Ultrastructural and histochemical observations on the principal cells of monkey epididymis

A correlative ultrastructural and histochemical study of the epididymal principal cells was carried out on six normal mature macaque monkeys with known reproductive histories. The outstanding cytologic feature of the principal cells was the abundance of infranuclear electron-dense granules (0.2-0.5 micronsm). These cellular inclusions are found in close proximity with large clusters of small mitochondria and to the subepithelial and periductular capillaries surrounding the basal epithelium. Histochemical tests revealed that these granules do not contain acid phosphatase, are not lipid, but do contain mucopolysaccharides and glycoprotein moieties. This intriguing morphological characteristic of the infranuclear region of the principal cells is similar throughout the entire length of the epididymis and appears to be unique in the monkey. The close relationship of these secretion type granules to mitochondria and their proximity to basal epithelial capillaries is in agreement with the concept of epididymal secretion and a possible endocrine function of the mammalian epididymis must be considered.