DAILY VARIATIONS OF SERUM DIAMINE OXIDASE AND THE INFLUENCE OF H1 ANDH2 BLOCKERS - A CRITICAL APPROACH TO ROUTINE DIAMINE OXIDASE ASSESSMENT

Objective and Design: Histamine in food has been shown to induce intol erance reactions mimicking food allergy. These reactions seem to be du e to impaired histamine metabolism caused by reduced diamine oxidase a ctivity. To validate routine serum diamine oxidase assessment, daily v ariations of diamine oxidase were evaluated. Methods: Blood was drawn from each of 20 healthy volunteers (10 female, 10 male; mean age 32.5 years) every 2h from 9 a.m. to 5 p.m., and diamine oxidase activity wa s measured using the C-14 putrescine method. To assess possible influe nces of H1 and H2 blockers on diamine oxidase activity, diphenhydramin e, ketotifen, cimetidine, and ranitidine were incubated at pharmacolog ic concentrations With human placental diamine oxidase (identical to n eutrophilic and eosinophilic diamine oxidase). Inhibition of diamine o xidase activity was calculated as the percentage of inhibition versus control. In addition, the known diamine oxidase inhibitors, dihydralaz ine and aminoguanidine, were used as positive controls. Results: Serum diamine oxidase levels showed no significant daily variations (0.041/-0.025; 0.037+/-0.022; 0.041+/- 0.023; 0.040+/-0.023; 0.038+/-0.025 n Kat/l) and no significant sex differences (female 0.040+/-0.028 nKat/l versus male 0.039+/-0.019 nKat/l). Antihistamines had no influence on diamine oxidase activity except for cimetidine, which caused 25% inhi bition at the highest dose tested (p < 0.0002) (positive control: amin oguanidine 85% inhibition (p< 0.0001), dihydralazine 68% inhibition (p < 0.0001)) and diphenhydramine, which caused 19% increase (p < 0.0001 ) of enzyme activity. Conclusion: Serum diamine oxidase levels do not show daily variations allowing assessment anytime during office hours. However, diagnostic interpretation of serum diamine oxidase levels ma y be difficult.