Intracellular localization of Prostatic Binding Protein (PBP) in rat prostate by light and electron microscopic immunocytochemistry.

Extra- and intracellular distribution of Prostatic Binding Protein (PBP) was studied in the different genital organs of the male rat by immunocytochemistry at the light and electron microscopic levels. PBP was extracted from cytosols of rat ventral prostate and used for immunization of rabbits. The specificity of the antiserum raised was tested by "western blotting" and immunoelectrophoresis. From the different fixatives tested for optimal structural and antigenic preservation of the ventral prostate a mixture containing 2.5% paraformaldehyde, 0.5% glutaraldehyde and 0.5% CaCl2 in cacodylate buffer, 0.05 M, pH 7.3 was selected. Using the immunofluorescence technique and the unlabeled antibody enzyme method PBP-immunoreactivity was detected at the light microscopic level in the luminal secretions of the ventral prostate. No reaction was observed with the seminal vesicle, the coagulating gland, the dorsal and lateral prostates, the epididymis and the testis. Intracellular secretory granules reacting with PBP antiserum were exclusively found in the secretory cells of the ventral prostate. Insufficiently fixed cells showed a diffuse generalized reaction of the cytoplasm indicating a leakage of the antigen from the secretory granules. Such artifacts were common in tissue sections processed with the preembedding-staining procedure. At the ultrastructural level therefore mostly the postembedding staining method was performed using both the unlabeled antibody enzyme method and the ferritin-labeled immunoglobulin technique in osmicated, Epon-embedded tissue. Labeling with either method was intense in the secretory granules and the condensing vacuoles, while the labeling density of the rough endoplasmic reticulum and the Golgi cisternae was in the background range. Castration experiments showed that secretory material displaying PBP immunoreactivity was retained within the acinar lumen of the gland for several days after castration, but was absent from most secretory cells already by four days after castration. Immunocytochemistry of PBP therefore is a very sensitive method for analysing the secretory activity and its androgen dependence of the prostate of the rat.