The effect of cannabinoids on sensory nerve function of guinea-pig bronchi

Dudášová A, Parsons M & Molleman A. School of Life Sciences, Faculty of Health and Human Sciences, University of Hertfordshire, Hatfield, Hertfordshire, AL10 9AB.

In guinea-pig airways cannabinoids can act on sensory nerves via cannabinoid CB2 receptors (Yoshihara et al., 2004), or vanilloid TRPV1 receptors (Tucker et al., 2001). We have shown that virodhamine (VIR), an endocannabinoid, causes a hyperpolarisation in the human bronchial epithelial cell line (unpublished observation). The present objective was to re-evaluate the role of the CB2 receptor in the inhibition of C-fibers and examine the functional pharmacology of VIR in the isolated guinea-pig bronchial preparation.

Main bronchial rings (4-5 mm) were dissected from Heston guinea-pigs (700-1000 g) of either sex and mounted in organ baths containing Krebs solution with indomethacin (10 μM) for recording of isometric contraction to exogenously applied drugs. Values are expressed as g contractions ±s.e.m. In addition, electrical field stimulation (EFS; 30 sec train, 10 Hz, 1 ms / 50 V pulses every 30 min) was used. In the presence of atropine, propranolol and the neutral endopeptidase inhibitor phosphoramidon (all at 1 μM) this produced non-adrenergic non-cholinergic (NANC) contractions, sensitive to tetrodotoxin (1 μM). Changes in the amplitude of NANC responses to cannabinoids were expressed as a percentage of the amplitude of stable contractions before addition of drugs. Data were evaluated using Student’s unpaired two-tailed t test. All drugs were dissolved in absolute ethanol with the exception of WIN55212-3 in which case the vehicle was DMSO.

The non-selective cannabinoid agonist WIN55212-2 (1 μM) significantly inhibited NANC responses by 37.5 % ±4.5 (P≤0.01, n=4). Its inactive isomer, WIN55212-3 (1 μM) failed to alter EFS contractions (n=3). The inhibitory effect of WIN55212-2 (1 μM) was reduced by the CB2-receptor antagonist SR144528 (100 nM) to 13.6 % ±4.6 (P≤0.05, n=6). In the presence of the CB1-receptor antagonist, SR141716A, WIN55212-2 (1 μM) produced 26.0 % ±3.4 inhibition (n=4), not significantly different from the control response induced by WIN55212-2 (1 μM) alone. VIR 1 μM and 10 μM (n=2 for both) had no effect on NANC contractions. In contrast, VIR (1-100 μM) produced concentration-dependent contractions of guinea-pig isolated bronchi with a maximum of 0.30 g ±0.06 (n=6) at 100 μM. The vehicle for VIR (absolute ethanol, 1.1 %) produced a small contraction (0.07 g ±0.04, n=5). The TRPV1 antagonist, capsazepine (10 μM), significantly attenuated the contractions induced by VIR (P≤0.05, n=3).TheNK1-receptor antagonist, SR140333 (1 μM) failed to significantly inhibit VIR evoked responses (n=7). In contrast, theNK2-receptor antagonist, SR48968 (100 nM) abolished the contractile responses to VIR (P≤0.01, n=6).

Our data suggest that in guinea-pig bronchi, WIN55212-2 (1 μM) exerts its inhibitory effect on sensory nerves through CB2-like cannabinoid receptors. The excitatory action of VIR is not mediated by CB receptors but involves activation of TRPV1 receptors on tachykinin releasing sensory nerve endings.

Tucker RC et al., (2001) Br J Pharmacol, 132:1127-35
Yoshihara S et al., (2004) Am J Respir Crit Care Med, 170:941-6

We would like to thank Sanofi for the SR compounds used in this study.