The role of membrane character in human sperm function
Description
Fertilization is a membrane-dependant event. Due to the involvement of membranes in the fertilization process, the integrity and function of sperm membranes influences their fertilizing ability. These studies investigate sperm membrane character in relation to function and fertilizing capacity The first phase of experiments used hydrogen peroxide to induce peroxidative damage to membrane phospholipids. As compared to controls, an increase in lipid peroxidation and decrease in sperm percent motility were observed following 15 minute treatment with 0.01% or 0.05% H$\sb2$O$\sb2.$ Increased lipid peroxidation was correlated with an observed decrease in the cholesterol:phospholipid ratio. The same treatment did not significantly alter sperm viability In order to further correlate membrane integrity and sperm function, the second phase of experimentation investigated the role of membrane damage in cryopreservation-induced alterations in sperm function. In one set of experiments, cryopreserved sperm samples that were thawed slowly exhibited reduced motility and increased lipid peroxidation compared to quickly thawed samples. In a second set of experiments, platelet activating factor (PAF) and pentoxifylline (PTX), two known sperm motility stimulants, were used as cryoprotective additives. Pre-freeze addition of both PAF and PTX significantly improved post-thaw motility. Lipid peroxidation was not affected by either agent The next phase of research was designed to determine whether protection from peroxidative damage and improved sperm function were related. Sodium nitroprusside (SNP) was used to scavenge oxygen radicals, which are potentially damaging to membrane phospholipids. In the preliminary investigation, 50 and 100 nM concentrations of SNP significantly improved the maintenance of post-thaw percent motility and viability, and sperm velocity for up to six hours. In a follow-up investigation, treatment with 50 nM SNP significantly improved acrosin enzyme activity and the percentage of sperm which completed the acrosome reaction Because preliminary experiments demonstrated an association between membrane integrity and sperm function, a more detailed examination of membrane phospholipid content was pursued in the final phase of experimentation. Mass spectroscopy was performed on membrane phospholipid extracts. Samples were divided into two groups for data analysis: Group A samples exhibited greater than 40% motility maintenance during the freeze-thaw process, Group B samples exhibited less than 40% motility maintenance. Samples in Group A generated spectra with significantly more activity and a different set of major peaks than did samples in Group B. The most significant peak generated by Group A samples was not generated by Group B samples, suggesting that differences in lipid composition affect sperm motion A general discussion of the results of all phases of experimentation, and propositions concerning their potential significance is included