Aim: We aimed to investigate in vitro effects of varenicline on spontaneous contractile responses of proximal and distal colon smooth muscle in control and IBS rats.
Methods: The animal model of IBS-like visceral hypersensitivity was induced by intra-colonic infusion of 0.5% Acetic Acid (AA) in saline once daily between postnatal days 8-21. Control animals received saline instead of AA. Experiments were performed at the end of the 8 weeks. Proximal and distal colon tissues were resected and concentration-dependent effects of varenicline were evaluated in vitro tissue bath.
Results: The mean pressure values of spontaneous contractions and KCL (80 mmol/L) responses of proximal and distal colonic segments were similar in control and IBS rats. Varenicline significantly decreased the mean pressure of spontaneous colonic contractions in both control and IBS rats compared to their baseline values in only distal colon (p<0.05). The relaxation responses of distal colons were not significantly different between IBS and control groups (p>0.05).
Conclusion: Varenicline decreased the mean pressure values of spontaneous colonic contractions only distal colon in both control and IBS rats. Varenicline may reduce the increased distal colonic response with direct effect, as well as improve partially the disrupted cholinergic response with in vivo partial agonist effect. Thus, varenicline may have a potential usage in IBS as an adjuvant.