Reversion of thermic-shock effect on ram spermatozoa by adsorption of seminal plasma proteins revealed by partition in aqueous two-phase systems

Centrifugal counter-current distribution (CCCD) in a dextran, Ficoll, poly(ethylene glycol) two-phase system was used to study the effect of seminal plasma proteins on the partition behaviour of ram spermatozoa exposed to thermal shock. Ram spermatozoa freed from seminal plasma by a 'swim-up' procedure were submitted to thermal shock and fractionated by CCCD. Cell viability decreased from 68% to 18% after the treatment, showing a slight displacement of the cells from the right (where a higher enrichment of live cells is found) to the centre of the profile. A change of the distribution profile was shown in the presence of either ram or bull seminal plasma. Bull seminal plasma was able to move the profile to the right, whereas ram seminal plasma increased the proportion of cells with enhanced affinity for the lower dextran-rich phase. Plasma proteins isolated from both seminal plasmas moved the profile to the right. In addition, cell viability rose to 48% after the CCCD run in the presence of ram plasma proteins. This restoring effect was lost when ram plasma proteins were thermally denatured. Bovine serum albumin was not only unable to move the profile to the right but even promoted displacement of the profile to the left. This negative effect was also observed when proteins from bull seminal plasma were in the presence of protein-free ram seminal plasma. However, proteins isolated from ram seminal plasma still restored the profile in the presence of bull seminal plasma freed from proteins. The results presented here strongly suggest that seminal plasma proteins are adsorbed by a spermatozoal surface previously exposed to thermic shock. These proteins would exert a highly specific protective effect on ram spermatozoa. In addition, in the ram seminal plasma there must be some factor which avoids this adsorption.