Wednesday, September 23, 2009

Central control of reflux; the Vagus nerve

The body has two safeguards against reflux, the diaphragmatic sphincter and the lower esophageal sphincter. Both are supposed to remain shut unless you swallow, burp, or vomit, but sometimes they malfunction and cause reflux. Typically, there are two kinds of malfunctions: (i) transient lower esophageal sphincter relaxations and (ii) weakness in one or both of the sphincters.

The first type of malfunction, transient lower esophageal sphincter relaxations, is basically a brief (i.e., a couple of seconds long) relaxation of the sphincters. Many things can cause these relaxations, including stomach distention, certain food items, and stress. Transient esophageal relaxations are likely the cause of most cases of GERD.

The second type of malfunction, sphincter weakness, is a more prolonged defect in one or both sphincters. Many things can cause such sphincter weakness, including stomach distention, abdominal pressure (such as from weight lifting or straining to go the bathroom), certain food items, certain medications, irritation of the esophagus, and stress. This type of malfunction seems to result in more serious GERD, especially when lying down at night.

Both types of malfunctions also seem to be under some form of central nervous system control via the Vagus nerve, with the result that reflux may be modulated, to some extent, by tweaking the neurotransmitters and receptors of the Vagus nerve. As I mentioned recently, cisapride seems to tighten esophageal sphincter pressure, likely by increasing the amount of acetlycholine in the Vagus nerve. Unfortunately for cisapride (and many other drugs in its class), it also increases the amount of acetlycholine elsewhere and can lead to some bad side effects (like cardiac arrhythmias).

Transient lower esophageal sphincter relaxations seem to be modulated by wide vareity of neurotranmitters, including GABA, glutamate, nitic oxide, and substance P, Cannabinoids. Melatonin, zinc, cholecystokinin, gastrin, atropine, and opioids may also play a role.

As you can see, there are many potential targets that could affect reflux. I will experiment with a number of substances that I know to affect one or more of these targets and that I consider safe. I am not interested in gambling (especially against the odds), so I am confining myself to only those foods & supplements that have been used well for long periods of time by large numbers of people. Results from these experiments will be the subject of numerous future blog posts.

Anatomical picture above is from here.

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