The epididymis re-visited: a personal view

The sperm maturation and storage functions of the epididymis are important determinants of ejaculate quality, and perhaps provide an avenue to male contraception. In the last 50 years, the creation of epididymal fertility profiles in laboratory animals was followed by recognition of new sperm maturation-related parameters (organization of the acrosome, of the sperm plasmalemma, and -S-S- -based structural change) which made it possible to confirm that a similar pattern of sperm maturation obtains in man. The novel sperm storage function of the cauda epididymidis in therian mammals is regulated by androgen, usually in conjunction with the low temperature of the scrotum. The temperature-dependence of the scrotal cauda is reflected in the secretory and ion transport functions of the epithelium, in its duct dimensions and so in sperm storage capacity. Moreover, a variety of indirect evidence suggests that an elevated temperature of the cauda created by clothing may be compromising its function in man. The pattern of change in the sperm plasmalemma involving sterols, and also glycosylphosphatidylinositol-linked macromolecules as spermatozoa enter the cauda region, may underlie the need for their capacitation subsequently in the female tract. Further, in a variety of taxa the anatomy of the scrotum, together with the U-shaped configuration of the epididymis/vas deferens, suggests that the cauda's storage function may also underlie the evolution of the scrotum. Finally, despite the still relative paucity of comparative evidence, we can consider now why the epididymis has come to be organized as it is.