Control of myogenic tone and agonist induced contraction of intramural coronary resistance arterioles by cannabinoid type 1 receptors and endocannabinoids.

Abstract

It was tested whether intrinsic CB1R activation modifies myogenic and agonist induced contraction of intramural coronary resistance arteries of the rat. CB1R protein was detected by immuno-histochemistry and by Western blot, its mRNA by qRT-PCR in their wall. Microsurgically prepared cylindrical coronary segments ( approximately 100-150mum) developed myogenic contraction ( approximately 20% of relaxed luminal diameter), from which a substantial relaxation ( approximately 15%) in response to WIN55212 (a specific agonist of the CB1Rs) has been found. CB1R-mediated relaxation was blocked by O2050 and AM251 (neutral antagonist and inverse agonist of the CB1R, respectively) and was partially blocked by the NO synthase blocker LNA. CB1R blockade enhanced myogenic tone and augmented AngII-induced vasoconstriction (from 17,8+/-1,2 to 29,1+/-2,9%, p <0,05). Inhibition of diacylglycerol lipase by tetrahydrolipstatin, (inhibitor of endogenous 2-AG production) also augmented coronary vasoconstriction. These observations prove that vascular endocannabinoids are significant negative modulators of the myogenic and agonist-induced tone of intramural coronary arterioles acting through CB1Rs.