Platelet-activating factor acetylhydrolase activity in seminal plasma from the bull, stallion, rabbit, and rooster

Platelet-activating factor (PAF) acetylhydrolase, which inactivates PAF, has been detected in human and bovine seminal plasma and may represent a mechanism for regulating sperm-derived PAF. This study was designed to characterize further PAF acetylhydrolase in seminal plasma from domestic animal species. Sperm-free seminal plasma from the bull, stallion, rabbit, and rooster was assayed for acetylhydrolase activity based on the release of [3H]acetate from PAF. As reported previously for bull seminal plasma, activity in stallion, rabbit, and rooster seminal plasma was linear with both time and protein concentration, with specific activities of 97.4, 1.2, and 0.33 nmol PAF hydrolyzed/mg protein/min, respectively. Activity in seminal plasma from the bull, rabbit, and rooster was calcium-independent whereas activity in stallion seminal plasma increased with added calcium (p < 0.01). Addition of EDTA partially inhibited acetylhydrolase activity in stallion seminal plasma but increased the specific activity in rabbit seminal plasma (p < 0.01). Enzyme activity in bull seminal plasma was nondialyzable (50,000 molecular weight cutoff), stable at pH 5.0, and heat-labile (> or = 60 degrees C). Very little activity was associated with bull seminal plasma lipoproteins isolated by KBr flotation or by precipitation with polyanions. These results demonstrate that PAF acetylhydrolase activity is present in seminal plasma from different species, with large differences in specific activity among species. These differences may be related to species differences in the physiological role of PAF and its regulation in sperm and male tract fluids.