Pharmacological profiling of the hemodynamic effects of cannabinoid ligands: a combined in vitro and in vivo approach.

The receptors mediating the hemodynamic responses to cannabinoids are not clearly defined due to the multifarious pharmacology of many commonly used cannabinoid ligands. While both CB1 and TRPV1 receptors are implicated, G protein-coupled receptor 55 (GPR55) may also mediate some of the hemodynamic effects of several atypical cannabinoid ligands. The present studies attempted to unravel the pharmacology underlying the in vivo hemodynamic responses to ACEA (CB1 agonist), O-1602 (GPR55 agonist), AM251 (CB1 antagonist), and cannabidiol (CBD; GPR55 antagonist). Agonist and antagonist profiles of each ligand were determined by ligand-induced GTPγS binding in membrane preparations expressing rat and mouse CB1 and GPR55 receptors. Blood pressure responses to ACEA and O-1602 were recorded in anesthetized and conscious mice (wild type, CB1 (-/-) and GPR55(-/-)) and rats in the absence and presence of AM251 and CBD. ACEA demonstrated GTPγS activation at both receptors, while O-1602 only activated GPR55. AM251 exhibited antagonist activity at CB1 and agonist activity at GPR55, while CBD demonstrated selective antagonist activity at GPR55. The depressor response to ACEA was blocked by AM251 and attenuated by CBD, while O-1602 did not induce a depressor response. AM251 caused a depressor response that was absent in GPR55(-/-) mice but enhanced by CBD, while CBD caused a small vasodepressor response that persisted in GPR55(-/-) mice. Our findings show that assessment of the pharmacological profile of receptor activation by cannabinoid ligands in in vitro studies alongside in vivo functional studies is essential to understand the role of cannabinoids in hemodynamic control.

Acute administration of cannabidiol in vivo suppresses ischaemia-induced cardiac arrhythmias and reduces infarct size when given at reperfusion.

BACKGROUND AND PURPOSE: Cannabidiol (CBD) is a phytocannabinoid, with anti-apoptotic, anti-inflammatory and antioxidant effects and has recently been shown to exert a tissue sparing effect during chronic myocardial ischaemia and reperfusion (I/R). However, it is not known whether CBD is cardioprotective in the acute phase of I/R injury and the present studies tested this hypothesis. EXPERIMENTAL APPROACH: Male Sprague-Dawley rats received either vehicle or CBD (10 or 50 microg kg(-1) i.v.) 10 min before 30 min coronary artery occlusion or CBD (50 microg kg(-1) i.v.) 10 min before reperfusion (2 h). The appearance of ventricular arrhythmias during the ischaemic and immediate post-reperfusion periods were recorded and the hearts excised for infarct size determination and assessment of mast cell degranulation. Arterial blood was withdrawn at the end of the reperfusion period to assess platelet aggregation in response to collagen. KEY RESULTS: CBD reduced both the total number of ischaemia-induced arrhythmias and infarct size when administered prior to ischaemia, an effect that was dose-dependent. Infarct size was also reduced when CBD was given prior to reperfusion. CBD (50 microg kg(-1) i.v.) given prior to ischaemia, but not at reperfusion, attenuated collagen-induced platelet aggregation compared with control, but had no effect on ischaemia-induced mast cell degranulation. CONCLUSIONS AND IMPLICATIONS: This study demonstrates that CBD is cardioprotective in the acute phase of I/R by both reducing ventricular arrhythmias and attenuating infarct size. The anti-arrhythmic effect, but not the tissue sparing effect, may be mediated through an inhibitory effect on platelet activation.