2.6. Induction of Colitis

Intrarectal (IR) administration of 5% acetic acid (AA) is an easy and reproducible experimental model for colitis induction that manifests the same features of human UC [33]. Rats were fasted for 16 h with free access to water and were then lightly anesthetized with pentobarbital sodium (30 mg/kg, IP).

Rectal administration of 1.0 mL of AA (5% v/v) was used to induce ulcerative colitis in all the groups except those labeled as the sham group. For this purpose, a polyethylene catheter was selected and inserted into the rectum of each fasted rat such that it enters up to 8 cm into the anus. Each rat was held for 45 s in an upside-down position to avoid any rectal emission of the AA. Further, to neutralize the severity of the AA solution, each rat rectum was washed with saline (0.5 mL).

Following 24 h of colitis induction and euthanizing these rats, the parameter of disease activity index (DAI) was scored for each rat. Their colon tissues were isolated for the assessment of any macroscopic and microscopic changes while biochemical estimations of oxidative stress-related indicators (malondialdehyde (MDA), glutathione (GSH), and catalase (CAT)) and cytokines (IL-6 and TNFα) were determined.