bluuebunny/crossref_metadata_2025 huggingface dataset:
Prejunctional and postjunctional actions of endogenous norepinephrine at the sympathetic neuroeffector junction in canine coronary arteries.
Authors: Cohen R A , Shepherd J T , Vanhoutte P M
Published: June 2012

The effects of endogenous and of exogenous norepinephrine were studied in isolated rings of canine left circumflex coronary artery and its first ventricular branch. Norepinephrine was released from adrenergic nerve endings by transmural electrical stimulation and by tyramine. In rings contracted with prostaglandin F2 alpha, transmural electrical stimulation resulted in frequency-dependent relaxations which were blocked by propranolol or tetrodotoxin; tyramine and exogenous norepinephrine caused concentration-dependent relaxations which were blocked by propranolol. The tyramine-induced relaxations also were inhibited by cocaine. The left circumflex artery was less sensitive than its branch to beta-adrenergic activation; this difference was significant even between rings of the two vessels immediately adjacent to the branching point and was abolished by phentolamine. In the presence of propranolol, transmural electrical stimulation, tyramine and phenylephrine, produced contractions of the left circumflex artery, but not the branch; these contractions were prevented by phentolamine. Phentolamine, but not prazosin, augmented the beta-adrenergic response of left circumflex artery to low frequency stimulation; in arteries preincubated with 3H-norepinephrine, this was accompanied by an increased overflow of tritiated neurotransmitter. The prejunctional effect of phentolamine was also evident in branch coronary arteries which exhibit no postjunctional alpha-adrenergic responses. With high frequency stimulation, both alpha-adrenergic antagonists equally augmented the relaxation of left circumflex artery; the efflux of tritiated norepinephrine was not different from untreated arteries. These experiments demonstrate, in isolated coronary arteries, that the primary adrenergic response to released endogenous norepinephrine is beta-adrenergic relaxation. The prejunctional effects of nonspecific alpha-adrenergic antagonists preclude their use in determining the importance of postjunctional coronary alpha-adrenergic receptor activation caused by sympathetic nerve stimulation.
Detection of acute myocardial infarction in closed-chest dogs by analysis of regional two-dimensional echocardiographic gray-level distributions.
Authors: Skorton D J , Melton H E , Pandian N G , Nichols J , Koyanagi S , Marcus M L , Collins S M , Kerber R E
Published: June 2012

We hypothesized that acute myocardial infarction could be detected in standard two-dimensional echocardiograms of closed-chest dogs by evaluating regional echo amplitude distributions using computerized image analysis. We tested this hypothesis by performing standard, 2.4 MHz two-dimensional echoes before and 2 days after circumflex coronary occlusion in seven closed-chest dogs. Control and infarcted regions of interest were studied in digitized stop-frame images. Average gray level was calculated for each region of interest, and the shape of the gray-level distribution was analyzed by calculation of skewness and kurtosis and by qualitative features of shape. Average gray level increased significantly from the pre- to postocclusion images in the infarcted regions (16.7 +/- 4.2 vs. 32.4 +/- 4.4 units, P less than 0.01), but not in the control regions (17.4 +/- 4 vs. 22.3 +/- 5.5., P = NS). Average gray level could not distinguish between infarcted and normal regions within the postocclusion images (36 +/- 5.2 vs. 33.6 +/- 5.8, P = NS). Three independent observers qualitatively evaluated histogram shape and correctly identified 7/7 MI regions (100% sensitivity) and 14/20 normal regions (70% specificity). Quantitatively, infarct regions exhibited a significant decrease in kurtosis from pre- to postocclusion images (7.1 +/- 4.0 vs. 5.2 +/- 2.9, P = NS). Within postocclusion images, infarcted regions displayed a significantly lower kurtosis than did normal regions (0.27 +/- .47 vs. 2.5 +/- 1.0, P less than .01). We conclude that acute myocardial infarction may be detected in closed-chest dogs by analyzing regional echo amplitude data from standard two-dimensional echocardiograms.
Morphometry of exercise-induced right ventricular hypertrophy in the rat.
Authors: Anversa P , Levicky V , Beghi C , McDonald S L , Kikkawa Y
Published: June 2012

In our morphometric study of the effects of exercise on the heart, male Wistar-Kyoto rats at 5 weeks of age were subjected daily to a moderate treadmill running program that lasted for 7 weeks. The heart responded to physical conditioning by different magnitudes of tissue growth of the right (22%) and left (7%) ventricular myocardium, the latter change not statistically significant. The increase in right ventricular volume was associated with a 25% enlargement of ventricular area, a 26% average lengthening of the myocytes, and no change in sarcomere length and in ventricular midwall thickness. Exercise produced significant alterations in the quantitative parameters of the microvasculature of the right ventricle, but no appreciable changes in the left ventricle. Right ventricular hypertrophy was characterized by an absolute 44% growth of the endothelial luminal surface brought about through a 16% increase in capillary numerical density, and a 41% augmentation of the total length of the capillary network. Maximum diffusion distance from the capillary wall to the mitochondria of myocytes decreased 10% as a result of capillary proliferation and the lack of lateral expansion of myocyte cross-sectional area. Evaluation of the subcellular constituents of myocytes showed no change in the mitochondria:myofibrils volume ratio, indicating a growth of these components proportional to each other and to the growth of the myocyte population as a whole. It was concluded that, as a result of running exercise, right ventricular growth is analogous to eccentric hypertrophy in which the structural adaptations of the capillary bed can be expected to improve the diffusion and transport of oxygen within the tissue.
Mechanism of biphasic contractions in strontium-treated ventricular muscle.
Authors: King B W , Bose D
Published: June 2012

Biphasic contractions were produced in dog trabeculae by replacing 90-95% of the calcium in the bathing solution with strontium. These conditions produced prolonged action potentials accompanied by contractions with two distinct phasic components. The early component disappeared slowly when the remaining Ca++ was removed, whereas the late component was eliminated quickly when Sr++ was removed. Manganese ion (0.25 mM) preferentially decreased the late component without changing the action potential, whereas caffeine and ryanodine decreased or eliminated the early component. Ryanodine did not alter the action potential. Isoproterenol rapidly increased the early component and, more slowly and to a lesser degree, increased the late component. The results suggest that the early component is caused by intracellular release of activator cation, probably from the sarcoplasmic reticulum, whereas the late component is the result of Sr++ entry across the sarcolemma, possibly by way of the slow inward current.
Effect of external force on relaxation kinetics in single frog atrial cardiac cells.
Authors: Tarr M , Trank J W , Goertz K K
Published: June 2012

The effects of external force on relaxation kinetics were investigated in isolated single frog (Rana catesbeiana) atrial cells. We found that force decay occurred at a maximum and constant rate for a significant portion of auxotonic relaxation, and this rate was linearly related to the peak force developed during auxotonic contraction. The slope of the linear relationship between the maximum rate of auxotonic force decay and peak auxotonic force was not affected by changes in the level of contractile activation produced by activating the cell with different stimulus durations. The rate of force change during auxotonic contraction and relaxation in the isolated cell is directly related to the average sarcomere velocity within the cell. Thus, the results indicate that during auxotonic relaxation the velocity of sarcomere extension is directly related to the peak auxotonic force, and sarcomere extension, during relaxation, is therefore affected by external force. The direct effect of external force on relaxation kinetics was confirmed by the observation that force changes imposed on the cell during relaxation immediately altered the velocity of the extending cell from any given length. However, data are also presented which demonstrate that rapid sarcomere extension occurs during relaxation under conditions where external forces are negligible. Thus, rapid sarcomere extension during relaxation does not require large external forces, and internal forces must play a role in sarcomere extension during relaxation. An explanation is given for these apparently contradictory results.
The feedback regulation of angiotensinogen production by components of the renin-angiotensin system.
Authors: Herrmann H C , Dzau V J
Published: June 2012

The in vivo generation of angiotensin appears to be dependent on both plasma renin and angiotensinogen concentrations. Much less is known about the control of hepatic angiotensinogen synthesis and release, as compared to that of renin. In this study, we examined the feedback regulation of angiotensinogen synthesis and release by various components of the renin-angiotensin system, using an in vitro rat liver slice system. Livers were removed for study from rats which were subjected to various systemic infusions or physiological perturbations. Infusion of angiotensin II has been reported to increase angiotensinogen release rate. However, infusion of angiotensin I (with simultaneous suppression of plasma renin by antirenin antibody infusion and angiotensin II production by captopril administration) had no effect on the angiotensinogen release rate. Direct infusion of renin in rats treated with captopril resulted in further suppression of the angiotensinogen release rate, compared with those given captopril alone. We postulate that renin (or des-angiotensin I-angiotensinogen) inhibits the angiotensinogen release rate, whereas angiotensin II stimulates it. Angiotensin I has no effect on angiotensinogen release rate. This hypothesis was evaluated further in rats with various physiological states. Indeed, when conditions were such that the renin-angiotensin system was completely suppressed, such as binephrectomy and antirenin antibody infusion, angiotensinogen release rate was markedly stimulated. When angiotensin II production was prevented by captopril treatment, angiotensinogen release rate declined. This appeared to be the case for all states of sodium balance. Thus, angiotensinogen release rate is subject to a complex feedback control by other components of the renin-angiotensin system.
Transitional blood flow zones between ischemic and nonischemic myocardium in the awake dog. Analysis based on distribution of the intramural vasculature.
Authors: Murdock R H , Harlan D M , Morris J J , Pryor W W , Cobb F R
Published: June 2012

The present study evaluates the transitional or border zone of intermediate blood flow reduction between nonischemic and ischemic regions after acute coronary artery occlusion in chronically instrumented dogs, using methods that minimize an admixture of ischemic and nonischemic myocardium in the tissue analyzed. The regions perfused by occluded and nonoccluded vessels were identified by tracing the extra and intramural distribution of the coronary vasculature from postmortem angiograms. Regional blood flow was evaluated in serial 3-mm-wide epicardial and endocardial zones from outside and inside the interface between occluded and nonoccluded vessels. The zone of intermediate reduction in blood flow between nonischemic and ischemic regions occurred in the first 3-mm section immediately inside the region supplied by the occluded vasculature. Mean blood flow in this region was reduced to 58 +/- 6% and 61 +/- 5% (+/- SEM) of nonischemic region blood flow at the lateral and medial epicardial margins, respectively, and 47 +/- 5% and 45 +/- 6% at the lateral and medial endocardial margins, respectively. In the remaining ischemic zone, significant differences in blood flow existed between epicardial and endocardial layers; these differences were highly variable between animals. The data indicate that when the analysis of regional blood flow following acute ischemia is based on the anatomic distribution of the coronary vasculature, the transitional or border zone of intermediate reduction in blood flow is limited to a narrow zone immediately inside the occluded vasculature. Studies performed in acutely anesthetized dogs in which the occluded region was perfused via a two-chamber blood reservoir that allowed maintenance of perfusion and exclusion of microspheres from the circumflex region indicate that intermediate reductions in blood flow at the border of the ischemic zone resulted from an admixture of normal myocardium and, thus, do not represent a border zone of intermediate ischemia.
Evidence for the existence of a family of biologically active angiotensin I-like peptides in the dog central nervous system.
Authors: Husain A , Bumpus F M , Smeby R R , Brosnihan K B , Khosla M C , Speth R C , Ferrario C M
Published: June 2012

A family of angiotensin I-like peptides has been derived from endogenous precursors present in dog cerebrospinal fluid after incubation with species homologous renin. These peptides are immunologically and pharmacologically similar to [Ile5]angiotensin I, and have molecular weights ranging between 1300 and 2200 daltons. The presence of precursors in the cerebrospinal fluid able to generate various biologically active angiotensin I-like peptides dissimilar to plasma angiotensin I supports the concept of a local angiotensin I-forming system in the brain.
Evidence for a local sympathetic venoarteriolar "reflex" in the dog hindleg.
Authors: Henriksen O , Amtorp O , Faris I , Agerskov K
Published: June 2012

The study was performed in order to determine whether a local sympathetic venoarteriolar "reflex" is present in the dog hindleg. Femoral artery blood flow was measured by an electromagnetic flowmeter probe, and blood flow in the thigh muscle and subcutaneous tissue distally in the paw was measured by the local 133Xe washout technique. Twenty experiments were carried out in seven dogs unilaterally sympathectomized 2-4 weeks previously. Resting vascular tone did not differ in the sympathectomized and nonsympathectomized legs. In the control leg, venous pressure elevation caused a decrease in femoral blood flow of 49% corresponding to an increase in vascular resistance of 58%. In muscle and subcutaneous tissue vascular resistance increased by 81% and 35%, respectively. In the denervated leg, venous stasis caused no change in total vascular resistance. In muscle the vascular resistance increased by only 24%. In subcutaneous tissue, vascular resistance decreased by 12%. The effect of acute lumbar sympathectomy was studied in another group of seven dogs. Operation caused an immediate decrease in vascular resistance of 40%. The increase in vascular resistance during venous stasis in the total leg, as well as in muscle and subcutaneous tissue, was not affected. However, acute lumbar sympathectomy combined with injection of phenoxybenzamine into the femoral artery almost abolished the vasoconstriction induced by venous stasis. In muscle, the increase in vascular resistance was still present, but considerably attenuated. In subcutaneous tissue, the normal response was completely blocked. Finally, local suction induced vasoconstriction in an adjoining area not subjected to changes in vascular transmural pressure, an effect that could be blocked by local neural blockade at the site of suction. The results strongly suggest that a local sympathetic veno-arteriolar (axon) "reflex" is present in muscle and subcutaneous tissue in the dog hindleg.
Attenuation of arterial baroreflex control of heart rate by left ventricular receptor stimulation in the conscious dog.
Authors: Holmberg M J , Gorman A J , Cornish K G , Zucker I H
Published: June 2012

The purpose of this investigation was to determine whether left ventricular receptor stimulation attenuates the arterial baroreflex control of heart rate in the conscious dog and to determine the role of cardiac efferent sympathetic and parasympathetic pathways in any interaction observed. Mean arterial blood pressure-heart rate function curves, which characterized arterial baroreflex control of heart rate, were constructed before (control) and during an infusion of veratrine into the left circumflex coronary artery. Peak sensitivity, the maximum absolute slope along the mean arterial blood pressure-heart rate curve, and heart rate range (maximum minus minimum heart rate) were reduced during intracoronary infusion of veratrine. The mean arterial blood pressure-heart rate relationship also was shifted to a lower pressure during intracoronary infusion of veratrine. In order to study the role of cardiac efferents in this interaction, we constructed mean arterial blood-pressure-heart rate curves during cholinergic blockade, cholinergic blockade plus intracoronary infusion of veratrine, beta 1-adrenergic blockade, and beta 1-adrenergic blockade plus intracoronary infusion of veratrine. The addition of intracoronary infusion of veratrine during cholinergic blockade produced a shift of the mean arterial blood pressure-heart rate curve down the ordinate axis (heart rate) and to a lower pressure; however, peak sensitivity and heart rate range remained unchanged. The addition of intracoronary infusion of veratrine during beta 1-adrenergic blockade resulted in reductions in peak sensitivity and heart rate range. These data indicate that left ventricular receptor stimulation attenuates arterial baroreflex control of heart rate and that the reduction of sensitivity and heart rate range is mediated by parasympathetic motoneurons common to both reflex arcs. On the other hand, resetting to a lower operational set point may be mediated by cardiac sympathetic motoneurons common to both reflex arcs.
Potential fields on the ventricular surface of the exposed dog heart during normal excitation.
Authors: Arisi G , Macchi E , Baruffi S , Spaggiari S , Taccardi B
Published: June 2012

We studied the normal spread of excitation on the anterior and posterior ventricular surface of open-chest dogs by recording unipolar electrograms from an array of 1124 electrodes spaced 2 mm apart. The array had the shape of the ventricular surface of the heart. The electrograms were processed by a computer and displayed as epicardial equipotential maps at 1-msec intervals. Isochrone maps also were drawn. Several new features of epicardial potential fields were identified: (1) a high number of breakthrough points; (2) the topography, apparent widths, velocities of the wavefronts and the related potential drop; (3) the topography of positive potential peaks in relation to the wavefronts. Fifteen to 24 breakthrough points were located on the anterior, and 10 to 13 on the posterior ventricular surface. Some were in previously described locations and many others in new locations. Specifically, 3 to 5 breakthrough points appeared close to the atrioventricular groove on the anterior right ventricle and 2 to 4 on the posterior heart aspect; these basal breakthrough points appeared when a large portion of ventricular surface was still unexcited. Due to the presence of numerous breakthrough points on the anterior and posterior aspect of the heart which had not previously been described, the spread of excitation on the ventricular surface was "mosaic-like," with activation wavefronts spreading in all directions, rather than radially from the two breakthrough points, as traditionally described. The positive potential peaks which lay ahead of the expanding wavefronts moved along preferential directions which were probably related to the myocardial fiber direction.
Fetal blood volume responses to acute fetal hemorrhage.
Authors: Brace R A
Published: June 2012

The purpose of this study was to explore the changes in fetal blood volume that occur after fetal hemorrhage. Fifteen unanesthetized, chronically catheterized fetal sheep averaging 130 +/- 3 (SD) days gestation were studied 4 to 6 (average 5) days after catheter implantation. The fetuses were hemorrhaged by continuous withdrawal from an arterial catheter over 5 minutes. On the average (n = 15), 13.9 +/- 5.3% of the initial volume was removed. Fluid gradually entered the fetal circulation during and after the hemorrhage. Thirty minutes after hemorrhage had been initiated, 53.0 +/- 22.0% restitution of the lost volume occurred. Thus, short-term fetal blood volume restitution after fetal hemorrhage averaged about twice that of the adult. Hemorrhages averaging 7.3 +/- 2.3% (n = 3), 12.9 +/- 1.0% (n = 8), and 21.0 +/- 3.3% (n = 4) were followed by 55.7 +/- 13.3%, 54.7 +/- 26.4%, and 47.7 +/- 19.9% restitution, respectively. Thus, fractional volume replacement appears independent of the shed volume over the range of 5-25% volume loss. The protein concentration in the fluid which entered the fetal vasculature averaged 53% of the plasma protein concentration, suggesting that the fetal interstitium was the primary source of the fluid. In summary, the data suggest that the fetus is able to replace rapidly about half of the volume lost due to rapid hemorrhage, and appears considerably better at controlling its blood volume immediately after rapid hemorrhage than the adult.
Phenytoin reduces calcium current in the cardiac Purkinje fiber.
Authors: Scheuer T , Kass R S
Published: June 2012

We have investigated the effects of phenytoin on the electrical and mechanical activity of isolated calf and dog cardiac Purkinje fibers. Phenytoin (5-100 microM) lowers and shortens the plateau phase of the Purkinje fiber action potential and reduces twitch tension. We studied the ionic basis of these effects by combining a conventional two-microelectrode voltage clamp procedure with pharmacological techniques that allow separation of time-dependent plateau membrane currents. We find that phenytoin reduces voltage-dependent calcium current in the Purkinje fiber. In addition, this drug slightly reduces two time-dependent outward currents. These effects of phenytoin on membrane current account, at least in part, for its influence on the action potential and twitch tension.
Endocardial pacing site affects left ventricular end-diastolic volume and performance in the intact anesthetized dog.
Authors: Grover M , Glantz S A
Published: June 2012

We investigated how pacing from different endocardial sites affects the left ventricular three-dimensional contraction pattern and performance in intact anesthetized dogs. We used data from the motion of radiopaque markers implanted in the left ventricular endocardium in an analysis based on the polar decomposition theorem to determine the left ventricle's three-dimensional principal directions and magnitudes of deformation, and its axis and angle of rotation during the cardiac cycle. This paper also derives a new procedure that permits statistical comparison of different left ventricular cavity deformation patterns. During normal sinus rhythm and pacing from the right atrium, left ventricular septum, left ventricular apex, and right ventricular apex, the principal directions of left ventricular deformation remained relatively fixed with respect to the left ventricle's anatomy, independent of heart rate and pacing site. These directions were oriented in septum-free wall, anterior-posterior, and apex-base directions. End-systolic pressure and volume did not vary significantly among pacing sites. End-diastolic volume varied significantly among pacing sites, with right ventricular apical pacing producing the smallest end-diastolic and stroke volume. These results reveal that beats produced by right ventricular apical pacing eject less blood compared with beats produced by right atrial, left ventricular septal, or left ventricular apical pacing.
Actions of adenosine and isoproterenol on isolated mammalian ventricular myocytes.
Authors: Belardinelli L , Isenberg G
Published: June 2012

We investigated the effects of adenosine and isoproterenol on enzymatically dispersed ventricular myocytes from bovine and guinea pig hearts. Intracellular stimulation of relaxed myocytes with regular striation patterns and normal resting potential resulted in action potentials with full plateaus accompanied by contractions. Adenosine in concentrations up to 0.2 mM had no significant effect on any of the action potential parameters or on the basal contractility. In contrast, in the same cells, adenosine effectively antagonized the stimulatory effect of isoproterenol. Isoproterenol (1-10 nM) prolonged the action potentials by 34-41%, displaced the plateau to more positive potentials, and caused a 3-fold increase in the extent of myocyte sarcomere shortening. In the presence of adenosine (5-50 microM), isoproterenol increased the action potential duration by only 8-9%, the shift of the plateau was nearly abolished, and the increase in the extent of myocyte sarcomere shortening was less than 10%. In some of the myocytes, isoproterenol (1-10 nM) induced depolarizing afterpotentials accompanied by aftercontractions. The afterdepolarizations occasionally reached threshold resulting in triggered sustained rhythmic activity. Adenosine (20-50 microM) not only reduced the amplitude of the afterdepolarizations and aftercontractions, but also abolished the sustained rhythmic activity. We conclude, first, that isolated ventricular myocytes respond to isoproterenol and adenosine; second, that adenosine has no direct effect, but effectively antagonizes the stimulatory actions of isoproterenol; third, that findings are consistent with the ones reported for multicellular ventricular preparations; fourth, that adenosine concentrations required to attenuate the actions of isoproterenol are in the range of adenosine concentrations released by cardiac cells when oxygen availability is limited and/or demand is increased; and fifth, that endogenously released adenosine may modulate the electrophysiological and contractile effects of catecholamines.
Contractile function, myosin ATPase activity and isozymes in the hypertrophied pig left ventricle after a chronic progressive pressure overload.
Authors: Wisenbaugh T , Allen P , Cooper G , Holzgrefe H , Beller G , Carabello B
Published: June 2012

Experimental right ventricular pressure-overload hypertrophy in small mammals is associated with early muscle dysfunction, even before the onset of overt pump failure. Experimental results are quite heterogeneous regarding muscle function of the pressure hypertrophied left ventricle. Muscle dysfunction of the right or left ventricle, when found, may be causally related to alterations of myosin ATPase activity and isozyme type. However, the effect of a gradual pressure overload, analogous to that which occurs in human aortic stenosis, on myocardial contractile function and myosin ATPase activity has not been studied in a large animal whose normal myosin isozyme pattern resembles that of man. We therefore studied pump performance, myocardial contractile function, and myosin ATPase activity and isozyme pattern in pigs with severe, gradually applied left ventricular pressure overload. Thirteen weeks after supravalvular aortic banding, 10 pigs grew more than 7-fold in body weight and were found to have an aortic stenosis area of 0.5 +/- 0.1 cm2 with a gradient of 93 +/- 12 mm Hg. Compared with nine control animals, the banded animals had a 67% increase in left ventricular mass relative to body weight without overt pump failure as measured by cardiac index and pulmonary artery wedge pressure. Left ventricular ejection performance, measured as shortening fraction, was maintained except in three animals with extreme hypertrophy, in which depressed ejection performance may have been due to an afterload mismatch, myocardial dysfunction, or both. Myocardial contractile function, determined from the end-systolic stress-diameter relationship, was normal except in two pigs in which ejection performance was depressed and left ventricular mass was more than doubled. Only the slow V3 isozyme of myosin ATPase was found in both normal and hypertrophied pig myocardium, and the ATPase activity was normal in pigs with all degrees of hypertrophy. Thus, in a large animal model of severe, gradual left ventricular pressure overload, in which myosin isozyme pattern remains apparently unaltered, moderate hypertrophy can be associated with normal myosin ATPase activity and contractile function that is normal by current methods of evaluation.
Compartmentalization of adriamycin and daunomycin in cultured chick cardiac myocytes. Effects on synthesis of contractile and cytoplasmic proteins.
Authors: Lewis W , Galizi M , Puszkin S
Published: June 2012

The affinity of two anthracycline antineoplastics [( 14C]adriamycin and [14C]daunomycin) for cultured embryonic chick heart cells was determined by measuring their uptake, compartmentalization into subcellular fractions, and effects on the synthesis of cytoplasmic and cytoskeletal proteins. Both drugs, at micromolar concentrations, were readily uptaken by myocytes and found to be concentrated in a light-buoyant-density fraction containing no lysosomes. Nuclear 14C drug content accounted for 20-25% of the drug incorporated. Binding of adriamycin was saturable within 90 minutes of drug exposure, and the uptake of [14C]adriamycin was inhibited 50% by verapamil and adenosine triphosphate. Uptake of [14C]daunomycin was not influenced by these compounds. Cytosolic and contractile protein synthesis measured by [35S]methionine incorporation into proteins was blocked 70% overall in each fraction after 6 hours of incubation with 2 microM adriamycin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by autoradiography and quantitative densitometry, revealed that actin synthesis was the least affected of the major proteins. Cardiac myocytes incubated for short periods of time with 2 microM adriamycin revealed subtle cytoplasmic changes in their organelles with the appearance of clear zones of cytoplasm containing short unorganized microfilaments. The deleterious effects of anthracyclines in heart cells are manifested early by rapid drug incorporation into myocytes and inhibition of cytoplasmic protein synthesis.
Morphology of rapidly frozen aortic endothelial cells. Glutaraldehyde fixation increases the number of caveolae.
Authors: McGuire P G , Twietmeyer T A
Published: June 2012

Using a Polaron E7200 quick freeze unit, we investigated the distribution of vesicles (caveolae) bound to the plasma membrane of aortic endothelial cells from adult Sprague-Dawley rats. Counts of caveolae from replicas of rapidly frozen, unfixed samples were made and compared with counts from both aldehyde-fixed, conventionally frozen, and rapidly frozen aortic samples. Aldehyde-fixed samples prepared for freeze fracture by either of the freezing methods revealed a significantly greater number of caveolae than did unfixed, rapidly frozen samples. These findings suggest that the relative number of caveolae is artifactually increased by exposure to aldehyde fixatives. We conclude that previous estimates of the rates of pinocytotic activity in vascular endothelial cells may contain substantial errors based on overestimates of caveolae and underestimates of subplasmalemmal "free" vesicles.
The oxygen sensitivity of hamster cheek pouch arterioles. In vitro and in situ studies.
Authors: Jackson W F , Duling B R
Published: June 2012

We tested the hypothesis that a parenchymally derived mediator is required for arterioles to exhibit oxygen sensitivity. To that end, the parenchyma was dissected and removed from around hamster cheek pouch arterioles, and the oxygen sensitivity of these "aparenchymal arteriolar segments" was studied, either in vitro, after cannulation, or in situ. Arteriolar segments in situ with and without parenchyma had similar oxygen sensitivities (20% constriction as Po2 increased from 15 to 150 mm Hg). Arteriolar occlusion, which eliminated blood flow in the in situ aparenchymal segments, did not eliminate their oxygen sensitivity. The oxygen-induced constriction in the occluded aparenchymal segments was blunted but not eliminated by covering the segments with glass plates to prevent changes in Po2 from occurring around these vessels. We hypothesized that propagation of a portion of the oxygen response might explain the persistent response in the covered and occluded arteriolar segments. Oxygen sensitivity could be shown in only 32% of the in vitro cannulated arterioles (16% mean constriction as Po2 increased from 20 to 150 mm Hg). In contrast, 75% of aparenchymal arterioles were sensitive to changes in Po2 in situ. These data led us to reject the hypothesis that a parenchymally derived mediator is absolutely required for arterioles to exhibit oxygen sensitivity. We infer that the oxygen sensitivity of hamster cheek pouch arterioles results partially or totally from the local action of oxygen on some component of the arteriolar wall or blood, that a portion of the oxygen response may be the result of a propagated phenomenon, and that the oxygen-sensitive component is fragile and is easily lost in preparation for in vitro measurements or in cannulation. It is emphasized that the O2 sensor need not reside in vascular smooth muscle.
Relationship of binding of a calcium channel blocker to inhibition of contraction in intact cultured embryonic chick ventricular cells.
Authors: Marsh J D , Loh E , Lachance D , Barry W H , Smith T W
Published: June 2012

To study the mechanism of action of calcium channel-blocking drugs in intact, functioning myocardial tissue under physiological conditions, we related the inhibition of contraction of spontaneously beating monolayers of cultured chick embryo ventricular cells to studies of binding of four calcium channel-blocking drugs to the same preparation under the same physiological conditions. Nitrendipine produced a concentration-dependent decrease in amplitude of contraction (IC50 = 23 nM) as determined by a computer-assisted optical-video system. Studies using [3H]nitrendipine and equilibrium-binding techniques revealed a high affinity binding site in ventricular homogenates (KD = 0.15 nM) and on intact cultured heart cells (KD = 0.26 nM, Bmax = 51 fmol/mg of protein). These dissociation constants are similar to those reported by other workers for ventricular homogenates, but 100-fold lower than the IC50 for the negative inotropic effect in intact cells. Computer analysis of displacement of [3H]nitrendipine by unlabeled nitrendipine yielded a slope factor of 0.76 and identified an additional low affinity binding site for nitrendipine with KD = 19 nM, in good agreement with the IC50 for inhibition of contraction. Verapamil partially interacted with nitrendipine binding, whereas diltiazem showed no interaction. We conclude that, in intact myocardial cells, there are two classes of binding sites for nitrendipine; interaction of dihydropyridines with the low affinity site appears to mediate their effects on contractile function.
Isolation and characterization of single canine cardiac purkinje cells.
Authors: Sheets M F , January C T , Fozzard H A
Published: June 2012

Single cardiac Purkinje cells should permit improved control of membrane potential during voltage clamp studies. We have developed a method for isolation of single canine Purkinje cells and studied their basic electrophysiological properties using conventional single and double microelectrode techniques. The single Purkinje cells appeared free of connective tissue, had regular striations, excluded trypan blue vital stain, and remained quiescent in solutions containing 1.8 mM calcium. Electrophysiological studies at 22 degrees C showed normal resting membrane potentials, and action potentials could be elicited by extracellular or intracellular stimulation. Plot of the upstroke velocity of the action potential (Vmax) vs. the holding potential showed a sigmoid curve with the peak mean Vmax of 167 V/sec, and voltage corresponding to half-maximal Vmax was about -70 mV. Plot of the overshoot of the action potential vs. the holding potential was similar, with maximal values of about +30 mV. The mean membrane input resistance was 21 M omega and the mean membrane capacitance was 360 pF. These experiments demonstrate that single Purkinje cells have electrical properties similar to intact Purkinje fibers and that they should be useful for more detailed electrophysiological experiments.
Cardiac and pulmonary norepinephrine release and removal in the dog.
Authors: Blombery P A , Heinzow B G
Published: June 2012

Norepinephrine extraction and spillover rates were determined in the heart and lungs of anesthetized dogs under resting conditions, during sympathetic stimulation, and during epicardial pacing. The fractional extraction of norepinephrine across the coronary and pulmonary vascular beds was measured from the venoarterial difference in tritiated norepinephrine after infusion of a tracer dose to a steady state level. Cardiac extraction averaged 0.299 +/- 0.03 and pulmonary extraction averaged 0.215 +/- 0.014; extraction was unaffected by sympathetic stimulation or pacing. Norepinephrine spillover from sympathetic nerve terminals in the heart and lungs was measured from the venoarterial difference in endogenous norepinephrine and plasma flow after correction for the extraction component. Cardiac norepinephrine spillover increased linearly with increasing frequency of sympathetic stimulation to 7.44 times resting levels at 2 Hz. During pacing, there was no change in cardiac norepinephrine spillover despite marked changes in heart rate. Norepinephrine spillover was demonstrated under resting conditions in the lung and was greater than observed in the heart. Pulmonary norepinephrine spillover increased with sympathetic stimulation to 4.15 times resting levels at 2 Hz. It is possible to separate the contributions of norepinephrine extraction and spillover to measured venoarterial differences of norepinephrine under physiological conditions in the dog.
Modulation of cellular calcium stores in the perfused rat heart by isoproterenol and ryanodine.
Authors: Hunter D R , Haworth R A , Berkoff H A
Published: June 2012

The inhibitory action of procaine on cellular calcium release was utilized to define a new cellular calcium pool which, under physiological conditions, is present only during catecholamine stimulation. Rat hearts labeled with 45Ca++ were perfused with medium containing procaine and EGTA at 23 degrees C to remove extracellular calcium, and then cellular calcium was released by removal of procaine and restoration of calcium. By this method we have identified a cellular calcium pool (pool C) whose release is inhibited by procaine, but which does not require extracellular calcium for its release. Release of pool C can also be triggered by caffeine. [We have previously identified a cellular calcium pool (pool A) whose release is triggered by caffeine, inhibited by procaine, and which does require extracellular calcium for its release.] When hearts were labeled for 3 minutes with perfusate containing 1 mM 45Ca++, 48 +/- 6 nmol Ca++/g wet weight was found in pool A, but only 3 +/- 1 nmol Ca++/g in pool C. However, if isoproterenol was present during labeling, the hearts contained 72 +/- 5 nmol Ca++/g in pool A and 42 +/- 6 nmol Ca++/g in pool C. When calcium concentration in the labeling perfusate was varied, with and without isoproterenol, it was found that pool C does not begin to fill until pool A is almost full. The same effect was seen when excess cellular calcium uptake was induced by removing sodium from the perfusate. Ryanodine (0.2 microM) induced contractile failure (t1/2 = 3.4 +/- 0.4 min) and depleted pool A in control hearts by 85%. Ryanodine also similarly depleted pools A and C in isoproterenol-treated hearts. When contractility was monitored at the same time as the hearts were labeled, a linear relationship between dP/dt and the sum of pools A and C was observed over a wide range of conditions. Pools A and C both selected strongly for calcium over barium. These observations suggest that both pools A and C are located in the sarcoplasmic reticulum and are intimately involved in the regulation of contractility.
The contractile state as the major determinant in the evolution of left ventricular dysfunction in the spontaneously hypertensive rat.
Authors: Mirsky I , Pfeffer J M , Pfeffer M A , Braunwald E
Published: June 2012

Female spontaneously hypertensive and normotensive rats were studied at 6, 12, 18, and 24 months of age to determine which characteristics of myocardial performance herald the onset of left ventricular dysfunction. Peak ejection fraction index was derived from measurements of peak stroke volume (in vivo volume loading) and passive pressure-volume relations. The myocardial stiffness constant (km, slope of the incremental modulus-stress relation, EINC = km sigma), chamber stiffness constant (kc, slope of the chamber stiffness-pressure relation, dP/dV = kcP), and left ventricular cavitary volume-to-wall volume ratio at 10 mm Hg) were calculated from the pressure-volume data and the contractile state was assessed from the ejection fraction index-afterload relations. In the normotensive rats, the myocardial stiffness constant was not affected by age, whereas, in the spontaneously hypertensive rats, the myocardial stiffness constant remained within normal limits until 18 months, at which time a significant increase in this index of myocardial stiffness occurred. Baseline and maximal cardiac indices and ejection fraction index of spontaneously hypertensive rats were normal from 6 to 18 months, but were markedly reduced at 24 months. This reduction in cardiac performance was associated with a decrease in the left ventricular chamber stiffness constant, i.e., kc. This decreased chamber stiffness, which occurred at a time when myocardial stiffness was increased, was due to a greater increase in cavity size than in myocardial stiffness. The left ventricular cavity-to-wall volume ratio of normotensive rats was not affected by age, whereas, in the spontaneously hypertensive rats, this ratio markedly declined by 18 months. The ejection fraction index-afterload relations i.e., a measure of the contractile state, of the 6- and 12-month-old spontaneously hypertensive rats were similar to those of the normotensive rats of all ages. However, a depression in the contractile state of the spontaneously hypertensive rats occurred at 18 months and was further depressed at 24 months. This abnormality of the contractile state was evident before the deterioration of cardiac performance, as reflected in a decrease in baseline and maximal cardiac indices, and dilation of the left ventricle occurred. The contractile state (ejection fraction index-afterload relation) is thus the most sensitive indicator of left ventricular dysfunction in spontaneously hypertensive rats.
Reactive dilation of large coronary arteries in conscious dogs.
Authors: Hintze T H , Vatner S F
Published: June 2012

To study the response of large coronary arteries to short periods of myocardial ischemia a pair of ultrasonic dimension transducers, a flow probe and a hydraulic occluder were implanted around the left circumflex coronary artery for the instantaneous and continuous measurement of external coronary artery dimensions and coronary blood flow, respectively. At 6.1 +/- 0.4 seconds after release of a 15-second occlusion, mean coronary blood flow increased by 255 +/- 30% from a preocclusion flow of 32 +/- 4.1 ml/min. At this time, large coronary arterial cross-sectional area was unchanged but increased slowly, reaching a peak 28 +/- 4.4% above preocclusion levels 61 +/- 3.2 seconds after occlusion, i.e., reactive dilation. During maximal reactive dilation, coronary blood flow had already returned to control levels, and heart rate, mean arterial pressure, left ventricular systolic pressure, and left ventricular dP/dt were not different from control. The reactive dilation was not affected if the occlusion occurred proximal or distal to where diameter was measured, or by combined alpha- and beta-adrenergic receptor blockade, ganglionic blockade, inhibition of prostaglandin synthesis, or by aminophylline. When the reactive hyperemia was prevented by constricting the coronary artery upon release of the coronary occlusion, the reactive dilation was not observed. Thus, large coronary arteries respond to brief periods of occlusion with reactive dilation. The time course of this response is distinctly different from the accompanying reactive hyperemia, and could be eliminated by preventing the marked increase in coronary blood flow following release from the brief period of coronary artery occlusion.
Reversal of changes in myocardial beta-receptors and inotropic responsiveness with regression of cardiac hypertrophy in renal hypertensive rats (RHR).
Authors: Ayobe M H , Tarazi R C
Published: June 2012

Our previous studies, in vivo and in vitro, have shown reduced inotropic responsiveness to isoproterenol of hypertrophied hearts in renovascular hypertensive rats. In the present study, we have investigated, in the same model, the effects of treatment either by nephrectomy or captopril on the inotropic responsiveness to isoproterenol and on the number and affinity of ventricular beta-receptors. Isoproterenol infusion of isolated hearts from renovascular hypertensive rats 12-18 weeks post-clipping produced lower inotropic responses (delta peak dP/dt) than age-matched sham-operated normotensive rats (P less than 0.001). Quantitative assessment of beta-adrenergic receptors in the same hearts showed a significant decrease in renovascular hypertensive rats ventricular receptor numbers, whether calculated per milligram membrane protein (22.3 +/- 2.66 fmol/mg vs. 37.9 +/- 4.34, P less than 0.005) or per gram wet ventricular weight (1.43 +/- 0.14 pmol/g vs. 2.2 +/- 0.21, P less than 0.005), with no significant change in Kd. Control of hypertension by either nephrectomy or captopril led to regression of hypertrophy 6 weeks after stabilization of blood pressure (12-18 weeks post-clipping) and returned both the ventricular receptor density and inotropic responsiveness toward normal. The improvement in inotropic responsiveness to isoproterenol in regressed hearts correlated with both the reduction in ventricular weight and the decrease of blood pressure. Regression of hypertrophy did not alter the relationship between inotropic response, receptor density, and ventricular weight. These results indicate that the increase in cardiac mass associated with renovascular hypertension may interfere with adrenergic support to the heart, and that proper control of hypertension and regression of hypertrophy could reverse that impairment and restore its responsiveness to adrenergic stimulation.
Early outward current in rat single ventricular cells.
Authors: Josephson I R , Sanchez-Chapula J , Brown A M
Published: June 2012

Voltage clamp experiments were conducted using single ventricular myocytes which had been dissociated enzymatically from adult rat hearts in order to examine further the membrane currents which contribute to the unusual plateau of the rat action potential. Membrane currents were recorded, using a single microelectrode (switching) voltage clamp circuit. From holding potentials near the resting potential (-80 to -90 mV), depolarizing clamp steps above -20 mV elicited an early outward current which overlapped in time with the slow inward current and displayed time-dependent inactivation. This is the first demonstration of a transient potassium current in an isolated ventricular myocyte. The early outward potential was voltage-inactivated at holding potentials of -50 to -40 mV and was blocked by 4-aminopyridine. The current was not dependent on Cao or ICa and was blocked by Bao. Double pulse experiments revealed that the time course for the recovery of the early outward current at -80 mV was rapid, and had a tau of 25 msec. The possible functional significance of this current is discussed.