Modulation of peristalsis by cannabinoid CB1 ligands in the isolated guinea-pig ileum

1 The effect of cannabinoid drugs on peristalsis in the guinea-pig ileum was studied. Peristalsis was induced by delivering fluid into the oral end of an isolated intestinal segment. Longitudinal muscle reflex contraction, threshold pressure and threshold volume to trigger peristalsis, compliance of the intestinal wall during the preparatory phase (a reflection of the resistance of the wall to distension) and maximal ejection pressure during the emptying phase of peristalsis were measured. 2 The cannabinoid agonists WIN 55,212-2 (0.3-300 nM) and CP55,940 (0.3-300 nM) significantly decreased longitudinal muscle reflex contraction, compliance and maximal ejection pressure, while increased threshold pressure and volume to elicit peristalsis. These effects were net: modified by the opioid antagonist naloxone (1 mu M) and by the alpha-adrenoceptor antagonist phentolamine (1 mu M). 3 The inhibitory effect of both WIN 55,212-2 and CP55,940 on intestinal peristalsis was antagonized by the cannabinoid CB1 receptor antagonist SR141716A (0.1 mu M), but not by the cannabinoid CB2 receptor antagonist SR144528 (0.1 mu M). 4 In absence of other drugs, the CB1 receptor antagonists SR141716A (0.01-1 mu M) and AM281 (0.01-1 mu M) slightly (approximatively 20%) but significantly increased maximal ejection pressure during the empty phase of peristalsis without modifying longitudinal muscle reflex contraction, threshold pressure, threshold volume to trigger peristalsis and compliance. 5 It is concluded that activation of CB1 receptors reduces peristalsis efficiency in the isolated guinea-pig, and that the emptying phase of peristalsis could be tonically inhibited by the endogenous cannabinoid system.