Linear sucrose gradient analyses reveal that all estrogeninduced and -dependent primary renal tumor cytosols examined contain an 8 S and variable amounts of 4 S receptor in low ionic buffer concentrations. Similar results were obtained with extracts of primary metastases of these tumors. Sucrose gradients containing high salt (0.4 m KCI) convert the 8 S receptor in both the hamster renal tumor and uterus to a 4 to 5 S complex. Scatchard plot analysis reveals that the renal tumor cytosol estradiol-receptor complex has a Ka of 1.7 × 109m-1 and 9.2 × 10-10m binding sites. Competition for the tritiated 17β-estradiol binding sites in the renal tumor was similar to that in the uterus with respect to estrogenic compounds. Nonestrogenic steroids exhibited minimal competition at the same concentrations or higher. Substitution in the ring structure, particularly in position 3 of the phenolic A-ring, resulted in a considerable loss in the ability of such compounds to compete for these receptors. Antiestrogens were effective competitors for these estrogen receptors only at higher concentrations relative to the tritiated estradiol.

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Supported by Grant HD 00006-12 from the National Institute of Child Health and Development; Grant CA 16854-01 from the National Cancer Institute, NIH; and Research Service, Veterans Administration Hospital, Minneapolis, Minn. Presented in part at the 57th Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, N. J., April 15 to 20, 1973.

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