Abnormal fluid transport by the epididymis as a cause of obstructive azoospermia

It has been known for more than a decade that in many mammalian species including man, spermatozoa once shed from the testis are immature, immotile and incapable of fertilizing the ovum. During their transit through the epididymis, they undergo various morphological and functional changes that confer on them the ability to ascend the female tract, to undergo an acrosome reaction, to penetrate the zona pellucida and to effect a successful fertilization. By the time spermatozoa have reached the cauda epididymidis, they are held in a quiescent state by factors in the epididymal fluid. The epididymis plays a vital role by creating a favourable fluid environment for sperm maturation and storage. The exact mechanisms underlying sperm maturation and storage are unclear and it appears that no single epididymal factor is held entirely responsible. In contrast, spermatozoa are directly bathed in the epididymal fluid; the fluidity of the microenvironmental has a direct effect on epididymal spermatozoa. The epididymal epithelium has been shown to transport electrolytes and water by processes involving ion pumps, ion carriers and ion channels. These components are under nervous, hormonal and paracrine control and are susceptible to interference by pharmacological agents. This paper reviews the physiology of electrolytes and fluid transport in the epididymis and describes how abnormal fluid transport across the epididymal duct could predispose towards epididymal obstruction, a condition that may occur in cystic fibrosis, Young's syndrome or other unexplained cases of male infertility.