Induction of progestin receptors in the rat MtTF sub(4) tumor of pituitary origin whose growth is inhibited by estradiol

When the MtTF sub(4) pituitary tumor was grown in male rats not treated by estradiol, the cytosol prepared from it contained very few binding sites for the synthetic ( super(3)H)ORG progestin. Following estradiol treatment there was a reversible increase of these binding sites. The ligand specificity and the sedimentation constant were shown to be similar to those of progestin receptors contained in other tissues. Daily treatment for 8 days with 10 mu g 17 alpha -estradiol. 50 mu g dihydrotestosterone or 50 mu g dexamethasone did not induce progestin binding.