In vitro vascular effects of Cannabidiol (CBD) in the rat isolated aorta

Saoirse O’Sullivan
University of Nottingham, Nottingham, United Kingdom

Cannabidiol (CBD) is another major component of Cannabis sativa that lacks the psychotropic effects of Δ9-tetrahydrocannabinol (THC). CBD is anti-inflammatory, anti-oxidant, neuroprotective and beneficial in diabetes (see Pertwee, 2007 for a recent review). However, the receptor sites of action for CBD remain largely unknown due to its low affinity for cannabinoid receptors. We have shown that THC causes time-dependent vasorelaxation of the rat isolated aorta, sensitive to peroxisome proliferator-activated receptor gamma (PPARγ) antagonism (O’Sullivan et al., 2005). The aim of the present study was to establish whether CBD activates PPARγ and whether similar vascular responses are observed.

Male Wistar rats (200-300 g) were killed by cervical dislocation. The thoracic aorta was isolated, cut into 3-5 mm lengths and mounted on a Mulvany-Halpern myograph. Vessels were bathed in oxygenated Krebs’ solution at 37°C and set to a baseline tension of 10 mN. U46619 and methoxamine were added to increase tone by at least 10 mN. When stable contraction was maintained, the vasorelaxant effect of a single dose of CBD (10 μM) or vehicle control (0.1% ethanol) on induced tone was assessed.

CBD (10 μM) caused significant relaxation of the rat aorta compared to vehicle-treated aortae at all time-points over 2 h (2 h, vehicle 20 ± 2 cf CBD 70 ± 4 % relaxation, mean ± SEM, n=13, P<0.001, Student’s t test). After 2 h, the residual relaxation (the vasorelaxant effect of CBD minus the vasorelaxant effect of vehicle and time) was 50 ± 3 % relaxation. In the presence of the PPARγ receptor antagonist GW9662 (1 μM), the residual vasorelaxant effect of CBD was reduced (2 h & GW9662, 33.0 ± 6.1 % relaxation, P<0.05, ANOVA). The vasorelaxant effect of CBD was not affected by removing the endothelium, nitric oxide synthase inhibition, PTX pre-treatment (200 ng ml-1, 2 h), capsaicin pre-treatment (10 μM, 1 h) or the CB1 receptor antagonist AM251 (1 μM). When arteries were contracted with a high K+ buffer, there was no difference in the vasorelaxant effect of CBD compared with control. By contrast, when tone was induced with U46619 in Ca2+-free Krebs-Hensleit solution, the vasorelaxant effect of CBD was blunted (2 h, 9.3 ± 2.5 % relaxation, P<0.01). The contractile response to the re-introduction of Ca2+ in Ca2+-free, high K+ buffer was also reduced in a concentration-dependent manner in the presence of CBD (Rmax vehicle 2.49 ± 0.06 g tension; & 1 μM CBD 2.10 ± 0.13, P<0.05; & 10 μM CBD 1.86 ± 0.11, P<0.01; & 30 μM CBD 1.38 ± 0.11, P<0.01).

The results of the present study demonstrate that CBD causes significant vasorelaxation overtime in the rat isolated aorta. In common with THC, this response could be partially inhibited by a PPARγ antagonist, however, the majority of the vasorelaxant effects of CBD appear to be through calcium channel inhibition.

Pertwee (2007) Br J Pharmacol. [IN PRESS]
O’Sullivan et al. (2005) Biochem Biophys Res Commun. 337:824-31.