Ultrastructural differences in efferent ducts and several regions of the epididymis of the hamster

Abstract The ultrastructure of the hamster efferent ducts and epididymis was studied and the results were correlated with previously published data on the composition of luminal fluid obtained by micropuncture. Samples of the efferent ducts and parts of the epididymis designated initial segment, caput, corpus, proximal cauda, distal cauda, and “epididymal vas” were prepared. The efferent ducts contained principal cells characterized by a profusion of apical vesicles and numerous very large vacuoles that were distributed throughout the cytoplasm. Ciliated cells had few vesicles and vacuoles. Occasional cells contained many particles resembling glycogen. In the epididymis, the following trends were observed. The height of the epithelium and the size of the principal cells declined from initial segment to distal cauda. Apical vesicles and vacuoles with a light content were extremely numerous in principal cells of the initial segment and decreased progressively in the more distal regions. In the initial segment, basal and perinuclear rough endoplasmic reticulum was abundant and was distended with a material that resembled newly synthesized protein. Further distally in the epididymis cisternae of the rough endoplasmic reticulum were narrow and contained little intracisternal material. Light cells containing many vesicles, vacuoles, and lysosome‐like structures were very prominent in the caudal segments. The epithelium of the epididymal vas had features intermediate between cauda epididymidis and ductus deferens. The cytoplasmic droplet in luminal sperm began to migrate caudally between the caput and corpus epididymidis and reached the posterior extremity of the middle piece in the distal cauda. Some degenerating sperm were observed in the lumen of the distal segments of the epididymis. The abundance of cytoplasmic vesicles and vacuoles in principal cells of the efferent ducts and initial segment of the epididymis correlated with the site of greatest fluid absorption as determined by micropuncture studies, suggesting that these structures are involved in absorption of fluid from the lumen. Between the caput and distal cauda epididymal segments, where absorption of sodium and potassium but not of fluid occurred, there were few vesicles and vacuoles in principal cells, but the “light” cells were large and numerous and contained many vacuoles. The principal cells of the initial segment were best equipped with rough endoplasmic reticulum to synthesize a protein.