such contact. Most of the sperm population with epithelial contact maintained intact plasma membranes during the pre-ovulatory period and showed acrosome reacted-like membrane changes during the post-ovulatory period. In contrast, plasma membranes in most of the spermatozoa with no epithelial contact were already broken before ovulation. Ovulation was also accompanied by a relocation of spermatozoa from the mucosal crypts/interfolds towards the more central part of the mucosal surface.