The role of COX and LOX products in mediating the relaxant responses to abnormal cannabidiol and acea in the porcine coronary artery

Nicola Silva1 , Rachel Knott1, Roger G. Pertwee2, Ruth Ross2 & Cherry L. Wainwright1 1School of Pharmacy, The Robert Gordon University, Schoolhill, Aberdeen. 2Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen.

Abnormal cannabidiol (AbCBD) has been reported to induce vasorelaxation via a novel non-CB1 or CB2 receptor (Offertaler et al., 2003), whereas the synthetic cannabinoid ACEA, an analogue of the endocannabinoid anandamide, is thought to act via the CB1 receptor (Sterin-Borda et al., 2005). We have recently reported that these agents induce relaxation of the porcine coronary artery through both the CB 1 and the transient receptor potential vanilloid type 1 (TRPV1) receptor (Silva et al., 2006). ACEA is a substrate for fatty acid amide hydrolase (FAAH) and, like anandamide, may also be susceptible to metabolism by cyclooxygenase 2 (COX-2). These metabolic pathways may be involved in generating the responses to ACEA Furthermore, whilst AbCBD is not metabolised by these enzymes, it is not known whether arachidonic acid metabolites generated through the COX and lipoxygenase (LOX) pathways contribute to the vasodilator responses to these agents. The aim of the present studies was to determine the effects of inhibition of COX-1, COX-2, LOX and FAAH on the vasodilator responses to AbCBD and ACEA.

Porcine hearts were obtained fresh from a local abattoir and the left anterior descending (LAD) coronary artery dissected free, cut into 3mm rings and suspended in 20ml baths (37ºC) containing gassed Krebs solution (95%O2/5%CO2) for measurement of isometric contraction and relaxation. Endothelium-intact rings were pre-contracted with 0.5μM U46619. Relaxations to cumulative additions of either AbCBD (10-9–10-4M) or ACEA (10-9–10-4M) were measured in the absence or presence of the FAAH inhibitors PMSF (1mM) or URB 597 (100nM) to determine the susceptibility of the compounds to hydrolysis. All subsequent experiments were then performed in the presence of URB 597 (100nM), to determine the effects of NS-398 (5µM; COX-2 inhibitor), SC-560 (100nM; COX-1 inhibitor) and NDGA (60µM; LOX inhibitor) on the relaxant responses to AbCBD and ACEA. Data are Emax ± s.e.m. of 6 or more artery rings from different hearts. All drugs were dissolved in ethanol and diluted with distilled water. Statistical analysis employed one-way ANOVA and Tukey’s post-test.

PMSF increased the maximum relaxation to both ACEA (Emax 45.6±8.5% vs 33.1±9.1%; P<0.05) and AbCBD (52.8±7.8% vs 40.5±6.2%; P<0.05), while the selective FAAH inhibitor, URB 597 did not alter the vasodilator responses to either ACEA (Emax 32.4±5.1%; P=ns) or AbCBD (36.4±4.8%;P=ns). In the presence of URB 597, the COX-2 inhibitor NS-398 significantly attenuated the relaxant response to both ACEA (Emax 11.4±3.6%; P<0.05) and AbCBD (Emax 7.9±4.1%; p<0.05), while the COX-1 inhibitor SC-560 significantly enhanced the relaxations to both agonists (Emax 60.2 ± 4.6% and 46.3 ± 3.9% for ACEA and AbCBD respectively; p<0.05). In contrast, the LOX inhibitor NDGA enhanced the response to ACEA (Emax 62.9 ± 5.2%; p<0.05) but not to AbCBD.

These observations suggest that COX-2 metabolites are important mediators of the relaxant response to ACEA and AbCBD. Furthermore, COX-1 and, in the case of ACEA, LOX metabolism serves to inactivate the mediators involved in the response.

Offertaler, L et al. (2003). Mol Pharmacol 63: 699-705.
Silva, N et al. (2006). 16th Annual Symposium on the Cannabinoids, Abs 178.
Sterin-Borda, L et al. (2005). Biochem Pharmacol 69: 1705-1713.