Short-term exercise training enhances functional sympatholysis through a nitric oxide-dependent mechanism

Area of Science:

• Exercise Physiology
• Cardiovascular Regulation
• Nitric Oxide Signaling

Background:

• Sympatholysis, the attenuated vasoconstrictor response to sympathetic nerve stimulation during exercise, is crucial for adequate blood flow to working muscles.
• The precise mechanisms, particularly the role of nitric oxide (NO), underlying exercise-induced sympatholysis remain incompletely understood.
• Investigating the impact of exercise training intensity on sympatholysis is essential for optimizing exercise prescriptions for cardiovascular health.

Purpose of the Study:

• To test the hypothesis that short-term mild- (M) and heavy-intensity (H) exercise training enhance sympatholysis via a nitric oxide (NO)-dependent mechanism.
• To determine the influence of training intensity on the magnitude of sympatholysis during muscle contraction.
• To elucidate the role of NO synthase inhibition in modulating sympatholysis following different exercise training regimens.

Main Methods:

• Sprague-Dawley rats were assigned to sedentary (S), mild-intensity (M), or heavy-intensity (H) exercise training groups for 4 weeks.
• Following training, rats were anesthetized and instrumented to measure arterial blood pressure and femoral artery blood flow.
• The triceps surae muscle was stimulated to contract at 30% and 60% of maximal contractile force (MCF), with femoral vascular conductance (FVC) assessed at rest and during contraction, with and without NO synthase inhibition.

Main Results:

• Sympatholysis, measured as the reduction in %FVC during sympathetic stimulation, was observed in all groups and increased with contraction intensity.
• Heavy-intensity (H) training significantly augmented sympatholysis at 30% MCF compared to mild-intensity (M) and sedentary (S) groups.
• At 60% MCF, both M and H training enhanced sympatholysis compared to S, with H showing the greatest effect.
• Nitric oxide synthase inhibition attenuated sympatholysis in H at 30% MCF and in both M and H groups at 60% MCF, but not in the S group.

Conclusions:

• Short-term exercise training potentiates sympatholysis in a manner that is dependent on the intensity of the training.
• The augmentation of sympatholysis by exercise training is mediated through a nitric oxide (NO)-dependent pathway.
• These findings suggest that exercise intensity plays a critical role in modulating vascular responses during exercise through NO signaling.