Oxytocin (OT) is a neuro hypophysary peptidic hormone traditionally known as a "female" hormone. This hormone plays a role in childbirth and in milk ejection. However, important endocrine and paracrine functions in the male reproductive tract has been suggested, including increased smooth muscle contractility (testes, epididymis, prostate), the induction of penile erection, the modulation of transport and maturation of sperm and sexual behavior .Because of the importance of this subject, the present study aimed to correlate the immunostaining of oxytocin receptors with the distribution of smooth muscle in the epididymis and testis of dogs. Testes and epididymides of five dogs were collected by elective orchiectomy and fixed in 10% buffered formaldehyde. Samples were fragmented, fixed for 24 h, and then transferred to 70% alcohol. After washing with phosphate buffered saline (PBS), samples were submitted to routine histological processing, deparaffinization, dehydration and recovery of antigenic sites. Incubation was then performed with primary anti-OTR human polyclonal antibody produced in rabbits and the polymer NOVOLINK (Nichirei ®).Our results showed that the morphological distribution of the smooth muscle of the epididymis and testicle is correlated with immunostaining of OTR receptors. The distribution of the musculature and the OTR immunostaining was observed in the testis and epididymis of dogs and myoepithelial cells, possibly relating to the events of muscle contraction and sperm movement in the genital tract, essential to the success of male reproductive success. This study corroborate with the compared study allowing the description of the role of oxytocin in the male reproductive system, since, so far, the basic descriptions in literature only mention their role in the female reproductive system.

Acknowledgements: The authors want to thank FAPESP for financial support (Process: 2013/00888-1 and 2013/25674-4).