Fig. 1 Source and effects of histamine in asthma. 2.1. 1.8) to N-methyl histamine, which is
itself me- were first differentiated into H1-and H2-receptors by Ash and Schild in 1966, 12
when it was found tabolised by monoamine oxidase to N-methylimidazole acetic acid, the
major urinary metabolite. that some responses to histamine were blocked by The remaining
histamine is metabolised by diamine low doses of mepyramine (pyrilamine), whereas
oxidase (EC 1.4. 3.6) to imidazole acetic acid, which others were insensitive. This …