The sperm acrosome reaction (AR) is an exocytotic event that involves multiple fusions between the outer acrosomal membrane and the overlying plasma membrane. It must occur before the spermatozoon penetrates the zona pellucida (ZP) (1 ). This exocytotic event is mandatory for fertilization because it enables passage of the sperm through the ZP and its subsequent fusion with the egg oolema. Many artificial stimuli are reported to trigger the AR, either by driving extracellular Ca2+ into the sperm cell (Ca2+ ionophores) or by acting through intracellular second messengers that are involved in the cascade leading to acrosomal exocytosis (2 ,3 ).
