Evidence for Androgen-Dependent Intracellular Binding of Prolactin in Rat Ventral Prostate Gland1

Abstract

In an attempt to localize endogenous prolactin (PRL) in rat ventral prostate gland at the light microscope level, the following 4-step immunohistochemical reaction sequence was applied to fixed tissue sections: goat anti-monkey .gamma.-globulin (AM.gamma.G), NIAMDD rabbit anti-rat PRL (APRL), goat anti-rabbit .GAMMA.-globulin: peroxidase conjugate (AR.GAMMA.G-per) and chromogenic substrate. AM.GAMMA.G was required to block the nonspecific staining pattern produced by direct binding of AR.GAMMA.G-per to the tissue and unmask that produced by APRL. APRL-dependent staining occurred in the Golgi region of ventral prostate epithelial cells. Golgi region staining was attenuated and eventually disappeared with increased APRL dilution and was not reproduced when normal rabbit serum or rabbit antisera to rat LH [luteinizing hormone] or rat TSH [thyrotropin] replaced APRL. Absorption of APRL with highly purified NIAMDD rat PRL (I-1) neither attenuated nor eliminated Golgi region staining. The APRL-dependent staining of rat ventral prostate gland probably was not due to endogenous PRL in the tissue. Nonabsorable APRL-dependent staining pattern is, as yet, unexplained but might involve binding of the PRL portion of APRL-PRL complexes to PRL binding sites in epithelial cells of ventral prostate gland. To test for PRL binding sites, tissue sections were exposed to varying doses of rat PRL I-1 before the 4-step immunohistochemical reaction sequence. PRL preincubation produced, in a dose-related fashion, immunospecific Golgi region staining indicative of intracellular PRL binding sites (IPBS). IPBS were androgen-dependent, disappearing after castration and returning when atrophic ventral prostate glands were stimulated by testosterone treatment. In androgen-restored tissue intracellular PRL binding occurred in the Golgi region or involved the entire cytoplasm. Whether or not androgen-dependent IPBS represent a physiological receptor for PRL in rat ventral prostate gland remains to be determined.