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In the "male factor" entity, the structural and functional correlation determining the sperm fertilizing capacity is constituted by a group of cellular factors that must be evaluated in the semen of the infertile men. Structurally the spermatozoa of the head, the middle piece and the flagellum. The head has a highly condensed haploid nucleus, surrounded by a thin layer of cytoplasmic material, which is covered in a cap-like fashion by the membrane limiting the acrosome. This last organelle, which has characteristics similar to those of a secretory granule, secretes in a programmed way the hydrolytic enzymes that facilitate the fertilization process. The middle piece contains the mitocondrail sheet, responsible for the energy metabolism of the sperm cell. The flagellum has the same basic structure of other cilia or flagella, but also has particular characteristics due to the presence of the outer dense fibers and the fibrous sheath. In the semen analysis from infertile men the abnormalities most frequently observed belong to the number, morphology, variability, motility of capacitation-acrosome reaction of the sperm cells. However, due to the apparent multifactorial etiology of the male factor, now a days we only have few options for medical or pharmacological treatment. In this paper we review the morphology and ultrastructure considered as "normal" in the human spermatozoa, as well as we describe the most frequent alterations in these parameters. At the same time, we discuss the impact of sperm motility and of the capacitation-acrosome reaction process in male fertility.

The recent advances in assisted reproduction procedures have helped to the better understanding of the female reproductive physiology and pathology, however, male infertility remains as a poor explained medical problem, nevertheless it occurs in almost 50% of infertile couples. Oligoasthenozoospermia is one of the more common causes of male infertility, therefore we measured in 10 patients with this diagnosis and in 10 fertile euspermic men, besides the parameters included in the standard semen analysis, the quantitative motility (photography method), capacitation-acrosome reaction and the sperm ability to fertilize zona-free hamster oocytes, with the aim to correlate the morphofunctional characteristics of the male gametes with their fertilizing capacity. The results showed significant differences in every parameter studied, including the correlation analysis. In relation with the in vitro induction of the acrosome reaction in both groups, we found significant correlations of the sperm fertilizing ability and the progressive sperm motility with this parameter (fertile group: RS = 0.834, P less than 0.005 & RS = 0.612, P less than 0.05; infertile group: RS = 0.986, P less than 0.001 & RS = 0.536, P less than 0.05 respectively), nevertheless the sperm rate which completed this process was low in relation to the total sperm population even in the fertile men (9.4 +/- 2.0% & 4.4 +/- 2.5% acrosome reacted cells after 18 h of incubation, in the fertile and infertile males respectively). The results also showed the presence of fully capacitated spermatozoa in both groups, since they penetrated the zona-free hamster eggs and decondensed their chromatin (73.9 +/- 13.4% & 10.4 +/- 7.7% penetrated eggs in the euspermic and oligoasthenozoospermic individuals respectively), however, the spermatozoa from the oligoasthenozoospermic men showed low polyspermy indexes too (0.1 penetrated spermatozoa/inseminated oocyte). In this last group we found, in addition, that the mean sperm velocity and the abnormal sperm morphology rate showed significant correlations with the fertilizing ability of the male gametes too (RS = 0.986, P less than 0.005 & RS = -0.942, P less than 0.005. respectively). These data allow us to suggest that before an infertile man is involved in any assisted reproduction program, the presence of possible morphofunctional alterations in the spermatozoa be analyzed, with the aim to be able to make a better prognosis about the success with these patients.

We briefly reviewed some ionic mechanisms participating in the fulfillment of the acrosome reaction processes, indicating the results obtained by the simultaneous and dynamic quantitation of sodium, potassium, calcium and hydrogen concentrations in the in incubation medium of human spermatozoa induced to achieve the acrosome reaction through the addition of cAMP and follicular fluid. At the same time, the participation of zinc and some enzymatic activities, like phospholipase A2, in the occurrence of this process, is indicated. A study is done about the sperm nuclear decondensation mechanisms, pointing at the importance of various participants in this event, like the disulfide groups reducing agents, some metalic ions and the glycosaminoglycanes, as well as a proposal of a mechanism which could be physiologically functional for the in vivo occurrence of this phenomenon. Finally we present some results explaining the DNA synthesis activation, which is repressed in the spermatozoa since the spermiogenesis final stages, and is indispensable for the chromosomic duplication required during egg segmentation.

We briefly reviewed some ionic mechanisms participating in the fulfillment of the acrosome reaction processes, indicating the results obtained by the simultaneous and dynamic quantitation of sodium, potassium, calcium and hydrogen concentrations in the in incubation medium of human spermatozoa induced to achieve the acrosome reaction through the addition of cAMP and follicular fluid. At the same time, the participation of zinc and some enzymatic activities, like phospholipase A2, in the occurrence of this process, is indicated. A study is done about the sperm nuclear decondensation mechanisms, pointing at the importance of various participants in this event, like the disulfide groups reducing agents, some metal ions and the glycosaminoglycans, as well as a proposal of a mechanism which could be physiologically functional for the in vivo occurrence of this phenomenon. Finally we present some results explaining the DNA synthesis activation, which is repressed in the spermatozoa since the spermiogenesis final stages, and is indispensable for the chromosomic duplication required during egg segmentation.

Mammalian sperm capacitation and the acrosome reaction (AR) are essential prerequisites for fertilization. This report examines part of the molecular events developed during capacitation and the AR of mammalian spermatozoa; especially those events related to sperm head membrane bound enzymes and phospholipids. For this purpose, it has been analysed results obtained from an in vitro capacitation/acrosome reaction inducing system for golden hamster spermatozoa. First of all, the analysis is focused in the phospholipid transmethylation reactions possibly occurring at plasma membrane level during capacitation and the AR; it is suggested too, that this pathway could provide the substrate for a sperm head membrane bound phospholipase A2 which is able to produce a lysophospholipid (a fusogen) and fatty acids; both of them, very likely involved in the late steps of the AR. These assumptions are confirmed by experiments demonstrating that exogenous lysophospholipids and/or cis-unsaturated fatty acids are able to accelerate AR in previously capacitated spermatozoa. It is also suggested future research in this field, which could involve a sperm phospholipase C specific for phosphatydil-inositol, 4.5 bisphosphate; its products, Inositol trisphosphate and diacylglycerol could act as second messengers with a probable physiological function during capacitation. Finally, an integrative mechanism for the AR-involving phospholipid methylation, acrosin activation, phospholipase A2 activation and endogenous lysophospholipids and fatty acids production is proposed as a model for discussion.