STUDY: The effects of Δ9-tetrahydrocannabinol in rat mesenteric vasculature, and its interactions with the endocannabinoid anandamide

ABSTRACT:

1. Δ⁹-tetrahydrocannabinol (THC) produces varying effects in mesenteric arteries: vasorelaxation (third-order branches, G3), modest vasorelaxation (G2), no effect (G1) and vasoconstriction (the superior mesenteric artery, G0).
2. In G3, vasorelaxation to THC was inhibited by pertussis toxin, but was unaffected by the CB₁ receptor antagonist, AM251 (1 μm), incubation with the TRPV1 receptor agonist capsaicin (10 μm, 1 h), the TRPV1 receptor antagonist capsazepine (10 μm) or de-endothelialisation.
3. In G3, vasorelaxation to THC was inhibited by high K⁺buffer, and by the following K⁺ channel inhibitors: charybdotoxin (100 nm), apamin (500 nm) and barium chloride (30 μm), but not by 4-aminopyridine, glibenclamide or tertiapin.
4. In G3, THC (10 and 100 μm) inhibited the contractile response to Ca²⁺ in a Ca²⁺-free, high potassium buffer, indicating that THC blocks Ca²⁺ influx.
5. In G0, the vasoconstrictor responses to THC were inhibited by de-endothelialisation and SR141716A (100 nm), but not by the endothelin (ET_A) receptor antagonist FR139317 (1 μm).
6. THC (1 and 10 μm) antagonised vasorelaxation to anandamide in G3 but not G0. THC did not antagonise the noncannabinoid verapamil, capsaicin or the CB₁ receptor agonist CP55,940. THC (10 and 100 μm) inhibited endothelium-derived relaxing factor (EDHF)-mediated responses to carbachol in a manner similar to the gap junction inhibitor 18α-glycyrrhetinic acid.
7. These data show that THC causes vasorelaxation through activation of K⁺ channels and inhibition of Ca²⁺ channels, and this involves non-CB₁, non-TRPV1 but G-protein-coupled receptors. In G0, THC does not cause relaxation and at high concentrations causes contractions. Importantly, THC antagonises the effects of anandamide, possibly through inhibition of EDHF activity.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1576168/