Decrease in glutathione (GSH) content in bovine sperm after cryopreservation: comparison between two extenders.

ABSTRACT

Growing evidence suggests that among the causes which deteriorate qualitative and functional characteristics of semen after freezing and thawing, there are those linked to oxidative stress and decrease detoxification of antioxidants present in the cells and seminal plasma. Overall, cryopreservation reduces the spermatozoal GSH content. In the present study we assessed the motility, capacitation status, ability to undergo acrosome reaction and levels of GSH in bovine spermatozoa after freezing and thawing, and compared the effects of the egg yolk tris-citrate and a commercial extenders (Bioxcell). Six semen samples were collected from each of five bulls and frozen and thawed in the two extenders. The level of total GSH of bovine spermatozoa detected in the raw semen ranged from 246.5 to 776.2 pmoles/mg of protein. The Bioxcell extender was superior in preserving GSH content (647.2+/-300.1 versus 223.6+/-154.0 pmoles/mL; P<0.05), motility levels (44.3+/-4.8 versus 41.8+/-4.0%; P<0.05), non-capacitated state (68.3+/-13.6 versus 61.3+/-17%; P<0.05) and a lower proportion of acrosome reacted spermatozoa post thaw (3.8+/-2.1 versus 6.3+/-3.1%; P<0.001) compared to egg yolk tris-citrate extender. These findings could be partially ascribed to the high GSH level contained in the commercial extender which seem able to alleviate oxidative damages to spermatozoa surviving freezing thawing procedures. Further researches are required in order to validate in vivo these results.