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 confir med that spermatozoa require some exposure to the epididymal environment fo r normal development of motility and fertilizing ability. in both of these species surgical redirection of spermatozoa from a region just distal to th e 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 si gnificantly reduce the number of spermatozoa in ejaculates or the total spe rm 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 va s deferens. Vas autografts in the rabbit and rat were used to bypass select ed epididymal segments. In rabbits, vascularized grafts were used as bridge s to bypass the distal caput and proximal corpus epididymidis. Despite high rates of graft survival and patency in this species, the motility and viab ility of ejaculated spermatozoa were similar to those observed following hi gh level vasoepididymostomy. In rats, non-vascularized vas grafts also show ed a high survival and patency rate. There was a transitory reduction in sp erm 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 dif ference was observed in sperm motility, sperm viability or fertility betwee n experimental groups and controls. Similar results were obtained when epid idymoepididymostomy was used as the surgical procedure to bypass the same r egions of the epididymis. The evidence considered in this review clearly sh ows that the proximity of vasoepididymal bypass to the testis is inversely related to the state of maturity of ejaculated spermatozoa. More surprising ly, perhaps, it reveals that exposure of spermatozoa to the distal caput an d proximal corpus regions of the epididymis in the rat is not obligatory fo r spermatozoa to develop a level of maturation in the remaining regions of the epididymis sufficient to ascend the female tract and fertilize ova. Thi s finding suggests that the epididymis is more flexible in its functions th an had been considered previously and that sperm maturation may not be as d ependent on specific regional functions of the epididymis as had been previ ously proposed.