Progestin and estrogen receptors: characterization and localization in rat submandibular glands, with special reference to epidermal growth factor.

By using progestin (P) and estrogen (E), the localization and characterization of both steroid receptors were examined in the submandibular gland (SMG) of 6-week-old immature castrated rats, with special reference to localization of epidermal growth factor (EGF). In the castrated male and female rats, both 3H-estradiol-17 beta (3H-E2 beta) and 3H-promegestone (3H-R5020) bound to SMG cytosol with high affinity and low capacity. These values were similar to those reported for other tissues. However, E-treatment after castration inhibited the specific binding. In sucrose density gradient ultracentrifugation, it was found that P receptors in both castrated males and females had a sedimentation coefficient of 7S, whereas E receptors had sedimentation coefficients of 4S and 7S. A histochemical study of the SMG of castrated male and female rats showed that the E-peroxidase complex (EPC)- and P-peroxidase complex (PPC)-stained cells were predominantly located in the epithelium of the duct system including the excretory duct and the granular convoluted tubules. Few cells were located in the intercalated duct, and none were found in the acinus. EGF-immunoreactive cells were also located in the epithelium of the same tissue region as in PPC- and EPC-stained sections. Moreover, E-treatment after castration inhibited the intensity of staining and immunoreactivity. These results clearly suggest that rat SMG contains specific P and E receptors which are mainly located in the epithelial cells of the duct system in which EGF-containing cells are identified. We discussed the possibility that P and E might affect EGF immunoreactivity, which reflects EGF production, through their receptors in the epithelium of the duct system.