Methylation of Histamine by Mouse Liver in Vitro

Summary. The exposed experiments give evidence that the histamine degradation in mouse liver is achieved by the methylating enzyme system, demonstrated in vivo by S chayer . Thus the main histamine metabolite found in slices is l‐methylimidazole‐4‐acetic acid. Furthermore, the histamine destruction is largely resistant to aminoguanidine which is a strong diamine oxidase inhibitor. Isobutyl‐isonicotinylhydrazin, a monoamine oxidase inhibitor, prevents the formation of l‐methylimidazole‐4‐acetic acid, but does not altogether exclude the formation of l‐methyl‐4–(β‐ami‐noethyl) imidazole. These characteristics are to be expected for the methylating enzyme system on account of recent findings in vivo (S chayer and K arjala 1956).