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Sequential increases in capillarization and mitochondrial enzymes in low-frequency-stimulated rabbit muscle
D Skorjanc1, F Jaschinski, G Heine
1Faculty of Biology, University of Konstanz, Germany.
The American Journal of Physiology
|April 8, 1998
Summary
Chronic low-frequency stimulation increases muscle capillarization and vascular endothelial growth factor (VEGF) mRNA levels. These vascular adaptations occur before significant increases in citrate synthase (CS) activity, indicating enhanced aerobic capacity.
Area of Science:
- Exercise physiology
- Muscle biology
- Vascular adaptation
Background:
- Skeletal muscle adaptation to exercise involves changes in capillarization and metabolic enzymes.
- Understanding the temporal relationship between these adaptations is crucial for optimizing training protocols.
Purpose of the Study:
- To investigate the time course of changes in muscle capillarization and mitochondrial enzyme activity in response to chronic low-frequency stimulation.
- To examine the role of vascular endothelial growth factor (VEGF) in mediating these adaptations.
Main Methods:
- Rabbit tibialis anterior muscles were subjected to chronic low-frequency stimulation for up to 50 days.
- Measurements included capillary density (CD), capillary-to-fiber ratio (C/F), intercapillary distance (ICD), mean capillary area (MCA), VEGF mRNA levels, and citrate synthase (CS) activity.
Main Results:
- Significant increases in CD and C/F, with decreases in ICD and MCA, were observed within 2 days, stabilizing by 14 days.
- VEGF mRNA showed a bimodal increase, with elevations at 1 day and 6-8 days.
- Citrate synthase activity increased after 8 days, suggesting a delayed enhancement of aerobic capacity.
Conclusions:
- Increased muscle contractile activity induces rapid capillarization, preceding increases in aerobic-oxidative potential.
- VEGF plays a role in mediating exercise-induced vascular adaptations in skeletal muscle.