Nitric oxide is a mediator of hypoxic coronary vasodilatation. Relation to adenosine and cyclooxygenase-derived metabolites

Adenosine signaling activates ATP-sensitive K+ channels in endothelial cells and pericytes in CNS capillaries

The dense network of capillaries composed of capillary endothelial cells (cECs) and pericytes lies in close proximity to all neurons, ideally positioning it to sense neuron- and glial-derived compounds that enhance regional and global cerebral perfusion. The membrane potential (V_M) of vascular cells serves as the physiological bridge that translates brain activity into vascular function. In other beds, the ATP-sensitive K⁺ (K_ATP) channel regulates V_M in vascular smooth muscle, which is absent in the capillary network. Here, with transgenic mice that expressed a dominant-negative mutant of the pore-forming Kir6.1 subunit specifically in brain cECs or pericytes, we demonstrated that K_ATP channels were present in both cell types and robustly controlled V_M. We further showed that the signaling nucleotide adenosine acted through A_2A receptors and the Gα_s/cAMP/PKA pathway to activate capillary K_ATP channels. Moreover, K_ATP channel stimulation in vivo increased cerebral blood flow (CBF), an effect that was blunted by expression of the dominant-negative Kir6.1 mutant in either capillary cell type. These findings establish an important role for K_ATP channels in cECs and pericytes in the regulation of CBF.

Anti-Anaphylactic Activity of Isoquercitrin (Quercetin-3-O-β-d-Glucose) in the Cardiovascular System of Animals

Effects of isoquercitrin (IQ) on anaphylactic responses were examined in cardiovascular systems of experimental animals. In pithed rats, IQ at 30 and 100 mg/kg (intravenous) significantly blunted both the initial hypertensive and the ensuing hypotensive responses during anaphylaxis. Death rate and tachycardia were also significantly inhibited after the same IQ doses in these rats. In isolated guinea pig hearts, IQ infusion at 30–100 μg/mL markedly reduced anaphylaxis-related coronary flow decrease, contractile force change, and heart rate responses (both tachycardia and arrhythmia). Cardiac histamine and creatine kinase releases were similarly diminished by IQ during anaphylaxis in the isolated guinea pig hearts. In two different isolated guinea pig vasculatures, the pulmonary artery and mesenteric arterial bed, anaphylactic vasoconstriction was reduced by IQ 30 and 100 μg/mL. It was observed that IQ had a marked inhibitory effect on histamine release from rat mast cells, and this mechanism was suggested as the major anti-anaphylactic mechanism. Direct inhibition of histamine-induced muscle contraction did not seem to be relevant, but IQ treatment successfully repressed intracellular calcium influx/depletion in mast cells. Overall, this study provided evidence for the beneficial effect of IQ on cardiac anaphylaxis, thus suggesting its potential applications in the treatment and prevention of related diseases.

Reactive oxygen species as mediators of oxygen signaling during fetal-to-neonatal circulatory transition

Reactive oxygen species (ROS) are frequently seen as pathological agents of oxidative stress. However, ROS are not always deleterious and can also act as cell signaling molecules. Vascular oxygen sensing and signaling during fetal-to-neonatal circulatory transition is a remarkable example of the physiological regulatory actions of ROS. The fetal relative hypoxic environment induces hypoxic pulmonary vasoconstriction (HPV) and ductus arteriosus (DA) relaxation favoring the presence of high pulmonary vascular resistance and right-to-left ductal shunt. At birth, the increase in oxygen tension causes relaxation of pulmonary arteries (PAs) and normoxic DA vasoconstriction (NDAV), thus diverting blood flow to the lungs. Although the response to changes in oxygen tension is diametrically opposite, the mechanisms responsible for HPV and NDAV appear to be the result of a similar interaction between triggering and modulating factors that lead to an increase in cytosolic Ca²⁺ concentration and Ca²⁺ sensitization of the contractile apparatus. Growing evidence points to an increase in ROS (mitochondria- and/or NADPH-derived superoxide and/or H₂O₂), leading to inhibition of voltage-gated K⁺ channels, membrane depolarization, and activation of voltage-gated L-type Ca²⁺ channels as critical events in the signaling pathway of both HPV and NDAV. Several groups of investigators have completed this pathway adding other elements such as neutral sphingomyelinase-derived ceramide, the sarcoplasmic/endoplasmic reticulum (through ryanodine and inositol 1,4,5-trisphosphate receptors), Rho kinase-mediated Ca²⁺ sensitization, or transient receptor potential channels. The present review focus on the role of ROS as mediators of the homeostatic oxygen sensing system during fetal and neonatal life not only in the PAs and DA but also in systemic arteries.

Low guanylyl cyclase activity in Weddell seals: implications for peripheral vasoconstriction and perfusion of the brain during diving

Nitric oxide (NO) is a potent vasodilator, which improves perfusion and oxygen delivery during tissue hypoxia in terrestrial animals. The vertebrate dive response involves vasoconstriction in select tissues, which persists despite profound hypoxia. Using tissues collected from Weddell seals at necropsy, we investigated whether vasoconstriction is aided by downregulation of local hypoxia signaling mechanisms. We focused on NO-soluble guanylyl cyclase (GC)-cGMP signaling, a well-known vasodilatory transduction pathway. Seals have a lower GC protein abundance, activity, and capacity to respond to NO stimulation than do terrestrial mammals. In seal lung homogenates, GC produced less cGMP (20.1 ± 3.7 pmol·mg protein-1·min-1) than the lungs of dogs (-80 ± 144 pmol·mg protein-1·min-1 less than seals), sheep (-472 ± 96), rats (-664 ± 104) or mice (-1,160 ± 104, P < 0.0001). Amino acid sequences of the GC enzyme α-subunits differed between seals and terrestrial mammals, potentially affecting their structure and function. Vasoconstriction in diving Weddell seals is not consistent across tissues; perfusion is maintained in the brain and heart but decreased in other organs such as the kidney. A NO donor increased median GC activity 49.5-fold in the seal brain but only 27.4-fold in the kidney, consistent with the priority of cerebral perfusion during diving. Nos3 expression was high in the seal brain, which could improve NO production and vasodilatory potential. Conversely, Pde5a expression was high in the seal renal artery, which may increase cGMP breakdown and vasoconstriction in the kidney. Taken together, the results of this study suggest that alterations in the NO-cGMP pathway facilitate the diving response.

Review findings included diminished coronary flow reserve after surgery in children with congenital heart disease and inflammation

AIM

The aim of this review was to develop a deeper knowledge of the physiology of coronary blood flow and coronary flow reserve in young patients with congenital heart disease and inflammatory diseases.

METHODS

We searched for papers published in English on coronary blood flow and coronary flow reserve using the PubMed and Google search databases. This identified 42 papers extending back to 1976 and a book from 2008 (Davis et al. Microcirculation. Boston, MA: Elsevier, 2008: 161-284).

RESULTS

Our review showed that the implications of coronary blood flow and coronary flow reserve in paediatric patients with congenital heart disease and inflammatory diseases are still not fully understood. However, a key finding was that coronary flow reserve was diminished in patients with congenital heart disease and inflammation after surgery, with or without a cardiopulmonary bypass. Other findings discussed by this review relate to volume and pressure overload in acyanotic congenital heart disease, reduced myocardial perfusion and cyanotic congenital heart disease.

CONCLUSION

We still have much to discover about paediatric patients with congenital heart disease and inflammatory diseases. Understanding the pathophysiology of coronary blood flow could help the postoperative treatment of such patients.

Influence of myocardial oxygen demand on the coronary vascular response to arterial blood gas changes in humans

It remains unclear if the human coronary vasculature is inherently sensitive to changes in arterial Po₂ and Pco₂ or if coronary vascular responses are the result of concomitant increases in myocardial O₂ consumption/demand ([Formula: see text]). We hypothesized that the coronary vascular response to Po₂ and Pco₂ would be attenuated in healthy men when [Formula: see text] was attenuated with β₁-adrenergic receptor blockade. Healthy men (age: 25 ± 1 yr, n = 11) received intravenous esmolol (β₁-adrenergic receptor antagonist) or volume-matched saline in a double-blind, randomized crossover study and were exposed to poikilocapnic hypoxia, isocapnic hypoxia, and hypercapnic hypoxia. Measurements made at baseline and after 5 min of steady state at each gas manipulation included left anterior descending coronary blood velocity (LAD_V; Doppler echocardiography), heart rate, and arterial blood pressure. LAD_V values at the end of each hypoxic condition were compared between esmolol and placebo. The rate-pressure product (RPP) and left ventricular mechanical energy (ME_LV) were calculated as indexes of [Formula: see text]. All gas manipulations augmented RPP, ME_LV, and LAD_V, but only RPP and ME_LV were attenuated (4-18%) after β₁-adrenergic receptor blockade ( P < 0.05). Despite attenuated RPP and ME_LV responses, β₁-adrenergic receptor blockade did not attenuate the mean LAD_V vasodilatory response compared with placebo during poikilocapnic hypoxia (29.4 ± 2.2 vs. 27.3 ± 1.6 cm/s) and isocapnic hypoxia (29.5 ± 1.5 vs. 30.3 ± 2.2 cm/s). Hypercapnic hypoxia elicited a feedforward coronary dilation that was blocked by β₁-adrenergic receptor blockade. These results indicate a direct influence of arterial Po₂ on coronary vascular regulation that is independent of [Formula: see text]. NEW & NOTEWORTHY In humans, arterial hypoxemia led to an increase in epicardial coronary artery blood velocity. β₁-Adrenergic receptor blockade did not diminish the hypoxemic coronary response despite reduced myocardial O₂ demand. These data indicate hypoxemia can regulate coronary blood flow independent of myocardial O₂ consumption. A plateau in the mean left anterior descending coronary artery blood velocity-rate-pressure product relationship suggested β₁-adrenergic receptor-mediated, feedforward epicardial coronary artery dilation. In addition, we observed a synergistic effect of Po₂ and Pco₂ during hypercapnic hypoxia.

Cavin-1 deficiency modifies myocardial and coronary function, stretch responses and ischaemic tolerance: roles of NOS over-activity

Caveolae and associated cavin and caveolins may govern myocardial function, together with responses to mechanical and ischaemic stresses. Abnormalities in these proteins are also implicated in different cardiovascular disorders. However, specific roles of the cavin-1 protein in cardiac and coronary responses to mechanical/metabolic perturbation remain unclear. We characterised cardiovascular impacts of cavin-1 deficiency, comparing myocardial and coronary phenotypes and responses to stretch and ischaemia-reperfusion in hearts from cavin-1 ^+/+ and cavin-1 ^-/- mice. Caveolae and caveolins 1 and 3 were depleted in cavin-1 ^-/- hearts. Cardiac ejection properties in situ were modestly reduced in cavin-1 ^-/- mice. While peak contractile performance in ex vivo myocardium from cavin-1 ^-/- and cavin-1 ^+/+ mice was comparable, intrinsic beating rate, diastolic stiffness and Frank-Starling behaviour (stretch-dependent diastolic and systolic forces) were exaggerated in cavin-1 ^-/- hearts. Increases in stretch-dependent forces were countered by NOS inhibition (100 µM L-NAME), which exposed negative inotropy in cavin-1 ^-/- hearts, and were mimicked by 100 µM nitroprusside. In contrast, chronotropic differences appeared largely NOS-independent. Cavin-1 deletion also induced NOS-dependent coronary dilatation, ≥3-fold prolongation of reactive hyperaemic responses, and exaggerated pressure-dependence of coronary flow. Stretch-dependent efflux of lactate dehydrogenase and cardiac troponin I was increased and induction of brain natriuretic peptide and c-Fos inhibited in cavin-1 ^-/- hearts, while ERK1/2 phospho-activation was preserved. Post-ischaemic dysfunction and damage was also exaggerated in cavin-1 ^-/- hearts. Diverse effects of cavin-1 deletion reveal important roles in both NOS-dependent and -independent control of cardiac and coronary functions, together with governing sarcolemmal fragility and myocardial responses to stretch and ischaemia.

Regulation of Coronary Blood Flow

The heart is uniquely responsible for providing its own blood supply through the coronary circulation. Regulation of coronary blood flow is quite complex and, after over 100 years of dedicated research, is understood to be dictated through multiple mechanisms that include extravascular compressive forces (tissue pressure), coronary perfusion pressure, myogenic, local metabolic, endothelial as well as neural and hormonal influences. While each of these determinants can have profound influence over myocardial perfusion, largely through effects on end-effector ion channels, these mechanisms collectively modulate coronary vascular resistance and act to ensure that the myocardial requirements for oxygen and substrates are adequately provided by the coronary circulation. The purpose of this series of Comprehensive Physiology is to highlight current knowledge regarding the physiologic regulation of coronary blood flow, with emphasis on functional anatomy and the interplay between the physical and biological determinants of myocardial oxygen delivery. © 2017 American Physiological Society. Compr Physiol 7:321-382, 2017.

Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

Chronic pantoprazole administration and ischemia--reperfusion arrhythmias in vivo in rats--antiarrhythmic or arrhythmogenic?

BACKGROUND

The safety of all proton pump inhibitors (PPIs) in patients with intrinsic cardiac disease has not been well studied. In the present study, the effect of PPI pantoprazole on ventricular arrhythmias induced by either ischemia or ischemia-reperfusion (I/R) was studied.

METHODS

The left main coronary artery (LAD) was ligated for 30 or 10 min followed by a 30-min reperfusion in anesthetized rats. Rats were pretreated with pantoprazole (1.3 mg/kg) or vehicle by gastric gavage (daily for 3 weeks) before ligation. Serum electrolytes levels were measured by the end of the third week before coronary ligation. Lactate dehydrogenase (LDH) activity and nitric oxide (NO) concentrations were measured at the end of the ischemia and IR injury.

RESULTS

Pantoprazole caused significant hyperkalemia by the end of third week compared with vehicle-treated rats. After LAD ligation (30 min), ventricular premature contractions (VPC), ventricular tachycardia (VT) and ventricular fibrillation (VF) were recorded in rats of the vehicle ischemia group. Pantoprazole pretreatment aggravate these arrhythmias and increased mortality. A 10-min period of ischemia followed by a 30-min reperfusion induced high incidence of VT (100%) and VF (80%) in the vehicle-treated group. The group of rats administered pantoprazole had significantly lower incidence and durations of VT and VF together with reduction of mortality rate. Pantoprazole significantly reduced serum LDH activity and NO release from myocardial tissue after both ischemia and I/R injury.

CONCLUSION

Pantoprazole aggravated ischemia-induced arrhythmias but had a significant antiarrhythmic effect on I/R-induced ventricular arrhythmias.

Proposed new lymphology combined with lymphatic physiology, innate immunology, and oncology

As one of the lymphatic functions, it is well known that the transport and drainage of hydrophilic substances including plasma protein through the lymphatic system play pivotal roles in maintaining the homeostasis of the internal environment between the cells in tissues in collaboration with the exchange of the substances through the blood capillaries and venules. The physiological functions of the lymphatic system have been studied by many investigations of microcirculation, i.e., Yoffey and Courtice, Ruszunyak et al., Földie and Casley-Smigh et al., Roddie, Schmid-Schönbein et al., and Ohhashi et al. On the other hand, it is also well known that the initial clinical signs of primary diseases such as inflammation, tumors, and circulatory disorders including infarction and thrombosis appear as functional abnormalities of the internal environment in tissues. These abnormalities of the functions are strongly related to immunological defense reactions around the internal environment and abnormal actions of the transport and drainage of the lymphatic system. Taking into consideration the current inspired findings in lymphatic physiology, innate immunology, and oncology, we have proposed a new lymphology combined with new knowledge of the three above-mentioned academic fields from a defense mechanism points of view. In this review, we would like to demonstrate comprehensively our latest studies related to the possibility of establishing a new lymphology, hoping the readers will evaluate this possibility.

Short-term hypoxic vasodilation in vivo is mediated by bioactive nitric oxide metabolites, rather than free nitric oxide derived from haemoglobin-mediated nitrite reduction

Local increases in blood flow--'hypoxic vasodilation'--confer cellular protection in the face of reduced oxygen delivery. The physiological relevance of this response is well established, yet ongoing controversy surrounds its underlying mechanisms. We sought to confirm that early hypoxic vasodilation is a nitric oxide (NO)-mediated phenomenon and to study putative pathways for increased levels of NO, namely production from NO synthases, intravascular nitrite reduction, release from preformed stores and reduced deactivation by cytochrome c oxidase. Experiments were performed on spontaneously breathing, anaesthetized, male Wistar rats undergoing short-term systemic hypoxaemia, who received pharmacological inhibitors and activators of the various NO pathways. Arterial blood pressure, cardiac output, tissue oxygen tension and the circulating pool of NO metabolites (oxidation, nitrosation and nitrosylation products) were measured in plasma and erythrocytes. Hypoxaemia caused a rapid and sustained vasodilation, which was only partially reversed by non-selective NO synthase inhibition. This was associated with significantly lower plasma nitrite, and marginally elevated nitrate levels, suggestive of nitrite bioinactivation. Administration of sodium nitrite had little effect in normoxia, but produced significant vasodilation and increased nitrosylation during hypoxaemia that could not be reversed by NO scavenging. Methodological issues prevented assessment of the contribution, if any, of reduced deactivation of NO by cytochrome c oxidase. In conclusion, acute hypoxic vasodilation is an adaptive NO-mediated response conferred through bioactive metabolites rather than free NO from haemoglobin-mediated reduction of nitrite.

The key role of nitric oxide in hypoxia: hypoxic vasodilation and energy supply-demand matching

SIGNIFICANCE

A mismatch between energy supply and demand induces tissue hypoxia with the potential to cause cell death and organ failure. Whenever arterial oxygen concentration is reduced, increases in blood flow--hypoxic vasodilation--occur in an attempt to restore oxygen supply. Nitric oxide (NO) is a major signaling and effector molecule mediating the body's response to hypoxia, given its unique characteristics of vasodilation (improving blood flow and oxygen supply) and modulation of energetic metabolism (reducing oxygen consumption and promoting utilization of alternative pathways).

RECENT ADVANCES

This review covers the role of oxygen in metabolism and responses to hypoxia, the hemodynamic and metabolic effects of NO, and mechanisms underlying the involvement of NO in hypoxic vasodilation. Recent insights into NO metabolism will be discussed, including the role for dietary intake of nitrate, endogenous nitrite (NO₂⁻) reductases, and release of NO from storage pools. The processes through which NO levels are elevated during hypoxia are presented, namely, (i) increased synthesis from NO synthases, increased reduction of NO₂⁻ to NO by heme- or pterin-based enzymes and increased release from NO stores, and (ii) reduced deactivation by mitochondrial cytochrome c oxidase.

CRITICAL ISSUES

Several reviews covered modulation of energetic metabolism by NO, while here we highlight the crucial role NO plays in achieving cardiocirculatory homeostasis during acute hypoxia through both vasodilation and metabolic suppression.

FUTURE DIRECTIONS

We identify a key position for NO in the body's adaptation to an acute energy supply-demand mismatch.

Cardiac MR imaging to measure myocardial blood flow response to the cold pressor test in healthy smokers and nonsmokers

PURPOSE

To determine if myocardial perfusion cardiac magnetic resonance (MR) imaging can show changes in myocardial blood flow (MBF) during the cold pressor test (CPT) and can allow identification of the differing endothelial function of smokers and nonsmokers when compared during adenosine stress.

MATERIALS AND METHODS

The study was approved by the institutional ethics review board and all participants gave informed written consent. Twenty-nine healthy volunteers (19 nonsmokers, 10 smokers; mean age ± standard deviation, 22 years ± 4) underwent 1.5-T MR imaging and analysis. Myocardial perfusion was assessed during rest, peak CPT, and adenosine hyperemia with a saturation-recovery gradient-echo pulse sequence (spatial resolution, 2.4 × 2.4 × 10 mm). Global, endocardial, and epicardial MBF were calculated by using Fermi-constrained deconvolution. Paired and independent t test statistical analyses were used to compare the responses between tests and groups. Regression analysis was performed to identify predictors of MBF change.

RESULTS

MBF at rest was similar between the nonsmoking and smoking groups (0.97 mL/g/min ± 0.4 vs 0.96 mL/g/min ± 0.3, respectively; P = .96). Nonsmokers responded to CPT with a 47% increase in MBF (1.43 mL/g/min ± 0.5) and smokers responded with a 27% increase (1.22 mL/g/min ± 0.4; P < .001). An endocardial-to-epicardial gradient existed at rest (nonsmokers, 1.10 [P = .002]; smokers, 1.30 [P = .01]) and CPT (nonsmokers, 1.19 [P < .001] smokers, 1.28 [P = .04]) but reversed during adenosine stress (nonsmokers, 0.89 [P = .03]; smokers, 0.92 [P = .42]).

CONCLUSION

Myocardial perfusion cardiac MR imaging during CPT can allow assessment of changes in MBF globally and in the separate myocardial layers in healthy smokers and nonsmokers. This allows the combined assessment of endothelium-dependent (CPT) and endothelium-independent (adenosine stress test) MBF reserve in a single study.

Assessment of vascular reactivity in the peripheral and coronary arteries by Cine 3T-magnetic resonance imaging in young normotensive adults after surgery for coarctation of the aorta

This study aimed to investigate whether coarctation of the aorta in infancy indicates an altered vascular reactivity in the peripheral and coronary arteries apart from the secondary effect of hypertension or other complications of the disease. Patients with repaired coarctation of the aorta have a high prevalence of premature cardiovascular complications. The etiology still is not fully understood, and the cause is most likely multifactorial. Endothelial function was assessed by peripheral flow mediated dilation (FMD) and coronary flow reserve (CFR) in a study of 10 control subjects and 10 patients with a successfully repaired coarctation of the aorta (mean age, 20.9 years; 20.5 years after repair). No one had re- or rest-coarctation of the aorta, hypertension, pathologic blood pressure response during exercise, or associated cardiac malformations such as bicuspid aortic valve. CFR was achieved by phase-contrast velocity encoding cine magnetic resonance imaging in the coronary sinus before and during infusion with adenosine (0.14 mg/kg/min). FMD was measured in the brachial artery before and after 5 min of arterial occlusion. A normal CFR and FMD was found in both groups. Most studies have been conducted with large, unselected groups. The current study group represented the best outcome of the coarctation spectrum (i.e., patients with no evidence of a residual gradient across the coarctation site or systemic hypertension). The findings reassuringly suggest that significant endothelial dysfunction and atherosclerotic changes were not present in this selected cohort.

Effects of L-NAME on coronary blood flow, infarct size and the extent of the no-reflow phenomenon

BACKGROUND

NOS inhibitors are a potential treatment for patients with cardiogenic shock during acute myocardial infarction. Despite hemodynamic efficacy, their effects on the extent of myocardial infarction (MI) and the no-reflow phenomenon (NRP) have not been clarified.

METHODS

Sixteen pigs underwent occlusion of the mid left anterior descending coronary artery for 1h followed by reperfusion for 2h. Coronary blood flow (CBF), distal to the occlusion site, was measured. In eight experiments, L-NAME (non selective NO synthetase inhibitor) administration began 10 min before the onset of reperfusion and continued for 2h (loading dose 1mg/kg, perfusion rate: 1mg/kg/h) (L-NAME group). Eight pigs received similarly normal saline (controls). At the end of each experiment, the myocardial area at risk (MAR) and extent of MI and NRP were measured.

RESULTS

Hemodynamics at baseline and during ischemia were similar in both groups. During reperfusion, the mean aortic blood pressure was significantly higher in the l-NAME group. In both groups, CBF reached a peak at 5 min of reperfusion, (no difference between groups). CBF gradually returned to baseline levels within 60 min of reperfusion in both groups. No statistically significant differences in the extent of the NRP (51.8 ± 19.7 vs 60.9 ± 11.4 p=0.35) and MI (77.9 ± 13.9 vs 77.1 ± 8.8 p=0.92), both expressed as a percentage of MAR, were observed between the L-NAME group and the control group.

CONCLUSIONS

L-NAME administration started immediately before and maintained throughout reperfusion has no effect on NRP and MI size. L-NAME might stabilize patients with post-MI cardiogenic shock without adverse effects on infarct size.

The optimal measure of microvascular function with velocity time integral for cardiovascular risk prediction

Recent evidence suggests that microvascular function may be important in cardiovascular risk prediction. One measure of microvascular function is hyperaemic velocity time integral (VTI). We assessed whether the VTI of more than one beat of reactive hyperaemia would provide a stronger correlate to traditional cardiovascular risk factors using a subset of subjects from the Firefighters and Their Endothelium (FATE) study. Vascular function was assessed by measurement of hyperaemic blood velocity with high-resolution ultrasound of the brachial artery. We evaluated three measures in the current analysis: the VTI of the first beat, average VTI of 10 beats, and maximum VTI of 10 beats post-cuff release. A total of 399 male subjects (45.5 ± 10 years) were included in this analysis. Univariate correlations between the three end points and cardiovascular risk factors were calculated, and multivariable regression models constructed. Intra-observer variability was approximately equal for all VTI end points (coefficient of variation: first = 1.6%, average = 1.4%, maximum = 1.4%). Univariate correlations between VTI and cardiovascular risk factors were similar across all three end points. In multivariable analyses, there were no differences in the relationships between cardiovascular risk factors and the various VTI end points ( R2 from 0.090 to 0.102). Age, systolic blood pressure, and BMI were predictors of the three VTI end points ( p < 0.05). In conclusion, the first beat of reactive hyperaemia remains the suitable measure of microvascular function.

Synthesis and characterization of functional elastomeric poly(ester amide) co-polymers

A new family of random co-poly(ester amides)s (co-PEAs) having reactive pendant functional carboxylic acid groups were synthesized by co-polycondensation of di-p-toluenesulfonic acid salts of bis-(L-alpha-amino acid (L-leucine and/or L-phenylalanine)) alpha,omega-alkylene diesters with active diesters of dicarboxylic acids using di-p-toluenesulfonic acid salt of L-lysine benzyl ester as a co-monomer. The lateral benzyl ester groups in the L-lysine segment of co-PEAs were subsequently transformed into free COOH groups by catalytic hydrogenolysis using Pd black as a catalyst. The co-PEA-based polyacids obtained, as well as the original co-PEA having lateral benzyl ester groups were characterized by standard methods. In vitro biodegradation studies in the presence of hydrolases like alpha-chymotrypsin and lipase showed significant enzymatic-catalyzed biodegradation of these co-PEAs. These co-PEA-based polyacids were used for covalent attachment of iminoxyl radicals (4-amino-TEMPO) and in vitro biodegradation of 4-aminoTEMPO attached polymer was studied along with releasing kinetic of iminoxyl radical.

Pathophysiology of coronary blood flow in congenital heart disease

OBJECTIVES

The aim was to investigate the effects of volume and pressure overload and increased coronary perfusion pressure on coronary flow (CF) in congenital heart disease (CHD) patients.

BACKGROUND

The effects of CHD on CF are poorly mapped.

METHODS

A total of 65 patients with acyanotic CHD and 49 age-matched healthy controls were examined by transthoracic Doppler echocardiography. Posterior descending artery flow was measured in patients with pulmonary valve stenosis (PS) and atrial septal defects (ASDs) i.e. in lesions with right ventricular pressure or volume overload, and left anterior descending artery flow in patients with coarctation of the aorta (CoA) and ventricular septal defect (VSD), in lesions with left ventricular pressure or volume overload. The CF data in each patient group were expressed as the percent of the median for healthy controls from the same age group.

RESULTS

The CF values were in VSD 172%, ASD 185%, PS 233%, and CoA 773% patients. In CoA patients body surface area (r=0.90, p<0.0001), systolic blood pressure (r=0.72, p<0.0001), diastolic blood pressure (r=0.77, p<0.0001), systolic wall tension (r=-0.77, p=0.004), and signs of inflammation (log CRP, r=-0.75, p=0.007) correlated with CF.

CONCLUSIONS

The increase in CF and velocity was most significant in patients with CoA. In newborns, increased coronary perfusion pressure seems to be the most important factor for increased CF, even if the pressure is not assumed to cause a significant increase in flow over the auto-regulatory range of 70-130mmHg. We also showed that inflammation decreases CF.

Hypoxic relaxation of penile arteries: involvement of endothelial nitric oxide and modulation by reactive oxygen species

Although obesity-related cardiovascular disease and hypoxia are associated with erectile dysfunction, little is known about the direct effects of hypoxia on penile arteries. In the present study, the effects of acute hypoxia (Po(2) = approximately 10 Torr, 20 min) were investigated in isolated penile arteries to determine the influence of endothelium removal, nitric oxide (NO) synthase (NOS), cyclooxygenase (COX), NADPH oxidase, changes in reactive oxygen species (ROS), and a high-fat diet. Hypoxia-relaxed penile arteries contracted with phenylephrine by approximately 50%. Relaxation to hypoxia and acetylcholine was reduced by endothelium removal and by inhibition of NOS (N(omega)-nitro-l-arginine) and COX (indomethacin) but was enhanced by Tempol and by NADPH oxidase inhibition with apocynin and gp91ds-tat. Basal superoxide levels detected by lucigenin chemiluminescence were reduced by Tempol and gp91ds-tat and were enhanced by NOS blockade. Hypoxic relaxant responses were enhanced by catalase and ebselen. Exogenous peroxide evoked relaxations of penile arteries, which were partially inhibited by endothelium removal and by the inhibition of COX and extracellular signal-regulated mitogen-activated protein kinase (MAPK) but enhanced by p38 MAPK blockade. The NO-dependent component of relaxation to hypoxia was impaired in penile arteries from high-fat diet-fed, obese rats associated with increased superoxide production. Thus hypoxic relaxation of penile arteries is partially mediated by endothelial NO in a manner that is normally attenuated by endogenous ROS production. Obesity further increases superoxide production and impairs the influence of NO. Therefore, cardiovascular disease involving decreased NO bioavailability and/or enhanced ROS generation may contribute to erectile dysfunction through impairing the relaxation of penile arteries to hypoxia.

Mitochondrial-derived hydrogen peroxide inhibits relaxation of bovine coronary arterial smooth muscle to hypoxia through stimulation of ERK MAP kinase

Mitochondrial reactive oxygen species (ROS) are potentially important in vascular oxygen-sensing mechanisms because hypoxia appears to be a stimulus for mitochondrial ROS generation; however, scavenging of endogenous ROS does not alter relaxation of endothelium-denuded bovine coronary arteries (BCA) to hypoxia. The purpose of this study was to investigate the influence of increasing mitochondrial ROS on the relaxation of BCA to hypoxia. Increasing mitochondrial superoxide with inhibitors of electron transport (10 microM rotenone and antimycin) and by opening mitochondrial ATP-dependent K+ channels with 100 microM diazoxide were observed in this study to attenuate relaxation of BCA precontracted with 30 mM KCl to hypoxia by 68-76% and 38%, respectively. This effect of rotenone is not prevented by inhibiting NADPH oxidase (Nox) activation or scavenging superoxide with Peg-SOD; however, it is reversed 85% and 26% by increasing the consumption of intracellular peroxide by 0.1 mM ebselen and 32.5 U/ml Peg-catalase. Because inhibition of extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase (10 microM PD-98059), but not src kinase or rho kinase, also reverses the effects of rotenone by 69%, the peroxide-elicited force-enhancing effects of ERK appear to be attenuating the response to hypoxia. Rotenone increased the phosphorylation of ERK (by 163%). Activation of ERK in BCA with 0.1 mM peroxide or endogenous peroxide generated by stimulating Nox2 with a stretch treatment or contraction with 100 nM U-46619 also attenuated relaxation to hypoxia. Thus coronary arterial relaxation to hypoxia may be attenuated by pathophysiological conditions associated with increased peroxide generation by mitochondria or other sources that stimulate ERK.

NOS inhibition blunts and delays the compensatory dilation in hypoperfused contracting human muscles

We previously demonstrated that skeletal muscle blood flow is restored in the exercising forearm during experimental hypoperfusion via local dilator and/or myogenic mechanisms. This study examined the role of nitric oxide (NO) in the restoration of blood flow to the active muscles during hypoperfusion. Eleven healthy subjects (10 men/1 woman; 25 +/- 1 yr of age) performed rhythmic forearm exercise (10% and 20% of maximum) while hypoperfusion was evoked by balloon inflation in the brachial artery above the elbow. Each trial included baseline, exercise, exercise with inflation, and exercise after deflation (3 min each). Forearm blood flow (FBF; ultrasound) and local (brachial artery catheter pressure, BAP) and systemic arterial pressure [mean arterial pressure (MAP); Finometer] were measured. The exercise bouts were repeated during N(G)-monomethyl-L-arginine (L-NMMA) infusion (NO synthase inhibition). Forearm vascular conductance (FVC; ml x min(-1) x 100 mmHg(-1)) was calculated from BF (ml/min) and BAP (mmHg). FBF and FVC fell acutely with balloon inflation during all trials (P < 0.01). Recovery of FBF and FVC [(inflation - nadir)/(steady-state exercise - nadir)] with L-NMMA administration was reduced during 20% exercise (FBF = 77 +/- 7% vs. 88 +/- 8%; FVC = 71 +/- 8% vs. 90 +/- 9%; P < 0.01) but not 10% exercise (FBF = 83 +/- 4% vs. 81 +/- 5%, P = 0.37; FVC = 75 +/- 10% vs. 76 +/- 7%; P = 0.44) compared with the respective control trial. The time to steady-state vasodilator response was substantially longer during the l-NMMA trials (10% = 74 +/- 4 s vs. 61 +/- 6 s; 20% = 53 +/- 4 s vs. 41 +/- 4 s; P < 0.05). Thus the magnitude and timing of the NO contribution to compensatory dilation during forearm exercise with hypoperfusion was dependent on exercise intensity. These observations suggest that NO is released by contracting muscles or that a portion of the dilation caused by ischemic metabolites is NO dependent.

Coronary blood flow responses to physiological stress in humans

Animal reports suggest that reflex activation of cardiac sympathetic nerves can evoke coronary vasoconstriction. Conversely, physiological stress may induce coronary vasodilation to meet an increased metabolic demand. Whether the sympathetic nervous system can modulate coronary vasomotor tone in response to stress in humans is unclear. Coronary blood velocity (CBV), an index of coronary blood flow, can be measured in humans by noninvasive duplex ultrasound. We studied 11 healthy volunteers and measured beat-by-beat changes in CBV, blood pressure, and heart rate during 1) static handgrip for 20 s at 10% and 70% of maximal voluntary contraction; 2) lower body negative pressure at -10 and -30 mmHg for 3 min each; 3) cold pressor test for 90 s; and 4) hypoxia (10% O(2)), hyperoxia (100% O(2)), and hypercapnia (5% CO(2)) for 5 min each. At the higher level of handgrip, mean blood pressure increased (P < 0.001), whereas CBV did not change [P = not significant (NS)]. In addition, during lower body negative pressure, CBV decreased (P < 0.02; and P < 0.01, for -10 and -30 mmHg, respectively), whereas blood pressure did not change (P = NS). The dissociation between the responses of CBV and blood pressure to handgrip and lower body negative pressure is consistent with coronary vasoconstriction. During hypoxia, CBV increased (P < 0.02) and decreased during hyperoxia (P < 0.01), although blood pressure did not change (P = NS), suggesting coronary vasodilation during hypoxia and vasoconstriction during hyperoxia. In contrast, concordant increases in CBV and blood pressure were noted during the cold pressor test, and hypercapnia had no effects on either parameter. Thus the physiological stress known to be associated with sympathetic activation can produce coronary vasoconstriction in humans. Contrasting responses were noted during systemic hypoxia and hyperoxia where mechanisms independent of autonomic influences appear to dominate the vascular end-organ effects.

Adaptative modifications of right coronary myocytes voltage-gated K+ currents in rat with hypoxic pulmonary hypertension

Chronic hypoxia (CH)-induced pulmonary hypertension (PHT) is well known to alter K+ channels in pulmonary myocytes. PHT induces right ventricle hypertrophy that increases oxygen demand; however, coronary blood flow and K+ channel adaptations of coronary myocytes during PHT remain unknown. We determined whether CH and PHT altered K+ currents and coronary reactivity and what impact they might have on right myocardial perfusion. Right ventricle perfusion, as attested by microspheres, was redistributed toward hypertrophied right ventricle [RV/LV (%)=0.59+/-0.07% in CH rats vs. 0.29+/-0.03 in control rats, P<0.05]. Whole-cell patch clamping showed a reduction of global outward current in hypoxic right coronary artery myocytes (H-RCA), whereas hypoxic left coronary artery myocytes exhibited an increase. K+ channel blockers revealed that a 4-aminopyridine (4AP)-sensitive current (Kv current) was decreased in H-RCA (14.3+/-1.1 vs. 23.4+/-2.5 pA/pF at 60 mV in control RCA, P<0.05) and increased in hypoxic left coronary artery myocytes (H-LCA; 26.4+/-3.8 vs. 11.8+/-1.6 pA/pF at 60 mV in control LCA, P<0.05). Constriction to 4AP was decreased in H-RCA when compared to normoxic control and increased in H-LCA when compared to LCA. Finally, we observed that the expression of Kv1.2 and Kv1.5 were lower in H-RCA than that in H-LCA. This study reveals that CH differentially regulates Kv channels in coronary myocytes. Hypoxia decreases Kv currents and therefore reduces vasoreactivity that contributes to an adaptative response leading to right hypertrophied ventricle perfusion enhancement at rest.

Regulation of Coronary Blood Flow During Exercise

Exercise is the most important physiological stimulus for increased myocardial oxygen demand. The requirement of exercising muscle for increased blood flow necessitates an increase in cardiac output that results in increases in the three main determinants of myocardial oxygen demand: heart rate, myocardial contractility, and ventricular work. The approximately sixfold increase in oxygen demands of the left ventricle during heavy exercise is met principally by augmenting coronary blood flow (∼5-fold), as hemoglobin concentration and oxygen extraction (which is already 70–80% at rest) increase only modestly in most species. In contrast, in the right ventricle, oxygen extraction is lower at rest and increases substantially during exercise, similar to skeletal muscle, suggesting fundamental differences in blood flow regulation between these two cardiac chambers. The increase in heart rate also increases the relative time spent in systole, thereby increasing the net extravascular compressive forces acting on the microvasculature within the wall of the left ventricle, in particular in its subendocardial layers. Hence, appropriate adjustment of coronary vascular resistance is critical for the cardiac response to exercise. Coronary resistance vessel tone results from the culmination of myriad vasodilator and vasoconstrictors influences, including neurohormones and endothelial and myocardial factors. Unraveling of the integrative mechanisms controlling coronary vasodilation in response to exercise has been difficult, in part due to the redundancies in coronary vasomotor control and differences between animal species. Exercise training is associated with adaptations in the coronary microvasculature including increased arteriolar densities and/or diameters, which provide a morphometric basis for the observed increase in peak coronary blood flow rates in exercise-trained animals. In larger animals trained by treadmill exercise, the formation of new capillaries maintains capillary density at a level commensurate with the degree of exercise-induced physiological myocardial hypertrophy. Nevertheless, training alters the distribution of coronary vascular resistance so that more capillaries are recruited, resulting in an increase in the permeability-surface area product without a change in capillary numerical density. Maintenance of α- and ß-adrenergic tone in the presence of lower circulating catecholamine levels appears to be due to increased receptor responsiveness to adrenergic stimulation. Exercise training also alters local control of coronary resistance vessels. Thus arterioles exhibit increased myogenic tone, likely due to a calcium-dependent protein kinase C signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, training augments endothelium-dependent vasodilation throughout the coronary microcirculation. This enhanced responsiveness appears to result principally from an increased expression of nitric oxide (NO) synthase. Finally, physical conditioning decreases extravascular compressive forces at rest and at comparable levels of exercise, mainly because of a decrease in heart rate. Impedance to coronary inflow due to an epicardial coronary artery stenosis results in marked redistribution of myocardial blood flow during exercise away from the subendocardium towards the subepicardium. However, in contrast to the traditional view that myocardial ischemia causes maximal microvascular dilation, more recent studies have shown that the coronary microvessels retain some degree of vasodilator reserve during exercise-induced ischemia and remain responsive to vasoconstrictor stimuli. These observations have required reassessment of the principal sites of resistance to blood flow in the microcirculation. A significant fraction of resistance is located in small arteries that are outside the metabolic control of the myocardium but are sensitive to shear and nitrovasodilators. The coronary collateral system embodies a dynamic network of interarterial vessels that can undergo both long- and short-term adjustments that can modulate blood flow to the dependent myocardium. Long-term adjustments including recruitment and growth of collateral vessels in response to arterial occlusion are time dependent and determine the maximum blood flow rates available to the collateral-dependent vascular bed during exercise. Rapid short-term adjustments result from active vasomotor activity of the collateral vessels. Mature coronary collateral vessels are responsive to vasodilators such as nitroglycerin and atrial natriuretic peptide, and to vasoconstrictors such as vasopressin, angiotensin II, and the platelet products serotonin and thromboxane A2. During exercise, ß-adrenergic activity and endothelium-derived NO and prostanoids exert vasodilator influences on coronary collateral vessels. Importantly, alterations in collateral vasomotor tone, e.g., by exogenous vasopressin, inhibition of endogenous NO or prostanoid production, or increasing local adenosine production can modify collateral conductance, thereby influencing the blood supply to the dependent myocardium. In addition, vasomotor activity in the resistance vessels of the collateral perfused vascular bed can influence the volume and distribution of blood flow within the collateral zone. Finally, there is evidence that vasomotor control of resistance vessels in the normally perfused regions of collateralized hearts is altered, indicating that the vascular adaptations in hearts with a flow-limiting coronary obstruction occur at a global as well as a regional level. Exercise training does not stimulate growth of coronary collateral vessels in the normal heart. However, if exercise produces ischemia, which would be absent or minimal under resting conditions, there is evidence that collateral growth can be enhanced. In addition to ischemia, the pressure gradient between vascular beds, which is a determinant of the flow rate and therefore the shear stress on the collateral vessel endothelium, may also be important in stimulating growth of collateral vessels.

Hyperoxia reduces basal release of nitric oxide and contracts porcine coronary arteries

AIM

The purpose of the present study was to investigate whether changes in nitric oxide (NO) concentration is involved in hyperoxia-induced vasoconstriction in porcine conduit coronary arteries.

METHODS

The effect of hyperoxia on NO release and vasoconstriction was evaluated by tension recording, microsensor measurements, and immunoblotting in porcine conduit coronary arteries contracted with U46619 or 5-hydroxytryptamine.

RESULTS

In endothelium-intact segments exchanging 20% O2, 5% CO2, 75% N2 (normoxia) for 95% O2, 5% CO2 (hyperoxia) increased contraction. In segments without endothelium hyperoxia-evoked contraction was abolished, but restored by an encircling donor segment with endothelium. An inhibitor of NOS, asymmetric dimethylarginine (ADMA, 300 mum), reduced hyperoxic contraction and basal NO concentration by, respectively, 38 +/- 12% and 46 +/- 3% (P < 0.05, n = 9). A NO donor, S-nitroso-N-acetylpenicillamine (SNAP), increased NO concentration and evoked relaxation to the same levels in normoxic and hyperoxic conditions. beta-actin and endothelial NO synthase (eNOS) protein expression was similar in normoxic and hyperoxic arterial segments. Phosphorylation of eNOS was unaltered in normoxia vs. hyperoxia, but phosphorylation of eNOS-Ser(1177) was increased and phosphorylation of eNOS-Thr(495) decreased by U46619. Blockers of ATP-sensitive, voltage-dependent and calcium-activated K+ channels did not change hyperoxic contraction. However, high extracellular K+ concentration or a second and third exposure to hyperoxia decreased contraction.

CONCLUSION

The present study provides direct evidence that hyperoxia reduces basal release of NO leading to depletable endothelium-dependent vasoconstriction in porcine coronary arteries independent of changes in eNOS phosphorylation.

Adenosine and hypoxic dilation of rat coronary small arteries: roles of the ATP-sensitive potassium channel, endothelium, and nitric oxide

The aims of the study were to examine the roles of the ATP-sensitive potassium (KATP) channel, the endothelium, and nitric oxide (NO) in the responses of rat coronary small arteries to adenosine and hypoxia. Segments of rat coronary vessel were investigated in vitro using pressure myography; all vessels studied developed stable spontaneous myogenic tone during equilibration. Glibenclamide (a KATP channel inhibitor) reversed pinacidil but not 2-deoxyglucose-induced dilation. Both adenosine and hypoxia dilated the vessels, and glibenclamide did not reverse these responses. Endothelial removal or NG-nitro-l-arginine methyl ester (l-NAME) inhibited the dilation to adenosine by ∼50%; subsequent addition of glibenclamide was without effect. Hypoxic dilation was completely inhibited by endothelium removal or l-NAME. We conclude that adenosine- and hypoxia-induced dilation of rat coronary arteries does not appear to involve the KATP channel. Adenosine-induced dilation is partially and hypoxic dilation is completely dependent on endothelium-derived NO.

Hypoxia promotes relaxation of bovine coronary arteries through lowering cytosolic NADPH

Hypoxia relaxes endothelium-denuded bovine coronary arteries (BCA) through mechanisms that do not appear to involve reactive oxygen species, prostaglandins, or nitric oxide. Because of similarities in the relaxation of BCA to hypoxia (Po(2) = 8-10 Torr) and inhibitors of the pentose phosphate pathway (PPP) including 6-aminonicotinamide and epiandrosterone, we measured NADPH and NADP and found that hypoxia caused NADPH oxidation (decreased NADPH/NADP). The relaxation to hypoxia was similar to previously reported properties of relaxation to PPP inhibitors in that both responses were associated with glutathione oxidation and depressed intracellular calcium release and calcium influx-mediated contractile responses. Inhibitors of potassium channels had minimal effects on these relaxation responses. Relaxation to hypoxia and PPP inhibitors were attenuated by a thiol reductant (3 mM dithiothreitol) and by eliciting contraction with an activator of protein kinase C (phorbol 12,13-dibutyrate). In the presence of contraction to U-46619, relaxation to hypoxia and PPP inhibitors were attenuated by the sarco(endo)plasmic reticulum Ca(2+)-ATPase pump inhibitor 200 microM cyclopiazonic acid and by 10 mM pyruvate. Hypoxia decreased BCA levels of glucose-6-phosphate but not ATP. Pyruvate prevented the hypoxia-elicited decrease in glucose-6-phosphate and glutathione oxidation, and it increased NADPH levels under hypoxia to levels observed under normoxia. Thus hypoxia causes a metabolic stress on the PPP that promotes BCA relaxation through processes controlled by lowering the levels of cytosolic NADPH.

Caffeic acid phenethyl ester ameliorates cerebral infarction in rats subjected to focal cerebral ischemia

The effects of caffeic acid phenethyl ester (CAPE), an antioxidant derived from propolis, on the infarct volume elicited by focal cerebral ischemia were studied on Long-Evans rats. Cerebral infarction was induced by microsurgical procedures with ligation of the right middle cerebral artery (MCA) and clipping of bilateral common carotid arteries (CCA) for 60 min. The rats were sacrificed 24 h later and serial brain slices of 2 mm thickness were taken and stained for the measurement of infarct area. CAPE was administered intravenously 15 min before MCA occlusion. Pretreatment of CAPE (0.1, 1 and 10 microg/kg) significantly reduced the total infarct volume from 169.6 +/- 14.5 mm3 (control) to 61.0 +/- 24.1 mm3 (0.1 microg/kg CAPE), 47.4 +/- 9.1 mm3 (1 microg/kg CAPE), and 42.4 +/- 8.7 mm3 (10 microg/kg CAPE), respectively. Plasma nitric oxide (NO) content was significantly increased in rats subjected to focal cerebral ischemia. It is concluded that CAPE possesses neuroprotective properties in focal cerebral ischemia injury in rats possibly through its antioxidant effect and/or via the upregulation of NO production.

Antiarrhythmic effect of caffeic acid phenethyl ester (CAPE) on myocardial ischemia/reperfusion injury in rats

OBJECTIVES

The present study was designed to determine the antiarrhythmic effect of caffeic acid phenethyl ester (CAPE), an active component of propolis, which exhibits antioxidant properties, in rats subjected to myocardial ischemia and ischemia-reperfusion (I/R) injury.

DESIGN AND METHODS

Rats were subjected to 30 min coronary artery occlusion for evaluating the effect of CAPE on the myocardial ischemia injury. While in the myocardial I/R injury study, the coronary artery was ligated for a 5-min period of ischemia followed by a 30-min period of reperfusion. Animals were pretreated with or without CAPE before coronary artery ligation and the severity of myocardial ischemia- and I/R-induced arrhythmias and mortality were compared.

RESULTS

Pretreatment of CAPE (0.1 and 1 microg/kg) not only reduced both the incidence and duration of ventricular tachycardia (VT) and ventricular fibrillation (VF) but also decreased the mortality during the myocardial ischemia and I/R injury period.

CONCLUSIONS

Our results suggest that CAPE is a potent antiarrhythmic agent with cardioprotective effects in myocardial ischemia and I/R injury rats.

Role of nitric oxide in the control of coronary resistance in teleosts

In mammals, the in vivo coronary blood flow and myocardial oxygen consumption are closely related via changes in coronary resistance in response to the metabolic demands of the myocardium. A fine neurohumoral regulation of coronary resistance holds true also in fish, and particularly in teleosts, where several vasoconstrictive and vasodilative mechanisms have been described, with numerous putative effectors, including prostanoids, acetylcholine, adrenaline, serotonin, adenosine, steroid hormones. Here, a resume is reported of the available evidence on the involvement of nitric oxide (NO) in the control of coronary resistance in teleosts and particularly in salmonids. Most of the evidence reported is from a comprehensive study performed on a Langedorff-type preparation of the isolated trout heart. Using a physio-pharmacological approach, the experiments performed on this preparation have demonstrated that trout coronary resistance is reduced by l-arginine (NOS substrate), nitroprusside and SNAP (NO donors) and is increased by the NOS inhibitors l-NNA and l-NAME. The vasodilation induced by nitroprusside is blocked by the guanylate cyclase inhibitor methylene blue. l-arginine increases NO release in the perfusate, while l-NNA reduces the release. NO release is inversely related with the coronary resistance. l-NNA inhibits the vasodilatory effects of acetylcholine, serotonin and adenosine. The vasodilation induced by adenosine is accompanied by NO release and involves stretch receptors. Hypoxia induces vasodilation and both adenosine and NO release in the preparation; the NO release under hypoxia is blocked by theophylline. On the whole these data indicate that NO plays a central role in the control of coronary resistance in trout. In particular, a main role for NO as an amplifier of the adenosine-mediated vasodilation under hypoxia can be hypothesized.

Current topics of physiology and pharmacology in the lymphatic system

We have reviewed physiological significance of rhythmical spontaneous contractions of collecting lymph vessels, which play a pivotal role in lymph transport and seem to control lymph formation through changing the pacemaker sites of the rhythmic contractions and contractile patterns of the lymphangions. A characteristic feature that the rhythmic pump activity works in vivo physiologically under the specific environment of lower oxygen tension in lymph (25-40 mm Hg) has been evaluated. With the characteristic feature, generation of endogenous nitric oxide (NO) from lymphatic endothelial cells and/or activation of ATP-sensitive potassium channels (K(ATP)) are reviewed to play crucial roles in the regulation of lymph transport at physiological or pathophysiological conditions. Chemical substances released from malignant tumor cells and tumor-derived parathyroid hormone-related peptide (PTHr-P) are also shown to cause a significant reduction of lymphatic pump activity through generation of endogenous NO and activation of K(ATP) channels. Finally, we have discussed physiological significance and roles of the lower oxygen tension in lymph, generation of endogenous NO, and activation of K(ATP) in lymph formation, lymph transport, and the functions of lymph nodes.

Nitric oxide contributes to right coronary vasodilation during systemic hypoxia

As arterial partial pressure of O(2) (Pa(O(2))) is reduced during systemic hypoxia, right ventricular (RV) work and myocardial O(2) consumption (MVo(2)) increase. Mechanisms responsible for maintaining RV O(2) demand/supply balance during hypoxia have not been delineated. To address this problem, right coronary (RC) blood flow and RV O(2) extraction were measured in nine conscious, instrumented dogs exposed to normobaric hypoxia. Catheters were implanted in the right ventricle for measuring pressure, in the ascending aorta for measuring arterial pressure and for sampling arterial blood, and in an RC vein. A flow transducer was placed around the RC artery. After recovery from surgery, dogs were exposed to hypoxia in a chamber ventilated with N(2), and blood samples and hemodynamic data were collected as chamber O(2) was reduced progressively to approximately 8%. After control measurements were made, the chamber was opened and the dog was allowed to recover. N(omega)-nitro-L-arginine (L-NNA) was then administered (35 mg/kg, via RV catheter) to inhibit nitric oxide (NO) production, and the hypoxia protocol was repeated. RC blood flow increased during hypoxia due to coronary vasodilation, because RC conductance increased from 0.65 +/- 0.05 to 1.32 +/- 0.12 ml x min(-1) x 100 g(-1) x L-NNA blunted the hypoxia-induced increase in RC conductance. RV O(2) extraction remained constant at 64 +/- 4% as Pa(O(2)) was decreased, but after L-NNA, extraction increased to 70 +/- 3% during normoxia and then to 78 +/- 3% during hypoxia. RV MVo(2) increased during hypoxia, but after L-NNA, MVo(2) was lower at any respective Pa(O(2)). The relationship between heart rate times RV systolic pressure (rate-pressure product) and RV MVo(2) was not altered by l-NNA. To account for L-NNA-mediated decreases in RV MVo(2), O(2) demand/supply variables were plotted as functions of MVo(2). Slope of the conductance-MVo(2) relationship was depressed by L-NNA (P = 0.03), whereas the slope of the extraction-MVo(2) relationship increased (P = 0.003). In summary, increases in RV MVo(2) during hypoxia are met normally by increasing RC blood flow. When NO synthesis is blocked, the large RV O(2) extraction reserve is mobilized to maintain RV O(2) demand/supply balance. We conclude that NO contributes to RC vasodilation during systemic hypoxia.

Antiallergic activity of a disaccharide isolated fromSanguisorba of?cinalis

The antiallergic activity of the natural disaccharide, 5-O-alpha-D-(3-C-hydroxymethyl)lyxofuranosyl-beta-D-(2-C-hydroxymethyl)arabinofuranose was evaluated using both in vivo and in vitro experimental models. Intravenously administered compound inhibited the passive cutaneous anaphylaxis response in rats in a dose-dependent manner (ED(50) = 9.6 mg/kg). The compound inhibited histamine release evoked by both compound 48/80 and calcium ionophore A23187 in rat peritoneal mast cells indicating that mast cell stabilization is the major mechanism of action for its antiallergic activity. In passively sensitized isolated guinea-pig hearts, an in vitro anaphylaxis model in which histamine release plays a key role for functional deterioration, the compound markedly diminished both coronary flow reduction and histamine release on challenge to the antigen. These data demonstrate that this antiallergic natural disaccharide exerts its effect via inhibition of mast cell mediator release.

Resveratrol protects myocardial ischemia-reperfusion injury through both NO-dependent and NO-independent mechanisms

We previously showed that resveratrol (3,4',5-trihydroxystilbene) stimulates NO production and is cardioprotective in rat heart subjected to ischemia-reperfusion (I/R rat heart). We now show that in I/R rat heart, inducible nitric oxide synthase (iNOS) expression is markedly induced, while expression of endothelial nitric oxide synthase (eNOS) and nueronal nitric oxide synthase (nNOS) is unchanged. In animals preconditioned with resveratrol (0.5 to 1 mg/kg body wt), I/R-induced iNOS induction is abrogated; however, expression of eNOS and nNOS is greatly upregulated. The protective effects of resveratrol on I/R rat heart include reduced rhythm disturbances, reduced cardiac infarct size, and decreased plasma levels of lactate dehydrogenase (LDH) and creatine kinase (CK). Among these, the reductions in LDH/CK levels and infarct size are NO-dependent as the coadministration of N(omega)-nitro-L-arginine methyl ester (L-NAME, 1 mg/kg body wt) with resveratrol abolishes the resveratrol effect. In contrast, the reductions in the severity of ventricular arrhythmia and mortality rate are not affected by L-NAME coadministration, suggesting that a NO-independent mechanism is involved.

Hypoxia increases Hsp90 binding to eNOS via PI3K-Akt in porcine coronary artery endothelium

This study examines the molecular mechanisms by which hypoxia regulates phosphorylated endothelial nitric oxide synthase (eNOS) activity and NO production in porcine coronary artery endothelial cells (PCAEC). Exposure to hypoxia (pO(2)=10 mmHg) for periods up to 3 h resulted in a time-dependent increase in eNOS protein expression and an early (15 min) and sustained increase in eNOS phosphorylation at Ser-1177. Exposure to hypoxia for 30 min led to a doubling in eNOS activity (control=6.2+/-4.4 vs hypoxia=14.1+/-5.0 fmol cGMP/microg protein, P<0.05) and NO release (control=5.9+/-0.8 vs hypoxia=11.8+/-1.2 nM/microg protein, P<0.05). Hypoxia also led to a significant increase in Akt phosphorylation and upregulation of Hsp90 binding to eNOS. Pretreatment of cells with either 1 microg/ml geldanamycin (a specific inhibitor of Hsp90) or 500 nM wortmannin (a specific PI3 kinase inhibitor) suppressed hypoxia-stimulated Akt and eNOS phosphorylation and significantly attenuated hypoxia-stimulated Hsp90 binding to eNOS. Both eNOS activity and NO production were inhibited by geldanamycin and wortmannin. Although hypoxia led to early activation of p42/44 mitogen-activated protein kinases (MAPK), inhibition of their pathway by PD98059 did not suppress hypoxia-stimulated eNOS phosphorylation and eNOS activity. These data demonstrate that hypoxia leads to increased eNOS phosphorylation via stimulated Hsp90 binding to eNOS and activation of the PI3-Akt pathway. We conclude that a coordinated interaction between Hsp90 and PI3-Akt may be an important mechanism by which eNOS activity and NO production is upregulated in hypoxic heart.

Coronary flow reserve in the newborn lamb: an intracoronary Doppler guide wire study

Recent studies indicate a severely reduced coronary flow reserve (CFR) in neonates with congenital heart disease. The significance of these studies remains debatable, as the ability of the anatomically normal neonatal heart to increase coronary flow is currently unknown. This study was designed to establish normal values for CFR in newborns after administration of adenosine [pharmacologic CFR (pCFR)] and as induced by acute hypoxemia (reactive CFR). Thirteen mechanically ventilated newborn lambs were studied. Coronary flow velocities were measured in the proximal left anterior descending coronary artery before and after adenosine injection (140 and 280 microg/kg i.v.) using an intracoronary 0.014-in Doppler flow-wire. Measurements were made at normal oxygen saturation (SaO(2)) and during progressive hypoxemia induced by lowering the fraction of inspired oxygen. CFR was defined as the ratio of hyperemic to basal average peak flow velocity. In a hemodynamically stable situation with normal SaO(2), pCFR was 3.0 +/- 0.5. pCFR decreased with increasing hypoxemia. Regression analysis showed a linear relation between SaO(2) and pCFR (R = 0.86, p < 0.0001). Reactive CFR obtained at severe hypoxemia (Sao(2) <30%) was 4.2 +/- 0.8, and no significant further increase in coronary flow velocity occurred by administration of adenosine. Newborn lambs have a similar capacity to increase coronary flow in response to both pharmacologic and reactive stimuli as older subjects. Administration of adenosine does not reveal the full capacity of the newborn coronary circulation to increase flow, however, as the flow increase caused by severe hypoxemia is significantly more pronounced.

The role of nitric oxide in vascular headache

Shortly after the invention of nitroglycerin (NTG), it was noticed that this substance is capable of inducing a violent headache. Only recently, it became known that this was due to the release of nitric oxide (NO) by NTG. As the molecular mechanism of migraine pain remains to be determined, NTG, being pro-drug for NO, has been used to study the aetiology and pathophysiology of migraine. Such studies with NTG- and also histamine-induced headaches, have led to propose that NO may be the causative molecule in migraine pain. The evidence supporting the role of NO in migraine is discussed, e.g. substances capable of inducing experimental vascular headache do so with NO as the common mediator, while drugs with antimigraine activity inhibit NO and the cascade of intracellular reactions triggered by NO. The importance of NO as a potential initiator of the migraine attack opens new directions for the pharmacological treatment of migraine and other vascular headaches.

Reduced perivascular PO2 increases nitric oxide release from endothelial cells

Many studies have suggested that endothelial cells can act as "oxygen sensors" to large reductions in oxygen availability by increasing nitric oxide (NO) production. This study determined whether small reductions in oxygen availability enhanced NO production from in vivo intestinal arterioles, venules, and parenchymal cells. In vivo measurements of perivascular NO concentration ([NO]) were made with NO-sensitive microelectrodes during normoxic and reduced oxygen availability. During normoxia, intestinal first-order arteriolar [NO] was 397 +/- 26 nM (n = 5), paired venular [NO] was 298 +/- 34 nM (n = 5), and parenchymal cell [NO] was 138 +/- 36 nM (n = 3). During reduced oxygen availability, arteriolar and venular [NO] significantly increased to 695 +/- 79 nM (n = 5) and 534 +/- 66 nM (n = 5), respectively, whereas parenchymal [NO] remained unchanged at 144 +/- 34 nM (n = 4). During reduced oxygenation, arteriolar and venular diameters increased by 15 +/- 3% and 14 +/- 5%, respectively: NG-nitro-L-arginine methyl ester strongly suppressed the dilation to lower periarteriolar Po2. Micropipette injection of a CO2 embolus into arterioles significantly attenuated arteriolar dilation and suppressed NO release in response to reduced oxygen availability. These results indicated that in rat intestine, reduced oxygen availability increased both arteriolar and venular NO and that the main site of NO release under these conditions was from endothelial cells.

Interactions of adenosine, prostaglandins and nitric oxide in hypoxia-induced vasodilatation: in vivo and in vitro studies

Adenosine, prostaglandins (PG) and nitric oxide (NO) have all been implicated in hypoxia-evoked vasodilatation. We investigated whether their actions are interdependent. In anaesthetised rats, the PG synthesis inhibitors diclofenac or indomethacin reduced muscle vasodilatation evoked by systemic hypoxia or adenosine, but not that evoked by iloprost, a stable analogue of prostacyclin (PGI(2)), or by an NO donor. After diclofenac, the A(1) receptor agonist CCPA evoked no vasodilatation: we previously showed that A(1), but not A(2A), receptors mediate the hypoxia-induced muscle vasodilatation. Further, in freshly excised rat aorta, adenosine evoked a release of NO, detected with an NO-sensitive electrode, that was abolished by NO synthesis inhibition, or endothelium removal, and reduced by ~50 % by the A(1) antagonist DPCPX, the remainder being attenuated by the A(2A) antagonist ZM241385. Diclofenac reduced adenosine-evoked NO release by ~50 % under control conditions, abolished that evoked in the presence of ZM241385, but did not affect that evoked in the presence of DPCPX. Adenosine-evoked NO release was also abolished by the adenyl cyclase inhibitor 2',5'-dideoxyadenosine, while dose-dependent NO release was evoked by iloprost. Finally, stimulation of A(1), but not A(2A), receptors caused a release of PGI(2) from rat aorta, assessed by radioimmunoassay of its stable metabolite, 6-keto PGF(1alpha), that was abolished by diclofenac. These results suggest that during systemic hypoxia, adenosine acts on endothelial A(1) receptors to increase PG synthesis, thereby generating cAMP, which increases the synthesis and release of NO and causes muscle vasodilatation. This pathway may be important in other situations involving these autocoids.

Retinoic acid suppression of endothelial nitric oxide synthase in porcine oocyte

The presence of endothelial nitric oxide synthase (eNOS) has been found in porcine oocytes, but its mRNA and protein levels remain relatively constant during hormonal stimulation. The present study was designed to determine the effect of retinoic acid on eNOS regulation in porcine oocytes during follicle-stimulating hormone (FSH) stimulation. Cumulus–oocyte complexes (COCs), prepared from small antral follicles of immature porcine ovaries, were cultured for 15 h and treated with FSH for an additional 48 h. eNOS mRNA and its protein were analyzed by reverse transcription – polymerase chain reaction and Western blotting, respectively. Retinoic acid had an inhibitory effect on the level of oocyte eNOS mRNA in a dose-dependent manner if COCs were exposed to retinoic acid before FSH stimulation. The inhibition of FSH action was reflected in a decrease in expression of c-fos mRNA. eNOS protein also decreased to approximately 50% of the control after exposure to 10 μM retinoic acid. However, the ability of NO synthesis was abolished in the oocytes prepared from retinoic acid pretreated COCs. These results suggest that retinoic acid has a strong inhibitory action on eNOS mRNA level and NO synthesis in the porcine oocyte.Key words: oocyte, retinoic acid, NO synthesis, eNOS, RT–PCR.

Nitric oxide in the human respiratory cycle

Interactions of nitric oxide (NO) with hemoglobin (Hb) could regulate the uptake and delivery of oxygen (O(2)) by subserving the classical physiological responses of hypoxic vasodilation and hyperoxic vasconstriction in the human respiratory cycle. Here we show that in in vitro and ex vivo systems as well as healthy adults alternately exposed to hypoxia or hyperoxia (to dilate or constrict pulmonary and systemic arteries in vivo), binding of NO to hemes (FeNO) and thiols (SNO) of Hb varies as a function of HbO(2) saturation (FeO(2)). Moreover, we show that red blood cell (RBC)/SNO-mediated vasodilator activity is inversely proportional to FeO(2) over a wide range, whereas RBC-induced vasoconstriction correlates directly with FeO(2). Thus, native RBCs respond to changes in oxygen tension (pO2) with graded vasodilator and vasoconstrictor activity, which emulates the human physiological response subserving O(2) uptake and delivery. The ability to monitor and manipulate blood levels of NO, in conjunction with O(2) and carbon dioxide, may therefore prove useful in the diagnosis and treatment of many human conditions and in the development of new therapies. Our results also help elucidate the link between RBC dyscrasias and cardiovascular morbidity.

Vitamin C prevents hyperoxia-mediated vasoconstriction and impairment of endothelium-dependent vasodilation

High arterial blood oxygen tension increases vascular resistance, possibly related to an interaction between reactive oxygen species and endothelium-derived vasoactive factors. Vitamin C is a potent antioxidant capable of reversing endothelial dysfunction due to increased oxidant stress. We tested the hypotheses that hyperoxic vasoconstriction would be prevented by vitamin C, and that acetylcholine-mediated vasodilation would be blunted by hyperoxia and restored by vitamin C. Venous occlusion strain gauge plethysmography was used to measure forearm blood flow (FBF) in 11 healthy subjects and 15 congestive heart failure (CHF) patients, a population characterized by endothelial dysfunction and oxidative stress. The effect of hyperoxia on FBF and derived forearm vascular resistance (FVR) at rest and in response to intra-arterial acetylcholine was recorded. In both healthy subjects and CHF patients, hyperoxia-mediated increases in basal FVR were prevented by the coinfusion of vitamin C. In healthy subjects, hyperoxia impaired the acetylcholine-mediated increase in FBF, an effect also prevented by vitamin C. In contrast, hyperoxia had no effect on verapamil-mediated increases in FBF. In CHF patients, hyperoxia did not affect FBF responses to acetylcholine or verapamil. The addition of vitamin C during hyperoxia augmented FBF responses to acetylcholine. These results suggest that hyperoxic vasoconstriction is mediated by oxidative stress. Moreover, hyperoxia impairs acetylcholine-mediated vasodilation in the setting of intact endothelial function. These effects of hyperoxia are prevented by vitamin C, providing evidence that hyperoxia-derived free radicals impair the activity of endothelium-derived vasoactive factors.