Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Obesity and blood pressure

30.09.2003


Does the body’s synthesis of certain substances affect the relationship between obesity and blood pressure?



The number of overweight Americans has reached record levels, and obesity now affects almost one in three citizens. Published findings from the 1999-2000 report of the National Health and Nutrition Examination Survey (NHANES), the definitive measure for weight matters in the United States, show that 59 million (31 percent) of adults are obese. One third of adult women are obese (33 percent), a rate slightly above men (28 percent). While there is little difference in obesity rates among men across racial/ethic lines, obesity rates for African-American, Mexican-American and white female are 50, 40 and 30 percent, respectively.

One reason obesity is considered a serious health problem is because it is an important factor for essential hypertension (high blood pressure with no identifiable cause). The exact mechanisms for obesity to cause essential hypertension are not fully understood, but it has been linked to the kidneys. These organs play a key role in regulating blood pressure and other substances which affect renal salt and water excretion, are important modulators of hypertension.


A New Study

One fatty acid -- arachidonic acid – is an endogenous fatty acid containing 20 carbons and 4 double bonds. It can be metabolized by cytochrome P450 (CYP) enzymes into different metabolites ("eicosanoids") in the kidneys. These eicosanoids have been shown to cause constriction or dilation of the blood vessels and affect the ion transport in the nephron, the basic unit of the kidneys. Based on the functions of these eicosanoids, a team of researchers has hypothesized that the synthesis of these substances is affected during obesity and that the substances are involved in the regulation of renal function and blood pressure in obesity.

The researchers are Mong-Heng Wang, Anita Smith, Yiqiang Zhou, Hsin-Hsin Chang, Songbai Lin, and Anne M. Dorrance, all of the Department of Physiology, Medical College of Georgia, Augusta, GA. They will report on the results of their study entitled "Down Regulation of Renal CYP-derived Eicosanoids Synthesis in Fat Rats" during the upcoming
Methodology

Three-week old male Sprague-Dawley rats were split into two groups: high fat (HR) rats, fed a modified chow containing 36% fat and control rats, which were fed normal rat chow.

The studies were carried out on 13-week old rats, and animals were fasted overnight prior to use. Blood pressure was measured after ten weeks of treatment, and only HF rats confirmed to be hypertensive were used in the study. The blood pressure was determined by tail-cuff method and all animals were maintained on a 12-hour light dark cycle and housed two to a cage.

After 10 weeks of treatment, the animals were sacrificed, and renal tissues (cortex, medulla, and papilla) and blood vessels were isolated for the measurements of the synthesis of eicosanoids and expression of CYP enzymes. The measurement of the synthesis of eicosanoids was conducted by HPLC method, and the expression of CYP enzymes was conducted by Western blot analysis. Data are expressed as mean ± SE. All data were analyzed by a one-way analysis of variance or the Student’s t-test for unpaired samples. Statistical significance was set at p<0.05.

Results

After ten weeks of treatment the researchers found that:
  • HF rats showed significantly higher systolic blood pressure, body weight, and fat:body weight ratio;

  • the activity for 20-hydroxyeicosatetraenoic acid (20-HETE, the major eicosanoid) synthesis was decreased by 46% in cortex, 43% in medulla, and 46% in papilla of HF rats;

  • activity for epoxyeicasatrienoic acids (EETs, the minor eicosanoids) was decreased by 46% in cortex, 31% in medulla, and 56% in papilla of HF rats. Interestingly, the changes in the rate of 20-HETE and EETs formation in different renal zones were consistent with the levels of expression of CYP4A and CYP2C23 proteins, respectively. Furthermore, there were no significant changes in the synthesis of these metabolites in the renal microvessels.

Conclusions

These results demonstrate that high fat diet causes the down regulation of CYP4A and CYP2C23 in renal tubules, and these proteins are responsible for renal 20-HETE and EETs formation. Since 20-HETE and EETs are known to inhibit sodium transport in the nephron, the downregulation of the synthesis of these eicosanoids can result in an increase of sodium reabsorption and sodium retention, which is responsible for the elevation of blood pressure.

Significance of the Findings

This study is the first to demonstrate that the synthesis of these eicosanoids and the expression of enzymes that catalyze their formation are altered in the renal tubular sites after the treatment of high fat diet. The change of the synthesis of these eicosanoids is associated with the elevation of blood pressure in HF rats. The study calls attention to the possibility that decreased synthesis of these eicosanoids at tubular sites during the treatment of HF diet impacts on the regulation of renal function and blood pressure.

The study also sets the basis for understanding the change of the synthesis of these eicosanoids in the renal tubular sites of fat rats, and the researchers will continue to pursue the regulatory mechanisms of this change in this animal model. Ultimately, additional knowledge can uncover new therapeutic targets and provide new information for the control and treatment of obesity-induced hypertension.


The American Physiological Society (APS) is one of the world’s most prestigious organizations for physiological scientists. These researchers specialize in understanding the processes and functions by which animals live, and thus ultimately underlie human health and disease. Founded in 1887 the Bethesda, MD-based Society has more than 11,000 members and publishes 3,800 articles in its 14 peer-reviewed journals each year.

Donna Krupa | EurekAlert!
Further information:
http://www.faseb.org/aps/

More articles from Health and Medicine:

nachricht Usher syndrome: Gene therapy restores hearing and balance
25.09.2017 | Institut Pasteur

nachricht MRI contrast agent locates and distinguishes aggressive from slow-growing breast cancer
25.09.2017 | Case Western Reserve University

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: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Fraunhofer ISE Pushes World Record for Multicrystalline Silicon Solar Cells to 22.3 Percent

25.09.2017 | Power and Electrical Engineering

Usher syndrome: Gene therapy restores hearing and balance

25.09.2017 | Health and Medicine

An international team of physicists a coherent amplification effect in laser excited dielectrics

25.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>