Stomach ulcers, also known as peptic ulcers, have an interesting history in medicine. It was originally believed that stress somehow caused them, and doctors didn’t have much advice to offer patients who were suffering from a peptic ulcer. In the 1980’s, however, Barry Marshall and Robin Warren ran some experiments suggesting that a Helicobactor pylori bacterial infection caused peptic ulcers. As with many new discoveries, the news was met with fierce skepticism in the scientific and medical communities. To quell the skeptics, Barry Marshall actually swallowed some H. pylori to prove his hypothesis. This remarkable feat provoked some scientists to begin experimenting with the bacterium, and they found that Marshall was correct. H. pylori causes ulcers by weakening the mucosal lining, allowing stomach acid to come into contact with the stomach lining. With numerous repeated studies finding consistent results, it seemed like a closed case. This discovery was such a big deal that Marshall and Warren even won a Nobel Prize for their work.
However, as with most things in human biology, a wrench was eventually thrown into the equation. It was later discovered that a significant portion of the population carries H. pylori in their stomach, but don’t exhibit ulcers. How could this be? Though all the details are still not fully elucidated, it seems there is a back-and-forth battle going on in the stomachs of people with H. pylori that is relatively harmless and asymptomatic – that is, until they become stressed.
Let’s assume you are one of the majority of people on earth who has H. pylori living in your stomach. The bacterium probably colonized your stomach long ago, but you haven’t noticed anything out of the ordinary. Suddenly, there is a tragic psychological stressor in your life: you lose your job, fail an important final, your significant other ends the relationship – pick your poison. After a few weeks, your life begins to improve and you are feeling better about yourself, except for the excruciating stomach pains you are experiencing, especially after eating. You decide to see a doctor and are prescribed an antibiotic to fight off an H. pylori infection. What happened?
Because a psychological stressor can cause a physiological stress response, your sympathetic nervous system kicks into gear at the onset of the stressor. When the body is eliciting a stress response, cortisol is released in large amounts. One of the properties of cortisol is anti-inflammation. This anti-inflammatory property works by inhibiting the synthesis of a group of compounds known as prostaglandins. More specifically, cortisol prevents the synthesis of arachidonic acid, a precursor to prostaglandin. But, what does this have to do with ulcers?
As it turns out, a particular prostaglandin known as PGE2 is responsible for regulation of both stomach acid secretion and mucous secretion. As with many compounds in the body, PGE2 will have varying effects depending upon the cellular receptor to which it binds. The body is remarkably conservative. Often the same molecule can be used for a wide range of effects depending upon the receptor to which it will bind. You can think of the molecule as a skeleton key and the receptors as a bunch of old doors. The key can open any of the doors, but there can be a very different outcome depending on which door is opened. If PGE2 binds EP3 receptors, acid secretion is inhibited; if it binds EP4 receptors, acid secretion is stimulated and mucous secretion is stimulated. This mechanism makes sense, as an increase in stomach acid would warrant extra mucous to protect the stomach lining. Following this logic, if stomach acid secretion is down (PGE2 binding EP3), the body is going to conserve a little energy by making cuts on mucosal production.
An analysis of this information reveals a few key points. First, it has been shown that cortisol is inversely correlated with stomach acid secretion. This means that PGE2 is binding to the EP3 receptors. So, more cortisol -> less PGE2 -> PGE2 binds EP3. This suggests that PGE2 has a higher affinity for EP3 receptors than it does for EP4 receptors, meaning that it will bind EP3 receptors until most of them are bound before it begins to bind EP4 receptors. So, when you stress, cortisol concentration rises. When cortisol concentration rises, prostaglandin production decreases. Low concentrations of prostaglandin mean PGE2 will bind EP3 preferentially over EP4. This results in a slowing down of stomach acid secretion, which in turn lowers mucosal secretion. The figure below shows a flow chart of events, starting with chronic stress and ending in a peptic ulcer.
This flow chart illustrates the cascade of events leading to an ulcer. In essence, H. pylori becomes an opportunistic pathogen. It takes advantage of the lower levels of mucous, which acts as a barrier between the stomach contents and the sensitive stomach lining.
Taking this information into account, the initial story begins to make more sense. After a few weeks of the blues, you find a new job, ace the test, and get the girl. Things are looking up. Because things are getting back to normal, the parasympathetic nervous system begins to take on its normal hours of operation and the sympathetic nervous system finally winds down. When this happens, your cortisol levels go back to basal levels, meaning that prostaglandin production is on the rise once again. PGE2 is being synthesized in larger amounts, and it begins binding EP4 receptors, turning on acid secretion and mucosal secretion. But there is a problem.
Over the past few weeks your acid secretion has been down and the stomach mucosal lining has thinned, and H. pylori has been proliferating at an increasing rate. With your normal defenses down, H. pylori has had the upper hand in the battle and has virtually wiped out the remainder of your mucosal lining and infected several cells in the lining of the stomach. As the parasympathetic system continues to stimulate digestion, the stomach acid overwhelms the under-mucoused stomach and begins to, quite literally, eat through the lining, resulting in an ulcer.
So, stress doesn’t “cause” the ulcer, but it weakens the mucosal lining, affording H. pylori an opportunity to finish clearing out the rest of the mucous and cause an infection.