Interactions between rat epididymal epithelium and spermatozoa.

We studied in the rat epididymis the presence of membrane-bounded vesicles in the stereociliar areas of the epithelial cells. The intimate contact between principal cell stereocilia and luminal spermatozoa was also explored. The epididymidis of adult male albino rats were fixed with Mollenhauer's fixative via the thoracic aorta; they were removed and the caput and the cauda were separated and fixed for 4 additional hours at 4 degrees C. After fixation, the samples were processed with routine techniques for transmission and scanning electron microscopy. The study showed membrane-bounded vesicles in the lumen of the caput and cauda epididymidis. They are present between stereocilia, in the most peripheral regions of the epididymal lumen, and in a stereocilia-free zone in the apical plasma membrane of the principal cells. The smaller vesicles are located near the apical surface of the latter, and the larger ones are located near the tips of the stereocilia. Their contents are electron lucent in some images and electron dense in others. In several thin sections some of the vesicles are observed to have a stalk. This suggests that the possible mode of production may be an exocytotic process. Some membrane-bounded vesicles were found to be in contact with the head or the tail of maturating spermatozoa. Moreover, an intimate contact was found to exist in the epididymidis between the plasma membranes of the spermatozoa and the stereocilia. These observations seem to suggest two possible mechanisms for sperm-epididymal cell relations: 1) release of a secretion product via the membrane-bounded vesicles and 2) direct contact between stereocilia and spermatozoa.