부산대학교 도서관

The presence of melatonin receptors on the surface of ram spermatozoa has led to speculation about melatonin having a role in sperm functionality. The aim of this study was to elucidate the mechanism through which melatonin regulates ram sperm capacitation induced by a cocktail containing cAMP-elevating agents. Cocktail samples capacitated in the presence of 1 µM melatonin showed lower percentages of capacitated spermatozoa (chlortetracycline staining; P < 0.001) together with a decrease in protein tyrosine phosphorylation (P < 0.01) and lower levels of reactive oxygen species (ROS) and cAMP (P < 0.05) compared with cocktail samples without the hormone. Determination of kinematic parameters, together with principal component and cluster analyses, allowed us to define four sperm subpopulations (SP). After 3 h of incubation with cAMP-elevating agents, the percentages of spermatozoa belonging to SP1 (high straightness) and SP4 (less-vigorous spermatozoa with non-linear motility) increased while SP2 and SP3 (rapid spermatozoa starting hyperactivation or already hyperactivated) decreased compared with the control sample. The presence of melatonin at 100 pM and 10 nM restored these subpopulations to values closer to those found in the control sample. These results indicate that melatonin at micromolar concentrations modulates ram sperm capacitation induced by cAMP-elevating agents, reducing ROS and cAMP levels, whereas at lower concentrations melatonin modifies motile sperm subpopulations. These findings warrant further studies on the potential use of melatonin for controlling capacitation in artificial insemination procedures. Melatonin is able to regulate sperm capacitation showing different effects depending on concentration, but its effect on spermatozoa incubated in high cAMP conditions is unknown. Our results indicate that melatonin at micromolar concentrations acts reducing ROS and cAMP levels, whereas at lower concentrations modifies motile sperm subpopulations that change during capacitation. These findings warrant further studies on the potential use of melatonin for controlling capacitation in artificial insemination procedures. [ABSTRACT FROM AUTHOR]