Sellke F W, Dai H B
Division of Cardiothoracic Surgery, Beth Israel Hospital, Boston, Massachussetts 02215.
Cardiovasc Res. 1993 Jul;27(7):1326-32. doi: 10.1093/cvr/27.7.1326.
The coronary microvenous system may be determinant of ventricular distensibility and of resistance to coronary flow under conditions of arteriolar dilatation. Because responses of venules have not been well defined, in vitro responses of porcine venules and arterioles to neurohumoral substances were examined.
Porcine subepicardial venules (125-250 microns in diameter) and arterioles (100-200 microns in diameter) were studied in a pressurised no flow state with video microscopical imaging and electronic dimension analysis. After precontraction of vessels with the thromboxane A2 analogue U46619, agents were applied extraluminally.
Responses of precontracted venules to sodium nitroprusside, adenosine, and adenosine 5' diphosphate (ADP) were comparable with those of similarly sized arterioles. By contrast, precontracted venules responded minimally to noradrenaline, whereas arterioles were dilated potently by this agent. Precontracted arterioles were dilated minimally by serotonin and were contracted slightly by acetylcholine, whereas venules dilated in response to either serotonin or acetylcholine. Serotonin and acetylcholine both produced greater contraction in non-precontracted arterioles than in non-precontracted venules. Responses of venules to most substances were minimally affected by changes in oxygen tension except when this was very low. Relaxation of venules by ADP, serotonin, and acetylcholine were all inhibited to varying degrees by indomethacin, methylene blue, and NG-methyl-L-arginine (L-NMMA). Both methylene blue and L-NMMA produced minimal but significant contraction of non-precontracted venules, indicating a small amount of basal release of endothelium derived relaxing factor.
Responses of coronary venules to acetylcholine, serotonin, and noradrenaline are opposite or of a significantly different magnitude when compared with the respective arteriolar responses. Relaxation of venules to ADP, serotonin, and acetylcholine is likely mediated at least in part by the release of endothelium derived relaxing factor and prostaglandins.
在小动脉扩张的情况下，冠状静脉系统可能是心室扩张性和冠状血流阻力的决定因素。由于小静脉的反应尚未明确界定，因此研究了猪小静脉和小动脉对神经体液物质的体外反应。
采用视频显微镜成像和电子尺寸分析，在加压无血流状态下研究猪心外膜下小静脉（直径125 - 250微米）和小动脉（直径100 - 200微米）。在用血栓素A2类似物U46619使血管预收缩后，将药物经血管外应用。
预收缩的小静脉对硝普钠、腺苷和腺苷5' - 二磷酸（ADP）的反应与同样大小的小动脉相当。相比之下，预收缩的小静脉对去甲肾上腺素反应极小，而小动脉对此药物有显著扩张作用。预收缩的小动脉对5 - 羟色胺扩张极小，对乙酰胆碱稍有收缩，而小静脉对5 - 羟色胺或乙酰胆碱均有扩张反应。5 - 羟色胺和乙酰胆碱在未预收缩的小动脉中产生的收缩作用均大于未预收缩的小静脉。除氧分压极低时外，小静脉对大多数物质的反应受氧分压变化的影响极小。ADP、5 - 羟色胺和乙酰胆碱引起的小静脉舒张均不同程度地受到吲哚美辛、亚甲蓝和NG - 甲基 - L - 精氨酸（L - NMMA）的抑制。亚甲蓝和L - NMMA均可使未预收缩的小静脉产生轻微但显著的收缩，表明有少量内皮源性舒张因子的基础释放。
与相应的小动脉反应相比，冠状小静脉对乙酰胆碱、5 - 羟色胺和去甲肾上腺素的反应相反或程度明显不同。小静脉对ADP、5 - 羟色胺和乙酰胆碱的舒张作用可能至少部分是由内皮源性舒张因子和前列腺素的释放介导的。
