Evaluation of diamine oxidase activity (DAO) in the rat intestinal mucosa by measuring expired14CO2 after oral administration of14C-putrescine

This study was performed to investigate whether mucosal diamine oxidase activity could be assessed by measuring expired14CO2 after oral administration of14C-putrescine. Immediately after giving 5 μCi of14C-putrescine, the14CO2 was collected at 1-h intervals for 8 h into a vial containing 1 ml of 10 mM hyamine hydroxide, 2 ml of ethanol, and an appropriate amount of phenolphthalein dye. The expired14CO2 caused the color to disappear. The amount of14CO2, determined by scintillation counting, reached a maximum 1 h after14C-putrescine administration, and gradually decreased thereafter. A positive correlation between the mucosal diamine oxidase activity and the maximal expired14CO2 value was obtained. There is no doubt that this test can be used to easily detect mucosal DAO activity and avoid the necessity of mucosal biopsy.