The role of lipophilicity in the extrahepatic disposition of aminostilbene derivatives following administration to rat.

1. Carcinogenic trans-4-dimethylaminostilbene and its unbound metabolites in rat tissues are highly lipophilic with partition coefficients of 10 000 to 80 000. The values for bibenzyl derivatives are somewhat lower. 2. Sulphates and glucuronic acid conjugates are present in liver, kidney, blood and bile, but not to any extent in other extrahepatic tissues. 3. The patterns of unbound metabolites in lung, spleen, adrenals, brain and fat after oral administration of 3H-labelled trans-4-dimethylaminostilbene, cis-4-dimethylaminostilbene and 4-dimethylaminobibenzyl have been determined. The concn. of tissue metabolites do not parallel plasma concn. of metabolites and do not correlate with lipophilicity. 4. Binding of trans-4-aminostilbene metabolites to tissue proteins is 3--5 times greater than that of cis-4-aminostilbene metabolites and more than 10 times higher than that of aminobibenzyl metabolites. In Zymbal gland, the target tissue for trans-4-dimethylaminostilbene carcinogenicity, the tissue concn. of reactive metabolites is insufficiently high to account for the specific effect. 5. The analysis of fat tissue provided circumstantial evidence that reactive metabolites bind covalently to fatty acids.