Role of endothelial dysfunction in coronary artery disease

Carotid atherosclerotic disease: A systematic review of pathogenesis and management

Carotid stenosis is an important contributor to ischemic stroke risk with resultant significant impact on neurological disability and death in adults and with worldwide implications. Management of carotid stenosis is impacted by whether there are associated symptoms along with the degree of stenosis. Understanding of the pathogenesis of carotid atherosclerosis or stenosis is important in management of carotid stenosis. Atherosclerotic plaque formation is a chronic insidious process with a number of potential contributors to the formation of such a plaque. The definition of atherosclerosis is not simply limited to abnormal deposition of lipid but also includes a chronic, complex, inflammatory process. Molecularly, in atherosclerosis, there is decreasing nitric oxide (NO) bioavailability, activity and/or expression of endothelial NO synthase, or increasing degradation of NO secondary to enhanced superoxide production. These above changes cause endothelial dysfunction leading to formation of foam cell followed by formation on lipid plaque. After lipid plaque formation, stable or unstable atherosclerotic plaque is formed depending on the calcium deposition over the lipid plaque. It continues to be clearly established that carotid intervention for symptomatic high-grade carotid stenosis is best managed with intervention either by carotid endarterectomy or carotid stenting. However, asymptomatic carotid stenosis is the subject of considerable controversy in terms of optimal management. This review of carotid atherosclerosis is an attempt to incorporate the information provided by more recent studies on pathogenesis and management which may help in the decision-making process for optimal management for protection against stroke.

Vasodilator prostanoids compensate for attenuated nitric oxide mediated vasodilation in type 1 diabetes

Background Previous research examining endothelial function and the biochemical pathways mediating vasodilation in type 1 diabetes has been conflicting. Both impaired and preserved nitric oxide (NO) mediated vasodilation have been reported whilst some authors have suggested enhanced vasodilator prostanoid (P) activity. The aim of this study was to determine the relative contributions of NO and P to endothelial function in a homogenous group of type 1 diabetic patients free of other confounding factors that may influence vascular behaviour.^f ^

Methods and results Endothelial function was assessed using forearm venous plethysmography in 16 patients with uncomplicated type 1 (duration of diabetes 16.8±2.5 years (mean±SEM), HbA1C 7.53±0.21% ) and 15 non-diabetic age and sex matched healthy control subjects. Forearm responses to the endothelium-dependent vasodilator, acetylcholine (ACh) (7.5, 15 and 30 µg/min), were recorded at baseline and after intra-arterial infusion of L-NMMA (a NO synthase inhibitor). Responses to ACh were re-examined following co-infusion of L-NMMA and indomethacin (a cyclo-oxygenase inhibitor). Responses to ACh were calculated as areas under the curve (AUC). At baseline vasodilator responses to ACh were similar (p=0.3) in diabetic and non-diabetic subjects. However, L-NMMA reduced ACh mediated responses to a lesser extent in diabetic subjects than control subjects (3±6% versus 18±3%; p<0.03 respectively). Co-infusion with indomethacin further reduced blood flow, but the relative decrease in AUC was greater in the diabetic group (28±3% vs. 14±3%; p<0.001). The contribution of biochemical pathways other than NO and P were similar in both diabetic and control groups (69±7% vs. 68±4%; p=0.45).

Conclusions Vasodilator responses to ACh were unchanged in type 1 diabetes but this was reliant up on enhanced P mediated activity compensating for attenuated NO activity. Furthermore, vasoactive substances in addition to NO and P contribute significantly to vascular tone in both diabetic and non-diabetic subjects.

Cyclovirobuxine D ameliorates acute myocardial ischemia by KATP channel opening, nitric oxide release and anti-thrombosis

Cyclovirobuxine D is an active compound extracted from Buxus microphylla, which has been used for treating acute myocardial ischemia in China. The present study was to investigate its mechanism on myocardial ischemia. Cyclovirobuxine D significantly increased cardiomyocytes viability injured by oxidation or hypoxia. It significantly reduced the infarct size induced by ligating the coronary artery in rats, and the effect was almost abolished by glibenclamide, a blocker of ATP sensitive potassium channel, but it was not influenced by cyclooxygenase-2 inhibitor celecoxib or estrogen receptor antagonist tamoxifen. In addition, cyclovirobuxine D significantly protected rat aorta endothelial cells against hypoxia and enhanced nitric oxide (NO) release from endothelial cells, which was inhibited by nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME). Furthermore, cyclovirobuxine D significantly decreased the weight of venous thrombus in rats. In conclusion, the action mechanism of cyclovirobuxine D on myocardial ischemia may be related with its cytoprotection, K(ATP) channel opening, NO generation stimulating and venous thrombosis inhibiting.

Differences in expression of cardiovascular risk factors among type 2 diabetes mellitus patients of different age

Atherosclerotic coronary heart disease and other forms of cardiovascular disease (CVD) are the major cause of mortality in type II diabetes (T2DM) as well as a major contributor to morbidity and lifetime costs. The purpose of this article is the identification of the biochemical parameters in plasma, which may serve as predisposition factors to CVD in T2DM patients of different ages. The variability of hyperglycemia, dyslipidemia, and inflammation with age progression was also studied for comparison. Four different diabetic groups allocated on the basis of the subjects' age (Group A: 15-25 years old; Group B: 26-40 years old; Group C: 40-60 years old; Group D: 60-80 years old) and consisting of 10 patients each, in parallel with 10 healthy controls matched for age, sex, and ethnic origin were screened for glucose, insulin, lipid profile (total cholesterol, triglycerides, LDL, and HDL), and inflammatory mediators (CRP, IL-6, and TNF-alpha). Significant differences were observed among the expressions of biochemical markers among different age groups. Hyperglycemia showed no variability with age whereas dyslipidemia correlated positively with age progression, as well as obesity, low physical activity, and family history of heart disease or diabetes. Marked inflammation was prominent only in Groups C and D. This article indicates that different biochemical parameters may be used for the assessment of CVD risk in T2DM patients of variable age.

Aged Rat Myocardium Exhibits Normal Adenosine Receptor-Mediated Bradycardia and Coronary Vasodilation But Increased Adenosine Agonist-Mediated Cardioprotection

The purpose of this study was to determine whether aged myocardium exhibits decreased responsiveness to adenosine A1 and A(2a) receptor activation. Studies were conducted in adult (4-6 months) and aged (24-26 months) Fischer 344 x Brown Norway hybrid (F344 x BN) rats. Effects of the adenosine A1/A(2a) agonist AMP579 were measured in isolated hearts and in rats submitted to in vivo regional myocardial ischemia. Aged isolated hearts exhibited lower spontaneous heart rates and higher coronary resistance, as well as normal A1- and A(2a)-mediated responses. There was no difference in control infarct size between adult and aged rats; however, AMP579 treatment resulted in a 50% greater infarct size reduction in aged rats (18 +/- 4% of risk area) compared to adult rats (37 +/- 3%). These findings suggest that adenosine A1 and A(2a) receptor-mediated effects are not diminished in normal aged myocardium, and that aged hearts exhibit increased adenosine agonist-induced infarct reduction.

The effects of fenofibrate on metabolic and vascular changes induced by chocolate-supplemented diet in the rat

Current evidences suggest that diet per se plays an important role in genesis of metabolic and vascular function abnormalities. We have investigated the effects of addition of a high-fat diet (chocolate) in the presence or absence of short-term (7 days) administration of fenofibrate on metabolic and vascular changes in adult male Wistar rats. Despite similarities in total body weight in all groups, compared with control fed groups, chocolate-supplemented animals had significantly higher plasma triacylglyceride and non-esterified fatty acids and leptin (for all, P<0.01), but not glucose or insulin levels. Fenofibrate treatment corrected metabolic changes. In the mesenteric arteries, responses to KCl and noradrenaline were significantly (for both, P<0.01) higher in chocolate-supplemented group. Furthermore, vasorelaxant responses to carbamylcholine, but not to sodium nitroprusside, were significantly (P<0.01) reduced in the chocolate-supplemented group. Although fenofibrate failed to improve noradrenaline and KCl responses, it was effective in improving carbamylcholine-induced vasorelaxation. These data suggest that high-fat diet has a profound effect on plasma lipid profile and vascular function. Furthermore, fenofibrate treatment may ameliorate high-fat diet effects on vascular function and metabolic changes.

Pathogenesis of Atherosclerosis

Atherosclerosis is no longer considered a disorder due to abnormalities in lipid metabolism. In fact, the inciting event of atherosclerosis is likely an inflammatory insult that occurs decades before the disease becomes clinically apparent. Rapidly evolving knowledge of the pathogenesis of atherosclerosis, coupled with novel, target-specific therapies, is revolutionizing the treatment of atherosclerosis. As a result, a variety of treatments are now undergoing evaluation for their ability to ameliorate the inflammatory pathways likely to cause the atherosclerotic process to initiate and propagate. Once initiated, atherosclerosis progresses as a result of a well-studied series of changes in the constituent cellular make-up of the vessel wall. Specific cytokine-mediated events in this cycle are required for lesional growth. The clinical manifestations of atherosclerosis occur so late in this process that interventions such as percutaneous coronary interventions can deal with isolated areas of disease; however, they do not influence the underlying disease process.

The role of coronary endothelial function testing in patients suspected for angina pectoris

Coronary vasomotor function plays an important role in onset and progression of coronary artery disease. Suwaidi [Circulation 101 (2000) 948] and Schächinger [Circulation 101 (2000) 1899] demonstrated that vasomotor dysfunction has a significant impact on events in patients with minimal coronary artery disease. Endothelial specific testing can be performed in coronary as well as peripheral arteries. However, non-coronary tests have a low correlation with the coronary vasomotor response, as assessed by acetylcholine. In large clinical prospective placebo-controlled trials, angiotensin-converting enzyme (ACE) inhibitors and lipid-lowering drugs reduce morbidity and mortality after myocardial infarction or myocardial infarction-induced heart failure. The same drugs restore endothelial dysfunction after myocardial infarction, as was demonstrated in small experimental and clinical studies. Recent studies in patients with coronary artery disease showed a relation with endothelial dysfunction and the occurrence of adverse coronary events. For this reason, it is important to develop methods to evaluate endothelial function.

The ratio of plasma to whole-blood serotonin may be a novel marker of atherosclerotic cardiovascular disease

Because atherosclerotic vascular lesions stimulate platelets, the platelets release serotonin (5-hydroxytryptamine, aka 5-HT). We therefore measured 5-HT concentrations not only in platelet-poor plasma but also in whole blood as a means of assessing vascular lesions. The plasma concentration of 5-HT tended to increase with age, whereas that in whole blood decreases. Therefore the ratio of the plasma to the whole-blood concentration of 5-HT (P/WB) increases with age. This may be a result of the activation of platelets in older subjects with atherosclerotic vascular damage. Patients who underwent coronary angiography (CAG) were classified into 4 groups according to diagnosis: effort-induced angina pectoris (eAP), old myocardial infarction (OMI), vasospastic angina pectoris (VSAP), and unstable angina (uAP). The mean plasma 5-HT concentration was significantly (P <.01) greater in patients with eAP, uAP, OMI, and VSAP than in healthy controls, whereas the concentration in whole blood was lower in patients with eAP than in healthy controls. When the P/WB ratios were calculated, the mean levels in all disease groups were significantly higher than that in the healthy controls. These findings suggested that 5-HT is released into the plasma from the platelets and that the concentration in the platelets decreases in patients with atherosclerosis.

Vascular endothelium and inflammatory process, in patients with combined Type 2 diabetes mellitus and coronary atherosclerosis: the effects of vitamin C

AIMS

Type 2 diabetes mellitus (DM) and coronary artery disease (CAD) are both associated with endothelial dysfunction and elevated oxidative and inflammatory state. We examined the effect of vitamin C on endothelial function and levels of soluble vascular cell adhesion molecule (sVCAM-1), interleukin-6 (IL-6) and tumour necrosis factor (TNF-alpha), in DM patients with or without CAD and in non-diabetic subjects.

METHODS

Thirty-seven patients with DM + CAD, 17 patients with DM without CAD and 21 non-diabetic subjects were divided into groups receiving vitamin C 2 g/day or no anti-oxidant for 4 weeks. Forearm blood flow was determined using venous occlusion gauge-strain plethysmography. Forearm vasodilatory response to reactive hyperemia was considered as index of endothelium-dependent dilation.

RESULTS

Baseline levels of IL-6 and TNF-alpha were significantly higher in patients with DM + CAD compared with patients with DM (P < 0.01) or non-diabetic subjects (P < 0.01). IL-6 and TNF-alpha levels were also higher in DM compared with non-diabetic subjects (P < 0.05). sVCAM-1 levels were lower in non-diabetic controls compared with DM + CAD (P < 0.05) or DM (P < 0.05). Reactive hyperaemia was higher in non-diabetic controls compared with DM + CAD (P < 0.001) or DM (P < 0.001). Vitamin C significantly increased reactive hyperaemia only in the DM + CAD group, while it had no effect on serum levels of sVCAM-1, TNF-alpha and IL-6 in any of the groups.

CONCLUSIONS

Type 2 diabetes mellitus is associated with impaired endothelial function and increased levels of TNF-alpha, IL-6 and sVCAM-1, especially in patients with DM and CAD. Vitamin C significantly increased forearm vasodilatory response to reactive hyperaemia only in patients with combined DM and CAD.

Fas induces apoptosis in human coronary artery endothelial cells in vitro

Background

Published work suggests that some types of endothelial cells undergo apoptosis in response to ligation of the receptor Fas (CD95, APO1) but other types are resistant. Because heterogeneity among endothelial cells from different tissues, has been demonstrated, the purpose of this study was to determine, if Fas ligation and/or activation by human Fas ligand induces apoptosis and caspase activities, in cultured human coronary artery endothelial cells, and the differences between TNF-a and FAS induced apoptosis in these cells.

Results

Cultured human coronary artery endothelial cells (HCAEC) were exposed to the monoclonal Fas-activating antibody CH-11, to purified recombinant human Fas ligand, to the Fas-neutralizing antibody ZB4, or to purified recombinant human TNF-α. Apoptosis was detected by assessment of chromatin condensation and nuclear fragmentation and by assay of the enzymatic activities of Caspase 1 and Caspase 3 with membrane-permeable substrates applied to intact cells. Fas protein was detected by immunoblotting of HCAEC lysates. Apoptosis was induced in HCAEC by purified Fas ligand or by the monoclonal activating antibody CH-11 at concentrations of 25 or 200 ng/ml, but not by nonspecific isotype-matched immunoglobulins. The apoptotic index elicited by either Fas activator was equal to that induced by TNF-a (3.0-3.6-fold versus control, p < 0.01). The Fas-neutralizing antibody ZB4 abrogated HCAEC apoptosis induced by CH-11, but had no inhibitory effect on apoptosis in response to TNF-a. Fas ligation significantly increased the activities of both Caspase 1 and Caspase 3 at 20 hours of stimulation (1.7- and 2.0-fold versus control, both p < 0.05); in contrast, purified TNF-a increased the activity of Caspase 3 but not Caspase 1 (2.1-fold, p < 0.05). Western blotting of HCAEC lysates with antibody CH-11 identified a single immunoreactive protein of 90 kDa.

Conclusions

Cultured human coronary artery endothelial cells express functional Fas capable of inducing apoptosis in response to either purified Fas ligand or receptor-activating monoclonal antibodies, at levels equal to those inducible by purified TNF-α. Immunologic studies and differential kinetics of caspase activation suggest that Fas and TNF-α induce apoptosis in HCAEC by signaling pathways that are distinct but equal in potency.

The effect of oxidative stress on endothelium-dependent and nitric oxide donor-induced relaxation: implications for nitrate tolerance

Increased inactivation of nitric oxide (NO) by superoxide has been implicated in nitrate tolerance. Here, we set out to compare the inhibitory effect of superoxide on endothelium-dependent, acetylcholine (ACh)-mediated vascular relaxation with that on the endothelium-independent effects of glyceryl trinitrate (GTN) and another NO donor drug, S-nitrosoglutathione (GSNO). Rings of thoracic aorta from adult male Wistar rats (350-450 g) were precontracted with phenylephrine (approximately EC(90)) prior to cumulative additions (10 nM/L-10 microM/L) of GTN, GSNO, or ACh. Rings were then treated with the superoxide generator pyrogallol (300 micromol/L) alone or following pretreatment with the Cu/Zn superoxide dismutase inhibitor diethyldithiocarbamate (DETCA; 100 micromol/L), and cumulative additions of the vasodilators were repeated. All experiments were conducted in the presence of catalase (3000 U/ml) to prevent accumulation of hydrogen peroxide. Relaxation to ACh was abolished by pyrogallol-derived superoxide. Relaxation to GSNO was significantly inhibited by superoxide (P < 0.05, n = 8) and was more pronounced at lower GSNO concentrations. However, GTN was relatively resistant to inhibition by superoxide with modest inhibition only occurring in rings pretreated with DETCA prior to pyrogallol (P < 0.05; n = 8). In contrast to GSNO, the inhibitory effect was more pronounced with high concentrations of GTN, suggesting that the mechanism underlying superoxide-mediated inhibition is different for the two NO donor drugs. Further experiments showed that vascular responses to ACh were not inhibited (P > 0.05, n = 6) in aortic rings made tolerant to GTN (10 micromol/L, 2-h incubation) and that treatment of vessels with the antioxidant vitamin C (1 mmol/L) successfully prevented the development of tolerance. Taken together, these results suggest that superoxide is not a major factor in tolerance in vitro and imply that the protective actions of vitamin C are unrelated to its antioxidant activity in this setting.

Cholesterol enrichment upregulates intercellular adhesion molecule-1 in human vascular endothelial cells

Hypercholesterolemia is a major risk factor for atherosclerosis, but the mechanism by which cholesterol activates the endothelium remains undocumented. The present investigation was undertaken to investigate the role of cholesterol, one of the bioactive moieties of the low-density lipoprotein (LDL) particle, in initiating of intracellular signaling in endothelial cells (ECs) and culminating in increased abundance of the intercellular adhesion molecule-1 (ICAM-1). Cholesterol was delivered to human umbilical vein ECs (HUVECs) via cholesterol-enriched liposomes. In HUVECs, the cellular cholesterol:phospholipid ratio increased after 1 h of exposure to cholesterol. The level of ICAM-1 increased in both mRNA and protein after 24 h of cholesterol exposure. ICAM-1 mRNA half-life was not affected by cholesterol exposure. Promoter studies showed greater than two-fold activation of the ICAM-1 gene expression after cholesterol exposure. Electrophoretic mobility shift assay showed that activator protein-1 (AP-1) activity substantially increased after 2 h of exposure to cholesterol. In contrast, cholesterol did not affect nuclear factor-kappaB (NF-kappaB) activity. Results of trans-reporting assay revealed 2.5-fold increased expression of the AP-1-dependent reporter gene after cholesterol exposure whereas NF-kappaB-dependent expression was not affected. The AP-1/Ets (-891 to -908) site, one of the three AP-1-like sites in the ICAM-1 promoter, was most responsive to cholesterol. These data demonstrate for the first time that cholesterol enrichment phenotypically modulates ECs by transcriptionally upregulating ICAM-1 expression.

Progesterone regulation of vascular thromboxane A(2) receptors in rhesus monkeys

We hypothesized that progesterone regulates thromboxane A(2) receptor (TxA(2)R) density in primate vascular muscle and that TxA(2)R density correlates with coronary reactivity in vivo and in vitro. Reactivity to serotonin + U-46619 was determined by angiography in surgically postmenopausal [ovariectomized (Ovx)] rhesus monkeys without progesterone replacement and after 2-wk progesterone treatment (1-2 ng/ml). In untreated Ovx animals, 100 micromol/l serotonin + 1 micromol/l U-46619 (syringe concentrations) provoked vasospasm-like constrictions in six of six monkeys; zero of six progesterone-treated monkeys developed vasospasms. Sustained Ca(2+) responses in vascular muscle cells isolated from Ovx coronaries (208 +/- 63% of basal 20 min after stimulation) treated with serotonin + U-46619 contrasted with transient Ca(2+) responses (143 +/- 18% of basal and decreasing 5 min after stimulation) in progesterone-treated monkeys. The maximum density of [1S-(1I,2J(5Z),3I(1E,3R*),4I)]-7-[3-(3-hydroxy-4-(4'-[(125)I]iodophenoxy)- 1-butenyl)-7-oxabicyclo[2.2.1]heptan-2-yl]-5-heptenoic acid ([(125)I]-BOP) binding was greater (P < 0.01) in carotid arteries and aortic membranes from Ovx (109 +/- 11 fmol/mg) compared with progesterone-treated (43 +/- 15 fmol/mg) monkeys. TxA(2)R immunolabeling revealed greater coronary TxA(2)R labeling in Ovx compared with progesterone-treated monkeys. The results suggest that progesterone can decrease arterial TxA(2)R in Ovx monkeys.

Hyperglycemia-induced ascorbic acid deficiency promotes endothelial dysfunction and the development of atherosclerosis

Dehydroascorbic acid, the oxidized form of vitamin C, is transported into mammalian cells via facilitative glucose transporters and hyperglycemia inhibits this process by competitive inhibition. This inhibited transport may promote oxidative stress and contribute to the increase in atherosclerotic cardiovascular disease observed in patients with diabetes mellitus. This review explores the importance of this proposed mechanism in light of current research. For example, recent reports suggest that administration of antioxidants, such as vitamin C, may slow atherogenesis by improving endothelium-dependent vasodilation in individuals with abnormal glucose and lipid metabolism, perhaps by preventing the oxidation of nitric oxide, an important regulator of vasomotor tone. Endothelial dysfunction plays a key role in the development of atherosclerosis and endothelial cells may be particularly affected by hyperglycemia-induced ascorbic acid deficiency as they line the interior of blood vessels. In addition, we discuss evidence of several other mechanisms by which vitamin C status may affect the development of atherosclerotic cardiovascular disease, particularly its inverse relationship to multiple cardiovascular disease risk factors and indicators. Given these factors, vitamin C administration is recommended during periods of both acute and chronic hyperglycemia to help preserve endothelial function.

Contraction coupled endothelial nitric oxide release: a new paradigm for local vascular control?

INTRODUCTION

Nitric oxide (NO), a potent vasodilator, is presumed to be constitutively released in most mammalian blood vessels. In isolated rat thoracic aorta, however, hemoglobin (Hb), a nitric oxide scavenger, elicited contraction only when the vessels were precontracted with an alpha adrenergic agonist. Does vascular contraction induce endothelial NO release?

METHODS

Thoracic aortic rings from male Sprague-Dawley rats were prepared with or without the endothelium. Vessel rings were contracted with several distinct types of contractile agonists and NO release was probed using a Hb contraction assay in the presence and absence of nitro-l-arginine methyl ester (NAME), a NO synthase inhibitor.

RESULTS

In vessel rings precontracted with norepinephrine, potassium chloride, arginine vasopressin, prostaglandin F(2alpha), or serotonin, Hb elicited significant additional contractions. In contrast, Hb failed to elicit significant contractions in vessel rings without the functional endothelium or vessels pretreated with NAME. The Hb mediated additional contraction was not inhibited by calmidazolium, a calmodulin antagonist, and protein kinase inhibitors staurosporine and 2,5-dihydromethylcinnamate. Intercellular gap junction inhibitor 2,3-butanedione monoxime at a low dose (<2 mM) significantly attenuated the NE/Hb mediated contractions but at a high dose (>15 mM) completely prevented both contractions. The contraction coupled NO release may be mediated through a mechanism distinct from the Ca(2+)-calmodulin-dependent endothelial NOS pathway.

CONCLUSIONS

In the isolated rat thoracic aorta, endothelial NO release may be coupled to contractile stimulus. This vascular property appears to render a unique local control mechanism independent of baroreflex and other central mechanisms.

Measurement of endothelial function by brachial artery flow-mediated vasodilation

In response to physical and chemical stimuli, the endothelium regulates vascular tone through the release of vasodilators, such as nitric oxide, and vasoconstrictors, such as endothelin. Increased blood flow is an important stimulus for endothelium-mediated vasodilation (flow-mediated vasodilation). Brachial artery flow-mediated vasodilation can be assessed using high-frequency ultrasound assessment of changes in brachial artery diameter after a 5-minute blood pressure cuff arterial occlusion. Endothelial dysfunction is demonstrated as reduced vasodilation, which is usually associated with the presence of coronary risk factors. Brachial artery flow-mediated vasodilation correlates with coronary artery flow-mediated vasodilation. Both indexes have been shown to predict long-term cardiovascular events. Whereas the clinical applicability of brachial artery flow-mediated vasodilation is unclear, it has become a frequently employed measure of endothelial function.

Mechanisms of coronary artery depolarization by uridine triphosphate

We sought to define the basic mechanisms by which pyrimidine nucleotides constrict rat coronary resistance arteries. Uridine triphosphate (UTP) caused a dose-dependent constriction in coronary arteries stripped of endothelium. UTP also depolarized and increased cytosolic Ca2+ in coronary smooth muscle cells. Nisoldipine, an antagonist of voltage-operated Ca2+ channels, blocked the rise in cytosolic Ca2+ and reduced UTP-induced vasoconstriction by approximately 75% which suggests a prominent role for depolarization in this constrictor response. The ionic basis of UTP-induced depolarization was subsequently explored in coronary smooth muscle cells using whole-cell patch-clamp electrophysiology. In the absence of K+ and with CsCl in the pipette, UTP (40 microM) activated a sustained inwardly rectifying current (-0.66 +/- 0.10 pA/pF at -60 mV). A 100 mM reduction in bath Na+ shifted the reversal potential of this current (from -2 +/- 1 to -28 +/- 4 mV) and reduced the magnitude (from -2.26 +/- 0.61 to -0.51 +/- 0.11 pA/pF). In addition to activating a depolarizing cation current, UTP inhibited hyperpolarizing outward currents. Specifically, UTP inhibited ATP-sensitive and voltage-dependent K+ currents yet had no effect on inwardly rectifying and Ca2+-activated K+ channels. This study indicates that electromechanical coupling is integral to pyrimidine-induced constriction in coronary resistance arteries.

Troglitazone corrects metabolic changes but not vascular dysfunction in dietary-obese rats

Insulin resistance has been attributed to the defect in vascular function associated with obesity, type 2 diabetes and dyslipidaemia. We have investigated vascular effects of chronic (3-week) administration of troglitazone on female Wistar rats with moderate dietary obesity. Compared with lean controls, untreated obese rats had significantly higher body weights, fat pad masses, plasma triglycerides, free fatty acids and leptin levels (for all P < 0.01). These metabolic changes were corrected by troglitazone treatment. In mesenteric arteries, responses to noradrenaline or KCl were similar in all groups. However, in noradrenaline-preconstricted arteries, vasorelaxations to acetylcholine and insulin were significantly (50-60% less than in lean, P < 0.001) attenuated in both untreated and troglitazone-treated obese rats. Relaxations to sodium nitroprusside showed similar but lesser impairment in both untreated and troglitazone-treated obese animals. Our data show that although troglitazone markedly improved obesity-induced metabolic changes, it failed to correct vascular dysfunction associated with obesity in female Wistar rats.

Reduced PO(2) and adenosine formation preserve arteriolar nitric oxide synthesis during sympathetic constriction in the rat intestine

Previous reports by this laboratory have indicated that a flow-dependent fall in arteriolar wall PO(2 )may be a stimulus for the sustained release of endothelial nitric oxide (NO) during sympathetic vasoconstriction in the superfused rat intestine. In this study, we tested the hypothesis that locally formed adenosine serves as the link between the fall in local PO(2) and NO synthesis under these conditions. Adenosine applied via pressurized micropipettes directly onto the wall or at a distance of 25 microm from the wall of first-order arterioles (resting diameter = 54 +/- 1 microm) elicited dose-dependent dilations of 15-46% that were significantly reduced by the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 10(-4) M). Arteriolar responses to sympathetic nerve stimulation were enhanced by 57-66% in the presence of L-NMMA or when tissue PO(2) was prevented from falling under a high O(2) superfusate. Adenosine deaminase (2.0 U/ml) or the selective A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (4 x 10(-4) M) completely blocked the enhancing effect of L-NMMA on sympathetic constriction. These results are consistent with the hypothesis that the fall in arteriolar wall and/or tissue PO(2) that accompanies sympathetic arteriolar constriction in the rat intestine can lead to local adenosine production, which in turn preserves endothelial NO release.

Adenosine diphosphate ribose dilates bovine coronary small arteries through apyrase- and 5'-nucleotidase-mediated metabolism

Cyclic adenosine diphosphate ribose and adenosine diphosphate ribose (ADPR) play an important role in the regulation of intracellular Ca(2+) release and K(+) channel activity in the coronary arterial smooth muscle. The role of these signaling nucleotides in the control of vascular tone has yet to be determined. The present study was designed to determine whether ADPR produces vasodilation in coronary arteries and to explore the mechanism of action of ADPR. ADPR (10-60 micromol/l) was found to produce endothelium-independent relaxation in a concentration-dependent manner in isolated and pressurized small bovine coronary arteries. The ADPR-induced vasodilation was substantially attenuated by adenosine deaminase (0.2 U/ml), and the P(1) purinoceptor antagonist 8-(p-sulfophenyl)theophylline (50 micromol/l), with maximal inhibitions of 60 and 80%, respectively. When the coronary arterial homogenates were incubated with ADPR, the production of adenosine and 5'-AMP was detected. The adenosine production was blocked by the 5'-nucleotidase inhibitor, alpha,beta-methylene adenosine 5'-diphosphate (MADP, 1 mmol/l), which was accompanied by a corresponding accumulation of 5'-AMP. This 5'-AMP accumulation was substantially inhibited by the apyrase inhibitor sodium azide (10 mmol/l). Moreover, ADPR was hydrolyzed into 5'-AMP by purified apyrase. In agreement with their inhibitory effect on the adenosine production, MADP and sodium azide significantly attenuated the vasodilator response to ADPR. The metabolism of ADPR to adenosine was only detected in cultured coronary arterial smooth muscle cells but not in endothelial cells. We concluded that ADPR produces vasodilation in small coronary arteries and that the action of ADPR is associated with the adenosine production via an apyrase- and 5'-nucleotidase-mediated metabolism.

Preserved tissue-type plasminogen activator release and endothelium-dependent vasodilation in postmenopausal women with NIDDM

We have recently shown that the net release of tissue-type plasminogen activator (t-PA) antigen can be rapidly enhanced by the muscarinic receptor stimulation in healthy males. Since diabetes mellitus has been associated with endothelial dysfunction, the aim of the present study was to compare the endothelium-derived local net release of t-PA with vasodilation in response to muscarinic receptor stimulation by metacholine (Mch) and fluid shear stress in a group of postmenopausal women with non-insulin-dependent diabetes mellitus (NIDDM), and to elucidate the influence of estrogen on this process. Six postmenopausal women with NIDDM were in randomized order exposed to step-wise intra-arterial infusions of Mch (0.1-0. 8-4.0 microg/min) and nitroprusside (SNP; 0.5-2.5-10.0 microg/min). Forearm blood flow (FBF) was assessed by plethysmography. The infusions with Mch and SNP were repeated during simultaneous intra-arterial infusion of 17-beta estradiol (E; 20 ng/min). During placebo infusion, FBF increased significantly in response to Mch and SNP (p<0.001), but no differences between Mch and SNP were found. In parallel to the blood flow increase in response to Mch stimulation, the t-PA net release was increased over 30 times (p<0.001). Estrogen did not produce any change in blood flow or net release of t-PA at baseline or in response to either drug (Mch or SNP). The present study demonstrates a preserved endothelium-dependent vasodilation and stimulated tissue-type plasminogen activator release in NIDDM postmenopausal women in response to Mch stimulation. Acute intra-arterial infusion of 17-beta estradiol did not affect the vasodilation or the t-PA net release.

Coronary artery blood flow: physiologic and pathophysiologic regulation

Acute myocardial ischemia, which results from a significant imbalance between myocardial oxygen demands and myocardial oxygen supply, occurs in as many as six million persons with atherosclerotic coronary artery disease in the United States. Accordingly, a clear understanding of the physiologic and pathophysiologic factors that influence coronary artery blood flow is important to the clinician and provides the basis for the judicious use of medications for the treatment of patients with atherosclerotic coronary artery disease. This review discusses the endothelial, metabolic, myogenic, and neurohumoral mechanisms of coronary blood flow regulation and the interaction of the different mechanisms in the regulation of coronary blood flow. The importance of nitric oxide in coronary blood flow regulation is emphasized. We also discuss the common clinical problems of hyperlipidemia and coronary atherosclerosis, coronary artery spasm, and systemic arterial hypertension that result in coronary artery endothelial dysfunction, the impaired production and increased inactivation of nitric oxide, and impairment in coronary blood flow regulation. This information is important to clinicians because more than forty million people in the United States have atherosclerotic or hypertensive heart disease and therefore are at risk for significant myocardial complications due to impairment of coronary blood flow regulation.

Emergence of low-molecular-weight heparins in cardiology

Drug therapy for the management of acute coronary syndromes is rapidly expanding. Over the past few years, a number of new antithrombotic agents have been introduced, including low-molecular-weight heparins. The epidemiology and pathophysiology of acute coronary syndromes are discussed, with a historical perspective on the use of antithrombotic therapy.

Coronary Doppler intensity changes during handgrip: a new method to detect coronary vasomotor tone in coronary artery disease

OBJECTIVES

This study evaluates whether a quantitative measurement of Doppler intensity during handgrip may disclose coronary vasomotor dysfunction in patients with coronary artery disease (CAD).

BACKGROUND

Atherosclerotic coronary segments show an exaggerated constrictive response to handgrip. The intensity of the scattered Doppler signal is proportional to the number of blood cells flowing through the vessel, and should be reduced during vasoconstriction. Therefore, changes in coronary flow during handgrip may be detected by measuring Doppler intensity rather than velocities.

METHODS

The distal left anterior descending coronary artery (LAD) was imaged by high-resolution transthoracic color Doppler echocardiography during handgrip in 47 patients: 15 with normal coronary arteries and 32 with significant CAD involving the LAD. The Doppler signal was acquired at 70 dB dynamic range at baseline, 30-s handgrip and 5 min recovery. Peak and mean flow velocity, pressure half-time, deceleration time (ms), deceleration rate (cm/s2) and mean gray level intensity (intensity units [IU]) of the Doppler spectrum were measured in diastole. RESULTS The velocity parameters did not change significantly during handgrip both in normal and CAD patients. The Doppler intensity significantly decreased during handgrip (from 87.0 +/- 32.8 to 57.7 +/- 35.3 IU; p < 0.001) in patients with CAD, and it increased or remained unchanged in normals (from 74.1 +/- 27.3 to 85.1 +/- 31.2 IU; p = NS). The sensitivity of Doppler intensity in detecting CAD was 84.4%, specificity 93.3%, negative predictive value 73.7% and positive predictive value 96.4%.

CONCLUSIONS

Doppler intensity measured by transthoracic echocardiography during handgrip allows the detection of CAD and coronary vasomotor dysfunction.

High-fat meals and endothelial function

Two recent studies on the effects of single high-fat meals on endothelial function have postulated an additional mechanism by which dietary lipids can impact atherosclerosis. These studies found that dietary lipids decrease the ability of blood vessels to dilate and that this modification of endothelial function was protected by dietary antioxidants. Although this research presents an interesting hypothesis, much more research is necessary to determine the importance of dietary factors on vasoactivity.

Endogenous adenosine inhibits P-selectin-dependent formation of coronary thromboemboli during hypoperfusion in dogs

The activation of platelets and the formation of neutrophil- platelet conjugates may lead to the development of thromboemboli. We studied whether blockade of adenosine receptors during coronary hypoperfusion may cause thromboemboli via P-selectin-dependent mechanisms in 30 open-chest dogs. When coronary blood flow was reduced to 20% of the control, it was stable at low levels with increases in adenosine levels. When 8-p-sulfophenyltheophylline, an adenosine receptor antagonist, was infused during coronary hypoperfusion, coronary blood flow decreased gradually and approached almost zero 20 min after its administration. Histological examination revealed thromboemboli in the small coronary vessels. During hypoperfusion in the presence of 8-p-sulfophenyltheophylline, the mAb against P-selectin attenuated both the reduction in coronary blood flow and the formation of thromboemboli, and improved contractile and metabolic dysfunction of the myocardium. Flow cytometric analysis indicated that the expression of P-selectin on platelet and neutrophil-platelet adhesion were increased during coronary hypoperfusion, and that both were further augmented by 8-p-sulfophenyltheophylline. Immunohistochemical examination showed no staining of P-selectin in the ischemic myocardium. Adenosine inhibited the thrombin-induced expression of P-selectin on platelet and neutrophil- platelet adhesion via adenosine A2 receptors. Adenosine appears to inhibit the formation of thromboemboli during coronary hypoperfusion by suppressing the expression of P-selectin on platelets and neutrophil-platelet adhesion.