Regulation of large coronary arteries

Innervation of the coronary arteries and its role in controlling microvascular resistance

The coronary circulation plays a crucial role in balancing myocardial perfusion and oxygen demand to prevent myocardial ischemia. Extravascular compressive forces, coronary perfusion pressure, and microvascular resistance are involved to regulate coronary blood flow throughout the cardiac cycle. Autoregulation of the coronary blood flow through dynamic adjustment of microvascular resistance is maintained by complex interactions among mechanical, endothelial, metabolic, neural, and hormonal mechanisms. This review focuses on the neural mechanism. Anatomy and physiology of the coronary arterial innervation have been extensively investigated using animal models. However, findings in the animal heart have limited applicability to the human heart as cardiac innervation is generally highly variable among species. So far, limited data are available on the human coronary artery innervation, rendering multiple questions unresolved. Recently, the clinical entity of ischemia with non-obstructive coronary arteries has been proposed, characterized by microvascular dysfunction involving abnormal vasoconstriction and impaired vasodilation. Thus, measurement of microvascular resistance has become a standard diagnostic for patients without significant stenosis in the epicardial coronary arteries. Neural mechanism is likely to play a pivotal role, supported by the efficacy of cardiac sympathetic denervation to control symptoms in patients with angina. Therefore, understanding the coronary artery innervation and control of microvascular resistance of the human heart is increasingly important for cardiologists for diagnosis and to select appropriate therapeutic options. Advancement in this field can lead to innovations in diagnostic and therapeutic approaches for coronary artery diseases.

Coronary microvascular dysfunction, arrythmias, and sudden cardiac death: A literature review

The coronary vascular system has a unique structure and function that is adaptive to myocardial demand. It is composed of a continuous network of vessels receding in size from epicardial arteries to the microvascular circulation. Failure to meet myocardial demand results in ischemia, angina, and adverse myocardial outcomes. It is evident that 50 % of patients with angina have a non-obstructive coronary disease and 66 % of these patients have coronary microvascular dysfunction (CMD). The impact of CMD on the atria and ventricles is exhibited through its association with atrial fibrillation and distortion of ventricular repolarization. Ultimately, this influence increases the risk of mortality, morbidity, and sudden cardiac arrest. CMD serves as an independent risk for atrial fibrillation, increases ventricular electrical inhomogeneity, and contributes to the progression of cardiac disease. The underlying pathogenesis may be attributed to oxidative stress evident through reactive oxygen species, impaired vasoactive function, and structural disorders such as fibrotic changes. Myocardial ischemia, brought about by a demand-supply mismatch in CMD, may create a milieu for ventricular arrythmia and sudden cardiac arrest through distortion of ventricular repolarization parameters such as QT dispersion and corrected QT dispersion.

Two-layer model of coronary artery vasoactivity

Since vascular tone is regulated by smooth muscle cells in the media layer, a multilayer mechanical model is required for blood vessels. Here, we performed biaxial mechanical tests in the intima-media layer of right coronary artery to determine the passive and active properties in conjunction with the passive properties of adventitia for a full vessel wall model. A two-layer (intima-media and adventitia) model was developed to determine the transmural stress and stretch across the vessel wall. The mean ± SE values of the outer diameters of intima-media layers at transmural pressure of 60 mmHg in active state were 3.17 ± 0.16 and 3.07 ± 0.18 mm at axial stretch ratio of 1.2 and 1.3, respectively, which were significantly smaller than those in passive state (i.e., 3.62 ± 0.19 and 3.49 ± 0.22 mm, respectively, P < 0.05). The inner and outer diameters in no-load state of intima-media layers were 1.17 ± 0.09 and 2.08 ± 0.09 mm, respectively. The opening angles in zero-stress state had values of 159 ± 21° for intima-media layers and 98 ± 15° for adventitia layers, which suggests a residual strain between the two layers. There were slightly decreased active circumferential stresses (<10%), but significantly decreased active axial stresses (>25%) in the intima-media layer compared with those in the intact vessel. This suggests that the adventitia layer affects vascular contraction. The two-layer analysis showed that the intima-media layer bears the majority of circumferential tensions, in contrast to the adventitia layer, while contraction results in decreased stress and stretch in both layers.

Biaxial vasoactivity of porcine coronary artery

The passive mechanical properties of blood vessel mainly stem from the interaction of collagen and elastin fibers, but vessel constriction is attributed to smooth muscle cell (SMC) contraction. Although the passive properties of coronary arteries have been well characterized, the active biaxial stress-strain relationship is not known. Here, we carry out biaxial (inflation and axial extension) mechanical tests in right coronary arteries that provide the active coronary stress-strain relationship in circumferential and axial directions. Based on the measurements, a biaxial active strain energy function is proposed to quantify the constitutive stress-strain relationship in the physiological range of loading. The strain energy is expressed as a Gauss error function in the physiological pressure range. In K(+)-induced vasoconstriction, the mean ± SE values of outer diameters at transmural pressure of 80 mmHg were 3.41 ± 0.17 and 3.28 ± 0.24 mm at axial stretch ratios of 1.3 and 1.5, respectively, which were significantly smaller than those in Ca(2+)-free-induced vasodilated state (i.e., 4.01 ± 0.16 and 3.75 ± 0.20 mm, respectively). The mean ± SE values of the inner and outer diameters in no-load state and the opening angles in zero-stress state were 1.69 ± 0.04 mm and 2.25 ± 0.08 mm and 126 ± 22°, respectively. The active stresses have a maximal value at the passive pressure of 80-100 mmHg and at the active pressure of 140-160 mmHg. Moreover, a mechanical analysis shows a significant reduction of mean stress and strain (averaged through the vessel wall). These findings have important implications for understanding SMC mechanics.

Heterogeneity in relaxation of different sized porcine coronary arteries to nitrovasodilators: role of PKG and MYPT1

The present study was to determine the role of the type I isoform of cGMP-dependent protein kinase (PKG I) and its downstream effector myosin phosphatase target subunit 1 (MYPT1) in the responses of different sized coronary arteries to nitrovasodilators. Relaxations of isolated porcine coronary arteries were determined by isometric tension recording technique. Protein levels of PKG I and its effectors were analyzed by Western blotting. The activities of PKG I and MYPT1 were studied by analyzing phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and MYPT1, respectively. Nitroglycerin, DETA NONOate, and 8-Br-cGMP caused greater relaxations in large than in small coronary arteries. Relaxations were attenuated to a greater extent by Rp-8-Br-PET-cGMPS (a PKG inhibitor) in large vs. small arteries. The expressions of PKG I and MYPT1 in large arteries were more abundant than in small arteries. DETA NONOate stimulated phosphorylation of VASP at Ser239 and inhibited phosphorylation of MYPT1 at Thr853 to a greater extent in large than in small arteries. A suppressed phosphorylation of MYPT1 at Thr853 was caused by 8-Br-cGMP in large but not small arteries, which was inhibited by Rp-8-Br-PET-cGMPS. These results suggest that the greater responsiveness of large coronary arteries to nitrovasodilators result in part from greater activities of PKG I and MYPT1. Dysfunction in nitric oxide signaling is implicated in the vulnerability of large coronary arteries to certain disorders such as atherosclerosis and spasm. Augmentation of PKG I-MYPT1 signaling may be of therapeutic benefit for combating these events.

Rho kinase is an effector underlying Ca2+-desensitizing hypoxic relaxation in porcine coronary artery

Acute hypoxia dilates most systemic arteries leading to increased tissue perfusion. We have previously shown that at high-stimulus conditions, porcine coronary artery was relaxed by hypoxia without a change in intracellular [Ca2+] ( 27 ). This Ca2+-desensitizing hypoxic relaxation (CDHR) was validated in permeabilized porcine coronary artery smooth muscle (PCASM) in which hypoxia decreased force and myosin regulatory light chain phosphorylation (p-MRLC) despite fixed [Ca2+] ( 10 ). Rho kinase-dependent phosphorylation of myosin phosphatase-targeting subunit 1 (p-MYPT1) is associated with decreased MRLC phosphatase activity and increased Ca2+ sensitivity of both p-MRLC and force. We recently reported that p-MYPT1 dephosphorylation was a key effector in CDHR ( 33 ). In the current study, we tested the hypothesis that Rho kinase and not p-MYPT1 phosphatase is the regulated enzyme involved in CDHR. We used α-toxin to permeabilize deendothelialized PCASM. CDHR was attenuated in contractions attributable to myosin light chain kinase (MLCK, in the presence of the Rho kinase inhibitor Y-27632). In contrast, hypoxia relaxed contractions attributable to Rho kinase phosphorylation of MYPT1 and MRLC or MRLC alone (in the presence of the MLCK inhibitor ML7). Using an in situ assay, we showed that Rho kinase activity, measured as thiophosphorylation of MYPT1 and MRLC, was nearly abolished by hypoxia. The in vitro activity of the catalytically active fragment of Rho kinase was not affected by hypoxia. Our evidence strongly implicates that hypoxia directly inhibits Rho kinase-dependent phosphorylation of MYPT1. This underlies the decreases in both p-MYPT1 and p-MRLC and thereby leads to the Ca2+-desensitizing hypoxic relaxation.

Ca2+-desensitizing hypoxic vasorelaxation: pivotal role for the myosin binding subunit of myosin phosphatase (MYPT1) in porcine coronary artery

Acute hypoxia dilates most systemic arteries leading to increased tissue perfusion. We showed that at high stimulus conditions, porcine coronary artery was relaxed by hypoxia without a change in [Ca(2+)](i). This 'Ca(2+)-desensitizing hypoxic relaxation' was validated in permeabilized porcine coronary artery smooth muscle (PCASM) in which hypoxia decreased force and myosin regulatory light chain phosphorylation (p-MRLC) despite fixed [Ca(2+)]. Rho kinase-dependent phosphorylation of MYPT1 (p-MYPT1) is associated with decreased MRLC phosphatase (MLCP) activity, and increased Ca(2+) sensitivity of both p-MRLC and force. We tested the hypothesis that hypoxia induces Ca(2+)-desensitizing hypoxic relaxation via dephosphorylation of p-MYPT1, consequently increasing MLCP activity and thus decreasing p-MRLC. alpha-Toxin-permeabilized PCASM pretreated with ATPgammaS did not relax in response to hypoxia. Moreover, when MRLC but not MYPT1 was protected from ATPgammaS thiophosphorylation by the MRLC kinase inhibitor ML7 (300 mum), hypoxia remained ineffective. In contrast, hypoxic relaxation was preserved with further addition of the Rho kinase inhibitor Y27632 (1 mum), to attenuate thiophosphorylation of MYPT1. Importantly, measurements of p-MRLC, and p-MYPT1 at T696 and T853 (human sequence) paralleled that of force. We conclude that Ca(2+)-desensitizing hypoxic relaxation requires dephosphorylation of p-MYPT1. Moreover, no kinases, other then those inhibited by ML7 and Y27632, nor their associated phosphoproteins can be involved in Ca(2+)-desensitizing hypoxic relaxation.

The effect of high thoracic epidural anesthesia on systolic and diastolic left ventricular function in patients with coronary artery disease

In patients with coronary artery disease, vasoconstriction is induced through activation of the sympathetic nervous system. Both alpha1- and alpha2-adrenergic epicardial and microvascular constriction are potent initiators of myocardial ischemia. Attenuation of ischemia has been observed when sympathetic nervous system activity is inhibited by high thoracic epidural anesthesia (HTEA). However, it is still a matter of controversy whether establishing HTEA may correspondingly translate into an improvement of left ventricular (LV) function. To clarify this issue, LV function was quantified serially before and after HTEA using a new combined systolic/diastolic variable of global LV function (myocardial performance index [MPI]) and additional variables that more specifically address systolic (e.g., fractional area change) or diastolic function (e.g., intraventricular flow propagation velocity [Vp]). High thoracic epidural catheters were inserted in 37 patients scheduled for coronary artery surgery, and HTEA was administered in the awake patients. Echocardiographic and hemodynamic measures were recorded before and after institution of HTEA. HTEA induced a significant improvement in diastolic LV function (e.g., Vp changed from 45.1 +/- 16.1 to 53.8 +/- 18.8 cm/s; P < 0.001), whereas indices of systolic function did not change. The change in the diastolic characteristics caused the MPI to improve from 0.51 +/- 0.13 to 0.35 +/- 0.13 (P < 0.001). We conclude that an improvement in cardiac function was due to improved diastolic characteristics.

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

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

Vascular oxygen sensing: detection of novel candidates by proteomics and organ culture

We have shown that the specific inhibition of hypoxia-induced relaxation by organ culture in porcine coronary arteries can be mimicked by treatment of control vessels with the protein synthesis inhibitor, cycloheximide. We hypothesize that organ culture of vascular smooth muscle results in the decreased expression of proteins that are critical for vascular oxygen sensing. Using two-dimensional gel electrophoresis and mass spectroscopy, we identified such candidate proteins. The expressions of the smooth muscle-specific protein, SM22, and tropomyosin are decreased after 24 h in organ culture. These results were confirmed by Western blot analysis. Other smooth muscle proteins (actin and calponin) exhibited little change. We also demonstrate a 50% downregulation in the small G protein, Rho, a potent modulator of Ca2+-independent force. These results indicate that organ culture preferentially inhibits the expression of certain smooth muscle proteins. This change in protein expression after organ culture correlates with the specific inhibition of hypoxic vasorelaxation. These results provide novel target pathways for investigation that are potentially important for vascular oxygen sensing.

Coronary vasospasm and the regulation of coronary blood flow

Under physiologic conditions, epicardial arteries contribute minimally to coronary vascular resistance. However, in the presence of endothelial dysfunction, stimuli that normally produce vasodilation may instead cause constriction. Examples include neural release of acetylcholine or norepinephrine, platelet activation and production of serotonin and thrombin, and release of local factors such as bradykinin. This shift from a primary endothelial-mediated vasodilator influence to one of endothelial dysfunction and unchecked vasoconstriction is precisely the milieu in which coronary vasospasm is observed. This condition, which typically occurs during periods of relatively sedentary activity, is associated with focal and transient obstruction of an epicardial arterial segment resulting in characteristic echocardiographic changes and symptoms of myocardial ischemia. This review highlights the current understanding of mechanisms regulating the coronary circulation during health and examines the pathophysiologic changes that occur with coronary spasm. Genetic and other predisposing conditions are addressed, as well as novel therapies based on recent mechanistic insights of the coronary contractile dysfunction associated with coronary spasm.

Energy cost of contraction in rat urinary bladder smooth muscle during anoxia

1. The aim of the present study was to investigate the effects of hypoxia on energy metabolism and contraction of rat urinary bladder smooth muscle, thereby gaining insight into the capacity of this smooth muscle to maintain contractile function when rendered hypoxic. 2. Isometric force, oxygen consumption, lactate production, heat production and unloaded shortening velocity were measured in isolated muscle strips under both aerobic and anaerobic conditions. Muscle strips were bathed in physiological saline solution with the anaerobic condition being created by replacing the oxygen bubbling the solution with nitrogen. 3. During contraction under anaerobic conditions, the rate of lactate production was increased 2.5-fold above that observed under aerobic conditions. This, however, only provided for a rate of ATP production of approximately 30% of that measured under aerobic conditions. Despite this, force maintenance was only slightly depressed, indicating that the metabolic cost of contraction was reduced in hypoxia. In support of this, the rate of heat production during contractions in anoxia was only approximately half of that under aerobic conditions, whereas, again, force was only slightly lower. Unloaded shortening velocity was significantly lower in anoxia, suggesting a slower cross-bridge turnover rate. 4. The results indicate that the economy of force maintenance is increased in bladder smooth muscle under hypoxic conditions and that this is due, at least in part, to a reduced rate of cross-bridge cycling. This may help to preserve bladder contractile function during periods of ischaemia that may be associated with bladder filling and emptying.

Hypoxic vasodilation in porcine coronary artery is preferentially inhibited by organ culture

Hypoxia (95% N2-5% CO2) elicits an endothelium-independent relaxation (45-80%) in freshly dissected porcine coronary arteries. Paired artery rings cultured at 37 degrees C in sterile DMEM (pH approximately 7.4) for 24 h contracted normally to KCl or 1 microM U-46619. However, relaxation in response to hypoxia was sharply attenuated compared with control (fresh arteries or those stored at 4 degrees C for 24 h). Hypoxic vasorelaxation in organ cultured vessels was reduced at both high and low stimulation, indicating that both Ca2+-independent and Ca2+-dependent components are altered. In contrast, relaxation to G-kinase (sodium nitroprusside) or A-kinase (forskolin and isoproterenol) activation was not significantly affected by organ culture. Additionally, there was no difference in relaxation after washout of the stimulus, indicating that the inhibition is specific to acute hypoxia-induced relaxation. Simultaneous force and intracellular calcium concentration ([Ca2+]i) measurements indicate the reduction in [Ca2+]i concomitant with hypoxia at low stimulus levels in these tissue is abolished by culture. Our results indicate that organ culture at 37 degrees C specifically attenuates hypoxic relaxation in vascular smooth muscle by altering dynamics of [Ca2+]i handling and decreasing a Ca2+-independent component of relaxation. Thus organ culture can be a novel tool for investigating the mechanisms of hypoxia-induced vasodilation.

Vagal neurostimulation in patients with coronary artery disease

We tested the hypotheses that (1) progression of coronary artery disease (CAD) increases sympathetic inflow to the heart, thus impairing cardiac blood supply, and (2) reduced sympathetic tone improves cardiac microcirculation and ameliorates severity of anginal symptoms. Electrical irritation of the nerve auricularis--a sensitive ramus of the vagus nerve--provides a central sympatholytic action. Using this technique, we studied the effects of vagal neurostimulation (VNS) on hemodynamics, the content of atrial noradrenergic nerves and the microcirculatory bed of CAD patients. VNS was performed in the preoperative period of CAD patients with severe angina pectoris. The comparison groups consisted of untreated patients with CAD or Wolff-Parkinson-White syndrome. Atrial tissue of patients with this syndrome (n = 6); with effort angina (n = 14); with angina at rest (n = 10); and with severe angina treated with VNS (n = 8) contained the following volume percentages of noradrenergic nerves: 1.7+/-0.1%, 1.3+/-0.3%, 0.5+/-0.1% (p < 0.05 vs. the other groups) and 1.3+/-0.2%, respectively. In these groups, cardiac microcirculatory vessels (diameter, 10-20 microm) had the following densities: 2.7+/-0.2%, 3.4+/-0.2%, 2.0+/-0.4% (p < 0.05 vs. the other groups) and 3.3+/-0.3%, respectively. VNS treatment abolished angina at rest, decreased heart rate and blood pressure. It improved left ventricular ejection fraction from 50+/-1.5% to 58+/-1.0% (p < 0.05), also changing left ventricular diastolic filling. The ratio of time velocity integrals of the early (Ei) to late (Ai) waves increased from 1.07+/-0.12 to 1.65+/-0.17 after VNS (p < 0.05). In electrocardiograms of VNS-treated patients, QRS- and QT-duration were shortened. the PQ-interval did not change, but T-wave configuration improved. In the postoperative period, heart failure occurred in 90% of the control group. vs. 12% in patients treated with VNS (p < 0.05). We conclude that CAD is characterized by overactivity of sympathetic cardiac tone. Vagal stimulation reduced sympathetic inflow to the heart, seemingly via an inhibition of norepinephrine release from sympathetic nerves. VNS' sympatholytic/vagotonic action dilated cardiac microcirculatory vessels and improved left ventricular contractility in patients with severe CAD.

Neuromodulation for chronic refractory angina

Neuromodulation is the use of therapies which alter the relationship between the heart, its autonomic innervation and the central nervous system with the objective of reducing the ischaemic burden and diminishing the perception of angina.

Transesophageal echocardiography (TEE) in the evaluation of the coronary arteries

With technical advancements, including high frequency, multiplane transducers, digital acquisition and display, and left-sided contrast agents, TEE is emerging as a promising method for evaluating coronary artery disease. Visualization of proximal coronary artery stenoses and coronary artery anomalies is already possible. Research studies using TEE measurement have contributed to understanding coronary artery physiology and may prove to be a valuable clinical tool in the future.

Coronary artery blood flow: physiologic and pathophysiologic regulation

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

Influence of nitric oxide on vascular, metabolic, and contractile responses to dobutamine in in situ canine hearts

The left anterior descending coronary arteries of 30 anesthetized, open-chest dogs were perfused via an extracorporeal circuit. Coronary blood flow (CBF), myocardial oxygen consumption (MVO2), and segmental shortening (SS) were measured. Studies were performed with coronary perfusion pressure (CPP) or CBF constant. With CPP constant, effects of intracoronary (IC) infusions of dobutamine (2.5, 5.0, or 10.0 microg/min) were evaluated alone (control) and after inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine methyl ester (L-NAME). With CBF constant, a NO donor (sodium nitroprusside [SNP] 80 microg/min IC) or nitroglycerin [NTG] 40 microg/min IC) or a releaser of endogenous NO (acetylcholine [ACh]; 20 microg/ min IC) was infused along with dobutamine. Increases in CBF during dobutamine and isoproterenol were compared before and after blockade of beta1-adrenergic receptors with atenolol. Dobutamine caused proportional, dose-dependent increases in CBF, MVO2, and SS, which were not altered by L-NAME. Administration of the NO donors or ACh during dobutamine markedly decreased CPP, but only ACh also reduced SS and MVO2. These latter effects persisted after L-NAME. Atenolol blunted increases in CBF by dobutamine more than those by isoproterenol. We conclude that endogenous NO did not modulate the coronary vasodilation or the increases in myocardial contractility and MVO2 during dobutamine. In addition, neither SNP nor NTG altered myocardial contractility or MVO2 in dobutamine-stimulated myocardium, whereas ACh had a negative inotropic effect in dobutamine-stimulated myocardium that was independent of NO.

IMPLICATIONS

Endogenous nitric oxide (NO) did not modulate increases in coronary blood flow, myocardial contractility, or myocardial oxygen consumption during intracoronary infusions of dobutamine. The NO donors sodium nitroprusside and nitroglycerin had no effect on contractility or oxygen consumption in dobutamine-stimulated myocardium. Acetylcholine had negative inotropic effect in dobutamine-stimulated myocardium that was independent of NO.

Computer-aided video angiometry in isolated rabbit hearts: a new method assessing epicardial coronary selectivity

The clinical value of coronary vasodilators in antianginal therapy depends on the ratio of their epicardial versus resistance coronary vessel actions. The coronary flow measured in standard isolated heart preparations, however, does not allow any conclusion about the function of epicardial vessels. Thus, we established a new technique assessing the epicardial coronary diameter directly by video angiometry. Pictures from the cardiac surface were taken by a videocamera mounted on a long-distance microscope. The video signal was digitized for computer-aided evaluation. An area of interest (AOI) was laid over the vascular section to be measured. The gray values of the pixels across the epicardial vessel were registered, and a mean curve of distribution was obtained by averaging the gray values from all video lines within the AOI. The inner epicardial coronary diameter resulted from the distance between the points of inflection of this mean curve of distribution. Experiments with NO-vasodilators and adenosine showed that epicardial coronary arteries of isolated perfused rabbit hearts have no appreciable tone. Pretreatment of the hearts with a combination of histamine (10[-6] mol/l), cimetidine (10[-5] mol/l), and adenosine (10[-7] mol/1), however, caused a marked contraction of the conductive vessels. NO-donors selectively dilated epicardial vessels in such pretreated hearts whereas adenosine increased both epicardial coronary diameter and coronary flow, with only a slight tendency toward preferential action on resistance vessels in low concentrations. Simultaneous registration of coronary flow and epicardial coronary diameter in isolated rabbit hearts pretreated with a spasmogenic drug combination (histamine, cimetidine, and adenosine) may be a feasible method assessing epicardial selectivity of coronary vasodilators.

Effects of hypercholesterolemia on the contractions to angiotensin II in the isolated aorta and iliac artery of the rabbit: role of arachidonic acid metabolites

The aim of this study was to investigate the effect of hypercholesterolemia on the angiotensin II-induced contractions in the isolated aorta and iliac artery of the rabbit, with respect to the role of arachidonate metabolites. Furthermore, the effect of the angiotensin-converting enzyme inhibitor ramipril was studied on the responses to angiotensin II in the cholesterol-fed rabbit. After 12 weeks of cholesterol diet (0.3%), endothelium-dependent relaxations to acetylcholine were significantly fewer compared with control (30.2 +/- 5.9% vs. 73.0 +/- 1.7%) in the aorta but not in the iliac artery of the rabbit. The angiotensin II- and methoxamine-induced contractions were also significantly lower compared with control in the aorta (101.4 +/- 6.7% vs. 60.9 +/- 4.2% and 160.2 +/- 5.7% vs. 135.8 +/- 8.0%, respectively) but not in the iliac artery. The lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) selectively attenuated the angiotensin II-induced contractions in rabbit aortic rings from the control group only in the presence of the endothelium, whereas it had no effect on the responses to angiotensin II in the cholesterol group (with or without endothelium). In the iliac artery, NDGA inhibited the responses to angiotensin II in both the control and cholesterol groups. Treatment with ramipril (0.33 mg/kg/day) significantly improved the maximal angiotensin II-induced contraction in the aorta of rabbits fed a cholesterol diet for 16 weeks to 61.0 +/- 7.3% (vs. 32.7 +/- 9.0% in the cholesterol group). We conclude that hypercholesterolemia leads to a reduction of angiotensin II-induced contractions in the aorta and not in the iliac artery of the rabbit. This reduction might be related to loss of endothelium-dependent lipoxygenase products and is partially reversed by ramipril.

Treatment of medically and surgically refractory angina pectoris with high thoracic epidural analgesia: initial clinical experience

Surgical sympathectomy can relieve symptoms of angina in patients with refractory angina. However, in these high-risk patients this thoracic surgery may result in significant morbidity and mortality rates. Similar sympathetic blockade can now be produced with high thoracic epidural analgesia (HTEA). From September 1995 to August 1996, we treated 10 consecutive patients with HTEA. These eight men and two women, aged 58 +/- 5 years, with extensive three-vessel coronary disease and ejection fractions of 40% +/- 5%, had New York Heart Association (NYHA) class IV angina despite medical therapy, including nitrates, beta-blockade, calcium channel blockade, and narcotics. HTEA was performed at the T1 through T4 levels with a catheter placed either percutaneously or surgically, with radiographic confirmation of catheter placement with an epidurogram or computed tomography scan. Bupivacaine (0.25% to 0.5%), an amide local anesthetic, was given as a bolus through the epidural catheter and then maintained either as a continuous infusion or an intermittent rebolus. The epidural catheter remained in place for 7 days in four patients, 14 days in three patients, and > or =90 days in three patients. Before consideration for HTEA, each patient was deemed unsuitable for or refused coronary bypass surgery and percutaneous coronary angioplasty and had NYHA class IV symptoms of angina. Seven of 10 patients required intravenous nitroglycerin and heparin and were unable to be discharged from the intensive care unit because of anginal symptoms. Two of these seven patients also required an intraaortic balloon pump for symptom control. After HTEA, all 10 patients had improved symptoms, with five patients improving to NYHA class II symptoms and five improving to NYHA class III. All seven patients receiving intravenous nitroglycerin, heparin, or intraaortic balloon pump support had these modalities discontinued. Six of these seven patients were subsequently discharged from the hospital. One patient died from a non-HTEA related cause. There were no HTEA-related deaths. There were three catheter-related complications necessitating catheter removal during 12 months of HTEA use. Local infection developed in one patient, one had catheter occlusion caused by fibrosis, and one patient had chronic back pain exacerbation from a paraspinous muscle spasm. No patient had a myocardial infarction or a significant arrhythmia. In patients with otherwise intractable angina pectoris, HTEA is an effective modality that produces symptomatic relief of angina pectoris and allows increased activity level.

Noradrenergic hyperinnervation may inhibit necrosis of coronary arterial smooth muscle cells in stroke-prone spontaneously hypertensive rats

Noradrenergic (NA) nerve fibre distribution and vascular smooth muscle morphology were investigated in the coronary artery of stroke-prone spontaneously hypertensive rats (SHRSP). Fluorescent NA nerve fibres of SHRSP aged 10, 30, 60, 90 and 180 days were examined by the glyoxylic acid method and compared with those of age-matched normotensive Wistar Kyoto (WKY) rats. The distribution densities of NA nerve fibres were measured by quantitative image analysis using the Interactive Bildanalyse System. The densities of NA nerve fibres of the left coronary artery of SHRSP were significantly higher than those of WKY rats at all ages examined. NA hyperinnervation in the coronary artery of SHRSP may be caused by the hyperfunction of the stellate ganglia which innervate the coronary arteries. Scanning electron microscopy observations showed that the surface of smooth muscle cells of the left coronary artery in SHRSP was smooth and similar to that of WKY rats at 120 days of age, but was slightly modified by more invaginations and projections than that in WKY rats at 180 days of age. No necrotic cells, however, were found in SHRSP. By transmission electron microscopy the smooth muscle cells in SHRSP were shown to be irregular in profile with deep indentations of the plasma membrane and surrounded by many layers of basal laminalike material, but no necrotic cells were found. We suggest that NA hyperinnervation protects the vascular smooth muscle cells from necrosis in the coronary artery of SHRSP by a trophic effect mediated by NA nerve fibres.

Effects of thoracic vs. lumbar epidural anaesthesia on systemic haemodynamics and coronary circulation in sevoflurane anaesthetized dogs

BACKGROUND

Although many investigators reported changes in coronary circulation during thoracic epidural anaesthesia (TEA), no previous studies have attempted to compare it with lumbar epidural anaesthesia (LEA) concerning coronary circulation. Our aim was to compare effects of TEA on systemic haemodynamics and coronary circulation with those of LEA in anaesthetized dogs.

METHODS

In dogs receiving 1.5% sevoflurane, 2% lidocaine (0.1 ml kg-1) was injected into the epidural space via an epidural catheter inserted at either the T7-T8 (TEA group, n = 8) or L5-L6 (LEA group, n = 8) interspace, and the same dose was repeated again 30 min later.

RESULTS

Heart rate and maximum left ventricular dP/dt decreased in the TEA group but were unchanged in the LEA group. Decreases in mean arterial pressure were found for both groups, and they were more substantial in the TEA than in the LEA group. Decreases in left ventricular minute work index were found for both groups, and they tended to be more substantial in the TEA than in the LEA group. Coronary perfusion pressure and blood flow decreased in both groups. Calculated coronary vascular resistance increased in the TEA group but was unchanged in the LEA group.

CONCLUSION

The most significant difference between TEA and LEA concerning coronary circulation was characterized by an increase in coronary vascular resistance in the TEA group, which was not present in the LEA group. The increase in coronary vascular resistance caused by TEA may be explained by a coronary vasoconstriction caused by a lower myocardial oxygen demand.

Vasoactivity of the coronary artery of rainbow trout, steelhead trout, and dogfish: lack of support for non-prostanoid endothelium-derived relaxation factors

This study surveyed and compared vasoactive responses of isolated coronary vessels from steelhead trout (Oncorhynchus mykiss), rainbow trout (also O. mykiss), and spiny dogfish (Squalus acanthias). The purpose of the investigation was twofold: to identify vasoactive controls that were possibly mediated by the vascular endothelium and to highlight the possible consequences on vasoactivity of the coronary lesions known to be present in the main coronary of salmonids but not dogfish. The test substances included acetylcholine, adenosine, adenosine triphosphate, adenosine diphosphate, serotonin, thrombin, bradykinin, prostaglandin F2α, prostaglandin I2, prostaglandin E2, and the fatty acids arachidonic acid, docosahexaenoic acid, and eicosapentaenoic acid. Acetylcholine, adenosine, adenosine triphosphate, adenosine diphosphate and prostaglandin F2αtypically produced contractions. Use of endothelial removal techniques and antagonists failed to reveal any relaxations that might involve the endothelium. Thrombin and bradykinin had no vasoactivity. Serotonin, prostaglandin I2, and prostaglandin E2produced relaxations that were not mediated by the endothelium. The powerful relaxations observed with prostaglandin I2and prostaglandin E2and the powerful contractions observed with prostaglandin F2αsuggest a major role of prostanoids in coronary vasoactivity in fish. These prostanoid-mediated mechanisms, in addition to the previously demonstrated powerful contractions with endothelin-1, point to an important role for the endothelium. No major qualitative or quantitative differences in vasoactivity could be related to differences in coronary lesion severity.

Comparison of the effects of exercise and cold pressor test on the vasomotor response of normal and atherosclerotic coronary arteries and their relation to the flow-mediated mechanism

This study was designed to assess the vasomotor response of coronary arteries to exercise and the cold pressor test, and its relationships with the endothelium-mediated dependent mechanism. Twenty-two patients were entered in the study. Group I was composed of 12 patients with a total cholesterol level < 200 mg/dl associated with angiographically smooth, normal coronary arteries. Group 2 consisted of 10 patients with both a cholesterol level > 240 mg/dl and angiographic luminal irregularities of the left anterior descending coronary artery. Coronary blood flow was assessed by a 0.018-inch tip guidewire during Doppler ultrasonography, and analysis of the coronary arterial dimension of the midportion of the left anterior descending coronary artery was performed by quantitative coronary angiography. Catecholamine concentrations were assessed at the different stages of the protocol. The rate-pressure product increased during both the cold pressure test and exercise (p < 0.001). Coronary blood flow velocity increased during the cold pressor and exercise tests by 24.5 +/- 10% and 72 +/- 42%, respectively (p < 0.001), and by 127 +/- 62% (p < 0.0001) after administration of papaverine. In group 1, the cold pressor test had a more pronounced vasodilating effect on epicardial coronary arteries (+11.2 +/- 16%) compared with group 2 (-2 +/- 9%, p < 0.05). Similarly, exercise had a vasodilating action in group 1 (11.3 +/- 15%) compared with group 2 (-1.9 +/- 8%, p < 0.05). Both responses were highly correlated (r = 0.92, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of endothelium-derived nitric oxide to coronary arterial distensibility: an in vivo two-dimensional intravascular ultrasound study

Reduced epicardial coronary arterial distensibility associated with early atherosclerosis may be mediated in part by reduced nitric oxide (NO) release. To directly assess the contribution of endogenous NO to coronary arterial distensibility, we examined the effect of intracoronary N omega nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase, and L-arginine, its natural substrate, on the circumflex artery in seven anesthetized dogs. We also used intracoronary acetylcholine to examine the effect of pharmacologically induced NO release on coronary distensibility. Electrocardiographically gated measurements of epicardial coronary lumen area were made by a blinded observer from images obtained with a 4.3F, 30 MHz intravascular ultrasound catheter. Aortic root pressure was continuously monitored, and neither systemic arterial pressure nor pulse pressure changed significantly with intracoronary drug administration. Change in lumen area (delta LA) from end systole to end diastole was measured, and an arterial distensibility index was calculated. Delta LA increased with acetylcholine from 8.2% +/- 0.5% at baseline to 16.3% +/- 2.8% (10(-6) mol/L; p < 0.001), with increases in both end-systolic and end-diastolic lumen area and decreased delta LA to 3.1% +/- 1.3% (p < 0.01). Lumen area and delta LA were both restored to baseline by L-arginine (10(-4)). The calculated distensibility index of the epicardial coronary artery was enhanced by acetylcholine, reduced below baseline by L-NAME, and restored to baseline by L-arginine.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary artery spasm. Multiple causes and multiple roles in heart disease

Myocardial infarction and sudden cardiac death may be initiated by a sudden intense localized contraction of coronary artery smooth muscle. When this event occurs around a vulnerable eccentric lipid-filled plaque, rupture and extrusion of plaque contents and exposure of collagen occur. This may sometimes be a silent and self-limiting event; other times it leads to thrombus formation. A second wave of spasm due to accumulated platelet and inflammatory mediators may compound the contractile consequences of the initiating event. Spasm involves intrinsic smooth muscle cell electrical mechanisms, hyper-responsive cells, and multiple agonists that synergize their actions, and the involvement of each mechanism varies at different times in the sequence of vascular occlusion. Study of spasm requires vascular systems that adequately model coronary artery responses of the ageing human heart. As previously emphasized, tissues obtained postmortem, and when possible from recipients during heart transplants, must be integral to theory building, alongside animal models, despite the experimental limitations such tissues impose. A multidisciplinary approach, at all levels of vascular physiology and pharmacology, will be necessary to understand coronary motor activity and human heart disease.

Mechanisms of ergonovine-induced hyperconstriction of coronary artery after x-ray irradiation in pigs

Mechanisms of ergonovine-induced coronary hyperconstriction were examined in vivo and in vitro in miniature pigs. To provoke coronary hyperconstriction, the endothelium of a segment of a major branch of the left coronary artery was denuded in 19 Göttingen miniature pigs (4 to 6 months of age). In Group I (n = 12), the denuded site of the coronary artery was selectively irradiated with 15Gy of x-ray twice, 3 and 4 months after endothelial denudation. The remaining 7 pigs were not irradiated (Group II). The vasoconstrictive effect of intracoronary administration of ergonovine (1 to 1000 microgram) was examined angiographically 3 months (just before irradiation in group I) and 5 months after denudation in the two groups. After the angiographical study, the vessels were isolated and isometric tensions were measured in an organ chamber. In the in vivo studies, ergonovine-induced vasoconstriction at the denuded and x-ray irradiated site in Group I was significantly greater than that at the control site or that at the denuded site in Group II. Pretreatments with serotonin receptor blockers (ketanserin or methysergide) significantly attenuated ergonovine-induced hyperconstriction, while an alpha-adrenergic receptor blocker (prazosin) did not (% inhibition; ketanserin 74 +/- 9%, p < 0.01, methysergide 60 +/- 10%, p < 0.01, prazosin 9 +/- 5%, NS). In the in vitro studies, ergonovine produced significantly greater tension at the denuded and x-ray irradiated site (Group I) than at the control site or at the denuded site (Group II). Ergonovine-induced endothelium-dependent relaxation was impaired at the denuded site in both groups to a similar extent. These results suggest that ergonovine-induced hyperconstriction at the denuded and x-ray irradiated coronary artery resulted mainly from the hyperreactivity of medial smooth muscle mediated by serotonin receptors.

Comparisons of the effects of nicorandil, pinacidil, nicardipine and nitroglycerin on coronary vessels in the conscious dog: role of the endothelium

1. The vasodilator properties of nicorandil on large and small coronary arteries were compared to those of nicardipine, pinacidil, nitroglycerin and acetylcholine in six conscious dogs. 2. Intravenous bolus injections of acetylcholine (0.1 micrograms kg-1), nitroglycerin (0.3-3 micrograms kg-1), pinacidil (10-100 micrograms kg-1), nicardipine (3-30 micrograms kg-1) and nicorandil (10-100 micrograms kg-1) dose-dependently increased circumflex coronary artery diameter and decreased coronary vascular resistance, indicating vasodilator effects on both conduit and resistance coronary arteries. 3. Three days after removal of the endothelium of the circumflex coronary artery (balloon angioplasty), pinacidil- and nicardipine-induced dilation of large coronary arteries was greatly reduced (both -76%, P < 0.01) whereas that produced by nitroglycerin and nicorandil was decreased only slightly and to a similar extent for both drugs (-19%, P < 0.01 and -28%, P < 0.05, respectively). 4. Thus in conscious dogs, nicardipine- and pinacidil-induced dilatation of large coronary arteries is endothelium-dependent. In contrast, the vasodilator effects of nitroglycerin and nicorandil on conduit vessels are endothelium-independent. 5. Finally, our results demonstrate that nicorandil dilates the large coronary arteries through its nitrate-like action and that the ATP-potassium channel opening properties of the drug are not involved in this effect in the conscious dog.

The acute dose-dependent effects of ethanol on canine myocardial perfusion

The acute effects of ethanol (1.0 g/kg and 1.5 g/kg, n = 4 and n = 5, yielding blood concentrations of 1.3 +/- 0.2 mg/ml and 2.4 +/- 0.3 mg/ml) on myocardial perfusion were studied in anesthetized, thoracotomized, artificially ventilated dogs by using a radioactive microsphere technique. The control group (n = 5) received saline. The smaller dose of ethanol decreased perfusion in the left ventricular myocardium from 0.737 +/- 0.122 to 0.555 +/- 0.122 ml/g/min (NS), whereas the greater dose nonsignificantly increased it, from 0.744 +/- 0.115 to 0.819 +/- 0.119 ml/g/min (p < 0.01 between the groups). These changes were most evident in subendocardial layers (p < 0.01 both within the groups and between the groups). The greater dose of ethanol increased systemic vascular resistance (p < 0.01 when compared to the control group). The changes in right ventricular myocardium were insignificant. The acute effect of ethanol on coronary blood flow is dose-dependent with small to moderate doses reducing demand for left ventricular flow but with increasing doses evoking not only an increase in demand for flow but also an increase in flow.

Effects of oral pretreatment with metoprolol on left ventricular wall motion, infarct size, hemodynamics, and regional myocardial blood flow in anesthetized dogs during thrombotic coronary artery occlusion and reperfusion

OBJECTIVES

To study the effects of oral pretreatment with metoprolol over 3 days on hemodynamics, left ventricular function, regional myocardial blood flow, and infarct size in an anesthetized dog model of thrombotic occlusion of the anterior descending coronary artery treated with thrombolysis.

METHODS

Ten dogs received 200 mg metoprolol (Selozok) orally and 8 dogs received placebo for 3 days twice daily and 1 hour before the experiment. Under general anesthesia, thrombotic occlusion was provoked by the copper-coil technique. Intracardiac pressures and their derivatives, cardiac output (thermodilution method), regional coronary blood flow (microspheres), global and regional left ventricular function (ventriculography), and infarct size (triphenyltetrazolium staining) were measured. Measurements were performed during control, after 60 minutes of occlusion, and after 30 and 90 minutes of reperfusion. Thrombolysis was performed in all dogs 60 minutes after occlusion by intravenous infusion of 10 micrograms/kg/min of rt-PA for 30 minutes.

RESULTS

During control cardiac output was lower, total peripheral resistance higher, and Tau and the left ventricular isovolumic relaxation time greater in the metoprolol group. During occlusion and after reperfusion, there were no significant hemodynamic differences between both groups. Blood flow to the area at risk and circumflex territory during occlusion were, respectively, 12.8 +/- 5.80 ml/100 g/min versus 9.65 +/- 8.35 ml/100 g/min (p > 0.05) and 42.58 +/- 7.86 ml/100 g/min versus 61.52 +/- 20.43 ml/100 g/min (p = 0.01) in the metoprolol- and placebo-treated dogs. The ratios of flow area at risk/circumflex territories in the epicardial, midmyocardial, and endocardial layers were, respectively, 0.44 +/- 0.20, 0.19 +/- 0.09, and 0.20 +/- 0.13 in the metoprolol- versus 0.24 +/- 0.16, 0.08 +/- 0.06, and 0.06 +/- 0.07 (p > or = 0.04) in the placebo-treated dogs. The ratio of flow endocardium/epicardium was higher (p > or = 0.02) in the active treatment group during the control period, both in the area at risk and circumflex territory; this was also the case in the circumflex territory at the end of the experiment (p = 0.003). Thirty minutes after occlusion, blood flow to the three layers of the area at risk rose to 2-3 times control values in both groups; a significant increase above control values also occurred in the circumflex territory. After 90 minutes reperfusion, blood flow to both territories was similar in both groups but was comparable to the control; however, in necrotic tissue of the subendocardial layer of both groups, flow fell below control values (p < 0.05). End-systolic volume rose from 21.2 +/- 7.4 ml to 36.1 +/- 11.5 ml (p < 0.05), end-diastolic volume remained constant (46.0 +/- 13.8 vs. 47.9 +/- 12.1 ml; p > 0.05), and ejection fraction fell from 53.9 +/- 8.3% to 25.8 +/- 10.2% (p < 0.05) at the end of the experiment in the metoprolol group. Respective figures for the placebo group were 19.4 +/- 7.9 versus 27.9 +/- 10.9 (p < 0.05), 38.5 +/- 13.0 versus 42.1 +/- 11.0 (p > 0.05), and 50.6 +/- 5.7 versus 35.5 +/- 11.7 (p < 0.05). Fractional shortening of the chords analyzed was similar in both groups during the control period; it fell significantly at the end of the experiment in three chords of the metoprolol group and in five chords of the placebo group. The apical chord in the placebo, but not in the metoprolol, dogs was dyskinetic: fractional shortening was -0.86 +/- 9.7 versus 7.5 +/- 13.5% (p > 0.05). The area at risk was 41.6 +/- 10.6 cm2 in metoprolol- and 40.5 +/- 7.2 cm2 in placebo-treated dogs (p > 0.05); the infarct size, expressed as a percentage of the area at risk, was 29.0 +/- 22.5% and 45.3 +/- 23.6% (p = 0.02), respectively.

CONCLUSIONS

Oral pretreatment with metoprolol limited infarct size and improved regional left ventricular function, probably due to its negative chronotropic and inotropic effects, and also due to an enhancement of collateral flow fr

Vascular relaxing mechanism of denopamine in isolated canine coronary, femoral, mesenteric, and renal arteries

We investigated the mechanism of vascular relaxation produced by denopamine (deno), an oral positive inotropic agent that has selective beta 1-adrenergic action. Deno concentration-dependently (0.1 microM-30 microM) relaxed ring segments of canine femoral, mesenteric, and renal arteries which were partially precontracted with 1 micron phenylephrine or norepinephrine, but did not relax those precontracted with 5 microM prostaglandin F2 alpha or 40 mM K+. The relaxation was not significantly inhibited by pretreatment with 10 microM propranolol or metoprolol. Deno produced a parallel rightward shift in concentration-response curves to phenylephrine in femoral and renal arteries. The Schild plot yielded linear regressions of slopes of 1.301 +/- 0.106 and 0.823 +/- 0.122, respectively, which were not significantly different from unity. The pA2 values of Deno against phenylephrine in femoral and renal arteries were 5.41 +/- 0.03 and 5.76 +/- 0.06, respectively. On the other hand, Deno concentration-dependently (10 nM-10 microM) relaxed ring segments of canine coronary arteries which were partially precontracted with 5 microM prostaglandin F2 alpha. The relaxation was significantly inhibited by pretreatment with 10 microM metoprolol. In conclusion, vascular smooth muscle relaxation by Deno was mediated through beta 1-adrenergic action in canine coronary arteries and through the blocking effect of alpha-adrenoceptors in canine femoral, mesenteric, and renal arteries.

ACE-inhibitors in coronary artery disease?

Angiotensin converting enzyme (ACE)-inhibitors are established in the treatment of arterial hypertension and heart failure. In recent years ACE-inhibitors have also been used in the treatment of patients with coronary artery disease (CAD), since from experimental data an antiischemic action of these agents is suggested. Antiischemic effects of ACE-inhibitors may be exerted through a reduction of myocardial oxygen demand, by a reduction of angiotensin-mediated coronary vasoconstriction, by an interaction with bradykinin and the prostaglandin system, by a modulation of endothelial control of vascular tone, and by an interaction with the sympathetic nervous system. However, clinical findings on potential beneficial effects of ACE-inhibitors in patients with CAD are inconsistent and controversial. While in hypertensive patients with CAD ACE-inhibitors generally seem to attenuate myocardial ischemia at rest and during exercise, a significant fraction of about 30% of normotensive patients with CAD does not benefit or even deteriorates. Lowering of coronary perfusion pressure and alteration of transmural blood flow distribution may be responsible for this. In patients with left ventricular dysfunction (SOLVD) or congestive heart failure (CONSENSUS, SOLVD) ACE-inhibitors have been proven to prevent progressive deterioration in left ventricular function and to reduce mortality. In patients with asymptomatic left ventricular dysfunction after myocardial infarction (SAVE), long-term administration of captropril was associated with an improvement in survival and reduced morbidity and mortality due to major cardiovascular events. Therefore, from a prognostic viewpoint patients with CAD and left ventricular dysfunction or congestive heart failure should be treated with ACE-inhibitors, although the clinical use of ACE-inhibitors in patients with ongoing angina pectoris may be limited by an aggravation of angina, presumably due to critically lowering coronary perfusion pressure. Finally, ACE-inhibitors failed to prevent restenosis after successful PTCA. In conclusion, from a prognostic viewpoint patients with CAD and congestive heart failure or left ventricular dysfunction should be treated with ACE-inhibitors. In hypertensive patients ACE-inhibitors generally seem to attenuate myocardial ischemia. In normotensive patients with CAD and angina pectoris but without left ventricular dysfunction ACE-inhibitors cannot generally be recommended at present, unless the patients, which may have benefit from ACE-inhibitor treatment can be better defined.

Effects of palytoxin on porcine coronary artery rings

Palytoxin, in concentrations as low as 100 fM, caused contractions of porcine coronary artery rings. Palytoxin concentrations of less than 1 nM caused slowly developing contractions which were not maximal even after 2 h. Rings contracted by 100 nM palytoxin achieved maximal tension by 10 min and relaxed to 53% of that maximum after 2 h. Verapamil (1 microM) reduced the rate of contractions induced by 10 nM palytoxin. Exposure of rings to greater than 10 nM palytoxin for 1-2 h reduced contractions to potassium 18 h later to 61% of the expected contraction and abolished those to palytoxin administered later. Both 10 and 100 nM palytoxin depleted potassium from coronary artery rings. Verapamil (10 microM) prevented potassium depletion by 10 nM palytoxin, but neither 10 microM verapamil nor 1 microM nifedipine prevented potassium depletion in rings exposed to 100 nM palytoxin. Thus, the contractile action and the potassium depleting action of palytoxin on the porcine coronary artery involve mobilization of nifedipine- and verapamil-sensitive calcium. Verapamil- and nifedipine-sensitive calcium was not required for depletion of potassium by the highest PTX concentration (100 nM), however.

Muscarinic cholinergic receptors in the human right coronary artery: a receptor binding and autoradiographic study

We used a combination of radioreceptor binding and autoradiographic techniques to study the pharmacological characteristics and anatomical localization of [3H]-quinuclidinyl benzilate (QNB) binding sites in the human right coronary artery. The ligand was bound to sections of the human right coronary artery in a manner consistent with the labelling of muscarinic receptors. The addition of pirenzepine or of carbachol to the incubation medium to generate displacement curves was indicative of the presence of M1 and M2 receptors in the right coronary artery. Autoradiography showed the localization of M1 sites primarily in the medial layer of the right coronary artery. M2 sites were located primarily in the adventitia. No [3H]-QNB binding sites were observed in the endothelium. A possible role of muscarinic receptors in the pathogenesis of coronary vasospasm is discussed.

The effect of hypercholesterolaemia and atherosclerosis on α-adrenoceptor-mediated vasoconstriction in conscious rabbits and rabbit aorta

Rabbits were fed a diet containing 1% cholesterol for 4 or 8 weeks and the constrictor responses to alpha-adrenoceptor agonists, as well as endothelium-dependent and endothelium-independent dilatation, were examined both in vivo and in vitro. The high cholesterol diet caused a significant elevation of plasma cholesterol concentration but no macroscopic evidence of atherosclerosis after 4 weeks whereas after 8 weeks there was a significant development of atherosclerotic lesions in the thoracic and abdominal aorta. In conscious rabbits pressor responses to the non-selective alpha-adrenoceptor agonist noradrenaline and the selective alpha 1-adrenoceptor agonist phenylephrine were enhanced after 4 weeks but returned to control levels after 8 weeks on the diet. The pressor responses to the alpha 2-adrenoceptor agonist B-HT 920 were reduced by the development of atherosclerosis. In the isolated thoracic aorta from these rabbits contractile responses to noradrenaline were impaired by hypercholesterolaemia whereas responses to phenylephrine were unaffected. Endothelium-dependent relaxation was impaired by hypercholesterolaemia both in vivo and in vitro after 4 and 8 weeks on the diet whereas endothelium-independent relaxation was not affected. These results indicate that the effect of hypercholesterolaemia on alpha-adrenoceptor-mediated constriction is dependent on: (1) the absence or presence of atherosclerotic lesions, (2) the size of the artery and (3) the subtype of alpha-adrenoceptor involved in the response. There does not appear to be any relationship between the loss of endothelium-dependent relaxation in hypercholesterolaemia and the observed changes in adrenergic vasoconstriction.

Effects of cocaine on epicardial coronary artery reactivity in miniature swine after endothelial injury and high cholesterol feeding. In vivo and in vitro analysis

The purpose of this study was to determine the effects of cocaine on vasoreactivity in the swine model. Eight miniature pigs underwent regional endothelial denudation of the left anterior descending coronary artery and were then fed a high cholesterol diet. Cross-sectional area (CSA) of coronary arteries was measured by quantitative angiography. Before denudation, intravenous cocaine (1, 3, and 10 mg/kg) decreased CSA of epicardial vessels by 19-44%. At 3 mo after the denudation, the percent reduction in CSA of the denuded vessels induced by the 10 mg/kg dose was significantly augmented compared to nondenuded vessels (59 +/- 5% vs. 48 +/- 4%, P less than 0.05). Under in vitro conditions where isometric force of isolated ring segments was measured, methoxamine (an alpha 1 agonist) or BHT-920 (an alpha 2 agonist) produced similar degrees of contraction of denuded and control vessels; however, cocaine in concentrations up to 3 x 10(-3) M did not produce contraction. These responses were unaffected by removal of the endothelium. Histologically, myointimal thickening was noted at the denuded site. The present study demonstrates an enhanced vasoreactivity of atherosclerotic coronary arteries to cocaine in vivo, the mechanism of which appears to be mediated by endogenous vasoactive substances rather than by a direct action of cocaine on vascular smooth muscle.

Kinin receptors mediating the effects of bradykinin on the coronary circulation in anaesthetized greyhounds

Bradykinin (BK, 0.05 micrograms/kg) or glyceryl trinitrite (5 micrograms/kg) injected into the left circumflex coronary artery of anaesthetized, open-chest greyhounds, caused pronounced increases in large coronary artery diameter (CD) and coronary blood flow (CBF), whereas des-Arg9-BK (0.05-0.3 micrograms/kg), a selective bradykinin B1 agonist, dose dependently elevated CBF but had little effect on CD. BK-induced increases in CD and CBF were not affected by the intracoronary infusion of a selective B1 receptor antagonist, des-Arg9-[Leu8]BK (40 micrograms/min), but were significantly reduced by the infusion of a selective B2 receptor antagonist, D-Arg0-[Hyp3,Thi5,8,D-Phe7] BK (10-12 micrograms/min). The antagonism was reversible and specific for BK since responses to glyceryl trinitrate were not affected. Bilateral vagotomy (n = 3) or autonomic blockade with atropine (0.1 mg/kg i.v.) and propranolol (1 mg/kg i.v.) (n = 5) resulted in significant attenuation of BK-induced increases in CBF but not that of CD. It is concluded that BK is a potent dilator of both conductance and resistance coronary vessels in anaesthetized greyhounds. The dilatation of conductance vessels appears to involve a selective interaction with B2 receptors, while BK-induced increase in CBF may be mediated by both B1 and B2 receptors and involve participation of neuroreflex mechanisms.

Alpha- and beta-adrenergic control of large coronary arteries in conscious calves

Large and small coronary arteries are subject to control by alpha- and beta-adrenergic mechanisms. However, controversy exists as to the distribution and physiological effects of alpha- and beta-adrenergic receptor subtypes in large coronary arteries. Studies in our laboratory have addressed these questions in conscious calves, chronically instrumented to measure large coronary artery diameter and coronary blood flow. Additionally, adrenergic receptor subtype distribution was determined using ligand binding assays in membrane preparations isolated from large coronary arteries of calves. Physiological results demonstrate, in contrast to the results of most previous studies, that both alpha 1- and alpha 2-adrenergic receptors elicit constriction of the large coronary artery. Studies with ganglionic blockade indicate that the constriction was unaltered by autonomic reflexes or presynaptic release of neurotransmitters. Selective beta-adrenergic receptor activation demonstrated that both beta 1- and beta 2-adrenergic receptors elicit dilation of large coronary arteries, and that the vasodilation was direct, i.e., it was not mediated by increases in coronary blood flow. Biochemical characterization of adrenergic subtype density indicated the presence of both alpha 1- and alpha 2-, as well as beta 1- and beta 2-adrenergic receptor subtypes. Thus, both biochemical and physiological data support the concept that large coronary arteries are regulated by both alpha 1- and alpha 2-, as well as beta 1- and beta 2-adrenergic receptor subtypes.

Endothelium and blood flow mediated vasomotion in the conscious dog

Numerous in vitro studies have demonstrated the important role of the vascular endothelium on the vasoactivity of vascular smooth muscle. Experimentation, particularly in conscious animals, is required to study the integrated role of endothelium in the regulation of vascular tone. This article reviews some of the evidence demonstrating endothelium mediated vasodilation and inhibition of vasoconstriction by the endothelium in the chronically instrumented conscious animal. Furthermore, a role for endothelial cells has been shown in the mechanism of blood flow-mediated vasodilation. Finally, the endothelium, through elaboration of constricting factors, e.g., endothelin, can also induce potent vasoconstriction. In the conscious animal endothelin elicits markedly differing degrees of vasoconstriction among the various regional vascular beds.

Peptide-containing nerve fibres in guinea-pig coronary arteries: immunohistochemistry, ultrastructure and vasomotility

The peptidergic innervation of guinea-pig coronary arteries was investigated by means of immunohistochemical, ultrastructural and in vitro pharmacological techniques. A network of nerves was demonstrated in all major epicardial arteries by means of an antiserum to the neuronal marker protein gene product 9.5. The majority of nerve fibres possessed neuropeptide Y (NPY) and tyrosine hydroxylase (TH) immunoreactivity, the number and distribution of nerves immunoreactive for NPY being similar to that of nerves containing TH immunoreactivity. Numerous nerve fibres displaying immunoreactivity for substance P, neuropeptide K and calcitonin gene-related peptide (CGRP) were also found. In double-stained preparations substance P immunoreactivity was co-localized with CGRP and with neuropeptide K immunoreactivities in the same varicose nerve fibres. Ultrastructural studies revealed the presence of numerous axon varicosities at the adventitial-medial border. NPY immunoreactivity was localized in large granular vesicles in nerve varicosities which also contained numerous small granular vesicles. Large granular vesicle-containing nerves also displayed immunoreactivity for dopamine-beta-hydroxylase. With an in vitro method, the vasomotor responses to perivascular peptides were characterized in epicardial and intramyocardial arteries. In epicardial arteries neither noradrenaline nor NPY elicited a contractile response. Only in some intramyocardial arteries was an NPY-mediated contraction demonstrated. No potentiating effect of noradrenaline and NPY was observed in either epicardial or intramyocardial arterial segments. In contrast, CGRP, substance P and vasoactive intestinal peptide (VIP) all produced a concentration-dependent relaxation of both epicardial and intramyocardial arteries. These results suggest that peptide-containing nerves associated with guinea-pig coronary arteries may predominantly be involved in mediating vasodilation.