Regional Distribution of the Histamine Metabolite, tele-Methylimidazoleacetic Acid, in Rat Brain: Effects of Pargyline and Probenecid

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Abstract
Tele-Methylimidazoleacetic acid (t-MIAA), a major brain histamine metabolite, was measured in 9 rat brains regions by a gas chromatography-mass spectrometric method that also measures the precursor amine, tele-methylhistamine (t-MH). The t-MIAA concentration of cerebellum, medulla-pons, midbrain, caudate nucleus, hypothalamus, frontal cortex, hippocampus and thalamus varied 15-fold, hypothalamus showing the highest level (2.21 nmol/g) and cerebellum the lowest (0.15 nmol/g). The concentrations of t-MIAA and t-MH were significantly correlated in all regions except midbrain, which had relatively more t-MIAA. Probenecid did not alter whole-brain t-MIAA levels. Treatment with pargyline, an inhibitor of monoamine oxidase, lowered the t-MIAA levels in all regions.