DAO and irritable bowel syndrome: Figure 2 shows that the levels of serum DAO activity in PI-IBS model group increased significantly compared with that in low-dose of HXZQ, middle-dose of HXZQ, and high-dose of HXZQ groups (14.67 ± 1.09, 14.79 ± 1.45, and 14.41 ± 0.63 versus 16.03 ± 1.01, **P < 0.01, *P < 0.05).