REGIONAL DIFFERENTIATION OF THE BLOOD-EPIDIDYMIS BARRIER IN STALLION (EQUUS-CABALLUS)

The occurrence, localization and ultrastructural characteristics of a blood-tissue barrier throughout the stallion proximal seminal excurren t duct system were studied by the exclusion of electron dense tracers and freeze-fracture techniques. Striking differences were observed in the distribution of lanthanum tracer and in the geometrical organizati on of the zonulae occludentes along the ductus efferentes, epididymide s and vas deferens. The zonulae occludentes domain, the principal stru ctural component of the blood-epididymis barrier, differed in permeabi lity, width and strand numbers along the ductus. The flow of tracer wa s not impeded by the vascular endothelium, the peritubular myoid layer or other surface membrane specialization. The tight junctions of the ductuli efferentes are poorly developed but unlike those of rats, guin ea pigs or man they are not associated with gap junctions. The result of the tracer experiments and the low number of tight junctional stran ds in the ductuli efferentes suggest that the barrier of the ductuli e fferentes corresponds to the 'leaky type'. In the epididymis the zonul ae occludentes are well developed throughout the duct. The greatest nu mber of strands, especially in the cauda epididymidis regions, correla tes well with a decreased junctional permeability in this area. Anothe r evidence for the existence of the stallion blood-epididymis barrier are the differences in the proteins electrophoretic profiles between b lood plasma as compared with the fluid inside the seminal ductus. This junctional complexes contribute to create a highly defined luminal fl uid microenvironment that ensures the sperm maturation and survival.