Development and use of surgical procedures to bypass selected regions of the mammalian epididymis: effects on sperm maturation.

Microsurgical procedures have been used to examine the function of selected regions of the epididymis. Vasoepididymostomy in the rabbit and rat confirmed that spermatozoa require some exposure to the epididymal environment for normal development of motility and fertilizing ability. In both of these species surgical redirection of spermatozoa from a region just distal to the initial segment into the vas deferens resulted in a significant reduction in sperm viability, motility and fertility compared with untreated animals. Surgical bypass of the distal cauda epididymidis in the rabbit did not significantly reduce the number of spermatozoa in ejaculates or the total sperm output accumulated during exhaustive ejaculations. The capacity of these bypass animals to store spermatozoa may be explained by the post-surgical formation of convolutions in the normally straight segment of the rabbit vas deferens. Vas autografts in the rabbit and rat were used to bypass selected epididymal segments. In rabbits, vascularized grafts were used as bridges to bypass the distal caput and proximal corpus epididymidis. Despite high rates of graft survival and patency in this species, the motility and viability of ejaculated spermatozoa were similar to those observed following high level vasoepididymostomy. In rats, non-vascularized vas grafts also showed a high survival and patency rate. There was a transitory reduction in sperm viability and motility 2 weeks after surgery which was associated with structural changes, especially in the epithelium, in vas bridge autografts during revascularization. Longer term observations (3 and 6 months) showed recovery of epithelial morphology and by three months after surgery, no difference was observed in sperm motility, sperm viability or fertility between experimental groups and controls. Similar results were obtained when epididymoepididymostomy was used as the surgical procedure to bypass the same regions of the epididymis. The evidence considered in this review clearly shows that the proximity of vasoepididymal bypass to the testis is inversely related to the state of maturity of ejaculated spermatozoa. More surprisingly, perhaps, it reveals that exposure of spermatozoa to the distal caput and proximal corpus regions of the epididymis in the rat is not obligatory for spermatozoa to develop a level of maturation in the remaining regions of the epididymis sufficient to ascend the female tract and fertilize ova. This finding suggests that the epididymis is more flexible in its functions than had been considered previously and that sperm maturation may not be as dependent on specific regional functions of the epididymis as had been previously proposed.