Biochemical characterization and immunohistochemical localization of progestin and estrogen receptors in castrate rat submandibular gland.

The physicochemical property and immunohistochemical localization of progestin (P) and estrogen (E) receptors (PR and ER) were examined in the submandibular gland (SMG) of 5-8-week-old castrated rats. The localization of epidermal growth factor (EGF) was simultaneously examined in the same tissue. The tissue cytosols from male and female rats specifically bound 3H-promegestone (3H-R5020) and 3H-estradiol-17 beta with high affinity and low capacity; the values were within the range of those reported for other tissues. However, E-treatment suppressed the specific P-binding in the female, whereas it did not in the male. On the contrary, E-treatment did not at all suppress specific E-binding in both sexes. Monoclonal antibodies against PR and ER were mainly located in the epithelium of the excretory duct and granular convoluted tubule, but not in the acinus. The monoclonal antibodies were also located in the large polygonal cell with irregular cell border, probably macrophage in the tissue. The EGF-immunoreactivity was observed in the epithelium of the same tissue region as that in which the monoclonal antibodies were located. The present results clearly suggest that the rat SMG tissue contains specific PR and ER that are mainly located in the epithelium of the duct system where EGF-producing cells are also located. The possibility that P and E may influence EGF-production through their receptors in this tissue was discussed.