The anandamide transport inhibitor AM404 activates vanilloid receptors

The possibility that the anandamide transport inhibitor N-(4-hydroxyphenyl)-5,8,11,14-eicosatetraenamide (AM404), structurally similar to the vanilloid receptor agonists anandamide and capsaicin, may also activate vanilloid receptors and cause vasodilation was examined. AM404 evoked concentration-dependent relaxations in segments of rat isolated hepatic artery contracted with phenylephrine. Relaxations were abolished in preparations pre-treated with capsaicin. The calcitonin-gene related peptide (CGRP) receptor antagonist CGRP-(8-37) also abolished relaxations. The vanilloid receptor antagonist capsazepine inhibited vasodilation by AM404 and blocked AM404-induced currents in patch-clamp experiments on Xenopus oocytes expressing the vanilloid subtype 1 receptor (VR1). In conclusion, AM404 activates native and cloned vanilloid receptors.     

Cannabinoid agonists induce relaxation in the bovine ophthalmic artery: evidences for CB1 receptors, nitric oxide and potassium channels

Glaucoma pathophysiology appears to involve vascular deficits, which may contribute to initiation and progression of the disease. Anandamide, the endogenous cannabinoid ligand, and WIN55212-2, a synthetic cannabinoid agonist, are able to evoke concentration-dependent relaxations in bovine ophthalmic artery rings, precontracted with 5-hydroxytryptamine (5-HT) (1 microM). Endothelium removal reduces cannabinoid agonist potency and efficacy. The selective cannabinoid 1 (CB1) receptor antagonists SR141716A (100 nM) and AM251 (100 nM) cause a shift to the right in the concentration-response curves to anandamide and WIN55212-2 in arterial rings both in the presence and in the absence of endothelium. In endothelium-intact arteries, the nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA, 300 microM), completely blocked the anandamide- and WIN55212-2-relaxant responses; by contrast, the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP, 100 microM) induced an increase in vasorelaxant responses to cannabinoid agonists. Relaxations to anandamide and WIN55212-2 were inhibited by iberiotoxin (IbTX, 200 nM), a blocker of large conductance, Ca2+-activated K+ channel (BK(Ca)), and by 4-aminopyridine (4-AP; 1 mM), a blocker of delayed rectifier K+ channel, whereas the blockade of K(ATP) channels by glibenclamide (5 microM) and of small conductance Ca2+-activated K+ channels (SK(Ca)) by apamin (100 nM) did not produce any effects. These data suggest that anandamide and WIN55212-2 relax the bovine ophthalmic artery by involving CB1 the cannabinoid receptor-sensitive pathway. In endothelium-intact arteries, relaxation occurs through activation of nitric oxide synthase cyclic GMP and Ca2+-activated K+ channels. They also cause endothelium-independent relaxation by involving potassium channel opening.     

Evidence of a novel site mediating anandamide-induced negative inotropic and coronary vasodilatator responses in rat isolated hearts

1. Cannabinoids are known to cause coronary vasodilatation and reduce left ventricular developed pressure (LVDP) in isolated hearts although the identity of the receptor(s) mediating these responses is unknown. Our objective was to pharmacologically characterize cannabinoid receptors mediating cardiac responses to the endocannabinoid, anandamide. 2. Dose-response curves for coronary perfusion pressure (CPP) and LVDP were constructed to anandamide, R-(+)-methanandamide, palmitoylethanolamide (PEA) and JWH015 in isolated Langendorff-perfused rat hearts. Anandamide dose-response curves were also constructed in the presence of antagonists selective for CB(1), CB(2) or VR(1) receptors. 3. Anandamide and methanadamide significantly reduced CPP and LVDP but the selective CB(2) receptor agonists, PEA and JWH015 had no significant effect, compared with equivalent vehicle doses. 4. Single bolus additions of the selective CB(1)-receptor agonist, ACEA (5 nmol), decreased LVDP and CPP. When combined with JWH015 (5 nmol) these responses were not augmented. 5. Anandamide-mediated reductions in CPP were significantly blocked by the selective CB(1) receptor antagonists SR 141716A (1 microM) and AM251 (1 microM) and the selective CB(2) receptor antagonist SR 144528 (1 microM) but not by another selective CB(2) receptor antagonist AM630 (10 microM) nor the vanilloid VR(1) receptor antagonist capsazepine (10 microM). 6. SR 141716A, AM281 and SR 144528 significantly blocked negative inotropic responses to anandamide that were not significantly affected by AM251, AM630 and capsazepine. 7. One or more novel sites mediate negative inotropic and coronary vasodilatatory responses to anandamide. These sites can be distinguished from classical CB(1) and CB(2) receptors, as responses are sensitive to both SR 141716A and SR 144528.     

Structure-activity relationship for the endogenous cannabinoid, anandamide, and certain of its analogues at vanilloid receptors in transfected cells and vas deferens

1. This study was directed at exploring the structure-activity relationship for anandamide and certain of its analogues at the rat VR1 receptor in transfected cells and at investigating the relative extent to which anandamide interacts with CB(1) and vanilloid receptors in the mouse vas deferens. 2. pK(i) values for displacement of [(3)H]-resiniferatoxin from membranes of rVR1 transfected CHO cells were significantly less for anandamide (5.78) than for its structural analogues N-(4-hydroxyphenyl)-arachidonylamide (AM404; 6.18) and N-(3-methoxy-4-hydroxy)benzyl-arachidonylamide (arvanil; 6.77). 3. pEC(50) values for stimulating (45)Ca(2+) uptake into rVR1 transfected CHO cells were significantly less for anandamide (5.80) than for AM404 (6.32) or arvanil (9.29). Arvanil was also significantly more potent than capsaicin (pEC(50)=7.37), a compound with the same substituted benzyl polar head group as arvanil. 4. In the mouse vas deferens, resiniferatoxin was 218 times more potent than capsaicin as an inhibitor of electrically-evoked contractions. Both drugs were antagonized to a similar extent by capsazepine (pK(B)=6.93 and 7.18 respectively) but were not antagonized by SR141716A (1 microM). Anandamide was less susceptible than capsaicin to antagonism by capsazepine (pK(B)=6.02) and less susceptible to antagonism by SR141716A (pK(B)=8.66) than methanandamide (pK(B)=9.56). WIN55212 was antagonized by SR141716A (pK(B)=9.02) but not by capsazepine (10 microM). 5. In conclusion, anandamide and certain of its analogues have affinity and efficacy at the rat VR1 receptor. In the mouse vas deferens, which seems to express vanilloid and CB(1) receptors, both receptor types appear to contribute to anandamide-induced inhibition of evoked contractions.     

Neurobehavioral activity in mice of N-vanillyl-arachidonyl-amide

We studied the cannabimimetic properties of N-vanillyl-arachidonoyl-amide (arvanil), a potential agonist of cannabinoid CB(1) and capsaicin VR(1) receptors, and an inhibitor of the facilitated transport of the endocannabinoid anandamide. Arvanil and anandamide exhibited similar affinities for the cannabinoid CB(1) receptor, but arvanil was less efficacious in inducing cannabinoid CB(1) receptor-mediated GTPgammaS binding. The K(i) of arvanil for the vanilloid VR(1) receptor was 0.28 microM. Administered i.v. to mice, arvanil was 100 times more potent than anandamide in producing hypothermia, analgesia, catalepsy and inhibiting spontaneous activity. These effects were not attenuated by the cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-chloro-phenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide.HCl (SR141716A). Arvanil (i.t. administration) induced analgesia in the tail-flick test that was not blocked by either SR141716A or the vanilloid VR(1) antagonist capsazepine. Conversely, capsaicin was less potent as an analgesic (ED(50) 180 ng/mouse, i.t.) and its effects attenuated by capsazepine. The analgesic effect of anandamide (i.t.) was also unaffected by SR141716A but was 750-fold less potent (ED(50) 20.5 microg/mouse) than capsaicin. These data indicate that the neurobehavioral effects exerted by arvanil are not due to activation of cannabinoid CB(1) or vanilloid VR(1) receptors.     

The endogenous lipid anandamide is a full agonist at the human vanilloid receptor (hVR1)

The endogenous cannabinoid anandamide was identified as an agonist for the recombinant human VR1 (hVR1) by screening a large array of bioactive substances using a FLIPR-based calcium assay. Further electrophysiological studies showed that anandamide (10 or 100 microM) and capsaicin (1 microM) produced similar inward currents in hVR1 transfected, but not in parental, HEK293 cells. These currents were abolished by capsazepine (1 microM). In the FLIPR anandamide and capsaicin were full agonists at hVR1, with pEC(50) values of 5. 94+/-0.06 (n=5) and 7.13+/-0.11 (n=8) respectively. The response to anandamide was inhibited by capsazepine (pK(B) of 7.40+/-0.02, n=6), but not by the cannabinoid receptor antagonists AM630 or AM281. Furthermore, pretreatment with capsaicin desensitized the anandamide-induced calcium response and vice versa. In conclusion, this study has demonstrated for the first time that anandamide acts as a full agonist at the human VR1.     

Effect of anandamide on nonadrenergic noncholinergic-mediated relaxation of rat corpus cavernosum

The purpose of this study was to investigate the effect of the endogenous cannabinoid anandamide on the nonadrenergic noncholinergic (NANC) relaxant responses to electrical field stimulation in isolated rat corpus cavernosum. The corporal strips were mounted under tension in a standard oxygenated organ bath with guanethidine sulfate (5 microM) and atropine (1 microM) (to produce adrenergic and cholinergic blockade). The strips were precontracted with phenylephrine hydrochloride (7.5 microM) and electrical field stimulation was applied at different frequencies to obtain NANC-mediated relaxation. The expression of CB1, CB2 and vanilloid receptor proteins within the rat corpus cavernosum was evaluated using western blot analysis. The results showed that the relaxant responses to electrical stimulation were significantly enhanced in the presence of anandamide at 1 and 3 microM. The potentiating effect of anandamide (1 microM) on relaxation responses was significantly attenuated by either the selective cannabinoid CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2, 4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251; 1 microM) or the vanilloid receptor antagonist capsazepine (3 microM), but not by the selective cannabinoid CB2 receptor antagonist 6-iodo-2-methyl-1-[2-(4-morpholinyl) ethyl]-1H-indol-3-yl (4-methoxyphenyl)methanone (AM630; 1 microM). Neither of these antagonists had influence on relaxation responses. Indomethacin (20 microM) had no effect on NANC-mediated relaxation in the presence or absence of anandamide (1 microM). Preincubation with Nw-Nitro-L-Arginine Methyl Ester (L-NAME; 1 microM) significantly inhibited the relaxation responses in the presence or absence of 1 microM anandamide. Although at 30 nM, L-NAME did not cause a significant inhibition of relaxant responses individually, it significantly inhibited the potentiating effect of anandamide (1 microM) on relaxation responses. Anandamide (1 microM) had no influence on concentration-dependent relaxant responses to sodium nitroprusside (10 nM-1 mM), a nitric oxide (NO) donor. The western blotting of corporal tissues demonstrated the existence of both vanilloid and CB1 receptors in corporal strips. In conclusion, our results showed that anandamide has a potentiating effect on NANC-mediated relaxation of rat corpus cavernosum through both CB1 and vanilloid receptors and the NO-mediated component of the NANC relaxant responses to electrical stimulation is involved in this enhancement.     

Anandamide and methanandamide induce both vanilloid VR1- and cannabinoid CB1 receptor-mediated changes in heart rate and blood pressure in anaesthetized rats

In anaesthetized rats activation of vanilloid receptors on sensory vagal nerves elicits rapid bradycardia and hypotension (Bezold-Jarisch reflex). Recent in vitro experiments revealed that the endogenous cannabinoid ligand anandamide acts as an agonist at the vanilloid VRI receptors. The present study was aimed at examining whether vanilloid VR1 receptors are involved in the cardiovascular effects of anandamide in the anaesthetized rat. Intravenous injection of anandamide, its stable analogue methanandamide and the vanilloid receptor agonist capsaicin produced a dose-dependent immediate and short-lasting decrease in heart rate and blood pressure with the following rank order of potencies: capsaicin > methanandamide > anandamide. This bradycardia was dose-dependently diminished by the selective vanilloid receptor antagonist capsazepine (0.3-3 micromol/kg) and the nonselective inhibitor of these receptors, ruthenium red (1-10 micromol/kg). Both antagonists reduced or tended to reduce the hypotension stimulated by the agonists. Following this bradycardia and hypotension (presumably evoked by the Bezold-Jarisch reflex; phase I), capsaicin, anandamide and methanandamide led to a brief vasopressor effect (phase II). Subsequently both anandamides, but not capsaicin, induced a more prolonged decrease in blood pressure (phase III). Capsazepine and ruthenium red (at doses up to 3 tmol/kg and 10 micromol/kg, respectively) failed to affect these changes in blood pressure. The cannabinoid CB1 receptor antagonist SR 141716 at 3 micromol/kg abolished the prolonged decrease in blood pressure (phase III) induced by anandamide and methanandamide, but had no effect on the reflex bradycardia and hypotension (phase I) and on the subsequent vasopressor effect (phase II) evoked by capsaicin, anandamide and methanandamide. In conclusion, the endogenous cannabinoid receptor agonist anandamide and its stable analogue methanandamide induce reflex bradycardia and hypotension (phase I) by activating the vanilloid VRI receptor. Whereas the mechanism underlying the brief vasopressor effect (phase II) is unknown, the prolonged hypotension (phase III) results from stimulation of the cannabinoid CB1 receptor.     

The endogenous cannabinoid agonist, anandamide stimulates sensory nerves in guinea-pig airways

The endogenous cannabinoid agonist, anandamide produced a modest contractile response in guinea-pig isolated bronchus compared with the vanilloid receptor agonist capsaicin. The contractile response to both anandamide and capsaicin was inhibited by the vanilloid receptor antagonist, capsazepine. Furthermore, the NK(2)-selective antagonist, SR48968 but not the NK(1)-selective antagonist, SR140333 inhibited contractile responses to anandamide. The contractile response to anandamide was abolished in tissues desensitized by capsaicin. However, anandamide failed to cross-desensitize the contractile response to capsaicin. The contractile response to anandamide was not significantly altered in the presence of the CB(1) receptor antagonist, SR141716A, nor the amidase inhibitor, phenylmethylsulphonyl fluoride (PMSF) but was significantly increased in the presence of the neutral endopeptidase inhibitor, thiorphan. The cannabinoid agonist, CP55,940 failed to significantly attenuate the excitatory non-adrenergic non-cholinergic (eNANC) response in guinea-pig airways. In contrast, the ORL(1) receptor agonist, nociceptin, significantly inhibited this response. The results demonstrate that anandamide induces a modest contractile response in guinea-pig isolated bronchus that is dependent upon the activation of vanilloid receptors on airway sensory nerves. However, cannabinoid receptors do not appear to play a role in this regard, nor in regulating the release of neuropeptides from airway sensory nerves under physiological conditions.     

Cannabinoid inhibition of capsaicin-sensitive sensory neurotransmission in the rat mesenteric arterial bed

The present study investigated whether cannabinoids can modulate neurotransmission mediated by capsaicin-sensitive sensory nerves in the rat isolated mesenteric arterial bed. Sensory neurogenic vasorelaxation mediated by electrical field stimulation was concentration-dependently attenuated by HU210 (0.1-3 microM), a cannabinoid receptor agonist (from 62+/-8.3% to 6+/-2.1% at 3 microM HU210). HU210 had no effect on relaxation to exogenous calcitonin gene-related peptide, indicating a prejunctional action. The action of HU210 (1 microM) was not affected by LY320135 (1 microM) or SR144528 (1 microM), cannabinoid CB(1) and CB(2) receptor antagonists, respectively. SR141716A (0.01-1 microM), a cannabinoid CB(1) receptor antagonist, concentration-dependently augmented vasorelaxation to electrical field stimulation, but had no effect on responses to calcitonin gene-related peptide and capsaicin, indicating a possible role of endogenous cannabinoids in sensory neurotransmission in rat mesenteric arteries. These data show that the cannabinoid receptor agonist HU210 inhibits prejunctionally sensory neurotransmission in rat mesenteric arteries and that this action is independent of cannabinoid CB(1)- or CB(2)-like receptors.     

Arvanil-induced inhibition of spasticity and persistent pain: evidence for therapeutic sites of action different from the vanilloid VR1 receptor and cannabinoid CB(1)/CB(2) receptors

Activation of cannabinoid receptors causes inhibition of spasticity, in a mouse model of multiple sclerosis, and of persistent pain, in the rat formalin test. The endocannabinoid anandamide inhibits spasticity and persistent pain. It not only binds to cannabinoid receptors but is also a full agonist at vanilloid receptors of type 1 (VR1). We found here that vanilloid VR1 receptor agonists (capsaicin and N-N'-(3-methoxy-4-aminoethoxy-benzyl)-(4-tert-butyl-benzyl)-urea [SDZ-249-665]) exhibit a small, albeit significant, inhibition of spasticity that can be attenuated by the vanilloid VR1 receptor antagonist, capsazepine. Arvanil, a structural "hybrid" between capsaicin and anandamide, was a potent inhibitor of spasticity at doses (e.g. 0.01 mg/kg i.v.) where capsaicin and cannabinoid CB(1) receptor agonists were ineffective. The anti-spastic effect of arvanil was unchanged in cannabinoid CB(1) receptor gene-deficient mice or in wildtype mice in the presence of both cannabinoid and vanilloid receptor antagonists. Likewise, arvanil (0.1-0.25 mg/kg) exhibited a potent analgesic effect in the formalin test, which was not reversed by cannabinoid and vanilloid receptor antagonists. These findings suggest that activation by arvanil of sites of action different from cannabinoid CB(1)/CB(2) receptors and vanilloid VR1 receptors leads to anti-spastic/analgesic effects that might be exploited therapeutically.     

Vasorelaxant effects of oleamide in rat small mesenteric artery indicate action at a novel cannabinoid receptor

Oleamide (cis-9-octadecenoamide) exhibits some cannabimimetic responses despite its low affinities at the currently known cannabinoid receptors. Here we have investigated whether or not it is a vasorelaxant in rat small mesenteric arteries. Oleamide elicited vasorelaxation (EC50=1.2+/-0.2 microM, Rmax=99.1+/-3.9%, n=8) which was reduced by endothelial removal. Nitric oxide synthase inhibition reduced the response (EC50=5.3+/-1.6 microM, Rmax=59.2+/-7.7%, n=7; P<0.01) as did blockade of Ca2+-sensitive K+ channels (KCa) with apamin plus charybdotoxin (both 50 nM) (EC50=2.1+/-0.2 microM, Rmax=58.4+/-1.9%, n=5; P<0.05). Desensitisation of vanilloid receptors with capsaicin (10 microM for 30 min) shifted the oleamide concentration-response curve approximately 30-fold to the right (n=7; P<0.01). Pertussis toxin (400 ng ml-1 for 2 h) caused a two-fold shift in the response curve (EC50=2.2+/-0.4 microM, Rmax=66.8+/-4.5%, n=6; P<0.01). Rimonabant (CB1 cannabinoid receptor antagonist; SR141716A; 3 microM) significantly inhibited relaxation induced by oleamide (EC50=3.5+/-0.3 microM, Rmax=75.1+/-1.9%; n=8; P<0.05). In contrast, neither the more selective CB1 receptor antagonist, AM251 (1 microM), nor the CB2 antagonist, SR144528 (1 microM), had significant effects. O-1918 (10 microM), a putative antagonist at a novel endothelial cannabinoid receptor (abnormal-cannabidiol site), markedly reduced the relaxation to oleamide (n=7; P<0.01).It is concluded that oleamide responses in the rat isolated small mesenteric artery are partly dependent on the presence of the endothelium, activation of Ca2+-sensitive K+ channels (KC)) and involve capsaicin-sensitive sensory nerves. Oleamide may share a receptor (sensitive to rimonabant and O-1918, and coupled to KC) and Gi/o) with anandamide in this vessel. This might be distinct from both of the known cannabinoid receptors and the novel abnormal-cannabidiol site.     

Heterogeneity in the mechanisms of vasorelaxation to anandamide in resistance and conduit rat mesenteric arteries

1 In order to address mechanistic differences between arterial vessel types, we have compared the vasorelaxant actions of anandamide in resistance (G3) and conduit (G0) mesenteric arteries. 2 Anandamide produced concentration-dependent relaxations of pre-constricted G3 arteries with a maximal response that was significantly greater than seen in G0. 3 The CB1 receptor selective antagonists SR141716A (100 nm) and AM251 (100 nm) caused reductions in the vasorelaxant responses to anandamide in both arteries. Maximal vasorelaxant responses to anandamide were reduced in both arteries after treatment with capsaicin to deplete sensory neurotransmitters (10 microm for 1 h). 4 Vasorelaxation to anandamide was not affected by the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 300 microm) in either artery. Only responses in G3 arteries were sensitive to removal of the endothelium. In G3 vessels only, vasorelaxation to anandamide was reduced by inhibition of EDHF activity with a combination of charybdotoxin (100 nm) and apamin (500 nm) in the presence of L-NAME (300 microm) and indomethacin (10 microm). 5 Antagonism of the novel endothelial cannabinoid receptor (O-1918, 1 microm) caused a reduction in the sensitivity to anandamide in G3 but not G0. 6 G3, but not G0, vessels showed a small reduction in vasorelaxant responses to anandamide after inhibition of gap junctional communication with 18alpha-GA (100 microm). 7 These results demonstrate that there are differences in the mechanisms of vasorelaxation to anandamide between conduit and resistance mesenteric arteries. In small resistance vessels, vasorelaxation occurs through stimulation of vanilloid receptors, CB1 receptors, and an endothelial receptor coupled to EDHF release. By contrast, in the larger mesenteric artery, vasorelaxation is almost entirely due to stimulation of vanilloid receptors and CB1 receptors, and is endothelium-independent.     

Endothelium-dependent mechanisms of the vasodilatory effect of the endocannabinoid, anandamide, in the rat pulmonary artery

Endocannabinoids exhibit vasodilatory properties and reduce blood pressure in vivo. However, the influence and mechanism of action of the prominent endocannabinoid, anandamide (AEA), in pulmonary arteries are not known. The present study determined the vascular response to AEA in isolated rat pulmonary arteries. AEA relaxed rat pulmonary arteries that were pre-constricted with U-46619. This relaxation was reduced by the following conditions:removal of the endothelium; in KCl pre-constricted preparations; in the presence of the potassium channel (K(Ca)) blockers, tetraethylammonium and the combination of charybdotoxin and apamin, and the prostacyclin receptor antagonist, RO1138452. Inhibitors of cyclooxygenase (indomethacin), nitric oxide (NO) synthase (N(G)-nitro-l-arginine methyl ester) and fatty acid amide hydrolase (URB597) alone or in combination diminished AEA-induced relaxation in endothelium-intact vessels. The remaining experiments were performed in the presence of URB597 to eliminate the influence of AEA metabolites. Antagonists of the endothelial cannabinoid receptor (CB(x)), O-1918 and cannabidiol, attenuated the AEA-induced response. Antagonists of CB(1), CB(2) and TRPV1 receptors, AM251, AM630 and capsazepine, respectively, did not modify the AEA-induced response. A reference activator of CB(x) receptors, abnormal cannabidiol, mimicked the receptor-mediated AEA effects. The present study demonstrated that AEA relaxed rat pulmonary arteries in an endothelium-dependent fashion via the activation of the O-1918-sensitive CB(x) receptor and/or prostacyclin-like vasoactive products of AEA. One or both of these mechanisms may involve K(Ca) or the NO pathway.     

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

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

Pharmacological separation of cannabinoid sensitive receptors on hippocampal excitatory and inhibitory fibers

Our earlier studies demonstrated that in the hippocampus, cannabinoids suppress inhibitory synaptic transmission via CB(1) cannabinoid receptors, whereas a novel cannabinoid-sensitive receptor modulates excitatory synapses (Katona, I. et al., Journal of Neuroscience 19 (1999) 4544; Hájos, N. et al., European Journal of Neuroscience 12 (2000) 3239; Hájos, N. et al., Neuroscience 106 (2001) 1). The novel receptor does not correspond to CB(2), since this receptor type is not expressed in the brain (Munro, S. et al., Nature 365 (1993) 61). Recent binding experiments revealed that the synthetic cannabinoid WIN 55,212-2 binds with lower affinity to brain membranes of CB(1) receptor-knockout mice indicating that pharmacological differences exist between these two types of cannabinoid receptors in the hippocampus (Breivogel et al., Molecular Pharmacology 60 (2001) 155). To analyze this difference in detail, we first determined the EC(50) values of WIN 55,212-2 for excitatory and inhibitory transmission in rat hippocampal slices using whole-cell patch-clamp recordings. The estimated EC(50) value for inhibitory postsynaptic currents (IPSC) evoked by electrical stimulation in CA1 pyramidal cells was 0.24 microM, whereas for excitatory postsynaptic currents (EPSC) it was 2.01 microM, respectively. The cannabinoid antagonist, AM251, blocked the WIN 55,212-2-induced inhibition of evoked IPSCs, but not of EPSCs, providing evidence for its selectivity for CB(1). We then tested the hypothesis of whether the cannabinoid effect on hippocampal excitatory neurotransmission is mediated via receptors with an affinity for vanilloid ligands. Co-application of the vanilloid receptor antagonist capsazepine (10 microM) with cannabinoids (WIN55,212-2 or CP55,940) prevented the reduction of EPSCs, but not of IPSCs. The amplitude of evoked EPSCs was also suppressed by superfusion of the vanilloid receptor agonist capsaicin (10 microM), an effect which could also be antagonized by capsazepine. In contrast, capsaicin did not change the amplitude of evoked IPSCs.These results demonstrate that WIN 55,212-2 is an order of magnitude more potent in reducing GABAergic currents via CB(1) than in inhibiting glutamatergic transmission via the new CB receptor. The sensitivity of the new CB receptor (and EPSCs) to vanilloid ligands, but not to the cannabinoid antagonist AM251, represents another pharmacological tool to distinguish the two receptors, since CB(1) (and its effect on IPSCs) is not modulated by vanilloids, but is antagonized by AM251.     

The effects of Delta9-tetrahydrocannabinol in rat mesenteric vasculature, and its interactions with the endocannabinoid anandamide

1 Delta9-tetrahydrocannabinol (THC) produces varying effects in mesenteric arteries: vasorelaxation (third-order branches, G3), modest vasorelaxation (G2), no effect (G1) and vasoconstriction (the superior mesenteric artery, G0). 2 In G3, vasorelaxation to THC was inhibited by pertussis toxin, but was unaffected by the CB1 receptor antagonist, AM251 (1 microM), incubation with the TRPV1 receptor agonist capsaicin (10 microM, 1 h), the TRPV1 receptor antagonist capsazepine (10 microM) or de-endothelialisation. 3 In G3, vasorelaxation to THC was inhibited by high K+ buffer, and by the following K+ channel inhibitors: charybdotoxin (100 nM), apamin (500 nM) and barium chloride (30 microM), but not by 4-aminopyridine, glibenclamide or tertiapin. 4 In G3, THC (10 and 100 microM) inhibited the contractile response to Ca2+ in a Ca2+-free, high potassium buffer, indicating that THC blocks Ca2+ influx. 5 In G0, the vasoconstrictor responses to THC were inhibited by de-endothelialisation and SR141716A (100 nM), but not by the endothelin (ET(A)) receptor antagonist FR139317 (1 microM).THC (1 and 10 microM) antagonised vasorelaxation to anandamide in G3 but not G0. THC did not antagonise the noncannabinoid verapamil, capsaicin or the CB1 receptor agonist CP55,940. 6 THC (10 and 100 microM) inhibited endothelium-derived relaxing factor (EDHF)-mediated responses to carbachol in a manner similar to the gap junction inhibitor 18alpha-glycyrrhetinic acid. 7 These data show that THC causes vasorelaxation through activation of K+ channels and inhibition of Ca2+ channels, and this involves non-CB1, non-TRPV1 but G-protein-coupled receptors. In G0, THC does not cause relaxation and at high concentrations causes contractions. Importantly, THC antagonises the effects of anandamide, possibly through inhibition of EDHF activity.     

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

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

Vasorelaxant activities of the putative endocannabinoid virodhamine in rat isolated small mesenteric artery

Virodhamine is a recently identified novel endocannabinoid. Cannabinoids may evoke vasorelaxation through novel receptors in the vasculature and/or through release of vasodilator peptides from sensory nerve endings. Virodhamine induced endothelium-dependent relaxation in the rat isolated small mesenteric artery mounted in a myograph and precontracted with methoxamine. Desensitization of vanilloid receptors by capsaicin did not affect relaxation responses to virodhamine. The CB(1) receptor antagonist SR 141716A (3 microM), but not the more CB(1)-selective blocker AM 251 (1 microM), attenuated the response, while two CB(2) receptor antagonists, SR 144528 (1 microM) and AM 630 (10 microM), had no effect. The novel antagonist for the putative endothelial 'abnormal-cannabidiol receptor', O-1918 (30 microM), inhibited virodhamine relaxations. Hence virodhamine may activate this novel receptor, which might also recognize SR 141716A. Inhibition of nitric oxide synthase (L-NAME 300 microM) did not affect relaxation to virodhamine but the responses were markedly reduced when tone was induced with 60 mM KCl, suggesting a role for the activation of K(+) channels. The Ca(2+)-activated K(+) channel (K(Ca)) blockers, apamin (50 nM) and charybdotoxin (50 nM), inhibited virodhamine vasorelaxation. Combination of these blockers with SR 141716A (3 microM) caused no further inhibition. It was concluded that virodhamine relaxes the rat small mesenteric artery by endothelium-dependent activation of K(Ca), perhaps via the putative abnormal-cannabidiol receptor.     

Anandamide induces cardiovascular and respiratory reflexes via vasosensory nerves in the anaesthetized rat

1. We tested the hypothesis that sensory nerves innervating blood vessels play a role in the local and systemic regulation of the cardiovascular and respiratory (CVR) systems. We measured CVR reflexes evoked by administration of anandamide (86 - 863 nmoles) and capsaicin (0.3 - 10 nmoles) into the hindlimb vasculature of anaesthetized rats. 2. Anandamide and capsaicin each caused a rapid dose-dependent reflex fall in blood pressure and an increase in ventilation when injected intra-arterially into the hindlimb. 3. Action of both agonists at the vanilloid receptor (VR1) on perivascular sensory nerves was investigated using capsazepine (1 mg kg(-1) i.a.) a competitive VR1 antagonist, ruthenium red (1 mg kg(-1) i.a.), a non-competitive antagonist at VR1, or a desensitizing dose of capsaicin (200 nmoles i.a.). The cannabinoid receptor antagonist SR141716 (1 mg kg(-1) i.a.) was used to determine agonist activity at the CB(1) receptor. 4. Capsazepine, ruthenium red, or acute VR1 desensitization by capsaicin-pretreatment, markedly attenuated the reflex CVR responses evoked by anandamide and capsaicin (P< 0.05; paired Student's t-test). Blockade of CB(1) had no significant effect on the responses to anandamide. 5. Local sectioning of the femoral and sciatic nerves attenuated CVR responses to anandamide and capsaicin (P< 0.05). Vagotomy or carotid sinus sectioning had no significant effect on anandamide- or capsaicin-induced responses. 6. These data demonstrate that both the endogenous cannabinoid, anandamide, and the vanilloid, capsaicin, evoke CVR reflexes when injected intra-arterially into the rat hindlimb. These responses appear to be mediated reflexly via VR1 located on sensory nerve endings within the hindlimb vasculature.