Evaluation of the relaxant effect of levetiracetam on isolated rat duodenum

Levetiracetam (LEV) is an approved drug for the treatment of some epileptic disorders. With few and controversial reports addressing its possible pharmacodynamic interactions, the current study aimed at studying the effect of LEV on isolated rat duodenal strips to enlighten its possible intestinal adverse effects using the isolated smooth muscle strips of rat duodenum. LEV showed a dose-dependent inhibition in KCl (80 mm)-induced contractions in normal Tyrode's solution. Moreover, preincubation with LEV (3 mm) in K⁺ -rich/Ca²⁺ -free medium led to a significant decrease in the maximum contractions (E_max ) coupled to a right shift of the cumulative CaCl₂ concentration curves implying a possible Ca²⁺ channel blocking potential. In addition, LEV exhibited a typical noncompetitive inhibition in the cumulative carbachol concentration curves evidenced as a decrease in E_max without the alteration of EC₅₀ , thus eliminating any possible role of the muscarinic receptors in the relaxant effect. To rule out other possible relaxant mechanisms, tests were conveyed in Tyrode's solution containing either 100 μm l-NAME or 10 μm glimepiride to test the possible relaxant roles exhibited by nitric oxide (NO) and K_ATP channel opening, respectively. None of the tested pathways was involved in LEV-mediated relaxation. Taken altogether, the results of the current study entail that LEV might exert a relaxant effect on intestinal smooth muscles through blocking L-type voltage-operated calcium channels, but not involving either NO release or K_ATP channel opening.