bluuebunny/crossref_metadata_2025 huggingface dataset:
Angiotensin II modulates cardiac Na+ channels in neonatal rat.
Authors: Moorman J R , Kirsch G E , Lacerda A E , Brown A M
Published: June 2012

Since chronic congestive heart failure syndromes are associated with both elevated circulating levels of angiotensin II and potentially lethal ventricular tachyarrhythmias, we investigated the effect of angiotensin II on voltage-dependent cardiac Na+ currents. Single-channel Na+ currents in neonatal rat ventricular myocytes were studied using the patch clamp method in the cell-attached mode. Angiotensin II applied outside the patch increased the frequency of opening and rates of activation and inactivation of single-channel Na+ currents within the patch. These effects were mimicked by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and were prevented by prior incubation with TPA. Therefore, we propose that angiotensin II modulates cardiac Na+ currents by a cytoplasmic second messenger, perhaps protein kinase C, and this may predispose toward arrhythmia.
Residual strain in rat left ventricle.
Authors: Omens J H , Fung Y C
Published: June 2012

Residual stress in an organ is defined as the stress that remains when all external loads are removed. Residual stress has generally been ignored in published papers on left ventricular wall stress. To take residual stress into account in the analysis of stress distributions in a beating heart, one must first measure the residual strain in the no-load state of the heart. Residual strains in equatorial cross-sectional rings (2-3 mm thick) of five potassium-arrested rat left ventricles were measured. The effects of friction and external loading were reduced by submersing the specimen in fluid, and a hypothermic, hyperkalemic arresting solution containing nifedipine and EGTA was used to delay the onset of ischemic contracture. Stainless steel microspheres (60-100 microns) were lightly imbedded on the surface of the slices, and the coordinates of the microspheres were digitized from photographs taken before and after a radial cut was made through the left ventricular free wall. Two-dimensional strains computed from the deformation of a slice after one radial cut were defined as the residual strains in that slice. It was found that the distributions of the principal residual stretch ratios were asymmetric with respect to the radial cut: in areas where substantial transmural strain gradients existed, the distributions of strain components were different on the two sides of the radial cut. A second radial cut produced deformations significantly smaller than those produced from the first radial cut. Hence, a slice with one radial cut may be considered stress free.(ABSTRACT TRUNCATED AT 250 WORDS)
Central beta-adrenergic mechanisms may modulate ischemic ventricular fibrillation in pigs.
Authors: Parker G W , Michael L H , Hartley C J , Skinner J E , Entman M L
Published: June 2012

A central noradrenergic process may permit expression of the stress-related increase in cardiac vulnerability to ventricular fibrillation (VF). Thus, the effect of central beta-adrenergic receptor blockade with L-propranolol (0.01 and 0.05 mg/kg) on ischemia-induced VF vulnerability was evaluated in the psychologically stressed pig model and compared with Ringer's solution and D-propranolol (0.05 mg/kg). The ischemia of a maximum 15-minute left anterior descending coronary artery occlusion was used since we previously determined that pigs surviving 15 minutes usually do not fibrillate. Time to the onset of VF was analyzed by time-to-event analysis and ranged from 0.75 to 13.8 minutes in vulnerable pigs. Intracerebroventricular administration of L-propranolol (0.05 mg/kg) prolonged the time to VF compared with Ringer's solution and D-propranolol (p less than 0.05). The high dose of L-propranolol also reduced the incidence of VF (7/15 fibrillated) compared with Ringer's solution (12/12 fibrillated) and D-propranolol (6/7 fibrillated). The lower dose of L-propranolol was without effect on VF vulnerability (7/9) fibrillated). The plasma concentration resulting from central administration of 0.05 mg/kg L-propranolol was found to be 9.05 +/- 3.25 ng/ml, which is significantly below therapeutic antiarrhythmic blood levels. We conclude that the reduced vulnerability to ischemia-induced VF after intracerebroventricular administration of propranolol is due to alteration of a central beta-adrenergic receptor-mediated phenomenon as opposed to an effect on the heart directly or to nonspecific membrane stabilization.
Congruence of total and perfused capillary network in rat brains.
Authors: Göbel U , Theilen H , Kuschinsky W
Published: June 2012

In awake normocapnic rats, the density of the total and of the perfused capillary network was determined in 10 brain areas. The density of perfused capillaries was measured by using fluorescein isothiocyanate (FITC) globulin or Evans blue as intravenous marker and by fluorescent microscopy. The density of morphologically existing capillaries was determined according to either the histochemical alkaline phosphatase method or a newly developed immunohistochemical fluorescent method that allows marking of the capillary wall constituent fibronectin with a primary antibody directed against fibronectin. This antibody is made visible by a second FITC-coupled antibody (indirect immunofluorescence). Comparison of perfused and existing capillary counts revealed high congruence when fluorescent results were compared. In contrast, the alkaline phosphatase technique yielded capillary counts that were consistently 30% lower than the fibronectin and the FITC globulin counts. The identity of the perfused and the morphologically existing capillary network could be confirmed by a newly developed double-staining technique. First, the perfused capillaries were quantified by intravascular Evans blue. Then, the existing capillaries were relocated in the same measuring field by the fibronectin technique. Such double staining resulted in identical capillary counts in 97% of all cases. The following conclusions have been reached: 1) Fluorescent methods show a perfusion of virtually all capillaries in the brain of the awake normocapnic rat. 2) The alkaline phosphatase technique appears to underestimate the capillary density in the rat brain.
Unidirectional block and reentry of cardiac excitation: a model study.
Authors: Quan W , Rudy Y
Published: June 2012

A computer model of a ring-shaped, one-dimensional cardiac fiber was used for examination of responses of propagation to premature stimuli applied under different degrees of both cell-to-cell coupling and membrane excitability. Results demonstrated the importance of cellular uncoupling in the genesis of unidirectional block and reentry. Propagation of excitation itself created a certain degree of functional inhomogeneity that provided necessary conditions for unidirectional block and reentry. The likelihood of induction of unidirectional block was proportional to the degree of cellular uncoupling. In contrast, uniform reduction in sodium channel conductance decreased the inducibility of unidirectional block. Nonsustained and sustained reentry was induced by a properly timed single premature stimulus during the refractory period of a propagating action potential. Reduction of the size of the reentry pathway resulted in an increased degree of interaction between the wavefront and its tail, which, in turn, changed the kinetics of the slow ionic channels, bringing about shortening of action potential duration. Alternans in action potential duration were also demonstrated during circus movement and were caused by the alternating kinetic properties of the slow ionic currents. Inhomogeneity along the reentry pathway in refractory period, in membrane excitability, in fiber cross-sectional area, or in gap junction resistance also provided conditions necessary for unidirectional block. The simulations suggested that an important role was played by cellular uncoupling in the genesis and maintenance of unidirectional block and reentry.
Alterations in elastin and collagen related to the mechanism of progressive pulmonary venous obstruction in a piglet model. A hemodynamic, ultrastructural, and biochemical study.
Authors: LaBourene J I , Coles J G , Johnson D J , Mehra A , Keeley F W , Rabinovitch M
Published: June 2012

We created an animal model to understand better the pathogenesis and underlying mechanism of progressive central pulmonary venous (PV) obstruction, a condition not amenable to current therapy. Twenty piglets underwent banding of their PVs, 18 had a sham operation, and 12 were nonoperated controls. After 1, 3, and 6 weeks hemodynamic data were obtained and correlated with ventricular weights, PV and pulmonary artery (PA) distensibilities (at 1 week), morphometric structural and ultrastructural analyses, and biochemical assessment of elastin determined gravimetrically (and by desmosine level at 1 week), collagen, and elastase activity. At 1 week, PV banding was associated with increased PV compliance (p less than 0.05). At 3 weeks, an increased PA pressure (Ppa) (p less than 0.05) was observed, unaccompanied by a rise in PV pressure (Pcw). In the PV, however, there was breakdown of the internal elastic lamina with apparent migration of smooth muscle cells from media to subendothelium. At 6 weeks, a rise in Pcw (p less than 0.01), a further rise in Ppa (p less than 0.01), and right ventricular hypertrophy (p less than 0.005) were observed. We also observed mild PV intimal thickening (p less than 0.01), complete degradation of elastic laminae (p less than 0.05), and an increase in collagen assessed morphometrically (p less than 0.01). The banding procedure resulted in an overall increase in PV elastin synthesis and in the proportion of elastin determined gravimetrically (p less than 0.05 for both) but not by desmosine level, suggesting the possibility of poor cross-linking of elastin, which might account for the early increased distensibility of the PV. However, our assay could not detect an increase in elastase activity associated with either the increased distensibility or the ultrastructural changes of elastin degradation. The increased Ppa was not associated with significant PA biochemical or structural changes. We speculate that in response to distal venous obstruction, early remodeling of the PVs increases distensibility, protecting the lung from venous congestion and blunting a rise in Pcw. PA hypertension precedes the rise in Pcw, likely because of reflex vasoconstriction. The subsequent modest rise in Pcw is already associated with extensive fibrosis of the PV, suggesting a reason for unsuccessful current therapy and a need for consideration of earlier assessment and intervention.
Evidence for cholinergic regulation of microvessel hydraulic conductance during tissue hypoxia.
Authors: Tucker V L , Huxley V H
Published: June 2012

Cholinergic regulation of single-vessel hydraulic conductivity (Lp) during normoxia and hypoxia was tested in single mesenteric vessels of pithed frogs (Rana pipiens). Capillaries were cannulated in situ and perfused with frog Ringer's solution containing 10 mg/ml albumin and human erythrocytes while the mesentery was continuously superfused with frog Ringer's solution (15 degrees C). Lp was first measured under normoxic (room air equilibrated) conditions by the modified Landis microocclusion method. Repeated measurements of filtration coefficient under control conditions, for periods up to 80 minutes, demonstrated that Lp did not change with time in normoxic vessels (n = 18). After initial control measurement (Lpo), perfusion with 1 microM acetylcholine increased Lp by 4.6 +/- 1.0-fold (mean +/- SEM, n = 6). The response to acetylcholine was antagonized by the addition of 10 microns atropine to the perfusate (Lp/Lpo = 1.8 +/- 0.4). Perfusion with atropine alone reduced Lp in three of six capillaries Lp/Lpo = 0.56 +/- 0.04); Lp in the remaining three vessels was unaffected. Tissue hypoxia was simulated by exposing the mesentery to deoxygenated superfusate Po2 less than or equal to 10 mm Hg) for 10-15 minutes. Tissue hypoxia had no effect on Lp in atropine-treated vessels (n = 8). Without atropine, tissue hypoxia increased Lp by 2.3 +/- 0.7-fold, whereas the addition of atropine completely antagonized this response (n = 5). In contrast to the inhibitory action of atropine during tissue hypoxia, Lp rose 5.2 +/- 1.6-fold (n = 4) in vessels simultaneously exposed to deoxygenated perfusate.(ABSTRACT TRUNCATED AT 250 WORDS)
Synthesis of lipoxygenase and epoxygenase products of arachidonic acid by normal and stenosed canine coronary arteries.
Authors: Rosolowsky M , Falck J R , Willerson J T , Campbell W B
Published: June 2012

Coronary vascular injury promotes blood cell-vessel wall interactions that influence arachidonic acid metabolism and coronary blood flow patterns. Since lipoxygenase and cytochrome P-450 epoxygenase metabolites of arachidonic acid are synthesized by vascular and inflammatory cells and have a variety of important biological actions, we investigated the metabolism of arachidonic acid by these pathways in normal and stenosed, endothelially injured canine coronary arteries. We found and confirmed by gas chromatography/mass spectrometry that primarily 12- and 15-hydroxyeicosatetraenoic acids (HETEs) are synthesized by both coronary artery segments. Lesser amounts of 11-, 9-, 8-, and 5-HETEs are also produced. 15-Ketoeicosatetraenoic acid is also synthesized. The synthesis of 14C-HETEs is fivefold to 10-fold greater by the stenosed than the normal coronary artery. Specific radioimmunoassays indicated that the stenosed coronary artery synthesized 93 +/- 14 and 1,102 +/- 154 ng/g of tissue of 15- and 12-HETE, respectively, while the normal coronary artery produced 17 +/- 3 and 162 +/- 68 ng/g of tissue of 15- and 12-HETE, respectively. Products comigrating with 14,15-; 11,12-; 8,9-; and 5,6-epoxyeicosatrienoic acids (EETs) and the corresponding dihydroxyeicosatrienoic acids (DHETs) were detected predominantly in stenosed coronary arteries by high-pressure liquid chromatography. The structures of the EETs were confirmed by GC/MS. The EETs and prostaglandin I2 produced endothelium-independent, concentration-related relaxations of dog coronary artery rings. These data indicate that normal and stenotic coronary arteries metabolize arachidonic acid to HETEs, DHETs, and EETs along with prostaglandins; however, the synthesis of these metabolites is greater in the stenosed, endothelially injured vessel. The EETs may be synthesized during the development of cyclic flow variations and counteract the vasoconstrictor effects of thromboxane A2.
Mechanisms underlying the development of ventricular fibrillation during early myocardial ischemia.
Authors: Pogwizd S M , Corr P B
Published: June 2012

The mechanisms underlying the development of ventricular fibrillation (VF) during early myocardial ischemia were assessed by use of a computerized three-dimensional mapping system capable of recording simultaneously from 232 intramural recording sites throughout the entire feline heart in vivo. Occlusion of the proximal left anterior descending coronary artery led to ventricular tachycardia (VT), which degenerated to VF in 1-5 minutes in four of 15 animals. Normal sinus beats immediately preceding the initiation of VT leading to VF demonstrated delayed activation (total activation time 133 +/- 14 msec), which was not significantly different from the activation time for normal sinus beats immediately preceding nonsustained VT (149 +/- 7 msec). Most of the conduction delay occurred in the subendocardial and midmyocardial regions in both groups. Initiation of VT leading to VF occurred by intramural reentry in three of the four cases. In one case, a mechanism responsible for the initiation of VT could not be assigned. The coupling interval of the initiating beats of VT ultimately leading to VF (210 +/- 15 msec) did not differ from that of nonsustained VT. Maintenance of the VT that led to VF was due primarily to intramural reentry (84% of cases) involving multiple activation sites in and around the border region of the ischemic zone. Nonreentrant mechanisms, arising in the subendocardium and subepicardium, also contributed to the maintenance of VT before development of VT. The transition from VT to VF was due exclusively to intramural reentry with initiation of the reentrant beats in the subendocardium and, occasionally, the subepicardium. Acceleration of the tachycardia by intramural reentry, along with very rapid and inhomogeneous recovery of excitability (as low as 50-60 msec), led to increased functional block and conduction delay. As a result, the total activation time for a given beat exceeded the coupling interval for that beat and led to the multiple reentrant circuits and multiple simultaneous activations characteristic of VF. Thus, the initiation and maintenance of VT leading to VF during early ischemia is due to intramural reentry, although nonreentrant mechanisms also contribute. However, the development of VF is due to continued intramural reentry and rapid recovery of excitability.
Nitrendipine binding in congestive heart failure due to myocardial infarction.
Authors: Dixon I M , Lee S L , Dhalla N S
Published: June 2012

Depressed cardiac pump function is the hallmark of congestive heart failure, and it is suspected that decreased influx of Ca2+ into the cardiac cell is responsible for depressed contractile function. Since Ca2+ channels in the sarcolemmal membrane are considered to be an important route for the entry of Ca2+, we examined the status of Ca2+ receptors/channels in failing rat hearts after myocardial infarction of the left ventricular free wall. For this purpose, the left coronary artery was ligated and hearts were examined 4, 8, and 16 weeks later; sham-operated animals served as controls. Hemodynamic assessment revealed decreased total mechanical energy (left ventricular systolic pressure x heart rate), increased left ventricular diastolic pressure, and decreased positive and negative dP/dt in experimental animals at 4, 8, and 16 weeks. Although accumulation of ascites in the abdominal cavity was evident at 4 weeks, other clinical signs of congestive heart failure in experimental rats were evident from the presence of lung congestion and cardiac dilatation at 8 and 16 weeks after induction of myocardial infarction. The density of Ca2+ receptors/channels in crude membranes, as assessed by [3H]nitrendipine binding assay, was found to be decreased in the uninfarcted experimental left ventricle at 8 and 16 weeks; however, no change in the affinity of nitrendipine was evident. A similar depression in the specific binding of another dihydropyridine compound, [3H]PN200-110, was also evident in failing hearts. Brain and skeletal muscle crude membrane preparations, unlike those of the right ventricle and liver, revealed a decrease in Ca2+ receptors/channels density in experimental animals at 16 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)
Coronary arteriolar myogenic response is independent of endothelium.
Authors: Kuo L , Chilian W M , Davis M J
Published: June 2012

The purpose of this study was to investigate if myogenic responses of isolated coronary arterioles were dependent on an intact, functional endothelium. Arterioles were located in situ by intracoronary perfusion with india ink-gelatin solution and then dissected and cannulated at both ends with glass micropipettes. Intraluminal pressure was initially set at 60 cm H2O; then the pressure was altered in steps of 20 cm H2O over a range of 20-140 cm H2O. Arterioles developed spontaneous tone and exhibited a significant myogenic response in physiological saline solution (36 degrees -37 degrees C). Arteriolar dilation and constriction were observed at lower (20-60 cm H2O) and higher (60-140 cm H2O) pressures, respectively. The presence of a functional and automatically intact endothelium was confirmed by relaxation to the endothelium-dependent vasodilator bradykinin and by transmission electron microscopy, respectively. After mechanical denudation of the endothelium with a specially designed abrasive micropipette, spontaneous tone and myogenic responses were preserved. Denudation of the endothelium was verified functionally (no response to bradykinin) and with transmission electron microscopy. Moreover, the mechanical denudation technique did not deleteriously affect smooth muscle because vasoconstrictor and vasodilator responses to nonendothelial-dependent drugs were the same before and after denudation. In summary, the present study demonstrates that pressure-dependent responses occur in isolated coronary arterioles and that this response is not dependent on the endothelium. Therefore, pressure-induced changes in coronary arteriolar tone are a true myogenic response in that they originate from smooth muscle.
Effects of amiloride on metabolism and contractility during reoxygenation in perfused rat hearts.
Authors: Weiss R G , Lakatta E G , Gerstenblith G
Published: June 2012

Myocardial recovery after hypoxia may be determined not only by the extent of metabolic depression during the hypoxic period but also by changes in cation contents as well. Calcium overload during reoxygenation, mediated in part by Na-Ca exchange and supported by the rise in cell sodium during hypoxia, may be one factor. The effects of amiloride (0.1 mM), a diuretic that inhibits Na(+)-H+ and Na-Ca exchanges in cardiac sarcolemma and mitochondria preparations, were studied during hypoxia-reoxygenation in the isovolumic, isolated rat heart. During hypoxia, cell sodium, measured using potassium ethylenediamine tetraacetate cobaltate as an extracellular marker, increased in amiloride and amiloride-free hearts, but there was no increase in cell calcium (3.3 +/- 0.3 vs. 3.6 +/- 0.9 mumol/g dry wt; p = NS). Amiloride did not alter developed pressure (DP), end-diastolic pressure (EDP), pH, or integrated areas of adenosine triphosphate (ATP) and phosphocreatine (PCr) (determined by phosphorus-31-nuclear magnetic resonance spectroscopy) during hypoxia or normal perfusion conditions. Forty minutes after reoxygenation, however, cell calcium was significantly lower in the amiloride (5.1 +/- 1.3 mumol/g dry wt) than in the amiloride-free group (10.4 +/- 1.8 mumol/g dry wt; p less than 0.001), and there was improved recovery of DP (percent of initial) (72 +/- 12% vs. 41 +/- 12%; p less than 0.001), PCr (99 +/- 9% vs. 70 +/- 14%; p less than 0.001), and pH (7.17 +/- 0.17 vs. 6.88 +/- 0.16; p less than 0.001) in the amiloride group. To determine whether this dose of amiloride inhibits the manifestations of sodium-mediated calcium gain in the same model during normoxia, the metabolic and functional sequelae of lithium-substituted low sodium (50 mM) perfusion were studied. Amiloride significantly limited the manifestations of sodium-mediated calcium gain as indexed (all expressed as percent of control) by a lower peak DP (221 +/- 25% vs. 284 +/- 20%) at 3 minutes, improved preservation of PCr (85 +/- 10% vs. 68 +/- 9%) and ATP (104 +/- 12% vs. 84 +/- 9%), lower rise in inorganic phosphate (201 +/- 74% vs. 332 +/- 106%), and a smaller fall in intracellular pH (7.01 +/- 0.04 vs. 6.70 +/- 0.15, p less than 0.05) for all metabolic parameters during a 20-minute period.(ABSTRACT TRUNCATED AT 400 WORDS)
Vascular reactivity during the progression of atherosclerotic plaque. A study in Watanabe heritable hyperlipidemic rabbits.
Authors: Kolodgie F D , Virmani R , Rice H E , Mergner W J
Published: June 2012

The effects of varying degrees of atherosclerotic plaque on vascular responsiveness in aortas of Watanabe heritable hyperlipidemic (WHHL) rabbits and New Zealand White (normal cholesterolemic) rabbits were studied. Ring segments from the aortic arch and thoracic aorta were mounted in organ chambers for isometric tension recording and measurement of endothelium-derived relaxing factor. WHHL rabbits were divided into three groups according to age: group 1, 3-5 months; group 2, 6-9 months; and group 3, 12-14 months. Atherosclerotic changes (expressed as a percent of total surface area) in the aortic arches in groups 1, 2, and 3 were 11 +/- 3% (mild), 28 +/- 6% (moderate), and 54 +/- 8% (severe) respectively; only occasional plaques were present in the thoracic aorta in all groups. Maximal contractions elicited with phenylephrine progressively decreased with increasing degrees of atherosclerotic plaque. Contractions evoked by histamine were augmented in all groups of WHHL rabbits when compared with controls, whereas those to serotonin were augmented only in vessels with mild atherosclerosis. As the severity of the intimal lesions increased, endothelium-dependent relaxations to acetylcholine, ATP, and calcium ionophore A23187 progressively decreased. Endothelium-independent relaxation to nitroglycerin was virtually complete in all segments. However, vessels with severe atherosclerosis were less sensitive to this agent as illustrated by a significant increase in the ED50 value. Scanning electron microscopy revealed a predominant loss of endothelial cells in the central regions of fibrous plaques. Thus, in WHHL rabbits, hypercholesterolemia and atherosclerosis result in an increased responsiveness of vascular smooth muscle to histamine and serotonin. Endothelium-mediated relaxation of vascular smooth muscle is reduced with the progression of atherosclerosis primarily due to a loss of endothelial cells.
Ischemic preconditioning reduces infarct size in swine myocardium.
Authors: Schott R J , Rohmann S , Braun E R , Schaper W
Published: June 2012

We evaluated the hypothesis that stunning swine myocardium with brief ischemia reduces oxygen demand in the stunned region and increases tolerance of myocardium to longer periods of ischemia. Wall function was quantified with ultrasonic crystals aligned to measure wall thickening, and stunning was achieved with two cycles of left anterior descending coronary artery (LAD) occlusion (10 minutes) and reperfusion (30 minutes), after which the LAD was occluded for 60 minutes and reperfused for 90 minutes. Infarct size (as a percent of risk region) was then determined by incubating myocardium with para-nitro blue tetrazolium. Regional oxygen demand was measured as myocardial oxygen consumption before the 60-minute LAD occlusion in the stunned region; tracer microspheres were used to determine blood flow, and blood from the anterior interventricular vein and left atrium was used to calculate oxygen saturations. After the second reperfusion period, wall thickening in the stunned region was reduced to 1.4 +/- 2.4% compared with 36.7 +/- 2.5% (mean +/- SEM) before ischemia (p less than 0.001). Regional myocardial oxygen consumption after stunning (3.1 +/- 0.7 ml O2/min/100 g) was no different from regional myocardial oxygen consumption before stunning (3.7 +/- 0.6 ml O2/min/100 g). In the nine pigs "preconditioned" by stunning, infarct size was 10.4 +/- 6.3% of the risk region compared with 48.0 +/- 12.7% in the six control pigs subjected to 60 minutes of ischemia without prior stunning (p less than 0.005). The risk regions were similar (14.4 +/- 1.5% vs. 14.6 +/- 1.9% of the left ventricle, preconditioned vs. control pigs, respectively). We conclude that stunning swine myocardium with two cycles of a 10-minute LAD occlusion followed by reperfusion increases ischemic tolerance but that changes in regional demand in stunned myocardium do not predict the marked reduction in infarct size that follows a subsequent 60-minute period of ischemia.
Effect of early diastolic loading on myocardial relaxation in the intact canine left ventricle.
Authors: Nikolic S , Yellin E L , Tamura K , Tamura T , Frater R W
Published: June 2012

Early transmitral flow (MiF) patterns depend strongly on the rate of fall of measured left ventricular pressure (Pm) determined by both the active decay of pressure (Pa) due to myocardial relaxation and the increase in pressure due to stretch of passive elements during filling (Pp). This study was designed to uncouple passive forces from deactivation in order to reveal the instantaneous rate and duration of myocardial relaxation. We assumed a parallel combination of passive and active elements: Pm(t,V) = Pa(t) + Pp(V), with no constraints on the form of Pa(t), where t is time and V is ventricular volume. Pp(V) was determined by a retrospective analysis of data obtained in 11 anesthetized dogs instrumented for volume clamping with a remote-controlled mitral valve, with left atrial and left ventricular micromanometers, and with an electromagnetic probe to measure MiF. The passive pressure-volume relation (both positive and negative portions) was determined by clamping at end-systolic volume or after various filling volumes, and fit to logarithmic functions. Pp(t) was then calculated from Pp(V) and V(t) (integral of MiF). Time to end relaxation (Ter) was defined as time when Pa = 0. During isovolumic relaxation, when dPp/dt = 0, dPm/dt is equal to the relaxation rate, dPa/dt. In completely isovolumic relaxations, asymptote P infinity = -7 +/- 6 mm Hg (thus, Pa is 7 mm Hg greater than Pm) and Ter = 40 +/- 15 msec, compared with 175 +/- 53 msec during normal filling. In high versus low inotropic state, Pa at the beginning of filling was greater (18.1 +/- 6.1 vs. 12.2 +/- 3.9 mm Hg), and Ter was shorter (170 +/- 42 vs. 228 +/- 43 msec). Active pressure Pa(t) during filling is not an exponential function, and at any time, it was always greater after filling than in nonfilling beats, which indicates an increase in the relaxation duration. We conclude that myocardial relaxation is modulated by filling, which slows its rate and increases its duration, and is therefore a function of both ventricular volume and time. Such a mechanism may have an important role in regulating the diastolic pressure-volume relation.
Coronary microvascular responses to reductions in perfusion pressure. Evidence for persistent arteriolar vasomotor tone during coronary hypoperfusion.
Authors: Chilian W M , Layne S M
Published: June 2012

The goals of this study were to test the following hypotheses: 1) Coronary autoregulatory adjustments to decreases in perfusion pressure occur primarily in coronary arterioles (less than 150 microns in diameter). 2) Small coronary arteries (greater than 150 microns in diameter) can be recruited to participate in the autoregulatory adjustments as perfusion pressure is progressively lowered. 3) Small arterioles are the location of vasodilator reserve in the coronary microcirculation during hypoperfusion. Studies were performed in anesthetized open-chest dogs in which coronary perfusion pressures were reduced to 80, 60, 40, and 30 mm Hg. During reductions in coronary perfusion pressure, measurements were made of systemic hemodynamics, myocardial blood flow (radioactive microspheres), and coronary microvascular diameters. Arterial pressure and heart rate were largely unchanged during the experimental maneuvers. Measurements of microvascular diameters in the beating heart were performed during epi-illumination via a stroboscopic light source synchronized to the cardiac cycle using fluorescence intravital microscopy. Coronary autoregulatory adjustments were evident during reductions in perfusion pressure from control (96 mm Hg) to 80 and 60 mm Hg. Blood flow was unchanged from control, and active vasodilation of coronary arterioles was observed. At 80 mm Hg, only coronary arterioles dilated (4.4 +/- 1.2%), whereas at 60 mm Hg both small arteries (4.9 +/- 2.2%) and arterioles (6.9 +/- 1.2%) demonstrated significant vasodilation (p less than 0.05). The magnitude of dilation (i.e., percent increase in diameter) was inversely related to the initial diameter; that is, the arterioles dilated to a greater extent, percentage wise, than the small arteries. At 40 mm Hg, myocardial blood flow decreased slightly from that under control conditions, but coronary arterioles dilated to a greater extent than at 60 mm Hg (8.1 +/- 1.6%); yet, microvessels were incompletely vasodilated, because adenosine produced a further increase in microvessel diameter (12.5 +/- 2.1%) (p less than 0.05). At a perfusion pressure of 30 mm Hg, arterioles demonstrated a decrease in vascular diameter (-0.2 +/- 2.1%), which was reversed by adenosine (11.1 +/- 3.1%). From these results we concluded the following: 1) Coronary autoregulatory adjustments involve primarily coronary arteriolar vessels, but small coronary arteries can be recruited to participate in the autoregulatory response. 2) The magnitude of vessel dilation appears to be inversely related to vascular diameter. 3) Coronary arterioles are not maximally vasodilated during coronary hypoperfusion, and these vessels may be the source of persistent vasomotor tone during coronary insufficiency.
Increased myocardial adenosine production and reduction of beta-adrenergic contractile response in aged hearts.
Authors: Dobson J G , Fenton R A , Romano F D
Published: June 2012

The contractile response of the aged adult heart to beta-adrenergic stimulation is known to be reduced compared with the young adult heart. Since endogenous adenosine exerts an antiadrenergic action in the heart, this study was undertaken to determine if the basal endogenous level of myocardial adenosine increases with age and whether this increase mediates the reduced responsiveness of aged heart to beta-adrenergic stimulation. Young (3-5 months) and aged (12-22 months) Sprague-Dawley adult rat hearts of CD and SD stock were perfused at constant pressure and paced at 270 contractions/min. The two age groups had a similar level of +dP/dtmax (index of contractility) under control conditions. Adenosine release into the coronary effluent was 30 +/- 3 nmol/min/g dry wt from young and 54 +/- 9 nmol/min/g dry wt from aged hearts. Inosine release was also greater from the aged hearts. Isoproterenol (10(-8) M) stimulation increased contractile state by 113% in young hearts and only 69% in aged hearts. Isoproterenol further increased the adenosine and inosine release from both age groups. Theophylline (5 x 10(-5) M), an adenosine antagonist, prevented the difference in the contractile response to isoproterenol stimulation between the young and aged hearts. Elevation of external calcium from 2 to 4 mM increased contractility equally in both age groups without influencing adenosine release. Myocardial oxygen consumption, coronary effluent PO2, oxygen supply-demand ratio, and lactate release were similar for both age groups, indicating that under the conditions studied the elevated release of adenosine by the aged hearts was not due to hypoxia. Aged (10-14 months) adult guinea pig hearts also displayed a reduced responsiveness to the isoproterenol stimulation and released more adenosine compared with young (3-4 months) adult guinea pig hearts. These findings suggest that enhanced adenosine levels that are present in the aged myocardium are responsible, in part, for the reduced contractile responsiveness of the older adult heart to beta-adrenergic stimulation.
Neutrophil-mediated microvascular dysfunction in postischemic canine skeletal muscle. Role of granulocyte adherence.
Authors: Carden D L , Smith J K , Korthuis R J
Published: June 2012

Recent studies implicate a role for granulocytes in the genesis of the microvascular and parenchymal cell dysfunction, which occurs upon reperfusion of ischemic tissues. Although the molecular mechanisms underlying this neutrophil-mediated injury are not completely understood, it is clear that an essential first step in granulocyte migration from the vascular lumen to the interstitial space is adherence to vascular endothelium. The purpose of this study was to determine whether prevention of neutrophil adherence with monoclonal antibody IB4 directed against the neutrophil CD11/CD18 glycoprotein adherence complex or neutrophil depletion with a specific polyclonal antineutrophil serum would attenuate the microvascular dysfunction seen in postischemic skeletal muscle. Changes in vascular permeability were assessed by measurement of the solvent drag reflection coefficient for total plasma proteins (sigma) in isolated canine gracilis muscle subjected to ischemia/reperfusion, ischemia/reperfusion plus antineutrophil serum, or ischemia/reperfusion plus IB4. Estimates of sigma averaged 0.83 +/- 0.04 in nonischemic, control gracilis muscles, while ischemia/reperfusion was associated with a marked increase in vascular permeability (decrease in sigma to 0.54 +/- 0.04) and vascular resistance (increased by 135 +/- 41% over the control value). Prevention of neutrophil adherence or neutrophil depletion prevented this increase in vascular permeability (sigma = 0.80 +/- 0.03 and 1.01 +/- 0.06, respectively) and resistance (decrease of 16.51 +/- 8.0% and increase of 2.4 +/- 4.6% over control values, respectively). The results of this study suggest that neutrophils play a critical role in the genesis of microvascular dysfunction in postischemic skeletal muscle. Furthermore, neutrophil adherence to vascular endothelium appears to be a prerequisite for the production of this injury.
Passive electrical properties, mechanical activity, and extracellular potassium in arterially perfused and ischemic rabbit ventricular muscle. Effects of calcium entry blockade or hypocalcemia.
Authors: Cascio W E , Yan G X , Kléber A G
Published: June 2012

The relation among passive electrical resistive properties, longitudinal conduction velocity, extracellular potassium concentration, [K+]o, and mechanical activity was investigated in the isolated rabbit papillary muscle during normal arterial perfusion and no-flow ischemia in the presence and absence of verapamil, or a reduced extracellular Ca2+ concentration [Ca2+]o. During normal arterial perfusion, verapamil (0.5 microM, free [Ca2+]o = 1.0 mM) and hypocalcemic blood perfusate (free [Ca2+]o = 0.4 mM) reduced the maximal isometric twitch tension by 48% and 78%, depolarized the resting membrane by +3 and +7 mV, decreased the extracellular longitudinal resistance (ro) by 15% and 26%, and increased conduction velocity by 4% and 6%, respectively. The changes in conduction velocity during these interventions were consistent with those predicted by linear cable theory (+3% and +9%) for the observed changes in ro. In contrast, verapamil shortened whereas a reduced [Ca2+]o lengthened action potential duration. Comparison of simultaneously measured longitudinal whole tissue resistance (rt), intracellular longitudinal resistance (ri), [K+]o, and resting tension during ischemia showed a close association between abrupt cell-to-cell electrical uncoupling, development of ischemic contracture, and the secondary rise of [K+]o, which all started to develop after approximately 15 minutes of ischemia. Electrical cell-to-cell uncoupling was completed within 15 minutes. In the presence of verapamil, the relation among the onset of electrical cell-to-cell uncoupling, secondary rise of [K+]o, and onset of ischemic contracture in ischemia was qualitatively the same as in its absence; however, these events were postponed by approximately 10 minutes, and the rates of contracture development and uncoupling were diminished. Conduction velocity decreased after 12 minutes of ischemia from 54 to 36 cm/sec in the absence of and from 61 to 46 cm/sec in the presence of verapamil. This slowing effect on impulse conduction could not be attributed to changes of electrical cell-to-cell coupling because at this time an increase in ri had not yet taken place. In the presence of a reduced [Ca2+]o, the resting tension and ri increased almost immediately after the onset of ischemia. Although the resting tension rose progressively throughout the course of ischemia, the ri showed a biphasic increase characterized by an early transient increase that reached a peak at 8 minutes (+87%) and a second, irreversible increase beginning at approximately 12 minutes. This final onset of electrical cell-to-cell uncoupling and the secondary rise of [K+]o were not different from the findings with a normal [Ca2+]o.(ABSTRACT TRUNCATED AT 400 WORDS)
Sympathetic and nonsympathetic neuropeptide Y-containing nerves in the rat myocardium and coronary arteries.
Authors: Corr L A , Aberdeen J A , Milner P , Lincoln J , Burnstock G
Published: June 2012

We have examined the neuropeptide Y-containing intrinsic nerves of the heart in young (6-week-old) and adult (4-month-old) rats to determine whether they project to the coronary arteries or are capable of doing so if the neuropeptide Y-containing extrinsic nerves are removed. Chronic treatment of neonates with guanethidine was used to permanently destroy the sympathetic nerves. In the young treated animals, 33-54% of the neuropeptide Y remained in the heart despite a 90-99% reduction in norepinephrine; these proportions did not change in the animals that were allowed to develop to adulthood. The level of neuropeptide Y in the right atrium of young animals was unexpectedly high (252 +/- 28.7 pmol/g) compared with adults (75.4 +/- 18.8 pmol/g). The coronary arteries in the control rats received a moderately dense supply of neuropeptide Y-containing nerves; after guanethidine, all neuropeptide Y-containing nerves innervating the large coronary arteries disappeared, but some were still seen in association with small resistance vessels. No compensatory proliferation of the intrinsic neuropeptide Y-containing neurons occurred in the adult sympathectomized animals, and the intrinsic nerves did not reinnervate the large coronary arteries. These results are discussed in relation to the clinical syndrome of coronary artery spasm.
In vitro study of the influence of radial wall motion on wall shear stress in an elastic tube model of the aorta.
Authors: Klanchar M , Tarbell J M , Wang D M
Published: June 2012

The purpose of this study was to determine the influence of radial motion of an arterial wall on the shear stress that flowing blood imposes on the wall (wall shear stress). Wall shear stress is known to influence endothelial cell function and may play a role in atherogenesis, but its magnitude and distribution in the circulation are not well understood. To simulate arterial wall motion, we used both straight and curved rubber tubing models in a mock circulatory system incorporating a variable impedance element distal to the model aorta. Wall shear rate was measured with a hot-film anemometer probe mounted flush on the tubing wall and free to move with the wall. Wall shear stress was determined as the product of wall shear rate and viscosity. By changing the distal impedance element, we determined the influence of the (temporal) phase angle between pressure and flow, or equivalently, tube diameter and flow, on wall shear stress. We observed a fivefold increase in peak wall shear stress and the onset of intense wall shear stress reversal sinusoidal flows as the phase angle between pressure and flow was reduced from -60 degrees to -80 degrees. Wall shear stresses were insensitive to this same phase angle when its value was between -10 degrees and -60 degrees. Theoretical predictions, also presented here, are in accord with these observations. The phenomena we have observed in elastic tubes may be important in the arterial system because the phase angle between the first harmonic of pressure and flow in the aorta of humans is usually near our sensitive range. This same phase angle becomes more negative in hypertensive patients and is influenced by vasoactive drugs.
Side-to-side slippage of myocytes participates in ventricular wall remodeling acutely after myocardial infarction in rats.
Authors: Olivetti G , Capasso J M , Sonnenblick E H , Anversa P
Published: June 2012

To determine whether acute left ventricular failure associated with myocardial infarction leads to architectural changes in the spared nonischemic portion of the ventricular wall, large infarcts were produced in rats, and the animals were killed 2 days after surgery. Left ventricular end-diastolic pressure was increased, whereas left ventricular dP/dt and systolic pressure were decreased, indicating the presence of severe ventricular dysfunction. Absolute infarct size, determined by measuring the fraction of myocyte nuclei lost from the left ventricular free wall, averaged 63%. Transverse midchamber diameter increased by 20%, and wall thickness diminished by 33%. The mural number of myocytes in this spared region of the left ventricular free wall decreased by 36% and the capillary profiles by 40%. The combination of these functional abnormalities and structural rearrangement of the wall resulted in a 7.8-fold increase in diastolic wall stress. A comparable analysis of the interventricular septum demonstrated a 24% reduction in the number of cells across the septal thickness, whereas capillaries were diminished by 26%. Moreover, a 7.2-fold elevation in diastolic stress was computed in this region of the ventricle. The augmentation in diastolic stress was associated with a 22% and a 16% myocyte cellular hypertrophy in the wall and septum, respectively. In conclusion, side-to-side slippage of myocytes in the myocardium occurs in association with ventricular dilatation after a large myocardial infarction and contributes to ventricular remodeling and the occurrence of decompensated eccentric hypertrophy.
Age-induced decreases in the messenger RNA coding for the sarcoplasmic reticulum Ca2(+)-ATPase of the rat heart.
Authors: Maciel L M , Polikar R , Rohrer D , Popovich B K , Dillmann W H
Published: June 2012

Age-associated slowing of cardiac relaxation related to the decline in the Ca2+ pump function of cardiac sarcoplasmic reticulum (SR) has been previously described. It is unclear if the decreased Ca2+ pump function results from a lower amount of Ca2(+)-ATPase protein or a decreased pumping activity of the enzyme. To determine if these alterations could be mediated by changes in the amount of the protein itself, the level of the messenger RNA (mRNA) coding for the Ca2(+)-ATPase of the SR of Fischer rat hearts (4- and 30-month-old rats) were quantitated with a Northern blotting technique. We observed that the levels of SR Ca2(+)-ATPase mRNA were 60% lower in old rats as compared with young rats, suggesting that a quantitative reduction in the levels of the corresponding protein could occur during aging to explain the delayed diastolic relaxation documented in old animals as opposed to a change in the specific activity of this enzyme. The thyroid hormone responsiveness of SR Ca2(+)-ATPase mRNA has been previously established. We have found in this study that the thyroxine levels were consistently lower in old rats; however, this difference was relatively small (4.3 +/- 0.7 and 3.1 +/- 0.8 micrograms/dl [mean +/- SD), respectively, in young and old rats). In addition, no age-induced decrease in 3,5,3'-triiodothyronine levels was observed, suggesting that the aging process itself may be responsible for the changes in SR Ca2(+)-ATPase mRNA levels.
Smooth muscle cells express urokinase during mitogenesis and tissue-type plasminogen activator during migration in injured rat carotid artery.
Authors: Clowes A W , Clowes M M , Au Y P , Reidy M A , Belin D
Published: June 2012

Although the level of plasminogen activator (PA) expression has been correlated with cellular proliferation and migration in vitro, this relation has not been established in tissue undergoing repair. In a rat model of arterial injury, we have measured the expression of PAs by vascular smooth muscle cells (SMCs) during entry into the growth cycle (0-24 hours) and subsequent migration from the media to the intima (starting at approximately 4 days). In normal rat carotid, low levels of urokinase-type PA (uPA) and tissue-type PA (tPA) are present; after removal of the endothelium, only uPA is detected in the media. uPA activity in extracts of carotid arteries increases and reaches a maximum between 16 and 24 hours after injury; uPA mRNA increases steadily and is maximal at 7 days. tPA activity appears at 3 days and is maximal at 7 days; tPA mRNA is present in normal vessels and reaches a maximum by 7 days. Most of the tPA in the media is associated with SMC and not with regenerating endothelium. Furthermore, tPA is present in the media before the SMCs migrate into the intima. These results demonstrate that PA expression by vascular SMCs is differentially regulated, with uPA present during mitogenesis and tPA during migration.