Cytochrome P-450 metabolites of 2-arachidonoylglycerol play a role in Ca2+-induced relaxation of rat mesenteric arteries

Stimulation of the calcium-sensing receptor induces relaxations through CGRP and NK1 receptor-mediated pathways in male rat mesenteric arteries

Stimulation of the calcium-sensing receptor (CaSR) regulates vascular contractility, but cellular mechanisms involved remain unclear. This study investigated the role of perivascular sensory nerves in CaSR-induced relaxations of male rat mesenteric arteries. In fluorescence studies, colocalisation between synaptophysin, a synaptic vesicle marker, and the CaSR was present in the adventitial layer of arterial segments. Using wire myography, increasing external Ca2+ concentration ([Ca2+]o) from 1 to 10 mM induced vasorelaxations, previously shown to involve the CaSR, which were inhibited by pretreatment with capsaicin. [Ca2+]o-induced vasorelaxations were partially reduced by the calcitonin gene-related peptide (CGRP) receptor blockers, CGRP 8-37 and BIBN 4096, and the neurokinin 1 (NK1) receptor blocker L733,060. The inhibitory effect of CGRP 8-37 required a functional endothelium whereas the inhibitory action of L733,060 did not. Complete inhibition of [Ca2+]o-induced vasorelaxations occurred when CGRP 8-37 and L733,060 were applied together. [Ca2+]o-induced vasorelaxations in the presence of capsaicin were abolished by the ATP-dependent K+ channel (KATP) blocker PNU 37883, but unaffected by the endothelium nitric oxide synthase (eNOS) inhibitor L-NAME. We suggest that the CaSR on perivascular sensory nerves mediate relaxations in rat mesenteric arteries via endothelium-dependent and -independent mechanisms involving CGRP and NK1 receptor-activated NO production and KATP channels, respectively.

Stimulation of the calcium-sensing receptor induces relaxations of rat mesenteric arteries by endothelium-dependent and -independent pathways via BKCa and KATP channels

Stimulation of the calcium-sensing receptor (CaSR) induces both vasoconstrictions and vasorelaxations but underlying cellular processes remain unclear. This study investigates expression and effect of stimulating the CaSR by increasing external Ca2+ concentration ([Ca2+ ]o ) on contractility of rat mesenteric arteries. Immunofluorescence studies showed expression of the CaSR in perivascular nerves, vascular smooth muscle cells (VSMCs), and vascular endothelium cells. Using wire myography, increasing [Ca2+ ]o from 1 to 10 mM induced vasorelaxations which were inhibited by the calcilytic Calhex-231 and partially dependent on a functional endothelium. [Ca2+ ]o -induced vasorelaxations were reduced by endothelial NO synthase (eNOS, L-NAME) and large conductance Ca2+ -activated K+ channels (BKCa , iberiotoxin), with their inhibitory action requiring a functional endothelium. [Ca2+ ]o -induced vasorelaxations were also markedly inhibited by an ATP-dependent K+ channel (KATP ) blocker (PNU37883), which did not require a functional endothelium to produce its inhibitory action. Inhibitor studies also suggested contributory roles for inward rectifying K+ channels (Kir ), Kv7 channels, and small conductance Ca2+ -activated K+ channels (SKCa ) on [Ca2+ ]o -induced vasorelaxations. These findings indicate that stimulation of the CaSR mediates vasorelaxations involving multiple pathways, including an endothelium-dependent pathway involving NO production and activation of BKCa channels and an endothelium-independent pathway involving stimulation of KATP channels.

Biosynthesis and metabolism of endocannabinoids and their congeners from the monoacylglycerol andN-acyl-ethanolamine families

The endocannabinoids 2-arachidonoyl-glycerol (2-AG) and N-arachidonoyl-ethanolamine (AEA) are eicosanoids implicated in numerous physiological processes like appetite, adipogenesis, inflammatory pain and inflammation. They mediate most of their physiological effect by activating the cannabinoid (CB) receptors 1 and 2. Other than directly binding to the CB receptors, 2-AG and AEA are also metabolized by most eicosanoid biosynthetic enzymes, yielding many metabolites that are part of the oxyendocannabinoidome. Some of these metabolites have been found in vivo, have the ability to modulate specific receptors and thus potentially influence physiological processes. In this review, we discuss the biosynthesis and metabolism of 2-AG and AEA, as well as their congeners from the monoacyl-glycerol and N-acyl-ethanolamine families, with a special focus on the metabolism by oxygenases involved in arachidonic acid metabolism. We highlight the knowledge gaps in our understanding of the regulation and roles the oxyendocannabinoidome mediators.

High Salt Upregulates Ca2+-Sensing Receptor Expression and Ca2+-Induced Relaxation of Contracted Mesenteric Arteries from Dahl Salt-Sensitive Rats

High Ca2+ lowers blood pressure in hypertension, but the mechanism is not clear. The missing link may be the perivascular sensory nerve Ca2+-sensing receptor (CaSR) that mediates a vasodilator system after activation by interstitial Ca2+ Our results show that high salt increased CaSR expression in mesenteric arteries as well as Ca2+ relaxation of contracted mesenteric arteries from salt-sensitive (SS) rats. The CaSR was expressed as a doublet (≈120-150 kDa) in arteries from animals fed a high-salt diet for 1-4 weeks. The higher molecular weight glycosylated protein increased in arteries from SS animals; however, expression of the low molecular mass high-mannose protein decreased over 4 weeks of feeding the diet. In tissues from salt-resistant (SR) rats, the diet decreased CaSR expression after 4 weeks. Ca2+ relaxation of mesenteric arteries under phenylephrine tone increased in SS rats but decreased in arteries from SR rats fed the high-salt diet. Ca2+-activated K+ channels have a larger role in Ca2+ relaxation of arteries in SR than SS rats. The data suggest that high salt epigenetically regulates the receptor at the translational level in vivo and that the in vitro effect of Ca2+ is on receptor trafficking and signaling. In conclusion, upregulated expression of the CaSR in salt sensitivity increased receptor-mediated vascular relaxation. These findings show that CaSR signaling may compensate for changes in the vasculature in salt-sensitive hypertension. SIGNIFICANCE STATEMENT: The perivascular sensory nerve Ca2+-sensing receptor (CaSR) mediates Ca2+ relaxation of isolated mesenteric arteries under tension. This receptor may therefore play a significant role in relaxation of resistance arteries in vivo, thus explaining the blood pressure-lowering effect of dietary Ca2+. The present studies describe the effect of high salt-induced upregulation of the CaSR in salt-sensitive rats and the roles played by Ca2+-activated K+ channels and nitric oxide in Ca2+ responses.

A study of abnormal cannabidiols system-mediated cardiovascular protection in disrupted gut/brain axis associated depression

Uncontrolled stress can lead to vascular injury, hypertension, arrhythmia, compromised immune system alteration in microbiota activity, and neurobehavioral changes, including depression. The gut microbiota has been recently developed, not only for major depressive disorders but also cardiovascular problems, as a therapeutic concern. Since then, >100 studies have studied the link between depression and cardiovascular disease (CVD), and have shown that depression is common (≈20%-35%) in patients with CVD, and seems to be indicative of negative heart effects in patients. Depressive symptoms patients have demonstrated an elevated platelet reactivity, reduced cardiac variability, and enhanced proinflammatory signals, which are all cardiovascular-related risk factors. The pathophysiology of depression-related CVD is nevertheless a challenge because of the heterogeneous depressive syndromes and the etiologies. The cardiovascular effects of tetrahydrocannabinol (THC) (the key psychotropic credential of cannabis) and endocannabinoids (THC endogenous equivalents which cause type 1 [CB1] and 2 [CB2] cannabinoids) have been extensively examined based on well-documented effects of marijuana smoke on blood pressure (BP) and heart rate (HR). Therefore, the aim of the review article is to establish the relationship of abnormal cannabidiols system-mediated cardiovascular protection in disrupted gut/brain axis associated depression to determine the translational potential of targeting abnormal cannabidiols receptors in clinical studies.

Heteromeric TRPV4/TRPC1 channels mediate calcium-sensing receptor-induced relaxations and nitric oxide production in mesenteric arteries: comparative study using wild-type and TRPC1-/- mice

We have previously provided pharmacological evidence that stimulation of calcium-sensing receptors (CaSR) induces endothelium-dependent relaxations of rabbit mesenteric arteries through activation of heteromeric TRPV4/TRPC1 channels and nitric oxide (NO) production. The present study further investigates the role of heteromeric TRPV4/TRPC1 channels in these CaSR-induced vascular responses by comparing responses in mesenteric arteries from wild-type (WT) and TRPC1^-/- mice. In WT mice, stimulation of CaSR induced endothelium-dependent relaxations of pre-contracted tone and NO generation in endothelial cells (ECs), which were inhibited by the TRPV4 channel blocker RN1734 and the TRPC1 blocking antibody T1E3. In addition, TRPV4 and TRPC1 proteins were colocalised at, or close to, the plasma membrane of endothelial cells (ECs) from WT mice. In contrast, in TRPC1^-/- mice, CaSR-mediated vasorelaxations and NO generation were greatly reduced, unaffected by T1E3, but blocked by RN1734. In addition, the TRPV4 agonist GSK1016790A (GSK) induced endothelium-dependent vasorelaxations which were blocked by RN1734 and T1E3 in WT mice, but only by RN1734 in TRPC1^-/- mice. Moreover, GSK activated cation channel activity with a 6pS conductance in WT ECs but with a 52 pS conductance in TRPC1^-/- ECs. These results indicate that stimulation of CaSR activates heteromeric TRPV4/TRPC1 channels and NO production in ECs, which are responsible for endothelium-dependent vasorelaxations. This study also suggests that heteromeric TRPV4-TRPC1 channels may form the predominant TRPV4-containing channels in mouse mesenteric artery ECs. Together, our data further implicates CaSR-induced pathways and heteromeric TRPV4/TRPC1 channels in the regulation of vascular tone.

The role of n-3 PUFA-derived fatty acid derivatives and their oxygenated metabolites in the modulation of inflammation

Notwithstanding the ongoing debate on their full potential in health and disease, there is general consensus that n-3 PUFAs play important physiological roles. Increasing dietary n-3 PUFA intake results in increased DHA and EPA content in cell membranes as well as an increase in n-3 derived oxylipin and -endocannabinoid concentrations, like fatty acid amides and glycerol-esters. These shifts are believed to (partly) explain the pharmacological and anti-inflammatory effects of n-3 PUFAs. Recent studies discovered that n-3 PUFA-derived endocannabinoids can be further metabolized by the oxidative enzymes CYP-450, LOX and COX, similar to the n-6 derived endocannabinoids. Interestingly, these oxidized n-3 PUFA derived endocannabinoids of eicosapentaenoyl ethanolamide (EPEA) and docosahexaenoyl ethanolamide (DHEA) have higher anti-inflammatory and anti-proliferative potential than their precursors. In this review, an overview of recently discovered n-3 PUFA derived endocannabinoids and their metabolites is provided. In addition, the use of chemical probes will be presented as a promising technique to study the n-3 PUFA and n-3 PUFA metabolism within the field of lipid biochemistry.

Protein Kinase C Downregulation Enhanced Extracellular Ca2+-Induced Relaxation of Isolated Mesenteric Arteries from Aged Dahl Salt-Sensitive Rats

The Ca²⁺-sensing receptor (CaSR) detects small changes in extracellular calcium (Ca²⁺ _e) concentration ([Ca²⁺]_e) and transduces the signal into modulation of various signaling pathways. Ca²⁺-induced relaxation of isolated phenylephrine-contracted mesenteric arteries is mediated by the CaSR of the perivascular nerve. Elucidation of the regulatory mechanisms involved in vascular CaSR signaling may provide insights into the physiologic functions of the receptor and identify targets for the development of new treatments for cardiovascular pathologies such as hypertension. Protein kinase Cα (PKCα) is a critical regulator of multiple signaling pathways and can phosphorylate the CaSR leading to receptor desensitization. In this study, we used automated wire myography to investigate the effects of CaSR mutation and small-interfering RNA downregulation of PKCα on CaSR-mediated relaxation of phenylephrine-contracted mesenteric arteries from aged Dahl salt-sensitive (SS) rats on a low-salt diet. The data showed minimal relaxation responses of arteries to Ca²⁺ _e in wild-type (SS) and CaSR mutant (SS-Casr^em1Mcwi) rats. Mutation of the CaSR gene had no significant effect on relaxation. PKCα expression was similar in wild-type and mutant rats, and small-interfering RNA downregulation of PKCα and/or inhibition of PKC with the Ca²⁺-sensitive Gӧ 6976 resulted in a >80% increase in relaxation. Significant differences in EC₅₀ values were observed between treated and untreated controls (P < 0.05 analysis of variance). The results indicate that PKCα plays an important role in the regulation of CaSR-mediated relaxation of mesenteric arteries, and its downregulation or pharmacological inhibition may lead to an increased Ca²⁺ sensitivity of the receptor and reversal of age-related changes in vascular tone. SIGNIFICANCE STATEMENT: G protein-coupled CaSR signaling leads to the regulation of vascular tone and may, therefore, play a vital role in blood pressure regulation. The receptor has several PKC phosphorylation sites in the C-terminal intracellular tail that mediate desensitization. We have previously shown that activation of the CaSR in neuronal cells leads to PKC phosphorylation, indicating that protein kinase C is an important regulator of CaSR function. Therefore, PKC in the CaSR signaling pathway in mesenteric arteries is a potential target for the development of new therapeutic approaches to treat hypertension and age-related vascular dysfunction. The present studies show that small-interfering RNA downregulation of PKCα and pharmacological inhibition of PKC enhanced CaSR-mediated relaxation of phenylephrine-contracted mesenteric arteries from aged Dahl salt-sensitive rats.

Important roles of the Ca2+-sensing receptor in vascular health and disease

Ca²⁺-sensing receptor (CaSR), a member of G protein-coupled receptor family, is widely expressed in the vascular system, including perivascular neurons, vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). When stimulated, CaSR can further increase the cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) in two ways: intracellular Ca²⁺ release from endo/sarcoplasmic reticulum (ER/SR) and extracellular Ca²⁺ entry through Ca²⁺-permeable cation channels. In endothelium, increased Ca²⁺ subsequently activate nitric oxide synthase (NOS) and intermediate conductance Ca²⁺-activated K⁺ channels (IKCa), resulting in vasodilation through NOS-mediated NO release or membrane hyperpolarization. In VSMCs, CaSR-induced intracellular Ca²⁺ increase causes blood vessel constriction. CaSR activation predominantly induces vasorelaxation of whole vascular tissues through VECs-dependent mechanisms; however, CaSR-induced Ca²⁺ signaling in VSMCs may play a braking role in CaSR-mediated vasorelaxation. Emerging evidence reveals the importance of CaSR in the regulation of vascular tone and blood pressure. Here, we summarized recent advances in CaSR-mediated vascular reaction and the underlying mechanisms in different species, including humans. In addition, several studies have demonstrated that CaSR dysfunction may be associated with some fatal vascular diseases, such as pulmonary arterial hypertension, primary hypertension, diabetes, acute myocardial infarction and vascular calcification. With the advance of studies on CaSR in vascular health and disease, it is expected positive modulators or negative modulators of CaSR used for the treatment of specific diseases may be promising therapeutic options for the prevention and/or treatment of vascular diseases.

From Phytocannabinoids to Cannabinoid Receptors and Endocannabinoids: Pleiotropic Physiological and Pathological Roles Through Complex Pharmacology

Apart from having been used and misused for at least four millennia for, among others, recreational and medicinal purposes, the cannabis plant and its most peculiar chemical components, the plant cannabinoids (phytocannabinoids), have the merit to have led humanity to discover one of the most intriguing and pleiotropic endogenous signaling systems, the endocannabinoid system (ECS). This review article aims to describe and critically discuss, in the most comprehensive possible manner, the multifaceted aspects of 1) the pharmacology and potential impact on mammalian physiology of all major phytocannabinoids, and not only of the most famous one Δ9-tetrahydrocannabinol, and 2) the adaptive pro-homeostatic physiological, or maladaptive pathological, roles of the ECS in mammalian cells, tissues, and organs. In doing so, we have respected the chronological order of the milestones of the millennial route from medicinal/recreational cannabis to the ECS and beyond, as it is now clear that some of the early steps in this long path, which were originally neglected, are becoming important again. The emerging picture is rather complex, but still supports the belief that more important discoveries on human physiology, and new therapies, might come in the future from new knowledge in this field.

Increased Renal 2-Arachidonoylglycerol Level Is Associated with Improved Renal Function in a Mouse Model of Acute Kidney Injury

Background: Acute kidney injury (AKI) is associated with a significantly increased risk of morbidity and mortality. Ischemia-reperfusion injury (IRI) is a major cause of AKI. In this study, we investigated the role of the endocannabinoid (EC) system in renal IRI using a well-established mouse model. Materials and Methods: Renal ischemia was induced in male C57BL/6 mice by clamping both kidney pedicles for 30 min followed by 24 h of reperfusion. To increase renal 2-arachidonoylglycerol (2-AG) levels, mice were pretreated with JZL184 (16 mg/kg), 30 min before IRI. Serum creatinine and blood urea nitrogen (BUN), renal tubular damage, renal content of ECs and renal expression of markers of inflammation and oxidative stress were measured. Results: Renal IRI was associated with significantly increased serum BUN and creatinine, increased tubular damage score, increased expression of renal markers of inflammation and oxidative stress and elevated renal 2-AG content. Pretreatment with JZL184 was associated with a significant increase in renal 2-AG content and there was also improved serum BUN, creatinine and tubular damage score. However, renal expression of inflammation and oxidative stress markers remained unchanged. Conclusions: This is the first report documenting that renal IRI is associated with an increase in kidney 2-AG content. Further enhancement of 2-AG levels using JZL184 improved indices of renal function and histology, but did not lower renal expression of markers of inflammation and oxidative stress. Further studies are needed to determine the mechanisms responsible for the effects observed and the potential value of 2-AG as a therapeutic target in renal IRI.

Stimulation of calcium-sensing receptors induces endothelium-dependent vasorelaxations via nitric oxide production and activation of IKCa channels

Stimulation of vascular calcium-sensing receptors (CaSRs) is reported to induce both constrictions and relaxations. However, cellular mechanisms involved in these responses remain unclear. The present study investigates the effect of stimulating CaSRs on vascular contractility and focuses on the role of the endothelium, nitric oxide (NO) and K(+) channels in these responses. In wire myography studies, increasing [Ca(2+)]o from 1mM to 6mM induced concentration-dependent relaxations of methoxamine pre-contracted rabbit mesenteric arteries. [Ca(2+)]o-induced relaxations were dependent on a functional endothelium, and were inhibited by the negative allosteric CaSR modulator Calhex-231. [Ca(2+)]o-induced relaxations were reduced by inhibitors of endothelial NO synthase, guanylate cyclase, and protein kinase G. CaSR activation also induced NO production in freshly isolated endothelial cells (ECs) in experiments using the fluorescent NO indicator DAF-FM. Pre-treatment with inhibitors of large (BKCa) and intermediate (IKCa) Ca(2+)-activated K(+) channels (iberiotoxin and charybdotoxin), and Kv7 channels (linopirdine) also reduced [Ca(2+)]o-induced vasorelaxations. Increasing [Ca(2+)]o also activated IKCa currents in perforated-patch recordings of isolated mesenteric artery ECs. These findings indicate that stimulation of CaSRs induces endothelium-dependent vasorelaxations which are mediated by two separate pathways involving production of NO and activation of IKCa channels. NO stimulates PKG leading to BKCa activation in vascular smooth muscle cells, whereas IKCa activity contributes to endothelium-derived hyperpolarisations.

Endocannabinoids and the Cardiovascular System in Health and Disease

The endocannabinoid system is widely distributed throughout the cardiovascular system. Endocannabinoids play a minimal role in the regulation of cardiovascular function in normal conditions, but are altered in most cardiovascular disorders. In shock, endocannabinoids released within blood mediate the associated hypotension through CB(1) activation. In hypertension, there is evidence for changes in the expression of CB(1), and CB(1) antagonism reduces blood pressure in obese hypertensive and diabetic patients. The endocannabinoid system is also upregulated in cardiac pathologies. This is likely to be cardioprotective, via CB(2) and CB(1) (lesser extent). In the vasculature, endocannabinoids cause vasorelaxation through activation of multiple target sites, inhibition of calcium channels, activation of potassium channels, NO production and the release of vasoactive substances. Changes in the expression or function of any of these pathways alter the vascular effect of endocannabinoids. Endocannabinoids have positive (CB(2)) and negative effects (CB(1)) on the progression of atherosclerosis. However, any negative effects of CB(1) may not be consequential, as chronic CB(1) antagonism in large scale human trials was not associated with significant reductions in atheroma. In neurovascular disorders such as stroke, endocannabinoids are upregulated and protective, involving activation of CB(1), CB(2), TRPV1 and PPARα. Although most of this evidence is from preclinical studies, it seems likely that cannabinoid-based therapies could be beneficial in a range of cardiovascular disorders.

Differential Effect of Renal Cortical and Medullary Interstitial Fluid Calcium on Blood Pressure Regulation in Salt-Sensitive Hypertension

BACKGROUND

Hypercalciuria is a frequent characteristic of hypertension. In this report we extend our earlier studies investigating the role of renal interstitial fluid calcium (ISF(Ca))(2+) as a link between urinary calcium excretion and blood pressure in the Dahl salt-sensitive (DS) hypertensive model.

METHODS

Dahl salt-sensitive and salt-resistant (DR) rats were placed on control (0.45%) and high (8%) salt diets to determine if changes in renal cortical and medullary ISF(Ca)(2+)correlated with changes in urinary calcium excretion and blood pressure.

RESULTS

We observed that renal ISFCa(2+) was predicted by urinary calcium excretion (P < 0.05) in DS rats but not DR rats. Renal cortical ISF(Ca)(2+) was negatively associated with blood pressure (P < 0.03) while renal medullary ISF(Ca)(2+) was positively associated with blood pressure in DS rats (P < 0.04). In contrast, neither urinary calcium excretion nor renal ISF(Ca)(2+) was associated with blood pressure in the DR rats under the conditions of this study.

CONCLUSION

We interpret these findings to suggest that decreased renal cortical ISF(Ca)(2+) plays a role in the increase in blood pressure following a high salt diet in salt hypertension perhaps by mediating renal vasoconstriction; the role of medullary calcium remains to be fully understood. Further studies are needed to determine the mechanism of the altered renal ISF(Ca)(2+) and its role in blood pressure regulation.

Gαi/o-dependent Ca(2+) mobilization and Gαq-dependent PKCα regulation of Ca(2+)-sensing receptor-mediated responses in N18TG2 neuroblastoma cells

A functional Ca(2+)-sensing receptor (CaS) is expressed endogenously in mouse N18TG2 neuroblastoma cells, and sequence analysis of the cDNA indicates high homology with both rat and human parathyroid CaS cDNAs. The CaS in N18TG2 cells appears as a single immunoreactive protein band at about 150 kDa on Western blots, consistent with native CaS from dorsal root ganglia. Both wild type (WT) and Gαq antisense knock-down (KD) cells responded to Ca(2+) and calindol, a positive allosteric modulator of the CaS, with a transient increase in intracellular Ca(2+) concentration ([Ca(2+)]i), which was larger in the Gαq KD cells. Stimulation with 1 mM extracellular Ca(2+) (Ca(2+)e) increased [Ca(2+)]i in N18TG2 Gαq KD compared to WT cells. Ca(2+) mobilization was dependent on pertussis toxin-sensitive Gαi/o proteins and reduced by 30 μM 2-amino-ethyldiphenyl borate and 50 μM nifedipine to the same plateau levels in both cell types. Membrane-associated PKCα and p-PKCα increased with increasing [Ca(2+)]e in WT cells, but decreased in Gαq KD cells. Treatment of cells with 1 μM Gӧ 6976, a Ca(2+)-specific PKC inhibitor reduced Ca(2+) mobilization and membrane-associated PKCα and p-PKCα in both cell types. The results indicate that the CaS-mediated increase in [Ca(2+)]i in N18TG2 cells is dependent on Gαi/o proteins via inositol-1,4,5-triphosphate (IP3) channels and store-operated Ca(2+) entry channels, whereas modulation of CaS responses involving PKCα phosphorylation and translocation to the plasma membrane occurs via a Gαq mechanism.

Task-specific enhancement of hippocampus-dependent learning in mice deficient in monoacylglycerol lipase, the major hydrolyzing enzyme of the endocannabinoid 2-arachidonoylglycerol

Growing evidence indicates that the endocannabinoid system is important for the acquisition and/or extinction of learning and memory. However, it is unclear which endocannabinoid(s) play(s) a crucial role in these cognitive functions, especially memory extinction. To elucidate the physiological role of 2-arachidonoylglycerol (2-AG), a major endocannabinoid, in behavioral and cognitive functions, we conducted a comprehensive behavioral test battery in knockout (KO) mice deficient in monoacylglycerol lipase (MGL), the major hydrolyzing enzyme of 2-AG. We found age-dependent increases in spontaneous physical activity (SPA) in MGL KO mice. Next, we tested the MGL KO mice using 5 hippocampus-dependent learning paradigms (i.e., Morris water maze (MWM), contextual fear conditioning, novel object recognition test, trace eyeblink conditioning, and water-finding test). In the MWM, MGL KO mice showed normal acquisition of reference memory, but exhibited significantly faster extinction of the learned behavior. Moreover, they showed faster memory acquisition on the reversal-learning task of the MWM. In contrast, in the contextual fear conditioning, MGL KO mice tended to show slower memory extinction. In the novel object recognition and water-finding tests, MGL KO mice exhibited enhanced memory acquisition. Trace eyeblink conditioning was not altered in MGL KO mice throughout the acquisition and extinction phases. These results indicate that 2-AG signaling is important for hippocampus-dependent learning and memory, but its contribution is highly task-dependent.

Involvement of neutral sphingomyelinase in the angiotensin II signaling pathway

The possibility that angiotensin II (ANG II) exerts its effects through the activation of neutral sphingomyelinase (nSMase) has not been tested in kidneys. The results of the present study provide evidence for the activity and expression of nSMase in rat kidneys. In isolated perfused rat kidney, ANG II-induced renal vasoconstriction was inhibited by GW4869, an inhibitor of nSMase. We used nSMase for investigating the signal transduction downstream of ceramide. nSMase constricted the renal vasculature. An inhibitor of ceramidase (CDase), N-oleoylethanolamine (OEA), enhanced either ANG II- or nSMase-induced renal vasoconstriction. To demonstrate the interaction between the nSMase and cytosolic phospholipase A2 (cPLA2) signal transduction pathways, we evaluated the response to nSMase in the presence and absence of inhibitors of arachidonic acid (AA) metabolism: arachidonyl trifluoromethyl ketone (AACOCF3), an inhibitor of cPLA2; 5,8,11,14-eicosatetraynoic acid (ETYA), an inhibitor of all AA pathways; indomethacin, an inhibitor of cyclooxygenase (COX); furegrelate, a thromboxane A2 (TxA2)-synthase inhibitor; and SQ29548 , a TxA2-receptor antagonist. In these experiments, the nSMase-induced renal vasoconstriction decreased. ANG II or nSMase was associated with an increase in the release of thromboxane B2 (TxB2) in the renal perfusate of isolated perfused rat kidney. In addition, the coexpression of the ceramide with cPLA2, was found in the smooth muscle layer of intrarenal vessels. Our results suggest that ANG II stimulates ceramide formation via the activation of nSMase; thus ceramide may indirectly regulate vasoactive processes that modulate the activity of cPLA2 and the release of TxA2.

Regulation of inflammation by cannabinoids, the endocannabinoids 2-arachidonoyl-glycerol and arachidonoyl-ethanolamide, and their metabolites

2-Arachidonoyl-glycerol (2-AG) and arachidonyl-ethanolamide (AEA) are endocannabinoids that have been implicated in many physiologic disorders, including obesity, metabolic syndromes, hepatic diseases, pain, neurologic disorders, and inflammation. Their immunomodulatory effects are numerous and are not always mediated by cannabinoid receptors, reflecting the presence of an arachidonic acid (AA) molecule in their structure, the latter being the precursor of numerous bioactive lipids that are pro- or anti-inflammatory. 2-AG and AEA can thus serve as a source of AA but can also be metabolized by most eicosanoid biosynthetic enzymes, yielding additional lipids. In this regard, enhancing endocannabinoid levels by using endocannabinoid hydrolysis inhibitors is likely to augment the levels of these lipids that could regulate inflammatory cell functions. This review summarizes the metabolic pathways involved in the biosynthesis and metabolism of AEA and 2-AG, as well as the biologic effects of the 2-AG and AEA lipidomes in the regulation of inflammation.

Endocannabinoids and their oxygenation by cyclo-oxygenases, lipoxygenases and other oxygenases

The naturally occurring mammalian endocannabinoids possess biological attributes that extend beyond interaction with cannabinoid receptors. These extended biological properties are the result of oxidative metabolism of the principal mammalian endocannabinoids arachidonoyl ethanolamide (anandamide; A-EA) and 2-arachidonoylglycerol (2-AG). Both endocannabinoids are oxidized by cyclo-oxygenase-2 (COX-2), but not by COX-1, to a series of prostaglandin derivatives (PGs) with quite different biological properties from those of the parent substrates. PG ethanolamides (prostamides, PG-EAs) and PG glyceryl esters (PG-Gs) are not only pharmacologically distinct from their parent endocannabinoids, they are distinct from the corresponding acidic PGs, and are differentiated from each other. Ethanolamides and glyceryl esters of the major prostanoids PGD2, PGE2, PGF2α, and PGI2 are formed by the various PG synthases, and thromboxane ethanolamides and glyceryl esters are not similarly produced. COX-2 is also of interest by virtue of its corollary central role in modulating endocannabinoid tone, providing a new therapeutic approach for treating pain and anxiety. Other major oxidative conversion pathways are provided for both A-EA and 2-AG by several lipoxygenases (LOXs), resulting in the formation of numerous hydroxyl metabolites. These do not necessarily represent inactivation pathways for endocannabinoids but may mimic or modulate the endocannabinoids or even display alternative pharmacology. Similarly, A-EA and 2-AG may be oxidized by P450 enzymes. Again a very diverse number of metabolites are formed, with either cannabinoid-like biological properties or an introduction of disparate pharmacology. The biological activity of epoxy and hydroxyl derivatives of the endocannabinoids remains to be fully elucidated. This review attempts to consolidate and compare the findings obtained to date in an increasingly important research area. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Vascular targets for cannabinoids: animal and human studies

Application of cannabinoids and endocannabinoids to perfused vascular beds or individual isolated arteries results in changes in vascular resistance. In most cases, the result is vasorelaxation, although vasoconstrictor responses are also observed. Cannabinoids also modulate the actions of vasoactive compounds including acetylcholine, methoxamine, angiotensin II and U46619 (thromboxane mimetic). Numerous mechanisms of action have been proposed including receptor activation, potassium channel activation, calcium channel inhibition and the production of vasoactive mediators such as calcitonin gene-related peptide, prostanoids, NO, endothelial-derived hyperpolarizing factor and hydrogen peroxide. The purpose of this review is to examine the evidence for the range of receptors now known to be activated by cannabinoids. Direct activation by cannabinoids of CB1 , CBe , TRPV1 (and potentially other TRP channels) and PPARs in the vasculature has been observed. A potential role for CB2, GPR55 and 5-HT1 A has also been identified in some studies. Indirectly, activation of prostanoid receptors (TP, IP, EP1 and EP4 ) and the CGRP receptor is involved in the vascular responses to cannabinoids. The majority of this evidence has been obtained through animal research, but recent work has confirmed some of these targets in human arteries. Vascular responses to cannabinoids are enhanced in hypertension and cirrhosis, but are reduced in obesity and diabetes, both due to changes in the target sites of action. Much further work is required to establish the extent of vascular actions of cannabinoids and the application of this research in physiological and pathophysiological situations.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Monoacylglycerols activate TRPV1--a link between phospholipase C and TRPV1

Phospholipase C-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate generates diacylglycerol, inositol 1,4,5-trisphosphate and protons, all of which can regulate TRPV1 activity via different mechanisms. Here we explored the possibility that the diacylglycerol metabolites 2-arachidonoylglycerol and 1-arachidonoylglycerol, and not metabolites of these monoacylglycerols, activate TRPV1 and contribute to this signaling cascade. 2-Arachidonoylglycerol and 1-arachidonoylglycerol activated native TRPV1 on vascular sensory nerve fibers and heterologously expressed TRPV1 in whole cells and inside-out membrane patches. The monoacylglycerol lipase inhibitors methylarachidonoyl-fluorophosphonate and JZL184 prevented the metabolism of deuterium-labeled 2-arachidonoylglycerol and deuterium-labeled 1-arachidonoylglycerol in arterial homogenates, and enhanced TRPV1-mediated vasodilator responses to both monoacylglycerols. In mesenteric arteries from TRPV1 knock-out mice, vasodilator responses to 2-arachidonoylglycerol were minor. Bradykinin and adenosine triphosphate, ligands of phospholipase C-coupled membrane receptors, increased the content of 2-arachidonoylglycerol in dorsal root ganglia. In HEK293 cells expressing the phospholipase C-coupled histamine H1 receptor, exposure to histamine stimulated the formation of 2-AG, and this effect was augmented in the presence of JZL184. These effects were prevented by the diacylglycerol lipase inhibitor tetrahydrolipstatin. Histamine induced large whole cell currents in HEK293 cells co-expressing TRPV1 and the histamine H1 receptor, and the TRPV1 antagonist capsazepine abolished these currents. JZL184 increased the histamine-induced currents and tetrahydrolipstatin prevented this effect. The calcineurin inhibitor ciclosporin and the endogenous "entourage" compound palmitoylethanolamide potentiated the vasodilator response to 2-arachidonoylglycerol, disclosing TRPV1 activation of this monoacylglycerol at nanomolar concentrations. Furthermore, intracerebroventricular injection of JZL184 produced TRPV1-dependent antinociception in the mouse formalin test. Our results show that intact 2-arachidonoylglycerol and 1-arachidonoylglycerol are endogenous TRPV1 activators, contributing to phospholipase C-dependent TRPV1 channel activation and TRPV1-mediated antinociceptive signaling in the brain.

Nitric-oxide synthase knockout modulates Ca²⁺-sensing receptor expression and signaling in mouse mesenteric arteries

Extracellular calcium (Ca²⁺(e))-induced relaxation of isolated, phenylephrine (PE)-contracted mesenteric arteries is dependent on an intact perivascular sensory nerve network that expresses the Ca²⁺-sensing receptor (CaSR). Activation of the receptor stimulates an endocannabinoid vasodilator pathway, which is dependent on cytochrome P450 and phospholipase A₂ but largely independent of the endothelium. In the present study, we determined the role of nitric oxide (NO) in perivascular nerve CaSR-mediated relaxation of PE-contracted mesenteric resistance arteries isolated from mice. Using automated wire myography, we studied the effects of NO synthase (NOS) gene knockout (NOS(-/-)) and pharmacologic inhibition of NOS on Ca²⁺(e)-induced relaxation of PE-contracted arteries. Endothelial NOS knockout (eNOS(-/-)) upregulates but neuronal NOS knockout (nNOS(-/-)) downregulates CaSR expression. NOS(-/-) reduced maximum Ca²⁺(e)-induced relaxation with no change in EC₅₀ values, with eNOS(-/-) having the largest effect. The responses of vessels to calindol and Calhex 231 indicate that the CaSR mediates relaxation. L-N⁵-(1-iminoethyl)-ornithine reduced Ca²⁺(e)-induced relaxation of PE-contracted arteries from C57BL/6 control mice by ≈38% but had a smaller effect in vessels from eNOS(-/-) mice. 7-Nitroindazole had no significant effect on relaxation of arteries from NOS(-/-) mice, but both N(G)-nitro-L-arginine methylester and N(G)-monomethyl-L-arginine significantly reduced the relaxation maxima in all groups. Interestingly, the nNOS-selective inhibitor S-methyl-L-thiocitrulline significantly increased the EC₅₀ value by ≈60% in tissues from C57BL/6 mice but reduced the maximum response by ≈80% in those from nNOS(-/-) mice. Ca²⁺-activated big potassium channels play a major role in the process, as demonstrated by the effect of iberiotoxin. We conclude that CaSR signaling in mesenteric arteries stimulates eNOS and NO production that regulates Ca²⁺(e)-induced relaxation.

Immunohistochemical and functional studies on calcium-sensing receptors in rat uterine smooth muscle

1. Activation of calcium-sensing receptors (CaS) leads to relaxation of vascular smooth muscle. However, the role of CaS in uterine smooth muscle is unknown. Therefore the aim of the present study was to investigate the expression and function of CaS in the uterus. 2. The expression of CaS in the oestrogen-dominated rat uterus was investigated using immunohistochemistry. The effects of putative CaS ligands on oxytocin-induced contractions of longitudinally orientated uterine strips from oestrogen-dominated rats were determined at reduced extracellular Ca²⁺ concentrations using conventional organ bath techniques. 3. Immunohistochemical evidence showed the presence of CaS in the endometrium and smooth muscle layers of the rat uterus. Oxytocin-induced contractions were inhibited by cations (Gd³⁺ > Ca²⁺ = Mg²⁺), polyamines (spermine > spermidine) and the positive allosteric modulators cinacalcet and calindol. However (R)- and (S)-cinacalcet were equipotent, indicating a lack of stereoselectivity, and the negative allosteric modulator calhex-231 also caused dose-dependent relaxation. In addition, although intermediate-conductance calcium-activated potassium channels and cytochrome P450-dependent signal transduction have been implicated in CaS-induced relaxation of vascular smooth muscle, neither Tram-34 nor miconazole (1 μmol/L), which block these pathways, respectively, had any effect on the ability of cinacalcet to inhibit oxytocin-induced contractions. 4. Calcium-sensing receptors are expressed in smooth muscle layers of the rat uterus and their ligands produce potent relaxation of longitudinally orientated uterine strips. However, the pharmacological profile of inhibition of contractility by CaS ligands is not consistent with a role for CaS in the regulation of uterine contractility in the rat.

Mesenteric artery contraction and relaxation studies using automated wire myography

Proximal resistance vessels, such as the mesenteric arteries, contribute substantially to the peripheral resistance. These small vessels of between 100-400 μm in diameter function primarily in directing blood flow to various organs according to the overall requirements of the body. The rat mesenteric artery has a diameter greater than 100 μm. The myography technique, first described by Mulvay and Halpern(1), was based on the method proposed by Bevan and Osher(2). The technique provides information about small vessels under isometric conditions, where substantial shortening of the muscle preparation is prevented. Since force production and sensitivity of vessels to different agonists is dependent on the extent of stretch, according to active tension-length relation, it is essential to conduct contraction studies under isometric conditions to prevent compliance of the mounting wires. Stainless steel wires are preferred to tungsten wires because of oxidation of the latter, which affects recorded responses(3).The technique allows for the comparison of agonist-induced contractions of mounted vessels to obtain evidence for normal function of vascular smooth muscle cell receptors. We have shown in several studies that isolated mesenteric arteries that are contracted with phenylyephrine relax upon addition of cumulative concentrations of extracellular calcium (Ca(2+)(e;)). The findings led us to conclude that perivascular sensory nerves, which express the G protein-coupled Ca(2+)-sensing receptor (CaR), mediate this vasorelaxation response. Using an automated wire myography method, we show here that mesenteric arteries from Wistar, Dahl salt-sensitive(DS) and Dahl salt-resistant (DR) rats respond differently to Ca(2+)(e;). Tissues from Wistar rats showed higher Ca(2+)-sensitivity compared to those from DR and DS. Reduced CaR expression in mesenteric arteries from DS rats correlates with reduced Ca(2+)(e;)-induced relaxation of isolated, pre-contracted arteries. The data suggest that the CaR is required for relaxation of mesenteric arteries under increased adrenergic tone, as occurs in hypertension, and indicate an inherent defect in the CaR signaling pathway in Dahl animals, which is much more severe in DS. The method is useful in determining vascular reactivity ex vivo in mesenteric resistance arteries and similar small blood vessels and comparisons between different agonists and/or antagonists can be easily and consistently assessed side-by-side(6,7,8).

Vascular actions of calcimimetics: role of Ca²(+) -sensing receptors versus Ca²(+) influx through L-type Ca²(+) channels

BACKGROUND AND PURPOSE

The calcimimetic, (R)-N-(3-(3-(trifluoromethyl)phenyl)propyl)-1-(1-napthyl)ethylamine hydrochloride (cinacalcet), which activates Ca²(+) -sensing receptors (CaR) in parathyroid glands, is used to treat hyperparathyroidism. Interestingly, CaR in perivascular nerves or endothelial cells is also thought to modulate vascular tone. This study aims to characterize the vascular actions of calcimimetics.

EXPERIMENTAL APPROACH

In rat isolated small mesenteric arteries, the relaxant responses to the calcimimetics, cinacalcet and (R)-2-[[[1-(1-naphthyl)ethyl]amino]methyl]-1H-indole hydrochloride (calindol) were characterized, with particular emphasis on the role of CaR, endothelium, perivascular nerves, K(+) channels and Ca²(+) channels. Effects of L-ornithine, which activates a Ca(2+) -sensitive receptor related to CaR (GPRC6A), were also tested.

KEY RESULTS

Cinacalcet induced endothelium-independent relaxation (pEC₅₀ 5.58 ± 0.07, E(max) 97 ± 6%) that was insensitive to sensory nerve desensitization by capsaicin or blockade of large-conductance Ca²(+) -activated K(+) channels by iberiotoxin. Calindol, another calcimimetic, caused more potent relaxation (pEC₅₀ 6.10 ± 0.10, E(max) 101 ± 6%), which was attenuated by endothelial removal or capsaicin, but not iberiotoxin. The negative modulator of CaR, calhex 231 or changes in [Ca²(+) ](o) had negligible effect on relaxation to both calcimimetics. The calcimimetics relaxed vessels precontracted with high [K(+) ](o) and inhibited Ca²(+) influx in endothelium-denuded vessels stimulated by methoxamine, but not ionomycin. They also inhibited contractions to the L-type Ca²(+) channel activator, BayK8644. L-ornithine induced small relaxation alone and had no effect on the responses to calcimimetics.

CONCLUSION AND IMPLICATIONS

Cinacalcet and calindol are potent arterial relaxants. Under the experimental conditions used, they predominantly act by inhibiting Ca²(+) influx through L-type Ca²(+) channels into vascular smooth muscle, whereas Ca²(+) -sensitive receptors (CaR or GPRC6A) play a minor role.

Caenorhabditis Elegans Mutants Predict Regulation of Fatty Acids and Endocannabinoids by the CYP-35A Gene Family

BACKGROUND

Cytochrome P450s (CYPs) are mono-oxygenases that metabolize endogenous compounds, such as fatty acids and lipid signaling molecules, and furthermore have a role in metabolism of xenobiotics. In order to investigate the role of CYP genes in fat metabolism at the molecular level, four Caenorhabditis elegans mutants lacking functional CYP-35A1, CYP-35A2, CYP-35A4, and CYP-35A5 were characterized. Relative amounts of fatty acids, as well as endocannabinoids, which regulate weight gain and accumulation of fats in mammals, were measured while fat contents in worms were visualized using Oil-Red-O staining.

RESULTS

The cyp-35A1 and cyp-35A5 mutants had a significantly lower intestinal fat content than wild-type animals, whereas cyp-35A2 and cyp-35A4 mutants appeared normal. The overall fatty acid compositions of CYP mutants did not alter dramatically, although modest but significant changes were observed. cyp-35A1 and cyp-35A5 mutants had significantly higher levels of C18:1n7 and lower C18:2n6c. All four mutants had higher relative amounts of C18:1n7 than the wild-type. In the cyp-35A5 mutant, the levels of the endocannabinoid anandamide were found to be 4.6-fold higher than in wild-type. Several fatty acid synthesis genes were over-expressed in cyp-35A1 including fat-2. Feeding oleic or elaidic triglycerides to wild-type animals demonstrated that cyp-35A1 transcriptional levels are insensitive to environmental exposure of these fats, while cyp-35A2, cyp-35A4, and cyp-35A5 were significantly down regulated.

CONCLUSION

These results demonstrate a dynamic role for CYP-35A subfamily members in maintaining the diversity of fatty acid profiles in C. elegans, and more generally highlight the importance of CYPs in generating both structural and signaling fatty acid functions in other organisms.

Effects of COX-2 inhibition on spinal nociception: the role of endocannabinoids

BACKGROUND AND PURPOSE

Recent studies suggest that the effects of cyclooxygenase-2 (COX-2) inhibition are mediated by cannabinoid receptor activation. However, some non-steroidal anti-inflammatory drugs inhibit the enzyme fatty acid amide hydrolase, which regulates levels of some endocannabinoids. Whether COX-2 directly regulates levels of endocannabinoids in vivo is unclear. Here, the effect of the COX-2 inhibitor nimesulide, which does not inhibit fatty acid amide hydrolase, on spinal nociceptive processing was determined. Effects of nimesulide on tissue levels of endocannabinoids and related compounds were measured and the role of cannabinoid 1 (CB(1)) receptors was determined.

EXPERIMENTAL APPROACH

Effects of spinal and peripheral administration of nimesulide (1-100 microg per 50 microL) on mechanically evoked responses of rat dorsal horn neurones were measured, and the contribution of the CB(1) receptor was determined with the antagonist AM251 (N-(piperidin-1-yl)-5-(-4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide), in anaesthetized rats. Effects of nimesulide on spinal levels of endocannabinoids and related compounds were quantified using liquid chromatography-tandem mass spectrometry.

KEY RESULTS

Spinal, but not peripheral, injection of nimesulide (1-100 microg per 50 microL) significantly reduced mechanically evoked responses of dorsal horn neurones. Inhibitory effects of spinal nimesulide were blocked by the CB(1) receptor antagonist AM251 (1 microg per 50 microL), but spinal levels of endocannabinoids were not elevated. Indeed, both anandamide and N-oleoylethanolamide (OEA) were significantly decreased by nimesulide.

CONCLUSIONS AND IMPLICATIONS

Although the inhibitory effects of COX-2 blockade on spinal neuronal responses by nimesulide were dependent on CB(1) receptors, we did not detect a concomitant elevation in anandamide or 2-AG. Further understanding of the complexities of endocannabinoid catabolism by multiple enzymes is essential to understand their contribution to COX-2-mediated analgesia.

Epoxyeicosanoid signaling in CNS function and disease

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites of cytochrome P450 epoxygenase enzymes recognized as key players in vascular function and disease, primarily attributed to their potent vasodilator, anti-inflammatory and pro-angiogenic effects. Although EETs' actions in the central nervous system (CNS) appear to parallel those in peripheral tissue, accumulating evidence suggests that epoxyeicosanoid signaling plays different roles in neural tissue compared to peripheral tissue; roles that reflect distinct CNS functions, cellular makeup and intercellular relationships. This is exhibited at many levels including the expression of EETs-synthetic and -metabolic enzymes in central neurons and glial cells, EETs' role in neuro-glio-vascular coupling during cortical functional activation, the capacity for interaction between epoxyeicosanoid and neuroactive endocannabinoid signaling pathways, and the regulation of neurohormone and neuropeptide release by endogenous EETs. The ability of several CNS cell types to produce and respond to EETs suggests that epoxyeicosanoid signaling is a key integrator of cell-cell communication in the CNS, coordinating cellular responses across different cell types. Under pathophysiological conditions, such as cerebral ischemia, EETs protect neurons, astroglia and vascular endothelium, thus preserving the integrity of cellular networks unique to and essential for proper CNS function. Recognition of EETs' intimate involvement in CNS function in addition to their multi-cellular protective profile has inspired the development of therapeutic strategies against CNS diseases such as cerebral ischemia, tumors, and neural pain and inflammation that are based on targeting the cellular actions of EETs or their biosynthetic and metabolizing enzymes. Based upon the emerging importance of epoxyeicosanoids in cellular function and disease unique to neural systems, we propose that the actions of "neuroactive EETs" are best considered separately, and not in aggregate with all other peripheral EETs functions.

Microsomal omega-hydroxylated metabolites of N-arachidonoyl dopamine are active at recombinant human TRPV1 receptors

N-Arachidonoyl dopamine (NADA) is an endogenous lipid that modulates signal transduction in neuronal and immune pathways. NADA activates the non-selective cation channel, transient receptor potential vanilloid type 1 (TRPV(1)) and cannabinoid receptor 1. That NADA is comprised of an arachidonic acid (AA) backbone suggests that it may be metabolized through many of the enzymes that act upon AA such as the other AA-derived signaling lipids, the endogenous cannabinoids. To investigate the metabolism of NADA through the cytochrome P450 (CYP450) metabolic pathway, we studied the in vitro rat liver microsomal production of hydroxylated metabolites and their activity at recombinant human TRPV(1) receptors. We showed that following microsomal activation in the presence of NADA, omega and (omega-1) hydroxylated metabolites (19- and 20-HETE-DA) were formed. These metabolites were active at recombinant human TRPV(1) receptors, inducing a dose-dependent calcium influx. Both metabolites exhibited lower potency compared to NADA. We conclude that CYP450 enzymes are capable of metabolizing this signaling lipid forming a larger family of potential neuromodulators.