Abnormal flow-mediated epicardial vasomotion in human coronary arteries is improved by angiotensin-converting enzyme inhibition A potential role of bradykinin

AbstractOBJECTIVESThis study was performed to determine whether angiotensin converting enzyme (ACE) inhibition improves endothelium-dependent flow-mediated vasodilation in patients with atherosclerosis or its risk factors and whether this is mediated by enhanced bradykinin activity.BACKGROUNDAbnormal coronary vasomotion due to endothelial dysfunction contributes to myocardial ischemia in patients with atherosclerosis, and its reversal may have an antiischemic action. Previous studies have shown that ACE inhibition improves coronary endothelial responses to acetylcholine, but whether this is accompanied by improved responses to shear stress remains unknown.METHODSIn 19 patients with mild atherosclerosis, metabolic vasodilation was assessed during cardiac pacing. Pacing was repeated during separate intracoronary infusions of low-dose bradykinin (BK) and enalaprilat. Endothelium-dependent and -independent vasodilation was estimated with intracoronary BK and sodium nitroprusside respectively.RESULTSEnalaprilat did not alter either resting coronary vascular tone or dilation with sodium nitroprusside, but potentiated BK-mediated dilation. Epicardial segments that constricted abnormally with pacing (−5 ± 1%) dilated (3 ± 2%) with pacing in the presence of enalaprilat (p = 0.002). Similarly, BK at a concentration (62.5 ng/min) that did not alter resting diameter in the constricting segments also improved the abnormal response to a 6 ± 1% dilation (p < 0.001). Cardiac pacing-induced reduction in coronary vascular resistance of 27 ± 4% (p < 0.001) remained unchanged after enalaprilat.CONCLUSIONSThus ACE inhibition: A) selectively improved endothelium-dependent but not -independent dilation, and B) abolished abnormal flow-mediated epicardial vasomotion in patients with endothelial dysfunction, in part, by increasing endogenous BK activity

Effect of l-Arginine on Human Coronary Endothelium-Dependent and Physiologic Vasodilation

AbstractObjectives. We hypothesized that l-arginine would improve abnormal coronary vasodilation in response to physiologic stress in patients with atherosclerosis and its risk factors by reversing coronary endothelial dysfunction.Background. Studies have demonstrated that physiologic coronary vasodilation correlates with endothelial function and that l-arginine, the substrate for nitric oxide synthesis, improves the response to acetylcholine (Ach).Methods. Changes in coronary blood flow and epicardial diameter response to Ach, adenosine and cardiac pacing were measured in 32 patients with coronary atherosclerosis or its risk factors and in 7 patients without risk factors and normal coronary angiograms.Results. Intracoronary l-arginine did not alter baseline coronary vascular tone, but the epicardial and microvascular responses to Ach were enhanced (both p < 0.001). The improvement after l-arginine was greater in epicardial segments that initially constricted with Ach; similarly, l-arginine abolished microvascular constriction produced by higher doses of Ach. Thus, there was a negative correlation between the initial epicardial and vascular resistance responses to Ach and the magnitude of improvement with l-arginine (r = −0.55 and r = −0.50, respectively, p < 0.001). d-Arginine did not affect the responses to Ach, and adenosine responses were unchanged with l-arginine. Cardiac pacing-induced epicardial constriction was abolished by l-arginine, but microvascular dilation remained unaffected.Conclusions. Thus, l-arginine improved endothelium-dependent coronary epicardial and microvascular function in patients with endothelial dysfunction. Prevention of epicardial constriction during physiologic stress by l-arginine in patients with endothelial dysfunction may be of therapeutic value in the treatment of myocardial ischemia

Mechanisms Underlying the Morning Increase in Platelet Aggregation: A Flow Cytometry Study

ObjectivesMechanisms underlying the morning increase in platelet aggregation produced by arising and assuming the upright posture were studied by examining 1) the expression on the platelet surface of activation-dependent markers; 2) platelet aggregation in whole blood; and 3) hematologic factors likely to influence aggregation.BackgroundThe morning increase in thrombotic cardiovascular events has been attributed, in part, to the morning surge in platelet aggregability, but its mechanisms are poorly understood.MethodsExpression of seven platelet surface antigens (including P-selectin, activated GPIIb-IIIa and GPIb-IX), whole-blood platelet aggregation, platelet count and hematocrit were measured before and after arising in 17 normal volunteers. The fibrinolytic variables, tissue-type plasminogen activator, plasminogen activator inhibitor 1 and catecholamine levels were also measured.ResultsOn arising and standing, platelet aggregation increased by 71% (p ≤ 0.01) and 27% (p ≤ 0.03) in response to collagen and adenosine diphosphate, respectively. However, there was no change in any of the activation-dependent platelet surface markers. Whole-blood platelet count and hematocrit increased by 15% and 7% (both p < 0.0001), respectively. Norepinephrine and epinephrine levels increased by 189% (p < 0.0001) and 130% (p < 0.01), respectively. Tissue-type plasminogen activator antigen increased (31%, p < 0.01), but there was no significant increase in plasminogen activator inhibitor 1, suggesting an overall increase in fibrinolysis on standing. Prothrombin fragment 1.2 increased by 28% (p < 0.02), indicating a small increase in thrombin generation. The increases in hematocrit and platelet count that occurred on standing were carefully mimicked in vitro and resulted in a 115% (p < 0.05) increase in platelet aggregation in response to adenosine diphosphate.ConclusionsThese data demonstrate that the morning increase in platelet aggregation is not accompanied by expression of activation-dependent platelet surface receptors and suggest that the increase in whole-blood aggregation may be primarily due to the increases in catecholamine levels, platelet count and hemocon-centration

MicroRNA Expression Profile in CAD Patients and the Impact of ACEI/ARB

Coronary artery disease (CAD) is the largest killer of males and females in the United States. There is a need to develop innovative diagnostic markers for this disease. MicroRNAs (miRNAs) are a class of noncoding RNAs that posttranscriptionally regulate the expression of genes involved in important cellular processes, and we hypothesized that the miRNA expression profile would be altered in whole blood samples of patients with CAD. We performed a microarray analysis on RNA from the blood of 5 male subjects with CAD and 5 healthy subjects (mean age 53 years). Subsequently, we performed qRT-PCR analysis of miRNA expression in whole blood of another 10 patients with CAD and 15 healthy subjects. We identified 11 miRNAs that were significantly downregulated in CAD subjects (P < .05). Furthermore, we found an association between ACEI/ARB use and downregulation of several miRNAs that was independent of the presence of significant CAD. In conclusion, we have identified a distinct miRNA signature in whole blood that discriminates CAD patients from healthy subjects. Importantly, medication use may significantly alter miRNA expression. These findings may have significant implications for identifying and managing individuals that either have CAD or are at risk of developing the disease

Endothelial dysfunction is associated with occult coronary artery disease detected by positron emission tomography

Objective: Silent myocardial ischemia is common in asymptomatic subjects without a prior history of coronary artery disease (CAD) and is associated with increased morbidity and mortality. Our objective was to determine whether endothelial dysfunction is associated with silent myocardial ischemia and whether the association is independent of genetic and familial factors. Material and methods: We examined 416 male monozygotic and dizygotic twins aged 47 to 63 years, free of symptomatic CAD. Subclinical ischemia was diagnosed by [13N] ammonia positron emission tomography at rest and after adenosine stress. Endothelial function was measured by flow-mediated dilation (FMD) of the brachial artery. Generalized estimating equations were used for analysis. Results: Fixed perfusion defects were found in 24 (6%) twins and reversible perfusion defects in 90 (22%) twins, indicating subclinical ischemia. There was an inverse correlation between FMD and the reversible perfusion defect score (r = − 0.14, p = 0.01) but not the fixed defect score (r = − 0.017, p = 0.73). From the lowest to the highest quartiles of FMD, the prevalence of reversible defects decreased from 28% to 14%, p = 0.008. In multivariable analysis, reversible defects were significantly associated with each quartile of decreasing FMD (OR = 1.3; 95% 1.1, 2.5). In 54 twin pairs discordant for endothelial dysfunction (FMD ≤ 7% dilation from baseline), twins with endothelial dysfunction had 9% higher likelihood of having perfusion defects than their co-twins without endothelial dysfunction (p = 0.041). Conclusions: Endothelial dysfunction is independently associated with silent ischemia and this association is not confounded by genetic or other shared familial factors