Role of oxytocin in the ejaculatory process

Area of Science:

• Reproductive Endocrinology
• Male Sexual Physiology
• Neuroendocrinology

Background:

• Oxytocin (OT) is a neurohypophysial hormone with incompletely understood male physiological roles.
• While OT is implicated in central regulation of penile erection, its function in ejaculation remains unclear.
• OT is released from the posterior pituitary during orgasm, suggesting a potential role in sperm progression.

Purpose of the Study:

• To investigate the role of oxytocin (OT) and its receptors (OTR) in the male ejaculatory process.
• To explore the localization and function of OTR in the epididymis.
• To determine the influence of sex steroids on OT-mediated epididymal contractility.

Main Methods:

• Immunohistochemical localization of OTR in rabbit and human epididymis.
• In vitro studies of OT-induced contractility and endothelin-1 (ET-1) release in epididymal epithelial cells.
• Experimental induction of hypogonadotropic hypogonadism in rabbits.
• Administration of estrogens and aromatase inhibitors (letrozole) to assess steroid regulation of OTR.

Main Results:

• OT receptors (OTR) are present in both smooth muscle and epithelial cells of the epididymis.
• OT stimulates epididymal contractility, partly via induction of endothelin-1 (ET-1) release from epithelial cells.
• Estrogens, but not androgens, restored OT-induced epididymal contractility in hypogonadotropic hypogonadal rabbits by up-regulating OTR expression.
• Estrogen deprivation via letrozole treatment resulted in OT hypo-responsiveness.

Conclusions:

• Oxytocin (OT) is involved in regulating epididymal contractility, contributing to the ejaculatory process.
• Epididymal OTR function and expression are modulated by sex steroids, particularly estrogens.
• Estrogens play a novel role in regulating male oxytocin responsiveness in the epididymis.