Histamine metabolism in asthma

Histamine and 1-methyl-imidazole-4-acetic acid, the end product of histamine metabolism via the ring-N methylation pathway, were measured in urine from asthmatic and nonasthmatic children on a histamine-restricted diet. No significant differences were found between the relative output values that could distinguish the asthmatic from the nonasthmatic children. The intermediary metabolite, methylhistamine, was also measured in some of these urine specimens, and no obvious differences were found between the proportions of the three substances that would suggest impairment of the methylation pathway of histamine metabolism in asthma.