COMPARISON BETWEEN THE EFFECTS OF TREATMENT IN-VITRO AND IN-VIVO WITHLIPOPOLYSACCHARIDE ON RESPONSIVENESS OF RAT THORACIC AORTA

Effects of treatment in vivo and in vitro with lipopolysaccharide (LPS ) on the responsiveness of rat thoracic aorta were examined. The endot helium-denuded aortic strips isolated 6 hr after intraperitoneal (i.p. ) administration of LPS (20 mg/kg), which could produce hemodynamic ch anges, relaxed in response to L-arginine. The same amplitude of relaxa tion was produced by L-arginine in the aortic strips incubated with a lower dose of LPS (1 mu g/ml) in vitro for 6 hr. Both relaxing respons es were inhibited by N-G-nitro-L-arginine (L-NOARG). The contractile r esponses to phenylephrine and KCl were reduced by LPS treatment in viv o or in vitro, but the extent of inhibition was greater in vivo than i n vitro. Further, the attenuation of contractile responses was complet ely reversed by L-NOARG in the strips treated in vitro, whereas the re versal by L-NOARG was incomplete in the strips treated with LPS in viv o. Endothelium-dependent relaxation induced by acetylcholine was atten uated by LPS in vivo but not in vitro. These results suggest that the hyporesponsiveness of rat thoracic aorta after treatment in vitro with LPS, which can produce hemodynamic changes, may be related to an enha nced NO production in the smooth muscle cells, while not only the NO p athway but also additional factors may be involved in the vascular hyp oresponsiveness of the sepsis rats. (C) 1994 Wiley-Liss, Inc.