Inhibition of rat kidney histamine-N-methyltransferase by biogenic amines.

Biogenic amines were found to inhibit the transfer of 3H-labelled methyl groups from S-adenosyl methionine to histamine by rat kidney histamine methyl transferase, the most potent being tyramine, tryptamine and their hydroxyl derivatives. There appeared to be no competition between histamine and other amines for methyl groups since methyl histamine was the only methylation product formed. The inhibition could not be explained by the formation of stable complexes between inhibitor and the methyl transferase. It is recommended that histamine determinations on biologic specimens by the radioenzymatic assay include a control with added authentic histamine.