Blood-Vessel Behavior May Be One Reason Blacks Are More Prone to High Blood Pressure

BUFFALO, N.Y. -- A cardiology researcher at the University at Buffalo may have found one answer to the question of why more blacks than whites have high blood pressure.

The answer appears to lie in the way the lining of blood vessels, the endothelium, responds to certain signals telling it to dilate. Bong Hee Sung, Ph.D., UB associate professor of medicine, has shown that in some blacks, blood vessels didn't relax and widen as they should in response to a normal blood vessel dilator. Dilation of blood vessels is one of the body's natural mechanisms for easing blood flow, thus lowering pressure.

Sung presented the study results recently at the 12th International Interdisciplinary Conference on Hypertension in Blacks in London.

Why the blood vessels don't relax and widen as expected remains unclear, Sung said. "These are all healthy people," she added. "They had normal glucose and cholesterol levels, and are not obese. There was no apparent reason for them to have endothelium dysfunction. Where this comes from, we don't know. We can't really say what the pathway is yet."

Sung and colleagues studied the blood-vessel response in a group of 12 healthy African Americans and 11 Caucasians, all of whom had normal blood pressure. They also showed normal fasting cholesterol levels, glucose levels, and other parameters known to affect blood pressure.

The researchers measured the diameter of a vein in the left hand of all participants and then introduced the vasoconstrictor norepinephrine into the vein to cause it to narrow. Veins of participants in both groups narrowed similarly.

Insulin, a vasodilator that acts on the endothelium in addition to regulating blood glucose, was added to the norepinephrine, and the vein diameter was measured again.

Results showed that veins remained narrowed in 5, or 42 percent, of the 12 African Americans, indicating they did not respond normally to insulin as a vasodilator.

Sung said the blunted response may be one of the mechanisms underlying the increased prevalence of hypertension in some blacks. "This subgroup of African Americans was resistant to the vasodilatory action of insulin. Nothing happened to their blood pressure when insulin was infused."

Sung said the finding reinforces the relationship between hypertension and diabetes, diseases that are both more prevalent among blacks than whites. Insulin resistance is a risk factor for adult-onset, or Type II, diabetes.

The question Sung and colleagues now are trying to answer is why an apparently healthy subgroup of blacks is not responding normally to insulin. She said the condition has important health consequences, and that once scientists know what causes it, they can work to prevent it.

Additional researchers on the study were Marilou Ching, M.D.; Surendra G. Gudapati, M.D., and Michael F. Wilson, M.D., all of the UB Department of Medicine.