Coronary artery blood flow: physiologic and pathophysiologic regulation

Small conductance calcium-activated potassium channel contributes to stress induced endothelial dysfunctions

Patients with Takotsubo syndrome displayed endothelial dysfunction, but underlying mechanisms have not been fully clarified. This study aimed to explore molecular signalling responsible for catecholamine excess induced endothelial dysfunction. Human cardiac microvascular endothelial cells were challenged by epinephrine to mimic catecholamine excess. Patch clamp, FACS, ELISA, PCR, and immunostaining were employed for the study. Epinephrine (Epi) enhanced small conductance calcium-activated potassium channel current (ISK1-3) through activating α1 adrenoceptor. Phenylephrine enhanced edothelin-1 (ET-1) and reactive oxygen species (ROS) production, and the effects involved contribution of ISK1-3. H2O2 enhanced ISK1-3 and ET-1 production. Enhancing ISK1-3 caused a hyperpolarization, which increases ROS and ET-1 production. BAPTA partially reduced phenylephrine-induced enhancement of ET-1 and ROS, suggesting that α1 receptor activation can enhance ROS/ET-1 generation in both calcium-dependent and calcium-independent ways. The study demonstrates that high concentration catecholamine can activate SK1-3 channels through α1 receptor-ROS signalling and increase ET-1 production, facilitating vasoconstriction.

HYBRID NANOFLUID FLOWS THROUGH A VERTICAL DISEASED CORONARY ARTERY WITH HEAT TRANSFER

Gold nanoparticles (AuNPs) are now widely used because of their synthesis compatibility and less toxicity in several biomedical applications such as cancer treatment. From the fluid mechanics point of view, we examine the behavior of a mixture of gold and Titanium Oxide nanoparticles, which suspended in the blood as a base fluid in the diseased coronary artery. The main goal of this paper is to examine and shed light on the hybrid nanofluid flows through a vertical diseased artery in the presence of the catheter tube with heat transfer. The mathematical model is established and then solved with the Laplace and the finite Hankel transforms. The inverse of the transformed functions has been calculated numerically. The velocity, the pressure, the impedance and the heat transfer are discussed graphically. It is noteworthy to mention that the mixture of the nanoparticles dispersed in the blood needs high pressure to push it. The impedance of blood is proportional to the overall volume concentration of the nanoparticles and Reynolds number.

Effects of Impella on Coronary Perfusion in Patients With Critical Coronary Artery Stenosis

BACKGROUND

Mechanical circulatory support devices are used to maintain hemodynamic stability during high-risk percutaneous coronary interventions. Little is known on the effects of such devices on coronary hemodynamics in patients with significant coronary stenosis. We sought to investigate whether mechanical circulatory support in the form of Impella (Abiomed Inc, Danvers, MA) can improve coronary hemodynamics in the presence of a critical coronary stenosis.

METHODS AND RESULTS

We examined coronary perfusion pressures and coronary pressure distal to a critical stenosis using a coronary pressure wire in 11 patients (12 coronary lesions) undergoing high-risk percutaneous coronary interventions with the use of mechanical circulatory support. Systemic, ventricular, and coronary hemodynamics were obtained at both minimum and maximum support levels before high-risk percutaneous coronary interventions. All patients had obstructive lesions with angiographically estimated diameter stenosis between 70% and 99% and distal coronary artery pressure to aortic pressure ratios between 0.44 and 0.88. When compared with minimum support, maximum support resulted in a decrease in the left ventricular end-diastolic pressure (27.3±8.6 versus 21.5±5.2 mm Hg; P=0.002) and increases in the mean systemic blood pressure (77.6±13.5 versus 88.2±12.2 mm Hg; P<0.001) and mean distal coronary pressure (51.8±20.2 versus 60.8±18.1 mm Hg; P<0.001). Effective coronary perfusion pressure (mean aortic pressure-left ventricular end-diastolic pressure) significantly increased with maximum support (49.8±15.7 versus 67.2±13.6 mm Hg; P<0.001). Diastolic perfusion pressure (diastolic blood pressure-left ventricular end-diastolic pressure) also significantly increased with maximum support (32.9±13.4 versus 52.0±11.6 mm Hg; P<0.001).

CONCLUSIONS

Mechanical circulatory support with Impella can improve distal coronary pressure and coronary perfusion pressures in the presence of critical coronary stenosis.

Myocardial oxygen balance during acute normovolemic hemodilution: A novel compartmental modeling approach

BACKGROUND

Hemodilution was introduced initially as a blood conservation technique to reduce allogeneic blood transfusion in patients undergoing surgical procedures. Although the technique has been approved by the National Institute of Health consensus panel, limits of hemodilution under anesthetic conditions have not been established as they have in animal models.

METHODS

A novel multi-compartmental modeling approach has been proposed that includes the effect of anesthesia to quantify the effect of hemodilution on myocardial oxygen balance during myocardial ischemia.

RESULTS

The results showed that isovolemic hemodilution would cause detrimental effects around a hematocrit of 15%. Even though the fall in oxygen content caused by the decrease in hemoglobin concentration was compensated by an increase in coronary blood flow induced by hypoxic vasodilation and decreased viscosity, the endocardial tissue received less oxygen compared to the epicardial regions, and this sub-endocardial ischemia eventually led to cardiac failure. Statistical analysis also showed that the type of acellular replacement fluid failed to affect the heart rate, the stroke index or the cardiac index during hemodilution, and supplemental oxygen improved the endocardial oxygen supply.

CONCLUSION

The model validates the clinical conclusions that sub-endocardial ischemia causes cardiac failure under extreme hemodilution conditions and the model can also be easily integrated into other human simulators.

Effect of intracoronary adenosine on ergonovine-induced vasoconstricted coronary arteries

BACKGROUND

This study aimed to evaluate the effect of adenosine on epicardial coronary artery diameter during ergonovine provocation testing.

METHODS

A total of 158 patients who underwent an ergonovine provocation test with intracoronary adenosine injection between 2011 and 2014 were selected. Patients were divided into four groups based on the severity of percent diameter stenosis following intracoronary ergonovine administration: Group 1, induced spasm < 50%; Group 2, 50-89%; Group 3, 90-99%; and Group 4, total occlusion.

RESULTS

Spasm positivity was observed in 44 (27.8%) cases in the study population (mean age, 57.4 ± ± 10.7 years). Intracoronary adenosine increased the diameter of the ergonovine-induced epicardial artery by 0.51 ± 0.31 mm, 0.73 ± 0.39 mm, 0.44 ± 0.59 mm, and 0.01 ± 0.04 mm in Groups 1, 2, 3, and 4, respectively. Subsequent administration of nitroglycerin further increased vessel diameter by 0.49 ± 0.28 mm, 0.93 ± 0.68 mm, 2.11 ± 1.25 mm, and 2.23 ± 0.69 mm in Groups 1, 2, 3, and 4, respectively. The ratios of adenosine-induced diameter to reference diameter were significantly lower in patients with spasm positive results (0.68 [0.59-0.76] vs. 0.18 [0.00-0.41], p < 0.001 in the study population; 0.60 [0.54-0.67] vs. 0.40 [0.27-0.44], p < 0.001 in Group 2) with the best cut-off value of 0.505 (sensitivity 0.955, specificity 0.921).

CONCLUSIONS

Intracoronary administration of adenosine dilated the ergonovine-induced vasoconstricted epicardial coronary artery. The ratio of adenosine-induced diameter to reference diameter was significantly lower in patients with spasm positive results.

The Adenosine Hypothesis Revisited: Modulation of Coupling between Myocardial Perfusion and Arterial Compliance

For over four decades the thoracic aortic ring model has become one of the most widely used methods to study vascular reactivity and electromechanical coupling. A question that is rarely asked, however, is what function does a drug-mediated relaxation (or contraction) in this model serve in the intact system? The physiological significance of adenosine relaxation in rings isolated from large elastic conduit arteries from a wide range of species remains largely unknown. We propose that adenosine relaxation increases aortic compliance in acute stress states and facilitates ventricular-arterial (VA) coupling, and thereby links compliance and coronary artery perfusion to myocardial energy metabolism. In 1963 Berne argued that adenosine acts as a local negative feedback regulator between oxygen supply and demand in the heart during hypoxic/ischemic stress. The adenosine VA coupling hypothesis extends and enhances Berne's "adenosine hypothesis" from a local regulatory scheme in the heart to include conduit arterial function. In multicellular organisms, evolution may have selected adenosine, nitric oxide, and other vascular mediators, to modulate VA coupling for optimal transfer of oxygen (and nutrients) from the lung, heart, large conduit arteries, arterioles and capillaries to respiring mitochondria. Finally, a discussion of the potential clinical significance of adenosine modulation of VA coupling is extended to vascular aging and disease, including hypertension, diabetes, obesity, coronary artery disease and heart failure.

Clinical implications of hypothermic ventricular fibrillation versus beating-heart technique during cardiopulmonary bypass for pulmonary valve replacement in patients with repaired tetralogy of Fallot

OBJECTIVES

This study aimed to compare the effects of hypothermic ventricular fibrillation and beating-heart techniques during cardiopulmonary bypass (CPB) on postoperative outcomes after simple pulmonary valve replacement in patients with repaired tetralogy of Fallot (TOF).

METHODS

We retrospectively reviewed the data of 47 patients with repaired tetralogy of Fallot at a single institution, who received pulmonary valve replacement under the ventricular fibrillation or beating-heart technique without cardioplegic cardiac arrest during CPB between January 2005 and April 2015.

RESULTS

The patients were divided into fibrillation (n = 32) and beating-heart (n = 15) groups. On comparing these groups, the fibrillation group had a larger sinotubular junction (27.1 ± 4.6 vs 22.1 ± 2.4 mm), had a longer operation duration (396 ± 108 vs 345 ± 57 min), required more postoperative transfusions (2.1 ± 2.6 vs 5.0 ± 6.3 units) and had a higher vasoactive-inotropic score at intensive care unit admission (8.0 vs 10, all P < 0.05). Echocardiographic data indicated that the systolic internal diameter of the left ventricle was larger in the fibrillation group than in the beating-heart group immediately after surgery and at the 1-year follow-up. Major adverse cardiac events occurred in 3 cases, all from the fibrillation group. Among 7 patients from the fibrillation group with transoesophageal echocardiography data during CPB, 6 had fully opened aortic valves during fibrillation, causing flooding into the left ventricle and left ventricle distension.

CONCLUSIONS

The postoperative outcomes are worse with the ventricular fibrillation technique than with the beating-heart technique during CPB for pulmonary valve replacement in patients with repaired tetralogy of Fallot.

Effect of interleukin-6 inhibition on coronary microvascular and endothelial function in myocardial infarction

OBJECTIVE

Interleukin-6 (IL-6) is a driver of inflammation and associated endothelial cell activation in acute coronary syndromes. We evaluated the effect of the IL-6 receptor antagonist tocilizumab on coronary microvascular function and endothelial dysfunction measured by coronary flow reserve (CFR) and markers of endothelial cell activation in patients with non-ST-elevation myocardial infarction (NSTEMI).

METHODS

This substudy was part of a two-centre, double-blind, randomised, placebo-controlled trial evaluating the effect of a single dose of tocilizumab in NSTEMI. Markers of endothelial cell activation (vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule-1 and von Willebrand factor) were assessed in 117 patients. In 42 of these patients, 20 assigned to placebo and 22 to tocilizumab, we measured CFR. Blood samples were obtained at seven consecutive time points between day 1 and 3. CFR was measured by transthoracic echocardiography during hospitalisation and after 6 months.

RESULTS

Tocilizumab did not affect CFR during hospitalisation (tocilizumab: 3.4±0.8 vs placebo: 3.3±1.2, p=0.80). CFR improved significantly in both groups at 6 months. Patients in the tocilizumab group had significantly higher area under the curve for VCAM-1 (median 622 vs 609 ng/mL/hour, tocilizumab and placebo respectively, p=0.003). There were inverse correlations between VCAM-1 and CFR in the placebo (hospitalisation: r=-0.74, p<0.01, 6 months: r=-0.59, p<0.01), but not in the tocilizumab group (hospitalisation: r=0.20, p=0.37, 6 months r=-0.28, p=0.20).

CONCLUSIONS

Tocilizumab did not affect CFR during hospitalisation or after 6 months. Tocilizumab increased VCAM-1 levels during hospitalisation, but this was not associated with reduced CFR in these patients.

Adaptive-Outward and Maladaptive-Inward Arterial Remodeling Measured by Intravascular Ultrasound in Hyperhomocysteinemia and Diabetes

Background: Coronary artery remodeling implies structural changes in the vessel wall in response to various pathophysiologic conditions. However, the classification of remodeling is unclear. We hypothesized that the adaptive, positive-outward remodeling is a reactive and compensatory response to the stress. The maladaptive negative-inward constrictive remodeling is a passive atherosclerotic condition in which the vessel becomes stiffer.

Methods: Patients with atherosclerotic lesions underwent intravascular ultrasound (IVUS) scans. The size of the vessels distal to and proximal to plaques were analyzed by IVUS. Diabetes was created in mice by an intraperitoneal injection of alloxan (65 mg/kg). To reduce remodeling, mice received ciglitazone, an agonist of peroxisome proliferators activated receptor-g (PPARg) in drinking water. After 8 weeks, atherosclerotic vessels were analyzed for collagen and elastin.

Results: IVUS data suggest an adaptive coronary arterial remodeling was a positive compensatory response to various pathologic stimuli; for example, with the deposition of atherosclerotic plaque, coronary arterial segments enlarged to maintain luminal area. This phenomenon was commonly observed during the initial phases of the development of atherosclerosis. However, negative coronary artery remodeling, or a decrease in vessel area with the formation of atherosclerotic plaque, was maladaptive and was associated with smoking, hypertension, hyperhomocysteinemia, diabetes mellitus, and also after percutaneous coronary interventions (restenosis). In diabetic mice, there was increased collagen and decreased elastin contents; however, treatment with ciglitazone ameliorated the decrease in elastin contents.

Conclusion: Global enlargement of the coronary vascular tree occurs during pressure and volume overload associated with ventricular hypertrophic states such as athletic conditioning, hypertensive heart disease, and dilated cardiomyopathy. On the other hand, maladaptive coronary arterial remodeling occurs in patients with severe deconditioning, diabetes mellitus, after coronary artery bypass surgery, and in some instances, postintervention.

Functional Tuning of Intrinsic Endothelial Ca2+ Dynamics in Swine Coronary Arteries

RATIONALE

Recent data from mesenteric and cerebral beds have revealed spatially restricted Ca(2+) transients occurring along the vascular intima that control effector recruitment and vasodilation. Although Ca(2+) is pivotal for coronary artery endothelial function, spatial and temporal regulation of functional Ca(2+) signals in the coronary endothelium is poorly understood.

OBJECTIVE

We aimed to determine whether a discrete spatial and temporal profile of Ca(2+) dynamics underlies endothelium-dependent relaxation of swine coronary arteries.

METHODS AND RESULTS

Using confocal imaging, custom automated image analysis, and myography, we show that the swine coronary artery endothelium generates discrete basal Ca(2+) dynamics, including isolated transients and whole-cell propagating waves. These events are suppressed by depletion of internal stores or inhibition of inositol 1,4,5-trisphosphate receptors but not by inhibition of ryanodine receptors or removal of extracellular Ca(2+). In vessel rings, inhibition of specific Ca(2+)-dependent endothelial effectors, namely, small and intermediate conductance K(+) channels (K(Ca)3.1 and K(Ca)2.3) and endothelial nitric oxide synthase, produces additive tone, which is blunted by internal store depletion or inositol 1,4,5-trisphosphate receptor blockade. Stimulation of endothelial inositol 1,4,5-trisphosphate-dependent signaling with substance P causes idiosyncratic changes in dynamic Ca(2+) signal parameters (active sites, event frequency, amplitude, duration, and spatial spread). Overall, substance P-induced vasorelaxation corresponded poorly with whole-field endothelial Ca(2+) measurements but corresponded precisely with the concentration-dependent change in Ca(2+) dynamics (linearly translated composite of dynamic parameters).

CONCLUSIONS

Our findings show that endothelium-dependent control of swine coronary artery tone is determined by spatial and temporal titration of inherent endothelial Ca(2+) dynamics that are not represented by tissue-level averaged Ca(2+) changes.

Female-favorable attenuation of coronary myogenic constriction via reciprocal activations of epoxyeicosatrienoic acids and nitric oxide

Epoxyeicosatrienoic acids (EETs) are metabolites of arachidonic acid via CYP/epoxygenases, which are catabolized by soluble epoxide hydrolase (sEH) and known to possess cardioprotective properties. To date, the role of sEH in the modulation of pressure-induced myogenic response/constriction in coronary arteries, an important regulatory mechanism in the coronary circulation, and the issue as to whether the disruption of the sEH gene affects the myogenic response sex differentially have never been addressed. To this end, experiments were conducted on male (M) and female (F) wild-type (WT) and sEH-knockout (KO) mice. Pressure-diameter relationships were assessed in isolated and cannulated coronary arteries. All vessels constricted in response to increases in intraluminal pressure from 60 to 120 mmHg. Myogenic vasoconstriction was significantly attenuated, expressed as an upward shift in the pressure-diameter curve of vessels, associated with higher cardiac EETs in M-KO, F-WT, and F-KO mice compared with M-WT controls. Blockade of EETs via exposure of vessels to 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) prevented the attenuated myogenic constriction in sEH-KO mice. In the presence of 14,15-EEZE, pressure-diameter curves of females presented an upward shift from those of males, exhibiting a sex-different phenotype. Additional administration of N(ω)-nitro-l-arginine methyl ester eliminated the sex difference in myogenic responses, leading to four overlapped pressure-diameter curves. Cardiac sEH was downregulated in F-WT compared with M-WT mice, whereas expression of endothelial nitric oxide synthase and CYP4A (20-HETE synthase) was comparable among all groups. In summary, in combination with NO, the increased EET bioavailability as a function of genetic deletion and/or downregulation of sEH accounts for the female-favorable attenuation of pressure-induced vasoconstriction.

Myocardial perfusion at rest in patients with Diabetes Mellitus Type 1 compared with healthy controls assessed with Multi Detector Computed Tomography

AIM

Type 1 diabetes mellitus (T1DM) is associated with an increased risk of ischemic heart disease (IHD). The relative contribution of structural and functional abnormalities of the coronary circulation determining clinically manifested IHD remains unknown. The aim of this study was to assess potential differences in myocardial perfusion at rest and coronary atherosclerosis between asymptomatic T1DM patients and healthy controls.

METHODS

Left ventricular (LV) myocardial perfusion at rest measured as LV myocardial Attenuation Density/LV blood pool Attenuation Density (MyoAD-ratio) and coronary artery atherosclerosis were evaluated with 320-multidetector computed tomography angiography in 57 asymptomatic T1DM patients and 114 sex and age matched controls.

RESULTS

In both groups median age was 53 years (p5,p95: 42,67) and 59.6% were men. Median duration of diabetes in the T1DM group was 35 years (p5,p95: 17,49). Median coronary calcium score was higher in T1DM patients (51 vs. 2, p=0.037) compared with controls. However, a similar frequency of >50% stenosis in one or more coronary arteries was found in T1DM patients and controls (18% vs. 14%, p=0.49). LV myocardial perfusion at rest (MyoAD-ratio) was 18% higher in T1DM patients than controls (0.13 vs. 0.11, p<0.0001). This difference was noted throughout all the LV myocardial segments. In a multiple regression analysis including diabetes, sex, age, cardiovascular risk factors, heart rate, calcium score and coronary stenosis >50%, MyoAD-ratio remained significantly higher in T1DM patients (p=0.0001).

CONCLUSIONS

LV myocardial perfusion at rest is higher in T1DM patients compared with controls independent of coronary atherosclerosis and cardiovascular risk factors.

In vitro effects of sodium nitroprusside and leptin on norepinephrine-induced vasoconstriction in human internal mammary artery

Aim

The biological and pharmacological properties of vessels used in coronary artery bypass graft (CABG) surgery are as important as their mechanical properties. The aim of this study was to investigate the possible role of protein kinase C (PKC)-dependent mechanisms in leptin-induced relaxation in the human internal mammary artery (IMA).

Methods

IMA rings, obtained from patients undergoing CABG surgery, were suspended in isolated tissue baths containing Krebs-Henseleit solution, which were continuously gassed with 95% O₂ and 5% CO₂ at 37°C.

Results

The IMA rings were pre-contracted with increasing concentrations of norepinephrine (NE 10^-9–10^-4 mol/l) and the relaxation responses to sodium nitroprusside (SNP), a nitrosovasodilator, and leptin were studied in the presence and absence of a PKC inhibitor. Leptin (1 μM) caused a dose-dependent relaxation in NE pre-contracted IMA rings. Pre-treatment with a PKC inhibitor significantly attenuated this vasorelaxatory response to leptin in human isolated IMA.

Conclusion

It was found that SNP and leptin caused significant relaxation of the NE pre-contracted human IMA rings, and PKC was probably the sub-cellular mediator for this effect. Our findings may have clinical or pharmacological importance as it could be hypothesised that obese subjects who have a left IMA bypass graft would have better myocardial perfusion.

Temperature-dependent release of ATP from human erythrocytes: mechanism for the control of local tissue perfusion

Human limb muscle and skin blood flow increases significantly with elevations in temperature, possibly through physiological processes that involve temperature-sensitive regulatory mechanisms. Here we tested the hypothesis that the release of the vasodilator ATP from human erythrocytes is sensitive to physiological increases in temperature both in vitro and in vivo, and examined potential channel/transporters involved. To investigate the source of ATP release, whole blood, red blood cells (RBCs), plasma and serum were heated in vitro to 33, 36, 39 and 42°C. In vitro heating augmented plasma or ‘bathing solution’ ATP in whole blood and RBC samples, but not in either isolated plasma or serum samples. Heat-induced ATP release was blocked by niflumic acid and glibenclamide, but was not affected by inhibitors of nucleoside transport or anion exchange. Heating blood to 42°C enhanced (P < 0.05) membrane protein abundance of cystic fibrosis transmembrane conductance regulator (CFTR) in RBCs. In a parallel in vivo study in humans exposed to whole-body heating at rest and during exercise, increases in muscle temperature from 35 to 40°C correlated strongly with elevations in arterial plasma ATP (r² = 0.91; P = 0.0001), but not with femoral venous plasma ATP (r² = 0.61; P = 0.14). In vitro, however, the increase in ATP release from RBCs was similar in arterial and venous samples heated to 39°C. Our findings demonstrate that erythrocyte ATP release is sensitive to physiological increases in temperature, possibly via activation of CFTR-like channels, and suggest that temperature-dependent release of ATP from erythrocytes might be an important mechanism regulating human limb muscle and skin perfusion in conditions that alter blood and tissue temperature.

Folic acid improves acetylcholine-induced vasoconstriction of coronary vessels isolated from hyperhomocysteinemic mice: an implication to coronary vasospasm

Human atherosclerotic coronary vessels elicited vasoconstriction to acetylcholine (Ach) and revealed a phenomenon of vasospasm. Homocysteine (Hcy) levels are elevated in the atherosclerotic plaque tissue, suggesting its pathological role in endothelial damage in atherosclerotic diseases. Accordingly, we examined the role hyperhomocysteinemia in coronary endothelial dysfunction, vessel wall thickness, lumen narrowing, leading to acute/chronic coronary vasospasm. The therapeutic potential and mechanisms of folic acid (FA) using hyperhomocysteinemic cystathionine beta synthase heterozygote (CBS-/+) and wild type (CBS+/+) mice were addressed. The CBS-/+ and CBS+/+ mice were treated with or without a Hcy lowering agent FA in drinking water (0.03 g/L) for 4 weeks. The isolated mouse septum coronary artery was cannulated and pressurized at 60 mmHg. The wall thickness and lumen diameters were measured by Ion-Optic. The vessels were treated with Ach (10(-8) -10(-5)  M) and, for comparison, with non-endothelial vasodilator sodium nitroprusside (10(-5)  M). The endothelium-impaired arteries from CBC-/+ mice constricted in response to Ach and this vasoconstriction was mitigated with FA supplementation. The level of endothelial nitric oxide synthase (eNOS) was lower in coronary artery in CBS-/+ than of CBS+/+ mice. Treatment with FA increased the levels of Ach-induced NO generation in the coronary artery of CBS-/+ mice. The results suggest that Ach induced coronary vasoconstriction in CBS-/+ mice and this vasoconstriction was ameliorated by FA treatment. The mechanisms for the impairment of vascular function and therapeutic effects of FA may be related to the regulation of eNOS expression, NO availability and tissue homocysteine.

Nitric oxide and coronary vascular endothelium adaptations in hypertension

This review highlights a number of nitric oxide (NO)-related mechanisms that contribute to coronary vascular function and that are likely affected by hypertension and thus become important clinically as potential considerations in prevention, diagnosis, and treatment of coronary complications of hypertension. Coronary vascular resistance is elevated in hypertension in part due to impaired endothelium-dependent function of coronary arteries. Several lines of evidence suggest that other NO synthase isoforms and dilators other than NO may compensate for impairments in endothelial NO synthase (eNOS) to protect coronary artery function, and that NO-dependent function of coronary blood vessels depends on the position of the vessel in the vascular tree. Adaptations in NOS isoforms in the coronary circulation to hypertension are not well described so the compensatory relationship between these and eNOS in hypertensive vessels is not clear. It is important to understand potential functional consequences of these adaptations as they will impact the efficacy of treatments designed to control hypertension and coronary vascular disease. Polymorphisms of the eNOS gene result in significant associations with incidence of hypertension, although mechanistic details linking the polymorphisms with alterations in coronary vasomotor responses and adaptations to hypertension are not established. This understanding should be developed in order to better predict those individuals at the highest risk for coronary vascular complications of hypertension. Greater endothelium-dependent dilation observed in female coronary arteries is likely related to endothelial Ca(2+) control and eNOS expression and activity. In hypertension models, the coronary vasculature has not been studied extensively to establish mechanisms for sex differences in NO-dependent function. Genomic and nongenomic effects of estrogen on eNOS and direct and indirect antioxidant activities of estrogen are discussed as potential mechanisms of interest in coronary circulation that could have implications for sex- and estrogen status-dependent therapy for hypertension and coronary dysfunction. The current review identifies some important basic knowledge gaps and speculates on the potential clinical relevance of hypertension adaptations in factors regulating coronary NO function.

Vascular control in humans: focus on the coronary microcirculation

Myocardial perfusion is regulated by a variety of factors that influence arteriolar vasomotor tone. An understanding of the physiological and pathophysiological factors that modulate coronary blood flow provides the basis for the judicious use of medications for the treatment of patients with coronary artery disease. Vasomotor properties of the coronary circulation vary among species. This review highlights the results of recent studies that examine the mechanisms by which the human coronary microcirculation is regulated in normal and disease states, focusing on diabetes. Multiple pathways responsible for myogenic constriction and flow-mediated dilation in human coronary arterioles are addressed. The important role of endothelium-derived hyperpolarizing factors, their interactions in mediating dilation, as well as speculation regarding the clinical significance are emphasized. Unique properties of coronary arterioles in human vs. other species are discussed.

The imbalance between coronary reserve and wall stress explains the severity of ventricular dysfunction in hypertension

BACKGROUND

The pathophysiologic role of coronary reserve impairment in hypertensive cardiac dysfunction is still debated. Previously, we demonstrated that satisfactory coronary vasodilatation may coexist with ventricular systolic dysfunction. It is conceivable that coronary reserve might otherwise be inappropriate for enhanced myocardial oxygen demand and may thus affect cardiac performance negatively.

HYPOTHESIS

Myocardial supply-demand imbalance contributes to the severity of ventricular dysfunction in hypertension (HTN).

METHODS

Fractional shortening (%) and end-systolic stress (10(3) x dyn x cm(-2)) were determined using echocardiography, and coronary reserve was calculated using transesophageal Doppler echocardiography. Coronary reserve/stress (cm2 x dyn(-1)) was utilized as a measure of supply-demand. Groups NL (20 healthy subjects), HTN1 (15 patients, fractional shortening > or = 30), HTN2 (19 patients, 20 < or = fractional shortening < 30), and HTN3 (21 patients, fractional shortening < 20) were constituted.

RESULTS

Compared with NL and HTN1, groups HTN2 and HTN3 had significantly (p < 0.05) greater end-systolic stress (NL = 72 +/- 16, HTN1 = 72 +/- 23, HTN2 = 143 +/- 32, HTN3 = 186 +/- 70). Coronary reserve was impaired in HTN3 alone (NL = 3.5 +/- 0.6, HTN1 = 3.4 +/- 1.0, HTN2 = 3.1 +/- 1.0, HTN3 = 2.6 +/- 1.1), but coronary reserve/stress was reduced in both HTN2 and HTN3 (NL = 50 +/- 12, HTN1 = 53 +/- 21, HTN2 = 22 +/- 7, HTN3 = 15 +/- 7). Stepwise regression analysis identified diastolic internal dimension, end-systolic stress, and coronary reserve/stress as independently associated with fractional shortening.

CONCLUSION

The imbalance between supply-demand explains the severity of hypertensive cardiac dysfunction and adds information to cardiac enlargement and elevated wall stress.

Age- and endothelium-dependent changes in coronary artery reactivity to serotonin and calcium

The influence of ageing and endothelium removal on the sensitivity and contractile response of rat coronary arteries to intracellular Ca2+ ([Ca2+]i) during activation with serotonin (5-HT) and membrane depolarisation with 125 mM K+ was investigated. The sensitivity and contractile response of coronary arteries to 5-HT were significantly higher in 2-year-old than in 3-month-old rats. The receptor responsible for the 5-HT-induced contractions in coronary arteries belongs to a population of 5-HT2 receptors in both young and old rats based on the Schild plot. The resting levels of [Ca2+]i and active tension were both increased by age and endothelium removal. During depolarisation with 125 mM K+, the sensitivity to [Ca2+]i and maximal tension induced by [Ca2+]i were not affected by age or endothelium. During activation with 10 microM 5-HT, the maximal tension induced by [Ca2+]i was increased by age but not affected by endothelium, whereas the sensitivity to [Ca2+]i was increased by endothelium removal. In conclusion, ageing is associated with an increased sensitivity to 5-HT in rat coronary small arteries. The increased sensitivity to 5-HT seems to involve an augmented contractile response to [Ca 2+]i in 5-HT-activated coronary arteries and a diminished endothelial basal vasodilator function.

Prostacyclin-mediated compensatory mechanism in the coronary circulation during acute NO synthase blockade

Nitric oxide (NO) in contrast to most prostanoids, plays a major role in the maintenance of coronary arterial tone under physiological conditions. However, in case of endothelial damage or other NO-depleting situations the importance of other vasodilating mechanisms may be increased. The aim of the present study was to investigate the crosstalk between the L-arginine - NO and the prostanoid systems in isolated rat hearts. Coronary flow and cardiac dynamics were measured in a standard Langendorff perfusion system. Application of indomethacin in the perfusion media failed to change coronary flow. Administration of L-NA, however, significantly decreased coronary flow by 24.8 +/- 2.3% (p < 0.01 vs. untreated control). In the presence of indomethacin, L-NA decreased coronary flow to an even greater extent by 35.8 +/- 5.2% (p < 0.05 vs. L-NA alone). Treatment of the preparations with L-NA or indomethacin failed to change cardiac work, coapplication of both drugs together, however, decreased cardiac work by 45 +/- 11% (p < 0.05 vs. untreated control). Heart rate remained constant throughout the experimental period and did not differ significantly between the treatment groups. The prostacyclin content of the effluent from the L-NA treated hearts was significantly higher than that of controls. We conclude that in case of decreased NO levels in the coronary circulation, arterial tone is maintained by prostacyclin production.

Physiological and pathophysiological roles of ATP-sensitive K+ channels

ATP-sensitive potassium (K(ATP)) channels are present in many tissues, including pancreatic islet cells, heart, skeletal muscle, vascular smooth muscle, and brain, in which they couple the cell metabolic state to its membrane potential, playing a crucial role in various cellular functions. The K(ATP) channel is a hetero-octamer comprising two subunits: the pore-forming subunit Kir6.x (Kir6.1 or Kir6.2) and the regulatory subunit sulfonylurea receptor SUR (SUR1 or SUR2). Kir6.x belongs to the inward rectifier K(+) channel family; SUR belongs to the ATP-binding cassette protein superfamily. Heterologous expression of differing combinations of Kir6.1 or Kir6.2 and SUR1 or SUR2 variant (SUR2A or SUR2B) reconstitute different types of K(ATP) channels with distinct electrophysiological properties and nucleotide and pharmacological sensitivities corresponding to the various K(ATP) channels in native tissues. The physiological and pathophysiological roles of K(ATP) channels have been studied primarily using K(ATP) channel blockers and K(+) channel openers, but there is no direct evidence on the role of the K(ATP) channels in many important cellular responses. In addition to the analyses of naturally occurring mutations of the genes in humans, determination of the phenotypes of mice generated by genetic manipulation has been successful in clarifying the function of various gene products. Recently, various genetically engineered mice, including mice lacking K(ATP) channels (knockout mice) and mice expressing various mutant K(ATP) channels (transgenic mice), have been generated. In this review, we focus on the physiological and pathophysiological roles of K(ATP) channels learned from genetic manipulation of mice and naturally occurring mutations in humans.

Mechanical factors in the production of coronary atheromata--old thoughts and new discoveries

The role of mechanical factors and hemodynamic shear stress in the production of coronary atheromatous disease appears certain. Its propagation is influenced by a variety of genetic transformations, disease states, and biofunctional and extraneous factors. Recent research attests to the high degree of complexity of the biochemical and physiologic processes involved. It is hoped that continued research will produce results that will allow the clinician to halt or reverse the process.

Severe acute coronary spasm following intracoronary radiation for in-stent restenosis: a case report

Intracoronary radiation therapy is currently the only available treatment for the prevention of recurrence of in-stent restenosis. We report a case of severe coronary spasm after excimer laser angioplasty, balloon angioplasty, and intracoronary gamma radiation in the right coronary artery (RCA) that resulted in an acute myocardial infarction. Treatment with 600 microg of intracoronary nitroglycerin resulted in minimal improvement; therefore, diltiazem 400 microg was administered intracoronary with total resolution of the spasm, restoring normal coronary blood flow without trace of acute dissection or thrombus inside the artery.

Determinants and prognostic significance of spontaneous coronary recanalization in acute myocardial infarction

Spontaneous recanalization (SR) occurs after the onset of acute myocardial infarction (AMI), but its clinical significance in the reperfusion era remains uncertain. We evaluated the determinants and prognostic significance of SR in 196 consecutive patients with AMI who underwent primary angioplasty at our institution. The study population was divided into 2 groups according to the presence (group I, n = 44) or absence (group II, n = 152) of SR (Thrombolysis In Myocardial Infarction [TIMI] anterograde > or = 2 flow on the preintervention angiogram). The primary end point was the occurrence, within 6-weeks after AMI, of death, nonfatal reinfarction, and congestive heart failure. Baseline characteristics were similar between the 2 groups. Peak levels of creatine kinase were lower in group I than in group II (2,500 +/- 1,800 vs 4,000 +/- 2,900 U/L, respectively, p < 0.05). The rate of TIMI flow grade 3 after intervention was higher in group I than in group II (93.2% vs 79.6%, respectively, p < 0.05), and patients in group I had a faster corrected TIMI frame count than those in group II (22.7 +/- 12.4 vs 30.3 +/- 22.8, respectively, p < 0.05). Preinfarction angina (odds ratio [OR] 2.18, 95% confidence interval [CI] 1.10 to 4.33, p < 0.05), heavy thrombi (OR 0.10, 95% CI 0.01 to 0.74, p < 0.05), and good angiographic collaterals (OR 0.12, 95% CI 0.02 to 0.89, p < 0.05) were independent predictors of SR. Death, reinfarction, and severe arrhythmia were not different between the 2 groups. However, heart failure occurred more frequently in group II than in group I (15.1% vs 2.3%, respectively, p < 0.05). The primary end point was also significantly lower in group I than in group II (4.5% vs 18.4%, respectively, p < 0.05). In conclusion, SR in AMI is associated with faster coronary flow, smaller infarct size, and a better clinical outcome after primary angioplasty.

Determinants of coronary blood flow following primary angioplasty for acute myocardial infarction

The aim of this study was to evaluate determinants of coronary blood flow following primary angioplasty (PA) in acute myocardial infarction (AMI). The corrected TIMI (thrombolysis in myocardial infarction) frame count and the TIMI flow grade were used as indexes of coronary blood flow, and its determinants were examined in 115 consecutive AMI patients who underwent PA (pain onset </= 12 hr). The following were validated as univariate predictors of slower corrected TIMI frame count: a lower pressure-derived farctional collateral flow (PDCF) index (P < 0.01), poor angiographic collaterals (P < 0.01), TIMI flow 0, 1 before PA (P < 0.05), and the presence of heavy thrombi (P < 0.01). The PDCF index and the presence of heavy thrombi were independent predictors of the corrected TIMI frame count. Likewise, the PDCF index (chi(2) = 12.9; P < 0.01) and the presence of heavy thombi (chi(2) = 11.4; P < 0.01) were independent predictors of TIMI 3 flow. In conclusion, collateral flow and the presence of thrombi are major determinants of coronary blood flow after PA in AMI.