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Mechanisms of anandamide-induced vasorelaxation in rat isolated coronary arteries.

ABSTRACT: 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, unaffected by the fatty acid amide hydrolase inhibitor, arachidonyl trifluoromethyl ketone (10 microM), and mimicked by the non-hydrolysable anandamide derivative, methanandamide. 3. Relaxations to anandamide were attenuated by the cannabinoid receptor antagonist, SR 141716A (3 microM), but unaffected by AM 251 (1 microM) and AM 630 (1 microM), 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 affected by inhibition of sensory nerve transmission with capsaicin (10 microM) or blockade of vanilloid VR1 receptors with capsazepine (5 microM). Nevertheless capsaicin relaxed coronary arteries in a concentration-dependent and capsazepine-sensitive manner, confirming 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 18alpha-glycyrrhetinic acid (100 microM) did not affect 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 effects of anandamide in coronary arteries, even though functional sensory nerves are present.

SUBMITTER: White R

PROVIDER: S-EPMC1573021 | biostudies-other | 2001 Oct

REPOSITORIES: biostudies-other

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Project description:Background and purposeThromboxane A(2) and endothelial dysfunction are implicated in the development of pulmonary hypertension. The receptor-transduction pathway for U46619 (9,11-dideoxy-9 alpha, 11 alpha-methanoepoxy prostaglandin F(2 alpha))-induced contraction was examined in endothelium-intact (E+) and denuded (E-) rat pulmonary artery rings.Experimental approachArtery rings were mounted on a wire myograph under a tension of 7-7.5 mN at 37 degrees C and gassed with 95% O(2)/5% CO(2). Isometric recording was made by using Powerlab data collection and Chart 5 software.Key resultsBoth E+ and E- contractile responses were sensitive to Rho-kinase inhibition and the chloride channel blocker NPPB [5-nitro-2-(3-phenylpropylamino)benzoic acid]. The E+ response was sensitive to the store-operated calcium channel blockers SKF-96365 {1-[B-[3-(4-methoxyphenyl)propoxy]-4-methoxy-phenethyl]-1H-imidazole hydrochloride} and 2-APB (2-amino ethoxy diphenylborate) (75-100 micromol x L(-1)). The E- response was sensitive to 2-APB (10-30 micromol x L(-1)), a putative IP(3) receptor antagonist, and the calcium and chloride channel blockers nifedipine, DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid) and niflumic acid but was insensitive to SKF-96365. Inhibiting K(V) with 4-AP in E+ rings exposed a contraction sensitive to nifedipine, DIDS and niflumic acid, whereas inhibiting BK(Ca) exposed a contraction sensitive to mibefradil, DIDS and niflumic acid. This indicates that removal of the endothelium allows the TP receptor to inhibit K(V), which may involve coupling to phospholipase C, because inhibition of phospholipase C with U73122 (1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-y]amino]hexyl]- 1H-pyrrole-2,5-dione) switched the E- pathway to the E+ pathway.Conclusions and implicationsThe results from this study indicate that distinct transduction pathways can be employed by the TP receptor to produce contraction and that the endothelium is able to influence the coupling of the TP receptor.

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Mechanisms of anandamide-induced vasorelaxation in rat isolated coronary arteries.

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