Beneficial effects of relaxin on motility characteristics of stored boar spermatozoa

BACKGROUND Relaxin is detected in seminal plasma of many species and its association with sperm motility may be beneficial in some aspects of assisted reproduction. Here, we immunolocalized relaxin receptors and investigated the effects of exogenous relaxin on motility characteristics, viability, and cAMP content of boar spermatozoa after storage. METHODS Commercial 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). On Day 0, spermatozoa were fixed for immunofluorescence detection of relaxin receptors RXFP1 and RXFP2 (Experiment 1). 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. Alive spermatozoa were purified and incubated (1 h-37°C) with 0, 50, or 100 ng relaxin/ml (Experiment 2a) and 0, 100, or 500 ng relaxin/ml (Experiment 2b). Afterward, aliquots of each treatment group were subjected to motility (Experiments 2), viability (Experiment 3) analyses, and cAMP quantification (Experiment 4). 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. RESULTS Both RXFP1 and RXFP2 receptors were immunolocalized on the entire spermatozoon. Relaxin concentration of 100 ng/ml significantly improved the proportions of motile, progressive, and rapid spermatozoa up to Day 2. Only 500 ng relaxin/ml provided beneficial effects on Day 4. The viability of spermatozoa was not affected by relaxin (100 ng/ml) during storage, but the extent of mitochondria membrane damages was significantly decreased. Furthermore, relaxin did not affect the cAMP contents of spermatozoa during storage, in our conditions. CONCLUSIONS Relaxin could be a valuable motility booster of stored- or aged-spermatozoa for assisted reproduction techniques. However, the related-intracellular signaling cascades of relaxin in boar spermatozoa remain undetermined.