nitroarginine and anandamide

The effects of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG) were determined on cholinergic contractility in strips of human colonic longitudinal muscle and circular muscle in vitro, in the presence of nitric oxide synthase blockade with N-nitro-l-arginine (10(-4) M). Anandamide and 2-AG inhibited longitudinal muscle and circular muscle contractile responses to acetylcholine (10(-9)-10(-4) M) in a concentration-dependent manner. This was unaltered following pretreatment with the cannabinoid CB(1) receptor-selective antagonist AM251 (10(-7) M), however in isolation AM251 elicited a significant rightward shift in the potency of acetylcholine-evoked contraction in both longitudinal muscle and circular muscle preparations. Pretreatment with an inhibitor of anandamide catabolism, arachidonoyl trifluoromethyl ketone (10(-5) M), alone caused a significant decrease in the potency of acetylcholine-evoked contraction in both longitudinal and circular muscle, but had no significant additional effect on the anandamide-induced (10(-5) M) suppression of contraction. Pretreatment with the cannabinoid CB(2) receptor inverse agonist JTE 907 (10(-6) M) neither influenced the potency of acetylcholine-evoked contraction alone nor prevented the potency shift in acetylcholine-evoked contraction in the presence of anandamide (10(-5) M). The findings of the present study indicate that the endocannabinoids anandamide and 2-arachidonoylglycerol suppress colonic cholinergic contractility via a non conventional cannabinoid or non-cannabinoid receptor-mediated pathway. Cholinergic contraction may be tonically modulated by endocannabinoids and/or products of arachidonate metabolism unrelated to endocannabinoid production. The extent of anandamide metabolism is not sufficient to influence the functional effects of its exogenous administration in human colonic tissue in vitro.

Topics: Acetylcholine; Arachidonic Acids; Cannabinoid Receptor Modulators; Cholinergic Fibers; Colon; Dose-Response Relationship, Drug; Endocannabinoids; Enzyme Inhibitors; Glycerides; Humans; Muscle Contraction; Nitric Oxide Synthase; Nitroarginine; Polyunsaturated Alkamides; Receptors, Cannabinoid

In the isolated rat mesenteric bed, the 1 min perfusion with 100 nm anandamide, a concentration that did not evoke vasorelaxation, elicited an acute release of 165.1 +/- 9.2 pmol nitric oxide (NO) that was paralleled by a 2-fold increase in cGMP tissue levels. The rise in NO released was mimicked by either (R)-(+)-methanandamide or the vanilloid receptor agonists resiniferatoxin and (E)-capsaicin but not by its inactive cis-isomer (Z)-capsaicin. The NO release elicited by either anandamide or capsaicin was reduced by the TRPV1 receptor antagonists 5'-iodoresiniferatoxin, SB 366791 and capsazepine as well as by the cannabinoid CB(1) receptor antagonists SR 141716A or AM251. The outflow of NO elicited by anandamide and capsaicin was also reduced by endothelium removal or NO synthase inhibition, suggesting the specific participation of endothelial TRPV1 receptors, rather than the novel endothelial TRPV4 receptors. Consistently, RT-PCR showed the expression of the mRNA coding for the rat TRPV1 receptor in the endothelial cell layer, in addition to its expression in sensory nerves. The participation of sensory nerves on the release of NO was precluded on the basis that neonatal denervation of the myenteric plexus sensory nerves did not modify the pattern of NO release induced by anandamide and capsaicin. We propose that low concentrations of anandamide, devoid of vasorelaxing effects, elicit an acute release of NO mediated predominantly by the activation of endothelial TRPV1 receptors whose physiological significance remains elusive.

Topics: Anilides; Animals; Arachidonic Acids; Cannabinoid Receptor Antagonists; Capsaicin; Cinnamates; Cyclic GMP; Diterpenes; Dose-Response Relationship, Drug; Endocannabinoids; Endothelium, Vascular; In Vitro Techniques; Male; Mesenteric Artery, Superior; Nitric Oxide; Nitroarginine; Perfusion; Piperidines; Polyunsaturated Alkamides; Pyrazoles; Rats; Rats, Sprague-Dawley; Rimonabant; RNA, Messenger; TRPV Cation Channels; Vasodilation