Role of platelet-activating factor in reproduction: sperm function

Since its discovery nearly thirty years ago, platelet-activating factor has emerged as one of the more important lipid mediators known. Platelet-activ ating factor (PAF; 1-O-alkyl-2- O-acetyl-sn-glycero-3-phosphorylcholine) ex ists endogenously as a mixture of molecular species with structural variant s of the alkyl moiety. PAF is a novel potent signaling phospholipid that ha s unique pleiotropic biological properties in addition to platelet activati on. PAF also plays a significant role in reproduction. PAF content in squir rel monkey sperm is significantly higher during the breeding season than th e non-breeding season. PAF content in human sperm has a positive correlatio n with seminal parameters and pregnancy outcomes. High-fertility boars have significantly more PAF in their sperm than low-fertility boars. The enzyme s (lyso-PAF-acetyltransferase and PAF-acetylhydrolase) necessary for PAF ac tivation and deactivation are present in sperm. PAF-acetylhydrolase may act as a "decapacitation factor". Removal of this enzyme during capacitation m ay promote PAF synthesis increasing motility and fertilization. PAF also pl ays a significant role in the fertilization process, enhancing the fertiliz ation rates of oocytes. Enhanced embryo development has also been reported in oocytes fertilized with PAF-treated sperm. PAF antagonists inhibit sperm motility, acrosome reaction, and fertilization, thus suggesting the presen ce of receptors for PAF. The PAF-receptor is present on sperm, with altered transcript levels and distribution patterns on abnormal cells. Whereas the exact mechanism of PAF in sperm function and reproduction is uncertain, it s importance in normal fertility is substantial. The reproductive significa nce of PAF activity in sperm and fertility plus the role of PAF in the esta blishment of pregnancy requires further study.