Interaction between human sperm cells and hamster oocytes after argon fluoride excimer laser drilling of the zona pellucida

Objectives: To provide conclusive evidence that sperm cells gain access to the perivitelline space exclusively through a laser-drilled opening. To assess the optimal size of the hole and to evaluate the efficacy of laser drilling in comparison with that of mechanical zona dissection. Design: An interspecies model of human sperm cell that interacts with a laser-drilled or partially zona-dissected hamster oocytes. Main Outcome Measures: Penetration rate into the perivitelline space as related to the size of the opening (group A [5 μm], group B [10 μm], and group C [15 μm]) and to the sperm cell concentrations (1 x 10⁶, 5 x 10⁶, and 10 x 10⁶ cells/mL) used for insemination. Results: For each sperm cell concentration, the penetration rate into the perivitelline space was lowest for group A followed by group C and highest for group B. When penetration was compared for each hole size, it was found that sperm concentration had no effect on the rate of penetration in groups A and C but significantly affected this rate in group B. The highest penetration rate of 73% was observed with a concentration of 10 x 10⁶ cell/mL and declined to 58% and 23% at 5 x 10⁶ cell/mL and 1 x 10⁶ cell/mL, respectively. Oocytes drilled by laser (10-μm hole) demonstrated a significantly higher penetration rate when compared with those treated by partial zone dissection (73% versus 20% and 58% versus 21% for sperm densities of 10 x 10⁶ cells/mL and 5 x 10⁶ cells/mL, respectively). Conclusion: Human sperm cells gain access into the perivitelline space of hamster oocytes exclusively through a hole drilled by an argon fluoride excimer laser. An opening of 10 μm was found to yield optimal results. Laser drilling of the zona pellucida seems to be superior to that of mechanical slitting in terms of sperm oolema interaction.