PRODUCTION AND PHYSIOLOGICAL ACTIONS OF ANANDAMIDE IN THE VASCULATUREOF THE RAT-KIDNEY

The endogenous cannabinoid receptor agonist anandamide is present in c entral and peripheral tissues. As the kidney contains both the amidase that degrades anandamide and transcripts for anandamide receptors, we characterized the molecular components of the anandamide signaling sy stem and the vascular effects of exogenous anandamide in the kidney. W e show that anandamide is present in kidney homogenates, cultured rena l endothelial cells (EC), and mesangial cells; these cells also contai n anandamide amidase. Reverse-transcriptase PCR shows that EC contain transcripts for cannabinoid type 1 (CB1) receptors, while mesangial ce lls have mRNA for both CB1 and CB2 receptors. EC exhibit specific, hig h-affinity binding of anandamide (K-d = 27.4 nM). Anandamide (1 mu M) vasodilates juxtamedullary afferent arterioles perfused in vitro; the vasodilation can be blocked by nitric oxide (NO) synthase inhibition w ith L-NAME (0.1 mM) or CB1 receptor antagonism with SR 141716A (1 mu M ), but not by indomethacin (10 mu M). Anandamide (10 nM) stimulates CB 1-receptor-mediated NO release from perfused renal arterial segments; a similar effect was seen in EC. Finally, anandamide (1 mu M) produces a NO-mediated inhibition of KCl-stimulated [H-3]norepinephrine releas e from sympathetic nerves on isolated renal arterial segments. Hence, an anandamide signaling system is present in the kidney, where it exer ts significant vasorelaxant and neuromodulatory effects.