Fertilizing ability of spermatozoa: its conditioning factors and methods of determination (review)

Fertilization is a complex process that results in the fusion of gametes. In order to obtain fertilizing ability, spermatozoa need to undergo post-ejaculation processes in the female reproductive tract. These include capacitation, hyperactivation, and acrosomal reaction. Capacitation is a complex process during which the sperm undergoes various changes in metabolism, intracellular concentrations of ions and other substances. The main factors of capacitation are the concentration of intracellular calcium ions, changes in the properties and structure of the plasma membrane, the pH of the medium, as well as the effect of progesterone and cholesterol on the sperm. The resulting hyperactivation leads to a change in the motility of the sperm, as a result of which it reaches the egg for further penetration into it. Then an acrosomal reaction occurs – the release of substances from the acrosome that ensure penetration through the transparent membrane of the oocyte. The fertilizing ability can be determined by various methods: the HBA test is based on the binding of spermatozoa to hyaluronic acid, SpermSlow is used to slow down spermatozoa in a hyaluronic-containing medium. The integrity of the acrosome and the motility of the sperm can be determined using the Acrobeads method, based on the formation of a complex of motile spermatozoa with immunoglobulins coated with antibodies against the protein from the inner surface of the acrosomal membrane. The SPA method allows us to determine the functional ability of spermatozoa to bind to the egg shell. In addition to direct methods that examine the basic parameters and functions of the sperm, there are methods that determine additional parameters, such as the level of oxidative stress and the factors that cause it, and the presence of disorders in the genetic apparatus of the male gamete. The level of oxidative stress and the amount of reactive oxygen species can be determined by reaction to thiobarbituric acid, reaction with nitrosine tetrazolium, by estimating the amount of carbonyl derivatives of amino acid residues in proteins, and by chemoluminescence analysis. DNA breaks can be detected using the TUNEL test, the DNA comet method is used to identify the degree of damage to genomic DNA, and the FISH method is used to analyze the chromosome set of a sperm cell. The cervix contains cervical mucus, which is a necessary factor for fertilization. The ability of spermatozoa to penetrate through it can be determined using auxiliary methods, for example, swim-up. Its essence lies in the fact that in a cultural environment, the natural movement of male gametes is imitated, and those that meet the requirements are selected. The concentration of spermatozoa and the degree of their motility in the cervical mucus are determined by a postcoital test. Taking into account the availability of these techniques from a logistical point of view, the development of domestic kits is relevant.

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