4 Summary
As spermatozoa migrate passively through the epi-didymis they may acquire from epididymal secretions low molecular weight, water-soluble compounds by a process of iso-volumetric regulation. These may be expended, along with obligatory cellular water, when the cells encounter hypo-osmolal fluids of the male acces-sory glands and female tract fluids. This process of regu-latory volume decrease (RVD) serves to maintain cell volume and prevent flagellar angulation that hinders sperm migration in the female tract. The channels responsible for RVD are located on the sperm cytoplasmic droplet. It is postulated that the inability of immature spermatozoa from the caput epididymidis to fertilize eggs as success-fully as mature spermatozoa from the cauda epididymidis reflects their lowered osmolyte content, which is inadequate for complete volume regulation when suspended in hypo-tonic insemination medium. This in turn leads to angulated flagella that prevent migration through the uterotubal junc-tion and failure to reach the eggs.