`Water controls blood pressure too`

Water raises alertness and blood pressure, according to a new study.

Updated: Jul 07, 2010, 13:07 PM IST

Washington: The health benefits of water are manifold. Now, add two more to the list -- it raises alertness and blood pressure, according to a new study.

Researchers at Vanderbilt University Medical Center
have carried out the study and found drinking water increases
the activity of the nervous system, which raises alertness,
blood pressure and energy expenditure.

They first observed water`s curious ability to
increase blood pressure about 10 years ago, in patients who
had lost their baroreflexes -- the system that keeps blood
pressure within a normal range.

"The observation came as a complete surprise.
We had to unlearn the idea that water had no effect on blood
pressure, which is what all medical students had been told
until the last couple of years," lead researcher Prof David
Robertson said.

Although water does not significantly raise blood
pressure in healthy young subjects with intact baroreflexes,
the researchers found that it does increase sympathetic
nervous system activity and constrict blood vessels (which
prevents pooling of blood in the extremities).

In their latest study, the researchers found water
introduced directly into the stomach or duodenum (the first
part of the small intestine) raised blood pressure, which
ruled out an oral or esophageal mechanism for the response.

They also tested a similar volume of saline. This did
not raise blood pressure, which suggested that stretch of the
tissues was not part of the mechanism and that perhaps water`s
lack of salt might be important.

The researchers ultimately determined that
water dilutes the plasma in the blood vessels leading away
from the duodenum and that this short-lived reduction in salt
concentration (hypo-osmolality) is responsible for water`s
blood pressure-raising (pressor) effect.

They implicated a protein called Trpv4 in the
mechanism: mice lacking the Trpv4 gene did not have a pressor
response to water.

While it is clear that water evokes a pressor
response, the normal role for this physiological system is not
certain. Because it raises sympathetic nervous system activity
-- and consequently energy expenditure -- it does promote
weight loss, Robertson said.

The newly discovered system and its molecular
mediators -- such as Trpv4 -- may be targets for blood
pressure regulation, particularly in situations of low blood
pressure and fainting, the researchers said.

The findings have been published in the latest edition
of the `Hypertension` journal.

PTI