Deletion of neuronal NOS prevents impaired vasodilation in septic mouse skeletal muscle.
OBJECTIVE
Sepsis-stimulated nitric oxide (NO) production impairs arteriolar responsiveness in skeletal muscle. Using wild type (WT), eNOS(-/-), iNOS(-/-) and nNOS(-/-) mice, we aimed to determine the key nitric oxide synthase (NOS) isoenzyme(s) responsible for the arteriolar hyporesponsiveness to acetylcholine (ACh) in septic skeletal muscle.


METHODS
Sepsis was induced by the cecal ligation and perforation procedure (24 h model). We measured the post-ACh increase in red blood cell velocity (V(RBC)) in a capillary fed by the stimulated arteriole as an index of vasodilation. NOS activity and protein expression in the muscle were measured by standard procedures.


RESULTS
In all non-septic mice, ACh increased V(RBC) by approximately 150% from baseline. Sepsis impaired this response in WT, eNOS(-/-) and iNOS(-/-) mice, but not in nNOS(-/-) mice. Accordingly, pharmacological inhibition of nNOS with 7-nitroindazole reversed this impairment in WT mice. cNOS (eNOS+nNOS) activity was elevated in septic WT mice; Western blots indicated that this occurred through a post-translational mechanism. iNOS protein activity/expression was negligible. ACh caused dilation via endothelial-derived relaxing factor (EDRF) in WT mice and via endothelial-derived hyperpolarizing factor (EDHF) in eNOS(-/-) mice. Although exogenous NO reduced EDHF-mediated dilation in eNOS(-/-) mice, NOS inhibition did not reverse the sepsis-impaired dilation in these mice.


CONCLUSIONS
In our 24-h mouse model of sepsis, NO in skeletal muscle is primarily derived from nNOS. Sepsis impairs both EDRF- and EDHF-mediated dilation in response to ACh. Both genetic deletion and inhibition of nNOS protect against this impairment when the dilation occurs via the EDRF but not EDHF pathway.
Lidington
Darcy
D
The Centre for Critical Illness Research, Lawson Health Research Institute, London, Canada.
Li
Fuyan
F
Tyml
Karel
K
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001160:Arterioles; D001685:Biological Factors / Q000378:metabolism; D001783:Blood Flow Velocity / Q000187:drug effects; D004730:Endothelium, Vascular / Q000201:enzymology* / Q000276:immunology; D045462:Endothelium-Dependent Relaxing Factors / Q000378:metabolism; D015151:Immunoblotting / Q000379:methods; D051379:Mice; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000276:immunology / Q000503:physiopathology*; D052248:Nitric Oxide Synthase Type I / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D018805:Sepsis / Q000201:enzymology* / Q000276:immunology / Q000503:physiopathology; D014664:Vasodilation / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D001685:Biological Factors; D045462:Endothelium-Dependent Relaxing Factors; D014665:Vasodilator Agents; C067410:endothelium-dependent hyperpolarization factor; C496319:NOS2 protein, human; C496314:NOS3 protein, human; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D000109:Acetylcholine