Localization of oxytocin receptors in the human and macaque monkey male reproductive tracts: evidence for a physiological role of oxytocin in the male.

The peptide oxytocin is present in tissues of the male reproductive tract from a variety of mammalian species. In the human, specific mRNA for oxytocin and the peptide itself have been identified in the testis, epididymis and prostate. The peptide has been shown to modulate both steroidogenesis and contractility in the male reproductive tract and may be involved in the pathogenesis of benign prostatic hyperplasia. We have performed Western blots and immunohistochemistry using a specific antibody to the human oxytocin receptor (OTR) to investigate the distribution and localization of the receptor in the human and macaque monkey (Macaca fasicularis). An immunoreactive band of approximately 55 kDa was detected in human and monkey uterine, testicular and prostatic tissues and in preparations of monkey caput and cauda epididymis. A second, less intense, band of 60 kDa was also seen in testicular and uterine tissue samples. No specific bands were detected in monkey muscle or in any tissue following incubation with mouse immunoglobulin (Ig)M. In the human and monkey testis staining for the OTR was present in the interstitial tissue and in Sertoli cells. Localization of the OTRs varied throughout the epididymis being expressed by epithelial cells proximally but confined to cells at the base of the epididymal ducts and to the surrounding smooth muscle layers distally. In the prostate OTR were localized to the stromal tissue surrounding the ducts. These findings correlate with sites of local production of the peptide and the observed biological actions of oxytocin, and thus support the evidence that oxytocin may play a physiological role in the male reproductive tract.