Differing sperm ability to penetrate the oocyte in vivo and in vitro as revealed using colloidal preparations

The penetration ability of boar (Sus scrofa domestica) spermatozoa exposed to viscous preparations under in vivo and in vitro fertilization conditions has been examined. Experiments involving induced ovulation in prepubertal animals and surgical insemination directly into the oviduct isthmus revealed an advantage of colloidal preparations. Based on within-animal comparisons, the incidence of penetration was 100% using both spermatozoa suspended in a viscous preparation of plant extracts and spermatozoa suspended in a control medium. However, percentages of monospermy were 22.2% in 54 oocytes inseminated with the control suspension compared with 62.5% in 48 oocytes inseminated with the colloidal preparation. An in vitro study involving 355 oocytes from slaughterhouse ovaries inseminated with in vitro–capacitated spermatozoa gave similar percentages of penetrated oocytes for both the control and colloidal suspensions. In this case, however, the percentage of monospermy was 32.7% in the control group compared with 10.6% for spermatozoa suspended in the colloidal preparation. Higher mean numbers of sperm inside the oocytes and higher numbers of sperm bound to the zona pellucida were also observed with the colloidal suspensions. In vitro motility and viability for spermatozoa in the colloidal suspensions were enhanced compared with that of the control group. Lower sperm membrane lipid disorder and reactive oxygen species generation were also observed in the viscous solution. These findings suggest that viscous fluids can enhance the ability of sperm to move, bind, and penetrate the oocyte in vitro, although this influence may be masked in vivo due to the already high viscosity in the oviductal fluid close to the time of ovulation.