Hormone that controls satiety also links obesity to high blood pressure

Date: Dec-05-2014 Obesity is a major risk for hypertension or high blood pressure,

which in turn increases the risk of cardiovascular diseases. But until now, there has been no precise explanation for the hypertension that follows weight gain.

Researchers found that the hormone leptin links obesity and high blood pressure - but some people who lack or cannot process the hormone do not have high blood pressure, despite being obese.

In a new study published in the journal Cell, researchers

from Monash University in Melbourne, Australia, and the University of

Cambridge in UK, describe how they found the hormone leptin is the link

between obesity and increased blood pressure.

Leptin is a hormone that regulates the amount of fat that is stored

in the body. It is released by fat cells and circulates in the

bloodstream to reach the brain, where it controls signals that trigger

storage of energy in fat reserves and also the release of energy from

those reserves.

As well as controlling energy expenditure, leptin also adjusts the

sensation of hunger, which is why it is referred to as the

"satiety" hormone.

For their study, the team - led by Professor Michael Cowley of Monash

University and Professor Sadaf Farooqi of the University of Cambridge -

compared healthy mice and humans with counterparts who have problems

producing or processing leptin.

They found that an increase in leptin in diet-induced obese mice

drove an increase in their blood pressure - but not if they were

deficient in leptin, or could not process it because their brains lacked

leptin receptors.

The team found a similar effect in humans. Some people who lacked

leptin or leptin receptors because of a genetic disorder, had low blood pressure, despite being obese.

Leptin controls blood pressure via circuits in the hypothalamus

In another part of the study, the researchers showed that leptin's

effect on blood pressure is handled through circuits in a part of the

brain known as the dorsomedial hypothalamus (DMH).

Blocking either leptin or leptin receptors in this part of the brains

of the diet-induced obese mice caused a rapid reduction in blood

pressure - regardless of changes in weight - note the researchers.

Lastly, the team carried out another experiment on diet-induced obese

mice bred not to express the leptin receptor gene. When they switched

the gene back on - the mice's blood pressure went up.

The authors conclude that these findings show that leptin couples

changes in weight to changes in blood pressure in mammals.

Prof. Cowley says high blood pressure is a well-known consequence of

obesity, and the findings explain how one leads to the other: "leptin, a

hormone secreted by fat, increases blood pressure."

Targeting leptin activity in the brain could help fight obesity

Prof. Farooqi says targeting how leptin acts in the brain to regulate

both weight and blood pressure could "offer a useful way of helping

people fight obesity and associated problems such as high blood pressure

and heart disease."

The team now plans to discover the precise pathways in the brain

through which leptin regulates blood pressure.

Funds for the study came from government, private, academic and

charitable organizations both in Australia and the UK.

Meanwhile in January 2013, Medical News Today learned of a

study that suggested therapies that boost leptin may relieve asthma in obese

people. In that study, researchers found that obesity-associated

asthma may be relieved with drugs that inhibit signaling through the

parasympathetic nervous system, which mediates leptin function.

Written by Catharine Paddock PhD

Not to be reproduced without permission.

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Courtesy: Medical News Today Note: Any medical information available in this news section is not intended as a substitute for informed medical advice and you should not take any action before consulting with a health care professional.