ORLANDO, Fla., Sept. 15 -- Leptin, a hormone believed to help regulate body weight, may also be involved in the regulation of blood pressure, according to research presented today at the American Heart Association's meeting on high blood pressure.
"It is possible that leptin is one of the regulators of blood pressure," says Hideki Takizawa, M.D., Ph.D., an instructor in the second department of internal medicine at the Sapporo Medical University in Sapporo, Japan.
In an earlier study, Takizawa's group found that blood levels of leptin were higher in normal weight people with high blood pressure than in individuals of similar size who had normal blood pressure. To further evaluate the relationship between leptin and blood pressure, the researchers studied 133 men and 263 women under age 65 who did not have diabetes and also had not taken medication for high blood pressure.
Leptin is a hormone manufactured in fat cells of the body. It affects food intake and energy expenditures by interacting with a receptor in the brain. Previous studies involving mice found that those who are missing the gene that regulates leptin production become fat. When they are given leptin, they eat less and lose weight.
But the situation is less clear-cut in humans. Obese people tend to have high leptin levels. Researchers believe these individuals may have a leptin resistance that blocks their ability to recognize or respond to the hormone.
When researchers adjusted for age, body mass index and insulin, they found that men with higher leptin levels also had higher diastolic blood pressure -- the pressure when the heart is resting between beats. "The data clearly indicate that high leptin levels are related to high blood pressure," Takizawa says.
He adds that although other studies have found that weight loss leads to a reduction in high blood pressure and leptin levels, further research is needed to determine if reduced leptin levels due to weight loss can reduce a person's risk of high blood pressure.
"Several factors are believed to affect leptin levels," Takizawa says. "One is the amount of fat volume (quantity) a person has because leptin is produced in fat cells. A second factor is whether the fat is deposited near the surface of the skin or deeper within the body. A third consideration is insulin, which stimulates leptin production." Insulin is a hormone that helps the body use glucose, a main food source.
Because so many things could affect leptin levels, the researchers used a method called regression analysis, in which they adjusted for some variables in order to determine the relative importance of others.
High blood pressure greatly increases the risk of heart attack, stroke and kidney failure. An estimated one in four adult Americans has high blood pressure. Although the condition often has no symptoms, it is easy to diagnose and usually controllable.
Co-authors include: Nobuyuki Ura, M.D., Ph.D.; Shigeyuki Saitoh, M.D., Ph.D.; Ling Wang, M.D.; Katsuhiro Higashiura, M.D., Ph.D.; Satoru Takagi, M.D., Ph.D.; Mikio Takada, M.D.; Nobuhiko Togashi, M.D.; Masahiro Nakano, M.D.; and Kazuaki Shimamoto, M.D., Ph.D.
Materials provided by American Heart Association. Note: Content may be edited for style and length.
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