PLATELET-ACTIVATING-FACTOR ACETYLHYDROLASE ACTIVITY IN SEMINAL PLASMAFROM THE BULL, STALLION, RABBIT, AND ROOSTER

Platelet-activating factor (PAF) acetylhydrolase, which inactivates PA F, has been detected in human and bovine seminal plasma and may repres ent a mechanism for regulating sperm-derived PAF. This study was desig ned to characterize further PAF acetylhydrolase in seminal plasma from domestic animal species. Sperm-free seminal plasma from the bull, sta llion, rabbit, and rooster was assayed for acetylhydrolase activity ba sed on the release of [H-3]acetate from PAF. As reported previously fo r bull seminal plasma, activity in stallion, rabbit, and rooster semin al plasma was linear with both time and protein concentration, with sp ecific activities of 97.4, 1.2, and 0.33 nmol PAF hydrolyzed/mg protei n/min, respectively. Activity in seminal plasma from the bull, rabbit, and rooster was calcium-independent whereas activity in stallion semi nal plasma increased with added calcium (p < 0.01). Addition of EDTA p artially inhibited acetylhydrolase activity in stallion seminal plasma but increased the specific activity in rabbit seminal plasma (p < 0.0 1). Enzyme activity in bull seminal plasma was nondialyzable (50 000, molecular weight cut-off), stable at pH 5.0, and heat-labile (greater- than-or-equal-to 60-degrees-C). Very little activity was associated wi th bull seminal plasma lipoproteins isolated by KBr flotation or by pr ecipitation with polyanions. These results demonstrate that PAF acetyt hydrolase activity is present in seminal plasma from different species , with large differences in specific activity among species. These dif ferences may bc related to species differences in the physiological ro le of PAF and its regulation in sperm and male tract fluids.