bluuebunny/crossref_metadata_2025 huggingface dataset:
Alkaline phosphatase activity of glutaraldehyde-treated bovine pericardium used in bioprosthetic cardiac valves.
Authors: Maranto A R , Schoen F J
Published: June 2012

Bioprosthetic valves fail frequently because of pathological mineralization, a process that begins in cell remnants of the glutaraldehyde (GLUT) fixed tissue. Other pathological cardiovascular calcification and physiological mineralization in skeletal/dental tissues are both largely initiated in cell-derived membranous structures (often called "matrix vesicles"), and the enzyme alkaline phosphatase (AP) likely has an important function in the pathogenesis of mineral nucleation. This study tested the hypothesis that AP might also be present in and contribute to calcification of bioprosthetic valves. AP activity of fresh and GLUT-treated bovine pericardium was measured by the conversion of p-nitrophenyl phosphate to p-nitrophenol. Following 24 hours in 0.6% HEPES-buffered GLUT and storage for 2 weeks in 0.2% GLUT, considerable AP hydrolytic activity remained in GLUT-treated tissue relative to that of fresh tissue (Vmax, 24 vs. 45 mumol reaction product/min/mg tissue protein, respectively), although binding was somewhat reduced (Km, 1.9 X 10(3) vs. 1.4 X 10(3) microM substrate, respectively). Enzyme reaction product was demonstrated in both fixed and fresh tissue by light microscopic histochemical studies, confirming the biochemical results. Reaction product was noted along membranes of vascular endothelial cells and interstitial fibroblasts, the sites of early calcific deposits in bioprosthetic valves, by ultrastructural examination of GLUT-treated tissue. We conclude that GLUT-treated bovine pericardium retains much of the hydrolytic activity of AP, an enzyme associated with normal skeletal and pathological cardiovascular and noncardiovascular mineralization, and suggest that further examination of the mechanistic role of this enzyme may stimulate new approaches for slowing or preventing calcification of bioprosthetic tissue.
Actions of a phorbol ester on factors regulating contraction in rabbit mesenteric artery.
Authors: Fujiwara T , Itoh T , Kubota Y , Kuriyama H
Published: June 2012

The effects of 12-o-tetradecanoylphorbol-13-acetate (TPA) on isometric tension, unloaded shortening velocity determined using the slack test (Vmax), and phosphorylation of myosin light chain (MLC20) were investigated in intact and skinned muscle tissues of the rabbit mesenteric artery. In intact muscles exposed to 128 mM K+, the Vmax reached a maximum before the peak of the phasic component of contraction and reduced proportionally with changes in the amplitude of the subsequent tonic contraction. TPA (0.1 microM) enhanced to a greater extent the amplitude of the tonic than the phasic contraction. During the tonic phase, TPA enhanced the Vmax and amplitude of the contraction more than the phosphorylation of MLC20. In skinned muscles, Ca2+ (0.3-1.0 microM) increased the force, Vmax and MLC20 phosphorylation, in a dose dependent manner. The relation between any two of the above three parameters was always linear. TPA (0.1 microM) with phosphatidylserine (50 micrograms/ml) time-dependently increased the force and Vmax observed with 0.3-0.5 microM Ca2+. The relation between the force and Vmax shifted in the direction of that observed in the presence of high Ca2+, but in 0.5 microM Ca2+, TPA with phosphatidylserine showed little change in the phosphorylation of MLC20. As estimated from the actions of TPA, protein kinase C may contribute to activation of contractile proteins through MLC20 phosphorylation dependent and other regulatory processes.
Flow-dependent dilation in a resistance artery still occurs after endothelium removal.
Authors: Bevan J A , Joyce E H , Wellman G C
Published: June 2012

Infusion of physiological saline solution into the lumen of a tonically contracted resistance artery in vitro caused active relaxation. After endothelium removal by rubbing, confirmed by scanning electron microscopy and loss of the relaxation response to acetylcholine (1 microM), flow relaxation was reduced from a mean of 70% to 37%. The latter change was significant (p less than 0.01). It is concluded that flow-relaxation in the resistance artery of the rabbit originates from both the tunica intima and the media.
Effects of alpha-human atrial natriuretic peptide on the interrelationship of arterial pressure, aortic nerve activity, and aortic diameter.
Authors: Hirooka Y , Takeshita A , Imaizumi T , Nakamura N , Tomoike H , Nakamura M
Published: June 2012

A previous study has suggested that atrial natriuretic peptide (ANP) alters arterial baroreflex control of lumbar and renal sympathetic nerve activity. To explore these mechanisms, we examined the interrelationship of arterial pressure, afferent aortic nerve activity, and aortic diameter in rabbits anesthetized with alpha-chloralose before and after sinoaortic denervation and bilateral vagotomy. Arterial pressure was decreased in stepwise fashion by intravenous infusion of alpha-human ANP (alpha-hANP, 0.1-1.0 microgram/kg/min) or sodium nitroprusside (SNP, 1-5 micrograms/kg/min). Both in rabbits with intact baroreceptors and in those with baroreceptors denervated, aortic nerve activity and the aortic diameter decreased during hypotension caused by the infusion of SNP but remained unchanged during hypotension caused by the infusion of alpha-hANP. In addition, we examined the effects of alpha-hANP and SNP on the responses of the aortic diameter and aortic nerve activity to rapid changes in arterial pressure caused by intravenous phenylephrine or nitroglycerin. Changes in aortic nerve activity and the aortic diameter in response to rapid changes in arterial pressure caused by phenylephrine or nitroglycerin were not different between the infusion of alpha-hANP and SNP. These results suggest that aortic nerve activity remains unchanged despite hypotension during the infusion of alpha-hANP, because alpha-hANP dilates the aorta. Since the aortic diameter increases, strain of aortic baroreceptors does not decrease. A second suggestion is that alpha-hANP does not alter aortic baroreceptor responses to changes in arterial pressure caused by phenylephrine or nitroglycerin.
Calcium currents are altered in the vascular muscle cell membrane of spontaneously hypertensive rats.
Authors: Rusch N J , Hermsmeyer K
Published: June 2012

Calcium currents were recorded during whole-cell voltage clamp in cultured azygos venous muscle cells from 1-3-day-old normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Different holding potentials were used to separate total cell current into its transient (T) and sustained or long-lasting (L) components. In recordings from 30 WKY and 30 SHR vascular cells, total cell calcium current was the same between cells from normotensive (167 +/- 20 pA) and hypertensive (139 +/- 15 pA) rats. However, the relative proportion of T and L calcium currents was different between WKY and SHR cells. In WKY cells, the peak amplitude of the L current was less than that of the T current (42 +/- 30% of total current), whereas in SHR cells, the L current was greater (62 +/- 3% of total current). Calcium currents in vascular muscle cells from SHR were activated and inactivated at more positive potentials than in cells from WKY. This study directly compares transmembrane calcium current in isolated cells from WKY and SHR blood vessels and shows that the proportions of T and L calcium channels activated by depolarization are altered in this genetic model of hypertension.
Differential accumulation of diacyl and plasmalogenic diglycerides during myocardial ischemia.
Authors: Ford D A , Gross R W
Published: June 2012

The recent discovery of neutral active choline and ethanolamine glycerophospholipid specific phospholipase C in myocardium (Wolf RA, Gross RW. J Biol Chem 1985;260:7295) has demonstrated a novel catabolic pathway that potentially contributes to the accumulation of amphiphilic metabolites during myocardial ischemia. To assess the potential importance of this pathway, we quantified the temporal course of alterations in myocardial 1-0-alk-1'-enyl-2-acyl-sn-glycerol (AAG) and 1,2-diacyl-sn-glycerol (DAG) content during control and ischemic intervals in an isolated perfused Langendorf model. AAG accumulated over fivefold to 8.70 and 18.27 nmol/g dry in 20- and 60-minute ischemic rabbit hearts, respectively (p less than 0.02). The only AAG molecular species that was detected in substantial amounts in control or ischemic rabbit hearts was 1-0-hexadec-1'-enyl-2-acyl-sn-glycerol. Since this molecular species is enriched in plasmenylcholine these findings suggest that AAG production is likely mediated by phospholipase C-catalyzed hydrolysis of plasmenylcholine. In contrast to ischemia-induced AAG accumulation, DAG content decreased during both control and globally ischemic perfusion intervals. In summary, these findings demonstrate that AAG, in contrast to DAG, accumulates during myocardial ischemia indicating that at least some metabolites of plasmalogen and diacyl phospholipids accumulate at differential rates during myocardial ischemia.
End-systolic pressure as a balance between opposing effects of ejection.
Authors: Hunter W C
Published: June 2012

Ejection has previously been thought to exert only negative effects on end-systolic left ventricular pressure, via mechanisms like shortening deactivation and the force-velocity relation. Whether ejection also exerted a positive influence on pressure generation was tested by comparing two successive beats: 1) the last beat of steady-state ejection versus 2) a totally isovolumic contraction at the end-systolic volume. In 12 isolated, blood-perfused canine hearts loaded with a simulated arterial system, ejecting end-systolic pressure exceeded isovolumic pressure by approximately 10 mm Hg when ejection fraction was 0.3. With both higher and lower ejection fractions, the excess of ejecting end-systolic pressure was smaller; beyond an ejection fraction of roughly 0.5, the trend reversed so that ejecting end-systolic pressure fell below isovolumic pressure. The maximum excess in ejecting end-systolic pressure was quite variable (1-17 mm Hg), but the pattern of its variation with ejection fraction was consistent. A correlate of the positive effect of ejection on ventricular pressure was found in the timing of end systole. For an ejection fraction of 0.4, the systolic duration of ejecting beats was approximately 45% longer than in isovolumic beats (range, 23-67%). Potentially, a positive effect of ejection might be due to a residual influence of the stronger activation of cardiac myofilaments early in ejecting systole during which the sarcomeres were at longer lengths than in the isovolumic beat at end-systolic volume (length-dependent activation). A hypothetical model based on this mechanism reproduced both of the positive effects of ejection that were observed: excess end-systolic pressure and prolonged duration of systole. Thus, the approximate load independence of end-systolic pressure could result from the counter balance between opposing influences of ejection.
Duration of ischemia is vital for collateral development: repeated brief coronary artery occlusions in conscious dogs.
Authors: Mohri M , Tomoike H , Noma M , Inoue T , Hisano K , Nakamura M
Published: June 2012

The effects of two types of repeated transient coronary artery occlusions on collateral development were examined in chronically instrumented, conscious dogs. A 2-minute coronary occlusion at 32-minute intervals (group 1, n = 11) or a 15-second occlusion at 4-minute intervals (group 2, n = 7) were repeated day and night without interruption. In both groups, the total duration of coronary occlusions each day was the same (90 minutes). Before and after repetitive occlusions of either group, effects of transient 2-minute coronary occlusion on regional segment shortening in the ischemic area were examined to assess the functional state of the collateral vessels. In group 1, systolic segment shortening in the area rendered ischemic was reduced to -97.8 +/- 17.7% of the preocclusive control value during 2 minutes of coronary occlusion. After 125-478 repetitive occlusions (3-11 days), the degree of hypokinesia during the 2-minute occlusion was significantly improved to -0.6 +/- 4.6% of the preocclusive value (p less than 0.001 vs. before the repetition). In group 2, it remained unchanged even after 3,500-5,450 repetitive occlusions (11-16 days): -111.8 +/- 8.2% before and -111.4 +/- 13.8% after the repetition of 15-second occlusions (NS). The ratio of peripheral coronary arterial pressure to aortic pressure during transient-coronary occlusion, measured by selective catheterization, was significantly higher in group 1 than in group 2 (64.4 +/- 5.3% vs. 20.7 +/- 1.3%, p less than 0.001). These findings suggest that myocardial ischemia of 2 minutes but not 15 seconds is vital to provide effective stimuli for angiogenesis.
Lipid alterations in isolated, working rat hearts during ischemia and reperfusion: its relation to myocardial damage.
Authors: van Bilsen M , van der Vusse G J , Willemsen P H , Coumans W A , Roemen T H , Reneman R S
Published: June 2012

Disturbances in lipid metabolism may play an important role in the onset of irreversible myocardial damage. To investigate the effect of ischemia and reperfusion on lipid homeostasis and to delineate its possible consequences for myocardial damage, Krebs-Henseleit-perfused, working rat hearts were subjected to various periods of no-flow ischemia (10 to 90 minutes) with or without 30 minutes of reperfusion. During ischemia, the rise in nonesterified fatty acids (NEFAs) was preceded by the accumulation of substantial amounts of glycerol, indicating the presence of an active triacylglycerol-NEFA cycle. The subsequent rise in NEFAs (from 0.25 to 1.64 mumol/g dry residue wt after 90 minutes [means]) coincided with the reduction of ATP to values lower than 10 mumol/g dry wt and the rise of AMP, a potent inhibitor of acyl-coenzyme A synthetase, to values exceeding 2 mumol/g dry wt, making the latter compound a good candidate to hamper the turnover of endogenous lipids during prolonged ischemia. Reperfusion resulted in an additional rise in NEFAs (up to 4.1 mumol/g dry residue wt after 60 minutes of ischemia). Neither ischemia nor reperfusion resulted in significant decreases in the tissue content of triacylglycerols and the various phospholipids. During reperfusion recovery of stroke volume was still adequate at tissue NEFA levels thought to be incompatible with normal mitochondrial function. A positive correlation (r = 0.81) was found between NEFA content of reperfused hearts and cumulative release of lactate dehydrogenase during reperfusion. Accordingly it is concluded that 1) reperfusion results in additional changes in myocardial lipid homeostasis, 2) the accumulating NEFAs are compartmentalized, possibly at the cellular level, and 3) the accumulation of NEFAs is a sensitive marker for myocardial cell damage.
Voltage- and use-dependent modulation of cardiac calcium channels by the dihydropyridine (+)-202-791.
Authors: Kamp T J , Sanguinetti M C , Miller R J
Published: June 2012

The modulation of L-type voltage sensitive calcium channels in isolated guinea pig ventricular myocytes by the dihydropyridine (+)-202-791 was examined with the whole-cell voltage-clamp technique with 1.8 mM Ba or Ca as the charge carrier. Striking voltage- and use-dependent effects of the dihydropyridine calcium channel "agonist" (+)-202-791 were revealed. From a holding potential of -60 mV, depolarizing test pulses in the presence of (+)-202-791 demonstrated a concentration-dependent (EC50, 177 nM) increase in the measured peak inward barium current compared to control. In contrast, more depolarized holding potentials (greater than or equal to -30 mV) (+)-202-791 caused a biphasic effect on the peak inward current resulting in a transient enhancement followed by a steady-state block. A saturable, concentration-dependent hyperpolarizing shift in the voltage dependence of current inactivation was observed in the presence of (+)-202-791 with an EC50 of 10.2 nM. The voltage dependence of current activation was also shifted in the hyperpolarizing direction in the presence of (+)-202-791. A use-dependent relative block by (+)-202-791 was observed after repetitive depolarizing test pulses at a frequency of 2 Hz. Thus, the single enantiomer (+)-202-791 can result in either an increase in the whole cell calcium channel current (favored by hyperpolarized holding potentials and low rates of stimulation) or block of calcium channel current (favored by depolarized holding potentials and high rates of stimulation). Various combinations of (-)-202-791, a reported calcium channel antagonist, and (+)-202-791 resulted in intermediate effects on voltage sensitive calcium or barium currents compared with the presence of either enantiomer alone, and no clear cooperative interactions between the enantiomers were observed in contrast to a previous single channel study (Kokuban S, Prod'ham B, Becker C, Porzig H, Reuter H: Studies on Ca channels in intact cardiac cells: Voltage-dependent effects and cooperative interaction of dihydropyridine enantiomers. Mol Pharmacol 1986;30:571-584). The results are discussed in relation to the possible presence of multiple dihydropyridine receptors associated with the voltage sensitive calcium channel.
Mechanisms of differential growth of heart ventricles in newborn pigs.
Authors: Peterson C J , Whitman V , Watson P A , Schuler H G , Morgan H E
Published: June 2012

The left ventricular free wall (LVFW) grew approximately three times faster than the right ventricular free wall (RVFW) during the first 10 days of life in neonatal pigs. Faster growth was associated with proportional increases in total RNA and messenger RNA. These findings indicated that greater capacity for protein synthesis was a major factor in accelerated growth. Despite faster growth, heart content of ribosomal subunits was higher in piglets than in 60-day-old pigs or adult rats, suggesting a relatively slower rate of peptide chain initiation than elongation. When hearts from 5-day-old pigs were perfused in vitro, protein synthesis was more rapid in the LVFW than in the RVFW. In the absence of added insulin, the higher rate was due to both greater efficiency and greater capacity for protein synthesis. In the presence of the hormone, greater capacity was responsible for the increased rate of protein synthesis in the LVFW as compared with the RVFW.
Heterogeneous microvascular coronary alpha-adrenergic vasoconstriction.
Authors: Chilian W M , Layne S M , Eastham C L , Marcus M L
Published: June 2012

We tested the hypothesis that humoral or neurogenic alpha-adrenergic activation in the coronary circulation would produce heterogeneous vascular reactions. To accomplish this, the epicardial coronary microcirculation was viewed through an intravital microscope using stroboscopic epi-illumination. Microvascular diameters were measured under control conditions during beta-adrenergic blockade (propranolol 1 mg/kg) and beta-adrenergic blockade with pacing; during coronary alpha-adrenergic activation in the presence of beta-adrenergic blockade with three doses of norepinephrine infusion (0.1, 0.5, and 1.0-2.0 micrograms/kg/min) or three frequencies of bilateral stellate nerve stimulation (2, 10, and 20 Hz); and during combined alpha- and beta-adrenergic blockade (phentolamine 2 mg/kg and propranolol 1 mg/kg). Diameters of both arterial and venous vessels were reduced during beta-adrenergic blockade but returned back to baseline with pacing. At the lowest level of norepinephrine infusion or frequency of bilateral stellate stimulation, microvessel constriction was not observed. At the higher doses of norepinephrine a -5.1 +/- 0.9% (1.0-2.0 micrograms/kg/min) and a -4.0 +/- 1.1% (0.5 micrograms/kg/min) decrease in diameter of arterial vessels greater than 100 microns in diameter were observed (p less than 0.05). At 10 Hz and 20 Hz of stellate stimulation, diameter decreased by -4.8 +/- 1.9% and -4.4 +/- 2.1%, respectively, in these relatively large vessels. Small coronary arterioles (less than 100 microns diameter) dilated significantly during the highest levels of nerve stimulation (9.2 +/- 2.5% increase in diameter) or infusion rate of norepinephrine (13.6 +/- 2.7% increase in diameter) (p less than 0.05). These constrictor and dilator responses were abolished following combined alpha- and beta-adrenergic blockade. Norepinephrine infusion resulted in a decrease in diameter of coronary veins and venules (7.2 +/- 1.3%) (p less than 0.05), whereas stellate stimulation did not significantly reduce venous and venular diameters. In summary, the coronary venous and venular vasculature responds to alpha-adrenergic activation from circulating norepinephrine but is not affected by stellate stimulation. In contrast, stellate stimulation and norepinephrine infusion elicit similar responses in the coronary arterial and arteriolar microvasculature. Constriction occurs in vessels greater than 100 microns in diameter, whereas dilation predominates in vessels less than 100 microns in diameter. Such heterogeneous arterial responses would undoubtedly result in a redistribution of coronary vascular resistance toward larger coronary arteries and arterioles.
Real-time and simultaneous measurement of tricuspid orifice and tricuspid anulus areas in anesthetized dogs.
Authors: Tamiya K , Higashidate M , Kikkawa S
Published: June 2012

Tricuspid valve orifice and tricuspid valve anulus areas were measured simultaneously in the anesthetized dog with a newly developed area-measuring system based on electromagnetic induction. This system permitted real-time monitoring of the area enclosed by the edges of valve leaflets and by the juncture of the valve leaflet and the cardiac wall in situ, without artificial constraint to the valve motion. Right atrial and right ventricular pressures were measured with two catheter-tipped micromanometers. During control state, tricuspid valve orifice area (TOA) increased up to its peak [1.38 +/- 0.26 cm2 (mean +/- SD)] coincidently with either atrial systole or rapid ventricular filling. Atrial contraction evoked distinct presystolic tricuspid anulus narrowing with concomitant slow TOA reduction. This slow TOA reduction began 30.0 +/- 16.1 msec before systolic atrioventricular pressure crossover, and the following rapid TOA decrease was completed 38.7 +/- 12.2 msec after systolic atrioventricular pressure crossover. TOA began to increase 48.4 +/- 30.4 msec before diastolic atrioventricular pressure crossover at the end portion of the isovolumic relaxation phase, opposing residual transvalvular pressure gradient (3.33 +/- 1.79 mm Hg). The slow presystolic TOA decrease was considered to be a reflection of the presystolic anulus narrowing caused by atrial systole. An isolated atrial contraction induced by administering 1 mg acetylcholine chloride into the atrioventricular node artery or by vagus nerve stimulation could produce complete valve closure. Even in an isolated atrial contraction, the inflection point that marks the boundary between slow "atriogenic" closure presumably due to anulus narrowing and rapid closure presumably due to hemodynamic force was easily identified.
Protection against autonomic denervation following acute myocardial infarction by preconditioning ischemia.
Authors: Miyazaki T , Zipes D P
Published: June 2012

To examine the effects of ischemic preconditioning on efferent autonomic responses following acute transmural myocardial ischemia/infarction (MI), the time course and extent of efferent sympathetic and vagal denervation were compared between control dogs that received a one-stage sustained coronary occlusion and preconditioned dogs that received four 5-minute coronary occlusions separated by 5 minutes of reperfusion before sustained occlusion. Effective refractory periods (ERP) basal and apical to MI were determined in the baseline state and during neural stimulation before and after preconditioning occlusions and 20, 60, 120, and 180 minutes after sustained occlusion by ligature ligation of diagonal branches of the left anterior descending coronary artery. In 10 control dogs with transmural MI, ERP shortening induced by bilateral ansae subclaviae stimulation (4-msec pulses, 2-4 Hz and 2-4 mA) was unchanged at basal sites but was attenuated at apical sites. Four of 40 apical test sites exhibited efferent sympathetic denervation (less than or equal to 2 msec shortening) 20 minutes after sustained occlusion. Thirteen of 40 apical sites became denervated during a 3-hour period. In 10 preconditioned dogs, ERP shortening at apical sites was unchanged after preconditioning occlusions and during the first 60 minutes of sustained ischemia but was attenuated at 120 minutes. Three of 40 apical test sites became denervated during a 3-hour period. The cumulative percentage of denervated apical test sites was significantly less in the preconditioned group compared with the control group (p = 0.006) despite a comparable degree of subepicardial involvement in the MI (8.2 +/- 1.0% vs. 8.4 +/- 1.4%, the ratio to the left ventricular circumference, mean +/- SEM). In 11 control dogs tested for efferent vagal response after MI, ERP prolongation induced by bilateral vagal stimulation (4-msec pulses, 20 Hz with current strength 0.05 mA greater than that required to produce asystole) was unchanged at basal sites, but was attenuated at apical sites, and five of 44 test sites exhibited denervation (less than or equal to 1 msec prolongation) 20 minutes after sustained coronary occlusion. Fourteen of 40 apical sites became denervated during a 3-hour period. In 10 preconditioned dogs, vagally induced ERP prolongation was unchanged both at basal and apical sites, and none of 36 apical test sites exhibited denervation after preconditioning and during a 3-hour period of sustained coronary occlusion (p less than 0.001 vs. control group) despite a comparable degree of subendocardial involvement in the MI (11.8 +/- 0.8% vs. 11.9 +/- 1.3%).(ABSTRACT TRUNCATED AT 400 WORDS)
Estimating cardiac transmembrane activation and recovery times from unipolar and bipolar extracellular electrograms: a simulation study.
Authors: Steinhaus B M
Published: June 2012

A model of one-dimensional action potential propagation was used to compare activation times and recovery times measured from simulated unipolar and bipolar electrograms with the activation and recovery times measured from simulated transmembrane action potentials. Theory predicts that the intrinsic deflection--the time of the maximum negative slope of the unipolar electrogram QRS complex--corresponds to the time of maximum positive slope of action potential depolarization. Similarly, the time of the maximum positive slope of the unipolar electrogram T wave corresponds to the time of maximum negative slope of action potential repolarization. This study showed that the difference between the unipolar electrogram activation time and the action potential activation time and the difference between the unipolar electrogram recovery time and the action potential recovery time were small during ideal conditions of uniform propagation in a long cable. Nonideal conditions, however, were associated with activation time differences in excess of 1.8 msec and recovery time differences in excess of 30 msec (243 msec in certain conditions). Nonideal conditions that had a major influence were changes in activation sequence, propagation in a short cable, and propagation through regions of nonuniform coupling resistance and/or nonuniform membrane properties. Nonideal conditions that had a smaller influence were variations in distance from the measurement site to the simulated tissue surface, nonzero reference potentials, and the addition of distant events. Recovery time differences were more sensitive to the nonideal conditions than were activation time differences, and both depended on the action potential shape. When distant events significantly contributed to the unipolar electrogram waveform, the time differences when bipolar electrograms were used were less than those when unipolar electrograms were used; however, under other conditions, the time differences were comparable. Results showed that activation times and especially recovery times measured from electrograms can be greatly affected by conditions independent of changes in the underlying action potential waveforms.
Identification of alpha 1-adrenergic receptors on sarcolemma from normal subjects and patients with idiopathic dilated cardiomyopathy: characteristics and linkage to GTP-binding protein.
Authors: Vago T , Bevilacqua M , Norbiato G , Baldi G , Chebat E , Bertora P , Baroldi G , Accinni R
Published: June 2012

Discontinuous density sucrose gradient centrifugation was used to isolate membrane vesicles from the left ventricle of three normal subjects (one prospective organ donor and two traffic victims whose hearts were obtained 1 hour after death) and nine patients undergoing cardiac transplantation as a consequence of idiopathic dilated cardiomyopathy. Sarcolemma-enriched subcellular fractions, detected in the interface between 8.55% and 25% sucrose, were identified by the increased activity of Na+,K+-ATPase and by enrichment in beta-adrenergic receptor density. The density of beta-adrenergic receptors was lower in vesicles from diseased hearts (610 +/- 71 fmol/mg protein) than in vesicles from normal hearts (1,410 +/- 226 fmol/mg protein; p less than 0.01). alpha 1-Adrenergic receptors were identified in these membrane vesicles by [3H]prazosin binding. Specific binding of [3H]prazosin was about 50% of the total binding at 1 nM, and alpha 1-adrenergic binding sites were saturable at approximately 3 nM. Scatchard analysis revealed 58 +/- 5 fmol/mg protein (KD = 0.90 +/- 0.08 nM) in pathological hearts and 30 +/- 5 fmol/mg protein (KD = 0.90 +/- 0.03 nM) in normal hearts (p less than 0.01). The displacement curve of (-)-norepinephrine in membrane vesicles from normal hearts delineated one subpopulation of alpha 1-adrenergic receptors; the addition of 0.1 mM GTP did not cause right shift. In membrane vesicles from diseased heart, the displacement curve of (-)-norepinephrine disclosed two subpopulations of alpha 1-adrenergic receptors. A right shift that occurred after addition of GTP showed that in this case alpha 1-adrenergic receptors were functionally coupled with GTP-binding protein.(ABSTRACT TRUNCATED AT 250 WORDS)
Renin-angiotensin II response to the hemodynamic pathology of ovines with ventricular septal defect.
Authors: Boucek M M , Chang R , Synhorst D P
Published: June 2012

We studied the response of the renin-angiotensin system (RAS) to a surgically created ventricular septal defect (VSD) in immature ovines and also the role of angiotensin II in the pathophysiology of VSD in the chronically instrumented ovine. Plasma renin activity (PRA) was increased from 2.39 +/- 1.1 to 3.78 +/- 1.4 ng/ml/hr (p less than 0.05, n = 17) after VSD but not after sham procedure. The change in PRA was positively correlated with the amount of left-to-right shunt through the VSD (r = 0.74, p less than 0.05). Inhibition of angiotensin II effect with saralasin (10 micrograms/kg/min) or angiotensin II production with captopril (2 mg/kg) lowered systemic resistance (Rs) by 14% and 34%, respectively (p less than 0.05), and raised pulmonary resistance (Rp) by 35% and 77%, respectively (p less than 0.05). Thirty minutes following captopril, the ratio of pulmonary to systemic flow (Qp/Qs) decreased from 3.31 +/- 0.18 to 2.15 +/- 0.18 (p less than 0.05) while total pulmonary flow fell from 7.15 +/- 0.38 to 5.92 +/- 0.34 l/min/M2 (p less than 0.05, n = 11). Systemic flow increased from 2.17 +/- 0.14 to 2.86 +/- 0.33 l/min/M2 (p less than 0.05) despite a reduction in left atrial pressure (17.3 +/- 1.0 vs. 13.0 +/- 1.7, p less than 0.01). Reinfusion of angiotensin II (0.02 micrograms/kg/min) into the central aorta after captopril returned the hemodynamics to baseline including a rise in Rs and fall in Rp. Exogenous angiotensin II alone (0.08 micrograms/kg/min) or a threefold stimulation in PRA with furosemide (2 mg/kg) caused little hemodynamic effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of oxygen withdrawal on active and passive electrical properties of arterially perfused rabbit ventricular muscle.
Authors: Riegger C B , Alperovich G , Kléber A G
Published: June 2012

Oxygen withdrawal from myocardial cells leads to changes of the transmembrane action potential (mainly action potential shortening), to cellular uncoupling, and to changes of vascular permeability. This study was aimed at the simultaneous measurement of electrical activity and passive electrical properties (extracellular and intracellular longitudinal resistance) in arterially perfused rabbit papillary muscles under different conditions of changed oxygen supply. These included 1) complete anoxia (erythrocyte-free perfusate), 2) hypoxia (PO2 between 23-28 mm Hg, erythrocytes present) in the presence and absence of glucose, and 3) normoxia with erythrocyte-free perfusate. Similarly to myocardial ischemia, rapid cellular uncoupling occurred only after an initial stable period of approximately 17 minutes, and it required complete anoxia. The marked shortening of the action potential developed before cellular uncoupling. In six out of eight experiments, the fibers were inexcitable when uncoupling started. In severe hypoxia, no significant change of internal longitudinal resistance was observed over 35-40 minutes. The time course of the extracellular longitudinal resistance was different from the change in intracellular resistance: A marked decrease occurred almost immediately after the onset of oxygen withdrawal. This decrease was followed by a small increase in conduction velocity, which was most likely due to a change in the interstitial compartment (edema). It was observed during anoxic as well as during hypoxic perfusion. We conclude that 1) cellular uncoupling in arterially perfused tissue requires almost complete oxygen lack and occurs with a delay of more than 10 minutes, 2) marked action potential shortening precedes uncoupling, and therefore can not simply be attributed to an increase in free, intracellular calcium, and 3) vascular endothelial function is more sensitive to oxygen withdrawal than the myocyte.
Regional left ventricular epicardial deformation in the passive dog heart.
Authors: McCulloch A D , Smaill B H , Hunter P J
Published: June 2012

Epicardial wall motion was measured on the left ventricular free wall in six isolated potassium-arrested dog hearts using a biplane video technique. Significant regional variations in epicardial deformations were recorded during static ventricular filling. Epicardial stretches varied linearly with cavity volume, sometimes exceeding 20% at physiological left ventricular end-diastolic pressures. The maximum component of epicardial stretch and the derived wall thinning increased substantially from the base to the apex on both the anterior and the posterior free walls of the left ventricle. In five hearts, the direction of greatest epicardial stretch at moderate and high filling pressures coincided closely with the local epicardial fiber direction, suggesting that the left-handed epicardial fiber helices stretch preferentially during passive filling to maximize end-diastolic fiber lengths. Epicardial rotation was always counterclockwise, consistent with a reduction in the pitch of the fiber helix during filling. These results suggest that, on the epicardial surface, the passive myocardium is anisotropic with respect to the local fiber direction. We suggest that the resulting torsional shear acts to minimize transmural gradients of fiber stretch.
SC-39026, a serine elastase inhibitor, prevents muscularization of peripheral arteries, suggesting a mechanism of monocrotaline-induced pulmonary hypertension in rats.
Authors: Ilkiw R , Todorovich-Hunter L , Maruyama K , Shin J , Rabinovitch M
Published: June 2012

In rats injected with the toxin monocrotaline, altered synthesis and distribution of pulmonary artery elastin suggest that increased elastase activity may be important in the development of vascular changes and progressive pulmonary hypertension. To test this hypothesis, male Sprague-Dawley rats (250-300 g) were given 40 mg/kg of the elastase inhibitor SC-39026 in a carboxymethylcellulose vehicle or vehicle only by gavage, 12 hours before and twice daily for 8 days after a single subcutaneous injection of either monocrotaline (60 mg/kg) or saline. Thirteen days after injection, indwelling cardiovascular catheters were inserted under pentobarbital anesthesia, and at 15 days after injection, pulmonary and systemic hemodynamic measurements were recorded with the animals awake. At post-mortem examination, the lungs were perfused and morphometric techniques applied for light and electron microscopic evaluation. Saline-injected rats given either SC-39026 or vehicle were similar in all features assessed. In contrast, monocrotaline-injected rats given SC-39026 had significantly lower mean pulmonary artery pressure than those given vehicle (21.0 +/- 1.6 vs. 27.5 +/- 0.8 mm Hg, p less than 0.05), and this correlated with a significant reduction in the number of abnormally muscularized arteries at alveolar wall level (r2 = 0.89, p less than 0.001). SC-39026 did not significantly reduce monocrotaline-induced medial hypertrophy of muscular arteries, endothelial injury, and associated subendothelial edema; nor was there a significant increase in the proportion of the medial elastin, although a trend was apparent. Additional groups of monocrotaline injected rats were followed 3 weeks after injection, but both SC-39026 and vehicle-treated rats were similar at this point. Our data suggest that increased serine elastase activity associated with endothelial injury may mediate early abnormal pulmonary vascular smooth muscle differentiation resulting in muscularization of normally nonmuscular peripheral arteries and pulmonary hypertension induced in rats by injection of the toxin monocrotaline. Lack of persistence of this protective effect suggests that there may be continued elastase activity in this model. Failure to inhibit medial hypertrophy with SC-39026 suggests that a different mechanism or a different elastase may be involved in this structural change.
Subcellular calcium content in cardiomyopathic hamster hearts in vivo: an electron probe study.
Authors: Bond M , Jaraki A R , Disch C H , Healy B P
Published: June 2012

In the Syrian cardiomyopathic hamster heart, abnormal cellular calcium regulation, resulting in cellular calcium overload, is believed to play a role in the pathogenesis of cardiac hypertrophy and failure. Alternatively, the primary abnormality may be coronary vasospasm, resulting in reperfusion-induced necrosis. According to the latter hypothesis, only those cells that suffer an ischemic insult would contain elevated calcium levels. To determine whether a generalized elevation in myocytic calcium exists in myopathic hamster hearts, we measured cellular and subcellular calcium concentrations by electron probe microanalysis in cryosections of 50-day and 96-day myopathic and control hearts, rapidly frozen in vivo. Total calcium content of ventricular homogenates from each group was also measured by atomic absorption spectrophotometry. No significant differences in subcellular calcium were found by electron probe microanalysis among 50-day and 96-day myopathics and their age-matched controls. In 50-day myopathic and control hearts, mitochondrial calcium was 0.7 +/- 0.2 and 0.9 +/- 0.2, respectively, and A-band calcium was 3.0 +/- 0.4 and 2.6 +/- 0.4 mmol calcium/kg dry wt(+/- SEM). Results from 96-day animals were similar. Localized regions of elevated calcium were found only at sites of necrotic foci: in Na+-loaded cells (mitochondria: 4.7 +/- 1.3 (SEM) mmol/kg dry wt), in dying cells (mitochondria: 72 +/- 22 (SEM) mmol/kg dry wt) or as extracellular deposits (7-10 mol/kg dry wt). Total calcium content of hearts from myopathic hamsters, as determined by atomic absorption spectrophotometry, was also 13 times (50-day) and 50 times (96-day) higher than controls. These results demonstrate that there is a marked heterogeneity in cellular calcium content in myopathic hamster hearts, but the data do not support the hypothesis of a generalized cellular calcium overload.
Cholinergic mechanisms in the cerebral circulation of the newborn piglet: effect of inhibitors of arachidonic acid metabolism.
Authors: Wagerle L C , Busija D W
Published: June 2012

The cerebrovascular response to cholinergic stimulation and the effect of inhibition of the lipoxygenase and cyclooxygenase pathways on the response to acetylcholine (ACh) was investigated in newborn piglets. Responsiveness of pial arterioles to ACh, methacholine, and nicotine was studied using a closed cranial window. Pial arteriolar diameter was measured using intravital microscopy. Pial arteriolar responses to ACh, 10(-8)-10(-4)M, applied to the cortical surface, were variable and dose-dependent. At low concentration, 10(-7)M, 45% of the arterioles increased diameter by 9 +/- 1%, 19% responded by decreasing diameter by 9 +/- 1%, and 35% did not respond. The response to high concentration, 10(-4)M, was a profound decrease in diameter, 28 +/- 3%, in 78% of the arterioles studied. These effects were abolished by atropine (0.5 mg/kg i.v.). Muscarinic agonist, methacholine, 10(-5)-10(-3)M, also resulted in a decrease in cerebral vascular diameter, while nicotine, 10(-6)-10(-4)M, had no effect. In six animals, administration of cyclooxygenase inhibitor, indomethacin (5 mg/kg i.v.), blocked the response to 10(-4)M ACh but did not affect the response to 10(-7)M ACh. In five animals, administration of lipoxygenase inhibitor, nordihydroguaiaretic acid (2 mg/kg i.v.) augmented the vasoconstrictor response at both ACh concentrations. The data suggest that, in the newborn piglet, vasoactive prostanoids released following cholinergic activation of a muscarinic-type receptor mediate vasoconstriction in cerebral arterioles.
Specific binding of [3H]LY186126, an analogue of indolidan (LY195115), to cardiac membranes enriched in sarcoplasmic reticulum vesicles.
Authors: Kauffman R F , Utterback B G , Robertson D W
Published: June 2012

LY186126 was found to be a potent inhibitor of type IV cyclic AMP phosphodiesterase located in the sarcoplasmic reticulum of canine cardiac muscle. This compound, a close structural analogue of indolidan (LY195115), was prepared in high specific activity, tritiated form to study the positive inotropic receptor(s) for cardiotonic phosphodiesterase inhibitors such as indolidan and milrinone. A high-affinity binding site for [3H]LY186126 was observed (Kd = 4 nM) in purified preparations of canine cardiac sarcoplasmic reticulum vesicles. Binding was proportional to vesicle protein, was inactivated by subjecting membranes to proteolysis or boiling, and was dependent on added Mg2+. Scatchard analysis suggested the presence of a single class of binding sites in the membrane preparation. Indolidan, milrinone, and LY186126 (all at 1 microM) produced essentially complete displacement of bound [3H]LY186126, while nifedipine, propranolol, and prazosin had little or no effect at this concentration. This represents the first reported use of a radioactive analogue to label the inotropic receptor for cardiotonic phosphodiesterase inhibitors. The results suggest that [3H]LY186126 is a useful radioligand for examining the subcellular site(s) responsible for positive inotropic effects of these drugs.
Digital angiographic impulse response analysis of regional myocardial perfusion: linearity, reproducibility, accuracy, and comparison with conventional indicator dilution curve parameters in phantom and canine models.
Authors: Eigler N L , Pfaff J M , Zeiher A , Whiting J S , Forrester J S
Published: June 2012

The system mean transit time (Tsys) of the impulse response function describing contrast material transit through the coronary circulation was determined from serial digital angiographic images. The linearity, reproducibility, and relations with regional myocardial perfusion and conventional time-density curve parameters, time to peak concentration (TPC), and exponential washout rate (k) were assessed in a dynamic flow x-ray phantom (n = 46) and in six open-chest dogs (n = 102) while coronary flow was altered by stenosis and/or hyperemic stimuli. In the phantom studies, the inverse of the system mean transit time (Tsys-1) closely predicted flow/volume (r = 0.99, slope = 0.99). In dogs, Tsys-1 was independent of the shape of the contrast bolus injection (single or double-peaked), class of contrast agent (ionic or nonionic), the type of hyperemic stimulus (dipyridamole, dipyridamole plus norepinephrine, transient total occlusion, or ionic contrast media), and was highly reproducible between adjacent myocardial regions served by the same artery (r = 0.98 +/- 0.01). There was a strong correlation between Tsys-1 and regional coronary flow for stenotic and/or hyperemic vessels (r = 0.94, distribution volume = 14.9 ml/100 g) over a wide range (0-514 ml/min/100 g). Tsys-1 performed better than conventional time-density curve parameters TPC-1 and k for predicting phantom flow/volume ratios and regional myocardial blood flow in the dog. These data suggest that both digital coronary angiography and coronary contrast transit can be modeled as linear systems and that impulse response analysis may provide accurate and reproducible estimates of regional myocardial blood flow.
Mechanisms underlying atriopeptin-induced increases in hematocrit and vascular permeation in rats.
Authors: Williamson J R , Holmberg S W , Chang K , Marvel J , Sutera S P , Needleman P
Published: June 2012

Infusion of atriopeptin into humans and animals induces diuresis, natriuresis, hemodynamic changes, and an increase in arterial hematocrit. The objective of the present study was to elucidate the mechanism(s) responsible for the increase in hematocrit in rats given atriopeptin-24 (AP-24). Infusion of AP-24 for 30 minutes increased large vessel and total vascular hematocrits by 10-15% while decreasing microvascular hematocrits by 9-26% in numerous tissues. Regional vascular permeation by [131I] bovine serum albumin was markedly increased (2-5.6-fold) in many tissues, consistent with a 16% decrease in plasma volume. AP-24 infusion had no effect on extracellular fluid volume or the volume of circulating red cells. Vascular resistance was decreased and was associated with a significant increase in blood flow in many, but not all, tissues. In the atrium and in the small and large intestine the percentage decrease in microvascular hematocrit exceeded the increase in blood flow. These observations indicate that the increase in large vessel hematocrit induced by AP-24 infusion 1) is accompanied by a decrease in (microvascular) hematocrit in many tissues, 2) reflects an increase in overall (i.e., total vascular hematocrit), and 3) is the consequence of a decrease in plasma volume resulting from a marked increase in the rate of vascular permeation by plasma constituents in multiple tissues.