p-Nonylphenol pretreatment during the late neonatal period has no effect on 3,2′-dimethyl-4-aminobiphenyl-induced prostate carcinogenesis in male F344 rats

The modifying effects of late neonatal administration of p-nonylphenol (NP), a suspected xenoestrogen, on 3,2′-dimethyl-4-aminobiphenyl (DMAB)-induced prostatic carcinogenesis were investigated in male F344 rats. Three-week-old rats received 25, 250 or 2000 ppm of NP in the diet for 3 weeks prior to DMAB treatment and were sacrificed at 67 weeks of age for histopathological assessment of lesions and Ki-67 immunohistochemical analysis of cell cycle kinetics. Dietary administration of NP during the sexually immature period had no effects on maturation of male sex organs. Incidence, multiplicity and areas of neoplastic lesions in the prostate and seminal vesicles, and Ki-67 labeling indices in normal-looking epithelium were not significantly different among the experimental groups. These results indicate that late neonatal treatment with NP has no modulating effects on DMAB-induced rat prostatic carcinogenesis.