Activation of CB₁receptors by 2-arachidonoylglycerol attenuates vasoconstriction induced by U46619 and angiotensin II in human and rat pulmonary arteries

Abstract

Recent evidence suggests that endocannabinoids acting via cannabinoid CB receptors may modulate vascular responses of various vasoconstrictors in the rodent systemic vasculature. The aim of the study was to investigate whether endocannabinoids modulate the contractile responses evoked by a thromboxane A analog (U46619), angiotensin II (ANG II), serotonin (5-HT), and phenylephrine, which stimulate distinct G protein-coupled receptors (thromboxane, ANG II type 1, 5-HT, and α-adrenergic receptors) in isolated endothelium-intact human and rat pulmonary arteries (hPAs and rPAs, respectively). The CB receptor antagonist AM251 (1 μM) and diacylglycerol lipase (2-arachidonoylglycerol synthesis enzyme) inhibitor RHC80267 (40 μM) enhanced contractions induced by U46619 in hPAs and rPAs and by ANG II in rPAs in an endothelium-dependent manner. AM251 did not influence vasoconstrictions induced by 5-HT or phenylephrine in rPAs. The monoacylglycerol lipase (2-arachidonoylglycerol degradation enzyme) inhibitor JZL184 (1 μM), but not the fatty acid amide hydrolase (anandamide degradation enzyme) inhibitor URB597 (1 μM), attenuated contractions evoked by U46619 in hPAs and rPAs and ANG II in rPAs. 2-Arachidonoylglycerol concentration-dependently induced relaxation of hPAs, which was inhibited by endothelium denudation or AM251 and enhanced by JZL184. Expression of CB receptors was confirmed in hPAs and rPAs using Western blotting and immunohistochemistry. The present study shows the protective interaction between the endocannabinoid system and vasoconstriction in response to U46619 and ANG II in the human and rat pulmonary circulation. U46619 and ANG II may stimulate rapid endothelial release of endocannabinoids (mainly 2-arachidonoylglycerol), leading to CB receptor-dependent and/or CB receptor-independent vasorelaxation, which in the negative feedback mechanism reduces later agonist-induced vasoconstriction.

Endocannabinoids modulate Gq/11 protein-coupled receptor agonist-induced vasoconstriction via a negative feedback mechanism

“…However, it was observed that eCBs cause vasodilation via mediators released from the endothelium or via activation of endothelial CB 1 receptors, see also Table . These data support the idea that this mechanism occurs, not just in VSMCs, but also in the endothelium . Taking into account the divergent expression of components of the eCB system (see Table ) and the vascular effects of eCBs (connected with their subsequent metabolism to the vasodilatory or/and vasoconstrictor products), the clear interpretation of the results often turns out to be quite problematic.…”

“…The blockade of CB 1 receptors resulted in the enhancement of the Ang II‐induced contraction in rPAs (by AM251), rat uterine artery (by rimonabant), rat and mouse gracilis artery as well as mouse saphenous artery (by O2050). Additionally, in the CB 1 ‐knockout mouse model, the inhibition of CB 1 receptors by O2050 did not enhance the Ang II‐induced vasoconstriction in isolated mouse aortas or saphenous arteries .…”

“…U46619 and Ang II produced much stronger vasoconstriction, in terms of the maximal response values, than either phenylephrine or 5‐HT in isolated rat pulmonary arteries (rPAs) . This suggests that production of eCBs in rPAs is dependent on agonist‐induced contraction force . Nonetheless, further studies in this field are necessary to confirm these assumptions.…”

“…It was shown that CB 1 receptors are expressed in both endothelial cells and VSMCs, for example of the rat aorta . Importantly, the vascular eCBs are produced mainly in the endothelium, and certain vasoconstrictors can induce release of eCBs from the arterial endothelium . However, it was observed that eCBs cause vasodilation via mediators released from the endothelium or via activation of endothelial CB 1 receptors, see also Table .…”

“…Thus, 5‐HT (rat; 10 μ m ) and phenylephrine (canine; 10 μ m ) stimulated smaller increases in the level of [Ca 2+ ] i compared to Ang II (rat, 10 μ m ) and TXA 2 analogue (U46619; rat, 0.1 μ m ). U46619 and Ang II produced much stronger vasoconstriction, in terms of the maximal response values, than either phenylephrine or 5‐HT in isolated rat pulmonary arteries (rPAs) . This suggests that production of eCBs in rPAs is dependent on agonist‐induced contraction force .…”