The processes of cooling and freezing/thawing produce physical and chemical stress on the sperm membrane, and this stress is associated with oxidative stress and reactive oxygen species (ROS) generation that further reduce sperm viability and fertilizing ability. It is known that the process of freezing is associated with a significant reduction of the intracellular reduced glutathione (GSH) content. The aim of these experiments was to investigate the effects of addition of GSH to thawing extenders on motility parameters and ROS generation in frozen-thawed ovine and caprine spermatozoa. Frozen spermatozoa from eight rams (Ovis aries) and eight bucks (Capra hircus) (generously provided by Ovigen, Zamora, Spain) were thawed in a water bath at 37�C for 30 s and resuspended in sperm-TALP medium (Parrish et al. 1986 Theriogenology 25, 591-600) without (control) and with addition of 1 mM or 5 mM GSH. After 30 min of incubation at 37�C, sperm motility was evaluated using a computer-assisted sperm analysis (CASA) system (SCA, Microptic, Barcelona, Spain). The recorded parameters of motility were: % total, % progressive, curvilinear velocity, straight-line velocity, average path velocity, linearity of the curvilinear trajectory, straightness, amplitude of lateral head displacement, wobble of the curvilinear trajectory and beat cross frequency. Another set of sperm samples was incubated in the presence of (0.7 �M) 22,72-dichlorodihydrofluorescein diacetate (Gadea et al. 2005 J. Androl. 26, 396-404) to estimate production of ROS by flow cytometry. Data were analyzed by two-way ANOVA, considering the specific sperm treatment (GSH addition) and the males as the main variables. In ram frozen spermatozoa, all of the motility parameters were significantly improved when the medium was supplemented with GSH (P < 0.01) with even better results when 5 mM GSH was used. As an example, progresive motility increased from 31.16% (control) to 39.17 and 43.97%, respectively, for 1 and 5 mM GSH. Despite of the male effect detected (P < 0.01), all eight rams studied presented a similar pattern (interaction P > 0.05). The generation of ROS was significantly reduced when GSH was added (6.23a for control vs. 5.32b and 3.85c for 1 and 5 mM, respectively; P < 0.01). In buck frozen spermatozoa, % motility and progressive motility were significantly higher in GSH groups than in the control (P < 0.01), with no differences between 1 and 5 mM GSH. However, for the other motility parameters, the differences were not significant, which probably could be related to differences in the pattern shown by different animals (interaction of buck by treatment P < 0.05). ROS generation was significantly reduced when GSH was added (7.50a for control vs. 4.32b and 2.70b for 1 and 5 mM, respectively; P < 0.01). The addition of GSH to the thawing medium had a positive influence on the parameters studied in both species, increasing the motility patterns and reducing the ROS generation. In conclusion, we can assume that the addition of reduced glutathione to the thawing medium exerts a protective effect on spermatozoa functionality.
This work was supported by AGL-2003-03144.
Do spermathecal morphology and inter-mating interval influence paternity in the polyandrous beetle Tribolium castaneum?
