Evaluation of a-adrenoceptor-mediated vasoconstriction to the subendocardial flow-coronary slosh phenomenon and intramyocardial arteriolar diameter change-

当心脏有肾上腺素能激活时，如在心血管屈曲或运动时，就会发生α -矛盾a-肾上腺素受体介导的冠状血管收缩。本研究的目的是验证一种假设，即肾上腺素受体介导的血管收缩可以减少冠状动脉舒张期和收缩期血流的来回振荡。用20 mhz脉冲多普勒测速仪测量麻醉开胸犬的冠状动脉间隔血流速度。高速系统使用光学发光微球来显示微血管中的血流速度。与心外膜动脉血流模式不同，速度波形的特征是完全舒张期血流和两个收缩期反向血流峰值（收缩期早期和中晚期，晃晃现象）。比较肾上腺素阻断前后去甲肾上腺素输注的收缩逆行速度和舒张正向速度。主动脉束带使收缩期主动脉压保持不变；心率控制在80、140和200次/分；α阻断后最大左室dP/dt不变。在各起搏速率下，阻断后的收缩逆行血流速度均显著增大，表明血管收缩通过改变冠状动脉阻抗减少收缩逆行血流。在相同的实验条件下，用微球测量第二组狗的跨壁血流量，在心率为250次/分钟时，a-肾上腺素能阻断左心室内层的血流，表明α -血管收缩的有益作用。总之，肾上腺素能-肾上腺素受体介导的冠状血管收缩在去甲肾上腺素输注期间减少了收缩逆行冠状动脉血流。这减少了冠状动脉循环中来回流动的振荡，这可能是运动时α血管收缩帮助维持左心室内层血液流动的机制。少

There is alpha paradoxical a-adreno-ceptor-mediated coronary vasoconstriction whenever there is adrenergic activation of the heart, as during cardiovascular eflexes or exercise. The aim of the this study was to test the hypothesis that alpha-adrenoceptor-mediated vasoconstriction lessens the to-and-fro oscillation of blood flow that occurs in the coronary arterial tree during systole and diastole. Septal coronary artery blood velocity was measured in anesthetized open-chest dogs with a 20-MHz pulsed Doppler velocimeter. The blood flow velocity in the microvessels was visualized by the high-speed system using an optically shinning microspheres. Unlike epicardial arterial flow patterns, the velocity waveform was characterized by exclusively diastolic flow and by two peaked systolic reverse flow (early and mid-to-late systole, slosh phenomenon). Systolic retrograde velocity and diastolic forward velocity were compared during norepinephrine infusion before and after alpha-adrenoceptor bloc … More kade with phenoxybenzamine. Systo lic aortic pressure was held constant by aortic banding ; heart rate was controlled by pacing at 80, 140, and 200 beats/min ; and maximum left ventricular dP/dt was unchanged by alpha-blockade. At each pacing rate, systolic retro-grade velocity was significantly greater after alpha-blockade, indicating that alpha-vasoconstriction reduced systolic retrograde flow by changing coronary vascular impedance. Transmural blood flow was measured with microspheres in a second group of dogs during the same experimental conditions, and flow to the inner layer of the left ventricle was diminished by a-adrenoceptor blockade at a heart rate of 250 beats/min, demonstrating a beneficial effect of alpha-vasoconstriction. In conclusion, adrenergic alpha-adrenoceptor-mediated coronary vasoconstriction reduces systolic retrograde coronary flow during norepinephrine infusion. This lessens to-and-fro flow oscillation in the coronary circulation and probably is the mechanism whereby alpha-vasoconstriction helps maintain blood flow to the inner layer of the left ventricle during exercise. Less