This study was carried out to determine the relative importance of α1- and α2-adrenergic vasoconstriction in opposing the increase in coronary blood flow, which occurs during exercise. The response of left circumflex coronary artery blood flow was examined during treadmill exercise in 16 chronically instrumented dogs during control conditions, after selective α2-blockade with intracoronary idazoxan. During control conditions, graded treadmill exercise resulted in progressive increases of coronary blood flow and decreases of coronary vascular resistance. Prazosin produced highly selective α1-adrenergic blockade; coronary blood flow was significantly higher and coronary vascular resistance significantly lower during all but the heaviest exercise stage after prazosin. Idazoxan produced highly effective, but only moderately selective, α2-adrenergic blockade. However, after idazoxan, coronary blood flow and coronary vascular resistance during exercise were not significantly different from control. Combined α1- and α2-adrenergic blockade was not more effective in increasing coronary blood flow during exercise than was α1-adrenergic blockade alone. These data support a role for α1-adrenergic coronary vasoconstriction in limiting the increase in coronary blood flow, which occurs during exercise, but do not support a role for α2-mediated coronary vasoconstriction during exercise.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|State||Published - 1989|