Coronary Microvessels Research Articles

Abstract 13106: Exercise Tests Cannot Be Used as a Diagnostic Tool for Detection of Coronary Microvessel Dysfunction

Introduction: Current guidelines indicate that patients with angina, a positive exercise test and no obstructive coronary artery disease (CAD) should be suspected of coronary microvessel dysfunction (CMD). The aim of this study was to investigate if exercise tests can identify patients with CMD. Methods: Women with angina pectoris and no obstructive CAD (<50% stenosis on CAG) were consecutively included in the study (n=763). Coronary flow reserve (CFR) was assessed by TTE during dipyridamole infusion (0.84 mg/kg) and information regarding results from exercise test ≤6 months prior to CAG and risk factors were obtained. Results were categorised as 1) positive based on occurrence of ECG changes or typical angina pectoris symptoms 2) negative or 3) inconclusive. Results: Exercise test had been performed prior to CAG in 283 of 642 patients (44 %). Patients lacking information were excluded (n=121). Patients with or without exercise test did not differ in CFR, age, smoking status, years of smoking, type-2 diabetes, BMI, hypertension, hypercholesterolemia or CAG result (all p>0.05).There were no significant differences in mean CFR between patients with a positive, inconclusive or negative test and the proportion with CMD (cut off 2.0 and 2.5, respectively) did not differ. Age, smoking status, type-2 diabetes, hypercholesterolemia or CAG results was similar (table). There was a tendency towards less hypertension in the group of patients with a negative test (p=0.051). Furthermore patients with a negative test had been smoking significantly less than patients with an inconclusive or positive test (p=0.04) Conclusions: No difference in CFR for patients with a positive, inconclusive or negative exercise test was observed. This lack of difference did not seem to be explained by an uneven distribution of risk factors between groups due to selection bias. Exercise tests cannot be used as diagnostic method for CMD, which supports the need for developing novel methods for diagnosing CMD.

Ultrastructural and metabolic features of stress-adaptive rearrangements of myocardium in infants after surgery-induced up-regulation of lipoperoxidation processes.

Surgical correction of complicated congenital heart disease in infants is terminated by postischemic reperfusion of myocardium accompanied with closure of more than 20% microvessels in the coronary bed by edematous endothelial cells, their bleb-like fragments, and aggregates of the blood formed elements. Degradation of the transmission capacity of the coronary microvessels developed in parallel with moderation of activity of the antiradical protection enzymes and positively correlated with the level of LPO secondary products, whose elevation during the surgery stages was not reduced by catalase activation.

Impact of Chronic Kidney Disease on Myocardial Blood Flow Regulation in Dogs

Background/Aims: Chronic kidney disease (CKD) increases cardiovascular risk possibly due to coronary microvessel dysfunction and impaired myocardial flow reserve. This study investigated the effects of CKD on the regulation and transmural distribution of myocardial blood flow along with oxygen demand during intravenous dobutamine-induced increases in cardiac work. Methods: CKD was produced in dogs by a two-stage subtotal nephrectomy (kidney ablation-infarction model). Serum creatinine and blood urea nitrogen were evaluated during the development of CKD along with systemic blood pressure (tail-cuff plethysmography). After 5 weeks, the CKD dogs were staged according to the International Renal Interest Society staging system; all dogs were anesthetized and surgically prepared for blood flow studies. Data analyses were performed between sham control (CTR) and stage 1 and 2 CKD dogs. Results: At baseline, myocardial blood flow and diastolic aortic pressure were similar for all groups. During intravenous dobutamine, myocardial blood flow was markedly higher than CTR even though hematocrit levels declined with the severity of CKD. In the CTR dogs, myocardial blood flow increased in direct relation to cardiac work. However, in the CKD dogs (stage 1 and 2), maximum blood flow was achieved with low-dose dobutamine, indicating that coronary autoregulation is more readily exhausted with minimal increases in cardiac work during CKD. Conclusion: We report that CKD markedly impairs coronary vascular reserve and myocardial blood flow regulation which could contribute to greater cardiovascular risk and poor clinical outcomes in CKD patients.

Obesity and coronary microvascular disease - implications for adipose tissue-mediated remote inflammatory response.

It is believed that obesity has detrimental effects on the coronary circulation. These include immediate changes in coronary arterial vasomotor responsiveness and the development of occlusive large coronary artery disease. Despite its critical role in regulating myocardial perfusion, the altered behavior of coronary resistance arteries, which gives rise to coronary microvascular disease (CMD) is poorly understood in obesity. A chronic, low-grade vascular inflammation has been long considered as one of the main underlying pathology behind CMD. The expanded adipose tissue and the infiltrating macrophages are the major sources of pro-inflammatory mediators that have been implicated in causing inadequate myocardial perfusion and, in a long term, development of heart failure in obese patients. Much less is known the mechanisms regulating the release of these cytokines into the circulation that enable them to exert their remote effects in the coronary microcirculation. This mini review aims to examine recent studies describing alterations in the vasomotor function of coronary resistance arteries and the role of adipose tissue-derived pro-inflammatory cytokines and adipokines in contributing to CMD in obesity. We provide examples of regulatory mechanisms by which adipokines are released from adipose tissue to exert their remote inflammatory effects on coronary microvessels. We identify some of the important challenges and opportunities going forward.

4‐HNE post‐translational modification of TRPV1: implications for diabetic cardiomyopathy (1155.8)

Previously our lab has shown TRPV1 ‐dependent regulation of myocardial blood flow (MBF) is disrupted in a db/db mouse model of diabetic cardiomyopathy (DCM). A crucial mechanism behind pathologies seen in diabetes is the imbalance in oxidative stress (OS) leading to increased lipid peroxidation (LPO). The LPO product 4‐hydroxynonenal (4‐HNE) is known to increase oxidative post translational modification (PTM) resulting in altered protein function. Investigation into the implications of this oxidative PTM on TRPV1 has yet to be examined. Accordingly, we hypothesized that 4‐HNE PTM of TRPV1 results in decreased functional expression leading to perfusion impairments in DCM. Initial experiments were performed to evaluate 4‐HNE modification of TRPV1. Pull down experiments on HEK cells constitutively expressing TRPV1, treated with H2O2 (to simulate OS) and 4‐HNE, resulted in increased 4‐HNE modified TRPV1 compared to control with a concomitant decrease in TRPV1 expression. Similar findings were demonstrated in hearts from diabetic animals and controls treated with H2O2 and 4‐HNE. Computer generated modeling identified numerous possible residues capable of undergoing 4‐HNE modification of which several were confirmed using mass spectroscopy. TRPV1 functional analysis using path‐clamp electrophysiology revealed blunted capsaicin‐mediated currents in the presence of 4‐HNE and/or prolonged H2O2 treatment. Similarly, 4‐HNE decreased capsaicin mediated increases in MBF and relaxation in isolated coronary microvessels. These data suggest that increased OS in a diabetic state leads to decreased TRPV1 functional expression resulting in perfusion impairments seen in DCM.

Stress echo applications beyond coronary artery disease

Stress echocardiography is an established method for the diagnosis and prognostic stratification of coronary artery disease. In the last few years, the tremendous technological and conceptual versatility of this technique has been increasingly applied in challenging diagnostic fields. Today, in the echocardiography laboratory we can detect not only ischaemia from coronary artery stenosis, but can also recognize abnormalities of the coronary microvessels, myocardium, heart valves, pulmonary circulation, alveolar-capillary barrier, and right ventricle. Therefore, we evaluate coronary arteries as well as coronary microvascular disease (associated with diabetes and hypertension), suspected or overt dilated cardiomyopathy, systolic and diastolic heart failure, hypertrophic cardiomyopathy, athletes' hearts, valvular heart disease, congenital heart disease, incipient or overt pulmonary hypertension, and heart transplant patients for early detection of chronic or acute rejection as well as potential donors for better selection of suitable donor hearts. From a stress echo era with a one-fits-all approach (wall motion by 2D-echo in the patient with known or suspected coronary artery disease) now we have moved on to an omnivorous, next-generation laboratory employing a variety of technologies (from M-Mode to 2D and pulsed, continuous and colour Doppler, to lung ultrasound and real-time 3D echo, 2D speckle tracking and myocardial contrast echo) on patients covering the entire spectrum of severity (from elite athletes to patients with end-stage heart failure) and ages (from children with congenital heart disease to the elderly with low-flow, low-gradient aortic stenosis). For each patient, we can tailor a dedicated stress protocol with a specific method to address a particular diagnostic question. Provided that the acoustic window is acceptable and the necessary expertise available, stress echocardiography is useful and convenient in many situations, from valvular to congenital heart disease, and whenever there is a mismatch between symptoms during stress and findings at rest. Increasing societal concern regarding cost, environment and radiation risks of medical imaging will lead to a preferential application of ultrasound over competing techniques, due to its unsurpassed versatility, portability, absence of radiation, and low cost.

Blunted coronary vasodilator response to uridine adenosine tetraphosphate in post-infarct remodeled myocardium is due to reduced P1 receptor activation

We previously demonstrated that uridine adenosine tetraphosphate (Up4A) exerts a potent vasodilator effect in the healthy porcine coronary vasculature. Since the coronary microvascular effects of Up4A after myocardial infarction (MI) are unknown, the present study investigated the response to Up4A in coronary microvessels from post-MI remodeled porcine myocardium, and the involvement of purinergic receptor subtypes. Coronary small arteries (diameter ∼150μm) were dissected from the apex of Sham-operated swine and swine in which MI had been produced 5 weeks earlier by transient (2h) occlusion of the left circumflex coronary artery, and mounted on Mulvany wire myographs. Up4A (10−9–10−5M) produced coronary vasodilation that was reduced in MI as compared to Sham-operated swine. Up4A-induced vasodilation was reduced by P1 blockade with 8-phenyltheophylline in Sham-operated swine and to a lesser extent in MI, while the attenuation by the A2A receptor blocker SCH58261 was similar in Sham-operated and MI swine. Up4A-induced vasodilation remained unaffected by non-selective P2 receptor antagonist PPADS, but was attenuated by selective P2X1 and P2Y1 receptor antagonists MRS2159 and MRS2179, albeit to a similar extent in Sham-operated and MI swine. These responses were paralleled by similar mRNA expression levels of A2A, P2X1 and P2Y1 receptors in MI compared to slaughterhouse control swine. Finally, attenuation of Up4A-induced coronary vasodilation by nitric oxide synthase inhibition was not attenuated in MI as compared to Sham-operated swine. In conclusion, blunted coronary vasodilation in response to Up4A in MI swine is most likely due to reduced activation of P1, rather than P2, receptors and does not involve a loss of NO bioavailability.

Cocaine-Induced Vasoconstriction in the Human Coronary Microcirculation

Background— Cocaine is a major cause of acute coronary syndrome, especially in young adults; however, the mechanistic underpinning of cocaine-induced acute coronary syndrome remains limited. Previous studies in animals and in patients undergoing cardiac catheterization suggest that cocaine constricts coronary microvessels, yet direct evidence is lacking. Methods and Results— We used myocardial contrast echocardiography to test the hypothesis that cocaine causes vasoconstriction in the human coronary microcirculation. Measurements were performed at baseline and after a low, nonintoxicating dose of intranasal cocaine (2 mg/kg) in 10 healthy cocaine-naïve young men (median age, 32 years). Postdestruction time-intensity myocardial contrast echocardiography kinetic data were fit to the equation y=A(1−e −βt ) to quantify functional capillary blood volume (A), microvascular flow velocity (β), and myocardial perfusion (A×β). Heart rate, mean arterial pressure, and left ventricular work (2-dimensional echocardiography) were measured before and 45 minutes after cocaine. Cocaine increased mean arterial pressure (by 14±2 mm Hg [mean±SE]), heart rate (by 8±3 bpm), and left ventricular work (by 50±18 mm Hg·mL −1 ·bpm −1 ). Despite the increases in these determinants of myocardial oxygen demand, myocardial perfusion decreased by 30% (103.7±9.8 to 75.9±10.8 arbitrary units [AU]/s; P <0.01) mainly as a result of decreased capillary blood volume (133.9±5.1 to 111.7±7.7 AU; P <0.05) with no significant change in microvascular flow velocity (0.8±0.1 to 0.7±0.1 AU). Conclusions— In healthy cocaine-naïve young adults, a low-dose cocaine challenge evokes a sizeable decrease in myocardial perfusion. Moreover, the predominant effect is to decrease myocardial capillary blood volume rather than microvascular flow velocity, suggesting a specific action of cocaine to constrict terminal feed arteries.

The Pediatric Infectious Disease Journal® Newsletter

The Pediatric Infectious Disease Journal® Newsletter

Obesity and statins are both independent predictors of enhanced coronary arteriolar dilation in patients undergoing heart surgery

BackgroundA paradoxical inverse relationship between body mass index, morbidity and mortality in patients with ischemic heart disease has been noted; but the underlying mechanisms remain unclear. Given that coronary resistance arteries are the primary regulators of myocardial blood flow, we examined the effects of obesity and medication on dilator function in coronary microvessels.MethodsBradykinin-induced coronary dilation was assessed by videomicroscopy in ex vivo coronary arterioles obtained from 64 consecutive patients undergoing heart surgery. Multi-variable linear regression and logistic regression were used to investigate the effects of obesity (BMI ≥ 30 kg/M2) and the influences of medications on vessel responses.ResultsIn isolated, pressurized (80 mmHg) coronary arterioles of obese and non-obese patient the active (73±4 vs. 79±13 μm) and passive (111 ± 5.5 vs. 118 ± 5.0 μm) diameters were similar. Bradykinin elicited substantial dilation in coronary arterioles, with a similar magnitude in obese and non-obese patients (to 10-8 M: 55 ± 5% vs. 46 ± 5%, P = 0.20), but with significantly enhanced sensitivity in obesity (EC50: 8.2x10-9 M vs. 1.9x10-8 M, respectively, P = 0.03). When adjusted for other risk factors and medications, obesity and statins were determined to be the only positive predictors of enhanced dilation, as assessed with multiple regression analysis. Moreover, obese patients with or without statin exhibited significantly increased coronary dilation to bradykinin, when compared to non-obese patients without statin therapy.ConclusionsObesity and statin therapy are independently associated with an enhanced dilator function of coronary arterioles in patients undergoing heart surgery, which may offer a potential mechanism for the better cardiovascular outcome described earlier as the obesity paradox.

ROS‐induced membrane lipid peroxidation impairs TRPV1 channels in the vasculature

A critical amount of reactive oxygen species (ROS) contributes to coronary blood flow (CBF) regulation; however, oxidative stress impairs CBF regulation. We have previously demonstrated TRPV1‐dependent coupling of CBF to metabolism is disrupted in diabetic cardiomyopathy (DCM). Accordingly, we hypothesized that basal levels of H2O2 stimulate TRPV1 whereas enhanced oxidative stress desensitizes TRPV1 via an H2O2 dependent post translational modification involving the lipid peroxidation product 4‐Hydroxynonenal (4‐HNE). Using contrast echocardiography, H2O2 dose‐dependently increased CBF in control and TRPV1−/− mice, yet was greater in controls compared to TRPV1−/−. Similarly, H2O2 potentiated capsaicin‐mediated CBF increases in controls. H2O2 caused robust dilation in control coronary microvessels (blunted in the presence of the TRPV1 inhibitor SB366791 and in TRPV1−/− vessels), suggesting H2O2 induced vasodilation occurs in part via TRPV1. H2O2 induced Ca2+ influx was TRPV1 dependent in HEK and TRPV1−/− endothelial cells (ECs) transfected with TRPV1 and further verified using Ca2+ imaging and electrophysiology. Lastly, ECs incubated with H2O2 (1hr) and 4‐ HNE (1hr) demonstrated increased 4‐HNE levels and 4‐HNE modified TRPV1 via western/co‐immunoprecipitation. These data suggest low levels of H2O2 can potentiate TRPV1 however, increased ROS concentrations as seen in DCM can lead to enhanced 4‐HNE levels which modulate TRPV1 and disrupt its signaling, resulting in tissue perfusion impairments.

Low‐dose intra‐nasal cocaine causes subclinical microvascular coronary ischemia in humans

We used myocardial contrast echocardiography (MCE) to test the hypothesis that cocaine, an indirect sympathomimetic, causes microvascular ischemia in the human heart. Measurements were performed at baseline and after low‐dose, non‐intoxicating, intranasal cocaine (2 mg/kg) in 10 healthy cocaine‐naïve men (median age 32 yrs). Destruction‐refill data on MCE were fit to the equation: y = A(1‐e− βt) to quantify functional capillary blood volume (A), flux rate (β) and myocardial blood flow (MBF) (Product of A and β). Heart rate (HR), mean arterial pressure (MAP), and left ventricular (LV) work (end‐systolic elastance × HR) were measured. Validation experiments included with‐in day reproducibility, control experiments using low‐dose dobutamine, and cross‐modality experiments comparing MCE with first‐pass magnetic resonance perfusion imaging. Cocaine caused a rise (p<.05) in MAP (+14±2 mmHg), HR (+8±3 bpm), and LV work (+50±18%). Despite this significant rise in oxygen demand, MBF declined significantly (103.7±9.8 to 75.9±10.8 a.u.) due mainly to reductions in capillary blood volume (133.9±5.1 to 111.7±7.7 a.u., p<.05) with no change in feed artery flow velocity (0.8±0.1 to 0.7±0.1 a.u.). We conclude that cocaine‐induced sympathoexcitation acts at the level of the coronary microvessels, to cause a mismatch between myocardial oxygen demand and MBF.

Functional relevance of genetic variations of endothelial nitric oxide synthase and vascular endothelial growth factor in diabetic coronary microvessel dysfunction

The prevalence of type 1 diabetes (T1D) is increasing worldwide and is associated with significant microvessel complications, of which nephropathy, retinopathy and neuropathy are the most commonly studied. Although clinically evident microvascular complications of diabetes are rarely seen in childhood, early vascular abnormalities develop during childhood and accelerate during puberty. Vascular endothelial growth factor (VEGF) is a major mediator of angiogenesis, which is regulated by endothelial nitric oxide synthase (NOS3) at several levels. Together, VEGF and NOS3 play an important role in the pathogenesis of the microvascular complications of diabetes. Genetic variations in NOS3 and VEGF critically regulate endothelial survival and function and increase the susceptibility of patients to develop severe microvessel complications. Identification of the risk factors for and improved understanding of the subclinical signs of these diabetic microvascular complications will enable implementation of therapeutic strategies, potentially changing the course of vascular complications and improving the prognosis of children, adolescents and young adults with diabetes. Moreover, early detection of these variations may have a prognostic value or may suggest interventional approaches to regulate these proteins in patients with diabetes.

Why Do Nitrates Have Limited Efficacy in Coronary Microvessels?

Editorial to: Lack of nitrates on exercise stress test results in patients with microvascular angina, by G. Russo et al.

Increased Tissue Angiotensin-Converting Enzyme Activity Impairs Bradykinin-Induced Dilation of Coronary Arterioles in Obesity

Bradykinin (BK) is a key mediator regulating coronary blood flow. It is degraded by angiotensin-converting enzyme (ACE), but what is unknown is whether enhanced tissue ACE activity interferes with BK-induced coronary vasodilation in obesity. Coronary arterioles (~100 μm) were isolated from rats on a normal or high-fat diet (HFD) and from lean or obese patients undergoing heart surgery (n=74). We found that BK-induced dilation was diminished in the coronary arterioles of HFD rats, when compared with controls. When administered in vitro, the ACE inhibitor, captopril, restored the coronary dilation response to BK in HFD rats, but did not affect control responses. Abundant ACE expression was detected in coronary endothelium, which was associated with increased ACE activity in HFD arterioles, as measured by increased response to the ACE substrate, angiotensin I. Moreover, we found that in the coronary arterioles of obese patients, BK-induced dilation was augmented by in vitro captopril administration. Correspondingly, ACE activity was increased in the coronary arterioles of obese patients when compared with the non-obese. Logistic regression analysis revealed that obese patients taking ACE inhibitors prior to surgery exhibited an enhanced dilation response to BK. We demonstrated augmented tissue ACE activity in the coronary arterioles of obese subjects, which leads to reduced coronary dilation response to BK. We provide a rationale for ACE inhibitor therapy in obese patients to improve dilatation of coronary microvessels.

Preserved endothelium-dependent dilatation of the coronary microvasculature at the early phase of diabetes mellitus despite the increased oxidative stress and depressed cardiac mechanical function ex vivo

BackgroundThere has been accumulating evidence associating diabetes mellitus and cardiovascular dysfunctions. However, most of the studies are focused on the late stages of diabetes and on the function of large arteries. This study aimed at characterizing the effects of the early phase of diabetes mellitus on the cardiac and vascular function with focus on the intact coronary microvasculature and the oxidative stress involved.Materials and methodsZucker diabetic fatty rats and their lean littermates fed with standard diet A04 (Safe) were studied at the 11th week of age. Biochemical parameters such as glucose, insulin and triglycerides levels as well as their oxidative stress status were measured. Their hearts were perfused ex vivo according to Langendorff and their cardiac activity and coronary microvascular reactivity were evaluated.ResultsZucker fatty rats already exhibited a diabetic state at this age as demonstrated by the elevated levels of plasma glucose, insulin, glycated hemoglobin and triglycerides. The ex vivo perfusion of their hearts revealed a decreased cardiac mechanical function and coronary flow. This was accompanied by an increase in the overall oxidative stress of the organs. However, estimation of the active form of endothelial nitric oxide synthase and coronary reactivity indicated a preserved function of the coronary microvessels at this phase of the disease. Diabetes affected also the cardiac membrane phospholipid fatty acid composition by increasing the arachidonic acid and n-3 polyunsaturated fatty acids levels.ConclusionsThe presence of diabetes, even at its beginning, significantly increased the overall oxidative stress of the organs resulting to decreased cardiac mechanical activity ex vivo. However, adaptations were adopted at this early phase of the disease regarding the preserved coronary microvascular reactivity and the associated cardiac phospholipid composition in order to provide a certain protection to the heart.

Exaggerated myocardial oxLDL amount and LOX-1 receptor over-expression associated with coronary microvessel inflammation in unstable angina

The pathophysiological relationship between coronary atherosclerosis and coronary microvessels remains undefined and the specific causative role of oxidatively modified low density lipoprotein (oxLDL) in human atherosclerosis is debated. The purposes of this study are to investigate whether coronary microvessels are involved in coronary atherosclerosis and whether increased myocardial oxLDL amount can be associated with coronary microvessel inflammation. A combination of immunohistochemical, RT-PCR and real-time PCR studies performed on myocardial biopsy specimens from patients with mitral stenosis (control hearts, CHs) and from unstable and stable angina patients (UAP and SAP), demonstrated that myocardial oxLDL was associated with a chronic low-grade inflammation in SAP and with a severe high grade inflammation in UAP. oxLDL amount was notably higher in UAP than in SAP and in UAP the high grade of inflammation was correlated with the increased amount of oxLDL in endothelial cells and macrophages. The exaggerated amount of oxLDL in UAP and the interaction of oxLDL with lectin-like oxLDL (LOX-1) receptor are amplified by the activation of transcriptional factor octamere 1 (OCT-1) with consequent activation of a series of inflammatory endothelial feed-back mechanisms resulting in LOX-1 gene over-expression, endothelial inflammation as well as uncontrolled nuclear factor kappa B (NFkB) activation. Moreover, in UAP genes for signal transducer and activator transcriptional factor 1α (STAT1α), angiotensin converting enzyme (ACE) and numerous pro-inflammatory cytokines were over-expressed. The present results may have clinical relevance because they show that coronary atherosclerosis is a disease not confined to the large arteries but involving the whole coronary tree. In UAP the exaggerated amount of myocardial oxLDL is associated with widespread high grade microvessel inflammation.

Uridine adenosine tetraphosphate is a novel vasodilator in the coronary microcirculation which acts through purinergic P1 but not P2 receptors

Uridine adenosine tetraphosphate (Up4A) has been identified as an endothelium-derived contracting factor, which acts through purinergic P2X and P2Y receptors. Since the coronary vascular actions of Up4A are unknown, we investigated the vasoactive profile of Up4A in coronary microvessels, and studied the involvement of purinergic receptor subtypes. Studies were performed in isolated porcine coronary small arteries (diameter∼250μm), with and without endothelial denudation, mounted on a Mulvany wire myograph. Purinergic receptor expression was assessed by real-time PCR. Up4A (10−9–10−5M) failed to induce contraction at basal tone, but produced concentration-dependent vasorelaxation in precontracted microvessels. Up4A was slightly less potent than adenosine, ATP, and ADP in producing vasorelaxation, but significantly more potent than UTP and UDP. mRNA expression of P2X4, P2Y1, P2Y2, P2Y4, P2Y6 and A2A, but not P2X1, receptors was observed. Up4A-induced vasodilation was unaffected by non-selective P2 receptor antagonist PPADS, P2X1 antagonist MRS2159, P2Y1 antagonist MRS2179 and P2Y6 antagonist MRS2578, but was markedly attenuated by non-selective P1 receptor antagonist 8PT and A2A antagonist SCH58261. Up4A-induced vasodilation was not affected by ectonucleotidase inhibitor ARL67156, suggesting that A2A stimulation was not the result of Up4A breakdown to adenosine. Up4A-induced vasodilation was blunted in denuded vessels; additional A2A receptor blockade further attenuated Up4A-induced vasodilation, suggesting that A2A receptor-mediated vasodilation is only partly endothelium-dependent. In conclusion, Up4A exerts a vasodilator rather than a vasoconstrictor influence in coronary microvessels, which is mediated via A2A receptors and is partly endothelium-dependent.

Disruption of TRPV1-mediated coupling of coronary blood flow to cardiac metabolism in diabetic mice: role of nitric oxide and BK channels

We have previously shown transient receptor potential vanilloid subtype 1 (TRPV1) channel-dependent coronary function is compromised in pigs with metabolic syndrome (MetS). However, the mechanisms through which TRPV1 channels couple coronary blood flow to metabolism are not fully understood. We employed mice lacking TRPV1 [TRPV1((-/-))], db/db diabetic, and control C57BKS/J mice to determine the extent to which TRPV1 channels modulate coronary function and contribute to vascular dysfunction in diabetic cardiomyopathy. Animals were subjected to in vivo infusion of the TRPV1 agonist capsaicin to examine the hemodynamic actions of TRPV1 activation. Capsaicin (1-100 μg·kg(-1)·min(-1)) dose dependently increased coronary blood flow in control mice, which was inhibited by the TRPV1 antagonist capsazepine or the nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine methyl ester (L-NAME). In addition, the capsaicin-mediated increase in blood flow was attenuated in db/db mice. TRPV1((-/-)) mice exhibited no changes in coronary blood flow in response to capsaicin. Vasoreactivity studies in isolated pressurized mouse coronary microvessels revealed a capsaicin-dependent relaxation that was inhibited by the TRPV1 inhibitor SB366791 l-NAME and to the large conductance calcium-sensitive potassium channel (BK) inhibitors iberiotoxin and Penetrim A. Similar to in vivo responses, capsaicin-mediated relaxation was impaired in db/db mice compared with controls. Changes in pH (pH 7.4-6.0) relaxed coronary vessels contracted to the thromboxane mimetic U46619 in all three groups of mice; however, pH-mediated relaxation was blunted in vessels obtained from TRPV1((-/-)) and db/db mice compared with controls. Western blot analysis revealed decreased myocardial TRPV1 protein expression in db/db mice compared with controls. Our data reveal TRPV1 channels mediate coupling of myocardial blood flow to cardiac metabolism via a nitric oxide-dependent, BK channel-dependent pathway that is corrupted in diabetes.

Ultrastructure of coronary microvessels during heart reperfusion after prolonged ischemia under conditions of various forms of artificial hypothermia

It has been found that, in children with Roger’s disease corrected under conditions of two fundamentally different procedures of anesthetic management, myocardial reperfusion after cardiac arrest under artificial hypothermic circulation is accompanied with obstruction of more than 70% of coronary bed microvessels, one-third of them being blocked with hydropic endothelial cells or their cystiform fragments. It hampers or even totally prevents their functioning in the postoperative period. The content of necrotic cells increases, while the three “working” cell types demonstrate a decrease in myocropinocytotic transport. Circulatory arrest during perfusionless hypothermia and immersion reperfusion do not result in a dramatic change of general morphology of microvessels as compared to the control group maintaining the endothelial cell population unaltered. Ultrastructural organization of endothelial microvessels displayed no features of intracellular regeneration. However, a heterogenic response of the structures responsible for transendothelial transfer of macromolecules provides the basis for the recovery of endothelium structure and function, as a patient’s temperature reaches the standard value.