Study of the acrosome reaction and the fertilizing ability of hamster epididymal cauda spermatozoa treated with antibodies against phospholipase A2 and/or lysophosphatidylcholine.

The present report describes experiments in vitro that were designed to evaluate the involvement of phospholipase A2 (PLA2) in the acrosome reaction of mammalian sperm and the interaction of gametes. Hamster spermatozoa were incubated in a defined medium (TALP) to induce capacitation and the acrosome reaction. This medium was supplemented with antibodies against porcine pancreatic PLA2 and/or lysophosphatidylcholine (LPC). For in vitro fertilization, spermatozoa and/or oocytes were incubated in TALP medium that contained PLA2-specific antibodies, LPC, or antibodies plus LPC. The antibodies inhibited the acrosome reaction in a dose-dependent manner, without any effect on sperm motility or hyperactivation. These antibodies also inhibited fertilization in vitro. LPC, a product of the reaction catalysed by PLA2, speeds up and synchronizes the acrosome reaction and facilitates penetration of the zona pellucida by spermatozoa, the fusion process and polyspermy. The results of addition of the antibodies plus LPC showed that LPC is able to reverse the inhibitory effects of the antibodies on the acrosome reaction and fertilization. It is possible that endogenous PLA2 plays a role in the final stages of the acrosome reaction and the interaction of gametes, perhaps through one of its reaction products, LPC. The role of LPC might be to stimulate the fertilizing ability of spermatozoa, as well as to induce changes in the zona pellucida and the oolemma that allow sperm-egg fusion. Thus, it seems possible that PLA2 and one of its reaction products might contribute to membrane-fusion events during mammalian fertilization.