The endothelium plays an important role in maintaining vascular tone and function. Essential hypertension may be associated with alterations in endothelial function. The effects of antihypertensive agents on endothelial function have not been fully evaluated in human hypertension and data on the forearm circulation of humans are controversial. The aim of this study was 1) to evaluate the endothelial function in hypertensive patients 2) to investigate whether vitamin C administration has benefit on the endothelial function and 3) to determine whether treatment with ACE inhibitor improve endothelial dysfunction in hypertensive patients.

The endothelial function was estimated using venous occlusion plethysmography(VOP) in 8 hypertensive patients and 8 healthy volunteers. The patients in the hypertension group were treated with enalapril, then examined again. The change of the forearm blood flow(FBF) was measured with the acetylcholine infusion through brachial artery and also with intra-arterial vitamin C. The measurement of forearm volume change was repeated for 7 times each stage.

Forearm blood flow response to acetylcholine was significantly enhanced with inra-arterial infusion of vitamin C in hypertensive group before antihypertensive treatment(302±58 % --< 446±43 %). Co-infusion of L-NMMA, an inhibitor of nitric oxide synthase, blunted forearm blood flow response to acetylcholine(Vit C(+; 446±43 % --< Vit C +L-NMMA; 229±23 %). After antihypertensive treatment with enalapril for 2 months in hypertensive group, endothelium-dependent vasorelaxation (vasodilatory response to acetylcholine) was significantly improved in treated group compared to before enalapril treatment(302±58 % --< 643±78 %).

Even though the mechanisms leading to depressed endothelial function in essential hypertension remains to be elucidated, our study shows that vitamin C and ACE inhibitor result in demonstrable improvement by a mechanism that is probably related to antioxidant activity.