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1 Department of Surgery, University of Colorado Health Sciences Center and The Veterans Affairs Hospital, Denver 80262; 3 Department of Pediatric Surgery, The Children's Hospital, Denver, Colorado 80218; and 2 Department of Surgery, Northwestern University, Chicago, Illinois 60611
Inducible nitric oxide synthase (iNOS)
is associated with vascular hypocontractility in systemic vessels after
endotoxin lipopolysaccharide (LPS) administration. Although lung iNOS
is increased after LPS, its role in the pulmonary circulation is
unclear. We hypothesized that whereas iNOS upregulation is responsible
for LPS-induced vascular dysfunction in systemic vessels, iNOS does not
play a significant role in the pulmonary artery (PA). Using isolated aorta (AO) and PA rings, we examined the effect of nonselective NOS
inhibition
[NG-monomethyl-L-arginine
(L-NMMA); 100 µmol/l] and selective iNOS inhibition
(aminoguanidine, AG; 100 µmol/l) on
1-adrenergic-mediated vasoconstriction (phenylephrine;
10
9 to
10
3 M) after LPS (Salmonella
typhimurium, 20 mg/kg ip). We also determined the presence of iNOS
using Western blot and immunohistochemistry. LPS markedly impaired AO
contractility (maximal control tension 1,076 ± 33 mg vs. LPS 412 ± 39 mg, P < 0.05), but PA contractility was unchanged (control
466 ± 29 mg vs. LPS 455 ± 27 mg, P > 0.05). Selective iNOS inhibition restored the AO's response to
vasoconstriction (LPS + AG 1,135 ± 54 mg, P > 0.05 vs.
control and P < 0.05 vs. LPS), but had no effect on the PA
(LPS + AG 422 ± 38 mg, P > 0.05 vs. control and LPS).
Western blot and immunohistochemistry revealed increased iNOS
expression in the AO after LPS, but iNOS was not detected in the PA.
Our results suggest that differential iNOS expression after LPS in
systemic and pulmonary vessels contributes to the phenomenon of
sepsis/endotoxemia-induced systemic hypotension and pulmonary hypertension.
aorta; pulmonary artery; aminoguanidine; NG-monomethyl-L-arginine; Salmonella tymphimurium
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