Rapid and simple determination of histamine-N-methyl transferase activity by high-performance liquid chromatography with UV detection

A rapid, simple and low-cost assay method of histamine-N-methyltransferase activity was developed. Methylhistamine, which was separated from the enzym atic reaction system on reversed-phase highperformance liquid chromatograph y using an ion-paired chromatographic technique, was detected spectrophotom etrically at 226 nm. The mobile phase used for the separation of methylhist amine was 0.05M NH4H2PO4 (pH 3.0) containing 2 mM of sodium octanesulfonate . The new assay technique could detect methylhistamine as an enzyme activit y product of histamine-N-methyltransferase in the brain and kidney of rats. Chloropheniramine maleate, an antihistamine, activated the histamine-N-met hyltransferase. Whether neurotransmitter or neuromodulator, the role of his tamine in the brain has not yet been made clear. Therefore, the present met hod could be applicable for the enzymatic investigation of histamine metabo lism in central nervous system or inflammatory reactions.