Metabolism and Covalent Binding of [3H]Benzo(a)pyrene by Isolated Perfused Lungs and Short-Term Trachea! Organ Culture of Cigarette Smoke-exposed Rats1

The metabolism and covalent binding of the environmen tal carcinogen benzo(a)pyrene, a constituent of cigarette smoke, has been determined in isolated perfused lungs of shamand cigarette smoke-exposed and 3-methylcholanthrene-pretreated male Wistar rats. Rats were exposed to cigarette smoke for 1 hr daily for either 1 or 10 days. Benzo(a)pyrene (2 nmoles) was instilled intratracheally, and metabolites in lungs and a nonrecirculating perfusate were determined. Benzo(a)pyrene was metabolized by isolated perfused lungs of sham-, cigarette smoke-exposed, and 3methylcholanthrene-treated animals to ethyl acetate-solu ble metabolites, which cochromatographed with 9,10-dihydro-9,10-dihydroxybenzo(a)pyrene, 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene, 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene, and 3-hydroxybenzo(a)pyrene. An unidentified me tabolite (Y) migrating between 4,5-dihydro-4,5-dihydroxybenzo(a)pyrene and 3-hydroxybenzo(a)pyrene was ob served in perfusates from lungs of animals that had been exposed either to cigarette smoke or 3-methylcholanthrene. Metabolite production was significantly increased by expo sure to either cigarette smoke or 3-methylcholanthrene. Tracheas of sham and smoke-exposed animals also con verted benzo(a)pyrene to metabolites that cochromato graphed with reference dihydrodiols and 3-hydroxybenzo(a)pyrene; however, no increase in metabolite pro duction was observed in the smoke-exposed animals. Dihy drodiols were the major ethyl acetate-soluble metabolites formed by the trachea, whereas 3-hydroxybenzo(a)pyrene was the major metabolite formed in lung perfusions. After intratracheal instillation of [3H]benzo(a)pyrene, the amount of covalently bound radioactivity was significantly in creased in the lungs of animals exposed to cigarette smoke compared to the corresponding sham-exposed animals.