Receptors characterization of intraperitoneally N-nitroso-N-methylurea-induced mammary tumors in rats

Mammary adenocarcinomas induced in female Sprague-Dawley rats by three intraperitoneal injections of N-nitroso-N-methylurea were studied in order to characterize their estrogen (ER), progesterone (PgR), prolactin (PRLR) and epidermal growth factor (EGFR) receptors. All samples evaluated showed the presence of ER and PgR in the cytosol fraction and PRLR and EGFR in the membrane fraction. Q (fmol/mg) and Kd (nM) values were as follows: ER, 56 ± 11 and 0.5 ± 0.1; PgR, 109 ± 25 and 2.2 ± 0.5 and PRLR, 355 ± 75 and 0.5 ± 0.2, respectively. In all tumors studied, two specific sites were found for EGFR one with Q1 = 22 ± 9 and Kd1 = 0.6 ± 0.3, and the other with Q2 = 125 ± 33 and Kd2 = 2.1 ± 0.5. Receptor content was found to be independent of tumor histopathological variety. Displacement index (DI) with estradiol and tamoxifen of [3H]E2-ER binding showed great heterogeneity, with values ranging from 0.01 to 1.54. No correlation between ER content and DI values was found. Antiestrogenic binding sites were not found in the microsomal fraction of ten mammary tumors examined. Proliferation of this experimental mammary tumor may be regulated by a complex interaction of steroid and polypeptide hormones, as well as growth factors.