Vasoconstrictor responsiveness of tail arteries from endotoxaemic rats

Continuous infusion of lipopolysaccharide in conscious rats mimics some aspects of cardiovascular dysfunction in septic shock. In the present study, contractile responsiveness of tail arteries taken from rats infused with lipopolysaccharide was investigated. Contractile responses to alpha,beta-methylene ATP and potassium chloride, but not to methoxamine, were greater after 24 h lipopolysaccharide infusion than in 2-h saline, 24-h saline and 2-h lipopolysaccharide groups. N(G)-nitro-L-arginine methyl ester augmented contractions to alpha,beta-methylene ATP and methoxamine in the 2-h saline, 24-h saline and 2-h lipopolysaccharide groups, but had no significant effect in the 24-h lipopolysaccharide group. Endothelium-independent vasorelaxant responses to sodium nitroprusside were greater in the 24-h lipopolysaccharide group compared to the other three groups. Relaxations to acetylcholine were not significantly different. In vitro incubation in medium containing lipopolysaccharide for 24 h had no significant effect on contractile responses of tail arteries compared to controls incubated in medium alone. These data indicate a possible impaired nitric oxide and/or endothelial function in tail arteries isolated from rats 24 h after lipopolysaccharide infusion. As hypercontractility was not evoked following in vitro incubation with lipopolysaccharide, the involvement of in vivo neurohumoral factors/mechanisms in the pathology of these changes is implicated.