Sepsis increases NOS-2 activity and decreases non-NOS-mediated acetylcholine-induced dilation in rat aorta

Introduction. Acetylcholine (Ach) is frequently used to assess endothelium- dependent vasodilation during sepsis. However, the effects of sepsis on con stitutive nitric oxide synthase activity (NOS-1 and -3) and other non-NOS e ffects of Ach are unclear. Methods. Sepsis was induced in rats by inoculation of an implanted sponge w ith Escherichia coli and Bacteroides fragilis (10(9) CFU each). Thoracic ao rtic rings (2 mm) were harvested at 24 h from septic (N = 9) and control (N = 9) rats and were suspended in physiological salt solution (PSS), PSS + L -N-6-(1-iminoethyl)lysine (L-NIL: NOS-2 inhibitor, 10 muM), or PSS + L-N-G- monomethylarginine (L-NMMA: NOS-1, -2, and -3 inhibitor, 60 muM). Rings wer e set at 1-g preload and precontracted with phenlyephrine (10(-8) M). Relax ation dose-response curves were generated with six doses of Ach (3 x 10(-8) to 10(-5) M). Results. Sepsis increased the maximal relaxation to Ach under basal conditi ons. NOS 2 inhibition with L-NIL decreased Ach-induced relaxation in contro ls (66% vs 84%, P < 0.05, two-way ANOVA) and more so in septic rats (44% vs 93%, P < 0.05). Total NOS inhibition with L-NMMA decreased Ach-induced rel axation to 45% (P < 0.05) in controls and to 30% (P < 0.05) in septic anima ls. Conclusions. Inhibition of NOS-1, -2, and -3 failed to abolish Ach-induced relaxation, suggesting the presence of other Ach-induced vasodilator mechan isms. NOS-2 inhibition reduced Ach-induced relaxation by 20-25% in the norm al thoracic aorta, but by 50% in septic animals. The remaining Ach-induced non-NOS vasodilation (after inhibition of NOS-1 + NOS-2 + NOS-3) was reduce d from 45% in normals to 30% in septic animals. Vascular dysregulation in s epsis is a complex event involving increased NOS-2, decreased :NOS-1 + NOS- 3, and decreased Ach-induced non-NOS vasodilator mechanisms. (C) 2001 Acade mic Press.