Biochemical and immunohistochemical characterization of prolactin binding in rat ventral, lateral, and dorsal prostate lobes.

A radioligand assay and the soluble peroxidase-antiperoxidase (PAP) technique were used to compare ovine and rat prolactin as ligands for the demonstration of prolactin binding sites in rat ventral, lateral, and dorsal prostate lobes. Biochemical techniques were effective in demonstrating prolactin binding sites in ventral prostate with both ovine and rat prolactin; however, binding sites could not be characterized in lateral or dorsal lobes with either ligand. Using the PAP technique, rat prolactin consistently produced a discrete, dense reaction product over binding sites in the Golgi zone of the ventral prostate; ovine prolactin produced a more dispersed pattern of staining throughout the entire supranuclear region of the cells. In ventral prostate, most epithelial cells were immunoreactive when either ligand was used. However, lateral prostate contained fewer densely immunoreactive cells than did ventral prostate, and rat prolactin was more effective in demonstrating these binding sites than was ovine prolactin. Dorsal prostate epithelium was highly immunoreactive for binding of both ligands; however, there was considerably more staining in this lobe that remained after absorption of the antibody with prolactin. These data suggest that the inability to demonstrate prolactin binding sites in the lateral lobe using radioligand assay may have been due to the fewer numbers of binding sites that were diluted below the sensitivity of the assay when a tissue homogenate preparation was used. Noncompetitive binding in the dorsal lobe, as seen in the radioligand assay, coincided with immunocytochemical findings of relatively high nonabsorbable background staining.