Cardiovascular effects of endocannabinoids--the plot thickens

An overview on synthetic and biological activities of cannabidiol (CBD) and its derivatives

(-)-Cannabidiol is a class of non-psychoactive plant cannabinoids derived from cannabis plants. Currently, Epidiolex (Cannabidiol) has been approved by the FDA for the treatment of two rare and severe forms of epilepsy related diseases, namely Lennox-Gastaut syndrome (LGS) and Dravet (DS). In addition, Cannabidiol and its structural analogues have received increasing attention due to their potential therapeutic effects such as neuroprotection, anti-epilepsy, anti-inflammation, anti-anxiety, and anti-cancer. Based on literature review, no comprehensive reviews on the synthesis of Cannabidiol and its derivatives have been found in recent years. Therefore, this article summarizes the published synthesis methods of Cannabidiol and the synthesis routes of Cannabidiol derivatives, and introduces the biological activities of some Cannabidiol analogues that have been studied extensively and have significant activities.

Pharmacognosy and Effects of Cannabinoids in the Vascular System

Understanding the pharmacodynamics of cannabinoids is an essential subject due to the recent increasing global acceptance of cannabis and its derivation for recreational and therapeutic purposes. Elucidating the interaction between cannabinoids and the vascular system is critical to exploring cannabinoids as a prospective therapeutic agent for treating vascular-associated clinical conditions. This review aims to examine the effect of cannabinoids on the vascular system and further discuss the fundamental pharmacological properties and mechanisms of action of cannabinoids in the vascular system. Data from literature revealed a substantial interaction between endocannabinoids, phytocannabinoids, and synthetic cannabinoids within the vasculature of both humans and animal models. However, the mechanisms and the ensuing functional response is blood vessels and species-dependent. The current understanding of classical cannabinoid receptor subtypes and the recently discovered atypical cannabinoid receptors and the development of new synthetic analogs have further enhanced the pharmacological characterization of the vascular cannabinoid receptors. Compelling evidence also suggest that cannabinoids represent a formidable therapeutic candidate for vascular-associated conditions. Nonetheless, explanations of the mechanisms underlining these processes are complex and paradoxical based on the heterogeneity of receptors and signaling pathways. Further insight from studies that uncover the mechanisms underlining the therapeutic effect of cannabinoids in the treatment of vascular-associated conditions is required to determine whether the known benefits of cannabinoids thus currently outweigh the known/unknown risks.

Acute effects of cannabis consumption on exercise performance: a systematic and umbrella review

INTRODUCTION

The goal of this systematic and umbrella review was to regroup all systematic reviews, non-systematic reviews and all original articles into one convenient publication that would facilitate the theoretical and applied scientific investigations directed on cannabis consumption and exercise performance, to update current findings on the matters, and assess evidence quality.

EVIDENCE ACQUISITION

The systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) method. A computer-based systematic search was conducted in September 2019 through the Pubmed, Scopus and SPORTDiscus databases. The reliability of the systematic search was assured by having the article selection process entirely repeated by a second author. Strength of evidence of the selected articles was assesses using a modified version of the Downs and Black Checklist.

EVIDENCE SYNTHESIS

The systematic search yielded a total of 8 peer-reviewed publications as well as 10 literature reviews. Results show that cannabis consumption prior to exercise induces decrements in performance (reduced ability to maintain effort, physical/maximal work capacity), undesired physiological responses (increased heart and breathing rate as well as myocardial oxygen demand) and neurological effects on balance (increased sway).

CONCLUSIONS

Based on the articles included in this review, the authors conclude that cannabis consumption has an ergolytic effect on exercise performance and therefore does not act as a sport performance enhancing agent as raised by popular beliefs. Thus, cannabis consumption prior to exercise should be avoided in order to maximize performance in sports. Further research should mimic modern THC dosage (150 mg).

A murine model of the exercise pressor reflex

KEY POINTS

The decerebrate mouse provides a novel working model of the exercise pressor reflex (EPR). The decerebrate mouse model of the EPR is similar to the previously described decerebrate rat model. Studying the EPR in transgenic mouse models can define exact mechanisms of the EPR in health and disease.

ABSTRACT

The exercise pressor reflex (EPR) is defined by a rise in mean arterial pressure (MAP) and heart rate (HR) in response to exercise and is necessary to match metabolic demand and prevent premature fatigue. While this reflex is readily tested in humans, mechanistic studies are largely infeasible. Here, we have developed a novel murine model of the EPR to allow for mechanistic studies in various mouse models. We observed that ventral root stimulation (VRS) in an anaesthetized mouse causes a depressor response and a reduction in HR. In contrast, the same stimulation in a decerebrate mouse causes a rise in MAP and HR which is abolished by dorsal rhizotomy or by neuromuscular blockade. Moreover, we demonstrate a reduced MAP response to VRS using TRPV1 antagonism or in Trpv1 null mice while the response to passive stretch remains intact. Additionally, we demonstrate that intra-arterial infusion of capsaicin results in a dose-related rise in MAP and HR that is significantly reduced by a selective and potent TRPV1 antagonist or is completely abolished in Trpv1 null mice. These data serve to validate the development of a decerebrate mouse model for the study of cardiovascular responses to exercise and further define the role of the TRPV1 receptor in mediating the EPR. This novel model will allow for extensive study of the EPR in unlimited transgenic and mutant mouse lines, and for an unprecedented exploration of the molecular mechanisms that control cardiovascular responses to exercise in health and disease.

Endocannabinoids in cerebrovascular regulation

The cerebral blood flow is tightly regulated by myogenic, endothelial, metabolic, and neural mechanisms under physiological conditions, and a large body of recent evidence indicates that inflammatory pathways have a major influence on the cerebral blood perfusion in certain central nervous system disorders, like hemorrhagic and ischemic stroke, traumatic brain injury, and vascular dementia. All major cell types involved in cerebrovascular control pathways (i.e., smooth muscle, endothelium, neurons, astrocytes, pericytes, microglia, and leukocytes) are capable of synthesizing endocannabinoids and/or express some or several of their target proteins [i.e., the cannabinoid 1 and 2 (CB1 and CB2) receptors and the transient receptor potential vanilloid type 1 ion channel]. Therefore, the endocannabinoid system may importantly modulate the regulation of cerebral circulation under physiological and pathophysiological conditions in a very complex manner. Experimental data accumulated since the late 1990s indicate that the direct effect of cannabinoids on cerebral vessels is vasodilation mediated, at least in part, by CB1 receptors. Cannabinoid-induced cerebrovascular relaxation involves both a direct inhibition of smooth muscle contractility and a release of vasodilator mediator(s) from the endothelium. However, under stress conditions (e.g., in conscious restrained animals or during hypoxia and hypercapnia), cannabinoid receptor activation was shown to induce a reduction of the cerebral blood flow, probably via inhibition of the electrical and/or metabolic activity of neurons. Finally, in certain cerebrovascular pathologies (e.g., subarachnoid hemorrhage, as well as traumatic and ischemic brain injury), activation of CB2 (and probably yet unidentified non-CB1/non-CB2) receptors appear to improve the blood perfusion of the brain via attenuating vascular inflammation.

Ischaemic strokes with reversible vasoconstriction and without thunderclap headache: a variant of the reversible cerebral vasoconstriction syndrome?

BACKGROUND

Reversible vasoconstriction (RV) may cause ischaemic stroke (IS) in the absence of any other defined stroke aetiology. The three objectives of our study were to evaluate the frequency of RV in a prospective series of young IS patients, to describe the detailed clinical-radiological features in the patients with RV and IS, and to compare these characteristics with those of reversible cerebral vasoconstriction syndrome (RCVS).

METHODS

We identified between October 2005 and December 2010, 159 consecutive young patients (<45 years) hospitalized for an acute IS confirmed by cerebral magnetic resonance imaging. An extensive diagnostic work-up was performed including toxicological urinary screening for cannabis, cocaine and amphetamines, and the usual biological, cardiac and vascular investigations for an IS in the young. We specifically studied patients with IS and RV, which was defined as multifocal intracranial arterial stenoses confirmed by intracranial arterial imaging that resolved within 3-6 months.

RESULTS

Out of 159 patients with IS, 21 (13%, 12 males, 9 females; mean age 32 years) had multifocal cerebral arterial stenoses that were fully reversible at 3-6 months, and no other cause for stroke. IS were located on posterior territory in 71% of cases, and vasoconstriction predominated on posterior cerebral and superior cerebellar arteries. Precipitating factors of IS and RV were the use of cannabis resin (n = 14), nasal decongestants (n = 2) and triptan (n = 1). Most cases (74%) had unusual severe headache, but none had thunderclap headache. None of 21 cases had reversible posterior leukoencephalopathy, cortical subarachnoid or intracerebral haemorrhage.

CONCLUSION

RV was the sole identified cause of IS in 13% of our cohort. These young patients with IS and RV may have a variant of RCVS, related to an increased susceptibility to vasoactive agents in some individuals. RV in our patients differs from the classical characteristics of RCVS by the absence of thunderclap headache, reversible brain oedema and subarachnoid or intracranial haemorrhage. Intracranial arteries should be looked for, by appropriate vascular imaging, in young patients with IS at the acute stage and during the follow-up period.

Role of endocannabinoids and cannabinoid-1 receptors in cerebrocortical blood flow regulation

Background

Endocannabinoids are among the most intensively studied lipid mediators of cardiovascular functions. In the present study the effects of decreased and increased activity of the endocannabinoid system (achieved by cannabinoid-1 (CB1) receptor blockade and inhibition of cannabinoid reuptake, respectively) on the systemic and cerebral circulation were analyzed under steady-state physiological conditions and during hypoxia and hypercapnia (H/H).

Methodology/Principal Findings

In anesthetized spontaneously ventilating rats the CB1-receptor antagonist/inverse agonist AM-251 (10 mg/kg, i.v.) failed to influence blood pressure (BP), cerebrocortical blood flow (CoBF, measured by laser-Doppler flowmetry) or arterial blood gas levels. In contrast, the putative cannabinoid reuptake inhibitor AM-404 (10 mg/kg, i.v.) induced triphasic responses, some of which could be blocked by AM-251. Hypertension during phase I was resistant to AM-251, whereas the concomitant CoBF-increase was attenuated. In contrast, hypotension during phase III was sensitive to AM-251, whereas the concomitant CoBF-decrease was not. Therefore, CoBF autoregulation appeared to shift towards higher BP levels after CB1-blockade. During phase II H/H developed due to respiratory depression, which could be inhibited by AM-251. Interestingly, however, the concomitant rise in CoBF remained unchanged after AM-251, indicating that CB1-blockade potentially enhanced the reactivity of the CoBF to H/H. In accordance with this hypothesis, AM-251 induced a significant enhancement of the CoBF responses during controlled stepwise H/H.

Conclusion/Significance

Under resting physiological conditions CB1-receptor mediated mechanisms appear to have limited influence on systemic or cerebral circulation. Enhancement of endocannabinoid levels, however, induces transient CB1-independent hypertension and sustained CB1-mediated hypotension. Furthermore, enhanced endocannabinoid activity results in respiratory depression in a CB1-dependent manner. Finally, our data indicate for the first time the involvement of the endocannabinoid system and CB1-receptors in the regulation of the cerebral circulation during H/H and also raise the possibility of their contribution to the autoregulation of CoBF.

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 study was 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 agonist WIN 55,212-2 and the potent CB1 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 L-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 141716A and L-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, L-NAME prevented the increase in cGMP levels caused by CB agonists.

CONCLUSION

These results show that the relaxation by the agonists may be through CB1 receptors. The decrease of CB relaxation responses by L-NAME, a nonspecific inhibitor of NO synthase, and the increase of cGMP levels in the SO tissues by CB agonists which decreased by L-NAME show that the relaxation effects of these agonists may also partially be via increasing the NO synthesis or release.

Cannabinoids and experimental models of multiple sclerosis

The inflammatory response is a hallmark in the development of autoimmune-mediated neurodegenerative diseases of the central nervous system (CNS). Research on these pathological phenomena is being extensively undertaken and experimental autoimmune encephalomyelitis (EAE) serves as a valuable animal model. Studies from this model have generated interesting insights into biological effects of cannabinoids and may, at least to a certain extent, reflect the cannabinoid-mediated protective mechanisms also in human diseases with similar characteristics, such as multiple sclerosis (MS). Cannabinoids are involved in regulation of the immune system. These effects comprise modulation of inflammatory reaction through components of the innate and adaptive immune responses. Cannabinoids also confer neuroprotection and assist neuroregeneration, thus maintaining a balance within the delicate CNS microenvironment and restoring function following pathological condition, commonly driven by neuroinflammation. Continued studies of cannabinoid actions in EAE pathogenesis should be beneficial for the better understanding of the mechanisms governing such a vast array of physiological effects and in development of new therapeutic strategies for the treatment of human neuroinflammatory and neurodegenerative diseases.

Cannabinoids, endocannabinoids, and related analogs in inflammation

This review covers reports published in the last 5 years on the anti-inflammatory activities of all classes of cannabinoids, including phytocannabinoids such as tetrahydrocannabinol and cannabidiol, synthetic analogs such as ajulemic acid and nabilone, the endogenous cannabinoids anandamide and related compounds, namely, the elmiric acids, and finally, noncannabinoid components of Cannabis that show anti-inflammatory action. It is intended to be an update on the topic of the involvement of cannabinoids in the process of inflammation. A possible mechanism for these actions is suggested involving increased production of eicosanoids that promote the resolution of inflammation. This differentiates these cannabinoids from cyclooxygenase-2 inhibitors that suppress the synthesis of eicosanoids that promote the induction of the inflammatory process.

Anandamide-mediated CB1/CB2 cannabinoid receptor--independent nitric oxide production in rabbit aortic endothelial cells

We have previously shown that the endocannabinoid anandamide and its metabolically stable analog (R)-methanandamide produce vasorelaxation in rabbit aortic ring preparations in an endothelium-dependent manner that could not be mimicked by other CB(1) cannabinoid receptor agonists (Am J Physiol 282: H2046-H2054, 2002). Here, we show that (R)-methanandamide and abnormal cannabidiol stimulated nitric oxide (NO) production in rabbit aortic endothelial cells (RAEC) in a dose-dependent manner but that other CB(1) and CB(2) receptor agonists, such as cis-3R-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4R-3(3-hydroxypropyl)-1R-cyclohexanol (CP55940) and (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl) pyrrolo-[1,2,3-d,e]-1,4-benzoxazin-6-yl]-1-naphthalenyl-methanone (WIN55212-2), failed to do so. CB(1) antagonists rimonabant [also known as SR141716; N-piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] and 6-methoxy-2-(4-methoxyphenyl)benzo[b]-thien-3-yl][4-cyanophenyl]methanone (LY320135) and CB(2) antagonist N-[(1S)-endo-1,3,3,-trimethylbicyclo[2.2.1]heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR144528) failed to block (R)-methanandamide-mediated NO production in RAEC. However, anandamide receptor antagonist (-)-4-(3-3,4-trans-p-menthadien-(1,8)-yl)-orcinol (O-1918) blocked (R)-methanandamide-mediated NO production in RAEC. Reverse transcriptase-polymerase chain reaction and Western blot analyses failed to detect the CB(1) receptor in RAEC, making this a good model to study non-CB(1) responses to anandamide. (R)-Methanandamide produced endothelial nitric-oxide synthase (eNOS) phosphorylation via the activation of phosphoinositide 3-kinase-Akt signaling. Inhibition of G(i) signaling with pertussis toxin, or phosphatidylinositol 3-kinase activity with 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), resulted in a decrease in (R)-methanandamide-induced Akt phosphorylation and NO production. Results from this study suggest that in RAEC, (R)-methanandamide acts on a novel non-CB(1) and non-CB(2) anandamide receptor and signals through G(i) and phosphatidylinositol 3-kinase, leading to Akt activation, eNOS phosphorylation, and NO production.

Effects of cannabinoid receptor activation on rabbit bisected vas deferens strips

1. In the present study, the effects of anandamide and WIN 55,212-2, cannabinoid receptor agonists, were investigated on electrical field stimulation (EFS)-induced biphasic twitch responses obtained from the epididymal and prostatic portions of rabbit vas deferens strips. 2. Anandamide and WIN 55,212-2 dose-dependently inhibited both the first and second phases of the EFS-induced twitch responses recorded from epididymal and prostatic portions of the vas deferens over the concentration range 10(-9) to 3 x 10(-6) mol/L. 3. The cannabinoid CB1 receptor antagonist AM 251 (10(-6) mol/L) and the cannabinoid CB2 receptor antagonist AM 630 (10(-6) mol/L) had no effect on the inhibitory action of anandamide on the biphasic twitch responses in the prostatic and epididymal portions of the rabbit vas deferens. 4. In both the prostatic and epididymal portions of the rabbit vas deferens, AM 251 significantly, but not completely, reversed the inhibitory effect of WIN 55,212-2 on the first phase of the twitch response. In contrast, AM 630 did not have any effect on the inhibitory action of WIN 55,212-2 in the rabbit vas deferens strips. 5. The inhibitory effects of anandamide or WIN 55,212-2 on EFS-induced twitch responses of both the prostatic and epididymal portions of the rabbit vas deferens were not altered in the presence of 10(-5) mol/L naloxone. 6. These results suggest that cannabinoid receptors may have a modulatory role in the regulation of sympathetic transmission in the rabbit vas deferens. However, further investigation is required to characterize the receptors involved.

Keep off the grass: marijuana use and acute cardiovascular events

Marijuana is one of the most widely used recreational substances in the world, considered by many consumers as a relatively safe drug with few significant side-effects. We report the case of a 21-year-old man who suffered an acute myocardial infarction following the use of marijuana, despite having no other identifiable risk factors for an acute cardiovascular event. We review the published medical literature regarding acute cardiovascular events following marijuana use and postulate a possible mechanism for this unusual pathological consequence of marijuana use.

VR1-Mediated Depressor Effects During High-Salt Intake

This study was designed to test the hypothesis that increased sensitivity of blood pressure to anandamide (AEA), an endocannabinoid compound, occurs during high-salt intake, which can be blocked by a selective vanilloid receptor 1(VR1) antagonist, capsazepine (CAPZ). Intravenous administration of a metabolically stable analog, methanandamide (MethA), dose-dependently decreased mean arterial pressure (MAP) in conscious rats fed a high-sodium diet (HS) for 3 weeks but it had a minimal effect in normal sodium (NS)-treated rats. The MethA-induced decrease in MAP was significantly attenuated but not abolished by CAPZ, or a selective cannabinoid receptor 1 (CB1) antagonist, SR141716A, administered separately in HS-treated rats. The MethA-induced depressor effect was prevented by the combined administration of CAPZ and SR141716A in HS-treated rats. Likewise, administration of capsaicin, a selective VR1 receptor agonist, dose-dependently decreased MAP in both HS- and NS-treated rats. The depressor effect of capsaicin was more profound in HS-treated rats, which was prevented by CAPZ. Western blot showed that expression of VR1 but not CB1 in mesenteric arteries was increased in HS-treated compared with NS-treated rats. Therefore, these data show that: (1) HS upregulates mesenteric VR1 expression; (2) HS increases sensitivity of blood pressure to AEA; and (3) HS-induced enhancement of the depressor effect of AEA can be prevented only when both VR1 and CB1 receptors are blocked. These results indicate that AEA contributes to the prevention of salt induced increases in blood pressure via, at least in part, activating the VR1 receptor.

Immunohistochemical localization of cerebrovascular cannabinoid CB1 receptor protein

Cannabinoids are powerful hypotensives and vasodilators. However, their mode of action is controversial. This study is the first to investigate the distribution of vascular CB1 receptor protein expression in situ. We used double-fluorescence and chromogenic immunohistochemistry to investigate patterns of CB1 protein expression in cerebrovascular tissue in rat brain sections. We found a layer of intense CB1 labeling immediately adjacent to the internal elastic lamina, consistent with myointimal and vascular smooth muscle cells, and diffuse labeling adventitial to this layer. We concluded that CB1 receptor are most intensely expressed in the vascular smooth muscle layer in cerebral arteries, and are likely to be chiefly responsible for the potent vasodilatory effect of cannabinoids.

Central effects of the cannabinoid receptor agonist WIN55212-2 on respiratory and cardiovascular regulation in anaesthetised rats

1 The primary aim was to study the central respiratory effects of cannabinoids (CB). To this end, the cannabinoid receptor agonist WIN55212-2 was injected into the cisterna magna of urethane-anaesthetised rats and changes in respiratory parameters were observed. The secondary aim was to observe the centrally elicited cardiovascular actions of WIN55212-2. Involvement of opioid mechanisms in the central effects of WIN55212-2 was also studied. 2 Intracisternal (i.c.) application of WIN55212-2 (1, 3, 10 and 30 microg kg(-1)) dose-dependently decreased the respiratory rate and minute volume. Tidal volume was slightly increased, whereas peak inspiratory flow remained unchanged. In addition, WIN55212-2 increased mean arterial pressure and the plasma noradrenaline concentration and decreased heart rate. 3 I.c. injection of WIN55212-3 (1, 3, 10 and 30 microg kg(-1)), an enantiomer of WIN55212-2 lacking affinity for cannabinoid receptors, elicited no effects. All effects of WIN55212-2 were prevented by the CB1 receptor antagonist SR141716 (2 mg kg(-1) i.v.). I.c. administration of the opioid receptor agonist DAMGO (0.1, 0.3, 1 and 3 microg kg(-1)) markedly lowered the respiratory rate, tidal volume, minute volume and peak inspiratory flow. These effects were attenuated by the opioid receptor antagonist naloxone (0.2 mg kg(-1) i.v.). In contrast, naloxone did not affect the respiratory and cardiovascular effects of i.c. administered WIN55212-2. 4 Our results show that activation of CB1 cannabinoid receptors in the brain stem depresses respiration and enhances sympathetic tone and cardiac vagal tone. Opioid mechanisms are not involved in these central cannabinoid effects.

Cannabinoids acting on CB1 receptors decrease contractile performance in human atrial muscle

Cannabinoids elicit hypotension mainly via activated CB(1) receptors and show complex cardiovascular actions. Effects on human heart muscle have not been studied yet. Isolated human atrial heart muscle preparations were stimulated by electrical field with 1 Hz to contract isometrically at optimal length and were challenged with the endogenous cannabinoid arachidonyl ethanolamide (anandamide), the metabolically stable analogue R-methanandamide, and the potent synthetic CB(1) receptor agonist HU-210. Anandamide dose-dependently decreased systolic force (82.2 +/- 4.8% and 60.8 +/- 6.8% of maximal systolic force for 0.1 and 1 microM, respectively, P < 0.05). The selective CB(1) receptor antagonist AM-251 (1 microM, P < 0.05), but not the CB(2) receptor antagonist, AM-630 (1 microM), the nitric oxide synthase inhibitor N omega-nitro-l-arginine methyl ester (l-NAME) (500 microM), or the cyclooxygenase inhibitor indomethacin (100 microM), prevented the effect. Contrary to indomethacin, l-NAME alone showed negative inotropic effects (72.1 +/- 3.54%, P < 0.001). The R-methanandamide (1 microM: 50.4 +/- 3.5%, P < 0.001) and HU-210 (1 microM: 60.1 +/- 3.8%, P < 0.001) had similar negative inotropic effects. The existence of CB(1) receptors on heart muscle was verified using Western blot analysis and immunofluorescence staining. The conclusion is that anandamide, R-methanandamide, and HU-210 decrease contractile performance in human atrial muscle via CB(1) receptors.

Selective ligands and cellular effectors of a G protein-coupled endothelial cannabinoid receptor

The cannabinoid analog abnormal cannabidiol [abn-cbd; (-)-4-(3-3,4-trans-p-menthadien-[1,8]-yl)-olivetol] does not bind to CB(1) or CB(2) receptors, yet it acts as a full agonist in relaxing rat isolated mesenteric artery segments. Vasorelaxation by abn-cbd is endothelium-dependent, pertussis toxin-sensitive, and is inhibited by the BK(Ca) channel inhibitor charybdotoxin, but not by the nitric-oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester or by the vanilloid VR1 receptor antagonist capsazepine. The cannabidiol analog O-1918 does not bind to CB(1) or CB(2) receptors and does not cause vasorelaxation at concentrations up to 30 microM, but it does cause concentration-dependent (1-30 microM) inhibition of the vasorelaxant effects of abn-cbd and anandamide. In anesthetized mice, O-1918 dose-dependently inhibits the hypotensive effect of abn-cbd but not the hypotensive effect of the CB(1) receptor agonist (-)-11-OH-Delta(9)-tetrahydrocannabinol dimethylheptyl. In human umbilical vein endothelial cells, abn-cbd induces phosphorylation of p42/44 mitogen-activated protein kinase and protein kinase B/Akt, which is inhibited by O-1918, by pertussis toxin or by phosphatidylinositol 3 (PI3) kinase inhibitors. These findings indicate that abn-cbd is a selective agonist and that O-1918 is a selective, silent antagonist of an endothelial "anandamide receptor", which is distinct from CB(1) or CB(2) receptors and is coupled through G(i)/G(o) to the PI3 kinase/Akt signaling pathway.

Plant-derived, synthetic and endogenous cannabinoids as neuroprotective agents. Non-psychoactive cannabinoids, 'entourage' compounds and inhibitors of N-acyl ethanolamine breakdown as therapeutic strategies to avoid pyschotropic effects

There is good evidence that plant-derived and synthetic cannabinoids possess neuroprotective properties. These compounds, as a result of effects upon CB(1) cannabinoid receptors, reduce the release of glutamate, and in addition reduce the influx of calcium following NMDA receptor activation. The major obstacle to the therapeutic utilization of such compounds are their psychotropic effects, which are also brought about by actions on CB(1) receptors. However, synthesis of the endogenous cannabinoids anandamide and 2-arachidonoylglycerol, which also have neuroprotective properties, are increased under conditions of severe inflammation and ischemia, raising the possibility that compounds that prevent their metabolism may be of therapeutic utility without having the drawback of producing psychotropic effects. In this review, the evidence indicating neuroprotective actions of plant-derived, synthetic and endogenous cannabinoids is presented. In addition, the pharmacological properties of endogenous anandamide-related compounds that are not active upon cannabinoid receptors, but which are also produced during conditions of severe inflammation and ischemia and may contribute to a neuroprotective action are reviewed.

Cardiovascular consequences of marijuana use

This review describes what is known about effects of marijuana and cannabinoids in relation to human physiological and disease outcomes. The acute physiological effects of marijuana include a substantial dose-dependent increase in heart rate, generally associated with a mild increase in blood pressure. Orthostatic hypotension may occur acutely as a result of decreased vascular resistance. Smoking marijuana decreases exercise test duration in maximal exercise tests, increases the heart rate at submaximal levels of exercise. Tolerance develops to the acute effects of marijuana smoking and delta9-tetrahydrocannibol (THC) over several days to a few weeks. The cardiovascular responses that occur in response to THC are mediated by the autonomic nervous system, with recent findings also demonstrating that the human cannabinoid receptor system plays a role in regulating the cardiovascular response. Although several mechanisms exist by which marijuana use might contribute to the development of chronic cardiovascular conditions or acutely trigger cardiovascular events, there are few data regarding marijuana/THC use and cardiovascular disease outcomes. A large cohort study showed no association of marijuana use with cardiovascular disease hospitalization or mortality. However, acute effects of marijuana use include a decrease of the time until the onset of chest pain in patients with angina pectoris; one study has shown that marijuana may trigger the onset of myocardial infarction. Patients who have coronary heart disease or are at high risk for the development of CHD should be cautioned about the potential hazards of marijuana use as a precipitant for clinical events. Research directions might include more studies of cardiovascular disease outcomes and relationships of marijuana with cardiovascular risk factors, studies of metabolic and physiologic effects of chronic marijuana use that may affect cardiovascular disease risk, increased understanding of the role of the cannabinoid receptor system in cardiovascular regulation, and studies to determine if there is a therapeutic role for cannabinoids in blood pressure control or for neuroprotection after stroke.

Cardiovascular system effects of marijuana

Marijuana and delta9-tetrahydrocannabinol (THC) increase heart rate, slightly increase supine blood pressure, and on occasion produce marked orthostatic hypotension. Cardiovascular effects in animals are different, with bradycardia and hypotension the most typical response. Cardiac output increases, and peripheral vascular resistance and maximum exercise performance decrease. Tolerance to most of the initial cardiovascular effects appears rapidly. With repeated exposure, supine blood pressure decreases slightly, orthostatic hypotension disappears, blood volume increases, heart rate slows, and circulatory responses to exercise and Valsalva maneuver are diminished, consistent with centrally mediated, reduced sympathetic, and enhanced parasympathetic activity. Receptor-mediated and probably nonneuronal sites of action account for cannabinoid effects. The endocannabinoid system appears important in the modulation of many vascular functions. Marijuana's cardiovascular effects are not associated with serious health problems for most young, healthy users, although occasional myocardial infarction, stroke, and other adverse cardiovascular events are reported. Marijuana smoking by people with cardiovascular disease poses health risks because of the consequences of the resulting increased cardiac work, increased catecholamine levels, carboxyhemoglobin, and postural hypotension.

Oxygenated metabolites of anandamide and 2-arachidonoylglycerol: conformational analysis and interaction with cannabinoid receptors, membrane transporter, and fatty acid amide hydrolase

This study was aimed at finding structural requirements for the interaction of the acyl chain of endocannabinoids with cannabinoid receptors, membrane transporter protein, and fatty acid amide hydrolase (FAAH). To this end, the flexibility of the acyl chain was restricted by introduction of an 1-hydroxy-2Z,4E-pentadiene system in anandamide (N-arachidonoylethanolamine, AEA) and 2-arachidonoylglycerol (2-AG) at various positions using different lipoxygenases. This brought about selectivity and attenuated the binding potency of AEA and 2-AG. Although the displacement constants were modest, 15(S)-hydroxy-eicosa-5Z,8Z,11Z,13E-tetraenoyl-N-(2-hydroxyethyl)amine was found to bind selectively to the CB(1) receptor, whereas its 1-arachidonoyl-sn-glycerol analogue and 13(S)-hydroxy-octadeca-9Z,11E-dienoyl-N-(2-hydroxyethyl)amine could selectively bind to the CB(2) receptor. 11(S)-Hydroxy-eicosa-5Z,8Z,12E,14Z-tetraenoyl-N-(2-hydroxyethyl)amine did not bind to either receptor, whereas 12(S)-hydroxy-eicosa-5Z,8Z,10E,14Z-tetraenoyl-N-(2-hydroxyethyl)amine did bind to both CB receptors with an affinity similar to that of AEA. All oxygenated anandamide derivatives were good inhibitors of FAAH (low micromolar K(i)) but were ineffective on the AEA transporter. 2-AG rapidly isomerizes into 1(3)-arachidonoyl-sn-glycerol. Both 1- and 3-arachidonoyl-sn-glycerol did not bind to either CB receptor and did not interfere with AEA transport. Thus, after it is isomerized, 2-AG is inactivated, thereby decreasing effective concentrations of 2-AG. Analysis of (1)H NMR spectra revealed that chloroform did not induce notably different conformations in the acyl chain of 15(S)-hydroxy-eicosa-5Z,8Z,11Z,13E-tetraenoic acid as compared with water. Molecular dynamics (MD) simulations of AEA and its analogues in the presence of explicit water molecules revealed that a tightly folded conformation of the acyl chain is not the only requirement for CB(1) binding. Structural details of the C(2)-C(15) loop, such as an sp(2) carbon at position 11, are necessary for receptor binding. The MD simulations may suggest that the average orientations of the pentyl tail of AEA and 12(S)-hydroxy-eicosa-5Z,8Z,10E,14Z-tetraenoyl-N-(2-hydroxyethyl)amine are different from that of the low-affinity, inactive ligands.

Exogenous anandamide protects rat brain against acute neuronal injury in vivo

The endocannabinoid anandamide [N-arachidonoylethanolamine (AEA)] is thought to function as an endogenous protective factor of the brain against acute neuronal damage. However, this has never been tested in an in vivo model of acute brain injury. Here, we show in a longitudinal pharmacological magnetic resonance imaging study that exogenously administered AEA dose-dependently reduced neuronal damage in neonatal rats injected intracerebrally with the Na(+)/K(+)-ATPase inhibitor ouabain. At 15 min after injury, AEA (10 mg/kg) administered 30 min before ouabain injection reduced the volume of cytotoxic edema by 43 +/- 15% in a manner insensitive to the cannabinoid CB(1) receptor antagonist SR141716A. At 7 d after ouabain treatment, 64 +/- 24% less neuronal damage was observed in AEA-treated (10 mg/kg) rats compared with control animals. Coadministration of SR141716A prevented the neuroprotective actions of AEA at this end point. In addition, (1) no increase in AEA and 2-arachidonoylglycerol levels was detected at 2, 8, or 24 hr after ouabain injection; (2) application of SR141716A alone did not increase the lesion volume at days 0 and 7; and (3) the AEA-uptake inhibitor, VDM11, did not affect the lesion volume. These data indicate that there was no endogenous endocannabinoid tone controlling the acute neuronal damage induced by ouabain. Although our data seem to question a possible role of the endogenous cannabinoid system in establishing a brain defense system in our model, AEA may be used as a structural template to develop neuroprotective agents.

Endogenous cannabinoids mediate hypotension after experimental myocardial infarction

OBJECTIVES

We sought to determine whether endocannabinoids influence hemodynamic variables in experimental models of acute myocardial infarction (MI).

BACKGROUND

Hypotension and cardiogenic shock are common complications in acute MI. Cannabinoids are strong vasodilators, and endocannabinoids are involved in hypotension in hemorrhagic and septic shock.

METHODS

The early effect of left coronary artery ligation on hemodynamic variables was measured in rats pretreated with the selective cannabinoid(1) receptor (CB(1)) antagonist SR141716A (herein referred to as SR, 6.45 micromol/kg body weight intravenously) or vehicle. Endocannabinoids produced in monocytes and platelets were quantified by liquid chromatography/mass spectrometry (LC/MS), and their effects on blood pressure and vascular reactivity were determined.

RESULTS

After MI, mean arterial pressure (MAP) dropped from 126 +/- 2 mm Hg to 76 +/- 3 mm Hg in control rats, whereas the decline in blood pressure was smaller (from 121 +/- 3 mm Hg to 108 +/- 7 mm Hg, p < 0.01) in rats pretreated with SR. SR increased the tachycardia that follows MI (change [Delta] in heart rate [HR] = 107 +/- 21 beats/min vs. 49 +/- 9 beats/min in control rats, p < 0.05). The MI sizes were the same in control rats and SR-treated rats. Circulating monocytes and platelets isolated 30 min after MI only decreased MAP when injected into untreated rats (DeltaMAP = -20 +/- 5 mm Hg), but not in SR-pretreated rats. The endocannabinoids anandamide and 2-arachidonyl glycerol were detected in monocytes and platelets isolated after MI, but not in cells from sham rats. Survival rates at 2 h after MI were 70% for control rats and 36% for SR-treated rats (p < 0.05). Endothelium-dependent arterial relaxation was attenuated in SR-treated rats (maximal relaxation: 44 +/- 3% [p < 0.01] vs. 70 +/- 3% in control rats) and further depressed by SR treatment (24 +/- 5%, p < 0.01 vs. MI placebo).

CONCLUSIONS

Cannabinoids generated in monocytes and platelets contribute to hypotension in acute MI. Cannabinoid(1) receptor blockade restores MAP but increases 2-h mortality, possibly by impairing endothelial function.

Anandamide-induced relaxation of sheep coronary arteries: the role of the vascular endothelium, arachidonic acid metabolites and potassium channels

1. The effects of the endocannabinoid, anandamide, and its metabolically stable analogue, methanandamide, on induced tone were examined in sheep coronary artery rings in vitro. 2. In endothelium-intact rings precontracted to the thromboxane A(2) mimetic, U46619, anandamide (0.01 - 30 microM) induced slowly developing concentration-dependent relaxations (pEC(50) [negative log of EC(50)]=6.1+/-0.1; R(max) [maximum response]=81+/-4%). Endothelium denudation caused a 10 fold rightward shift of the anandamide concentration-relaxation curve without modifying R(max). Methanandamide was without effect on U46619-induced tone. 3. The anandamide-induced relaxation was unaffected by the cannabinoid receptor antagonist, SR 141716A (3 microM), the vanilloid receptor antagonist, capsazepine (3 and 10 microM) or the nitric oxide synthase inhibitor, L-NAME (100 microM). 4. The cyclo-oxygenase inhibitor, indomethacin (3 and 10 microM) and the anandamide amidohydrolase inhibitor, PMSF (70 and 200 microM), markedly attenuated the anandamide response. The anandamide transport inhibitor, AM 404 (10 and 30 microM), shifted the anandamide concentration-response curve to the right. 5. Precontraction of endothelium-intact rings with 25 mM KCl attenuated the anandamide-induced relaxations (R(max)=7+/-7%), as did K(+) channel blockade with tetraethylammonium (TEA; 3 microM) or iberiotoxin (100 nM). Blockade of small conductance, Ca(2+)-activated K(+) channels, delayed rectifier K(+) channels, K(ATP) channels or inward rectifier K(+) channels was without effect. 6. These data suggest that the relaxant effects of anandamide in sheep coronary arteries are mediated in part via the endothelium and result from the cellular uptake and conversion of anandamide to a vasodilatory prostanoid. This, in turn, causes vasorelaxation, in part, by opening potassium channels.

Neuroprotection by Delta9-tetrahydrocannabinol, the main active compound in marijuana, against ouabain-induced in vivo excitotoxicity

Excitotoxicity is a paradigm used to explain the biochemical events in both acute neuronal damage and in slowly progressive, neurodegenerative diseases. Here, we show in a longitudinal magnetic resonance imaging study that Delta(9)-tetrahydrocannabinol (Delta(9)-THC), the main active compound in marijuana, reduces neuronal injury in neonatal rats injected intracerebrally with the Na(+)/K(+)-ATPase inhibitor ouabain to elicit excitotoxicity. In the acute phase Delta(9)-THC reduced the volume of cytotoxic edema by 22%. After 7 d, 36% less neuronal damage was observed in treated rats compared with control animals. Coadministration of the CB(1) cannabinoid receptor antagonist SR141716 prevented the neuroprotective actions of Delta(9)-THC, indicating that Delta(9)-THC afforded protection to neurons via the CB(1) receptor. In Delta(9)-THC-treated rats the volume of astrogliotic tissue was 36% smaller. The CB(1) receptor antagonist did not block this effect. These results provide evidence that the cannabinoid system can serve to protect the brain against neurodegeneration.

Novel physiologic functions of endocannabinoids as revealed through the use of mutant mice

The presence in the mammalian brain of specific receptors for marijuana triggered a search for endogenous ligands, several of which have been recently identified. There has been growing interest in the possible physiological functions of endocannabinoids, and mutant mice that lack cannabinoid receptors have become an important tool in the search for such functions. To date, studies using CB1 knockout mice have supported the possible role of endocannabinoids in retrograde synaptic inhibition in the hippocampus, in long-term potentiation and memory, in the development of opiate dependence, and in the control of appetite and food intake. They also suggested the existence of as yet unidentified cannabinoid receptors in the cardiovascular and central nervous systems. The use of CB2 receptor knockout mice suggested a role for this receptor in macrophage-mediated helper T cell activation. Further studies will undoubtedly reveal many additional roles for this novel signaling system.

Hemodynamic effects of cannabinoids: coronary and cerebral vasodilation mediated by cannabinoid CB(1) receptors

Activation of peripheral cannabinoid CB(1) receptors elicits hypotension. Using the radioactive microsphere technique, we examined the effects of cannabinoids on systemic hemodynamics in anesthetized rats. The potent cannabinoid CB(1) receptor agonist HU-210 ([-]-11-OH-Delta(9) tetrahydrocannabinol dimethylheptyl, 10 microg/kg i.v.) reduced mean blood pressure by 57+/-5 mm Hg by decreasing cardiac index from 37+/-1 to 23+/-2 ml/min/100 g (P<0.05) without significantly affecting systemic vascular resistance index. HU-210 elicited a similar decrease in blood pressure following ganglionic blockade and vasopressin infusion. The endogenous cannabinoid anandamide (arachidonyl ethanolamide, 4 mg/kg i.v.) decreased blood pressure by 40+/-7 mm Hg by reducing systemic vascular resistance index from 3.3+/-0.1 to 2.3+/-0.1 mm Hg min/ml/100 g (P<0.05), leaving cardiac index and stroke volume index unchanged. HU-210, anandamide, and its metabolically stable analog, R-methanandamide, lowered vascular resistance primarily in the coronaries and the brain. These vasodilator effects remained unchanged when autoregulation was prevented by maintaining blood pressure through volume replacement, but were prevented by pretreatment with the cannabinoid CB(1) receptor antagonist SR141716A (N-[piperidin-1-yl]-5-[4-chlorophenyl]-1-[2,4-dichlorophenyl]-4-methyl-1H-pyrazole-3-carboxamide HCl; 3 mg/kg i.v.). Only anandamide and R-methanandamide were vasodilators in the mesentery. We conclude that cannabinoids elicit profound coronary and cerebral vasodilation in vivo by direct activation of vascular cannabinoid CB(1) receptors, rather than via autoregulation, a decrease in sympathetic tone or, in the case of anandamide, the action of a non-cannabinoid metabolite. Differences between the hemodynamic profile of various cannabinoids may reflect quantitative differences in cannabinoid CB(1) receptor expression in different tissues and/or the involvement of as-yet-unidentified receptors.

Endocannabinoids as cardiovascular modulators

Cannabinoids, the bioactive constituents of the marijuana plant and their synthetic and endogenous analogs cause not only neurobehavioral, but also cardiovascular effects. The most important component of these effects is a profound decrease in blood pressure and heart rate. Although multiple lines of evidence indicate that the hypotensive and bradycardic effects of anandamide and other cannabinoids are mediated by peripherally located CB1 cannabinoid receptors, anandamide can also elicit vasodilation in certain vascular beds, which is independent of CB1 or CB2 receptors. Possible cellular mechanisms underlying these effects and the cellular sources of vasoactive anandamide are discussed.

New perspectives on enigmatic vanilloid receptors

In spite of the rapid advances in our understanding of vanilloid-receptor pharmacology in the PNS, the function of vanilloid receptors in the brain has remained elusive. Recently, the endocannabinoid anandamide has been proposed to function as an endogenous agonist at the vanilloid receptor VR1. This is an exciting hypothesis because the localization of VR1 overlaps with that of anandamide and its preferred cannabinoid receptor CB(1) in various brain areas. The interaction of anandamide and/or related lipid metabolites with these two completely separate receptor systems in the brain clearly places VR1 in a much broader role than pain perception. At a practical level, the overlapping ligand recognition properties of VR1 and CB(1) might be exploited by medicinal chemistry. For example, arvanil, a 'chimeric' ligand that combines structural features of capsaicin and anandamide, promises to be an interesting lead for new drugs that interact at both vanilloid and cannabinoid receptors.

Comparative biology of the endocannabinoid system possible role in the immune response

In this review we discuss data showing that the endogenous cannabinoid system, represented by cannabinoid receptors, endogenous cannabinoid receptor ligands and enzymes for the biosynthesis and degradation of these ligands, is conserved throughout evolution from coelenterates to man. This signaling system has been suggested to play several roles in animals, including the regulation of cell development and growth, nervous functions, reproduction and feeding behavior. In this article, however, we shall describe with more detail the possible function of the endogenous cannabinoid system in the modulation of immune response in organisms from the lower to the higher levels of animal evolution.