US researchers said the finding could lead to a genetic test which could allow the development of new ways of diagnosing or treating the disease.

People with high blood pressure, called hypertension, are at higher risk of having a stroke or heart attack, and can suffer other health problems.

Blood pressure is the force exerted by the blood against artery walls.

Developing a test for these abnormalities may lead to new means of diagnosing or treating the disease Kendall Blumer, Washington University School of Medicine

A range of medications are available, but often doctors cannot determine which one is most suitable for a patient because the underlying cause of hypertension is unknown in 90 to 95% of cases.

Maintaining pressure

Scientists do know that certain hormones and neurotransmitters, which transmit nerve impulses, send out signals which cause tiny arteries known as arterioles to constrict, causing blood pressure to rise.

They also help to regulate blood pressure by altering the levels of electrolyte, liquid that conducts electricity, and fluid in the kidneys.

However scientists did not know how the hormones and neurotransmitters maintained normal blood pressure when conditions changed, such as when a person suddenly stood up or started running.

It was thought a protein called "regulator of G protein signalling 2" (RGS2) was involved in blood pressure regulation.

Researchers from Washington University School of Medicine looked at mice who lacked both copies of the RGS2 gene, which is responsible for RGS2 production.

They also looked at mice which only lacked one copy of the gene.

Both groups were compared to normal mice.

It was found that all the mice who lacked one or both of the genes had very high blood pressure.

The researchers say their finding that even those missing one gene were hypertensive shows the protein is crucial for controlling blood pressure.

'Insights'

Further tests showed it was possible to treat the mice with the genetic defect by giving them substances which block the action of a hormone called angiotensin II, which causes arterioles to constrict, increasing blood pressure.

The researchers say this suggests RGS2 stops the action of angiotensin II, enabling arterioles to relax and blood pressure to decline.

If there is little or no RGS2, the effect of angiotensin II is prolonged, so blood pressure remains high, they say.

Kendall Blumer, professor of cell biology and physiology at Washington University School of Medicine, who led the research, said: "These findings provide new insights into the cause of hypertension and how normal blood pressure is regulated.

"This may lead to a way of determining the underlying cause of a person's hypertension and the most effective treatment for that individual."

He added: "We hypothesise that genetic defects or differences that affect the amount or function of this protein may increase the risk of developing hypertension.

"Developing a test for these abnormalities may lead to new means of diagnosing or treating the disease."

The team plan to carry out further research to see exactly how RGS2 works.

The research is published in the Journal of Clinical Investigation.