MODULATION OF PROSTAGLANDIN SYNTHESIS IN MAMMALIAN SPERM ACROSOME REACTION

Exogenous arachidonic acid induces the acrosome reaction and the production of the prostaglandins PGE(2) and PGF(2 alpha) in bovine spermatozoa. Exogenous PGE(2) also induces the acrosome reaction and PGF(2 alpha) synthesis. To understand better the role of PGE(2) in the induction of PGF(2 alpha) synthesis through modulation of phospholipase A(2), inhibitors of this enzyme were used. The effects of PGE(2) were blocked by phospholipase A(2) inhibitors and this inhibition was reversed by addition of arachidonic acid. These data indicate that PGE(2) activates phospholipase A(2) to produce arachidonic acid. To determine whether protein kinase C modulates phospholipase A(2) activity in this process, staurosporin, an inhibitor of protein kinase C, was used. The effect of PGE(2) on PGF(2), production is inhibited by staurosporin and this inhibition was reversed by addition of arachidonic acid indicating that protein kinase C is involved in phospholipase A(2) activation. The effect of exogenous arachidonic acid or PGE(2) on the acrosome reaction is blocked by lipoxygenase inhibitors but not by inhibitors of cyclo-oxygenase, indicating that lipoxygenase products are involved in the mechanism of the acrosome reaction. The presented data shed light on the cross-talk between cyclo-oxygenase and lipoxygenase and their involvement in the sperm acrosome reaction. It is suggested that cyclo-oxygenase products modulate the activity of lipoxygenase which is a key enzyme in the mechanism leading to the acrosome reaction. Stimulation of cyclo-oxygenase to synthesize PGE(2) activates phospholipase A(2) to release arachidonic acid which is the substrate for lipoxygenase activity. Thus, the role of cyclo-oxygenase products is probably to reactivate the phospholipase A(2) which was initially activated via the signal transduction cascade.