It is now well established that the peptide oxytocin can act as a paracrine factor as well as a classic hormone. Oxytocin is produced locally in both the testis and ovary, where it may modulate both steroidogenesis and contractility of the male and female reproductive tracts. The peptide is also present in the prostate and seminal fluid and there is growing evidence that oxytocin may be produced in the prostate. Within the prostate, oxytocin has been shown to increase growth of the epithelial tissue and increase both muscular tone and contractile activity. Furthermore, prostatic concentrations of the peptide are regulated by androgens. It is hypothesized that oxytocin may act as a paracrine factor to regulate cell growth and that this may be secondary to its effects on the enzyme 5 alpha-reductase which converts testosterone to dihydrotestosterone. In addition, oxytocin may be involved in the pathophysiology of benign prostatic hyperplasia.
K Whittington, SJ Assinder, T Parkinson, KR Lapwood, and HD Nicholson
Oxytocin is present in the male reproductive tract and has been shown to increase contractility in the epididymis and to modulate steroidogenesis. This study investigated the effects of oxytocin in the testis in vivo, and the presence and cellular localization of oxytocin receptors in the reproductive tract of rams. During the breeding season, mature rams underwent efferent duct ligation before injection of either oxytocin (20 microg) or oxytocin plus an oxytocin antagonist (20 microg) into the testicular artery; the contralateral testicular artery received saline. Injection of oxytocin caused a significant increase (P < 0.05) in the concentration of spermatozoa collected from the rete testis. This effect was not observed after treatment with the oxytocin antagonist plus oxytocin. Western blot analysis performed using a specific oxytocin receptor antibody (020) identified a single immunoreactive band of 66 kDa in testicular and epididymal tissue. This band was present in uterine tissue but not in liver or muscle. Immunocytochemistry identified oxytocin receptors on Leydig and Sertoli cells of the testis, on epithelial cells throughout the epididymis, on peritubular smooth muscle cells in the cauda epididymidis, and on the epithelial cells and circular smooth muscle layer of the ductus deferens. These findings indicate that oxytocin can modulate sperm transport in the ram testis. A role for oxytocin in promoting sperm transit is supported by the localization of oxytocin receptors in the cauda epididymis and ductus deferens, and the presence of receptors on Leydig, Sertoli and epididymal epithelial cells provides further evidence that oxytocin may be involved in the local regulation of steroidogenesis.