An Endogenous Cannabinoid as an Endothelium-Derived Vasorelaxant

101

111

1 The cannabinoid arachidonyl ethanolamide (anandamide) caused concentration-dependent relaxation of 5-HT-precontracted, myograph-mounted, segments of rat left anterior descending coronary artery. 2 This relaxation was endothelium-independent, una ected by the fatty acid amide hydrolase inhibitor, arachidonyl tri¯uoromethyl ketone (10 mM), and mimicked by the non-hydrolysable anandamide derivative, methanandamide. 3 Relaxations to anandamide were attenuated by the cannabinoid receptor antagonist, SR 141716A (3 mM), but una ected by AM 251 (1 mM) and AM 630 (1 mM), more selective antagonists of cannabinoid CB 1 and CB 2 receptors respectively. Palmitoylethanolamide, a selective CB 2 receptor agonist, did not relax precontracted coronary arteries. 4 Anandamide relaxations were not a ected by inhibition of sensory nerve transmission with capsaicin (10 mM) or blockade of vanilloid VR1 receptors with capsazepine (5 mM). Nevertheless capsaicin relaxed coronary arteries in a concentration-dependent and capsazepine-sensitive manner, con®rming functional sensory nerves were present. In contrast, capsazepine and capsaicin did inhibit anandamide relaxations in methoxamine-precontracted rat small mesenteric arteries. 5 Relaxations to anandamide were inhibited by TEA (1 mM) or iberiotoxin (50 nM), blockers of large conductance, Ca 2+ -activated K + channels (BK Ca ). Gap junction inhibition with 18a-glycyrrhetinic acid (100 mM) did not a ect anandamide relaxations. 6 This study shows anandamide relaxes the rat coronary artery by a novel mechanism. Anandamide-induced relaxations do not involve the endothelium, degradation into active metabolites, or activation of cannabinoid CB 1 or CB 2 receptors, but may involve activation of BK Ca . Vanilloid receptor activation also has no role in the e ects of anandamide in coronary arteries, even though functional sensory nerves are present. British Journal of Pharmacology (2001) 134, 921 ± 929

Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Mechanisms of anandamide‐induced vasorelaxation in rat isolated coronary arteries

White

Bottrill

et al. 2001

101

111

“…The nature of the EDHF is still unresolved, but possible candidates include a cytochrome P 450 metabolite (Bauersachs et al, 1994), perhaps an epoxyeicosatrienoic acid (EET; Fisslthaler et al, 1999), an endogenous cannabinoid (Randall et al, 1996) or potassium ions (Edwards et al, 1998). Moreover, evidence has been reported suggesting that the process of relaxation involves hyperpolarization of endothelial cells (Edwards et al, 1998; and consequent gap junctional transmission between endothelium and smooth muscle, resulting in smooth muscle hyperpolarization and relaxation (Davies et al, 1988;Beny, 1990;Chaytor et al, 1998).…”

Section: Discussionmentioning

confidence: 99%

Dominant role of an endothelium‐derived hyperpolarizing factor (EDHF)‐like vasodilator in the ciliary vascular bed of the bovine isolated perfused eye

McNeish

Wilson

Martin

2001

1 The roles of the endothelium-derived nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor (EDHF) in mediating vasodilator responses to acetylcholine and bradykinin were assessed in the ciliary vascular bed of the bovine isolated perfused eye preparation. 2 Vasodilatation to acetylcholine or bradykinin was una ected by the nitric oxide synthase inhibitor, L-NAME (100 mM), or the cyclo-oxygenase inhibitor,¯urbiprofen (30 mM), but was virtually abolished following treatment with a high concentration of KCl (30 mM), or by damaging the endothelium with the detergent, CHAPS (0.3%, 2 min). 3 Acetylcholine-induced vasodilatation was una ected by glibenclamide (10 mM), an inhibitor of ATP-sensitive K + channels (K + ATP ), but was signi®cantly attenuated by TEA (10 mM), a nonselective inhibitor of K + channels. 4 The small conductance calcium-sensitive K + channel (SK + Ca ) inhibitor, apamin (100 nM), and the large conductance calcium-sensitive K + channel (BK + Ca ) inhibitor, iberiotoxin (50 nM), had no signi®cant e ect on acetylcholine-induced vasodilatation. In contrast, the intermediate (IK + Ca )/large conductance calcium-sensitive K + channel inhibitor, charybdotoxin (50 nM), powerfully blocked these vasodilator responses, and uncovered a vasoconstrictor response. 5 The combination of apamin (100 nM) with a sub-threshold concentration of charybdotoxin (10 nM) signi®cantly attenuated acetylcholine-induced vasodilatation, but the combination of apamin (100 nM) with iberiotoxin (50 nM) had no e ect. 6 In conclusion, blockade by a high concentration of KCl, by charybdotoxin, or by the combination of apamin with a sub-threshold concentration of charybdotoxin, strongly suggests that vasodilatation in the bovine isolated perfused eye is mediated by an EDHF. British Journal of Pharmacology (2001) 134, 912 ± 920

“…Early reports indicated that anandamide acted via the release of nitric oxide (Deutsch et al, 1997). However, in rat mesenteric vessels, vasorelaxant effects of anandamide are largely insensitive to inhibition of nitric oxide synthase (Randall et al, 1996;White & Hiley, 1997;Ja´rai et al, 1999). Although nitric oxide does not appear to mediate responses to anandamide, the vasorelaxation is partly endothelium-dependent, in some, but not all preparations (White & Hiley, 1997;Chaytor et al, 1999;Ja´rai et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

Characterisation of the vasorelaxant properties of the novel endocannabinoid N‐arachidonoyl‐dopamine (NADA)

O’Sullivan

Kendall

Randall

2004

1 We have investigated the vascular effects of N-arachidonoyl-dopamine (NADA), a novel endocannabinoid/vanilloid. NADA caused vasorelaxant effects comparable to those of anandamide in small mesenteric vessels (G3), the superior mesenteric artery (G0) and in the aorta. 2 In G3, addition of N G -nitro-L-arginine methyl ester (300 mM) or the dopamine (D 1 ) receptor antagonist (SCH23390, 1 mM) did not affect responses to NADA. In the presence of 60 mM KCl, after de-endothelialisation, or after K þ channel inhibition with charybdotoxin (100 nM) and apamin (500 nM), relaxant responses to NADA were inhibited. 3 In G3, pretreatment with the vanilloid receptor (VR) agonist capsaicin (10 mM) or the VR antagonist capsazepine (10 mM) reduced vasorelaxation to NADA. 4 In G3, application of the CB 1 antagonist SR141716A at 1 mM but not 100 nM reduced the potency of NADA. Another CB 1 antagonist, AM251 (100 nM and 1 mM), did not affect vasorelaxation to NADA. After endothelial denudation, SR141716A (1 mM) did not reduce the responses further. A combination of capsaicin and SR141716A (1 mM) reduced vasorelaxation to NADA further than with capsaicin pretreatment alone. The novel endothelial cannabinoid (CB) receptor antagonist O-1918 opposed vasorelaxation to NADA in G3. 5 In the superior mesenteric artery (G0), vasorelaxation to NADA was not dependent on an intact endothelium and was not sensitive to O-1918, but was sensitive to capsaicin and SR141716A or AM251 (both 100 nM). 6 The results of the present study demonstrate for the first time that NADA is a potent vasorelaxant. In G3, the effects of NADA are mediated by stimulation of the VR and the novel endothelial CB receptor, while in G0, vasorelaxation is mediated through VR 1 and CB 1 receptors.