Endocannabinoids as physiological regulators of colonic propulsion in mice

Background & Aims: Activation of enteric cannabinoid CB₁ receptors inhibits motility in the small intestine; however, it is not known whether endogenous cannabinoids (anandamide and 2-arachidonylglycerol) play a physiologic role in regulating intestinal motility. In the present study, we investigated the possible involvement of endocannabinoids in regulating intestinal propulsion in the mouse colon in vivo. Methods: Intestinal motility was studied measuring the expulsion of a glass bead inserted into the distal colon; endocannabinoid levels were measured by isotope-dilution gas chromatography-mass spectrometry; anandamide amidohydrolase activity was measured by specific enzyme assays. CB₁ receptors were localized by immunohistochemistry. Results: Anandamide, WIN 55, 212-2, cannabinol (non-selective cannabinoid agonists), and ACEA (a selective CB₁ agonist) inhibited colonic propulsion; this effect was counteracted by SR141716A, a CB₁ receptor antagonist. Administered alone, SR141716A increased motility, whereas the inhibitor of anandamide cellular reuptake, VDM11, decreased motility. High amounts of 2-arachidonylglycerol and particularly anandamide were found in the colon, together with a high activity of anandamide amidohydrolase. CB₁ receptor immunoreactivity was colocalized to a subpopulation of choline acetyltransferase-immunoreactive neurons and fiber bundles in the myenteric plexus. Conclusions: We conclude that endocannabinoids acting on myenteric CB₁ receptors tonically inhibit colonic propulsion in mice.