Abstract
The structure and function of blood vessels varies along the vascular tree, and alterations found in hypertension are also different. The aim of this study was to determine whether non-invasive measurement of endothelial function in conduit arteries reflects that of subcutaneous resistance arteries measured in vitro. Sixteen essential hypertensive patients (aged 50 +/- 2 years) were studied. Flow-mediated dilation (FMD) during reactive hyperemia (endothelium-dependent) and sublingual nitroglycerin (NTG)-induced dilatation (endothelium-independent) were assessed in brachial arteries by ultrasound. Structure, and acetylcholine (10(-9) to 10(-4) mol/l) and sodium nitroprusside (SNP, 10(-8) to 10(-3) mol/l)-induced vasorelaxation of resistance arteries dissected from gluteal subcutaneous biopsies were measured in vitro using a pressurized myograph. Brachial artery FMD and NTG-induced dilatation were 8.4 +/- 1.0 and 18.1 +/- 1.4%, respectively. Resistance arteries of hypertensive patients showed greater media:lumen ratio (8.6 +/- 0.4 versus 5.9 +/- 0.3% in normotensive subjects, P< 0.01), and maximal acetylcholine responses was diminished to 75 +/- 6% compared to normotensive subjects (97 +/- 2%, P< 0.01). FMD correlated with maximal acetylcholine responses (r2 = 0.57, P< 0.001). FMD did not correlate significantly with the media: lumen ratio of resistance arteries (r2 = -0.22, P= 0.07). By multivariate analysis, FMD predicted resistance artery endothelial function independently of age, sex, body mass index, blood lipid status and lumen diameter of brachial artery (beta = 0.81, P< 0.001). Endothelial dilatory responses are similar in large and small arteries in hypertensive patients. Abnormal FMD in the brachial artery predicts the presence of endothelial dysfunction in human resistance arteries, suggesting that impairment of endothelial function is a generalized alteration in hypertension. Ultrasound measurement of endothelial dysfunction in the brachial artery appears to be less sensitive than in-vitro measurement in resistance arteries.
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