Identification of Histamine Metabolite 1-methyl,4-imidazole Acetic Acid in Human Urine and its Absence in Status Asthmaticus

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Abstract
The histamine metabolite l-methyl,4-imidazole acetic acid has been extracted and identified in human urine. The indentification is by comparison with pure and isotopic l-methyl,4-imidazole acetic acid on paper chromatograms and by comparison of the ultra-violet absorption spectra. In patients admitted in status asthmaticus with eosinophilia no l-methyl,4-imidazole acetic acid could be identified in the urine extracts before steroid therapy. In contrast, chromatograms prepared from the urine collection of controls and of patients with eosinophilia but no asthma showed l-methyl,4-imidazole acetic acid. The significance of this observation is discussed, and it is suggested that in status asthmaticus histamine is not being made available for methylation.