Metabolism of [c]-histamine in heart-lung-liver preparations of cats

The metabolism of injected [(14)C]-histamine was studied in heart-lung-liver preparations and heart-lung preparations from cats. When the liver was included in the circulation the injected histamine was rapidly eliminated from the blood, some of its metabolites appearing in the blood within 2 min after the injection. More than 70% of the injected histamine was metabolized to 1-methylimidazol-4-ylacetic acid. In the heart-lung preparations [(14)C]-histamine disappeared much more slowly from the blood and the major metabolite was 4-(2-aminoethyl)-1-methylimidazole (methylhistamine). Less than 4% of the injected (14)C was recovered in the form of imidazol-4(or 5)-ylacetic acid. In none of the experiments was there any measurable formation of acetylhistamine.