*4.2. Sample Collection*

At the end of the experiment, all rats were anesthetized and sacrificed to collected blood samples through the eyeballs. The blood samples were centrifuged at 4 ◦C, 3200× *g*, for 10 min to obtain serum for further analysis. The duodenum, jejunum, and ileum were divided into two parts, one part fixed in 10% buffered formalin for morphology analysis, the rest for collecting mucosa, and frozen in liquid nitrogen for further analysis.

#### *4.3. Serum Diamine Oxidase (DAO) and* D*-Lactate Acid (D-LA)*

Serum DAO activity and D-LA level were measured with commercial kits (Nanjing Jiancheng Institute of Bioengineering, Nanjing, China).
