Intestinal expression of diamine oxidase (DAO) and the relationship between blood DAO activity and haptoglobin concentration in diarrheal calves.

The objectives of this study were (1) to confirm the expression of diamine oxidase (DAO) in the intestines of healthy calves immune-histologically and to clarify whether the expression of DAO in the intestines of calves with diarrhea differs from that of healthy animals, and (2) to clarify the relationship between DAO and intestinal inflammation using haptoglobin (HPT), a biomarker commonly used to evaluate inflammation. The abomasum, duodenum, jejunum and ileum, cecum, colon, and rectum of each animal were sampled at necropsy for immunohistochemical staining targeting DAO. DAO was diffusely expressed in all areas from the abomasum to the rectum in healthy calves, whereas its expression was reduced in calves with diarrhea. Four Japanese black calves with mild dehydration caused by diarrhea were included in the study to investigate the potential relationship between DAO and HPT. DAO activity was extremely low in diarrhea cases, whereas HPT levels were high. When an oral rehydration solution (ORS) was administered to these cases for three consecutive days, HPT significantly decreased logarithmically and fecal properties returned to normal on the fourth day of treatment. In contrast, DAO activities were significantly increased by oral rehydration therapy (ORT), and DAO activities were significantly negatively correlated with HPT concentrations. The present results confirmed that DAO is expressed in the epithelial cells of the intestinal mucosa in cattle, and that both the small and large intestines significantly contribute to blood DAO levels. Furthermore, DAO expression was reduced by enteritis.