222 SPECIES SPECIFICITY OF PORCINE SPERM MOTILITY REDUCTION BY A HIGH MOLECULAR WEIGHT FRACTION OF OVIDUCTAL FLUID

Abstract

The significance of sperm motility with respect to fertilization is widely recognized and used as a criterion to assess the quality of ejaculates. Observations of sperm behavior in the oviductal isthmus of several species have shown that their motility is suppressed in this physiological environment because the spermatozoa bind to the oviductal epithelial cells, forming a sperm reservoir prior to ovulation (Hunter 1981 J. Reprod. Fertil. 63, 109–117; Hunter and Wilmut 1984 Reprod. Nutr. Dev. 24, 597–608). Once the spermatozoa are released from the reservoir, they progress toward the ampullar region to reach the oocyte, and an increase in motility at this point could, potentially, be crucial. It has been demonstrated that a soluble fraction of oviductal epithelial cell apical plasma membrane proteins (sAPM) suppresses sperm motility and enhances sperm survival (Holt et al. 2005 Reprod. Fertil. Dev. 17, 683–692; Satake et al. 2006 J. Exp. Biol. 209, 1560–1572). However, few studies to date have investigated the influence of oviductal fluid (OF), the natural medium into which spermatozoa are released from the reservoir, on sperm motility. Consequently, this study aimed to determine the effects of different soluble fractions of OF on sperm motility and the species specificity of such effects. OF from pigs and cows was collected and selectively filtered to obtain two different fractions with molecular weights higher or lower than 100 kD. Diluted semen samples from 14 different boars were exposed to bicarbonate/CO₂ (to stimulate maximum motility) in the presence or absence of OF fractions. Sperm trajectories were measured using a Hobson Sperm Tracker (Hobson Tracker, Ltd., Sheffield, UK) and analyzed by PATN analysis as described previously to identify subpopulations of high and low motility spermatozoa (Abaigar et al. 1999 Biol. Reprod. 60, 32–41; Satake et al. 2006). The results showed that neither of the bovine OF fractions affected the proportions of the fast linear boar sperm subpopulation in the samples, which was similar to that of the control. However, when the high molecular weight fraction of porcine OF was used, a significant suppression of the fast linear sperm subpopulation was observed (P ≤ 0.05). These data support the hypothesis that species-specific, high molecular weight components in OF are involved in the suppression of sperm motility. Further studies are required to confirm the significance of this finding, although it may not be unreasonable to speculate that the OF, in addition to other sperm selection mechanisms, acts to protect oocytes against fertilization by poor quality spermatozoa (Okada et al. 1986 J. Submicrosc. Cytol. 18, 233–247). In fact, similar results demonstrating that oviductal fluid decreases sperm motility have been obtained in cow (Grippo et al. 1995 J. Reprod. Fertil. 105, 57–64) and rabbit (Overstreet and Cooper 1979 J. Reprod. Fertil. 55, 53–59).

This work was supported by MEC and FEDER (PR2006-0506 and AGL2006-03495).