Identification and partial characterization of α-1,4-glucosidase activity in equine epididymal fluid

An Update on Semen Physiology, Technologies, and Selection Techniques for the Advancement of In Vitro Equine Embryo Production: Section I

Simple Summary

Male fertility is often estimated by simple sperm assessment, and therefore, it is crucial to establish species-specific baselines for normal sperm parameters. In this paper, sperm physiology, function, and common abnormalities in stallions will be reviewed.

Abstract

As the use of assisted reproductive technologies (ART) and in vitro embryo production (IVP) expand in the equine industry, it has become necessary to further our understanding of semen physiology as it applies to overall fertility. This segment of our two-section review will focus on normal sperm parameters, beginning with development and extending through the basic morphology of mature spermatozoa, as well as common issues with male factor infertility in IVP. Ultimately, the relevance of sperm parameters to overall male factor fertility in equine IVP will be assessed.

Components of stallion seminal plasma and the effects of seminal plasma on sperm longevity

Seminal plasma is a mixture of secretions produced in the testes, epididymides and accessory sex glands, and ejaculated as several consecutive fluid fractions. The composition of seminal plasma and the effects on sperm longevity vary between fractions and individual stallions. This review focuses on the sequence of ejaculation, constituents of seminal plasma and their potential use as fertility markers as well as the influence of seminal plasma on spermatozoa during storage.

Neutral α-glucosidase activity in mouse: a marker of epididymal function?

Neutral α-glucosidase (NAG) activity is considered a functional epididymal marker in several species. Unlike the rat, no NAG activity has been detected in mice. The aims of the present study were to evaluate NAG secretory activity (the supernatant of the incubated tissue) in mouse epididymis and to determine whether it could be used as a functional epididymal marker. Epididymides (whole or in parts) were incubated in the presence or absence of testosterone (10−5 m) and secretory NAG activity was compared with known positive controls. Furthermore, we compared enzyme activity in epididymides from well-fed and undernourished mice (50% food restriction for 21 days), a model that alters the epididymal maturation processes. Spectrophotometric analysis revealed NAG activity in mouse epididymis (22.6 ± 3.7 mU g–1 tissue; n = 4), being higher in the caput. NAG activity was statistically higher in the caput than in the corpus and in the cauda. No significant differences existed between the caput NAG activity and complete epididymis NAG activity. In undernourished mice, we confirmed changes in epididymal maturation observed previously (i.e. increased number of immature spermatozoa and diminution of the sperm concentration). Concordantly, the epididymides of undernourished mice exhibited decreased enzyme secretory activity, which increased to values similar to those seen in controls following incubation in the presence of testosterone (22.5 ± 2.6, 12.5 ± 1.0 and 22.4 ± 3.7 mU g–1 tissue, n = 9 in control (n = 7), undernourished (n = 9) and undernourished + testosterone groups (n = 9), respectively). In conclusion, NAG activity was detected in mouse epididymis. Although the present study supports the possibility of using NAG as an epididymal marker, more studies are necessary to effectively prove that NAG activity can be used as an epididymal marker.

The role of stallion seminal proteins in fertilisation

Seminal plasma proteins are secretory proteins originating mainly from the epididymis and the accessory sex glands. They are involved in the remodelling of the sperm surface which occurs during sperm transit through the male genital tract and continues later at ejaculation. During this process, collectively called post-testicular sperm maturation, the spermatozoa acquire the ability to fertilise an egg. Seminal plasma proteins have been shown to contribute to early and central steps of the fertilisation sequence, e.g. the establishment of the oviductal sperm reservoir, modulation of capacitation and gamete interaction. The major equine seminal plasma proteins belong to three protein classes, which contain widely occurring protein modules. Fn-2 type proteins are characterised by two or four tandemly arranged Fn-2 modules and have been implicated in the modulation of sperm capacitation. Multiple members of the cysteine-rich secretory proteins (CRISP) have been identified in the male genital tract of a number of species. CRISP proteins have been shown to be involved in various functions related to sperm-oocyte fusion, innate host defense function and ion channel blockage. Spermadhesins occur only in ungulate species. Their carbohydrate- and zona pellucida-binding properties would suggest a role of these proteins in gamete recognition. The major proteins of equine seminal plasma have been isolated and characterised regarding their expression along the male genital tract, protein structure and their functions.