Promoting effects of ethinyl estradiol on development of renal proliferative lesions induced by N-nitrosobis (2-oxopropyl)amine in female Syrian golden hamsters.

The modulating effects of female sex hormones, ethinylestradiol and levonorgestrel, on the development of renal proliferative lesions after initiation with N-nitrosobis(2-oxopropyl)amine (BOP) were investigated. Three groups of female Syrian golden hamsters, each comprising 30 animals, were given four weekly s.c. injections of BOP (10 mg/kg body weight) and then fed diet containing 1 ppm ethinylestradiol (group 1: BOP/EE), diet containing 10 ppm levonorgestrel (group 2) or basal diet (group 3) for the next 27 weeks. As hormone controls, two groups of 20 female hamsters each received diet containing 1 ppm ethynylestradiol (group 4) and 10 ppm levonorgestrel (group 5) from week 3 for 27 weeks without the prior initiation treatment. The severity of diffuse anisokarya, characterized by varied nuclear size and the incidence of dysplasias of the proximal tubular epithelia induced by BOP, were significantly increased in the BOP/EE group, indicating the promoting effects of the hormone. In the renal dysplastic lesions (small-cluster, cystic, clear-cell and acidophilic cell types), adenomas and nephroblastomas, increases in the numbers of argyrophilic proteins associated with nucleolar organizer regions (NOR) in the nucleus, suggesting a high proliferative activity, were seen in dysplasia of acidophilic cell types and adenomas. In addition, the number of bizarre NOR per nucleus was significantly higher in adenomas than in dysplasias and highest in nephroblastomas. This morphological change in NOR should therefore be a useful parameter for the diagnosis of malignancy of renal tumors.