Elevated circulating levels of anandamide after administration of the transport inhibitor, AM404

The biological actions of the endogenous cannabinoid anandamide are termina ted by carrier-mediated transport into neurons and astrocytes, followed by enzymatic hydrolysis. Anandamide transport is inhibited by the compound N-( 4-hydroxyphenyl)arachidonylamide (AM404). AM404 potentiates several respons es elicited by administration of exogenous anandamide, suggesting that it m ay also protect endogenous anandamide from inactivation. To test this hypot hesis, we studied the effects of AM404 on the plasma levels of anandamide u sing high-performance liquid chromatography/mass spectrometry (HPLC/MS). Sy stemic administration of AM404 (10 mg kg(-1) intraperitoneal, i.p.) caused a gradual increase of anandamide in rat plasma, which was significantly dif ferent from untreated controls at 60 and 120 min after drug injection. In p lasma, both AM404 and anandamide were associated with a plasma protein, whi ch we identified as albumin by non-denaturing polyacrylamide gel electropho resis. AM404 (10 mg kg(-1), i.p.) caused a time-dependent decrease of motor activity, which was reversed by the cannabinoid CB, receptor antagonist N- (piperidin-1-yl)-5-(4-chlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydr ochloride (SR141716A, 0.5 mg kg(-1), i.p). These results are consistent wit h the hypothesis that AM404 inhibits anandamide inactivation in vivo. (C) 2 000 Elsevier Science B.V. All rights reserved.