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 steroi dogenesis and seminiferous tubule contractility. Oxytocin has also bee n detected in the epididymis of the ram where active uptake of the pep tide from luminal fluid has been demonstrated. This study was performe d to investigate whether oxytocin is present in the rat epididymis, an d 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 concentrati on of the peptide in both intact and castrated rats. Efferent duct lig ation (EDL) did not affect the presence of oxytocin in the epididymis. Immunoactive oxytocin was localized in discrete cells of the epitheli um of the caput epididymis, with les staining apparent in the initial segment and cauda epididymis. Staining disappeared from the caput epid idymis following castration, but reappeared following testosterone sup plementation. No obvious alteration in staining was observed in the ca uda epididymis after EDL. These data demonstrate for the first time th e presence of oxytocin in the epididymis of the rat and that the pepti de may be regulated by androgens. They further suggest an epididymal s ource of the peptide.