Showing papers in "Circulation Research in 1983"

Carotid bifurcation atherosclerosis. Quantitative correlation of plaque localization with flow velocity profiles and wall shear stress.

Abstract: The distribution of nonstenosing, asymptomatic intimal plaques in 12 adult human carotid bifurcations obtained at autopsy was compared with the distribution of flow streamline patterns, flow velocity profiles, and shear stresses in corresponding scale models. The postmortem specimens were fixed while distended to restore normal in vivo length, diameter, and configuration. Angiograms were used to measure branch angles and diameters, and transverse histological sections were studied at five standard sampling levels. Intimal thickness was determined at 15 degrees intervals around the circumference of the vessel sections from contour tracings of images projected onto a digitizing plate. In the models, laser-Doppler anemometry was used to determine flow velocity profiles and shear stresses at levels corresponding to the standard specimen sampling sites under conditions of steady flow at Reynolds numbers of 400, 800, and 1200, and flow patterns were visualized by hydrogen bubble and dye-washout techniques. Intimal thickening was greatest and consistently eccentric in the carotid sinus. With the center of the flow divider as the 0 degree index point, mid-sinus sections showed minimum intimal thickness (0.05 +/- 0.02 mm) within 15 degrees of the index point, while maximum thickness (0.9 +/- 0.1 mm) occurred at 161 +/- 16 degrees, i.e., on the outer wall opposite the flow divider. Where the intima was thinnest, along the inner wall, flow streamlines in the model remain axially aligned and unidirectional, with velocity maxima shifted toward the flow divider apex. Wall shear stress along the inner wall ranged from 31 to 600 dynes/cm2 depending on the Reynolds number. Where the intima was thickest, along the outer wall opposite the flow divider apex, the pattern of flow was complex and included a region of separation and reversal of axial flow as well as the development of counter-rotating helical trajectories. Wall shear stress along the outer wall ranged from 0 to -6 dynes/cm2. Intimal thickening at the common carotid and distal internal carotid levels of section was minimal and was distributed uniformly about the circumference. We conclude that in the human carotid bifurcation, regions of moderate to high shear stress, where flow remains unidirectional and axially aligned, are relatively spared of intimal thickening. Intimal thickening and atherosclerosis develop largely in regions of relatively low wall shear stress, flow separation, and departure from axially aligned, unidirectional flow. Similar quantitative evaluations of other atherosclerosis-prone locations and corresponding flow profile studies in geometrically accurate models may reveal which of these hemodynamic conditions are most consistently associated with the development of intimal disease.

Agonist-induced endothelium-dependent relaxation in rat thoracic aorta may be mediated through cGMP.

Abstract: The present study investigates the hypothesis that endothelium-dependent relaxation of vascular smooth muscle may be mediated through the formation of cGMP. Relaxation of the rat thoracic aorta to acetylcholine, histamine, and Ca++ ionophore A23187 was associated with increased levels of cGMP in a time- and concentration-dependent manner, whereas cAMP levels were unaltered. Removal of the endothelium prevented relaxation to these agents and prevented the increased levels of cGMP. Removal of the endothelium after exposure to acetylcholine only partially decreased the elevated levels of cGMP, suggesting that the changes in cGMP occurred within the smooth muscle cells. Eicosatetraynoic acid, an inhibitor of lipoxygenase and cyclooxygenase, and quinacrine, an inhibitor of phospholipase, prevented and reversed acetylcholine-induced relaxation, respectively, and inhibited acetylcholine-induced increased levels of cGMP. In contrast, sodium nitroprusside-induced relaxation and increased levels of cGMP were independent of the presence of the endothelium, exposure to eicosatetraynoic acid, and quinacrine. The present results support the hypothesis that vascular smooth muscle relaxation induced by some agents is dependent on the presence of the endothelium and is mediated through the formation of an endothelial factor that increases cGMP levels in smooth muscle.

Blood pressure and heart rate variabilities in normotensive and hypertensive human beings.

Abstract: Blood pressure and heart rate variabilities were studied in 89 ambulant normotensive or essential hypertensive subjects in whom blood pressure was recorded intra-arterially for 24 hours (Oxford method) under standardized living conditions. Data were analyzed beat to beat by a computer to provide mean values of the 48 half hours of the 24-hour period. Variabilities were assessed by the standard deviation and variation coefficients separately obtained for each half hour, as well as by the standard deviations and variation coefficients obtained by averaging the 48 mean values. In each subject, blood pressure and heart rate varied markedly either among or within half hours, indicating the existence of relatively longand short-term variabilities during the 24 hours. When averaged for all subjects, the long-term variabilities showed only one systematic component, i.e., the marked reduction occurring during sleep. Sleep was further responsible for a marked reduction in the short-term blood pressure and heart rate variabilities. These variabilities showed marked (though nonsystematic) modifications, even outside sleep, which were positively related to the blood pressure and heart rate means. Modifications in blood pressure and heart rate means and short-term variabilities were also positively related to each other. All these features were common to normotensives and hypertensives. In hypertensives, the absolute long and short-term blood pressure variabilities were greater than in normotensives, but the percent blood pressure variabilities were similar. Heart rate variabilities (both absolute and percent) were similar in normotensive and hypertensive subjects. Heart rate variabilities were also similar whether the subjects had impaired or preserved baroreflex control of heart rate (vasoactive drug technique). These findings uncover a number of factors that are associated with and responsible for blood pressure and heart rate variabilities in human beings. The nature of these factors suggest a primary role of central nervous mechanisms in the production of these phenomena and in the overall cardiovascular modulation, with no substantial difference between conditions of normal and chronically elevated blood pressure. (Circ Res 53: 96-104, 1983)

Resting membrane potential, extracellular potassium activity, and intracellular sodium activity during acute global ischemia in isolated perfused guinea pig hearts.

Abstract: Transmembrane potentials, extracellular potassium activity, and intracellular sodium activity were determined during acute global ischemia in Langendorff perfused guinea pig ventricles by microelectrode techniques. Resting membrane potential decreased with a sigmoidal time course from -82 mV to -49.5 +/- 2.7 mV (SD, n = 6) and extracellular potassium activity increased from 4 to 5 mM to 14.7 +/- 1.3 mM (n = 8) during 15 minutes of ischemia. The estimated potassium equilibrium potential was 7 mV more negative than resting membrane potential prior to occlusion, but approached resting membrane potential during ischemia. An increase in extracellular potassium accumulation occurred when heart rate was increased abruptly from 60 to 170 beats/min. After rapid stimulation, a transient decrease of extracellular potassium activity occurred which was abolished in the presence of 10(-6) M strophanthidin. If the preparations were paced before and after aortic occlusion at a constant rate, potassium accumulation was independent of heart rate within a range of 50-170 beats/min. Intracellular sodium activity was 8.8 +/- 2.8 mM (n = 8) prior to occlusion and decreased slightly to values between 4.7 and 7.6 mM after 10-15 minutes of ischemia. The results suggest that relative potassium permeability largely predominates over relative sodium permeability during the decrease of resting membrane potential after interruption of aortic flow. Furthermore, active sodium-potassium exchange compensates for the rate-dependent fraction of potassium efflux and maintains a low intracellular sodium activity. For reasons of electroneutrality, the potassium efflux underlying extracellular potassium accumulation must be balanced by an equivalent charge movement which is not carried by sodium. The most probable hypothesis regarding the charge carriers is that net potassium efflux occurs secondary to efflux of phosphate and lactate generated during ischemia.

History of calcium antagonists.

Abstract: The discovery of Ca++ antagonism as a new principle of action of coronary drugs reaches back to 1964, when we reported that two new compounds, later given the generic names verapamil (Iproveratril) and prenylamine, mimicked the cardiac effects of simple Ca++ withdrawal in that they diminished Ca++-dependent high energy phosphate utilization, contractile force, and oxygen requirement of the beating heart without impairing the Na+-dependent action potential parameters. Since these effects, clearly distinguishable from beta-receptor blockade, could promptly be neutralized with elevated Ca++, beta-adrenergic catecholamines, or cardiac glycosides, measures that restored the Ca++ supply to the contractile system, we introduced in 1969 the term Ca++ antagonist as a novel drug designation. In an extensive search for other Ca++ antagonists, a considerable number of substances that also met these criteria were identified in our laboratory, i.e., D 600, nifedipine, niludipine, nimodipine, perhexiline, fendiline, terodiline. In 1975 Japanese pharmacologists contributed diltiazem to this group. According to our studies, all specific Ca++ antagonists interfere with the uptake of labelled Ca++ into the myocardium and prevent myocardial necrotization arising from deleterious intracellular Ca++ overload; they also block excitation-contraction coupling of vascular smooth muscle, and in this manner, lower Ca++-dependent coronary vascular tone and neutralize all types of experimental coronary spasms. According to our voltage-clamp studies, these antagonists basically act as specific inhibitors of the slow transsarcolemmal Ca++ influx but do not (or only slightly) affect the fast Na+ current that initiates normal myocardial excitation. However, Ca++ antagonists can counteract SA and AV nodal automaticity, AV conduction, and ectopic impulse discharge because, in these cases, Ca++ ions necessarily act as transmembrane electric charge carriers.

Effect of positive inotropic agents on the relation between oxygen consumption and systolic pressure volume area in canine left ventricle.

Abstract: We analyzed the effect of positive inotropic agents on the relation between left ventricular oxygen consumption and the systolic pressure-volume area. Pressure-volume area is a measure of total mechanical energy for ventricular contraction, and is a specific area in the ventricular pressure-volume diagram circumscribed by the end-systolic and end-diastolic pressure-volume relation curves and the systolic segment of the pressure-volume trajectory. Either epinephrine (1 microgram/kg per min, iv) or calcium ion (0.03 mEq/kg per min, iv) was administered to canine excised cross-circulated hearts. These agents increased an index of ventricular contractility, Emax, or the slope of the end-systolic pressure-volume line, by 70%. The regression lines of ventricular oxygen consumption on pressure-volume area in control and in enhanced contractile states were of the same formula: ventricular oxygen consumption (ml O2/beat per 100 g) equals A times pressure-volume area (mm Hg ml/beat per 100 g) plus a constant B. Coefficient A remained unchanged at 1.8 X 10(-5) ml oxygen/(mm Hg ml), but constant B increased from 0.03 ml oxygen/beat per 100 g by more than 50% with either agent. The reciprocal of A reflects the energy conversion efficiency for the total mechanical energy, and this efficiency remained near 36%. The increase in B was equal to the directly measured increment in ventricular oxygen consumption for mechanically unloaded contraction. The basal metabolism remained unchanged. We conclude that the augmented oxygen consumption under the acutely enhanced contractile state with either epinephrine or calcium was caused primarily by an increased energy utilization associated with the excitation-contraction coupling.

Myosin isoenzymes in normal and hypertrophied human ventricular myocardium.

Abstract: We tested the hypothesis that hypertrophy of the human heart is associated with the redistribution of ventricular isomyosins. Human cardiac myosin was isolated from autopsy samples of left ventricular free wall of patients with cardiac hypertrophy and of fetal, young, and adult subjects without heart disease. The following parameters were studied: electrophoretic migration in denaturing and non-denaturing conditions; immunological cross-reactivities with three different types of antibodies; and early phosphate burst size and steady state ATPase activities stimulated by K+-EDTA, Ca++, Mg++, and actin. The antibodies were chosen for their ability to recognize selectively the rat V1 and V3 cardiac isomyosins. The first type was a monoclonal antibody, CCM-52, prepared against embryonic chick cardiac myosin, the second was an anti-beef atrial myosin, and the third was an anti-rat V1 myosin. CCM-52 reacted with a greater affinity with rat V3 than with rat V1, and was a probe of mammalian V3. Anti-beef atrial myosin and anti-rat V1 myosin both recognized specifically beef atrial and rat V1 myosins, and were thus considered as probes of mammalian V1. Under non-denaturing conditions, human myosins migrated as rat V3 isomyosin; under denaturing conditions, no difference was observed in any of the electrophoretic parameters between all samples tested, except for the fetal hearts which contained a fetal type of light chain. The immunological studies indicated that human myosins were composed mostly of a V3 type (HV3), but contained also some V1 isomyosin. A technique was developed to quantify the amount of human VI isomyosin which was found to range from almost 0 to 15% of total myosin, and to vary from one heart to the other, regardless of the origin of the heart. Enzymatic studies showed no significant difference between normal, hypertrophied, and fetal hearts in any of the activities tested. However, there was a significant correlation between Ca++-stimulated ATPase activities and HV1 amount (at 0.05 M KCl, n = 18, r2 equal 0.49, P less than 0.01; at 0.5 M KCl, n = 18, r 2 = 0.5, P less than 0.01). These data demonstrate the heterogeneity of human ventricular myosin, which appears to be composed, as in other mammalian species, of V1 and V3 isoforms of different ATPase activities (V1 greater than V3). However it seems that V1 to V3 shifts do not appear to be of physiological significance in the adaptation of human heart to chronic mechanical overloads.

Effect of sulfinpyrazone on homocysteine-induced endothelial injury and arteriosclerosis in baboons.

Abstract: The effect of sulfinpyrazone on endothelial injury induced by homocysteine has been studied both in vitro, using cultured human umbilical vein endothelial cells, and in vivo, using a primate model of homocysteine-induced arteriosclerosis. Oral sulfinpyrazone (250 mumol/kg body weight per day in three divided doses) in eight chronically homocystinemic baboons (0.14 +/- 0.04 mM plasma homocystine) decreased the extent of aortic endothelial injury as measured morphometrically by silver staining techniques, compared with six untreated comparably homocystinemic animals (denuded surface averaged 0.5% with range 0-2.1 vs 7.7 +/- 1.6%, respectively; P less than 0.001). Sulfinpyrazone therapy to homocystinemic baboons also normalized platelet survival and turnover measurements (5.1 +/- 0.4 days and 70,000 +/- 11,000 platelets/microliter per day vs. 2.8 +/- 0.6 days and 179,000 +/- 19,000 platelets/microliter per day in untreated homocystinemic controls; P less than 0.001). Sulfinpyrazone therapy also reduced the size and frequency of homocysteine-induced intimal lesion formation (P less than 0.001). Although sulfinpyrazone reduced the amount of specific 51Cr release from cultured human umbilical vein endothelial cells induced by 10 mM homocysteine after 24 hours of co-incubation, no effect was observed in assays of endothelial cell detachment when sulfinpyrazone (10(-5) M) or its thioether metabolite were pre- or co-incubated during 24 hours with homocysteine (2.5-10 mM). These data suggest that sulfinpyrazone may protect endothelial cells from injury in vivo by some apparently indirect mechanism.

Hydrogen peroxide and hydroxyl radical mediation of activated leukocyte depression of cardiac sarcoplasmic reticulum. Participation of the cyclooxygenase pathway.

Abstract: Human peripheral blood leukocytes, activated by phorbol myristate acetate, disrupt canine sarcoplasmic reticulum calcium transport, in vitro, by an oxygen-derived free radical mechanism. Activated leukocytes significantly depress Ca++ uptake activity and Ca++ -stimulated, Mg++ -dependent ATPase activity. The depression is completely inhibited by sodium-azide (0.1 mM) or the combination of superoxide dismutase (10 micrograms/ml) and catalase (10 micrograms/ml). Exogenous hydrogen peroxide (0.441-4.41 mM) uncoupled Ca++ uptake activity from ATP hydrolysis, and this effect was inhibited by catalase. Mannitol alone did not inhibit the effects of activated leukocytes, but superoxide plus mannitol (20-100 mM) resulted in normal ATPase activity, while Ca++ uptake remained depressed. In the presence of indomethacin and ibuprofen, activated leukocytes depressed Ca++ uptake and had no effect on ATPase activity. 2-Amino-methyl-4-t-butyl-6-iodophenol (MK-447) further depressed Ca++ uptake and partially inhibited the effect on ATPase activity. Indomethacin plus catalase completely inhibited the effects of activated leukocytes on cardiac sarcoplasmic reticulum. We conclude, first, that activated leukocytes depress canine cardiac sarcoplasmic reticulum Ca++ transport by an oxygen-free radical mechanism with the generation of hydrogen peroxide and hydroxyl radical. In addition to the classical membrane NADPH oxidase system, significant oxygen radical generation can occur through the cyclooxygenase pathway of arachidonic acid metabolism, and seems to be responsible for the generation of the hydroxyl radical.

The effects of cardiac sympathetic nerve stimulation on perfusion of stenotic coronary arteries in the dog.

Abstract: The interaction of sympathetic vasoconstriction with the coronary reserve distal to stenoses and the role of α-adrenergic mechanisms in the genesis of myocardial ischemia were studied in 42 anesthetized open-chest dogs. Left cardiac sympathetic nerve stimulation was performed after bilateral cervical vagotomy: with intact coronary arteries, with an intermediate stenosis, and with a severe stenosis on the circumflex coronary artery. Stenoses were produced by a wire snare and defined as intermediate by the reduction of the reactive hyperemia repayment following a 15-second occlusion from 460 ± 100 to 140 ± 30%; a severe stenosis was defined by only 25 ± 8% reactive hyperemia repayment. Cardiac sympathetic nerve stimulation decreased the end-diastolic coronary resistance of intact coronary arteries from 0.79 ± 0.05 to 0.53 ± 0.06 mm Hg × min × 100 g/ml (P < 0.01) and the end-diastolic poststenotic resistance of the moderately stenosed arteries from 0.65 ± 0.08 to 0.50 ± 0.07 mm Hg × min × 100 g/ml (P < 0.01). Cardiac sympathetic nerve stimulation increased the end-diastolic resistance distal to severe stenoses from 0.57 ± 0.04 to 0.97 ± 0.18 mm Hg × min × 100 g/ml (P < 0.01). This stimulation resulted in net lactate production of the circumflex-perfused myocardium; four dogs died by ventricular fibrillation. There was a hyperbolic correlation of the cardiac sympathetic nerve stimulation-induced change in resistance to the degree of coronary hyperemic reserve (r = 0.81). Phentolamine (2 μg/kg, iv) and rauwolscine (0.2 μg/kg, iv) prevented the increase in resistance distal to severe stenoses during cardiac sympathetic nerve stimulation, whereas prazosin (1.2 μg/ kg, iv) was ineffective. After j3-blockade with propranolol (2 μg/kg, iv), rauwolscine still prevented the increase in poststenotic resistance during cardiac sympathetic nerve stimulation. We conclude that there is a continuous unmasking of sympathetic vasoconstriction with increasing severity of a stenosis and, thus, decreasing coronary reserve. This vasoconstriction is mediated by postjunctional o2-receptors and can induce myocardial ischemia distal to severe coronary stenoses.

Actions of adenosine and isoproterenol on isolated mammalian ventricular myocytes.

Abstract: We investigated the effects of adenosine and isoproterenol on enzymatically dispersed ventricular myocytes from bovine and guinea pig hearts. Intracellular stimulation of relaxed myocytes with regular striation patterns and normal resting potential resulted in action potentials with full plateaus accompanied by contractions. Adenosine in concentrations up to 0.2 mM had no significant effect on any of the action potential parameters or on the basal contractility. In contrast, in the same cells, adenosine effectively antagonized the stimulatory effect of isoproterenol. Isoproterenol (1-10 nM) prolonged the action potentials by 34-41%, displaced the plateau to more positive potentials, and caused a 3-fold increase in the extent of myocyte sarcomere shortening. In the presence of adenosine (5-50 microM), isoproterenol increased the action potential duration by only 8-9%, the shift of the plateau was nearly abolished, and the increase in the extent of myocyte sarcomere shortening was less than 10%. In some of the myocytes, isoproterenol (1-10 nM) induced depolarizing afterpotentials accompanied by aftercontractions. The afterdepolarizations occasionally reached threshold resulting in triggered sustained rhythmic activity. Adenosine (20-50 microM) not only reduced the amplitude of the afterdepolarizations and aftercontractions, but also abolished the sustained rhythmic activity. We conclude, first, that isolated ventricular myocytes respond to isoproterenol and adenosine; second, that adenosine has no direct effect, but effectively antagonizes the stimulatory actions of isoproterenol; third, that findings are consistent with the ones reported for multicellular ventricular preparations; fourth, that adenosine concentrations required to attenuate the actions of isoproterenol are in the range of adenosine concentrations released by cardiac cells when oxygen availability is limited and/or demand is increased; and fifth, that endogenously released adenosine may modulate the electrophysiological and contractile effects of catecholamines.

Mechanism of adenosine inhibition of catecholamine-induced responses in heart.

Abstract: The properties of adenosine inhibition of catecholamine-induced responses were investigated, using an isolated rat heart preparation. Perfusion of hearts with 0.1 microM isoproterenol increased myocardial cAMP content 2.8-fold, activation of cAMP-dependent protein kinase 4.4-fold, phosphorylase a formation 3.4-fold, left ventricular pressure 1.8-fold, rate of ventricular pressure development 2.1-fold, and rate of ventricular relaxation 2.2-fold within 1 minute. When perfused with the isoproterenol, 10 microM adenosine reduced the catecholamine-produced increase in cAMP, cAMP-dependent protein kinase, and phosphorylase by 30-40%, and the elevation in left ventricular pressure and rate of ventricular pressure development by 40-70% within 40 seconds. More than 2 minutes were required for the nucleoside to significantly reduce the isoproterenol-elicited increase in the rate of ventricular relaxation. Perfusion of adenosine alone at concentrations from 0.1 to 10 microM were without effect on the above parameters. Theophylline at 50 microM had no effect alone on the above parameters but blocked the inhibitory actions of adenosine on the isoproterenol-induced responses. In the presence of 15 mM Mg++ adenosine reduced by approximately 56% the 2-fold increase in myocardial membrane adenylate cyclase activity produced by 1 microM isoproterenol without affecting basal or fluoride-stimulated activity. Adenosine also reduced the isoproterenol-induced increase in enzyme activity assayed at 1-2 mM Mg++, a level that more closely approximates the intracellular activity of the ion. The results suggest that physiological concentrations of adenosine attenuate the catecholamine-induced increase in cAMP content, cAMP-dependent protein kinase activation, phosphorylase a formation, and contractile parameters in the working heart, via reducing the beta-adrenergic activation of adenylate cyclase.

The relationship of human atrial cellular electrophysiology to clinical function and ultrastructure.

Abstract: Although previous studies have described the electrophysiological and ultrastructural characteristics of human cardiac fibers, no attempt has been made as yet to describe quantitatively the relationship between the ultrastructural and cellular electrophysiological derangements occurring with cardiac disease, and their clinical manifestations. In this study, we used standard microelectrode techniques to record the action potential characteristics of human atrial fibers obtained during cardiac surgery and correlated the electrophysiological parameters with clinical and ultrastructural data. Ultrastructure was studied by optical and electron microscopy. We found a multiple linear regression among maximum diastolic potential, atrial size and pressure, P wave duration and ultrastructure changes. Proliferations of Z band material, widening of intercalated discs, and degenerative changes were quantified and correlated with electrophysiological and clinical data. These studies emphasize the relationship between hemodynamic anomalies and resultant changes in both human atrial fiber structure and electrical function. Finally, the likelihood of occurrence of arrhythmias can be predicted using the analytic method described.

Salvage of myocardial function by coronary artery reperfusion 1, 2, and 3 hours after occlusion in conscious dogs.

Abstract: The effects of coronary artery occlusion and reperfusion at 1 hour (1-hr group), 2 hours (2-hr group), and 3 hours (3-hr group) were compared with a permanently occluded group (P group) on measurements of overall left ventricular and regional endocardial function over a 4-week period. The studies were conducted in conscious dogs 1-2 weeks after recovery from instrumentation with solid state left ventricular pressure gauges, aortic, and left atrial catheters, hydraulic occluders, and Doppler flow transducers on the left anterior descending or left circumflex coronary arteries, and multiple pairs of ultrasonic transducers implanted in the endocardial third of the left ventricular free wall to measure endocardial segment shortening. During coronary artery occlusion, similar effects were observed in the four groups. At 1 hour after coronary artery occlusion, three classes of ischemia-induced dysfunction were observed; dyskinetic (systolic shortening completely lost and replaced by paradoxical bulging), severely hypokinetic (systolic shortening depressed by 65-95%), and moderately hypokinetic (systolic shortening depressed by 40-65%). Compared with the P group, significant (P less than 0.05) return of systolic shortening and velocity of shortening gradually occurred over the 4-week period following reperfusion in all classes of segments in the 1-hour group. In the 2-hour group, systolic shortening returned in the moderately and severely hypokinetic segments, but was slight and not significant in the dyskinetic segments. In the 3-hour group, significant systolic shortening returned only in the moderately hypokinetic segments. The effects of isoproterenol, 0.04 micrograms/kg per min, and exercise were compared on "salvaged" dyskinetic segments prior to and at 1, 2, 3, and 4 weeks after coronary artery occlusion and reperfusion. The responses to isoproterenol were significantly depressed at 1 week after reperfusion and gradually recovered over the 4-week period. At 3-4 weeks after reperfusion, severe exercise also increased shortening and velocity of shortening in "salvaged" segments. Thus, in the conscious dog, coronary artery reperfusion at 1 hour after coronary artery occlusion results in substantial return of endocardial function even in the most severely ischemic myocardium. The "salvaged" myocardium responds adequately to myocardial stress with increases in the extent and velocity of systolic shortening, as long as 3-4 weeks after reperfusion are allowed for recovery. However, after 3 hours of coronary artery occlusion, little salvage of regional myocardial function can be induced by acute reperfusion in this model.

Vascular smooth muscle cell hypertrophy and hyperploidy in the Goldblatt hypertensive rat

Abstract: Our major objective in this study was to examine the hypothesis that the aortic smooth muscle cell hypertrophy and hyperploidy observed in previous studies of spontaneously hypertensive rats is not peculiar to that model, but also occurs in Sprague-Dawley rats made hypertensive by a Goldblatt procedure (two-kidney, one-clip model). Flow microfluorometric and microdensitometric analysis of smooth muscle cell DNA content showed a significant increase in the frequency of tetraploid smooth muscle cells from 5.6 +/- 0.9% in controls to 14.6 +/- 1.94% in hypertensives 1 month after Goldblatt surgery. Neither differences in ploidy nor elevation in blood pressure were apparent 2 weeks after surgery. The frequency of polyploid smooth muscle cells increased with age, duration of hypertension, and level of blood pressure. Analysis of the interrelationship between smooth muscle cell ploidy and hypertrophy in 5-month post-surgery Goldblatts by cytospectrophotometric measurements of the protein and DNA content of individual smooth muscle cells showed that tetraploid and octaploid cells from Goldblatt rats had 64% and 129% greater protein mass, respectively, than diploid cells. In addition, the mean protein mass of smooth muscle cells from Goldblatts was approximately 100% greater than that of normotensive controls, with each of the ploidy classes in Goldblatts having a higher frequency and mass than the corresponding cells in controls. Estimates of cell number per centimeter aortic length, based on measurements of average DNA/cell and total aortic medial DNA, showed no difference between hypertensives and controls. Furthermore, the rate of accumulation of polyploid cells could account for the increased frequency of cells undergoing DNA synthesis as measured by [3H]thymidine autoradiography. Thus, smooth muscle cell hypertrophy, not hyperplasia, was responsible for the increased mass of smooth muscle in aortas of Goldblatt hypertensive rats compared with normotensive controls, and this smooth muscle cell hypertrophy was accompanied by an increase in DNA ploidy.

Dynamic ventricular interaction in the conscious dog.

Abstract: In nine conscious, chronically instrumented dogs, ultrasonic dimension transducers measured left ventricular anterior-posterior and septal-free wall minor axis and major axis diameters. Matched micromanometers measured right and left ventricular transmural and transeptal pressures. Ventricular pressures and volumes were varied by inflation of implanted vena caval and pulmonary artery occluders, and the functional significance of the two types of ventricular interaction, i.e., direct and series, was determined. The left ventricle was represented by a modified ellipsoidal geometry. Left ventricular stroke volume calculated from the dimension data correlated well with that measured directly from ascending aortic electromagnetic flow probes during all interventions (r greater than or equal to 0.96). Partial pulmonary artery occlusion significantly increased right ventricular diastolic and systolic pressures as compared to values obtained during control and venal caval occlusion. During pulmonary artery occlusion, latitudinal septal eccentricity was increased throughout the cardiac cycle compared to control and vena caval occlusion (P less than 0.05), indicating leftward interventricular septal shifting and significant alteration of left ventricular shape. The normalized diastolic pressure-volume curve was shifted to the left with pulmonary artery occlusion compared to control and indicated a decrease in left ventricular chamber compliance. However, when selected cardiac cycles with similar end-diastolic volumes from vena caval and pulmonary artery occlusions were compared, parameters of left ventricular systolic function (stroke volume, percent systolic shortening, peak aortic blood flow, peak left ventricular pressure, and its first derivative) remained relatively constant. These data suggest that mean myocardial fiber length is the major preload determinant of left ventricular systolic function independent of chamber pressure and shape, and that direct ventricular interaction mediated by interventricular septal shifting has minimal effects on systolic myocardial performance in this model. Thus, series ventricular interaction during acute imbalances in biventricular loading, where the output of the right ventricle determines the input of the left, seems to be far more important than direct interaction to the regulation of overall cardiac function.

Heterogeneity of the action potential in isolated rat ventricular myocytes and tissue.

Abstract: The objectives of this study were to measure action potential parameters in enzyme-dissociated, adult rat ventricular myocytes stimulated at 1 Hz, to compare these measurements with those obtained from intact ventricular tissue, and to determine myocyte and tissue responses at stimulus frequencies between 0.1 and 5 Hz. Action potentials were characterized in terms of amplitude, overshoot, resting potential, duration at 25% and 75% repolarization (APD25, APD75), and Vmax. Based on statistical differences in APD25 and APD75, myocyte action potentials were classified as type I (3.1 +/- 1.0 and 21.5 +/- 3.6 msec), type II (7.4 +/- 1.1 and 38.2 +/- 6.7 msec), or type III (14.5 +/- 1.9 and 46.0 +/- 4.1 msec). Action potentials corresponding to type I were found in right ventricular endocardium and right papillary muscles, and those corresponding to types II and III in the left ventricular endocardium [apex, middle (II); base (III)] and left papillary muscles (II). Myocytes and papillary muscles responded to increases in driving rate with nearly identical lengthening of APD25 and shortening of APD75. The one exception was at 5 Hz where a lengthening of the APD75 occurred in some myocytes. We conclude that action potential configuration in rat ventricle is heterogeneous, and that this is reflected by the different types of action potentials in isolated myocytes. It is likely that the magnitude of a transient outward current is a determinant of action potential configuration, and that slow reactivation of this current is a significant factor underlying the stimulus frequency response.

Interaction of verapamil and other calcium channel blockers with alpha 1- and alpha 2-adrenergic receptors.

Abstract: To determine the specificity of the previously demonstrated competition of verapamil with radioligand binding to alpha-adrenergic receptors, we examined the interaction of calcium channel blockers with alpha 1- and alpha 2-adrenergic receptors on several tissues. Verapamil competed for [3H] prazosin binding to alpha 1-adrenergic receptors and for [3H]yohimbine binding to alpha 2-adrenergic receptors in several tissues (human platelets, rat kidney and heart, and cultured muscle cells) with dissociation constants of 0.6-6 microM. The calcium channel blockers D600, D591, fendiline, and prenylamine--which are structural analogues of verapamil--also competed for [3H]yohimbine binding to human platelets. Two other calcium channel blockers, diltiazem and nifedipine, did not compete for [3H] yohimbine binding to human platelets or [3H]prazosin binding to membranes prepared from rat ventricles. We used [3H]nitrendipine binding to identify putative calcium channels on rat myocardial membranes. Nifedipine and verapamil blocked these [3H]nitrendipine-binding sites on ventricular membranes, but epinephrine and prazosin did not, indicating that the ventricular alpha 1 receptors and calcium channels are distinct. We found no specific [3H]nitrendipine binding to human platelets. We conclude that the interaction of verapamil with alpha-adrenergic receptors is not receptor subtype or tissue specific, that interaction with alpha-adrenergic receptors is not a property of all calcium channel blockers, and that the interaction of verapamil with alpha-adrenergic receptors and its interaction with calcium channels occur at at least two distinct sites.

Coronary arterial spasm in ischemic heart disease and its pathogenesis. A review.

Abstract: Coronary arterial spasm plays an important role iun the production not only of variant angina but, also, of resting angina other than variant angina, of some exertional angina, and of some acute myocardial infarction. Coronary arterial spasm is most likely to occur at rest, particularly from midnight to early morning, and is usually not provoked by exercise in the daytime. This is related to the fact that the tone of coronary artery is increased from midnight to early morning, whereas it is decreased in the daytime after physical activities. Coronary arterial spasm can be induced by exercise, cold pressor test, hyperventilation, Valsalva maneuver, and the administration of pharmacological agents such as sympathomimetic agents (epinephrine, norepinephrine, etc.), beta-blocking agents (propranolol, etc.), parasympathomimetic agents (methacholine, pilocarpine, etc.), ergot alkaloids (ergonovine, ergotamine, etc.), alcohol, and others, particularly in the morning when spontaneous coronary arterial spasm is most likely to occur. Diltiazem and nifedipine, calcium-blocking agents, prevent coronary arterial spasm induced by these procedures in almost all patients. Phentolamine, an alpha-blocking agent, also suppresses coronary arterial spasm induced by these procedures in 81% of the patients. On the other hand, propranolol, a beta-blocking agent, is not only ineffective in suppressing coronary arterial spasm in 82% of the patients, but aggravates coronary arterial spasm in 41% of the patients. The acute attack of coronary arterial spasm can be promptly relieved by the administration of nitroglycerin.

Recovery of left ventricular segmental function after long-term reperfusion following temporary coronary occlusion in conscious dogs. Comparison of 2- and 4-hour occlusions.

Abstract: We compared the recovery of left ventricular segmental function with long-term reperfusion after two periods of coronary artery occlusion in conscious dogs to determine the relationship between the severity and duration of a temporary ischemic insult and the potential for recovery of contractile function. Twenty-seven awake dogs, previously instrumented with ultrasonic crystals for measuring regional left ventricular net systolic wall thickening, underwent 2 (group I) or 4 (group II) hours of left anterior descending coronary artery occlusion, followed by 1 month of reperfusion. Dogs were studied 24 hours after reperfusion and at weekly intervals for 1 month, after which the contractile reserve of left ventricular segments was assessed by their response to dopamine and postextrasystolic potentiation. The myocardial infarctions produced in the experimental model were relatively small. Left ventricular segments were classified by their severity of contractile dysfunction 1 hour after left anterior descending occlusion: class 1, >67% pre-occlusion net systolic wall thickening; class 2, 0–66.9%; class 3, <0% (paradoxical thinning). Class 1 segments in both groups showed trivial changes in net systolic wall thickening and regional myocardial blood flow (measured with 9–15 jtm microspheres) with left anterior descending occlusion and reperfusion. Class 2 segmental net systolic wall thickening was 32 ± 5 (SEM) and 30 ± 4% of control (P < 0.005 vs. control values) 1 hour after left anterior descending occlusion in groups I and II, respectively; endocardial blood flow to these segments decreased 56 ± 13% and 49 ± 12% (P < 0.05 vs. control values). Class 3 segments displayed severe dyskinesis (net systolic wall thickening = —43 ± 6% and —33 ± 5%, groups I and II) and reductions in endocardial blood flow during left anterior descending occlusion [—81 ± 10% and —78 ± 8% (P < 0.05)]. Segmental function of class 2 and 3 segments in group I dogs improved significantly with long-term reperfusion, attaining values of net systolic wall thickening of 66 ± 9 and 26 ± 9% control, respectively, at 1 month. Mean values of net systolic wall thickening attained by class 2 and 3 segments in this group during postextrasystolic potentiation were 93 ± 7 and 50 ± 13, respectively. In contrast, the net systolic wall thickening of class 2 segments in group II dogs did not change significantly with long-term reperfusion (net systolic wall thickening = 37 ± 12 at 1 month) and the average net systolic wall thickening attained by these segments with postextra- systolic potentiation was 51 ± 10%. Class 3 segments in group II dogs underwent a reversal of paradoxical thinning, but were essentially akinetic (net systolic wall thickening = 12 ± 12%) after 1 month of reperfusion and did not demonstrate significant inotropic reserve. The extent of segmental necrosis paralleled the degree of contractile dysfunction in the three segment classes, but was not significantly different between groups I and II. Similarly, macrohistochemically determined area-at-risk and gross infarct size were not different between the two groups of dogs. Thus, reperfusion after 2 hours of left anterior descending occlusion eventually improves the contractile function at sites of moderate and severe dysfunction, whereas long-term reperfusion after 4 hours of left anterior descending occlusion does not restore contractile function to class 2 segments significantly, nor does it restore important degrees of contractile function to severely dyskinetic segments. These differences in recovery of contractile function apparently are not attributable to greater segmental necrosis, larger areas of infarction, or ultimate alterations in segmental coronary blood flow.

Morphometry of exercise-induced right ventricular hypertrophy in the rat.

Abstract: In our morphometric study of the effects of exercise on the heart, male Wistar-Kyoto rats at 5 weeks of age were subjected daily to a moderate treadmill running program that lasted for 7 weeks. The heart responded to physical conditioning by different magnitudes of tissue growth of the right (22%) and left (7%) ventricular myocardium, the latter change not statistically significant. The increase in right ventricular volume was associated with a 25% enlargement of ventricular area, a 26% average lengthening of the myocytes, and no change in sarcomere length and in ventricular midwall thickness. Exercise produced significant alterations in the quantitative parameters of the microvasculature of the right ventricle, but no appreciable changes in the left ventricle. Right ventricular hypertrophy was characterized by an absolute 44% growth of the endothelial luminal surface brought about through a 16% increase in capillary numerical density, and a 41% augmentation of the total length of the capillary network. Maximum diffusion distance from the capillary wall to the mitochondria of myocytes decreased 10% as a result of capillary proliferation and the lack of lateral expansion of myocyte cross-sectional area. Evaluation of the subcellular constituents of myocytes showed no change in the mitochondria:myofibrils volume ratio, indicating a growth of these components proportional to each other and to the growth of the myocyte population as a whole. It was concluded that, as a result of running exercise, right ventricular growth is analogous to eccentric hypertrophy in which the structural adaptations of the capillary bed can be expected to improve the diffusion and transport of oxygen within the tissue.

Effects of sympathetic stimulation and changes in arterial pressure on segmental resistance of cerebral vessels in rabbits and cats.

Abstract: The purpose of this study was to determine directly segmental cerebral vascular resistance during sympathetic stimulation and changes in arterial pressure. We measured pressure in pial arteries in anesthetized rabbits and cats with a servo-null pressure-measuring device. Cerebral blood flow was measured with microspheres. Using these measurements we calculated large artery resistance and small vessel resistance. Under control conditions, large artery resistance accounted for approximately 40% of total cerebral vascular resistance. Sympathetic stimulation increased large artery resistance and reduced pial artery pressure. Cerebral blood flow and total cerebral vascular resistance did not change significantly. To examine constrictor responses of small cerebral vessels, we raised cerebral perfusion pressure by obstructing the descending aorta. During increases in arterial pressure from 70 to 110 mm Hg, large artery resistance tended to increase and small vessel resistance increased significantly. We conclude that, although sympathetic stimulation has little effect on total cerebral vascular resistance under normal conditions, it has important effects on segmental vascular resistance and cerebral microvascular pressure, and that sympathetic stimulation and increases in systemic arterial pressure within the physiological range have markedly different effects on segmental resistance; i.e., sympathetic stimulation produces constriction only in large arteries, and increases in systemic arterial pressure within the physiological range produce constriction primarily in small vessels.

Effect of regional ischemia on the left ventricular end-systolic pressure-volume relationship of isolated canine hearts.

Abstract: We studied the effects of regional ischemia on the left ventricular isovolumic end-systolic pressure-volume relationship (ESPVR) in six excised, blood-perfused canine ventricles. We created different extents of regional ischemia by ligating various branches of the coronary arteries while keeping the coronary arterial pressure constant (80 mm Hg). The extent of regional ischemia (Rm) relative to the total mass of the left ventricular myocardium was determined by regional myocardial blood flow measured by the radioactive microsphere technique. With regional ischemia, the ESPVR shifted rightward without significant change in slope in the physiologic end-systolic pressure range. In the subphysiological end-systolic pressure range, however, its slope became lower than control. In order to quantify the degree of the rightward shift, we measured the extrapolated volume axis intercept (Vo) by fitting a straight line to the ESPVR in the physiological range under control and ischemic conditions. The shift in Vo (delta Vo) associated with ischemia was linearly correlated with Rm (delta Vo = 50.7Rm-0.6, n = 28, r = 0.944, P less than 0.001). We conclude that the major effect of acute regional ischemia on the ESPVR in the physiological pressure range is a parallel rightward shift. This forms a striking contrast to the effect of global ischemia (under which only the slope is affected without a substantial change in Vo).

Renal adrenoceptor mediation of antinatriuretic and renin secretion responses to low frequency renal nerve stimulation in the dog.

Abstract: L'antinatriurese pendant la stimulation nerveuse renale a pour mediateur les α, recepteurs renaux et non pas les α 2 ou β adrenorecepteurs renaux. La secretion de renine a pour mediateurs les β,-adrenorecepteurs

Determinants of a protective effect of glucose and insulin on the ischemic myocardium. Effects on contractile function, diastolic compliance, metabolism, and ultrastructure during ischemia and reperfusion.

Abstract: The efficacy of hyperglycemia and insulin therapy for reducing ischemic myocardial injury is controversial and unproven. Accordingly, factors that might influence the effects of hyperglycemia and insulin were studied in isolated perfused rabbit hearts at two degrees of global ischemia, either "severe" or "moderate." During the ischemic period, different groups (n = 15-28/group) received either 100 mg/100 ml glucose-no insulin (control group), 500 mg/100 ml glucose + 100 mU/ml insulin (G + I), or 100 mg/100 ml glucose + 400 mg/100 ml mannitol (osmotic control). During moderate ischemia, effective washout of myocardial lactate was maintained, and hyperglycemia and insulin doubled the glycolytic flux, completely prevented contracture during ischemia, decreased contracture during reperfusion, increased recovery of postischemic contractile function, decreased ultrastructural damage, and increased high energy phosphate levels. Hyperglycemia and insulin increased glycolytic flux only after 30 minutes of ischemia had elapsed, suggesting that endogenous glycogen provided adequate glycolytic substrate prior to this time. The mannitol-glucose substrate had no beneficial effects, indicating that the hyperglycemia and insulin substrate had a metabolic rather than an osmotic mechanism of action. In contrast, during severe ischemia, tissue lactate washout was ineffective; the hyperglycemia and insulin substrate increased glycolytic flux by only 15% and produced no persistent beneficial effects. These results suggest that hyperglycemia and insulin therapy is beneficial to the ischemic myocardium when two conditions are met. First, the degree of myocardial perfusion, although in the ischemic range, must be adequate to prevent the accumulation of high tissue levels of lactate which inhibit glycolysis and prevent any glycolytic stimulation by hyperglycemia and insulin. Second, the ischemic myocardium must be "glucose dependent" for glycolytic substrate; in our studies this occurred after 30-45 minutes of sustained ischemia, probably because myocardial glycogen stores became depleted.

Effect of exercise on the relationship between myocardial blood flow and systolic wall thickening in dogs with acute coronary stenosis.

Abstract: Relationships between regional myocardial perfusion and transmural function, both during treadmill exercise and at rest, were examined in conscious dogs with varying degrees of coronary stenosis produced by a hydraulic occluder. In 13 dogs we measured myocardial blood flow with microspheres (10-12 microns in diameter) and regional systolic wall thickening (%). During exercise with coronary stenosis, myocardial blood flow was characterized by nonuniform distribution, and associated with regional dysfunction. The relationships between normalized myocardial blood flow and normalized %wall thickening during exercise with coronary stenosis were linear, with significantly different slopes (mean myocardial blood flow: y = 1.23x - 0.16, r = 0.93; subendocardial myocardial blood flow: y = 1.50x - 0.02, r = 0.86; subepicardial myocardial blood flow: y = 0.83x - 0.18, r = 0.87). To fill the gap between available subendocardial and subepicardial data during exercise with coronary stenosis and control points, however, would require nonlinear components. In 10 of the dogs, coronary stenosis at rest was also produced to compare regional myocardial blood flow - %wall thickening relations at rest with those during steady state exercise. The absolute mean myocardial blood flow - %wall thickening relation during exercise with coronary stenosis (y = 11.6x - 1.9, r = 0.90) was significantly shifted rightward from the resting relation (y = 25.3x -2.1, r = 0.80). However, when changes in %wall thickening were plotted vs. myocardial blood flow per beat, the relationships at rest and exercise were nearly superimposable. Likewise, relations between normalized myocardial blood flow and changes in %wall thickening at rest and exercise were not significantly different. We conclude: %wall thickening during exercise is directly related to changes in mean myocardial blood flow but is related in nonlinear fashion to changes in subepicardial and subendocardial myocardial blood flow; %wall thickening may provide a reliable index of the relative transmural flow distribution during exercise as well as at rest; during brief bouts (5-8 minutes) of exercise with coronary stenosis, the relationship between stabilized regional contractile dysfunction and level of myocardial blood flow per beat is the same as that during coronary stenosis at rest.

Triggered ventricular rhythms in 1-day-old myocardial infarction in the dog.

Abstract: Triggered activity developed in depolarized Purkinje fibers (maximum diastolic potential -59.3 +/- 9.9 mV) during superfusion with normal Tyrode's solution in 84% of subendocardial preparations from 1-day-old canine infarct. Triggered activity occurred when a delayed afterdepolarization attained threshold potential and spontaneously terminated after a subthreshold delayed afterdepolarization. Triggered activity was initiated either by stimulated beats or by the background slow Purkinje automaticity. When multiple stimulated beats were required, the amplitude of the afterdepolarization increased and the coupling interval decreased when the stimulation frequency and/or the number of stimulated beats increased. Varying degrees of entrance and exit block around sites of triggered activity were common, and some triggered activity manifested as a parasystolic rhythm. In preparations showing subthreshold delayed afterdepolarizations, both epinephrine (2.5 x 10(-6) M) and increasing [Ca++]o, (from 2.7 to 8.1 mM) increased the amplitude of afterdepolarizations and resulted in triggered activity. On the other hand, verapamil (2.2 x 10(-6) M) resulted in exit block around sites of triggered activity and/or completely suppressed afterdepolarizations and triggered activity. Isochronal mapping of endocardial activation during the initiation and perpetuation of triggered activity elucidated a focal site of origin from Purkinje fibers overlying the infarct and showed no evidence of a circus movement of excitation. The in vitro triggered activity may explain the spontaneous multiform ventricular rhythms seen in the intact heart.

The contractile state as the major determinant in the evolution of left ventricular dysfunction in the spontaneously hypertensive rat.

Abstract: Female spontaneously hypertensive and normotensive rats were studied at 6, 12, 18, and 24 months of age to determine which characteristics of myocardial performance herald the onset of left ventricular dysfunction. Peak ejection fraction index was derived from measurements of peak stroke volume (in vivo volume loading) and passive pressure-volume relations. The myocardial stiffness constant (km, slope of the incremental modulus-stress relation, EINC = km sigma), chamber stiffness constant (kc, slope of the chamber stiffness-pressure relation, dP/dV = kcP), and left ventricular cavitary volume-to-wall volume ratio at 10 mm Hg) were calculated from the pressure-volume data and the contractile state was assessed from the ejection fraction index-afterload relations. In the normotensive rats, the myocardial stiffness constant was not affected by age, whereas, in the spontaneously hypertensive rats, the myocardial stiffness constant remained within normal limits until 18 months, at which time a significant increase in this index of myocardial stiffness occurred. Baseline and maximal cardiac indices and ejection fraction index of spontaneously hypertensive rats were normal from 6 to 18 months, but were markedly reduced at 24 months. This reduction in cardiac performance was associated with a decrease in the left ventricular chamber stiffness constant, i.e., kc. This decreased chamber stiffness, which occurred at a time when myocardial stiffness was increased, was due to a greater increase in cavity size than in myocardial stiffness. The left ventricular cavity-to-wall volume ratio of normotensive rats was not affected by age, whereas, in the spontaneously hypertensive rats, this ratio markedly declined by 18 months. The ejection fraction index-afterload relations i.e., a measure of the contractile state, of the 6- and 12-month-old spontaneously hypertensive rats were similar to those of the normotensive rats of all ages. However, a depression in the contractile state of the spontaneously hypertensive rats occurred at 18 months and was further depressed at 24 months. This abnormality of the contractile state was evident before the deterioration of cardiac performance, as reflected in a decrease in baseline and maximal cardiac indices, and dilation of the left ventricle occurred. The contractile state (ejection fraction index-afterload relation) is thus the most sensitive indicator of left ventricular dysfunction in spontaneously hypertensive rats.