O-11: Dynamics of Flagellar Force Generated by A Hyperactivated Spermatozoon

Background: To clarify the mechanism of sperm penetration through the zona pellucida, the flagellar force generated by a hyperactivated spermatozoon was evaluated using the resistive force theory applied to the hyperactivated flagellar waves that were obtained from the mammalian spermatozoa. Materials and Methods: The hydrodynamic calculation of the flagellar force of the activated (non-hyperactivated) and hyperactivated mammalian spermatozoon was carried out by applying resistive force theory to the flagellar waves that were obtained using high-speed video microscopy and digital image processing. Results: The head of the activated spermatozoon moved in a nearly straight path, suggesting that mainly propulsive force, which was parallel to the longitudinal sperm head axis, was effective. On the other hand, the head of the hyperactivated spermatozoon moved in a small circular or figure-of-eight path, suggesting that the flagellar force had the transverse component, which was perpendicular to the longitudinal sperm head axis, larger than the propulsive force. No difference in the maximum propulsive force was found between the activated and hyperactivated spermatozoa. The maximum transverse force (45 pN) of the hyperactivated monkey spermatozoon was ~2.5 times its propulsive force. As the beat frequency of the flagellar beating remarkably decreased during the hyperactivation, the slowly oscillating transverse force (5 Hz) by the hyperactivated spermatozoon seems to be most effective for sperm penetration through the zona pellucida. Conclusion: The hyperactivated spermatozoon penetrates through the zona pellucida by the shear force generated by the slow oscillation of the transverse force while pushing the zona surface by the propulsive force.