A link between stress hormones and bacteria may explain how emotional shock or over-exertion can trigger heart attacks.
Scientists found that hormones released during stress caused thin sheets of bacteria called biofilms on arterial walls to disperse.
In the process, the bugs produce enzymes that may free clots from plaque deposits on artery walls into the bloodstream.
US lead researcher David Davies, from Binghamton University in New York, said: “Our hypothesis fitted with the observation that heart attack and stroke often occur following an event where elevated levels of catecholamine hormones are released into the blood and tissues, such as occurs during sudden emotional shock or stress, sudden exertion or over-exertion.”
The scientists grew different species of bacteria taken from diseased carotid arteries affected by atherosclerosis, the build-up of thick plaques on the walls of blood vessels.
They found multiple bacterial species living as biofilms in the walls of every carotid artery tested.
Certain molecular signals can cause the biofilms to release enzymes that digest the scaffolding anchoring the bacteria in place.
The enzymes have the potential to attack nearby tissues, causing the arterial plaques to rupture and release clumps of material into the blood stream.
To test the theory, the scientists exposed biofilms formed on the inner walls of silicone tubing to the stress hormone norepinephrine. Levels of the hormone were similar to those found in the body following stress or exertion.
“At least one species of bacteria - Pseudomonas aeruginosa - commonly associated with carotid arteries in our studies, was able to undergo a biofilm dispersion response when exposed to norepinephrine, a hormone responsible for the fight-or-flight response in humans,” said Dr Davies. Norepinephrine is also known as noradrenalin.
The freeing of clots caused by biofilm dispersal could trigger a heart attack, say the scientists.
The research, published in the online journal mBio, suggests that managing bacteria within an arterial plaque site may be as important as managing cholesterol, they add.