Cardiac Vagal Nerve Activity Increases During Exercise to Enhance Coronary Blood Flow

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Regulation
• Exercise Physiology

Background:

• The role of vagal nerve activity during exercise has been debated, with 'complete vagal withdrawal' being a common assumption.
• Recent research challenges this notion, suggesting a more complex interaction between the vagal system and cardiac function during physical activity.

Purpose of the Study:

• To investigate the hypothesis that cardiac vagal activity increases during exercise.
• To determine the neurotransmitters involved in maintaining cardiac function and coronary blood flow during exercise, beyond acetylcholine.

Main Methods:

• Chronic direct recordings of cardiac vagal nerve activity, cardiac output, coronary artery blood flow, and heart rate in conscious sheep during treadmill exercise.
• Pharmacological blockade of acetylcholine and vasoactive intestinal peptide (VIP), alongside vagal branch denervation, to assess their roles.

Main Results:

• Directly recorded cardiac vagal nerve activity increased significantly during exercise.
• Left cardiac vagal branch denervation attenuated exercise-induced increases in coronary artery blood flow, cardiac output, and heart rate.
• VIP antagonism, but not acetylcholine blockade, significantly reduced coronary artery blood flow during exercise, similar to vagal denervation.

Conclusions:

• Cardiac vagal nerve activity increases during exercise and is essential for maintaining cardiac function.
• Vasoactive intestinal peptide (VIP) is identified as the primary mediator for dynamic modulation of coronary artery blood flow during exercise.