Mechanism of the hypotensive action of anandamide in anesthetized rats

Polymeric Nanomicelles Loaded with Anandamide and Their Renal Effects as a Therapeutic Alternative for Hypertension Treatment by Passive Targeting

We have previously demonstrated significant in vitro natriuretic effects of anandamide (AEA) nanoformulation in polymeric nanoparticles, whose size prevents their accumulation in organs, such as the kidneys. Therefore, it is of particular interest to design and test nanostructures that can pharmacologically accumulate in these organs. In this regard, we prepared and characterized polymeric nanomicelles (~14 and 40 nm). Likewise, their biodistribution was determined. Spontaneously hypertensive rats (SHR) and normotensive rats (WKY), n = 3 per group, were divided into five treatment conditions: control, sham, free AEA freshly dispersed in aqueous solution or 24 h after its dispersion, and AEA encapsulated in nanomicelles. The kidneys were the main site of accumulation of the nanoformulation after 24 h. Freshly dispersed free AEA showed its classical triphasic response in SHR, which was absent from all other treatments. Nanoformulated AEA produced a sustained antihypertensive effect over 2 h, accompanied by a significant increase in fractional sodium excretion (FSE %). These effects were not observed in WKY, sham, or free AEA-treated rats after 24 h of its aqueous dispersion. Without precedent, we demonstrate in vivo natriuretic, diuretic, and hypotensive effects of AEA nanoformulation in polymeric nanomicelles, suggesting its possible use as a new antihypertensive agent with intravenous administration and passive renal accumulation.

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.

Fatty acid amide hydrolase activity in the dorsal periaqueductal gray attenuates neuropathic pain and associated dysautonomia

The complexity of neuropathic pain and its associated comorbidities, including dysautonomia, make it difficult to treat. Overlap of anatomical regions and pharmacology of sympathosensory systems in the central nervous system (CNS) provide targets for novel treatment strategies. The dorsal periaqueductal gray (dPAG) is an integral component of both the descending pain modulation system and the acute stress response and is critically involved in both analgesia and the regulation of sympathetic activity. Local manipulation of the endocannabinoid signaling system holds great promise to provide analgesia without excessive adverse effects and also influence autonomic output. Inhibition of fatty acid amide hydrolase (FAAH) increases brain concentrations of the endocannabinoid N-arachidonoylethanolamine (AEA) and reduces pain-related behaviors in neuropathic pain models. Neuropathic hyperalgesia and reduced sympathetic tone are associated with increased FAAH activity in the dPAG, which suggests the hypothesis that inhibition of FAAH in the dPAG will normalize pain sensation and autonomic function in neuropathic pain. To test this hypothesis, the effects of systemic or intra-dPAG FAAH inhibition on hyperalgesia and dysautonomia developed after spared nerve injury (SNI) were assessed in male and female rats. Administration of the FAAH inhibitor PF-3845 into the dPAG reduces hyperalgesia behavior and the decrease in sympathetic tone induced by SNI. Prior administration of the CB1 receptor antagonist AM281, attenuated the antihyperalgesic and sympathetic effects of FAAH inhibition. No sex differences were identified. These data support an integrative role for AEA/CB1 receptor signaling in the dPAG contributing to the regulation of both hyperalgesia behavior and altered sympathetic tone in neuropathic pain.

The Therapeutic Potential of the Endocannabinoid System in Age-Related Diseases

The endocannabinoid system (ECS) dynamically regulates many aspects of mammalian physiology. ECS has gained substantial interest since growing evidence suggests that it also plays a major role in several pathophysiological conditions due to its ability to modulate various underlying mechanisms. Furthermore, cannabinoids, as components of the cannabinoid system (CS), have proven beneficial effects such as anti-inflammatory, immunomodulatory, neuromodulatory, antioxidative, and cardioprotective effects. In this comprehensive review, we aimed to describe the complex interaction between CS and most common age-related diseases such as neuro-degenerative, oncological, skeletal, and cardiovascular disorders, together with the potential of various cannabinoids to ameliorate the progression of these disorders. Since chronic inflammation is postulated as the pillar of all the above-mentioned medical conditions, we also discuss in this paper the potential of CS to ameliorate aging-associated immune system dysregulation.

Acute and long-term effects of cannabinoids on hypertension and kidney injury

Cannabinoids and their endogenous and synthetic analogs impact blood pressure and contribute to the incidence of hypertension. It was previously reported that the endocannabinoid system plays an important role in developing hypertension; however, it was also shown that cannabinoids elicit profound hypotension associated with hemorrhagic, cardiogenic, and endotoxic shock. This study aimed to test acute and chronic effects of an endogenous ligand of cannabinoid receptor anandamide (AEA) on blood pressure and kidney injury in vivo in conscious Dahl salt-sensitive (SS) rats. We demonstrated that acute i.v. bolus administration of a low or a high doses (0.05 or 3 mg/kg) of AEA did not affect blood pressure for 2 h after the injection in Dahl SS rats fed a normal salt diet (0.4% NaCl). Neither low nor high doses of AEA had any beneficial effects on blood pressure or kidney function. Furthermore, hypertensive rats fed a HS diet (8% NaCl) and chronically treated with 3 mg/kg of AEA exhibited a significant increase in blood pressure accompanied by increased renal interstitial fibrosis and glomerular damage at the late stage of hypertension. Western blot analyses revealed increased expression of Smad3 protein levels in the kidney cortex in response to chronic treatment with a high AEA dose. Therefore, TGF-β1/Smad3 signaling pathway may play a crucial role in kidney injury in SS hypertension during chronic treatment with AEA. Collectively, these data indicate that prolonged stimulation of cannabinoid receptors may result in aggravation of hypertension and kidney damage.

ZnO Nanoparticles Induce Dyslipidemia and Atherosclerotic Lesions Leading to Changes in Vascular Contractility and Cannabinoid Receptors Expression as Well as Increased Blood Pressure

ZnO nanoparticles (ZnONPs) have been shown to have therapeutic potential in some diseases such as diabetes and cancer. However, concentration-dependent adverse effects have also been reported. Studies which evaluate the effects of ZnONPs on the cardiovascular system are scarce. This study aimed to evaluate the cardiovascular effects of a low dose of ZnONPs administered chronically in healthy rats. Changes in dyslipidemia biomarkers, blood pressure, aortic wall structure, vascular contractility, and expression of cannabinoid receptors in the aorta wall were evaluated. Healthy rats were divided into two groups: control or treated (one, two, and three months). The treated rats received an oral dose of 10 mg/kg/day. The results showed that treatment with ZnONPs induced dyslipidemia from the first month, increasing atherosclerosis risk, which was confirmed by presence of atherosclerotic alterations revealed by aorta histological analysis. In in vitro assays, ZnONPs modified the aorta contractile activity in response to the activation of cannabinoid receptors (CB1 and CB2). The expression of CB1 and CB2 was modified as well. Moreover, ZnONPs elicited an increase in blood pressure. In conclusion, long-time oral administration of ZnONPs induce dyslipidemia and atherosclerosis eliciting alterations in aorta contractility, CB1 and CB2 receptors expression, and an increase in blood pressure in healthy rats.

Role of the Endocannabinoidome in Human and Mouse Atherosclerosis

The Endocannabinoid (eCB) system and its role in many physiological and pathological conditions is well described and accepted, and includes cardiovascular disorders. However, the eCB system has been expanded to an "-ome"; the endocannabinoidome (eCBome) that includes endocannabinoid-related mediators, their protein targets and metabolic enzymes, many of which significantly impact upon cardiometabolic health. These recent discoveries are here summarized with a special focus on their potential involvement in atherosclerosis. We described the role of classical components of the eCB system (eCBs, CB1 and CB2 receptors) and eCB-related lipids, their regulatory enzymes and molecular targets in atherosclerosis. Furthermore, since increasing evidence points to significant cross-talk between the eCBome and the gut microbiome and the gut microbiome and atherosclerosis, we explore the possibility that a gut microbiome - eCBome axis has potential implications in atherosclerosis.

The endocannabinoid anandamide has an anti-inflammatory effect on CCL2 expression in vascular smooth muscle cells

Endocannabinoids are important lipid-signaling mediators. Both protective and deleterious effects of endocannabinoids in the cardiovascular system have been reported but the mechanistic basis for these contradicting observations is unclear. We set out to identify anti-inflammatory mechanisms of endocannabinoids in the murine aorta and in human vascular smooth muscle cells (hVSMC). In response to combined stimulation with cytokines, IL-1β and TNFα, the murine aorta released several endocannabinoids, with anandamide (AEA) levels being the most significantly increased. AEA pretreatment had profound effects on cytokine-induced gene expression in hVSMC and murine aorta. As revealed by RNA-Seq analysis, the induction of a subset of 21 inflammatory target genes, including the important cytokine CCL2 was blocked by AEA. This effect was not mediated through AEA-dependent interference of the AP-1 or NF-κB pathways but rather through an epigenetic mechanism. In the presence of AEA, ATAC-Seq analysis and chromatin-immunoprecipitations revealed that CCL2 induction was blocked due to increased levels of H3K27me3 and a decrease of H3K27ac leading to compacted chromatin structure in the CCL2 promoter. These effects were mediated by recruitment of HDAC4 and the nuclear corepressor NCoR1 to the CCL2 promoter. This study therefore establishes a novel anti-inflammatory mechanism for the endogenous endocannabinoid AEA in vascular smooth muscle cells. Furthermore, this work provides a link between endogenous endocannabinoid signaling and epigenetic regulation.

A case report positive for synthetic cannabinoids: are cardiovascular effects related to their protracted use?

The use of synthetic cannabinoids is being increasingly recognised worldwide, but the chemical compositions and physiological effects of these drugs are poorly characterised and are continually changing. New substances are constantly being added to the content of synthetic cannabinoids and they are rarely identified on toxicological screening tests. Due to their structures synthetic cannabinoids and their effects have been compared to the psychoactive compound, Δ-9-tetrahydrocannabinol (THC), found in marijuana. On the molecular level, they are potent cannabinoid receptor agonists that also may have affinity for other types of receptors such as those on platelets. Reported symptoms of toxicity include anxiety, agitation, paranoia, hallucinations, tachycardia, hypertension, excessive sweating, nausea, and vomiting. They can also be linked to serious adverse cardiovascular events and can affect the cardiovascular system causing hypotension and bradycardia, myocardial infarction, atrial fibrillation, prolonged QTc, and Mobitz type II atrioventricular block, as well as interfere with the aggregation of platelets. We present a case report of a cardiac tamponade with toxicological findings positive for synthetic cannabinoids. This case highlights the importance of testing routinely for novel psychoactive compounds, and recognising their potential to cause life-threatening conditions.

Cannabinoids and Cardiovascular System

Cannabinoids influence cardiovascular variables in health and disease via multiple mechanisms. The chapter covers the impact of cannabinoids on cardiovascular function in physiology and pathology and presents a critical analysis of the proposed signalling pathways governing regulation of cardiovascular function by endogenously produced and exogenous cannabinoids. We know that endocannabinoid system is overactivated under pathological conditions and plays both a protective compensatory role, such as in some forms of hypertension, atherosclerosis and other inflammatory conditions, and a pathophysiological role, such as in disease states associated with excessive hypotension. This chapter focuses on the mechanisms affecting hemodynamics and vasomotor effects of cannabinoids in health and disease states, highlighting mismatches between some studies. The chapter will first review the effects of marijuana smoking on cardiovascular system and then describe the impact of exogenous cannabinoids on cardiovascular parameters in humans and experimental animals. This will be followed by analysis of the impact of cannabinoids on reactivity of isolated vessels. The article critically reviews current knowledge on cannabinoid induction of vascular relaxation by cannabinoid receptor-dependent and -independent mechanisms and dysregulation of vascular endocannabinoid signaling in disease states.

Role of Nitric Oxide in the Cardiovascular and Renal Systems

The gasotransmitters are a family of gaseous signaling molecules which are produced endogenously and act at specific receptors to play imperative roles in physiologic and pathophysiologic processes. As a well-known gasotransmitter along with hydrogen sulfide and carbon monoxide, nitric oxide (NO) has earned repute as a potent vasodilator also known as endothelium-derived vasorelaxant factor (EDRF). NO has been studied in greater detail, from its synthesis and mechanism of action to its physiologic, pathologic, and pharmacologic roles in different disease states. Different animal models have been applied to investigate the beneficial effects of NO as an antihypertensive, renoprotective, and antihypertrophic agent. NO and its interaction with different systems like the renin–angiotensin system, sympathetic nervous system, and other gaseous transmitters like hydrogen sulfide are also well studied. However, links that appear to exist between the endocannabinoid (EC) and NO systems remain to be fully explored. Experimental approaches using modulators of its synthesis including substrate, donors, and inhibitors of the synthesis of NO will be useful for establishing the relationship between the NO and EC systems in the cardiovascular and renal systems. Being a potent vasodilator, NO may be unique among therapeutic options for management of hypertension and resulting renal disease and left ventricular hypertrophy. Inclusion of NO modulators in clinical practice may be useful not only as curatives for particular diseases but also for arresting disease prognoses through its interactions with other systems.

A Systematic Review of the Complex Effects of Cannabinoids on Cerebral and Peripheral Circulation in Animal Models

While cannabis is perceived as a relatively safe drug by the public, accumulating clinical data suggest detrimental cardiovascular effects of cannabinoids. Cannabis has been legalized in several countries and jurisdictions recently. Experimental studies specifically targeting cannabinoids' effects on the cerebral vasculature are rare. There is evidence for transient vasoconstrictive effects of cannabinoids in the peripheral and cerebral vasculature in a complex interplay of vasodilation and vasoconstriction. Vasoreactivity to cannabinoids is dependent on the specific molecules, their metabolites and dose, baseline vascular tone, and vessel characteristics as well as experimental conditions and animal species. We systematically review the currently available literature of experimental results in in vivo and in vitro animal studies, examining cannabinoids' effects on circulation and reactive vasodilation or vasoconstriction, with a particular focus on the cerebral vascular bed.

Cannabinoids in the Cardiovascular System

Cannabinoids are known to modulate cardiovascular functions including heart rate, vascular tone, and blood pressure in humans and animal models. Essential components of the endocannabinoid system, namely, the production, degradation, and signaling pathways of endocannabinoids have been described not only in the central and peripheral nervous system but also in myocardium, vasculature, platelets, and immune cells. The mechanisms of cardiovascular responses to endocannabinoids are often complex and may involve cannabinoid CB₁ and CB₂ receptors or non-CB_1/2 receptor targets. Preclinical and some clinical studies have suggested that targeting the endocannabinoid system can improve cardiovascular functions in a number of pathophysiological conditions, including hypertension, metabolic syndrome, sepsis, and atherosclerosis. In this chapter, we summarize the local and systemic cardiovascular effects of cannabinoids and highlight our current knowledge regarding the therapeutic potential of endocannabinoid signaling and modulation.

Vascular Dysfunction in a Transgenic Model of Alzheimer's Disease: Effects of CB1R and CB2R Cannabinoid Agonists

There is evidence of altered vascular function, including cerebrovascular, in Alzheimer's disease (AD) and transgenic models of the disease. Indeed vasoconstrictor responses are increased, while vasodilation is reduced in both conditions. β-Amyloid (Aβ) appears to be responsible, at least in part, of alterations in vascular function. Cannabinoids, neuroprotective and anti-inflammatory agents, induce vasodilation both in vivo and in vitro. We have demonstrated a beneficial effect of cannabinoids in models of AD by preventing glial activation. In this work we have studied the effects of these compounds on vessel density in amyloid precursor protein (APP) transgenic mice, line 2576, and on altered vascular responses in aortae isolated ring. First we showed increased collagen IV positive vessels in AD brain compared to control subjects, with a similar increase in TgAPP mice, which was normalized by prolonged oral treatment with the CB1/CB2 mixed agonist WIN 55,212-2 (WIN) and the CB2 selective agonist JWH-133 (JWH). In Tg APP mice the vasoconstriction induced by phenylephrine and the thromboxane agonist U46619 was significantly increased, and no change in the vasodilation to acetylcholine (ACh) was observed. Tg APP displayed decreased vasodilation to both cannabinoid agonists, which were able to prevent decreased ACh relaxation in the presence of Aβ. In summary, we have confirmed and extended the existence of altered vascular responses in Tg APP mice. Moreover, our results suggest that treatment with cannabinoids may ameliorate the vascular responses in AD-type pathology.

The CB1 antagonist, SR141716A, is protective in permanent photothrombotic cerebral ischemia

Modulation of the endocannabinoid system has been shown to have a significant impact on outcomes in animal models of stroke. We have previously reported a protective effect of the CB1 antagonist, SR141716A, in a transient reperfusion mouse model of cerebral ischemia. This protective effect was in part mediated by activation of the 5HT1A receptor. Here we have examined its effect in a mouse model of permanent ischemia induced by photoinjury. The CB1 antagonist was found to be protective in this model. As was the case following transient ischemia reperfusion, SR141716A (5mg/kg) resulted in smaller infarct fractions and stroke volumes when utilized both as a pretreatment and as a post-treatment. In contrast to the effect in a transient ischemia model, the pretreatment effect did not depend on the 5HT1A receptor. Neurological function correlated favorably to the reduction in stroke size when SR141716A was given as a pretreatment. With the incidence of stroke predicted to rise in parallel with an ever aging population, understanding mechanisms underlying ischemia and therapeutics remains a paramount goal of research.

Components of the cannabinoid system in the dorsal periaqueductal gray are related to resting heart rate

The present study was undertaken to examine whether variations in endocannabinoid signaling in the dorsal periaqueductal gray (dPAG) are associated with baseline autonomic nerve activity, heart rate, and blood pressure. Blood pressure was recorded telemetrically in rats, and heart rate and power spectral analysis of heart rate variability were determined. Natural variations from animal to animal provided a range of baseline values for analysis. Transcript levels of endocannabinoid signaling components in the dPAG were analyzed, and endocannabinoid content and catabolic enzyme activity were measured. Higher baseline heart rate was associated with increased anandamide content and with decreased activity of the anandamide-hydrolyzing enzyme, fatty acid amide hydrolase (FAAH), and it was negatively correlated with transcript levels of both FAAH and monoacylglycerol lipase (MAGL), a catabolic enzyme for 2-arachidonoylglycerol (2-AG). Autonomic tone and heart rate, but not blood pressure, were correlated to levels of FAAH mRNA. In accordance with these data, exogenous anandamide in the dPAG of anesthetized rats increased heart rate. These data indicate that in the dPAG, anandamide, a FAAH-regulated lipid, contributes to regulation of baseline heart rate through influences on autonomic outflow.

Anandamide and its metabolites: what are their roles in the kidney?

Anandamide (AEA) is the N-acyl ethanolamide of arachidonic acid, an agonist of cannabinoid and non-cannabinoid receptors in the body. The kidneys are enriched in AEA and in enzymes that metabolize AEA, but the roles of AEA and its metabolites in the kidney remain poorly understood. This system likely is involved in the regulation of renal blood flow and hemodynamics and of tubular sodium and fluid reabsorption. It may act as a neuromodulator of the renal sympathetic nervous system. AEA and its cyclooxygenase-2 metabolites, the prostamides, in the renal medulla may represent a unique antihypertensive system involved in the long-term control of blood pressure. AEA and its metabolites are also implicated as modulators of inflammation and mediators of signaling in inflammation. AEA and its metabolites may be influential in chronic kidney disease states associated with inflammation and cardiovascular diseases associated with hyperhomocysteinemia. The current knowledge of the roles of AEA and its derivatives highlights the need for further research to define and potentially exploit the role of this endocannabinoid system in the kidney.

Enhanced vasorelaxation effect of endogenous anandamide on thoracic aorta in renal vascular hypertension rats

Emerging evidence has indicated that anandamide (AEA) is able to stimulate vasorelaxation in both spontaneously hypertensive rats (SHRs) and L-NAME-induced hypertensive rats. Yet it remains unknown whether AEA modulates vasomotion of the aorta in renovascular hypertensive (RVH) rats. The aim of present study is to explore the effect of AEA on the relaxation of thoracic aortas in two-kidney one-clip (2K1C)-induced RVH rats. It is demonstrated that AEA stimulates a pronounced relaxation in the aortas of 2K1C rats compared with sham rats. The enhanced relaxation caused by AEA in aortas from 2K1C rats was diminished in the presence of the cannabinoid receptor-1 (CB₁ ) antagonist AM251 and the CB₂ receptor antagonist AM630. Likewise, the vasodilation action of AEA was blocked in L-NAME-treated or endothelium-denuded aortas. The Western blot results revealed that the expression of CB₁ and CB₂ receptors was increased in the 2K1C rat aortas compared with sham rats. The phosphorylation of endothelial nitric oxide synthase (p-eNOS) at the activation site Ser1177 was enhanced in AEA-treated rings from 2K1C rats in both time-dependent and dose-dependent manners. The augmented p-eNOS expression was inhibited by the co-treatment with AM251 or AM630. Taken together, the present study demonstrated that AEA enhanced endothelium-dependent aortic relaxation through activation of both CB₁ and CB₂ receptors and P-eNOS/NO pathway in 2K1C rats.

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.

Cannabinoid receptor type 1 activation by arachidonylcyclopropylamide in rat aortic rings causes vasorelaxation involving calcium-activated potassium channel subunit alpha-1 and calcium channel, voltage-dependent, L type, alpha 1C subunit

Cannabinoids are key regulators of vascular tone, some of the mechanisms involved include the activation of cannabinoid receptor types 1 and 2 (CB); the transient receptor potential cation channel, subfamily V, member 1 (TRPV1); and non-(CB(1))/non-CB2 receptors. Here, we used the potent, selective CB(1) agonist arachidonylcyclopropylamide (ACPA) to elucidate the mechanism underlying vascular tone regulation. Immunohistochemistry and confocal microscopy revealed that CB(1) was expressed in smooth muscle and endothelial cells in rat aorta. We performed isometric tension recordings in aortic rings that had been pre-contracted with phenylephrine. In these conditions, ACPA caused vasorelaxation in an endothelium-independent manner. To confirm that the effect of ACPA was mediated by CB(1) receptor, we repeated the experiment after blocking these receptors with a selective antagonist, AM281. In these conditions, ACPA did not cause vasorelaxation. We explored the role of K(+) channels in the effect of ACPA by applying high-K(+) solution to induce contraction in aortic rings. In these conditions, the ACPA-induced vasorelaxation was about half that observed with phenylephrine-induced contraction. Thus, K(+) channels were involved in the ACPA effect. Furthermore, the vasorelaxation effect was similarly reduced when we specifically blocked calcium-activated potassium channel subunit alpha-1 (KCa1.1) (MaxiK; BKCa) prior to adding ACPA. Finally, ACPA-induced vasorelaxation was also diminished when we specifically blocked the calcium channel, voltage-dependent, L type, alpha 1C subunit (Ca(v)1.2). These results showed that ACPA activation of CB(1) in smooth muscle caused vasorelaxation of aortic rings through a mechanism involving the activation of K(Ca)1.1 and the inhibition of Ca(v)1.2.

Role of pre-junctional CB1, but not CB2 , TRPV1 or GPR55 receptors in anandamide-induced inhibition of the vasodepressor sensory CGRPergic outflow in pithed rats

Stimulation of the perivascular sensory outflow in pithed rats produces vasodepressor responses mediated by CGRP release. Interestingly, endocannabinoids such as anandamide (which interacts with CB1 , CB2 , TRPV1 and GPR55 receptors) can regulate the activity of perivascular sensory nerves in dural blood vessels by modulating CGRP release. Yet, as no publication has reported whether this mechanism is operative in the healthy systemic vasculature, this study has specifically analysed the receptors mediating the potential inhibitory effects of the cannabinoid (CB) receptor agonists anandamide (non-selective), JWH-015 (CB2 ) and lysophosphatidylinositol (GPR55) on the rat vasodepressor sensory CGRPergic outflow (an index of systemic vasodilatation). Healthy pithed rats were pre-treated with consecutive i.v. continuous infusions of hexamethonium, methoxamine and the above agonists. Electrical spinal (T9 -T12 ) stimulation of the vasodepressor sensory CGRPergic outflow or i.v. injections of α-CGRP produced frequency-dependent or dose-dependent vasodepressor responses. The infusions of anandamide in a dose-dependent manner inhibited the vasodepressor responses by electrical stimulation (remaining unaffected by JWH-015 or lysophosphatidylinositol), but not those by α-CGRP. After i.v. administration of antagonists, the inhibition by 3.1 μg/kg min anandamide was: (i) potently blocked by 31-100 μg/kg NIDA41020 (CB1 ), (ii) unaffected by 180 μg/kg AM630 (CB2 ), 31 μg/kg cannabidiol (GPR55) or 31-100 μg/kg capsazepine (TRPV1) and (iii) slightly blocked by 310 μg/kg AM630. The above doses of antagonists were enough to block their respective receptors. These results suggest that anandamide-induced inhibition of the vasodepressor sensory CGRPergic outflow is mainly mediated by pre-junctional activation of CB1 receptors, with no pharmacological evidence for the role of CB2 , TRPV1 or GPR55 receptors.

Endocannabinoid system as a potential mechanism for n-3 long-chain polyunsaturated fatty acid mediated cardiovascular protection

The presence of an active and functioning endocannabinoid (EC) system within cardiovascular tissues implies that this system has either a physiological or pathophysiological role (or both), and there is a substantial literature to support the notion that, in the main, they are protective in the setting of various CVD states. Moreover, there is an equally extensive literature to demonstrate the cardio- and vasculo-protective effects of n-3 long-chain (LC)-PUFA. It is now becoming evident that there appears to be a close relationship between dietary intervention with n-3 LC-PUFA and changes in tissue levels of EC, raising the question as to whether or not EC may, at least in part, play a role in mediating the cardio-and vasculo-protective effects of n-3 LC-PUFA. This brief review summarises the current understanding of how both EC and n-3 LC-PUFA exert their protective effects in three major cardiovascular disorders (hypertension, atherosclerosis and acute myocardial infarction) and attempts to identify the similarities and differences that may indicate common or integrated mechanisms. From the data available, it is unlikely that in hypertension EC mediate any beneficial effects of n-3 LC-PUFA, since they do not share common mechanisms of blood pressure reduction. However, inhibition of inflammation is an effect shared by EC and n-3 LC-PUFA in the setting of both atherosclerosis and myocardial reperfusion injury, while blockade of L-type Ca2+ channels is one of the possible common mechanisms for their antiarrhythmic effects. Although both EC and n-3 LC-PUFA demonstrate vasculo- and cardio-protection, the literature overwhelmingly shows that n-3 LC-PUFA decrease tissue levels of EC through formation of EC–n-3 LC-PUFA conjugates, which is counter-intuitive to an argument that EC may mediate the effects of n-3 LC-PUFA. However, the discovery that these conjugates have a greater affinity for cannabinoid receptors than the native EC provides a fascinating avenue for further research into novel approaches for the treatment and prevention of atherosclerosis and myocardial injury following ischaemia/reperfusion.

Shivering and tachycardic responses to external cooling in mice are substantially suppressed by TRPV1 activation but not by TRPM8 inhibition

Mild decrease of core temperature (32-34°C), also known as therapeutic hypothermia, is a highly effective strategy of neuroprotection from ischemia and holds significant promise in the treatment of stroke. However, induction of hypothermia in conscious stroke patients is complicated by cold-defensive responses, such as shivering and tachycardia. Although multiple thermoregulatory responses may be altered by modulators of thermosensitive ion channels, TRPM8 (transient receptor potential melastatin 8) and TRPV1 (TRP vanilloid 1), it is unknown whether these agents affect cold-induced shivering and tachycardia. The current study aimed to determine the effects of TRPM8 inhibition and TRPV1 activation on the shivering and tachycardic responses to external cooling. Conscious mice were treated with TRPM8 inhibitor compound 5 or TRPV1 agonist dihydrocapsaicin (DHC) and exposed to cooling at 10°C. Shivering was measured by electromyography using implanted electrodes in back muscles, tachycardic response by electrocardiography, and core temperature by wireless transmitters in the abdominal cavity. The role of TRPM8 was further determined using TRPM8 KO mice. TRPM8 ablation had no effect on total electromyographic muscle activity (vehicle: 24.0 ± 1.8; compound 5: 23.8 ± 2.0; TRPM8 KO: 19.7 ± 1.9 V·s/min), tachycardia (ΔHR = 124 ± 31; 121 ± 13; 121 ± 31 beats/min) and drop in core temperature (-3.6 ± 0.1; -3.4 ± 0.4; -3.6 ± 0.5°C) during cold exposure. TRPV1 activation substantially suppressed muscle activity (vehicle: 25.6 ± 3.0 vs. DHC: 5.1 ± 2.0 V·s/min), tachycardia (ΔHR = 204 ± 25 vs. 3 ± 35 beats/min) and produced a profound drop in core temperature (-2.2 ± 0.6 vs. -8.9 ± 0.6°C). In conclusion, external cooling-induced shivering and tachycardia are suppressed by TRPV1 activation, but not by TRPM8 inhibition. This suggests that TRPV1 agonists may be combined with external physical cooling to achieve more rapid and effective hypothermia.

Circulating anandamide and blood pressure in patients with obstructive sleep apnea

OBJECTIVE

Obstructive sleep apnea chronically increases blood pressure through sympathetic nervous system activation. In animals, hypertension and sympathetic activity are restrained by cannabinoid receptor activation. Therefore, we hypothesized that increased blood pressure in patients with obstructive sleep apnea is associated with increased circulating endocannabinoid concentrations.

METHODS

Arterial oxygen saturation and apnea/hypopnea episodes were recorded in 29 patients with normal glucose tolerance, 26 patients with type 2 diabetes mellitus, and 21 patients obese subjects without sleep apnea. We determined seated blood pressure, insulin, glucose, and high-sensitive C-reactive protein in the morning, and insulin sensitivity by euglycemic-hyperinsulinemic clamp the next day. Anandamide, the sum of 1-arachidonoylglycerol and 2-arachidonoylglycerol, and oleoylethanolamide were measured in plasma by liquid chromatography-tandem mass spectrometry.

RESULTS

Endocannabinoid concentrations in sleep apnea patients were increased compared to obese individuals without disordered nocturnal breathing. Correction for variables of obesity and insulin resistance almost completely abrogated this difference in endocannabinoids. Anandamide strongly correlated with blood pressure in sleep apnea patients (r = 0.60 for SBP and r = 0.58 for DBP, P < 0.001). In multivariate regression analysis, anandamide was a stronger determinant of blood pressure than sleep apnea severity, obesity, insulin resistance, and inflammation.

CONCLUSION

Obstructive sleep apnea patients show positive correlations between blood pressure and venous anandamide concentrations independent of confounding factors. Our data suggest a previously not recognized role of the endocannabinoid system for blood pressure regulation in patients with high risk for hypertension and cardiovascular disease.

TRPV1 ablation aggravates inflammatory responses and organ damage during endotoxic shock

To test the hypothesis that ablation of transient receptor potential vanilloid type 1 (TRPV1) channels leads to exacerbated inflammatory responses and organ damage during endotoxic shock, lipopolysaccharide (LPS; 5 million endotoxin units/kg of body weight) was injected intraperitoneally (i.p.) into wild-type (WT) and TRPV1-null mutant (TRPV1(-/-)) mice. Mean arterial pressure and heart rate, determined by radiotelemetry, were severely depressed after LPS injection into WT and TRPV1(-/-) mice, with no distinction between the two strains. At 24 h after LPS injection, renal glomerular hypercellularity and hepatocellular injury were observed in both strains, accompanying further elevated serum levels of creatinine and alanine aminotransferase in TRPV1(-/-) mice compared to those in WT mice. At 6 or 24 h after LPS injection, neutrophil recruitment into kidneys and livers, serum cytokine (tumor necrosis factor alpha [TNF-α], interleukin 1β [IL-1β], IL-6) and renal chemokine (KC, macrophage inflammatory protein 2 [MIP-2]) levels, and renal VCAM-1 and ICAM-1 expression were greater in TRPV1(-/-) mice than WT mice. In addition, increased plasma calcitonin gene-related peptide (CGRP) levels observed in WT mice 6 h after LPS injection were absent in TRPV1(-/-) mice. Thus, TRPV1 ablation aggravates inflammatory responses, including neutrophil infiltration, proinflammatory cytokine production, and adhesion molecule expression, leading to intensified organ damage during endotoxic shock in the absence of worsened circulatory failure. The data indicate that TRPV1 activation may attenuate endotoxin-induced organ damage, possibly via its anti-inflammatory action rather than alteration of hemodynamics.

Cannabinoid receptor 1 signaling in cardiovascular regulating nuclei in the brainstem: A review

Cannabinoids elicit complex hemodynamic responses in experimental animals that involve both peripheral and central sites. Centrally administered cannabinoids have been shown to predominantly cause pressor response. However, very little is known about the mechanism of the cannabinoid receptor 1 (CB₁R)-centrally evoked pressor response. In this review, we provided an overview of the contemporary knowledge regarding the cannabinoids centrally elicited cardiovascular responses and the possible underlying signaling mechanisms. The current review focuses on the rostral ventrolateral medulla (RVLM) as the primary brainstem nucleus implicated in CB₁R-evoked pressor response.

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.

Endocannabinoid modulation of jejunal afferent responses to LPS

BACKGROUND

Endocannabinoids influence immune function and nociceptive signaling. This study examines cannabinoid modulation of sensory signaling from the GI tract following an acute inflammatory response triggered by systemic administration of bacterial lipopolysaccharide (LPS).

METHODS

A segment of proximal jejunum was intubated, to measure intraluminal pressure, in anesthetized rats. Afferent impulse traffic was recorded from a single isolated paravascular nerve bundle supplying the jejunal loop. Drugs and LPS were administered intravenously and changes in afferent firing were determined.

KEY RESULTS

The non-selective cannabinoid agonist, WIN55,212-2 (1 mg kg(-1) i.v.) and the anandamide transport inhibitor, VDM11 (1 mg kg(-1) i.v.) but not the fatty acid amide hydrolase (FAAH) inhibitor, URB597 (0.3 mg kg(-1)) caused a significant increase in afferent activity. The WIN55,212-2-induced afferent response was mediated by activation of CB(1) receptors whereas the VDM11 response was mediated by both CB(1) and CB(2) receptor mechanisms. LPS (10 mg kg(-1)) evoked an increase in afferent activity which was significantly reduced in the presence of WIN55,212-2 and VDM11 but not URB597. The inhibitory effect of WIN55,212-2 was prevented by CB(1) but not CB(2) receptor antagonism. In contrast, the inhibitory effect of VDM11 remained unaltered after CB(1) or CB(2) receptor blockade.

CONCLUSIONS & INFERENCES

Endocannabinoids play a role in modulating afferent signaling and may represent a target for the treatment of visceral hypersensitivity. In contrast to the effects of blocking endocannabinoid uptake (VDM11), inhibiting breakdown of endocannabinoids (URB597) had no effect on baseline or LPS induced afferent firing. Therefore, uptake of cannabinoids rather than breakdown via FAAH terminates their action in the GI tract.

Triphasic blood pressure responses to cannabinoids: do we understand the mechanism?

The cannabinoids comprise three major classes of substances, including compounds derived from the cannabis plant (e.g. Δ(9) -tetrahydrocannabinol and the chemically related substances CP55940 and HU210), endogenously formed (e.g. anandamide) and synthetic compounds (e.g. WIN55212-2). Beyond their psychotropic effects, cannabinoids have complex effects on blood pressure, including biphasic changes of Δ(9) -tetrahydrocannabinol and WIN55212-2 and an even triphasic effect of anandamide. The differing pattern of blood pressure changes displayed by the three types of compounds is not really surprising since, although they share an agonistic effect at cannabinoid CB(1) and CB(2) receptors, some compounds have additional effects. In particular, anandamide is known for its pleiotropic effects, and there is overwhelming evidence that anandamide influences blood pressure via (i) CB(1) receptors, (ii) TRPV1 receptors, (iii) endothelial cannabinoid receptors and (iv) degradation products. This review is dedicated to the description of the effects of externally added cannabinoids on cardiovascular parameters in vivo. First, the cardiovascular effects of cannabinoids in anaesthetized animals will be highlighted since most data have been generated in experiments of that type. The text will follow the three phases of anandamide on blood pressure, and we will check to which extent cardiovascular changes elicited by other cannabinoids show overlap with those effects or differ. The second part will be dedicated to the cardiovascular effects of the cannabinoids in conscious animals. In the third part, cardiovascular effects in humans will be discussed, and similarities and differences with respect to the data from animals will be examined.

Update on the role of cannabinoid receptors after ischemic stroke

Cannabinoids are considered as key mediators in the pathophysiology of inflammatory diseases, including atherosclerosis. In particular, they have been shown to reduce the ischemic injury after acute cardiovascular events, such as acute myocardial infarction and ischemic stroke. These protective and anti-inflammatory properties on peripheral tissues and circulating inflammatory have been demonstrated to involve their binding with both selective cannabinoid type 1 (CB₁) and type 2 (CB₂) transmembrane receptors. On the other hands, the recent discoveries of novel different classes of cannabinoids and receptors have increased the complexity of this system in atherosclerosis. Although only preliminary data have been reported on the activities of novel cannabinoid receptors, several studies have already investigated the role of CB₁ and CB₂ receptors in ischemic stroke. While CB₁ receptor activation has been shown to directly reduce atherosclerotic plaque inflammation, controversial data have been shown on neurotransmission and neuroprotection after stroke. Given its potent anti-inflammatory activities on circulating leukocytes, the CB₂ activation has been proven to produce protective effects against acute poststroke inflammation. In this paper, we will update evidence on different cannabinoid-triggered avenues to reduce inflammation and neuronal injury in acute ischemic stroke.

Endocannabinoid system in cardiovascular disorders - new pharmacotherapeutic opportunities

The long history of Cannabis sativa had its development stimulated and oriented for medicine after the discovery and chemical characterization of its main active ingredient, the 9-tetrahydrocannabinol (9-THC). Consequently, a binding site for 9-THC was identified in rat brains and the first cannabinoid receptor (CB1) was cloned, followed by the CB2 and by the discover of two endogenous agonists: anandamide and 2-arachidonoyl glycerol. Cannabinoid receptors, endocannabinoids and the enzymes that catalyze its synthesis and degradation constitute the endocannabinoid system (ECS), which plays an important role in the cardiovascular system. In vivo experiments with rats have demonstrated the action of anandamide and 2-AG on the development of atherosclerotic plaque, as well as an effect on heart rate, blood pressure, vasoactivity and energy metabolism (action in dyslipidemia and obesity). Recent studies with an antagonist of CB1 receptors showed that the modulation of ECS can play an important role in reducing cardiovascular risk in obese and dyslipidemic patients. Similarly, studies in rats have demonstrated the action of CB2 receptors in adhesion, migration, proliferation and function of immune cells involved in the atherosclerotic plaque formation process. The evidence so far gathered shows that the modulation of ECS (as agonism or antagonism of its receptors) is an enormous potential field for research and intervention in multiple areas of human pathophysiology. The development of selective drugs for the CB1 and CB2 receptors may open a door to new therapeutic regimens.This review article aims to address the key findings and evidences on the modulation of ECS, in order to prospect future forms of therapeutic intervention at the cardiovascular level. A recent, emerging, controversial and of undoubted scientific interest subject, which states as a potential therapeutic target to reach in the 21^st century.

The differential effect of CB1 receptors on the discharge of afferent and efferent fibres supplying the rat jejunum

BACKGROUND

The cannabinoid receptor (CB(1) ) is expressed on GI sensory neurons and is suggested to play a role in food intake, inflammation and nociception. Expression of CB(1) in the nodose is influenced by nutritional status. Our aim was to determine the functional response of afferent and efferent fibres supplying the proximal jejunum to the CB(1) agonist docosatetraenylethanolamide (DEA) in fed and fasted animals.

METHODS

Experiments were performed on anesthetized rats, either fed ad libitum or fasted for 24 h. Blood pressure was recorded via the carotid artery and the proximal jejunum intubated to measure intraluminal pressure. A single paravascular nerve bundle was isolated and attached to an electrode for recording either afferent or efferent impulse traffic.

KEY RESULTS

Docosatetraenylethanolamide (1 mg kg(-1) , i.v.) had a depressor effect on blood pressure but surprisingly had little effect on afferent nerve activity in fed animals. In fasted animals the afferent response to DEA was augmented, however, the blood pressure effect was attenuated. In contrast, DEA caused a significant and prolonged increase in efferent firing, which was diminished in fasted animals. Bilateral cervical vagotomy had no effect on the DEA-mediated efferent response, however, hexamethonium (10 mg kg(-1) ) abolished excitation and unmasked an inhibitory effect of DEA.

CONCLUSIONS & INFERENCES

Docosatetraenylethanolamide has only a modest effect on intestinal afferent firing but a profound effect on efferent function, which is modulated by changes in nutritional status. The persistent response after vagotomy and block by hexamethonium suggests DEA is acting centrally, although there may be an inhibitory effect at the level of the postganglionic sympathetic neuron.

Inhibitor of fatty acid amide hydrolase normalizes cardiovascular function in hypertension without adverse metabolic effects

The enzyme fatty acid amide hydrolase (FAAH) catalyzes the in vivo degradation of the endocannabinoid anandamide, thus controlling its action at receptors. A novel FAAH inhibitor, AM3506, normalizes the elevated blood pressure and cardiac contractility of spontaneously hypertensive rats (SHR) without affecting these parameters in normotensive rats. These effects are due to blockade of FAAH and a corresponding rise in brain anandamide levels, resulting in CB₁ receptor-mediated decrease in sympathetic tone. The supersensitivity of SHR to CB₁ receptor-mediated cardiovascular depression is related to increased G protein coupling of CB₁ receptors. Importantly, AM3506 does not elicit hyperglycemia and insulin resistance seen with other FAAH inhibitors or in FAAH⁻/⁻ mice, which is related to its inability to inhibit FAAH in the liver due to rapid hepatic uptake and metabolism. This unique activity profile offers improved therapeutic value in hypertension.

The potential for clinical use of cannabinoids in treatment of cardiovascular diseases

Cannabinoids, the constituents of the marijuana plant and their analogs, have not only neurobehavioral but also cardiovascular effects. Great advances in the last couple of decades have led to better understanding of the physiological effects of the cannabinoids and of their role in various cardiovascular pathologies. The potential therapeutic use of cannabinoids in various cardiac diseases, such as ischemic injury, heart failure, and cardiac arrhythmias, has been studied in animal models. The purpose of this article is to review the physiological cardiovascular properties of cannabinoids and to summarize the knowledge related to their potential therapeutic use.

Increased susceptibility to cardiovascular effects of dihydrocapcaicin in resuscitated rats. Cardiovascular effects of dihydrocapsaicin

Background

Survivors of a cardiac arrest often have persistent cardiovascular derangements following cardiopulmonary resuscitation including decreased cardiac output, arrhythmias and morphological myocardial damage. These cardiovascular derangements may lead to an increased susceptibility towards the external and internal environment of the cardiovascular system as compared to the healthy situation.

Methods

Here we tested the hypothesis that the cardiovascular system in healthy rats and rats resuscitated from a cardiac arrest may be differentially affected by a transient receptor potential vanilloid type 1 agonist, by continuous intravenous infusion of dihydrocapsaicin (DHC).

Results

Compared to baseline, infusion of DHC caused an initial increase in mean arterial blood pressure in both healthy and resuscitated rats of 25% and 10%, respectively. Also, we observed an initial response of tachycardia in both healthy and resuscitated rats of 30% and 20%, respectively. Then, at high levels of DHC infusion (> 2.0 mg/kg/hr) we observed two single episodes of transient bradycardia and hypotension in 33% of the healthy rats, which was consistent with a TRPV1 agonist induced Bezold-Jarisch reflex. In contrast, in resuscitated rats we observed multiple episodes of bradycardia/hypotension in 100% of the rats and at a dose of DHC of 0.65 mg/kg/hr. Notably, this DHC effect could be completely blocked in the resuscitated rats by pre-treatment with atropine, a muscarinic acetylcholine antagonist.

Conclusions

Our results indicate that the susceptibility of the rats towards TRPV1 agonist induced Bezold-Jarisch reflex is increased in those resuscitated from cardiac arrest compared to the healthy situation.

Fluorescent ligand binding reveals heterogeneous distribution of adrenoceptors and 'cannabinoid-like' receptors in small arteries

BACKGROUND AND PURPOSE

Pharmacological analysis of synergism or functional antagonism between different receptors commonly assumes that interacting receptors are located in the same cells. We have now investigated the distribution of alpha-adrenoceptors, beta-adrenoceptors and cannabinoid-like (GPR55) receptors in the mouse arteries.

EXPERIMENTAL APPROACH

Fluorescence intensity from vascular tissue incubated with fluorescent ligands (alpha(1)-adrenoceptor ligand, BODIPY-FL-prazosin, QAPB; beta-adrenoceptor ligand, TMR-CGP12177; fluorescent angiotensin II; a novel diarylpyrazole cannabinoid ligand (Tocrifluor 1117, T1117) was measured with confocal microscopy. Small mesenteric and tail arteries of wild-type and alpha(1B/D)-adrenoceptor-KO mice were used.

KEY RESULTS

T1117, a fluorescent form of the cannabinoid CB(1) receptor antagonist AM251, was a ligand for GPR55, with low affinity for CB(1) receptors. In mesenteric arterial smooth muscle cells, alpha(1A)-adrenoceptors were predominantly located in different cells from those with beta-adrenoceptors, angiotensin receptors or cannabinoid-like (GPR55) receptors. Cells with beta-adrenoceptors predominated at arterial branches. Endothelial cells expressed beta-adrenoceptors, alpha-adrenoceptors and cannabinoid-like receptors. Only endothelial alpha-adrenoceptors appeared in clusters. Adventitia was a rich source of G protein-coupled receptors (GPCRs), particularly fibroblasts and nerve tracts, where Schwann cells bound alpha-adrenoceptor, beta-adrenoceptor and CB-receptor ligands, with a mix of separate receptor locations and co-localization.

CONCLUSIONS AND IMPLICATIONS

Within each cell type, each GPCR had a distinctive heterogeneous distribution with limited co-localization, providing a guide to the possibilities for functional synergism, and suggesting a new paradigm for synergism in which interactions may be either between cells or involve converging intracellular signalling processes.

Endocannabinoids and cardiac contractile function: pathophysiological implications

Endocannabinoids are part of a bioactive lipid signaling system, not only in the central nervous system but also in various peripheral organs. Accumulating evidence implicates dysregulation of the endocannabinoid system (ECS) in the pathogenesis of various cardiovascular diseases, including hypertension, atherosclerosis, myocardial infarction, hemorrhagic or septic shock, heart failure and cardiovascular complications of liver cirrhosis. Even though the benefit of chronic cannabinoid 1 (CB1) receptor blockade with the currently available compounds may not outweigh the risks in chronic conditions such as obesity, modulation of the ECS may hold great therapeutic promise in various cardiovascular conditions/disorders. In this review we will discuss recent advances in understanding the role of CB1 receptors and endocannabinoids in the regulation of cardiac function in cirrhotic cardiomyopathy and in doxorubicin-induced heart failure.

Differential endocannabinoid regulation of baroreflex-evoked sympathoinhibition in normotensive versus hypertensive rats

Previously, we found that endocannabinoids acting at cannabinoid 1 receptors in the nucleus tractus solitarius prolonged baroreflex inhibition of renal sympathetic nerve activity in normotensive Sprague Dawley rats. The current study investigated whether endocannabinoid signaling was altered in spontaneously hypertensive rats, a model marked by elevated sympathetic activity and depressed baroreflex responses. The effects of endocannabinoids in the nucleus tractus solitarius on baroreflex control of renal sympathetic nerve activity evoked by systemic pressor changes or by direct stimulation of nucleus tractus solitarius neurons, which produced depressor and sympathoinhibitory responses, were studied in Sprague Dawley rats, Wistar Kyoto rats, and spontaneously hypertensive rats. Evoked responses were compared before and after microinjection of AM404, which prolonged actions of endogenous endocannabinoids, or microinjection of an endocannabinoid, anandamide, into the baroreceptive region of the nucleus tractus solitarius. AM404 microinjections significantly prolonged evoked sympathoinhibition in Sprague Dawley and Wistar Kyoto rats, but had little effect in spontaneously hypertensive rats. Microinjections of anandamide prolonged sympathoinhibition in Sprague Dawley rats, with lesser effects in Wistar Kyoto rats and no effects in spontaneously hypertensive rats. Parallel studies found that density of binding sites of endocannabinoids in the nucleus tractus solitarius was significantly reduced in spontaneously hypertensive rats versus the normotensive rats. Results indicate that attenuated function of the endocannabinoid system in the nucleus tractus solitarius of spontaneously hypertensive rats resulted in less modulation of baroreflex-evoked sympathoinhibition and that reduced cannabinoid 1 receptor density could contribute to blunted baroreflex-induced sympathoinhibition and elevated sympathetic tone characteristic of spontaneously hypertensive rats.

Acute hypertension reveals depressor and vasodilator effects of cannabinoids in conscious rats

BACKGROUND AND PURPOSE

The cardiovascular effects of cannabinoids can be influenced by anaesthesia and can differ in chronic hypertension, but the extent to which they are influenced by acute hypertension in conscious animals has not been determined.

EXPERIMENTAL APPROACH

We examined cardiovascular responses to intravenous administration of anandamide and the synthetic cannabinoid, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo[1,2,3-de]-1,4-benzoxazin-6-yl]-1-naphthalenylmethanone (WIN55212-2), in conscious male Wistar rats made acutely hypertensive by infusion of angiotensin II (AII) and arginine vasopressin (AVP). Rats were chronically instrumented for measurement of arterial blood pressure and vascular conductances in the renal, mesenteric and hindquarters beds.

KEY RESULTS

Anandamide dose-dependently decreased the mean arterial blood pressure of rats made hypertensive by AII-AVP infusion, but not normotensive rats. Interestingly, acute hypertension also revealed a hypotensive response to WIN55212-2, which caused hypertension in normotensive animals. The enhanced depressor effects of the cannabinoids in acute hypertension were associated with increased vasodilatation in hindquarters, renal and mesenteric vascular beds. Treatment with URB597, which inhibits anandamide degradation by fatty acid amide hydrolase, potentiated the depressor and mesenteric vasodilator responses to anandamide. Furthermore, haemodynamic responses to WIN55212-2, but not to anandamide, were attenuated by the CB(1) receptor antagonist, AM251 [N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophen yl)-4-methyl-1H-pyrazole-3-carboxamide].

CONCLUSIONS AND IMPLICATIONS

These results broadly support the literature showing that the cardiovascular effects of cannabinoids can be exaggerated in hypertension, but highlight the involvement of non-CB(1) receptor-mediated mechanisms in the actions of anandamide.

The emerging role of the endocannabinoid system in cardiovascular disease

Endocannabinoids are endogenous bioactive lipid mediators present both in the brain and various peripheral tissues, which exert their biological effects via interaction with specific G-protein-coupled cannabinoid receptors, the CB(1) and CB(2). Pathological overactivation of the endocannabinoid system (ECS) in various forms of shock and heart failure may contribute to the underlying pathology and cardiodepressive state by the activation of the cardiovascular CB(1) receptors. Furthermore, tonic activation of CB(1) receptors by endocannabinoids has also been implicated in the development of various cardiovascular risk factors in obesity/metabolic syndrome and diabetes, such as plasma lipid alterations, abdominal obesity, hepatic steatosis, inflammation, and insulin and leptin resistance. In contrast, activation of CB(2) receptors in immune cells exerts various immunomodulatory effects, and the CB(2) receptors in endothelial and inflammatory cells appear to limit the endothelial inflammatory response, chemotaxis, and inflammatory cell adhesion and activation in atherosclerosis and reperfusion injury. Here, we will overview the cardiovascular actions of endocannabinoids and the growing body of evidence implicating the dysregulation of the ECS in a variety of cardiovascular diseases. We will also discuss the therapeutic potential of the modulation of the ECS by selective agonists/antagonists in various cardiovascular disorders associated with inflammation and tissue injury, ranging from myocardial infarction and heart failure to atherosclerosis and cardiometabolic disorders.

Differential stimulatory effects of cannabinoids on VIP release and NO synthase activity in synaptosomal fractions from rat ileum

Cannabinoid-1 (CB1) and CB2 receptors are present on neurons of the enteric nervous system. Our aim was to study whether cannabinoid receptor activation is involved in the regulation of VIP release and NO synthesis in isolated fractions of nerve terminals from rat ileum. VIP was measured by RIA and NO synthesis was analyzed using a L-[3H]arginine assay. Anandamide stimulated VIP release (basal: 245.9+/-12.4pg/mg, 10(-6)M: 307.6+/-11.7pg/mg, [n=6, P<0.05], 10(-7)M: 367.0+/-26.1pg/mg, [n=6, P<0.01]). The cannabinoid receptor agonist WIN 55,212-2 had similar effects (basal: 250.5+/-37.4pg/mg, 10(-6)M: 320.9+/-34.7pg/mg; [n=4, P<0.05]). The stimulatory effect of anandamide was blocked by the selective CB2 receptor antagonist, SR144528 (10(-7)M) (anandamide 10(-6)M: 307.6+/-11.7pg/mg; +SR144528: 249.0+/-26.3pg/mg, [n=6, P<0.05]), whereas the selective CB1 receptor antagonist SR141716 A had no effect. NO synthesis was stimulated by anandamide ([fmol/mg/min] basal: 0.08+/-0.01, 10(-6)M: 0.16+/-0.03; 10(-7)M: 0.13+/-0.02, n=4, P<0.05) and WIN 55,212-2 ([fmol/mg/min] basal: 0.05+/-0.01, 10(-6)M: 0.1+/-0.02, n=4, P<0.05). The anandamide reuptake inhibitor, AM 404 increased basal NOS activity ([fmol/mg/min] control: 0.1+/-0.04, 10(-6)M: 0.28+/-0.08, n=7, P<0.05). The stimulatory effect of anandamide on NO synthase was not antagonized by antagonists at the CB1, CB2 or TRPV1 receptor, respectively. In conclusion, in enteric nerves anandamide stimulates VIP release by activation of a CB2 receptor specific pathway, while the stimulation of NO production suggests the existence of an additional type of cannabinoid receptor in the enteric nervous system.