Cannabidiol selectively inhibits the contraction of rat small resistance arteries: Possible role for CGRP and voltage-gated calcium channels

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Abstract

The pharmacology of cannabidiol, the non-psychoactive major component of Cannabis sativa, is of growing interest as it becomes more widely prescribed. This study aimed to examine the effects of cannabidiol on a wide range of contractile agents in rat small resistance arteries, in comparison with large arteries, and to explore its mechanism of action. The vascular actions of cannabidiol were also contrasted with effects on the contractions of bronchial, urogenital, cardiac and skeletal muscles. Isolated small or large arteries were incubated with cannabidiol (0.3–3 μM) or vehicle and concentration-contraction response curves were completed to various agents, including endothelin-1, arginine vasopressin, methoxamine, 5-HT, α-methyl 5-HT and U46619. In small arteries, the effects of cannabidiol were tested in the presence of antagonists of CB1 or CB2 receptors, calcitonin gene-related peptide (CGRP), nitric oxide synthase, cyclooxygenase, PPARγ or a combination. The role of L-type voltage-operated calcium channels was also assessed. Cannabidiol 1–3 μM significantly inhibited the contraction of small resistance arteries to all tested agents through a combination of mechanisms that include CGRP and L-type calcium channels. However, large arteries were insensitive to cannabidiol. Cannabidiol (10–100 μM) was largely without effect in bronchi, atria and hemidiaphragm, but 100 μM attenuated maximum contractions in vasa deferentia. Cannabidiol's effects in the clinical range (1–3 μM) appear to be specific to small resistance arteries. This high sensitivity of the resistance arterial circulation to cannabidiol may offer a therapeutic opportunity in peripheral vascular disease that excludes off-target sites such as the heart and non-vascular smooth muscle.

Introduction

Cannabidiol, the non-psychoactive major component of Cannabis sativa, is increasingly prescribed for a range of medical applications, including as an anxiolytic, anti-inflammatory, antiemetic, analgesic, antipsychotic and anticonvulsant (Mechoulam et al., 2002). Additionally, in 2018 the USA Food and Drug Administration approved an oral solution of cannabidiol (Epidiolex®, GW Pharmaceuticals) for the treatment of seizures associated with rare forms of childhood epilepsy following a clinical trial in children with Dravet or Lennox-Gastaut syndrome (Devinsky et al., 2017, 2018a). In a dose-ranging safety trial of cannabidiol 5, 10 and 20 mg/kg/day, plasma levels of cannabidiol at day 22 were approximately 110, 220 and 380 ng/ml which equate to concentrations of 0.35, 0.70 and 1.2 μM, respectively (Devinsky et al., 2018b). A similar cannabidiol plasma concentration of 1.4 μM was measured in children with epilepsy after 8 weeks of cannabidiol 25 mg/kg/day (Geffrey et al., 2015). No cardiovascular effects were reported in either study (Devinsky et al., 2018b; Geffrey et al., 2015). In healthy adult volunteers (average body weight 77 kg), cannabidiol 600 mg (7.8 mg/kg) caused a fall in mean arterial pressure (≈5 mmHg) and increased heart rate (+10 beats/min) 2 h after oral dosing (Jadoon et al., 2017).

In studies with isolated arteries such as rat aorta, cannabidiol 10 μM enhanced vasorelaxation to acetylcholine in arteries preincubated with cannabidiol for 2 h (Stanley et al., 2013) and induced time-dependent vasorelaxation of precontracted arteries acutely treated with cannabidiol for 2 h (O'Sullivan et al., 2009). Further, in rat isolated small mesenteric arteries precontracted with phenylephrine, acute cannabidiol administration caused maximum relaxation with a pIC50 of 5.66 ± 0.06 (Baranowska-Kuczko et al., 2020; Offertaler et al., 2003). This full relaxation of small mesenteric resistance arteries has also been reported for anandamide, while the larger superior mesenteric artery only relaxed by 40% (Randall et al., 2004). In human isolated large pulmonary arteries precontracted with U46619, acute cannabidiol 10 μM did not cause relaxation. Further, in the same paper, in rat small mesenteric arteries (250 μm i.d.) pretreatment with cannabidiol 1 μM had no effect on phenylephrine concentration-response curves (Baranowska-Kuczko et al., 2020). The general pharmacological properties of cannabidiol have recently been reviewed (McPartland et al., 2015); its Appendix S2 is a detailed literature review regarding the interaction of cannabidiol with many pharmacological targets.

In the present work, we aimed to quantify the effects of clinically used concentrations of cannabidiol on a wide range of contractile agents in rat small resistance arteries and compared these with larger arteries. We have also explored the mechanism of action of cannabidiol in small resistance arteries. Finally, we compared the vascular action of cannabidiol with the contraction of various non-vascular tissues – bronchial, urogenital, cardiac and skeletal muscles.

Our results show that cannabidiol 1–3 μM (i.e. in the clinical range) significantly inhibited the contraction of small resistance arteries through a combination of mechanisms that include calcitonin gene-related peptide (CGRP) and L-type voltage-operated calcium channels. Interestingly, these effects appear to be specific to small resistance arteries as no large artery or non-vascular tissue appeared to be sensitive to cannabidiol. These findings have implications for targeting the therapeutic effects of cannabidiol.

Section snippets

Materials and methods

The Animal Ethics Committee of the University of Melbourne approved experiments (approval #10246) in accordance with The Australian Code for the care and use of animals for scientific purposes (8th edition, 2013, National Health and Medical Research Council, Canberra). Male Sprague-Dawley rats (10–12 weeks old, Biomedical Animal Facility, Melbourne, Australia) were used in this study and housed in groups of 3–4 in standard cages under constant climatic conditions (21 °C, 12 h light/dark cycle),

Effects of cannabidiol on the contraction of small mesenteric arteries

Cannabidiol 3 μM inhibited the contraction of rat isolated small mesenteric arteries to each of the contractile agents tested (endothelin-1, arginine vasopressin, U46619, methoxamine, 5-HT and α-methyl-5-HT) with marked attenuation of the maximum response (Rmax) to each agent (Fig. 1 and Table 1). With endothelin-1, cannabidiol 3 μM caused a small 2.6-fold rightward shift in the agonist pEC50 (P < 0.05; Fig. 1A) with a 55% decrease in Rmax (P < 0.0001); lower cannabidiol concentrations of

Discussion

Our study has quantified the potent effect of (−)-cannabidiol, at therapeutic concentrations (1–3 μM), in inhibiting the contraction by multiple agents of small resistance arteries, but not large conduit arteries. We also show that non-vascular smooth muscle is generally unaffected by cannabidiol even at 10–100 times the therapeutic plasma level. The sensitivity of the small resistance arteries to cannabidiol involves CGRP and voltage-operated calcium channels.

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