Vagal tone and the inflammatory reflex

En studie som beskriver mekanismene bak hvordan vagus nerven henger sammen med immunsystemet. Med en sterk vagusnerve (høy HRV) kan betennelser dempes.

http://www.ccjm.org/content/76/Suppl_2/S23.long

Inhibition of sympathoexcitatory circuits is influenced by cerebral structures and mediated via vagal mechanisms. Studies of pharmacologic blockade of the prefrontal cortex together with neuroimaging studies support the role of the right hemisphere in parasympathetic control of the heart via its connection with the right vagus nerve. Neural mechanisms also regulate inflammation; vagus nerve activity inhibits macrophage activation and the synthesis of tumor necrosis factor in the reticuloendothelial system through the release of acetylcholine. Data suggest an association between heart rate variability and inflammation that may support the concept of a cholinergic anti-inflammatory pathway.

The neurovisceral integration model of cardiac vagal tone integrates autonomic, attentional, and affective systems into a functional and structural network. This neural network can be indexed by heart rate variability (HRV). High HRV is associated with greater prefrontal inhibitory tone. A lack of inhibition leads to undifferentiated threat responses to environmental challenges.

The cholinergic anti-inflammatory pathway

Acetylcholine and parasympathetic tone inhibit proinflammatory cytokines such as interleukin (IL)-6. These proinflammatory cytokines are under tonic inhibitory control via the vagus nerve, and this function may have important implications for health and disease.5

The cholinergic anti-inflammatory pathway is associated with efferent activity in the vagus nerve, leading to acetylcholine release in the reticuloendothelial system that includes the liver, heart, spleen, and gastrointestinal tract. Acetylcholine interacts with the alpha-7 nicotinic receptor on tissue macrophages to inhibit the release of proinflammatory cytokines, but not anti-inflammatory cytokines such as IL-10.

Approximately 80% of the fibers of the vagus nerve are sensory; ie, they sense the presence of proinflammatory cytokines and convey the signal to the brain. Efferent vagus nerve activity leads to the release of acetylcholine, which inhibits tumor necrosis factor (TNF)-alpha on the macrophages. Cytokine regulation also involves the sympathetic nervous system and the endocrine system (the hypothalamic-pituitary axis).

Inverse relationship between HRV and CRP

In a study of 613 airplane factory workers in southern Germany, vagally mediated HRV was inversely related to high-sensitivity CRP in men and premenopausal women, even after controlling for urinary norepinephrine as an index of sympathetic activity.6

Inverse relationship between HRV and fibrinogen

In a related report from the same study, vagal modulation of fibrinogen was investigated.7 Fibrinogen is a large glycoprotein that is synthesized by the liver. Plasma fibrinogen is a measure of systemic inflammation crucially involved in atherosclerosis.

CONCLUSION

The brain and the heart are intimately connected. Both epidemiologic and experimental data suggest an association between HRV and inflammation, including similar neural mechanisms. Evidence of an association between HRV and inflammation supports the concept of a cholinergic anti-inflammatory pathway.

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