Vasorelaxation to N-oleoylethanolamine in rat isolated arteries: mechanisms of action and modulation via cyclooxygenase activity.

BACKGROUND AND PURPOSE: The endocannabinoid-like molecule N-oleoylethanolamine (OEA) is found in the small intestine and regulates food intake and promotes weight loss. The principal aim of the present study was to evaluate the vascular effects of OEA. EXPERIMENTAL APPROACH: Perfused isolated mesenteric arterial beds were pre-contracted with methoxamine or high potassium buffers and concentration-response curves to OEA were constructed. Combinations of inhibitors to block nitric oxide production, sensory nerve activity, cyclooxygenase activity, potassium channels, chloride channels and gap junctions, and a cannabinoid CB(1) receptor antagonist, were used during these experiments. The effects of OEA on caffeine-induced contractions in calcium-free buffer were also assessed. Isolated thoracic aortic rings were used as a comparison. KEY RESULTS: OEA caused concentration-dependent vasorelaxation in rat isolated mesenteric arterial beds and thoracic aortic rings, with a greater maximal response in mesenteric vessels. This relaxation was sensitive to inhibition of sensory nerve activity and endothelial removal in both preparations. The cyclooxygenase inhibitor indomethacin reversed the effects of capsaicin pre-treatment in perfused mesenteric arterial beds and indomethacin alone enhanced vasorelaxation to OEA. The OEA-induced vasorelaxation was inhibited by a CB(1) receptor antagonist only in aortic rings. In mesenteric arteries, OEA suppressed caffeine-induced contractions in calcium-free buffer. CONCLUSIONS AND IMPLICATIONS: The vasorelaxant effects of OEA are partly dependent on sensory nerve activity and a functional endothelium in the vasculature. In addition, vasorelaxation to OEA is enhanced following cyclooxygenase inhibition. OEA may also interfere with the release of intracellular calcium in arterial preparations.

Cardiovascular effects of cannabinoids in conscious spontaneously hypertensive rats.

BACKGROUND AND PURPOSE: In anaesthetized spontaneously hypertensive rats (SHR), there is evidence for up-regulation of cannabinoid (CB1) receptors: antagonism of CB1 receptors causes a rise in blood pressure, and administration of the endocannabinoid, anandamide, or inhibition of anandamide degradation causes hypotension. These findings have led to the suggestion that the endocannabinoid system may be a therapeutic target in hypertension. However, since the cardiovascular responses to cannabinoids are substantially influenced by anaesthesia, the purpose of this study was to assess regional haemodynamic responses to cannabinoid receptor stimulation and inhibition in conscious SHR. EXPERIMENTAL APPROACH: Cardiovascular responses to i.v. administration of anandamide, the cannabinoid receptor agonist, WIN 55212-2, and the CB(1) receptor antagonist, AM 251, were measured in male SHR, Wistar Kyoto rats and outbred Wistar rats, chronically instrumented for recording renal, mesenteric and hindquarters haemodynamics in the conscious, freely-moving state. KEY RESULTS: Hypotensive responses to anandamide and WIN 55212-2 only occurred in SHR, but these were relatively modest and not associated with CB1 receptor-mediated vasodilatation. In SHR only, anandamide caused bradycardia, which was inhibited by AM 251. Furthermore, a pressor response to CB1 receptor antagonism occurred only in SHR, but was not associated with vasoconstriction. Moreover, there was some evidence for CB1 receptor-mediated vasoconstrictor actions of anandamide in SHR, which was not seen in the normotensive strains. CONCLUSIONS AND IMPLICATIONS: The results are consistent with activation of CB1 receptors in SHR by endogenous ligands exerting an antihypertensive effect, but the findings do not indicate enhanced CB1 receptor-mediated vasodilator mechanisms in SHR.

Effects of chronic nitric oxide synthase inhibition on the cardiovascular responses to cannabinoids in vivo and in vitro.

BACKGROUND AND PURPOSE: Since the vasorelaxant potency of the endocannabinoid anandamide is enhanced in perfused mesenteric vascular beds from rats made hypertensive by chronic inhibition of NO synthase (L-NAME in drinking water), we hypothesized that in vivo, anandamide-induced vasodilatation would be similarly enhanced in L-NAME-treated animals. EXPERIMENTAL APPROACH: Male Sprague-Dawley rats were given L-NAME in drinking water (7.5 mg kg(-1) day(-1)) for 4 weeks. Relaxant effects of anandamide were measured in perfused mesenteric vascular beds and in isolated small mesenteric arteries. Renal, mesenteric and hindquarters haemodynamic responses to anandamide, methanandamide, the synthetic cannabinoid agonist WIN-55212-2 and the cannabinoid receptor antagonist AM251 were assessed in conscious, chronically-instrumented rats. KEY RESULTS: Vasorelaxant responses to anandamide were enhanced in the perfused mesentery but not in isolated mesenteric resistance vessels. In vivo, anandamide caused vasodilatation only in the hindquarters vascular bed and only in control rats. Methanandamide caused a late-onset (40 min after administration) tachycardia, mesenteric and hindquarters vasoconstriction, and renal vasodilatation, which did not differ between control and L-NAME-treated rats. AM251 had no effect on resting blood pressure in control or L-NAME-treated rats and WIN55212-2 caused pressor and renal and mesenteric vasoconstrictor responses, with hindquarters vasodilatation in both groups of animals. CONCLUSIONS AND IMPLICATIONS: The results provide no in vivo evidence for enhanced vasodilator responses to cannabinoids, or up-regulation of endocannabinoids or their receptor activity, following chronic NO synthase inhibition.