Measurement and Characterization of Histamine and Methylhistamine in Human Urine under Histamine-Rich and Histamine-Poor Diets

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A radioimmunoassay for histamine was used to measure histamine and 1-methylhistamine (MH) in human urine samples. The detection limit of this assay was 2 ng/ml for histamine and 0.5 ng/ml for MH. Cation exchange high performance liquid chromatography (HPLC) on a Bio-Gel TSK SP-5 PW column with gradient elution was capable of separating histamine from its precursor L-histidine and its metabolites MH and 1-methylimidazole acetic acid (MIAA). The concentration of MH-immunoreactive materials in healthy volunteers with no dietary restrictions was 202 +/- 92 micrograms/24 h (mean +/- SD; n = 14). The excretion of MH-like material, expressed as micrograms of MH per 24 h, was not significantly different before or after the intake of histamine-rich food: 217 +/- 88 vs. 276 +/- 135 micrograms/24 h (n = 10). However, in urine samples collected in individual fractions, the levels of MH immunoreactivity were significantly increased after a histamine-rich meal in comparison to the corresponding fractions which were taken a day earlier at the same time intervals after a histamine-low diet (p < 0.03). HPLC characterization of MH immunoreactivity revealed the presence of histamine, MH and a compound with the same retention time as MIAA. The ratio of histamine, MH and MIAA in controls without dietary restrictions, as determined by HPLC analysis, was 50 +/- 6, 47 +/- 5 and 3 +/- 1%, respectively. After a histamine-rich meal the ratio was 97 +/- 2% for histamine, 1% for MH and 2 +/- 1% for MIAA.

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