The Oxytocin Receptor in Spermatozoa May Originate From Both Spermatogenesis and Epididymal Maturation, and Regulates Capacitation.

Background: The oxytocin receptor (OR) is a G-protein-coupled receptor recently identified in human spermatozoa, whose origin and role in sperm physiology remain unknown.

Objectives: In this study, using the pig as a model, we examine the presence of the OR in ejaculated spermatozoa through immunofluorescence and immunoblotting, and investigate the receptor's origin in the male gamete via immunohistochemistry in testicular and epididymal tissues. Additionally, we assess the involvement of the OR in in vitro capacitation and the acrosome reaction by utilizing physiological concentrations of agonists (oxytocin and carbetocin) and an antagonist (L-371,257).

Results: The results indicate that, in addition to the expected presence in ejaculated spermatozoa, the OR is expressed during spermatogenesis. Besides, this receptor is found in Leydig and Sertoli cells, as well as in the principal, basal, and apical cells of the epididymis. Furthermore, our data suggest that, during epididymal maturation, the OR could be incorporated in spermatozoa via extracellular vesicles within the apical blebs. The OR is involved in sperm capacitation, as the combination of the antagonist (L-371,257) and the agonist (carbetocin) increases intracellular calcium levels and membrane lipid disorders, which are known as capacitation markers.

Conclusions: The presence of the OR in mammalian spermatozoa could originate from both spermatogenesis and epididymal maturation. Moreover, in the male gamete, this receptor regulates sperm capacitation by interacting with its ligand in the female reproductive tract.