Ocular activity of topically administered anandamide in the rabbit

Marijuana and its psychoactive constituents, cannabinoids, reduce intraocular pressure (IOP) in humans and animals. Because anandamide, a recently discovered endogenous ligand of cannabinoid receptors, reportedly shows cannabimimetic pharmacological activity, we examined its effect on the eye. Varying amounts of anandamide, in 50 microL of light mineral oil, were topically applied to a rabbit eye and changes in IOP and ocular symptoms were monitored. Anandamide (50 micrograms to 1 mg) induced a significant decrease in IOP within 1 hour after administration; maximum reduction occurred at 2 hours; and there was a return to baseline by 7 hours following administration. A noticeable hyperemia of conjunctival blood vessels was also noted 2 hours after administration. Neither mineral oil alone or with palmitylethanolamide (an analogue of anandamide) caused a significant decrease in IOP or conjunctival hyperemia. This study indicates that anandamide does produce cannabimimetic effect in rabbit eyes.