The objective of this study was to evaluate the impact of hypertension on endothelial function. Essential hy­pertension is an important risk factor for atherosclerosis and endothelial dysfunction is the earliest event in atherogenesis because endothelium play an important role in the modula­tion of vascular tone by releasing EDRF identified as nitric oxide. We assessed endothelial function in 48 subjects (12 hypertensive and their 12 normotensive siblings with their con­trol groups). B-mode ultrasonography was used to measure the diameter of the brachial artery, endothelium-dependent dilatation was assessed as the change in diameter of the artery during reactive hyperemia (flow mediated dilatation FMD). FMD was less in patients with hypertension (0.055±0.035) than their control (0.113±0.017) (P<0.001). Also FMD
was less in the hypertensive siblings (0.109±00.019) than their control (0.19±0.039) (P<0.001). These re­sults indicate that hypertensive pa­tients had decreased FMD of brachial artery during reactive hyperemia, a finding which also present in their si­blings although in normotensive range