SAN ANTONIO — Increased levels of adrenal steroids appear to contribute prominently to metabolic syndrome in African Americans, Dr. Theodore A. Kotchen said at a meeting of the American Heart Association Council for High Blood Pressure Research.
“We speculate that the finding of a relatively high plasma aldosterone and low plasma renin activity in hypertensive African Americans may represent a forme fruste or mild variant of the spectrum of disorders that we refer to as primary aldosteronism,” said Dr. Kotchen, professor of medicine at the Medical College of Wisconsin, Milwaukee.
The prevalence of hypertension in African Americans is among the greatest anywhere in the world. Their hypertension-related cardiovascular event rates are also high. A 1970 study of more than 35,000 consecutive autopsies concluded that hypertensive African Americans have an increased prevalence of adrenocortical hyperplasia and adenomas.
To examine the relationship between adrenal steroids—specifically, aldosterone and cortisol—and metabolic syndrome risk factors in African Americans, Dr. Kotchen and his coinvestigators studied 182 hypertensive and 215 normotensive African Americans aged 18–55 years in an inpatient clinical research unit. Roughly half were women. All subjects had temporarily discontinued antihypertensive and lipid-lowering medications weeks beforehand.
The mean plasma aldosterone value of 8.4 ng/dL in hypertensive subjects was significantly higher than the 6.3 ng/dL in normotensives. Both late-night and early-morning salivary cortisol levels were significantly higher in hypertensive individuals as well.
In contrast, plasma renin activity was inversely related to blood pressure, indicating that the increase in aldosterone in hypertensive African Americans isn't renin mediated.
Overall, 17% of study participants met criteria for metabolic syndrome. Plasma aldosterone levels were significantly higher in subjects with metabolic syndrome than in those without it.
Moreover, both aldosterone and blood pressure were significantly correlated with each of the individual elements of metabolic syndrome: waist circumference, cholesterol, triglycerides, body mass index, low HDL cholesterol, plasma insulin, and insulin resistance.
On the basis of these observations, Dr. Kotchen offered the following speculation regarding the potential mechanisms involved in obesity-related hypertension in African Americans: Environmental and perhaps genetic factors contribute to the development of central obesity, which triggers increased activity of β-hydroxysteroid dehydrogenase in visceral adipose tissue. This enzyme converts metabolically inactive cortisone into active cortisol, which promotes adipogenesis and adipose tissue hypertrophy in target tissues, creating a vicious cycle that leads to further increases in cortisol.