This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lindsey, W. F. Articles by Beattie, C. W. Search for Related Content PubMed PubMed Citation Articles by Lindsey, W. F. Articles by Beattie, C. W.

Influence of the Estrous Cycle during Carcinogen Exposure on Nitrosomethylurea-induced Rat Mammary Carcinoma¹

Division of Surgical Oncology [W. F. L., T. K. D., C. W. B.] and Department of Pharmacology [C. W. B.], University of Illinois Medical Center; Department of Surgery, Cook County Hospital [W. F. L., T. K. D.]; and Hektoen Institute for Medical Research, Chicago, Illinois 60612

The influence of individual stages of the rat estrous cycle during exposure to I-nitroso-I-methylurea (NMU) on mammary tumor incidence, latency, number, and cytosol receptor dynamics for estrogen and progesterone was determined. Virgin female Buffalo rats were separated into three groups on Day 53 according to their vaginal smear pattern. NMU (5 mg/100 g body weight, i.v.) was administered in three monthly doses beginning at 53 to 55 days of age on diestrus, proestrus, or estrus between 9:00 and 11:00 a.m. Groups of rats had their second and third injections of NMU on the same day of the estrous cycle as their initial injection. All animals were killed during the morning on a diestrus day. Receptors for estrogen and progesterone were determined by a modified dextrancoated charcoal method and by sucrose density gradient analysis.

Mean latencies to first tumor appearance in diestrus, proestrus, and estrus groups were 104.4, 83.6, and 91.4 days, respectively (p < 0.05, diestrus versus estrus and proestrus) following the first NMU injection. The mean number of tumors per rat was significantly higher in rats injected on proestrus (4.5) or estrus (4.3) than on diestrus (2.0). Estradiol bound to receptor sedimented at 8 and 4 s and was suppressed by diethylstilbesterol and estradiol. Progesterone receptor migrated to 7.8 and 4 s regions. Estrogen receptor incidence (100%) and content (16.7 fmol/mg cytosol protein) was highest in rats injected on diestrus. In the proestrus and estrus injected groups, estrogen receptor incidence was 95 and 63% and content was 10.2 and 11.2 fmol/mg protein, respectively. The affinity of estradiol for its receptor was not significantly altered in any group. Although there were no statistically significant differences in progesterone receptor incidence or affinity between groups, progesterone receptor content (74.6 fmol/mg cytosol protein) was significantly higher in tumors from rats injected on proestrus than on diestrus. These data suggest that the prevailing hormonal milieu of the estrous cycle during NMU exposure may be critically important to the subsequent biological behavior and steroid receptor status of carcinogen-induced rat mammary tumors.

¹ This study was supported by Biologic Research Support Grant 7870 from the University of Illinois and Grant CB 84421 from the National Cancer Institute, NIH.

² To whom requests for reprints should be addressed, at Division of Surgical Oncology, University of Illinois Medical Center, 840 South Wood Street, Chicago, ILL. 60612.

Received 7/18/80. Accepted 7/ 2/81.

This article has been cited by other articles:

				Y.-C. Chou, R. C. Guzman, S. M. Swanson, J. Yang, H. M. Lui, V. Wu, and S. Nandi Induction of mammary carcinomas by N-methyl-N-nitrosourea in ovariectomized rats treated with epidermal growth factor Carcinogenesis, April 1, 1999; 20(4): 677 - 684. [Abstract] [Full Text] [PDF]