The effects of estrogen on single dose dimethylnitrosamine carcinogenesis in male inbred Crl/CDF rats

Abstract

The effect of longterm estrogen treatment (estradiol valerate) on male rats injected i.p. once with dimethylnitrosamine (DMN, 30 mg/kg, with protein starvation), was studied in 167 male inbred Crl/CDF rats. DMN was given at 40 days (immature rats) or at 90 days (mature rats) to investigate the action of carcinogen and hormone at different stages of development. Estrogen reduced life expectancy of male animals, and was associated with greatly increased breast tumour incidence (to 30%) compared with controls (3%, p p p p p p < 0.001), but only developed in mature DMN-treated rats if they received estrogen as well.