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Hypertension and central obesity are two conditions closely linked, but the mechanisms responsible for obesity-associated hypertension are still unclear. In the last few years, several studies addressed the role of endothelin-1 (ET-1) in the development and maintenance of hypertension. This study was designed to evaluate plasma ET-1 in normotensive and hypertensive central obese subjects compared with a lean healthy group. Our final goal was to analyze the relationship between plasma ET-1, blood pressure, and left ventricular structure and function in central obese subjects (both normotensives and hypertensives). ET-levels have been assessed by the radioimmunoassay method in 20 lean normotensives and in 57 central obese subjects; 30 of them were hypertensives and 27 of them were normotensives. Twenty-four-hour mean blood pressure (MBP/24 h) by noninvasive ambulatory blood pressure monitoring, left ventricular mass/ height (LVM/H), and left ventricular ejection fraction (LVEF) by echocardiography and peak filling rate (PFR) by radionuclide study were also measured. ET levels were significantly (P < .05) higher in obese hypertensives and obese normotensives than in lean normotensives. In addition, ET levels were significantly (P < .05) higher in obese hypertensives than in obese normotensives. ET were directly related to LVM/ H (r = 0.86; P < .001) and MBP/24 h (r = 0.48; P < .009) but only in obese hypertensives. Multiple regression analysis indicated that ET-1 plasma levels remain an independent predictor of MBP/ 24 h and LVM/H also when age was included in the analysis. These data suggest that obesity-associated hypertension is characterized by an endothelial dysfunction that may contribute to the higher cardiovascular risk detectable in these patients.