In vitro functional evidence of neuronal cannabinoid CB1 receptors in human ileum

We investigated the effect of the cannabinoid agonist (+)WIN-55212-2 on hum an ileum longitudinal smooth muscle preparations, either electrically stimu lated or contracted by carbachol. Electrical field stimulation mostly activ ated cholinergic neurons, since atropine and tetrodotoxin (TTX), alone or c oincubated, reduced twitch responses to a similar degree (85%). (+)WIN-5521 2-2 concentration-dependently inhibited twitch responses (IC50 73 nM), but had no additive effect with atropine or TTX. The cannabinoid CB1 receptor a ntagonist SR 141716 (pA(2) 8.2), but not the CB2 receptor antagonist, SR 14 4528, competitively antagonized twitch inhibition by (+)WIN-55212-2. Atropi ne but not (+)WIN-55212-2 or TTX prevented carbachol-induced tonic contract ion. These results provide functional evidence of the existence of prejunctional cannabinoid CB1-receptors in the human ileum longitudinal smooth muscle. A gonist activation of these receptors prevents responses to electrical field stimulation, presumably by inhibiting acetylcholine release. SR 141716 is a potent and competitive antagonist of cannabinoid CBI receptors naturally expressed in the human gut.