Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Finding the link between fat and high blood pressure

10.09.2003


How fat contributes to high blood pressure is the focus of a new study at the Medical College of Georgia that is part of a National Institutes of Health initiative to understand the relationship between obesity and cardiovascular disease.


Drs. Gregory A. Harshfield and Paule Barbeau are looking at how fat contributes to high blood pressure.



"You have obesity and you have hypertension. Where is the link?" says Dr. Gregory A. Harshfield, principal investigator on the $1.4 million grant from the NIH’s National Heart, Lung and Blood Institute that will study 160 adolescents, half lean and half overweight or obese, in pursuit of that link. Dr. Paule Barbeau, exercise physiologist, is a co-investigator

Obesity is a risk factor for high blood pressure, which is a major risk factor for cardiovascular disease.


The Augusta researchers and others leaders in the field of hypertension say that obesity may increase pressure by increasing volume rather than constriction.

"We think it’s increased volume because of sodium handling," Dr. Harshfield says. "When we put people under stress, the normal response is to increase your blood pressure through vasoconstriction." The kidneys also hold onto sodium to help increase blood volume throughout the body. As the stress ends, so should these normal physiological responses.

But Dr. Harshfield’s studies at MCG’s Georgia Prevention Institute have shown that some people keep holding onto sodium long after the stress has gone, delaying a process called natriuresis, the body’s way of eliminating sodium. His studies have shown this mechanism is impaired in about 30 percent of adolescent blacks and 15 percent of adolescent whites; the prolonged, elevated pressures may contribute to the development of hypertension.

Fat, or adipose tissue, was once considered storage material only, says Dr. Barbeau. "Now we realize that it secretes all kinds of substances, such as angiotensinogen (which constricts blood vessels) and leptin. The more fat you have, the more of these substances you make."

And different fat depots secrete different substances. Subcutaneous fat, or fat under the skin, secretes leptin, an appetite suppressant also involved in functions such as reproduction and blood pressure regulation. Visceral fat, packed in and around the organs in the abdominal cavity, secretes angiotensinogen, which makes angiotensin II, a powerful vasoconstrictor that also directs the kidneys to absorb more sodium.

"When you gain weight, leptin is supposed to be secreted by the adipose tissue and that tells your brain, ’Don’t eat that much,’" Dr. Barbeau says. "But for some reason, in obese people, that feedback loop doesn’t work any more," she says, equating the scenario to a type 2 diabetic’s resistance to insulin.

Another leptin-driven system seems to fail as well in the obese and contribute to hypertension. Leptin tells the brain to keep producing the neurotransmitter catecholamine which gears up the stress-triggered sympathetic nervous system. Catecholamine, in turn, is supposed to shut down leptin production, but, inexplicably, that doesn’t happen either, says Dr. Harshfield.

The researchers say that stress increases angiotensin II levels and therefore blood pressure. Furthermore, in obese individuals, fat-produced leptin and angiotensinogen keep the blood pressure up by interfering with the natural process of sodium excretion that should occur when the stress is gone. The net result may be early development of hypertension and the damage it causes major organs such as the heart and kidneys.

"How stress interacts with fat in the production of damage to the kidneys is what we are looking at primarily," Dr. Harshfield says. "I think what we are going to see is that in the high-fat kids, the stress will produce greater sodium retention and longer levels of elevated blood pressure."

The MCG researchers began recruiting the 15- to 19-year-olds this fall, a mixture of black and white males and females. Each participant engages in a protocol developed by Dr. Harshfield that includes two hours of rest followed by an hour-long stressful video game, then two more hours of rest. Blood pressure and sodium excretion are measured throughout. Participants are put on a diet for three days prior to the test protocol to regulate their sodium levels. They also get a dual-energy X-ray absorptiometry, or DXA, study to measure body fat, and an MRI at MCG Medical Center to assess visceral fat in the abdominal cavity, as well as studies to look at the size of the heart’s pumping chamber and kidney function.

"This is a logical place to go with the work we already are doing," Dr. Harshfield says, which is why he opted to pursue the proposal request from the National Heart, Lung and Blood Institute for novel approaches to help clarify the biologic basis of obesity-related cardiovascular problems such as hypertension and atherosclerosis.

Today more than 60 percent of Americans are either overweight or obese and Drs. Harshfield and Barbeau have seen some of the ill effects in the young people who come to the Georgia Prevention Institute with hopes of being a healthy participant in a study only to learn they already have high blood pressure or other problems.

"This is a highly meritorious application from an established productive (principal investigator) and outstanding investigative team," reviewers of the grant proposal wrote. "The goal of this study is to test a hypothesis that links adolescent obesity to cardiovascular disease through impaired stress-evoked pressure natriuresis. This is an interesting and novel hypothesis, and will be adequately approached by the proposed studies. Whether or not the hypothesis turns out to be correct, important new data will result from the proposed study."


For more information about study participation, call the Georgia Prevention Institute at (706) 721-1755.

Toni Baker | EurekAlert!
Further information:
http://www.mcg.edu/

More articles from Health and Medicine:

nachricht One gene closer to regenerative therapy for muscular disorders
01.06.2017 | Cincinnati Children's Hospital Medical Center

nachricht The gut microbiota plays a key role in treatment with classic diabetes medication
01.06.2017 | University of Gothenburg

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>