Efeito da adição dos antioxidantes glutationa peroxidase e cisteína ao diluidor de congelação do sêmen equino

Abstract

The cryopreservation of equine semen represents an important applied reproductive biotechnology of this species. When exposed to low temperatures, spermatozoa suffer structural modifications, occurring oxidative stress when there is imbalance between the production of reactive oxygen species (- ROS) and the amount of antioxidants present in seminal plasma. The objective of this study was to analyze the effect of the addition of different concentrations of the antioxidants glutathione peroxidase (GPx) and cysteine in equine frozen semen medium. Five Quarter Horse stallions, with proven fertility were used. Semen samples were collected with artificial vagina and diluted in Botu Crio added with antixodants: G1= Control (without antioxidants); G2= 0.5 mM of N-Acetil-Cysteine; G3= 1 mM of N-Acetil-Cysteine; G4 = 1 U of Glutathione Peroxidase (GPx) and G5= U of Glutathione Peroxidase (GPx). Semen samples were packed straws (0.5 mL; 150 x 106 concentration of spermatozoa/straw), frozen in automated method and stored in liquid Nitrogen (– 196 °C). Semen samples were thawed (37 °C per 30 seconds) and submitted to sperm analyses (kinematic, plasma membrane and acrosome integrity, and potential of mitocondrial membrane), immediately after thawing (T0) and after 60 minutes (T60). Semen samples supplemented with GPx 5 U and cysteine 0.5 mM did not show difference (P>0.05) on the percentage of sperms with high percentage of potential of mitocondrial membrane, as well as with intact acrosome and plasma membrane between T0 and T60 times. Frozen samples with cisteine 1 mM showed high (P<0.05) of gametes with intact acrosome than those of GPx 1 and 5 U and cisteine 0.5mM. Spermatozoa with higher percentage of potential of mitocondrial membrane was founded in T60 (P<0.05) in stallion 5 than stallions 1 and 2. The sperm kinematic evidenced a high values of VCL and VAP (P<0.05) in control samples, in T0 than T60. In general, the stallion 4 presented high values (P<0.05) of kinematic parameters than other stallions. It can be concluded that addition of cysteine (1mM) in equine frozen semen medium preserved better the acrosome integrity and that the individual response of each stallion influence significantly the results of the sperm analysis.