Difference in abundance of blood and lymphatic capillaries in the murine epididymis.

It is well known that the epididymis is responsible for the transportation, storage, and maturation of spermatozoa, and that it has four segments: i.e., initial segment, caput, corpus, and cauda. Previous studies revealed the presence of a very dense network of blood capillaries only in the initial segment; however, the relative distribution of blood and lymphatic capillaries has remained unknown. In the present study, we investigated the distribution of intraepididymal blood and lymphatic capillaries in mice by use of monoclonal antibodies against CD31 and lymph vessel endothelium HA-receptor 1, respectively. The results showed that lymphatic networks were quite scarce in the initial segment and strikingly abundant in the cauda compared with the other two regions. In sharp contrast, blood capillaries were abundant in both the initial segment and cauda but sparse in the other two regions. This observation suggests that the characteristic distribution of blood and lymphatic capillaries in the epididymis contributes to the different roles of each epididymal region.