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cGMP is decreased after acute ischemia in chronically ischemic canine limbs
M T Eginton1, B W Mays, H Kelley
1Department of Vascular Surgery, Medical College of Wisconsin, and the, Milwaukee, Wisconsin.
Insights
Chronic partial ischemia in dogs blunted the expected increase in cyclic guanosine monophosphate (cGMP) levels during acute ischemia and reperfusion. This suggests nitric oxide activity may be altered, independent of endothelial or inducible nitric oxide synthase (eNOS/iNOS) expression changes.
Area of Science:
- Vascular Biology
- Skeletal Muscle Physiology
- Ischemia-Reperfusion Injury
Background:
- Chronic partial ischemia may alter skeletal muscle responses to acute ischemia and free radical formation.
- Understanding these alterations is crucial for managing conditions involving compromised blood flow.
Purpose of the Study:
- To investigate the impact of chronic partial ischemia on skeletal muscle's response to acute ischemia and reperfusion.
- To examine changes in cyclic guanosine monophosphate (cGMP) and nitric oxide synthase (NOS) expression.
Main Methods:
- A chronic ischemic state was induced in dogs by ligating the femoral artery.
- After 8 weeks, acute ischemia and reperfusion were applied to the hindlimb.
- Plasma cGMP levels and skeletal muscle eNOS/iNOS expression were analyzed and compared to controls.
Main Results:
- Dogs with chronic ischemia showed no significant increase in cGMP during acute ischemia or reperfusion.
- Control dogs exhibited elevated cGMP levels during ischemia and reperfusion.
- Expression levels of eNOS and iNOS were similar between chronic ischemia and control groups.
Conclusions:
- Chronic partial ischemia in this model did not alter eNOS or iNOS protein levels.
- The lack of cGMP increase suggests nitric oxide activity is attenuated or altered by chronic ischemia.
- cGMP levels, reflecting nitric oxide activity, may not increase in response to acute ischemia in a chronically compromised state.
Background:
A chronic partially ischemic state may alter the skeletal muscle response to acute ischemia and free radical formation.
Methods:
In order to investigate this hypothesis, a chronic ischemic state was established by ligating the right femoral artery of four mongrel dogs. ABIs were decreased from 1.05 +/- 0.25 preligation to 0.54 +/- 0.14 at 6 weeks (P = 0.04). At the end of 8 weeks, the hindlimb was subjected to 3 h of acute ischemia by clamping the iliac artery. The clamp was then released for 2 h of reperfusion. Plasma samples from the right iliac vein were taken during the ischemia-reperfusion period for analysis of cGMP. Tibialis anterior biopsies for Western analysis of eNOS and iNOS were taken upon completion of reperfusion. Comparisons to control dogs subjected to the acute ischemia and reperfusion without prior femoral artery ligation were made.
Results:
cGMP levels were increased in the controls at 3 h of ischemia (3539 +/- 350) and 2 h of reperfusion (2880 +/- 269). The chronic ischemia group did not develop a corresponding increase in cGMP at 3 h of ischemia (2762 +/- 251) or after 2 h of reperfusion (2102 +/- 130). Western analysis of eNOS and iNOS revealed similar levels in both groups. Analysis of eNOS revealed 0.6429 +/- 0.086 and 0.5916 +/- 0.072 (densitometric units +/- SEM) for study and control dogs, respectively. Analysis of iNOS revealed 0.3401 +/- 0.067 and 0.2475 +/- 0.066 for study and control dogs, respectively.
Conclusion:
Previous ligation of the femoral artery resulting in chronic partial ischemia in this model demonstrated no increase in cGMP following acute ischemia that was not accompanied by a change in eNOS or iNOS levels. Nitric oxide activity is reflected by cGMP levels, which may increase in response to free radicals in the acute setting of complete ischemia.