EFFECTS OF ANANDAMIDE ON CANNABINOID RECEPTORS IN RAT-BRAIN MEMBRANES

Anandamide (arachidonylethanolamide) is a compound recently isolated f rom porcine brain as a putative endogenous ligand at cannabinoid recep tors. The present studies examined the effects of anandamide on cannab inoid receptor binding sites and adenylyl cyclase in rat brain membran es. Receptor binding experiments, conducted at 25 degrees for 90 min, apparently resulted in significant degradation of anandamide, since an andamide (10 mu M) had little effect on [H-3]WIN 55212-2 binding in ce rebellar membranes. Addition of the general serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) protected against this degradatio n, resulting in an IC50 value of 90 nM for anandamide versus [H-3]WIN 55212-2 binding. Anandamide inhibited adenylyl cyclase in cerebellar m embranes in a GTP-dependent manner, exhibiting a maximal inhibition le vel slightly less than that of WIN 55212-2 and CP-55,940, with an IC50 value of 1.9 mu M. The effect of anandamide on adenylyl cyclase was r egion-specific, with maximal inhibition occurring in cerebellum and st riatum. These results suggest that anandamide acts at G-protein-couple d cannabinoid receptors in brain with properties similar to those of e xogenous cannabinoids.