Effects of Cannabinoid Agonists on Sheep Sphincter of Oddi in vitro

Background/Aims: According to recent studies, the endocannabinoid system plays an important role in both physiological and pathophysiological situations. The purpose of the present studywas to investigate the effects of cannabinoid (CB) agonists on isolated sheep sphincter of Oddi (SO) in vitro.Methods: The isolated sheep SO tissues were mounted in organ baths and tested for isometric tension and cyclic GMP levels (cGMP) in response to the non-selective CB receptor agonistWIN55,212-2 and the potent C131 receptor agonist methanandamide in the presence and absence of the selective CB1 antagonist SR 141716A, the selective CB2 antagonist SR 144528 and the nonspecific inhibitor of nitric oxide (NO) synthase I-NAME. Results: CB agonists relaxed SO in a concentration-dependent manner. These relaxations did not reduce in the presence of SR 144528 but were significantly reduced by SR 141716Aand I-NAME. Carbachol significantly increased the cGMP levels compared with the control group and both of the CB receptor agonists significantly increased the cGMP levels compared with the control and carbachol groups.On the other hand, I-NAME prevented the increase in cGMP levels caused by CB agonists. Conclusion: These results show that the relaxation by the agonists maybe through CB1 receptors.The decrease of CB relaxation responses by I-NAME, a nonspecific inhibitor of NO synthase, and the increase of cGMP levels in the SO tissues by CB agonists which decreased by I-NAME show that the relaxation effects of these agonists may also partially bevia increasing the NO synthesis or release.