Equine seminal plasma was shown to contain membrane vesicles that are similar to the well characterized prostasomes in human seminal plasma. Determination of nucleoside and nucleotide concentrations of these particles have shown that ATP, ADP and adenosine are the main components of the nucleotidic pool. 5' nucleotidase, endopeptidase and dipeptidyl peptidase IV activities have been found on the surface of the particles. The interaction between these prostasome-like vesicles and spermatozoa was demonstrated by electron micrograph scans which revealed the steps of a fusion-like process leading to mixing of the membranes. In addition, endopeptidase activity, a marker enzyme of these seminal vesicles that is normally absent from equine spermatozoa, was shown to be acquired by these cells after interaction with the vesicles. The addition of these vesicles to equine spermatozoa resulted in the modification of adenylate catabolism. Therefore, a role in stabilizing the energy charge of the spermatozoa thus allowing longer viability is proposed for these organelles.
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