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.

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.

Anandamide, WIN 55,212-2, cannabinol (nonselective 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.

We conclude that endocannabinoids acting on myenteric CB₁ receptors tonically inhibit colonic propulsion in mice.