Nitric oxide-dependent and -independent inhibition by lipopolysaccharide of phosphoinositide hydrolysis in vascular smooth muscle

The present study was designed in order to clarify the mechanisms of dimini shed phosphoinositide (PI) hydrolysis by lipopolysaccharide (LPS) in blood vessels. In vitro pretreatment of rat aortic strips with LPS (1 mug/ml) for 10 or 24 hrs inhibited 5-hydroxytryptamine (5-HT, 100 muM)-induced inosito l monophosphate accumulation in a time-dependent manner. Coincubation of th e aortas with NO-monomethyl-L-arginine (LNMMA, 1 mM) completely prevented t he early diminution of 5-HT-stimulated PI hydrolysis after 10-hr exposure t o LPS but did not affect the delayed diminution after 24-hr exposure. Coinc ubation with cycloheximide (1 muM) did not prevent the delayed LPS-induced diminution of phosphoinositide hydrolysis. Tetraethylammonium (10 mM) did n ot restore the diminished phosphoinositide hydrolysis after 24-hr exposure to LPS, suggesting that the diminution is not due to K+ channel activation. Sodium fluoride (10 mM)-induced inositol monophosphate accumulation was al so decreased in the aortic strips after LPS incubation for 24 hrs, and this decrease was not prevented by coincubation with LNMMA. LPS incubation time -dependently increased nitric oxide (NO) production in the aortas, which wa s completely inhibited by LNMMA or cycloheximide. These results suggest tha t NO is mainly involved in the inhibitory action of LPS on stimulated-PI hy drolysis in the early stage, while in the later stage, a factor(s) besides NO causes attenuation of the stimulated-PI hydrolysis. (C) 2001 Elsevier Sc ience Inc. All rights reserved.