Histochemical localization of zinc ions in the epididymis of the rat.

In the present study, the autometallograpic zinc sulphide technique, an improved version of the original Timm sulphide-silver method, was used. This technique reveals a particular pool of ionic zinc that is chelatable by diethyldithiocarbamate. At the light microscopical level, no reaction for zinc was found in tissues of young prepubertal rats. In adult mating and non-mating rats low zinc staining was found in the head and intermediate epididymis whereas the tail of the epididymis demonstrated high levels of zinc ions. Sections from the epididymal tail revealed a 'compartmentalization', based on pronounced differences in staining intensity along the epididymal ducts. At higher magnification zinc ions were found in the apical part of the principal cell and in the lumen. At the ultrastructural level autometallographic grains were located in vesicles and in lysosome-like structures of the apical parts of the principal cells. The luminal grains were found either associated with sperm cells, with the surface of the large microvilli (stereocilia), or free in the seminal fluid. The variation in content of zinc ions in the epididymal epithelium and lumen suggests that zinc ions are secreted into the lumen from the epididymal tail and may somehow be involved in maturation of the sperm cells.