Exercise-induced cardioprotection: a role for eNOS uncoupling and NO metabolites

Area of Science:

• Cardiovascular Physiology
• Exercise Science
• Molecular Cardiology

Background:

• Exercise is known to protect the heart against ischemia-reperfusion (IR) injury.
• The role of endothelial nitric oxide synthase (eNOS) activation in exercise-induced cardioprotection is not fully understood.

Purpose of the Study:

• To investigate if eNOS activation modulation during IR contributes to exercise-induced cardioprotection.
• To explore the mechanism linking exercise training, eNOS activity, and myocardial protection against IR injury.

Main Methods:

• Isolated rat hearts from sedentary and exercised rats were subjected to IR using a Langendorff apparatus.
• Nitric oxide synthase (NOS) inhibitors (L-NAME, L-NIO) and tetrahydrobiopterin (BH₄) were used to modulate eNOS activity.
• Measurements included eNOS phosphorylation, eNOS coupling, S-nitrosylated proteins, malondialdehyde, and protein nitrotyrosination.

Main Results:

• Exercise training conferred protection against IR injury, which was abolished by NOS inhibitors, confirming eNOS dependence.
• Exercised hearts showed reduced eNOS phosphorylation and coupling during early reperfusion despite higher baseline levels.
• Despite eNOS uncoupling, exercised hearts exhibited increased S-nitrosylated proteins and reduced oxidative stress markers (malondialdehyde, nitrotyrosination).
• BH₄ treatment, which stabilized eNOS dimers, increased oxidative stress and abolished cardioprotection in exercised hearts.

Conclusions:

• Exercise-induced cardioprotection against IR injury is dependent on eNOS.
• eNOS uncoupling during reperfusion, rather than increased activity, is crucial for this protection.
• This uncoupling, coupled with enhanced antioxidant capacity, limits cytotoxic peroxynitrite formation in exercised hearts.