Moderate aerobic exercise may physically remodel the nerves that regulate the heart, with markedly different effects on the left and right sides of the body, according to a study led by researchers at the University of Bristol. The findings, observed in rats, could eventually help researchers develop more targeted treatments for arrhythmias, angina, chest pain and stress-induced “broken heart” syndrome, although studies in humans are still needed.
The research offers a new perspective on how physical activity affects the autonomic nervous system, which automatically controls vital functions including heartbeat, breathing and digestion.
Exercise changes the heart’s hidden control system
The autonomic nervous system includes pathways that increase the heart rate when the body needs more oxygen, such as during exercise or stressful situations. Small groups of nerve cells called stellate ganglia play an important role in this process.
Located on either side of the lower neck and upper chest, the stellate ganglia send signals that influence heart rate and other aspects of heart function. The new research suggests that regular exercise changes these nerve clusters in ways that differ substantially between the two sides of the body.
Dr Augusto Coppi, the study’s lead author and a senior lecturer in veterinary anatomy at the University of Bristol, said: “Our findings show that there is a previously hidden left-right pattern in the body’s ‘autopilot’ system that helps the heart work.”
“We showed that these neural clusters act like dimmer switches in the heart, and that regular, moderate exercise switches them on in a unilaterally specific way. This may help explain why some treatments work better on one side, and could help doctors more accurately and effectively target treatment in the future.”
Ten weeks of exercise produced major changes in the nerves
To study the effects of exercise, researchers examined rats that completed 10 weeks of moderate aerobic training. Aerobic exercise includes activities that raise the heart rate and breathing, such as brisk walking, swimming and cycling.
The research involved scientists from University College London in the UK, the University of São Paulo and the Federal University of São Paulo in Brazil.
The team used an advanced three-dimensional analysis technique called stereology to examine the neurons. The method allows researchers to estimate the number, size and distribution of cells within tissue.
In trained rats, the right cardiovascular neural cluster contained approximately four times as many neurons as the left cluster. This was markedly different from the pattern seen in untrained rats.
The neurons also changed size, but in opposite directions on the two sides. Neurons on the left nearly doubled in size, while those on the right became slightly smaller.
The results suggest that exercise does not affect all of the nerves controlling the heart in the same way. Instead, it may trigger distinct structural adaptations on the left and right sides of the autonomic nervous system.
Could the findings improve heart treatments?
The discovery could eventually have implications for conditions involving abnormal nerve activity around the heart.
Arrhythmia occurs when the heart beats too quickly, too slowly or irregularly. Angina is chest pain or discomfort usually caused by insufficient blood flow to the heart muscle. Stress-induced “broken heart” syndrome involves a sudden weakening of the heart muscle, often following intense mental or physical stress.
Some patients with these conditions are treated by reducing excessive nerve signals reaching the heart. Stellate ganglion nerve blocks temporarily inhibit nerve activity, while denervation procedures block specific nerve pathways.
A better understanding of differences between the left and right stellate ganglia could eventually help doctors determine which side to target.
Dr Coppi said: “Irregular heart rhythms known as arrhythmias, stress-induced ‘broken heart’ syndrome, and certain types of chest pain are often treated by suppressing overactive stellate ganglia (a pair of small nerve hubs in the lower neck/upper chest that send ‘go faster’ signals to the heart).”
“By mapping how the left and right ganglia change with exercise, this study provides clues that could one day fine-tune treatments such as nerve blocks or denervation to the side that is most likely to be effective. This finding is in early stages in rats, so clinical studies will need to follow.”
What comes next?
Although the structural changes were substantial, researchers have not yet established exactly how they affect heart function.
The team plans to investigate whether the differences between the left and right nerve groups influence how the heart operates at rest and during physical activity. They also intend to examine whether similar patterns occur in other animal models and, eventually, in humans.
For human research, scientists hope to use non-invasive markers that can provide information about neural activity without surgery or tissue removal.
If the same differences between the two sides are found in humans, the results could help guide more individualized treatments for arrhythmias, difficult-to-treat angina pectoris and stress-induced “broken heart” syndromes.
Dr Coppi added: “Understanding these left-right differences may help personalize treatments for heart rhythm disorders and angina pectoris. Our next step is to test how these structural changes map to function and whether similar patterns emerge in larger animals and humans.”
Source: www.sciencedaily.com
