Sepsis increases NOS-2 activity and decreases non-NOS-mediated acetylcholine-induced dilation in rat aorta.
BACKGROUND
Acetylcholine (Ach) is frequently used to assess endothelium-dependent vasodilation during sepsis. However, the effects of sepsis on constitutive nitric oxide synthase activity (NOS-1 and -3) and other non-NOS effects of Ach are unclear.


METHODS
Sepsis was induced in rats by inoculation of an implanted sponge with Escherichia coli and Bacteroides fragilis (10(9) CFU each). Thoracic aortic 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 microM), or PSS + l-N(G)-monomethylarginine (l-NMMA: NOS-1, -2, and -3 inhibitor, 60 microM). Rings were set at 1-g preload and precontracted with phenlyephrine (10(-8) M). Relaxation 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 conditions. NOS 2 inhibition with l-NIL decreased Ach-induced relaxation in controls (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 relaxation to 45% (P < 0.05) in controls and to 30% (P < 0.05) in septic animals.


CONCLUSIONS
Inhibition of NOS-1, -2, and -3 failed to abolish Ach-induced relaxation, suggesting the presence of other Ach-induced vasodilator mechanisms. NOS-2 inhibition reduced Ach-induced relaxation by 20-25% in the normal 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 reduced from 45% in normals to 30% in septic animals. Vascular dysregulation in sepsis is a complex event involving increased NOS-2, decreased NOS-1 + NOS-3, and decreased Ach-induced non-NOS vasodilator mechanisms.
Beach
P K
PK
Department of Surgery, University of Louisville, Louisville, Kentucky 40292, USA.
Spain
D A
DA
Kawabe
T
T
Harris
P D
PD
Garrison
R N
RN
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000201:enzymology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008239:Lysine / Q000031:analogs & derivatives / Q000494:pharmacology; D008297:Male; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D051381:Rats; D017207:Rats, Sprague-Dawley; D018805:Sepsis / Q000378:metabolism*; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology*; D019323:omega-N-Methylarginine / Q000494:pharmacology
D004791:Enzyme Inhibitors; C090663:N(6)-(1-iminoethyl)lysine; D014665:Vasodilator Agents; D019323:omega-N-Methylarginine; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496322:Nos1 protein, rat; C496318:Nos2 protein, rat; C496316:Nos3 protein, rat; D008239:Lysine; D000109:Acetylcholine