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Physical Fitness Reduces Hypertensive Influence Of Leptin On Blood Pressure, Regardless Of Body Fat

Regular physical activity counts more than percentage of body fat in terms of systolic blood pressure - a measure of how hard the body has to work to pump blood against the resistance of the blood vessel walls, according to a new study reported at Experimental Biology 2007 in Washington, DC.

The presentation on April 30, by Medical College of Georgia scientist Dr. Joseph Cannon, is part of the scientific presentation of the American Physiological Society.

The results, part of an ongoing study of the relationship between obesity and hypertension at the Medical College of Georgia, represent another step forward in understanding the role of leptin, a hormone produced by fat cells. As the amount of fat stored in fat cells increases, these cells release leptin into the blood to signal to the brain that the body has had enough to eat. For some reason, the feedback loop does not work well in obese people. Leptin also influences blood pressure regulation and may contribute to hypertension in obese individuals.

The results of this new study, says Medical College of Georgia scientist Dr. Joseph Cannon, suggest that body fat, through leptin, influences the constantly changing diameter and stiffness of the blood vessels involved in vessel resistance and hypertension, but that physical activity and fitness reduce this influence, even in heavy women. 

A team of Medical College of Georgia and University of Georgia physiologists, physical therapists and physician assistants studied 46 healthy women. By design, the group included both sedentary lean women and active heavy women. The women ranged in age from 25-40 years. Their body fat, as measured by a sensitive x-ray methodology, ranged from lean (21 percent) to obese (50 percent). Habitual physical activity was determined by questionnaire, and aerobic fitness was tested using a stationary bicycle.

In the present study, serum leptin concentrations correlated with blood pressure in women with less than average aerobic fitness - regardless of their percentage of body fat.The women who were more aerobically fit showed no relationship between serum leptin and blood pressure, again regardless of their percentage of body fat.

Since aerobic fitness has some element of genetic determination, the investigators reanalyzed the data from the standpoint of habitual physical activity rather than from measures of actual aerobic fitness. The same relationships were observed:  greater physical activity was associated with lower blood pressure in both heavy and lean women. Serum leptin levels correlated with blood pressure only in the more sedentary women.

Co-investigators with Dr. Cannon were Manning J. Sabatier, Elaina L. Marinik, Sara Haddow, Earl Schwark, Gloria J. Sloan, Michael F. Bergeron, and Kevin K. McCully. The study was funded by the Medical College of Georgia Research Institute.

Physiology is the study of how molecules, cells, tissues and organs function in health and disease. Established in 1887, the American Physiological Society (APS) was the first U.S. society in the biomedical sciences field. The Society represents more than 10,500 members and publishes 15 peer-reviewed journals with a worldwide readership.