Angiotensin II-mediated hypertension in the rat increases vascular superoxide production via membrane NADH/NADPH oxidase activation. Contribution to alterations of vasomotor tone.
Objective: To test the hypothesis that angiotensin II-induced hypertension is associated with increased vascular superoxide production and to characterize the oxidase involved, and to demonstrate the role of angiotensin type-1 receptor in these processes using Losartan co-administration
Materials & Equipment Checklist
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Equipment3
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View Abstract
We tested the hypothesis that angiotensin II-induced hypertension is associated with an increase in vascular .O2- production, and characterized the oxidase involved in this process. Infusion of angiotensin II (0.7 mg/kg per d) increased systolic blood pressure and doubled vascular .O2- production (assessed by lucigenin chemiluminescence), predominantly from the vascular media. NE infusion (2.75 mg/kg per d) produced a similar degree of hypertension, but did not increase vascular .O2- production. Studies using various enzyme inhibitors and vascular homogenates suggested that the predominant source of .O2- activated by angiotensin II infusion is an NADH/NADPH-dependent, membrane-bound oxidase. Angiotensin II-, but not NE-, induced hypertension was associated with impaired relaxations to acetylcholine, the calcium ionophore A23187, and nitroglycerin. These relaxations were variably corrected by treatment of vessels with liposome-encapsulated superoxide dismutase. When Losartan was administered concomitantly with angiotensin II, vascular .O2- production and relaxations were normalized, demonstrating a role for the angiotensin type-1 receptor in these processes. We conclude that forms of hypertension associated with elevated circulating levels of angiotensin II may have unique vascular effects not shared by other forms of hypertension because they increase vascular smooth muscle .O2- production via NADH/NADPH oxidase activation.
Protocol Steps
1
Angiotensin II infusion
Infuse angiotensin II to induce hypertension and measure resulting vascular superoxide production
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Note: Dose: 0.7 mg/kg per day. This treatment increased systolic blood pressure and doubled vascular superoxide production
View evidence from paper
“Infusion of angiotensin II (0.7 mg/kg per d) increased systolic blood pressure and doubled vascular .O2- production”
2
Norepinephrine infusion control
Infuse norepinephrine as a control hypertensive agent to compare vascular effects
Not specifiedNot specified
Note: Dose: 2.75 mg/kg per day. Produced similar degree of hypertension but did not increase vascular superoxide production
View evidence from paper
“NE infusion (2.75 mg/kg per d) produced a similar degree of hypertension, but did not increase vascular .O2- production”
3
Measure vascular superoxide production
Assess vascular superoxide production using lucigenin chemiluminescence, with focus on vascular media
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Note: Superoxide production was predominantly from the vascular media
View evidence from paper
“doubled vascular .O2- production (assessed by lucigenin chemiluminescence), predominantly from the vascular media”
4
Enzyme inhibitor studies
Use various enzyme inhibitors and vascular homogenates to characterize the oxidase source
Not specifiedNot specified
Note: Studies identified the predominant source as an NADH/NADPH-dependent, membrane-bound oxidase
View evidence from paper
“Studies using various enzyme inhibitors and vascular homogenates suggested that the predominant source of .O2- activated by angiotensin II infusion is an NADH/NADPH-dependent, membrane-bound oxidase”
5
Assess vascular relaxation responses
Test vascular relaxations to acetylcholine, calcium ionophore A23187, and nitroglycerin
Not specifiedNot specified
Note: Angiotensin II-induced hypertension was associated with impaired relaxations to these agents, while NE-induced hypertension was not
View evidence from paper
“Angiotensin II-, but not NE-, induced hypertension was associated with impaired relaxations to acetylcholine, the calcium ionophore A23187, and nitroglycerin”
6
Superoxide dismutase treatment
Treat vessels with liposome-encapsulated superoxide dismutase to assess correction of impaired relaxations
Not specifiedNot specified
Note: Relaxations were variably corrected by this treatment, supporting superoxide involvement
View evidence from paper
“These relaxations were variably corrected by treatment of vessels with liposome-encapsulated superoxide dismutase”
7
Losartan co-infusion study
Administer Losartan concomitantly with angiotensin II to determine angiotensin type-1 receptor involvement
Not specifiedNot specified
Note: Losartan co-administration normalized both vascular superoxide production and relaxations
View evidence from paper
“When Losartan was administered concomitantly with angiotensin II, vascular .O2- production and relaxations were normalized, demonstrating a role for the angiotensin type-1 receptor”