Abstract
The aim of this study was to investigate the effects of repeated administrations of relatively low doses of 7,12-dimethylbenz[a]anthracene (DMBA) on the induction of mammary carcinomas (MCs) and dysplasias (MDs) in rats. DMBA at 0, 0.1, 0.2, 0.5 and 1 mg for female rats, and at 0, 0.5, 1 and 2 mg for male rats was administered twice weekly after weaning. In female rats, repeated administration of 1 mg DMBA induced MCs while 0.1 mg DMBA induced MDs in all animals. The incidence of MCs increased and the latent period shortened while the incidence of MDs decreased in a dose-dependent manner. In male rats, repeated administration of 2 mg DMBA induced MCs in all animals. The incidence of MCs increased and the latent period shortened in a dose-dependent manner while the incidence of MDs increased by repeated administration of 1 mg DMBA. These results suggest that the total exposure of chemical carcinogens may be responsible for the induction of MCs or MDs, and that MDs may be more dependent on female sex hormones than MCs.
