Health New Zealand (Commonwealth Union) – A recent study has shed new light on the vagus nerve, traditionally associated with its role in promoting the ‘rest and digest’ response, revealing its significant involvement in the realm of exercise.
Conventionally, exercise science has operated on the premise that the ‘fight or flight’ sympathetic nervous system takes center stage during physical activity, heightening heart rate, while the ‘rest and digest’ parasympathetic nervous system diminishes in activity.
However, Associate Professor Rohit Ramchandra from the University of Auckland’s Department of Physiology challenges this established understanding. According to his research, the prevalent notion, based on indirect estimates and certain assumptions, has been debunked. Dr. Ramchandra’s study has uncovered that the activity of the ‘rest and digest’ vagal nerves actually increases during exercise.
This discovery highlights the complex and multifaceted role of the vagus nerve, adding a new dimension to our comprehension of its function, particularly within the context of physical activity.
“Our study focused on a different mediator, vasoactive intestinal peptide (VIP) and it shows that the vagus nerve releases this peptide during exercise, which helps the coronary vessels dilate allowing more blood to pump through the heart,” says Associate Professor Ramchandra.
“Our group has used ‘tour de force’ electrical recording techniques to directly monitor vagal nerve activity in exercising sheep and has found the activity in these vagal nerves going to the heart increases during exercise.
”For the heart to sustain a high level of pumping, it needs a greater blood flow during exercise to fuel the increased work it is doing: our data indicate that the increase in vagal activity does just this.”
During physical exertion, the heart experiences a substantial increase, about four to five times, in the volume of blood it pumps per minute. This heightened demand necessitates the heart to beat at an accelerated rate and with increased force.
The heart’s ability to manage this surge in blood flow is intricately controlled by a network of nerves known as the autonomic nervous system. These nerves, aptly named ‘autonomic’ because they function involuntarily, emanate from the brain.
Among these neural pathways are the ‘fight or flight’ or sympathetic nerves, responsible for priming the body for action, and the ‘rest and digest’ vagal nerves, classified as parasympathetic. The vagal nerve serves as a vital connection between the brain and internal organs, including the gastrointestinal system, governing responses associated with the ‘rest and digest’ parasympathetic nervous system.
The recent research has unveiled a remarkable revelation: the parasympathetic and sympathetic nervous systems work in tandem during exercise, synergistically aiding the heart in pumping blood more vigorously and rapidly.
Furthermore, the study delved into the role of mediators released by the cardiac vagal nerve, shedding new light on the intricate mechanisms at play in regulating the heart’s performance during physical activity.
Dr. Ramchandra indicated that prior research has predominantly fixated on the neurotransmitter acetylcholine released by the cardiac vagus nerve, although it has proven to have no bearing on their exercise capabilities.
Dr. Julia Shanks, the primary author of the study, indicated that the vasoactive intestinal peptide, originally identified in the gastrointestinal tract for its role in digestion, has emerged as a crucial factor in exercise.
The trial was conducted using sheep as the chosen subjects due to their remarkable similarity to humans in terms of essential aspects such as cardiac anatomy and physiology. Furthermore, they serve as a well-established animal model, aiding in the exploration of strategies to combat heart disease that can be translated effectively to human applications.
These pivotal findings hold the potential to be applied in the context of various diseases, including heart failure, where individuals may struggle to engage in physical exercise.
