Epididymal compounds and their influence on the metabolism and survival of spermatozoa

Epididymal fluid, which is derived from testicular fluid, contains several unusual compounds. Little information is available on the composition of the testicular fluid of primates, but the fluid of the ram, bull, boar, and rat contains high concentrations of inositol and certain amino acids. Analyses have been made of epididymal fluid collected from the cauda epididymis of the Rhesus monkey and several nonprimate species (e.g., ram, bull, dog, stallion, rabbit, guinea pig, rat, and hamster), but similar information on the human is lacking. Cauda epididymal fluid appears to be similar in composition from one mammalian species to another. However, the epididymal plasma differs considerably from blood, lymph, and other extracellular fluids. The environment of spermatozoa in the epididymis is, therefore, highly specialized, and presumably in some way contributes to the prolonged survival of spermatozoa in this organ, and provides substrates for the metabolism of the spermatozoa. The chief characteristics of the cauda epididymal plasma are the low concentration of inorganic ions and the high levels of several unusual organic constituents namely, glycerylphosphorylcholine, carnitine, sialic acid, amino acids, glycosidases, and phosphatases. At least one antifertility compound, namely, orally administered α‐chlorohydrin, appears to be concentrated in the epididymis. Studies on laboratory animals, domestic species, and man, suggest that it inhibits enzymes of the glycyolytic pathway in spermatozoa, and this may be the basis for its antifertility activity.