Toxicology, 48 (1988) 71-80 Elsevier ScientificPublishers Ireland Ltd. EFFECT OF BUTYLATED HYDROXYANISOLE ADDED IN VITRO OR ADMINISTERED TO RATS ON N,N-DIBUTYLNITROSAMINE AND N-BUTYL-N-(4-HYDROXYBUTYL) NITROSAMINE METABOLISM BY POST-MITOCHONDRIAL SUPERNATANT OF LIVER HOMOGENATES ROBERTA PASTORELLI, ANNALISA ANCIDEI, EMILIO BENFENATI, ROBERTO FANELLI and LUISA AIROLDI Laboratory of Environmental Pharmacology and Toxicology, Istituto di Ricerche Farmacologiche 'Mario Negri'; Via Eritrea 62, 20157 Milano (Italy) (Received March 24th, 1987) (Accepted August 9th, 1987) SUMMARY The effect of butylated hydroxyanisole (BHA) on P-450-dependent co- hydroxylation of N,N-dibutylnitrosamine (NDBA) to N-butyl-N-(4-hydroxy- butyl)nitrosamine (BBN), and the further oxidation of BBN to N-butyl-N- (3-carboxypropyl)nitrosamine (BCPN) by the alcohol[aldehyde dehydro- genase system was investigated using the post-mitochondrial supernatant of liver homogenates ($9) from acutely and chronically BHA pretreated animals or $9 fractions from untreated rats with BHA added. Acute oral BHA (50 and 250 mg. kg-1) did not change NDBA co-oxidation, which was reduced by 35% only when the compound was administered 0.5% in the diet for 3 weeks. BCPN formation from BBN was unaffected by acute and chronic BHA pretreatment. In order to verify whether BHA or its metabolite(s) had a direct effect on NDBA and BBN oxidation, the compound was added to $9 fractions from untreated rats at various concentrations. Only when BHA concentrations were equimolar or in a 10-fold molar excess to the substrate concentration, we observed 30-50% inhibition of BBN formation and a reduced BCPN formation (60-80% of control values), from BBN. Thus, only at very high BHA concentra- tions could we confirm the inhibition of P-450-dependent mixed function Address all correspondence to: Dr. L. Airoldi. Abbreviations: BBN, N-butyl-N-(4-hydroxybutyl)nitrosamine;BCPN, N-butyl-N-(3-carboxy- propyl)nitrosamine; BHA, butylated hydroxyanisole; NDBA, N,N-dibutylnitrosamine;$9, post- mitochondrial supernatant of liver homogenate. o3oo-483x/88/$o3.5o © 1988Elsevier ScientificPublishers Ireland Ltd. Printed and Published in Ireland 71