įrom this background, it appears that the presence of relaxin in seminal plasma or semen preparation is favorable to sperm function and progression within the female genital tract. At present, the knowledge of the physiological effects of relaxin on spermatozoa of many species is still limited. The interaction of relaxin with its receptor RXFP1 has the potential to activate a variety of intracellular pathways in a possible cell type-dependent manner, which leads to the production of cAMP generally known as the major intra-cellular transducer of relaxin in somatic cells. Both receptors have been differentially detected in mature spermatozoa of boars and men, as well as in reproductive tracts of rats, boars, and monkeys through, almost exclusively, indirect technical approaches. Indeed, relaxin has been described as the endogenous ligand of the membrane G-protein coupled receptor, RXFP1 (LGR7) however, it is still able to bind, at lower affinity, to the closely associated receptor, RXFP2 (LGR8). It is likely that the aforementioned effects of relaxin are results of its interaction with specific plasma membrane receptors that have been characterized in various reproductive and non-reproductive tissues. ![]() Additionally, experimental studies conducted with men and boars spermatozoa demonstrated direct stimulatory effects of relaxin on sperm motility, while revealing further effects of relaxin on mitochondrial function, capacitation, acrosome reaction, cAMP production, and calcium accumulation in spermatozoa. Indeed, positive correlations have been found between immunoreactivity levels of seminal relaxin and sperm motility in both humans and animals, which findings are consistent with other studies reporting decreased sperm motility in seminal plasma preparations supplemented with relaxin antiserum. Despite these differences and regardless of the species, relaxin secretions are found in seminal plasma and its levels are associated with sperm motility of semen ejaculates. The prostate is well-established as the major site of relaxin production in humans, primates, and rats, whereas testes appear as the major source in dogfish sharks and boars. Various reproductive tissues of males express relaxin and, depending on the species, the prostate and/or the testes appear as the main sources of its production. The effects of relaxin in females are well-documented, especially during early (e.g., implantation and placentation) and late (e.g., growth and softening of the uterine cervix) pregnancy, but its roles in male reproductive organs are still not fully understood. It has been described as a member of the insulin family proteins found in various reproductive and non-reproductive tissues and having pleiotropic functions in both males and females. Relaxin is a polypeptide of about 6 kDa discovered decades ago and also known as a hormone of pregnancy in many mammals. However, the related-intracellular signaling cascades of relaxin in boar spermatozoa remain undetermined. Relaxin could be a valuable motility booster of stored- or aged-spermatozoa for assisted reproduction techniques. Furthermore, relaxin did not affect the cAMP contents of spermatozoa during storage, in our conditions. The viability of spermatozoa was not affected by relaxin (100 ng/ml) during storage, but the extent of mitochondria membrane damages was significantly decreased. Only 500 ng relaxin/ml provided beneficial effects on Day 4. Relaxin concentration of 100 ng/ml significantly improved the proportions of motile, progressive, and rapid spermatozoa up to Day 2. Resultsīoth RXFP1 and RXFP2 receptors were immunolocalized on the entire spermatozoon. Data (3–4 independent replicates) were statistically analyzed (ANOVA followed by pairwise comparisons) and p values less or equal to 0.05 was set for significant difference. Afterward, aliquots of each treatment group were subjected to motility (Experiments 2), viability (Experiment 3) analyses, and cAMP quantification (Experiment 4). ![]() Alive spermatozoa were purified and incubated (1 h-37☌) with 0, 50, or 100 ng relaxin/ml (Experiment 2a) and 0, 100, or 500 ng relaxin/ml (Experiment 2b). Semen aliquots were taken from the same dose at Day 0, Day 1, and Day 2 (Experiment 2a), and Day 2 and Day 4 (Experiment 2b) for analyses. On Day 0, spermatozoa were fixed for immunofluorescence detection of relaxin receptors RXFP1 and RXFP2 (Experiment 1). MethodsĬommercial doses of boar semen were obtained on the collection day (Day 0) and kept in shipping containers at room temperature for up to 4 days (Day 4). Here, we immunolocalized relaxin receptors and investigated the effects of exogenous relaxin on motility characteristics, viability, and cAMP content of boar spermatozoa after storage. ![]() Relaxin is detected in seminal plasma of many species and its association with sperm motility may be beneficial in some aspects of assisted reproduction.
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