Entourage effect of N-palmitoylethanolamide on vasorelaxation to the endocannabinoid, N–arachidonoylethanolamide occurs via TRPV1 receptors

W.-S. Vanessa Ho
School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom

The production of the endocannabinoid, N-arachidonoylethanolamide (anandamide) is often accompanied by larger concentrations of ethanolamides derived from different fatty acids, particularly N-palmitoylethanolamide (PEA). It has been proposed that the congener PEA might potentiate the effects of anandamide (so called “entourage effects”) by acting on fatty acid amide hydrolase (FAAH) or Transient Receptor Potential Vanilloid type 1 (TRPV1) receptors. In the rat small mesenteric artery, degradation by FAAH limits vasorelaxation to anandamide (Ho & Randall, 2007) and anandamide acts partly via activation of TRPV1 receptors (White et al., 2001). Therefore, this study was undertaken to examine the potential entourage effects of PEA on mesenteric relaxation to anandamide. Male Wistar rats (200-300g) were sacrificed by cervical dislocation. The third-order branches of the superior mesenteric artery (2mm long) were mounted in a wire myograph and maintained at 37°C in gassed (95% O2/5% CO2) Krebs-Henseleit solution (Ho & Randall, 2007). Vessels were precontracted with 10μM methoxamine. Relaxations to cumulative addition of anandamide or PEA to precontracted vessels are expressed as mean±s.e.m (n≥4 rats) and analysed by two-way analysis of variance of the whole data set. Inhibitors were incubated with vessels for 60min followed by washing out (capsaicin), 45min (URB597; 3’-carbamoyl biphenyl-3-yl-cyclohexylcarbamate) or 5min (PEA) before determination of a concentration-relaxation curve. P<0.05 was considered statistically significant.

In endothelium-intact vessels, PEA potentiated the relaxation to anandamide (control: pEC50=6.5±0.1; Emax=98±1%; + 10μM PEA: pEC50=6.9±0.2; Emax=97±2%; P<0.01). As reported previously (Ho & Randall, 2007), the FAAH inhibitor URB597 also potentiated anandamide relaxations (control: pEC50=6.4±0.1; Emax=98±1%; + 1μM URB597: pEC50=6.9±0.2; Emax=93±6%; P<0.01). Interestingly, further addition of PEA appeared to cause an additive effect (+ URB597 + PEA: pEC50=7.2±0.2; Emax= 99±1%; P<0.01 vs control or with URB597 alone). Treatment with capsaicin, which desensitizes the TRPV1 receptor system, greatly inhibited anandamide relaxations (control: pEC50=6.6±0.1; Emax=101±1%; + 10μM capsaicin: pEC50=6.9±0.4; Emax=44±15%; P<0.01), and abolished the potentiation effect of PEA (+ capsaicin + PEA: pEC50=6.8±0.3; Emax=45±6%; P<0.01 vs control). PEA itself caused concentration-dependent relaxation, but was much less potent than anandamide (pEC50=5.2±0.1; Emax=76±9%). Relaxation to PEA was slightly potentiated by URB597 (+ 1μM URB597: pEC50=5.7±0.3; Emax=81±5%; P<0.05), and attenuated by capsaicin treatment (control: pEC50=5.3±0.2; Emax=84±6%; + 10μM capsaicin: pEC50=5.2±0.1; Emax=45±10%; P<0.01). In conclusion, PEA enhances vasorelaxant responses to anandamide in the rat small mesenteric artery. These data also suggest that this entourage effect is likely mediated by the TRPV1 receptor system, and not FAAH-mediated degradation of anandamide

Ho WS & Randall MD (2007). Br J Pharmacol 150: 641-651
White R et al. (2001). Br J Pharmacol 134: 921-929



This study was supported by the British Heart Foundation and Anne McLaren Fellowship