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.

The long-term effects of oxytocin administration on the testis were studied using intratesticular implants. Adult male rats had an Accurel device containing 20 micrograms oxytocin (releasing approximately 200 ng/day) implanted into the parenchyma of each testis; control animals received empty devices. The animals were killed at weekly intervals for 4 weeks. Some animals were perfused and the testes processed for light and electron microscopy. Blood was collected from the remaining animals for the measurement of testosterone, dihydrotestosterone, LH, FSH and oxytocin; epididymal sperm counts were measured and the testes were extracted and radioimmunoassayed for testosterone, dihydrotestosterone and oxytocin. Long-term administration of oxytocin resulted in a significant reduction in testicular and plasma testosterone levels throughout the 4-week period examined and, after 14 days of treatment, lipid droplets were seen in the Leydig cells of treated but not control animals. Concentrations of dihydrotestosterone in the plasma and testes of the oxytocin-treated animals, however, were significantly elevated after 7 and 14 days and at no time fell below control values. Plasma FSH levels were also lower in the oxytocin-treated animals. Intratesticular oxytocin treatment did not affect LH or oxytocin concentrations in the plasma, epididymal sperm counts or the number of Leydig cells in the testis. Empty Accurel devices had no effect on testicular morphology. This study provides the first evidence that oxytocin in vivo can modify steroidogenesis in the testis.

Contractions of seminiferous tubules and epididymal duct walls promote spermiation and sperm transfer, and they are thought to be stimulated by the related peptides oxytocin and vasopressin. This study tested the hypothesis that if oxytocin and/or vasopressin play a physiological role in sperm shedding and transport, then local or circulating concentrations of these peptides would increase during puberty. Testes, epididymides, and trunk blood of sheep at stages during the first spermatogenic wave were collected, and radioimmunoassay measured significant increases in testicular and epididymal oxytocin during spermatogenesis. No changes were measured in circulating oxytocin or in local or circulating vasopressin. Localization and synthesis was investigated by immunohistochemistry and Western blot analysis employing antibodies recognizing epitopes of either oxytocin, oxytocin-associated neurophysin, vasopressin, or vasopressin-associated neurophysin. Marked expression of both oxytocin and its associated neurophysin in testicular Leydig and epididymal principal cells was seen, and weak neurophysin immunoreactivity was also identified in Sertoli cells. The intercellular distribution of oxytocin varied between regions of the epididymis, suggesting several roles for oxytocin. Vasopressin synthesis was not apparent in either tissue. These results confirm the presence and development of paracrine oxytocinergic systems in the ram testis and epididymis of ram during puberty while questioning the physiological importance of vasopressin.

Oxytocin is present in the mammalian testis where it increases contractility of seminiferous tubules in vitro and has been implicated in sperm transport. The

The bovine oxytocin gene has been expressed in the testes of two independent transgenic mouse lines. Hybridization and RNase protection analysis showed that the oxytocin transgene was transcribed from the normal functional promoter in the Sertoli cells of the seminiferous tubules in a developmentally regulated manner. Immunohistochemistry indicated that both oxytocin and neurophysin epitopes were expressed together in the Sertoli cells at stages I\p=n-\Vand X\p=n-\XIIof the cycle of the seminiferous epithelium. Furthermore, analysis with high-performance liquid chromatography showed that there was a tenfold increase in the amount of amidated oxytocin present in testicular extracts from the transgenic mice. However, there appeared to be no detectable effect of this overproduction of hormone on testicular morphology or fertility parameters. A significant decrease by 50% was detected only in the levels of intratesticular testosterone and dihydrotestosterone. The results point to a local paracrine role for oxytocin in the modulation of Leydig cell function.