Increased susceptibility of angiographically smooth left anterior descending coronary artery to an impairment of vasoresponse to acetylcholine, and the relation between impaired vasoresponse and low-density lipoprotein cholesterol level

Nitric oxide function in atherosclerosis

Atherosclerosis is a chronic inflammatory process in the intima of conduit arteries, which disturbs the endothelium-dependent regulation of the vascular tone by the labile liposoluble radical nitric oxide (NO) formed by the constitutive endothelial nitric oxide synthase (eNOS). This defect predisposes to coronary vasospasm and cardiac ischaemia, with anginal pain as the typical clinical manifestation. It is now appreciated that endothelial dysfunction is an early event in atherogenesis and that it may also involve the microcirculation, in which atherosclerotic lesions do not develop. On the other hand, the inflammatory environment in atherosclerotic plaques may result in the expression of the inducible NO synthase (iNOS) isozyme. Whether the dysfunction in endothelial NO production is causal to, or the result of, atherosclerotic lesion formation is still highly debated. Most evidence supports the hypothesis that constitutive endothelial NO release protects against atherogenesis e.g. by preventing smooth muscle cell proliferation and leukocyte adhesion. Nitric oxide generated by the inducible isozyme may be beneficial by replacing the failing endothelial production but excessive release may damage the vascular wall cells, especially in combination with reactive oxygen intermediates.

Relationship between plasma oxidized low-density lipoprotein and the coronary vasomotor response to acetylcholine in patients with coronary artery disease

The present study examined the relation of plasma oxidized low-density lipoprotein (LDL) levels to plasma LDL cholesterol levels and the impairment of endothelium-dependent coronary vasorelaxation in patients with coronary artery disease (CAD). In the first study, the relationship between plasma levels of oxidized LDL and LDL cholesterol were investigated in 88 patients with CAD. In the second study, the changes in the diameter of the left anterior descending (LAD) and the left circumflex (LCX) coronary arteries were measured after intracoronary administration of acetylcholine (15 microg) and isosorbide dinitrate (2.5 mg) in 15 patients with CAD. Plasma oxidized LDL levels were determined with a sandwich enzyme-linked immunosorbent assay. Plasma oxidized LDL levels did not correlate with plasma LDL cholesterol levels (r=-0.03, p=NS). The % diameter changes (mean+/-SEM) in the LAD and LCX after intracoronary acetylcholine were -8.3+/-3.5% and -10+/-4.2%, respectively. The % diameter changes in the LAD and LCX after intracoronary isosorbide dinitrate were 23+/-4.8% and 23+/-5.1%, respectively. The % diameter changes in the LAD and LCX inversely correlated with plasma oxidized LDL levels after intracoronary acetylcholine (LAD: r=-0.55, p=0.03; LCX: r=-0.59, p=0.02), but were not after intracoronary isosorbide dinitrate. Plasma LDL cholesterol, triglyceride, and high-density lipoprotein cholesterol levels did not correlate with the coronary vasoreaction to acetylcholine. In conclusion, plasma oxidized LDL levels do not correlate with plasma LDL-cholesterol levels and are related to impairment of endothelium-dependent coronary vasodilation in patients with CAD.

Effect of plaque burden on coronary vasoreactivity in early atherosclerosis

Coronary atherosclerosis, during its initial stages of development, may result in abnormal endothelium-dependent vasomotor responses. The relation between the degree of vasoreactivity and the amount of atheromatous plaque load has not been decisively determined. The aim of the present study was to investigate the effects of segmental plaque burden on endothelium-dependent and independent coronary stimulation. We studied 37 individual coronary segments along the course of coronary arteries that had angiographically either nonvisible or nonobstructive atheromatous lesions. Endothelium-dependent and independent stimulation of each segment from 10 patients with known significant coronary artery disease was examined with intracoronary administrations of normal saline, acetylcholine 10(-6) M and 10(-5) M, and nitroglycerin, respectively, using quantitative coronary angiography. Simultaneous vasomotor effects on the microcirculation were evaluated by a Doppler guidewire (Flowire). Subsequently, intracoronary ultrasound was used at each segment for detailed morphometric and composition analysis. By quantitative coronary angiography, when compared with normal saline, acetylcholine produced a reduction in minimal lumen diameter of 15.2 +/- 25.6%, and nitroglycerin produced an increase of 18.0 +/- 22.5%. The degree of vasoconstriction induced by acetylcholine correlated inversely (r = 0.51, p = 0.001) to the amount of segmental maximal plaque thickness. No relation between the response to nitroglycerin and the parameters obtained by intracoronary ultrasound was documented. Fibrous coronary plaques showed less vasomotor changes than plaques with mixed echogenicity, probably due to a significantly larger plaque burden. Acetylcholine produced overall a differential vasomotor response in the epicardial segments (vasoconstriction) compared with the microcirculation (vasodilation). These results indicate that in early atheromatous coronary lesions, the degree of endothelium-dependent vasoconstrictive response is inversely related to the amount of segmental plaque burden.