Epididymal oxytocin in the rat: its origin and regulation

Oxytocin is localized to the Leydig cells of the testis in the rat and several other species where it is postulated to play a role in steroidogenesis and seminiferous tubule contractility. Oxytocin has also been detected in the epididymis of the ram where active uptake of the peptide from luminal fluid has been demonstrated. This study was performed to investigate whether oxytocin is present in the rat epididymis, and the origin of the peptide. Immunoactive oxytocin was detected in the epididymis of all control animals examined (147.7 +/- 41.7 pg/g). Total epididymal oxytocin was reduced significantly following castration (p < 0.05). Testosterone treatment also reduced the epididymal concentration of the peptide in both intact and castrated rats. Efferent duct ligation (EDL) did not affect the presence of oxytocin in the epididymis. Immunoactive oxytocin was localized in discrete cells of the epithelium of the caput epididymis, with less staining apparent in the initial segment and cauda epididymis. Staining disappeared from the caput epididymis following castration, but reappeared following testosterone supplementation. No obvious alteration in staining was observed in the cauda epididymis after EDL. These data demonstrate for the first time the presence of oxytocin in the epididymis of the rat and that the peptide may be regulated by androgens. They further suggest an epididymal source of the peptide.