Bovine sperm capacitation utilizing amino acids and endogenous lipids

The mechanisms by which spermatozoa generate the energy required for successful fertilization, as well as the related energy sources, have not been fully elucidated. We aimed to study the role of amino acids and endogenous lipids as the only oxidative substrates in bull sperm capacitation. Sperm samples were incubated in a capacitation medium with or without classical oxidative substrates. We used L-carnitine and etomoxir, an inducer and an inhibitor of fatty acid β-oxidation, respectively, to evaluate endogenous lipid consumption. Additionally, we used sodium salicylate, an inhibitor of oxidative deamination, to assess the utilization of exogenous amino acids. We evaluated sperm motility, viability, capacitation, and ammonia production for each treatment. In a capacitation medium without classical oxidative substrates, spermatozoa preserved their motility and viability but failed to undergo capacitation. The addition of L-carnitine significantly improved sperm capacitation, whereas the addition of etomoxir diminished sperm motility. Ammonia production increased in the presence of amino acids, while salicylate counteracted this effect. Sperm capacitation was observed in media with classical oxidative substrates regardless of the presence of amino acids. However, capacitation was not detected, and motility diminished in the media with only amino acids added. We demonstrated that the catabolism of endogenous lipids can sustain sperm capacitation as a unique energy source. On the other hand, although amino acids can be deaminated by spermatozoa, they cannot be used to sustain sperm capacitation. These findings offer novel insights into the energy-dependent processes in bull sperm capacitation and have significant implications for developing assisted reproductive technologies.