Inhibition of benzo[a]pyreneinduced mammary carcinogenesis by retinyl acetate

ABSTRACT-The administration of a 250-ppm retinyl acetate dietary supplement for various periods relative to intragastric administration of 50 mg benzo[a]pyrene (BP) significantly in-hibited the induction of mammary cancers in virgin female inbred LEW/Mai rats. With day of BP administration taken as time O. groups receiving the retinoid from weeks-2 to +1. +1 to +90. +20 to +90. and-2 to +90 showed a significant reduction in tumor response as compared to controls. The inhibition of carcinogenesis achieved by a +1 to +20 administration schedule was temporary; the tumor yield was suppressed initially but returned to control levels by week 60. Autoradiographic analysis of mammary glands from 50-day-old rats indicated that a 2-week exposure to supplemental retinyl acetate significantly reduced the mammary gland parenchymal cell labeling index in ductal. alveolar. and terminal end bud structures. Beginning the retiny