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Skeletal muscle blood flow abnormalities in rats with a chronic myocardial infarction: rest and exercise
1Department of Medicine, Pennsylvania State University, Hershey 17033.
Abstract:
The purpose of this study was to determine the regional distribution of blood flow deficit in the skeletal muscle vascular bed of rats with a chronic myocardial infarction (MI) and heart failure (HF). Accordingly, blood flow was determined (via radioactive microspheres) in rats with a small infarction (MI less than 30%) and in rats with a large (MI greater than 30%) infarction, induced by surgically ligating the left main coronary artery, and compared with rats that had received a sham operation. Results demonstrate that blood flow to the hindlimb musculature was significantly (P less than 0.05) less during a given level of treadmill exercise (20% grade and speed of 28 m/min) in the MI groups of rats compared with their sham counterparts. These differences in hindlimb blood flow were the result of blood flow deficits found in the individual muscles of the thigh and leg. Moreover, the blood flow deficits were more pronounced in the MI greater than 30% group of rats compared with the MI less than 30% group. The blood flow deficits found for the MI greater than 30% group of rats were positively correlated with the percentage of fast-twitch oxidative-glycolytic fibers and negatively correlated with the percentage of fast-twitch glycolytic fibers found in the individual muscles. Our study supports the contention that MI rats demonstrate skeletal muscle blood flow abnormalities during exercise. It appears that the degree of blood flow abnormalities produced in rats is dependent on the size of the MI and the amount of left ventricular dysfunction produced in the HF state.
Insights
Rats with chronic myocardial infarction (MI) and heart failure (HF) exhibit reduced skeletal muscle blood flow during exercise. This deficit is more severe with larger infarcts and linked to specific muscle fiber types.
Area of Science:
- Cardiovascular Physiology
- Skeletal Muscle Metabolism
- Heart Failure Pathophysiology
Background:
- Chronic myocardial infarction (MI) often leads to heart failure (HF).
- HF can impair blood flow regulation in peripheral vascular beds.
- Skeletal muscle blood flow abnormalities during exercise are a potential consequence of HF.
Purpose of the Study:
- To investigate the regional distribution of skeletal muscle blood flow deficits in rats with chronic MI and HF.
- To compare blood flow in rats with small (MI < 30%) versus large (MI > 30%) infarctions.
- To correlate blood flow deficits with specific skeletal muscle fiber types.
Main Methods:
- Induction of MI in rats via surgical ligation of the left main coronary artery.
- Determination of regional skeletal muscle blood flow using radioactive microspheres during treadmill exercise.
- Histological analysis to quantify muscle fiber types (fast-twitch oxidative-glycolytic and fast-twitch glycolytic).
Main Results:
- Rats with MI showed significantly reduced hindlimb muscle blood flow during exercise compared to sham-operated controls.
- Blood flow deficits were more pronounced in rats with larger MI (MI > 30%).
- Deficits in the large MI group correlated positively with fast-twitch oxidative-glycolytic fibers and negatively with fast-twitch glycolytic fibers.
Conclusions:
- Myocardial infarction in rats leads to skeletal muscle blood flow abnormalities during exercise.
- The severity of these blood flow abnormalities is dependent on the size of the MI and the degree of left ventricular dysfunction.
- These findings highlight the impact of heart failure on peripheral circulation and muscle function.