Effect of high-dose estrogen on growth and steroid receptor activity in DMBA-induced mammary tumors and uteri of rats.
High doses of estrogen (5-500 micrograms) induce regression of hormone-dependent DMBA mammary tumors in rats at the same rate and degree as treatment with the antiestrogen C1628 (Parke-Davis). In contrast, high dose estrogen stimulated growth of uteri in tumor-bearing rats, while C1628 was antiuterotrophic. Within 72 h following treatment with estrogen, diethylstilbestrol (DES), or C1628, changes in the levels of estrogen receptor (ER) and progesterone receptor (PgR) were evident in both uterine and mammary tumor tissue. Both estrogen and antiestrogen induced depression of the total cytosolic ER and altered the 8S/4S receptor ratio. The tumor cytosolic ER levels of DES- and C1628-treated rats were 4.67 +/- 1.7 fmol/mg protein and 15.89 +/- 3.1 fmol/mg protein, respectively, compared to 48.89 +/- 13.6 fmol/mg protein in tumors of untreated rats. In spite of reduced levels of cytosolic ER, there was an apparent increase in the 8S/4S ratio (62% increase in 8S/4S ER ratio compared to control 8S/4S ratio; p less than 0.05). Total uterine cytosolic ER was low after treatments with DES (5.69 +/- 2.08 fmol/mg protein) or C1628 (94.76 fmol/mg +/- 30.3 fmol/mg protein), as compared to untreated controls (188.2 +/- 7.6 fmol/mg protein). The cytosolic PgR was consistently high in tumors of control rats (42.99 +/- 11.9 fmol/mg protein) and in castrated rats treated with high doses of DES or C1628 (DES, 55.15 +/- 27.0; C1628, 65.07 +/- 9.8 protein).
D000818:Animals; D002369:Castration; D004054:Diethylstilbestrol / Q000494:pharmacology*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy*; D009594:Nitromifene / Q000494:pharmacology*; D011759:Pyrrolidines / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011960:Receptors, Estrogen / Q000187:drug effects / Q000378:metabolism; D011980:Receptors, Progesterone / Q000187:drug effects / Q000378:metabolism; D014599:Uterus / Q000187:drug effects*
D011759:Pyrrolidines; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D004958:Estradiol; D009594:Nitromifene; D004054:Diethylstilbestrol