Blood-tissue barriers in the male reproductive tract of the dog: a morphological study using lanthanum nitrate as an electron-opaque tracer

Blood-tissue barriers preventing an uncontrolled exchange of larger molecules between adjacent but metabolically separate compartments have been demonstrated in various organs. One prominent example is the blood-testis barrier which has been investigated in a number of species. A key function of this barrier is to shield developing germ cells from the immune system in order to avoid autoimmune reactions. This requirement also applies to the male excurrent duct system. Yet, very few investigations have addressed the morphology of the blood-epididymal barrier. The goal of the present study, therefore, was to revisit the blood-testis barrier in the dog and to identify the structures constituting the blood-epididymal barrier in this species. Lanthanum nitrate was used as a tracer for electron microscopy. In the testis, lanthanum had free access to the intercellular space of the seminiferous epithelium up to the Sertoli cell junctions. Similarly, epithelial tight junctions were found to represent the permeability barrier in the epididymis. The present study highlights species differences with respect to the blood-testis barrier and extends the knowledge of the blood-epididymal barrier by providing morphofunctional data in this domestic species.