News · Heart & Metabolic
Gut bacteria may raise blood pressure by dampening a serotonin signal to the vagus nerve, rat study finds
Scientists have suspected for years that gut microbes influence blood pressure. Experiments in rats, backed by colon samples from 10 people, point to a nerve pathway that carries the message.
- This work was done mainly in rats, with colon samples from just 5 people with and 5 without high blood pressure.
- Rats and people with high blood pressure had less serotonin signaling in the gut and its nerves.
- Rats given gut microbes from hypertensive rats showed the same drop in serotonin signaling.
- Restoring serotonin signaling in gut nerves eased high blood pressure in rats.
- No probiotic, microbe transplant or new treatment was tested in people.
Most people think of high blood pressure as a problem of the heart, arteries and kidneys, and most treatments aim there. Yet evidence has been building that the gut, and the microbes living in it, also play a part. A study done mainly in rats, with supporting colon samples from 10 people, has traced one route by which gut microbes might push blood pressure up.
The route runs through serotonin made in the gut and a nerve that carries signals from the colon. When that signal weakened, blood pressure rose. When researchers restored it in rats, blood pressure came down.
Why look to the gut for high blood pressure?
The authors point out that hypertension affects more than 1 billion individuals worldwide, and that a significant proportion of patients remain resistant to the currently available therapies. Conventional treatments focus on the heart, kidneys and brain.
Research on the gut microbiota, the community of microbes in the intestines, has suggested these organisms influence blood pressure. What has been missing, the authors say, is a clear mechanism: how would bacteria in the colon send a message that changes pressure in the arteries?
What role do serotonin and the vagus nerve play?
Serotonin is best known as a chemical messenger in the brain, but it is also made in the gut, where it acts as a local signal. Some nerve endings in the colon carry a receptor for serotonin called 5HT3a, which lets them sense it.
Those nerve endings belong to the vagus nerve, a long nerve that links the brain with organs in the chest and abdomen. It carries signals between the gut and the brain, and the brain helps control blood pressure.
How did the researchers connect gut bacteria to blood pressure in rats?
Writing in Circulation, the team combined several approaches. They transferred gut microbes between rats with normal and high blood pressure using fecal microbiota transplants. They used genetically engineered rats that let them switch on, remove, or restore the specific vagal nerve cells that sense serotonin in the colon. And they tracked blood pressure continuously with implanted monitors.
They also examined colon biopsies from people. Samples came from 5 adults with normal blood pressure and 5 with high blood pressure, aged 36 to 75.
What changed in rats and people with high blood pressure?
In rats with high blood pressure, there was markedly less serotonin in the gut and less signaling through the serotonin-sensing vagal nerves. The same drop showed up in the colon samples from people with high blood pressure.
The microbe transplants linked this to the bacteria. Rats given gut microbes from hypertensive rats developed the same weakening of serotonin signaling.
The most important experiment came last. When the researchers restored serotonin signaling in the vagal nerve cells serving the colon, high blood pressure in the rats was alleviated. That moves the finding from a pattern to a working mechanism, at least in rats.
What can’t a rat study with 10 human samples tell us?
The human evidence here is thin. Ten people is enough to see whether the same change is present, not to show how common it is or whether it matters for their blood pressure.
No treatment was tested in people. The study does not show that probiotics, dietary changes or microbe transplants would lower anyone’s blood pressure, and nobody should try those in place of prescribed treatment on the strength of this work.
Could the gut-nerve pathway lead to new blood pressure treatments?
The authors see a promising new target, particularly for people whose high blood pressure resists current treatment and who have an imbalanced gut microbiota. That would take years of work, starting with confirming the pathway in larger groups of people.
In the meantime, the most useful step is the simplest one. MedlinePlus notes that high blood pressure usually has no symptoms, so the only way to find out if you have it is to get regular checks from a health care provider. This study adds a new piece to the picture of why blood pressure rises, and it suggests the gut may deserve a place in that story.
People also ask
What did the study find?
A marked decrease in both intestinal serotonin and vagal 5HT3a receptor signaling was observed in hypertensive rats and humans, and in rats given fecal microbiota from hypertensive rats. The researchers showed that this intestinal serotonin signaling through vagal nerves is a crucial link between the gut microbiota and blood pressure, and that recovering it in colon-innervating vagal neurons can alleviate hypertension.
What is the vagus nerve?
A long nerve that connects the brain with organs in the chest and abdomen, including the gut. It carries signals in both directions.
What is a fecal microbiota transplant?
Moving gut microbes from one individual's stool into another's gut. Here it was done between rats to see whether microbes from hypertensive animals changed the recipients.
Isn't serotonin a brain chemical?
It is best known for its role in the brain, but serotonin is also made in the gut, where it acts as a signal. This study focused on serotonin in the colon.
Should I take probiotics for high blood pressure?
This study does not support that. No probiotic or microbe-based treatment was tested, and people with high blood pressure should follow their health care provider's advice. This is general information rather than medical advice.
Why does this matter if blood pressure drugs already exist?
The authors note that a significant proportion of patients do not respond well to current treatments. A gut-based pathway could eventually offer a different target.