SUMMARYThis work analysed intracellular calcium stores of boar spermatozoa subjected to 'in vitro' capacitation (IVC) and subsequent progesterone-induced acrosome exocytosis (IVAE). Intracellular calcium was analysed through two calcium markers with different physico-chemical properties, Fluo-3 and Rhod-5N. Indicative parameters of IVC and IVAE were also evaluated. Fluo-3 was located at both the midpiece and the whole head. Rhod-5N was present at the sperm head. This distribution did not change in any of the assayed conditions. Induction of IVC was concomitant with an increase in both head and midpiece Ca 2+ signals. Additionally, while IVC induction was concurrent with a significant (p < 0.05) increase in sperm membrane permeability, no significant changes were observed in O 2 consumption and ATP levels. Incubation of boar spermatozoa in the absence of calcium showed a loss of both Ca 2+ labellings concomitantly with the sperm's inability to achieve IVC. The absence of extracellular calcium also induced a severe decrease in the percentage of spermatozoa exhibiting high mitochondrial membrane potential (hMMP). The IVAE was accompanied by a fast increase in both Ca 2+ signalling in control spermatozoa. These peaks were either not detected or much lessened in the absence of calcium. Remarkably, Fluo-3 marking at the midpiece increased after progesterone addition to sperm cells incubated in a medium without Ca 2+. The simultaneous addition of progesterone with the calcium chelant EGTA inhibited IVAE, and this was accompanied by a significant (p < 0.05) decrease in the intensity of progesterone Ca 2+ -induced peak, O 2 consumption and ATP levels. Our results suggest that boar spermatozoa present different calcium deposits with a dynamic equilibrium among them and with the extracellular environment. Additionally, the modulation role of the intracellular calcium in spermatozoa function seems to rely on its precise localization in boar spermatozoa.

SUMMARYAlthough cryopreservation of stallion spermatozoa allows long-term preservation of spermatozoa from particular stallions and facilitates international trade, it is understood to inflict damages on sperm cells that may finally reduce their fertilizing ability. In addition, individual differences are known to exist in the sperm ability to withstand freeze-thawing protocols. To date, these differences have mainly been reported on the basis of sperm motility and membrane integrity. For this reason, the present work sought to determine differences between good (good freezability ejaculates: GFE) and poor (poor freezability ejaculates: PFE) freezability stallion ejaculates in other sperm parameters, including peroxide and superoxide levels, potential of mitochondrial membrane and nuclear integrity. With this purpose, a total of 24 stallion ejaculates were cryopreserved and classified into two groups (GFE vs. PFE), depending on their sperm membrane integrity and motility after freeze-thawing. From the total of 24 ejaculates, 13 were classified as GFE and the other 11 were classified as PFE. Apart from differences in sperm membrane permeability and lipid disorder after freezethawing, GFE presented significantly (p < 0.05) higher percentages of viable spermatozoa with high content of peroxides and of superoxides than PFE. In contrast, and despite cryopreservation of stallion spermatozoa increasing DNA fragmentation and disrupting disulphide bonds in sperm head proteins, no significant differences between GFE and PFE were seen. We can thus conclude that good and poor freezability stallion ejaculates differ in their reactive oxygen species levels after cryopreservation, but not in the damage extent on sperm nucleus.

Incubation of boar spermatozoa in a capacitation medium with oligomycin A, a specific inhibitor of the F0 component of the mitochondrial ATP synthase, induced an immediate and almost complete immobilisation of cells. Oligomycin A also inhibited the ability of spermatozoa to achieve feasible in vitro capacitation (IVC), as measured through IVC-compatible changes in motility patterns, tyrosine phosphorylation levels of the acrosomal p32 protein, membrane fluidity and the ability of spermatozoa to achieve subsequent, progesterone-induced in vitro acrosome exocytosis (IVAE). Both inhibitory effects were caused without changes in the rhythm of O2 consumption, intracellular ATP levels or mitochondrial membrane potential (MMP). IVAE was accompanied by a fast and intense peak in O2 consumption and ATP levels in control spermatozoa. Oligomycin A also inhibited progesterone-induced IVAE as well as the concomitant peaks of O2 consumption and ATP levels. The effect of oligomycin on IVAE was also accompanied by concomitant alterations in the IVAE-induced changes on intracellular Ca2+ levels and MMP. Our results suggest that the oligomycin A-sensitive mitochondrial ATP-synthase activity is instrumental in the achievement of an adequate boar sperm motion pattern, IVC and IVAE. However, this effect seems not to be linked to changes in the overall maintenance of adequate energy levels in stages other than IVAE.

SUMMARYThe main aim of this work was to evaluate how supplementing freezing media with reduced glutathione (GSH) affected the 'in vivo' fertilizing ability of boar semen subjected to cryopreservation procedures. With this purpose, 12 ejaculates coming from 12 boars were cryopreserved in the presence or absence of 2 mM GSH, whereas the same number of extended ejaculates coming from the same boars was used as negative/farm controls. Eight different sperm parameters (levels of free-cysteine residues in sperm nucleoproteins, DNA fragmentation, sperm viability, acrosome-membrane integrity, intracellular peroxide and superoxide levels, and total and progressive sperm motility) were evaluated before freezing and after 30 and 240 min of thawing. In addition, a total of 180 multiparous sows were used in the field fertility trials, the females being randomly divided into three groups and inseminated with extended, frozen-thawed control or frozen-thawed semen supplemented with 2 mM GSH. The presence of GSH in the freezing media significantly (p < 0.05) increased farrowing rates and the number of total born piglets and alive born piglets, and partially counteracted the cryopreservation-induced damages inflicted on frozen-thawed spermatozoa. We can thus conclude that supplementing freezing media with 2 mM GSH greatly improves boar sperm cryopreservation technology, as it significantly improves the fertilizing ability of frozen-thawed spermatozoa.

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