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

Abstract

1 The e ects 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 mM) 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 e ect on U46619-induced tone. 3 The anandamide-induced relaxation was una ected by the cannabinoid receptor antagonist, SR 141716A (3 mM), the vanilloid receptor antagonist, capsazepine (3 and 10 mM) or the nitric oxide synthase inhibitor, L-NAME (100 mM). 4 The cyclo-oxygenase inhibitor, indomethacin (3 and 10 mM) and the anandamide amidohydrolase inhibitor, PMSF (70 and 200 mM), markedly attenuated the anandamide response. The anandamide transport inhibitor, AM 404 (10 and 30 mM), 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 mM) or iberiotoxin (100 nM). Blockade of small conductance, Ca 2+ -activated K + channels, delayed recti®er K + channels, K ATP channels or inward recti®er K + channels was without e ect. 6 These data suggest that the relaxant e ects 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.

The complexities of the cardiovascular actions of cannabinoids

“…In respect of the latter, it has been shown that sensory nerves do not play a role in coronary vessels from several species (Grainger & Boachie-Ansah, 2001;White et al, 2001;Ford et al, 2002). This indicates that the actions of anandamide may be dependent on vanilloid receptor density and/or density of perivascular nerve in a given blood vessel.…”

“…In the rat aorta, anandamide causes approximately a 20% maximal relaxation (O'Sullivan et al, 2004a), while in the rabbit aorta, this has been reported to be 80% (Mukhopadhyay et al, 2002). Similarly, in the rat coronary vessels anandamide causes about 30-40% relaxation (White et al, 2001), 50% relaxation in bovine vessels (Pratt et al, 1998) but 80% relaxation in ovine vessels (Grainger & Boachie-Ansah, 2001). However, anandamide does not cause vasorelaxation in porcine coronary vessels (Fleming et al, 1999).…”

“…Studies are divided into those where anandamide acts directly and those where its actions are dependent on metabolism. For example, there is evidence from bovine and ovine coronary vessels (Pratt et al, 1998;Grainger & Boachie-Ansah, 2001) that vasorelaxation to anandamide is dependent on metabolism via epoxygenase or cyclooxygenase pathways. However, in rat mesenteric vessels it is universally reported that vasorelaxation to anandamide is unaffected by cyclooxygenase inhibition (White & Hiley, 1997).…”

Endocannabinoid anandamide mediates hypoxic pulmonary vasoconstriction

“…Herein, we demonstrate that AEA mediates hypoxic pulmonary vasoconstriction and is also involved in pulmonary hypertension via its degradation to FAAH-dependent metabolites. Effects of endocannabinoids on vascular tone have been mainly attributed to direct endocannabinoid signaling via surface receptors (1, 2, 21) so far, whereas degradation pathways of endocannabinoids have been thought to play a minor role (4,22). FAAH is the principal AEAdegrading enzyme, thereby limiting the effects of AEA at cannabinoid receptors.…”

Vasodilatory and Electrophysiological Actions of 8-iso-Prostaglandin E2 in Porcine Coronary Artery

“…In the porcine coronary artery, vasodilators such as bradykinin stimulate production of reactive oxygen species by cytochrome P450 enzymes in the endothelium (Fleming et al, 2001) and trigger a series of events that results in activation of large-conductance Ca 2ϩ -dependent K ϩ currents and vasodilation (Barlow and White, 1998;Hayabuchi et al, 1998b;Pomposiello et al, 1999). One of these events appears to include release of a cyclooxygenase-independent metabolite of arachidonic acid Cohen, 1991, 1992;Hecker et al, 1994;Weintraub et al, 1995;Chataigneau et al, 1998;Hayabuchi et al, 1998a), one which is not a cannabinoid (Chataigneau et al, 1998;Pomposiello et al, 1999;Grainger and Boachie-Ansah, 2001). Although many acknowledge that cytochrome P450 plays a key role in the production of EDHF(s) in this tissue Fleming et al, 2001;Busse et al, 2002), it is not clear whether the vasoactive metabolite is an epoxyeicosatrienoic acid or some oxygen free radical, which could, in turn, lead to generation of isoprostanes.…”