Evaluation of diamine oxidase activity (DAO) in the rat intestinal mucosa by measuring expired 14CO2 after oral administration of 14C-putrescine.

This study was performed to investigate whether mucosal diamine oxidase activity could be assessed by measuring expired 14CO2 after oral administration of 14C-putrescine. Immediately after giving 5 mu Ci of 14C-putrescine, the 14CO2 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 expired 14CO2 caused the color to disappear. The amount of 14CO2, determined by scintillation counting, reached a maximum 1 h after 14C-putrescine administration, and gradually decreased thereafter. A positive correlation between the mucosal diamine oxidase activity and the maximal expired 14CO2 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.