Skeletal muscle microvascular oxygenation dynamics in heart failure: exercise training and nitric oxide-mediated...

Area of Science:

• Cardiovascular Physiology
• Skeletal Muscle Metabolism
• Exercise Science

Background:

• Chronic heart failure (CHF) impairs nitric oxide (NO)-mediated regulation of skeletal muscle oxygenation, leading to faster microvascular oxygenation (PO2mv) kinetics during exercise.
• Exercise training in healthy individuals improves PO2mv kinetics via NO-dependent mechanisms.
• The role of NO in exercise training-induced improvements in muscle oxygenation in CHF remains unclear.

Purpose of the Study:

• To test if exercise training improves contracting muscle microvascular oxygenation in CHF rats.
• To determine if improved NO-mediated function contributes to exercise training-induced benefits in CHF rats.

Main Methods:

• CHF rats were assigned to sedentary or progressive treadmill exercise training groups.
• Microvascular oxygenation (PO2mv) was measured using phosphorescence quenching in the spinotrapezius muscle.
• Experiments were conducted under control, NO donor (SNP), and NO synthase blockade (L-NAME) conditions.

Main Results:

• Exercise-trained CHF rats exhibited improved peak oxygen uptake and muscle citrate synthase activity compared to sedentary rats.
• Exercise training significantly slowed the PO2mv fall during contractions (increased mean response time; MRT) in CHF rats.
• The training-induced improvement in MRT was not abolished by L-NAME, indicating NO-independence.

Conclusions:

• Exercise training improves skeletal muscle microvascular oxygenation (slows PO2mv kinetics) in rats with CHF.
• Improved NO-mediated function is not essential for these training-induced improvements.
• Alternative mechanisms likely contribute to enhanced muscle oxygenation following exercise training in CHF.