Immunocytochemical localization of metallothionein in the rat prostate gland

Metallothionein (MT), which binds zinc and other metals, was localized within the rat prostatic complex at light and electron microscopic levels utilizing immunocytochemistry. Two groups of mature, male Sprague‐Dawley rats were injected with cadmium chloride subcutaneously (2 mg/kg body weight) to induce the synthesis of MT, and were sacrificed 48 h postinjection. From the first group, prostatic tissue from the three lobes was prepared for light microscopy. The indirect peroxidase antiperoxidase procedure was used for MT localization using rabbit anti‐MT as the primary antibody. The three lobes of the rat prostate demonstrated a positive reaction for MT, but among the lobes variations in the intensity and localization of the reaction product occurred. Tissues from the second group of animals were prepared for electron microscopy. Using the indirect immunogold labeling technique with anti‐MT, MT localization was confirmed in the rough endoplasmic reticulum, secretory vesicles, secretory products, and subepithelial connective tissue. These localizations suggest that MT binds zinc both intra‐ and extracellularly, where it may function in zinc storage and metabolism.