Steroid metabolism and steroid receptors in dimethylbenz(a)anthracene-induced rat mammary tumors.

Mammary tumors were induced in rats by treatment with dimethylbenz(a)anthracene. Cytosol receptors for 17 beta-estradiol and progesterone were estimated by means of sucrose density gradient centrifugation, and the metabolism of [14C]progesterone, [14C]testosterone, and 17 beta-[14C]estradiol by minced tumor tissue was studied. The estradiol receptor (ER) and progesterone receptor (PR) levels of the tumors varied considerably from less than 5 to 48 fmol/mg protein for ER and to 243 fmol/mg protein for PR. Considering a receptor level lower than 5 fmol/mg protein to be negative, four groups of tumors were found: ER-negative and PR-negative; ER-positive and PR-negative; ER-negative and PR-positive; ER-positive and PR-positive. In dimethylbenz(a)anthracene-induced tumor tissue, high 5 alpha-reductase and 20 alpha-hydroxysteroid dehydrogenase activities and somewhat lower 3 alpha-hydroxysteroid dehydrogenase and 6 alpha-hydroxylase activities were found. No aromatization was detectable. Steroids, especially estradiol, were also metabolized in a high degree to unextractable metabolites. It was concluded that steroid metabolism of dimethylbenz(a)anthracene-induced rat mammary tumors was not related to the ER and/or PR concentration of tumor tissue.