It has previously been shown that the rat cauda epididymidis actively reabsorbs Na+ in exchange with K+. This coupled Na+/K+ transport is stimulated by aldosterone. These transport processes create a low Na+ and high K+ environment which appears to be (in part) responsible for sperm quiescence during storage. The effects of aldosterone antagonist, spironolactone, on the electrolyte and water content of the cauda epididymidis, sperm motility initiation and fertility of male rats were investigated in the present study. It was found that treatment of rats with spironolactone (10 mg/kg per day for 4 to 17 days) led to a significant fall in K+ (18%) and sperm (21.5%) concentrations in the cauda epididymal fluid. However, the Na+ concentration remained unchanged. The fall in sperm concentration may be taken to indicate an increase in fluid volume which is secondary to an inhibition of water absorption. When corrected for an increase in volume, there was no change in the amount of K+ in the fluid but the amount of intraluminal Na+ was increased. Despite a fall in K+ and sperm concentration, the capacity of the cauda sperm to initiate motility and fertility of the animals were apparently not affected by spironolactone treatment. It is concluded that the fertility capacity of spermatozoa is rather resistant to drugs which interfere with electrolyte and water transport across the caudal epididymal epithelium.

The epididymis secretes C1- upon stimulation with secretory agonists. This creates an osmotic gradient for isosmotic fluid secretion. Electrolyte and fluid secretion by the epididymis regulates the fluidity of the luminal content. Defective secretion in cystic fibrosis leads to obstruction and atrophy of the epididymis, hence to male infertility.

Sperm maturation in the rat epididymis is dependent on the secretion of specific proteins by the epididymal epithelium and subsequent interaction of these proteins with spermatozoa. Evidence has shown that fertility and motility development of epididymal spermatozoa may be impaired by interfering the interaction of these proteins with spermatozoa. When the spermatozoa reach the cauda epididymidis, they are fully mature but their longevity is maintained by being stored in a quiescent state in the cauda. The unique ionic medium therein (low Na+, low Ca2+, high K+ and low pH) suppresses sperm motility and hence reserving energy for the vital processes of capacitation and fertilization. During ejaculation, when the spermatozoa are mixed with the copious secretion from the accessory glands they burst into vigorous motility. This results from an influx of sodium coupled to efflux of K+ and H+ across the mature sperm membrane. In the presence of a peptide secreted by the cauda epididymidis, these ionic events activate the already mature but otherwise inactive spermatozoa to full motility.