Fatemeh Amin - Department of Physiology and Pharmacology, School of Medicine, Physiology-Pharmacology Research Center, Rafsanjan University of Medical Sciences, Rafsanjan, Iran.
Mohammad Hossein Boskabady - Department of Physiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran,
Zahra Ghasemi - Neurogenic Inflammation Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
Mehrdad Jalali - Department of Physiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran,
Arghavan Memarzia - Department of Physiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran,
Saeideh Saadat - Department of Physiology, School of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran,

Introduction: Allium cepa (A.cepa) showed various pharmacological activities in previous studies. In this study, the relaxant effect of A. cepa extract (ACE) and its possiblemechanism on tracheal smooth muscle (TSM) was assessed. Materials and Methods: TSM was contractedby (60mM) KCl or (10μM) methacholine and the effectsofcumulative concentrations of ACE and theophylline as positive control were assesed on non-incubated and incubated TSM with propranolol, chloropheniramin, diltiazem, atropine, glibenclamide and indomethacin. Results: A. cepa showed concentration-dependent relaxant effects on KCl and methacholine induced contraction in non-incubated TSM (P<0.01 to P<0.001). The relaxant effects of Allium cepa were not significantly different between nonincubated and incubated tissues with glibenclamide, atropine, chloropheniramin and indomethacin. The plant extract showed significant lower relaxant effects in incubated TSM with propranolol and diltiazem compared tonon-incubated tissues. EC50 values of ACE (ACE concentration causing 50% of the maximum relaxation effect) in incubated TSM with propranolol and diltiazem were significantly lowerthan non-incubated tissues) P<0.001 and P<0.05 respectively). There were not significant differences between the relaxant effects of various concentrations of the extract of A. cepa and theophylline. There were significant correlations between ACE and theophylline concentrations and their relaxant effects (P<0.05 to P<0.001) Conclusions: The ACE showed relatively potent relaxant effect on TSM which was comparable to the effect of theophylline. A β2-adrenergic stimulatory and/or calcium channelblockade are suggested as the possible mechanisms for the relaxant effect of the plant.

Cepa extract, Relaxant effect, Tracheal smith muscle.