Bache R J, Dai X Z, Herzog C A, Schwartz J S
Department of Medicine, University of Minnesota Medical School, Minneapolis.
Circ Res. 1987 Nov;61(5 Pt 2):II36-41.
This study was made to evaluate the relative importance of alpha 1- and alpha 2-adrenergic vasoconstrictor influences in opposing the increase in coronary blood flow that occurs during exercise. The effects of selective alpha 1-adrenergic blockade with prazosin were compared with nonselective alpha-adrenergic blockade with phentolamine on coronary hemodynamics during exercise in chronically instrumented dogs. During control conditions, graded treadmill exercise resulted in progressive increases of myocardial oxygen consumption; this was associated with increased coronary blood flow as well as with increased myocardial oxygen extraction. Although prazosin and phentolamine caused similar reductions of arterial pressure, phentolamine increased heart rate, myocardial oxygen consumption, and coronary blood flow at equivalent exercise levels, and prazosin did not significantly alter these variables. These effects of phentolamine appeared to result from blockade of presynaptic alpha 2-adrenergic receptors, which normally modulate norepinephrine release, that resulted in increased sympathetic effects on the heart. However, at comparable levels of myocardial oxygen consumption, prazosin and phentolamine resulted in similar significant increases of coronary venous PO2 and decreases of coronary vascular resistance. These data support a modest role for alpha 1-adrenergic coronary vasoconstriction during exercise but fail to document an additional role for postsynaptic alpha 2-adrenergic coronary vasoconstriction during exercise.
本研究旨在评估α1和α2肾上腺素能血管收缩作用在对抗运动期间冠状动脉血流量增加方面的相对重要性。将哌唑嗪选择性α1肾上腺素能阻滞的效果与酚妥拉明非选择性α肾上腺素能阻滞的效果进行比较，观察其对慢性植入仪器的犬运动期间冠状动脉血流动力学的影响。在对照条件下，分级跑步机运动导致心肌耗氧量逐渐增加；这与冠状动脉血流量增加以及心肌氧摄取增加有关。尽管哌唑嗪和酚妥拉明引起相似程度的动脉压降低，但在同等运动水平下，酚妥拉明增加心率、心肌耗氧量和冠状动脉血流量，而哌唑嗪未显著改变这些变量。酚妥拉明的这些作用似乎是由于阻断了通常调节去甲肾上腺素释放的突触前α2肾上腺素能受体，从而导致交感神经对心脏的作用增强。然而，在心肌耗氧量相当的水平下，哌唑嗪和酚妥拉明导致冠状动脉静脉PO2显著增加和冠状动脉血管阻力降低的程度相似。这些数据支持α1肾上腺素能冠状动脉血管收缩在运动期间起适度作用，但未能证明突触后α2肾上腺素能冠状动脉血管收缩在运动期间起额外作用。
