DOSE-DEPENDENT INDUCTION OF MAMMARY CARCINOMAS IN FEMALE SPRAGUE-DAWLEY RATS WITH 2-AMINO-1-METHYL-6-PHENYLIMIDAZO[4,5-B]PYRIDINE

The dose-dependence of 2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridin e (PhIP) induction of mammary carcinomas was investigated in female Sp rague-Dawley (SD) rats given PhIP in the diet for 48 weeks at concentr ations of 0, 25, 100 and 200 ppm in experiment 1, and 0, 12.5, 50 in e xperiment 2. Yields of ductular lesions, including intraductal papillo mas and carcinomas, as well as papillo-tubular and solid-tubular carci nomas, showed dependence on the dose, with the respective total incide nces being 0, 4.8, 25, 72.2 and 0, 10 and 35%. There was thus no appar ent carcinogen exposure threshold. The present results confirmed the c arcinogenicity demonstrated in a previous study using F344 rats and re vealed the SD rat strain to be more susceptible.