The gas best known for being used in many stink bombs may also control blood pressure, say US researchers.
Small amounts of hydrogen sulphide - a toxic gas generated by bacteria living in the human gut - are responsible for the foul odour of flatulence.
But it seems the gas is also produced by an enzyme in blood vessels where it relaxes them and lowers blood pressure.
The findings in mice may lead to new treatments for high blood pressure, the Science journal reported.
Researchers at Johns Hopkins University, in Maryland, found that the gas is produced in the cells lining blood vessels by an enzyme called CSE.
In mice engineered to be deficient in this enzyme, levels of hydrogen sulphide were almost depleted compared with levels in normal mice.
The CSE-deficient mice also had blood pressure measurements about 20% higher than the normal mice, comparable to serious hypertension in humans.
When the engineered mice were given a drug which relaxes normal blood vessels - methacholine - there was no difference, indicating the gas is responsible for the relaxation.
Another gas, nitric oxide, is already known to be involved in the control of blood pressure.
Researcher Dr Solomon Snyder said: "Now we know hydrogen sulphide's role in regulating blood pressure, it may be possible to design drug therapies that enhance its formation as an alternative to the current methods of treatment for hypertension."
Professor Amrita Ahluwalia, an expert in vascular pharmacology at Barts and The London Medical School, said: "This study shows that smelly hydrogen sulphide is also likely to have a role in regulating blood pressure and it will be a bit of an impetus for scientists to develop more specific tools to work out what's going on.
"We know hydrogen sulphide is not good for us at high levels but it seems that at the lower levels in the body it is essential."
Dr Allan MacDonald, a reader in pharmacology at Glasgow Caledonian University, said: "Treatments based on hydrogen sulphide could become important in a variety of cardiovascular diseases," he said.
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