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Selective iNOS inhibition attenuates acetylcholine- and bradykinin-induced vasoconstriction in
L G Fischer1, D J Horstman, K Hahnenkamp
1Department of Anesthesiology, University of Virginia, Health Sciences Center, Charlottesville 22906-0010, USA.
Background:
Nonselective nitric oxide synthase (NOS) inhibition has detrimental effects in sepsis because of inhibition of the physiologically important endothelial NOS (eNOS). The authors hypothesized that selective inducible NOS (iNOS) inhibition would maintain eNOS vasodilation but prevent acetylcholine- and bradykinin-mediated vasoconstriction caused by lipopolysaccharide-induced endothelial dysfunction.
Methods:
Rats were administered intraperitoneal lipopolysaccharide (15 mg/kg) with and without the selective iNOS inhibitors L-N6-(1-iminoethyl)-lysine (L-NIL, 3 mg/kg), dexamethasone (1 mg/kg), or the nonselective NOS inhibitor Nomega-nitro-L-arginine methylester (L-NAME, 5 mg/kg). Six hours later, the lungs were isolated and pulmonary vasoreactivity was assessed with hypoxic vasoconstrictions (3% O2), acetylcholine (1 microg), Biochemical Engineering, and bradykinin (3 microg). In additional lipopolysaccharide experiments, L-NIL (10 microM) or 4-Diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP, 100 microM), a selective muscarinic M3 antagonist, was added into the perfusate.
Results:
Exhaled nitric oxide was higher in the lipopolysaccharide group (37.7+/-17.8 ppb) compared with the control group (0.4+/-0.7 ppb). L-NIL and dexamethasone decreased exhaled nitric oxide in lipopolysaccharide rats by 83 and 79%, respectively, whereas L-NAME had no effect. In control lungs, L-NAME significantly decreased acetylcholine- and bradykinin-induced vasodilation by 75% and increased hypoxic vasoconstrictions, whereas L-NIL and dexamethasone had no effect. In lipopolysaccharide lungs, acetylcholine and bradykinin both transiently increased the pulmonary artery pressure by 8.4+/-2.0 mmHg and 35.3+/-11.7 mmHg, respectively, immediately after vasodilation. L-NIL and dexamethasone both attenuated this vasoconstriction by 70%, whereas L-NAME did not. The acetylcholine vasoconstriction was dose-dependent (0.01-1.0 microg), unaffected by L-NIL added to the perfusate, and abolished by 4-DAMP.
Conclusions:
In isolated perfused lungs, acetylcholine and bradykinin caused vasoconstriction in lipopolysaccharide-treated rats. This vasoconstriction was attenuated by administration of the iNOS inhibitor L-NIL but not with L-NAME. Furthermore, L-NIL administered with lipopolysaccharide preserved endothelium nitric oxide-dependent vasodilation, whereas L-NAME did not.
Insights
Selective inducible nitric oxide synthase (iNOS) inhibition in sepsis preserves vasodilation while preventing vasoconstriction. This approach using L-NIL offers a potential therapeutic strategy for sepsis-induced endothelial dysfunction.
Area of Science:
- Pharmacology
- Physiology
- Biochemistry
Background:
- Nonselective nitric oxide synthase (NOS) inhibition is detrimental in sepsis due to blocking endothelial NOS (eNOS).
- Lipopolysaccharide (LPS) induces endothelial dysfunction, leading to altered vasoreactivity.
- Selective inhibition of inducible NOS (iNOS) is hypothesized to mitigate these effects.
Purpose of the Study:
- To investigate the effects of selective iNOS inhibition on pulmonary vasoreactivity in a rat model of sepsis.
- To determine if selective iNOS inhibition preserves eNOS-dependent vasodilation while preventing vasoconstriction induced by LPS.
- To compare the effects of selective iNOS inhibition with nonselective NOS inhibition.
Main Methods:
- Rats were treated with LPS and either a selective iNOS inhibitor (L-NIL), dexamethasone, or a nonselective NOS inhibitor (L-NAME).
- Pulmonary vasoreactivity was assessed using hypoxic vasoconstriction, acetylcholine, and bradykinin challenges in isolated perfused lungs.
- The role of muscarinic M3 receptors was investigated using 4-DAMP.
Main Results:
- LPS increased exhaled nitric oxide, which was reduced by L-NIL and dexamethasone, but not L-NAME.
- In LPS-treated lungs, acetylcholine and bradykinin induced vasoconstriction, which was attenuated by L-NIL and dexamethasone but not L-NAME.
- L-NIL preserved endothelium nitric oxide-dependent vasodilation in LPS-treated lungs, unlike L-NAME.
Conclusions:
- Selective iNOS inhibition with L-NIL attenuates LPS-induced vasoconstriction in isolated perfused lungs.
- L-NIL preserves eNOS-dependent vasodilation in the context of LPS administration.
- Selective iNOS inhibition represents a promising therapeutic strategy for sepsis-related endothelial dysfunction.