In defense of a function for the human epididymis.

In view of reports that the human epididymis may play no role in human fertility, literature on the fertilizing capacity of epididymal spermatozoa was reviewed. The survey indicates that under the circumstances of their retrieval, human epididymal and testicular spermatozoa may have the ability to fertilize human eggs both in vivo and in vitro. Although the "fertility profile" of the normal epididymis cannot be explored in man, a fair assumption would be that fertilizing capacity develops fully in the distal part of the tract, judging from the higher motility and egg fusing ability of sperm taken from these regions of unobstructed tissue. Motility and fertilizing capacity observed with IVF or artificial insemination, in which sperm are obtained from obstructed ducts, may occur at a level in the tract more proximal than normal, as in animals. The pregnancies resulting from aspiration of spermatozoa from, or anastomosis of the vas deferens to, the efferent ducts are of great clinical interest, but the pathological state of the tissue precludes definitive statements about the functioning of a normal epididymis. In the former case, the immediate origin of the fertilizing spermatozoon and the nature of the secretions previously bathing it are unknown and in the latter case the time needed before pregnancies occur is much greater than anticipated had fertile sperm been present in the proximal epididymis. The evidence supports neither the view that testicular sperm are inherently fertile nor that a simple aging of sperm cells is sufficient for the fertilizing potential of spermatozoa to be realized. It emphasizes, rather, the importance of the environment to which the sperm cells are subjected. Under abnormal conditions other accessory glands may secrete compounds that are necessary for the maturation of spermatozoa. Before more information is known of the exact situation existing, or having existed, in pathological human tissues from which fertilizing human spermatozoa can be obtained, great caution should be exercised in interpreting the results of pregnancies arising from the in vivo and in vitro insemination of testicular or epididymal spermatozoa.