Regulation and failure of coronary circulation

Endothelial driving factors pathophysiologically affect the regulation of coronary circulation. To investigate the regulation of vascular function by endothelium-derived relaxing factor (EDRF) and endothelial cells, endothelium-dependent relaxation impairment was studied in acute ischemia-reperfusion injury in large coronary artery and coronary microvasculature. EDRF (NO) production and release were inhibited due to ischemia-reperfusion injury to the endothelium of large coronary arteries. There was an increased sensitivity selective to ET-1 in large coronary arteries exposed to ischemia and reperfusion. Reduced endothelium-dependent relaxation and augmented ET-1 sensitivity in large coronary arteries suggest the existence of spasmogeneity in reperfused blood vessels. Ischemia and reperfusion also brought about various morphological and functional changes in the reperfused coronary microvasculature. Edema of perivascular interstitium and endothelial cells was the main observation and caused a decrease in the ability of the microvascular bed to dilate because of extravascular compression. To examine the long-term suppression of NO synthesis accompanying endothelial dysfunction, the long-term reactions of coronary arteries and myocardium due to chronic inhibition of NO synthesis by continuously infused L-NAME was investigated. Endothelial cell impairment, proliferation and disarrangement of medial smooth muscle cells, microvascular injury due to platelet thrombi and increased perivascular fibrous tissue were found in rat coronary arteries. Myocardial fibrosis due to coronary microvascular injury was observed. These changes in coronary arterial and myocardial structure were suppressed by ACE inhibitors. Therefore, ACE inhibitors are useful in the treatment of coronary microvascular impairments.