Morphology, growth characteristics and oestrogen-binding capacity of DMBA-induced mammary tumours from ovariectomized rats.

Tumors were induced in 46 of 52 female Sprague-Dawley rats by gastric intubation of 5 mg of DMBA dissolved in 1 ml of sesame oil given weekly for 5 weeks. From 4 weeks after the final dose tumors were recorded and measured. Bilateral ovariectomy was done 3 days before sacrifice and assay. Excised tumors were immediately immersed in ice-cold Tris-EDTA buffer. Sections were prepared for histological examination. The assay was done by sucrose density centrifugation after administration of (2467-tritiated)-estradiol-17beta in vivo 3 minutes before killing and/or in vitro. For specific estrogen-binding proteins the capacity to bind (tritiated)-estradiol-17beta was not related to the growth characteristics time of appearance or time between ovariectomy and assay. Different tumors had estrogen-binding capacities unrelated to the percentage of neoplastic cells in the tumor amount of inflammation mast cell infiltration or presence of fluid-filled cysts. The number of mitoses and the lipid content of the tumors were correlated with the estrogen-binding capacity in that it was lower in tumors with many mitoses and in those with much lipid in the epithelial cells. Of 19 adenocarcinomas 6 did not regress after ovariectomy. In 5 of the regressed tumors a new growth phase was seen beginning 2 months after ovariectomy. Tumors encountered other than mammary adenocarcinomas were an extraosseous osteosarcoma fibroadenomas and zymbal-gland tumors.