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Traumatic brain injury disrupts cerebrovascular tone through endothelial inducible nitric oxide synthase expression and nitric oxide gain of function.

Villalba N, Sonkusare SK, Longden TA, Tran TL, Sackheim AM, Nelson MT, Wellman GC, Freeman K - J Am Heart Assoc (2014)

Bottom Line: Our objective was to elucidate the mechanism of decreased cerebral artery tone after TBI.Expression of the inducible isoform of NO synthase was upregulated in cerebral arteries isolated from animals with TBI, and the inducible isoform of NO synthase inhibitor 1400W restored myogenic responses following TBI.The mechanism of profound cerebral artery vasodilation after TBI is a gain of function in vascular NO production by 60‐fold over controls, resulting from upregulation of the inducible isoform of NO synthase in the endothelium.

View Article: PubMed Central - PubMed

Affiliation: From the Departments of Pharmacology, University of Vermont, Burlington, VT

ABSTRACT

Background: Traumatic brain injury (TBI) has been reported to increase the concentration of nitric oxide (NO) in the brain and can lead to loss of cerebrovascular tone; however, the sources, amounts, and consequences of excess NO on the cerebral vasculature are unknown. Our objective was to elucidate the mechanism of decreased cerebral artery tone after TBI.

Methods and results: Cerebral arteries were isolated from rats 24 hours after moderate fluid‐percussion TBI. Pressure‐induced increases in vasoconstriction (myogenic tone) and smooth muscle Ca2+ were severely blunted in cerebral arteries after TBI. However, myogenic tone and smooth muscle Ca2+ were restored by inhibition of NO synthesis or endothelium removal, suggesting that TBI increased endothelial NO levels. Live native cell NO, indexed by 4,5‐diaminofluorescein (DAF‐2 DA) fluorescence, was increased in endothelium and smooth muscle of cerebral arteries after TBI. Clamped concentrations of 20 to 30 nmol/L NO were required to simulate the loss of myogenic tone and increased (DAF‐2T) fluorescence observed following TBI. In comparison, basal NO in control arteries was estimated as 0.4 nmol/L. Consistent with TBI causing enhanced NO‐mediated vasodilation, inhibitors of guanylyl cyclase, protein kinase G, and large‐conductance Ca2+‐activated potassium (BK) channel restored function of arteries from animals with TBI. Expression of the inducible isoform of NO synthase was upregulated in cerebral arteries isolated from animals with TBI, and the inducible isoform of NO synthase inhibitor 1400W restored myogenic responses following TBI.

Conclusions: The mechanism of profound cerebral artery vasodilation after TBI is a gain of function in vascular NO production by 60‐fold over controls, resulting from upregulation of the inducible isoform of NO synthase in the endothelium.

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Sensitivity of vascular smooth muscle to exogenous nitric oxide in cerebral arteries from control and TBI animals. Summary data showing the vasodilatory response to addition of spermine NONOate in the presence of (A) l‐NNA (100 μmol/L) and (B) paxilline (1 μmol/L) in arteries from control (n=3) and TBI (n=4) animals. Repeated‐measures one‐way ANOVA, *P<0.05. TBI indicates traumatic brain injury.
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fig08: Sensitivity of vascular smooth muscle to exogenous nitric oxide in cerebral arteries from control and TBI animals. Summary data showing the vasodilatory response to addition of spermine NONOate in the presence of (A) l‐NNA (100 μmol/L) and (B) paxilline (1 μmol/L) in arteries from control (n=3) and TBI (n=4) animals. Repeated‐measures one‐way ANOVA, *P<0.05. TBI indicates traumatic brain injury.

Mentions: The data presented indicate that TBI leads to a gain of function of endothelial NO production to cause a profound loss of pressure‐induced vasoconstriction. To determine the NOS isoenzymes that contribute to increased NO following TBI, expression of eNOS, iNOS, and nNOS was assessed by qPCR (Figure 7A). iNOS was significantly increased (≈10‐fold) in cerebral arteries from TBI animals compared with control animals. Interestingly, eNOS was unchanged, and nNOS was modestly but significantly decreased in arteries after TBI. To examine the functional impact of TBI‐induced iNOS upregulation, pressurized arteries were exposed to the selective iNOS inhibitor 1400W.45–47 Nonselective NOS inhibition with l‐NNA caused constrictions in control arteries (15±2% n=5) but caused substantially greater constrictions in TBI arteries (32±4%, n=5; P<0.05) (Figure 7B and 7C). Inhibition of iNOS caused only a slight constriction in cerebral arteries from control animals; in contrast, cerebral arteries from TBI animals exhibited a marked constriction in response to iNOS inhibition (26±3%, n=4) (Figure 7B and 7D). The specific nNOS inhibitor AAAN48 (30 μmol/L) did not alter tone in arteries from either control or TBI animals (Figure 7B). Furthermore, arteries from control and TBI animals responded similarly to an NO donor in the presence of l‐NNA (100 μmol/L) (Figure 8A), demonstrating that NO sensitivity of vascular SM was unaltered by TBI. These data support the idea that, although basal eNOS‐catalyzed NO production contributes to diameter regulation in arteries from control animals, endothelial iNOS upregulation underlies the NO gain of function and profound vasodilation observed in cerebral arteries after TBI.


Traumatic brain injury disrupts cerebrovascular tone through endothelial inducible nitric oxide synthase expression and nitric oxide gain of function.

Villalba N, Sonkusare SK, Longden TA, Tran TL, Sackheim AM, Nelson MT, Wellman GC, Freeman K - J Am Heart Assoc (2014)

Sensitivity of vascular smooth muscle to exogenous nitric oxide in cerebral arteries from control and TBI animals. Summary data showing the vasodilatory response to addition of spermine NONOate in the presence of (A) l‐NNA (100 μmol/L) and (B) paxilline (1 μmol/L) in arteries from control (n=3) and TBI (n=4) animals. Repeated‐measures one‐way ANOVA, *P<0.05. TBI indicates traumatic brain injury.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4338739&req=5

fig08: Sensitivity of vascular smooth muscle to exogenous nitric oxide in cerebral arteries from control and TBI animals. Summary data showing the vasodilatory response to addition of spermine NONOate in the presence of (A) l‐NNA (100 μmol/L) and (B) paxilline (1 μmol/L) in arteries from control (n=3) and TBI (n=4) animals. Repeated‐measures one‐way ANOVA, *P<0.05. TBI indicates traumatic brain injury.
Mentions: The data presented indicate that TBI leads to a gain of function of endothelial NO production to cause a profound loss of pressure‐induced vasoconstriction. To determine the NOS isoenzymes that contribute to increased NO following TBI, expression of eNOS, iNOS, and nNOS was assessed by qPCR (Figure 7A). iNOS was significantly increased (≈10‐fold) in cerebral arteries from TBI animals compared with control animals. Interestingly, eNOS was unchanged, and nNOS was modestly but significantly decreased in arteries after TBI. To examine the functional impact of TBI‐induced iNOS upregulation, pressurized arteries were exposed to the selective iNOS inhibitor 1400W.45–47 Nonselective NOS inhibition with l‐NNA caused constrictions in control arteries (15±2% n=5) but caused substantially greater constrictions in TBI arteries (32±4%, n=5; P<0.05) (Figure 7B and 7C). Inhibition of iNOS caused only a slight constriction in cerebral arteries from control animals; in contrast, cerebral arteries from TBI animals exhibited a marked constriction in response to iNOS inhibition (26±3%, n=4) (Figure 7B and 7D). The specific nNOS inhibitor AAAN48 (30 μmol/L) did not alter tone in arteries from either control or TBI animals (Figure 7B). Furthermore, arteries from control and TBI animals responded similarly to an NO donor in the presence of l‐NNA (100 μmol/L) (Figure 8A), demonstrating that NO sensitivity of vascular SM was unaltered by TBI. These data support the idea that, although basal eNOS‐catalyzed NO production contributes to diameter regulation in arteries from control animals, endothelial iNOS upregulation underlies the NO gain of function and profound vasodilation observed in cerebral arteries after TBI.

Bottom Line: Our objective was to elucidate the mechanism of decreased cerebral artery tone after TBI.Expression of the inducible isoform of NO synthase was upregulated in cerebral arteries isolated from animals with TBI, and the inducible isoform of NO synthase inhibitor 1400W restored myogenic responses following TBI.The mechanism of profound cerebral artery vasodilation after TBI is a gain of function in vascular NO production by 60‐fold over controls, resulting from upregulation of the inducible isoform of NO synthase in the endothelium.

View Article: PubMed Central - PubMed

Affiliation: From the Departments of Pharmacology, University of Vermont, Burlington, VT

ABSTRACT

Background: Traumatic brain injury (TBI) has been reported to increase the concentration of nitric oxide (NO) in the brain and can lead to loss of cerebrovascular tone; however, the sources, amounts, and consequences of excess NO on the cerebral vasculature are unknown. Our objective was to elucidate the mechanism of decreased cerebral artery tone after TBI.

Methods and results: Cerebral arteries were isolated from rats 24 hours after moderate fluid‐percussion TBI. Pressure‐induced increases in vasoconstriction (myogenic tone) and smooth muscle Ca2+ were severely blunted in cerebral arteries after TBI. However, myogenic tone and smooth muscle Ca2+ were restored by inhibition of NO synthesis or endothelium removal, suggesting that TBI increased endothelial NO levels. Live native cell NO, indexed by 4,5‐diaminofluorescein (DAF‐2 DA) fluorescence, was increased in endothelium and smooth muscle of cerebral arteries after TBI. Clamped concentrations of 20 to 30 nmol/L NO were required to simulate the loss of myogenic tone and increased (DAF‐2T) fluorescence observed following TBI. In comparison, basal NO in control arteries was estimated as 0.4 nmol/L. Consistent with TBI causing enhanced NO‐mediated vasodilation, inhibitors of guanylyl cyclase, protein kinase G, and large‐conductance Ca2+‐activated potassium (BK) channel restored function of arteries from animals with TBI. Expression of the inducible isoform of NO synthase was upregulated in cerebral arteries isolated from animals with TBI, and the inducible isoform of NO synthase inhibitor 1400W restored myogenic responses following TBI.

Conclusions: The mechanism of profound cerebral artery vasodilation after TBI is a gain of function in vascular NO production by 60‐fold over controls, resulting from upregulation of the inducible isoform of NO synthase in the endothelium.

Show MeSH
Related in: MedlinePlus