Body's Appetite Suppressant Leptin Linked to High Blood Pressure in African Americans

Researchers at the Medical College of Wisconsin Cardiovascular Research Center have found a physiological link between leptin and pulse rate in African Americans.

Leptin, a hormone made by the body's fat cells, increases as stored fat increases in an effort to shut down appetite. As expected, they found that high circulating leptin levels in 33 African American, overweight sibling pairs with high blood pressure, did not trigger weight loss. However, they also found that high leptin levels correlated with high pulse rate along with increased weight. Both are major causes of hypertension (high blood pressure) and resulting heart disease.

One third of African Americans have high blood pressure and African Americans are 70% more likely to die of heart attacks than are whites.

"It has been known for years that a person's heart rate and body weight are very powerful predictors of future hypertension," explains Clarence E. Grim, MD, formerly a Professor of Medicine at the Medical College of Wisconsin.

It is also known that for some reason in people who become obese, the brain does not "see" the high leptin levels made by the body's increasing fat mass and therefore appetite does not decrease to keep weight down, according to Dr. Grim. "From animal studies we know that high leptin levels increase heart rate and blood pressure. Thus the chronic high leptin levels in obese African Americans, especially women, may be a critical link to their high blood pressure. This failed signal could prove to be an important link to obesity and heart disease."

The results of the study were presented recently at the 14th Annual International Society of Hypertension meeting on Hypertension In Blacks in Toronto, Canada.

As part of a study to identify the genetic factors influencing blood pressure in African Americans, researchers studied the heart rate and body mass index of 33 sibling pairs who had both high blood pressure and high blood cholesterol. The average age of the 27 males and 39 females was 44 years. Studies were conducted at the Medical College's Clinical Research Center at Froedtert Hospital, a major affiliate of the Medical College. All volunteers were withdrawn from medications for at least one week prior to being measured for body weight index, heart rate, high blood pressure and levels of hormones including leptin.

The average body mass index (BMI) was 30 kg/m2 (very obese is 30 or greater). Leptin levels were nearly four times higher in women than in men. When the blood levels of leptin were related to the other factors, it was found that leptin levels were most highly correlated with the BMI and then heart rate. Leptin levels, heart rate and BMI were highly correlated between sibling pairs, suggesting an important genetic link to these factors.

The researchers suggest that increased body weight triggers a corresponding increase in heart rate through a complex mechanism governed by amounts of leptin released from fatty tissue. These effects of leptin on the nervous and endocrine systems may contribute to a genetic susceptibility to hypertension when weight gain occurs in African Americans.

The next step is to study the effect of leptin infusions into people with normal blood pressure to see if it raises heart rate and blood pressure, according to Dr. Grim. "If a drug that blocks the effects of leptin on the blood pressure regulating systems is developed it could provide a new way to treat the high blood pressure associated with obesity."

The study was supported in part by a National Institutes of Health Special Center of Research (SCOR) - Genetics of Hypertension Grant. Co-directors of the grant at MCW are Theodore Kotchen, MD, Professor of Medicine, Allen W. Cowley, Jr., PhD, Professor and Chairman of Physiology and principal investigator of SCOR, Richard J. Roman, PhD, Professor of Physiology. Pavel Hamet, MD, is director of a Canadian component of the study in Montreal.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.