PLATELET-DERIVED AND MACROPHAGE-DERIVED ENDOGENOUS CANNABINOIDS ARE INVOLVED IN ENDOTOXIN-INDUCED HYPOTENSION

Macrophages are the primary cellular targets of bacterial lipopolysacc haride (LPS), but the role of macrophage-derived cytokines in LPS-indu ced septic shock is uncertain. Recent evidence indicates that activati on of peripheral CB1 cannabinoid receptors contributes to hemorrhagic hypotension and that macrophage-derived anandamide as well as unidenti fied platelet-derived substances may be contributing factors. Here we demonstrate that rat platelets contain the endogenous cannabinoid 2-ar achidonyl glyceride (2-AG), as identified by reverse phase high-perfor mance liquid chromatography, gas chromatography, and mass spectrometry , and that in vitro exposure of platelets to LPS (200 mu g/ml) markedl y increases 2-AG levels, LPS-stimulated, but not control, macrophages contain anandamide, which is undetectable in either control or LPS-sti mulated platelets. Prolonged hypotension and tachycardia are elicited in urethane-anesthetized rats treated 1) with LPS (15 mg/kg i.v.); 2) with macrophages plus platelets isolated from 3 ml of blood from an LP S-treated donor rat; or 3) with rat macrophages or 4) platelets preinc ubated in vitro with LPS (200 mu g/ml). In all four cases, the hypoten sion but not the tachycardia is prevented by pretreatment of the recip ient rat with the CB1 receptor antagonist SR141716A (3 mg/kg i.v.), wh ich also inhibits the hypotensive response to anandamide or 2-AG, The hypotension elicited by LPS-treated macrophages or platelets remains u nchanged in the absence of sympathetic tone or after blockade of nitri c oxide synthase, These findings indicate that platelets and macrophag es generate different endogenous cannabinoids, and that both 2-AG and anandamide may be paracrine mediators of endotoxin-induced hypotension via activation of vascular CB1 receptors.