Avaliação de espermatozoides ovinos criopreservados em Tris-gema acrescido de antioxidantes enzimáticos e não-enzimáticos

Abstract

The objective of this work was to evaluate the effect of addition of antioxidants superoxide dismutase (SOD), glutathione (GSH), catalase (CAT), vitamin E (Trolox), and the association between CAT and SOD to Tris egg-yolk ram semen freezing extender. We used five Santa Inês breed rams, with history of fertility, and the ejaculates obtained by artificial vagina. The pool of semen samples were diluted in Tris egg-yolk plus glycerol 5% supplemented with antioxidants, according to the experiments and experimental groups: Exp 1 (G1= control group, G2= 25 U/mL SOD; G3= 50 U/mL SOD; G4= 100 U/mL SOD; G5= 2 mM GSH; G6= 5 mM GSH and G7= 7 mM GSH) and Exp 2 (G1= control group, G2= 30 μM Trolox, G3= 60 μM Trolox, G4= 120 μM Trolox, G5= 25 U/mL CAT, G6= 50 U/mL CAT; G7= 100 U/mL CAT, G8= 100 U/mL SOD + 25 U/mL CAT), at concentration of 240 x 106 spermatozoa/mL. Semen was stored in straws (0.25 mL), frozen using an automated system and stored in liquid nitrogen (- 196 °C). After thawing (37 ºC/30 seconds), samples were analyzed for plasma membrane integrity (iMP), acrosome (IAC) and mitochondrial membrane potential (MMP) with fluorescent probes, kinematics sperm by CASA, and ultrastructure spermatozoa by transmission electron microscopy (TEM). In Exp 1, evaluation was performed in vivo, with the semen used in embryo transfer program. In the Exp 1, significant differences (P<0.05) were observed among groups for total motility (MT), straightness (STR) and oscillation index (WOB) and the GSH 7 mM was lower in MT and higher in STR, and GSH 5 e 7 mM groups were greater in WOB when compared to control, SOD 25 and 100 U/mL. Ultrastructure study showed acrosome better (P<0.05) preserved after freezing in SOD (50 and 100 U/mL) and GSH (5 and 7 mM), whereas mitochondria from control group together with 7 mM GSH suffered further damage. The plasma membrane remained preserved after freezing, regardless of group. For in vivo fertilization, SOD group gave better results than GSH (P>0.05). For Exp 2, CAT 100 U/mL showed a lower percentage (P<0.05) of spermatozoa with intact acrosome. Significant differences (P<0.05) were observed among groups on the kinematics sperm (progressive motility, linearity, straightness, oscillation index, straight line velocity and velocity average path), and were higher for Trolox (30 and 60 μM) and lower for CAT (50 and 100 U/mL). On ultrastructural evaluation, CAT (50 and 100 U/mL) had lower acrosome preservation (P<0.05) and CAT 25 U/mL was higher (P<0.05) than CAT 100 U/ml for the preservation of plasma membrane. Thus, we conclude that the addition of GSH at a concentration of 7mm and 50 CAT and 100 U/mL do not preserve the structural integrity of spermatozoa after cryopreservation; the addition of SOD 100 U/mL, Trolox 60 and 120 mM, and association of CAT 25 U/mL + SOD 100 U/mL provide better preservation of sperm membranes of ram after freezing.