Increased response of brachial artery diameter to norepinephrine in hypertensive patients

The hyperresponsiveness of small arteries to norepinephrine is well documented in essential hypertensive patients. Our objective was to investigate in situ the reactivity to norepinephrine of the diameter of large arteries, which are involved in the arterial disease of hypertension as well as small arteries. Brachial artery diameter, blood flow velocity, local volumic blood flow, and local vascular resistances were determined noninvasively with a pulsed Doppler system in 19 patients with essential hypertension and 9 normotensive subjects, before and after the administration of placebo (glucose) or increasing doses of norepinephrine (10, 20, and 40 ng.kg-1.min-1 iv) given in a single-blind fashion. In hypertensive patients, norepinephrine (40 ng.kg-1.min-1) induced 1) a significant decrease in brachial artery diameter, local blood velocity, volumic flow, and conductance and 2) a small increase in mean arterial pressure. These hemodynamic changes did not occur in the placebo group and were significantly greater in hypertensive patients than in normotensive subjects, although plasma norepinephrine increased to the same extent in both groups. We conclude that in hypertensive patients the increase in vascular reactivity to norepinephrine involves not only the resistive vessels but also the large arteries thus decreasing their conducting and buffering function.