Uptake and hepatobiliary fate of two hepatocarcinogens, N,N-dimethyl-4-aminoazobenzene and 3'-methyl-N,N-dimethyl-4-aminoazobenzene, in the rat.

Two radiolabeled hepatocarcinogens, N,N-dimethyl-4-aminoazobenzene (DAB) and 3'-methyl-N,N-dimethyl-4-aminoazobenzene (3'-Me-DAB), were rapidly cleared from the blood of rats after i.v. administration, with half-lives of 40 and 70 sec, respectively. Rates of hepatic uptake and biliary secretion of [14C]-3'-Me-DAB were double that of [14C]DAB within 30 min of administration. Two hr after azo dye injection, the hepatic output into bile of [14C]-3'-Me-DAB-derived radioactivity was three times that of [14C]DAB. Fifty and 75% of the total 3'-Me-DAB-derived radioactivity was recovered in blood, liver, and bile 30 and 120 min after injection while only 30 to 40% of the administered [14C]DAB-derived radioactivity was recovered at these times. We postulate the existence of an extrahepatic azo dye accumulation site which may compete with the ability of the liver to clear azo dye from the circulation and which releases 3'-Me-DAB-derived radioactivity more readily than that of DAB. Azo dye metabolites were isolated from liver, bile, and blood. The chromatographic pattern of liver metabolites generated in vivo by rats which received either hepatocarcinogen was obtained and compared with that of biliary metabolites. With either azo dye, some metabolites were located exclusively in the liver, some were secreted immediately into bile, while others were present in both liver and bile, indicating selectivity in biliary excretion.