Endogenous cannabinoids contribute to remote ischemic preconditioning via cannabinoid CB2 receptors in the rat heart

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Abstract

In addition to well-known neurobehavioral effects, endogenous cannabinoids exert diverse cardiovascular actions. Recently, they have been suggested to protect the myocardium against ischemia/reperfusion injury. The aim of this study is to examine the contribution of endogenous cannabinoids to cardioprotection afforded by remote ischemic preconditioning. Three groups of remote preconditioned (15 min of mesenteric artery occlusion followed by 15 min of reperfusion) and three groups of sham-operated rats were included in the study. Animals were pretreated intravenously by vehicle, cannabinoid CB1 (AM251, 1 mg/kg) or CB2 (AM630, 1 mg/kg) receptor antagonist 15 min prior to remote preconditioning or sham operation. Myocardial injury was induced by 30 min of coronary artery occlusion followed by 2 h of reperfusion. The resultant arterial hypotension, ventricular arrhythmias, and infarct size were compared among the groups. Remote preconditioning exerted potent cardioprotection manifested as significant reductions in infarct size (P < 0.001) as well as number and duration of arrhythmias (P < 0.01, 0.01 and 0.05 for premature ventricular contractions, ventricular tachycardias and fibrillations; respectively). The cannabinoid CB1 receptor antagonist pretreatment had no significant effect on ischemia-induced hypotension, arrhythmias or infarct size. On the other hand, the cannabinoid CB2 receptor antagonist pretreatment abolished the protective effects of remote preconditioning on infarct size (P < 0.01) and arrhythmias (P < 0.01), without any significant effect on ischemia-induced hypotension. The results of this study suggest that endogenous cannabinoids, through acting on cannabinoid CB2 receptors, are involved in the cardioprotective phenomenon of remote ischemic preconditioning, induced by mesenteric artery occlusion and reperfusion.

Introduction

Remote ischemic preconditioning or preconditioning at a distance is a cardioprotective phenomenon which was first described by Przyklenk et al. (1993) in the canine model of myocardial ischemia/reperfusion. In their report, brief episodes of ischemia in one vascular bed protected remote virgin myocardium from subsequent sustained coronary occlusion (intra-cardiac remote preconditioning). A similar adaptive phenomenon, inter-organ remote preconditioning, has also been reported which is triggered by ischemia/reperfusion of other organs such as kidneys (Takaoka et al., 1999), intestines (Wolfrum et al., 2002), and limbs (Kharbanda et al., 2002, Kristiansen et al., 2005, Weinbrenner et al., 2002, Weinbrenner et al., 2004) in a variety of other species. Despite the promising results of the preliminary explorations of the clinical application of this clinically feasible procedure (Gunaydin et al., 2000), the mechanisms responsible for this phenomenon and its signaling pathways are still remained elusive.

In addition to their well-known neurobehavioral effects (Howlett et al., 2004), endogenous cannabinoids exert important physiological roles in cardiovascular system, such as hypotension and bradycardia (Randall et al., 2002, Randall et al., 2004, Wagner et al., 1998). These effects are considered to be due to activation of specific G-protein-coupled, cannabinoid CB1 and CB2, receptors (Niederhoffer and Szabo, 1999). Although cannabinoid CB1 receptors are preferentially located on brain, the cardiovascular depressor effects of cannabinoids appear to mostly involve cannabinoid CB1 receptors expressed in peripheral tissues, including blood vessels, the heart, and sympathetic nerve terminals (Batkai et al., 2004). The possible contribution of cannabinoid CB2 receptors, which are mainly located on peripheral non-neuronal cells (Niederhoffer and Szabo, 1999) including cardiovascular system, to modulation of cardiovascular function is less well documented.

Recent investigations have proposed the involvement of endogenous cannabinoids in infarct size-reducing effects conferred by lipopolysaccharide (Lagneux and Lamontagne, 2001) and heat stress (Joyeux et al., 2002), as well as endothelial protection afforded by classic ischemic preconditioning (Bouchard et al., 2003) in isolated rat hearts. However, the roles of endogenous cannabinoids in infarct size-reducing and anti-arrhythmic effects of remote ischemic preconditioning have not yet been evaluated. Therefore, we examined the cardioprotective effects of endogenous cannabinoids in the well-known model of remote preconditioning induced by a brief episode of mesenteric artery occlusion and reperfusion in intact rats.

Section snippets

Animals

Animals were handled in accordance with the criteria outlined in the “Guide for the Care and Use of Laboratory Animals” (NIH US publication 85-23 revised 1996). Male Sprague–Dawley rats weighing 200–250 g were used. Animals were housed in groups of 3–4 in a room controlled at 22 ± 1°C and maintained in an alternating 12-h light/12-h dark cycles, and were allowed free access to food and water.

Study groups and experimental protocols

Animals were randomly divided into 6 groups:

  • 1.

    Vehicle + sham operation: Vehicle was intravenously administered

Hemodynamic parameters

As presented in Table 1, there was no significant difference in basal hemodynamic parameters among the groups. Variations in mean arterial pressure, as the percentage of the basal mean arterial pressure, is summarized in Fig. 1. AM251, but not AM630, treatment resulted in significant mean arterial pressure elevation in both sham-operated and preconditioned groups compared to the basal levels (P < 0.05). Mean arterial pressure was significantly elevated by mesenteric artery occlusion (P < 0.01) and

Discussion

This study provides evidence that endogenous cannabinoids contribute to the cardioprotective effects of remote preconditioning, conferred by a brief episode of mesenteric artery occlusion and reperfusion. This cardioprotection, manifested as reduction in the infarct size and severity of arrhythmias, seems to be mediated through cannabinoid CB2 receptors.

In this study we used AM251 as a specific cannabinoid CB1 receptor antagonist. AM251 is structurally very close to SR 141716A (rimonabant)

Acknowledgment

The authors are grateful to Dr. Ali Reza Mani (The UCL Institute of Hepatology, Royal Free & University College Medical School, UCL) for his support to this study.

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