bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Basic Nuclear Proteins on Cardiac Muscle Function
Authors: SCHWARTZ ARNOLD , LASETER ARLINE H. , FERGUSON GARY G.
Published: June 2012

A method for the preparation of semipurified basic proteins from cardiac muscle was presented. At low ionic strengths (below 0.05) and in the presence of Mg
++
, these compounds, as well as purified histones from a variety of tissues, inhibited the Mg
++
-
ATP
ase activity of cardiac and skeletal muscle actomyosin or myofibrillar suspensions. Under similar conditions, a retardation of superprecipitation occurred. At high ionic strengths (above 0.06) the histones stimulated the Mg
++
-
ATP
ase.

In the presence of Ca
++
, and at all ionic strengths studied, the histones elicited a marked stimulation of actomyosin
ATP
ase.

Administration of histones to anesthetized, open-chest guinea pigs, caused a significant depression of the force of contraction of the hearts. These data suggest a possible involvement of basic nuclear proteins in cardiac activity.
Effects of Respiratory Center Activity on the Heart
Authors: Levy Matthew N. , DeGeest Hilaire , Zieske Harrison , Levy Donald
Published: June 2012

Rhythmic fluctuations in heart rate and ventricular contractility at the frequency of the respiratory movements were observed in innervated, isovolumetric, canine, left ventricle preparations. The heart rate and contractility waves probably represent the radiation of activity from the respiratory centers to the cardiac autonomic centers within the central nervous system. In spontaneously beating hearts, the respiratory cardiac arrhythmia is mediated via the vagi predominantly, although a slight arrhythmia is still evident after bilateral vagotomy. The greater the vagal tone, the greater is the amplitude of the arrhythmia.

In paced hearts, the contractility waves exhibit significantly greater phase lags than do the heart rate waves in unpaced beats. The magnitude of the contractility waves varies inversely with the respiratory frequency. These waves are more prominent after bilateral vagotomy. Therefore, sympathetic influences appear to predominate in the mediation of the contractility waves, although the change in wave amplitude after vagotomy must be ascribed partly to the deceleration of respiratory frequency which occurs after vagotomy. The contractility waves represent rhythmic augmentations of contractility above a base line level after vagal section.
Uptake and Release of Cholesterol by Rabbit Atheromatous Lesions
Authors: Newman H. A. I. , Zilversmit D. B.
Published: June 2012

Rabbits were fed 1 g of cholesterol per day for 92 days. At the end of this period all animals were transferred to Purina rabbit chow for 63 days at which time half of the animals were fed cholesterol again and half were continued on Purina chow. After either two or three weeks, flux of cholesterol into aorta was measured with C
14
-cholesterol. The flux of cholesterol into the aortas with similar degrees of atheromatosis varied directly with the plasma cholesterol concentrations.

Rabbits were injected with serum containing C
14
-cholesterol in the free form only. Esterification of C
14
-cholesterol entering the aorta was minimal. Apparently esterified aortic cholesterol is derived by direct transfer from plasma.

Influx and release of cholesterol were investigated in vitro under different conditions of incubation. Boiling of the aorta or the addition of cyanide and fluoride did not stop influx of cholesterol. The release of cholesterol from boiled aortic halves was, for free cholesterol 25% of the amount of the C
14
in control halves and, for esterified cholesterol, 3% of the control.
Separation of Responses of Arteries and Veins to Sympathetic Stimulation
Authors: Zimmerman Ben G.
Published: June 2012

Lumbar sympathetic nerve stimulation produced an increase in arterial, small vessel and venous segmental resistances in the perfused hind paw of the dog. Repeating the stimulation, after having sectioned the somatic nerve bundles accompanying the main arterial supply of the paw, brought about an increase only in venous resistance which was equal to or greater than that obtained in the control period. This venous constrictor response was reduced greatly by the intravenous administration of adrenergic neuronal blocking drugs, by local infiltration of procaine around the paw, or by transection of the subcutaneous tissue around the paw and the nerves accompanying the veins. These results indicated that sympathetic postganglionic fibers supplying the arteries and small vessels were derived from nerve bundles accompanying the arteries (tibial and deep fibular nerves). The fibers supplying the veins are distributed more diffusely in that they are found in somatic nerve bundles accompanying the veins themselves, in the tibial nerve, and in the subcutaneous tissue of the paw.
Paradoxical Effects of Epinephrine on Excitation-Contraction Coupling in Cardiac Muscle
Authors: Kavaler Frederic , Morad Martin
Published: June 2012

The possibility that the inotropic action of epinephrine might be mediated through an effect on the excitation-contraction coupling process was explored, using techniques for measurement of isometric tension, together, in some experiments, with recording of the transmembrane potential time course from short lengths of cat papillary muscle. Four observations relevant to this question, have been made: (1) Extracellular calcium concentration can be raised and extracellular sodium concentration lowered to a point at which contraction cannot be further augmented by the addition of epinephrine. (2) The early relaxation induced by epinephrine occurs well in advance of membrane repolarization. This effect is antagonized by increasing calcium concentration, although the action of epinephrine in augmenting developed tension appears to be synergistic with that of calciumion. (3) The length-tension relationship is undiminished in the calcium-rich (8.1 mmoles /liter), sodium-poor (75 mEq/liter) medium. (4) Epinephrine, in a dose (1 to 2 µg/ml) which markedly augments twitch tension, profoundly decreases tension developed by the same preparation during a potassium chloride contracture; this is the case for both the frog ventricle strip and the cat papillary muscle. A preliminary concept of the ionic mechanism of excitation-contraction coupling, compatible with these facts and with some others, is described.
Cardiovascular Effects of Sustained Norepinephrine Infusions. II. Morphology
Authors: Schenk Eric A. , Moss Arthur J.
Published: June 2012

The major toxic effect of norepinephrine (NE) infusion in dogs, cats, and rabbits in doses relatively comparable to those used clinically has been shown to be on the heart. Noncardiac lesions were those of congestion, and were seen in animals receiving the higher doses. The dogs in these dose groups showed evidence of progressive deterioration of cardiac function. All dogs which developed cardiac lesions also developed an acute adrenalitis.

The cardiac lesions in all animals consisted of focal degeneration and necrosis of myofibers, and subendocardial hemorrhage. These lesions healed within two weeks by fibrosis.
Spectrum of Congenital Cardiac Anomalies Produced in Chick Embryos by Mechanical Interference with Cardiogenesis
Authors: Gessner Ira H.
Published: June 2012

Stage 19 to 20 white leghorn chick embryos were subjected to an operative manipulation in which a wire device was passed under the outflow tract of the cardiac tube, and allowed to remain in place from 24 to 60 hours. The embryos were then permitted to develop until hatching. Twenty-eight embryos, including eight sham operated controls, all of whom were normal, survived to at least the 18th embryonic day, and are included in this report. A spectrum of cardiac anomalies was produced as follows: group 1, widening of the left ventricular outflow tract unassociated with other defects; group 2, widening of the left ventricular outflow tract with a subaortic ventricular septal defect, 0.8 mm or less in its greatest dimension; group 3, a large ventricular septal defect, 1.5 mm or more in its greatest dimension, with varying degrees of abnormal position of the aorta, including "overriding" of the aorta, but with maintenance of continuity between the aortic and mitral valve annuli; group 4, the double outlet syndrome, in which both great vessels arise from the anatomic right ventricle with complete muscular separation between the aortic and mitral valves. In the time period studied, the double outlet syndrome represents the extreme of the continuum. However, it is possible that other forms of this spectrum exist, some perhaps incompatible with embryonic life, and that these may be produced by changing the experimental technique.
Coronary Vascular Development in Response to Increased Right Ventricular Pressure Loads
Authors: Overy H. R. , Vogel John H. K. , Grover Robert F. , Blount S. Gilbert
Published: June 2012

Pressure loads were applied to the right ventricles of newborn lambs and adult sheep by surgical narrowing of the lumen of the main pulmonary artery. Significant increases in right ventricular weight and in the diameter of the right coronary artery occurred in both age groups of animals, compared with corresponding control animals. The evidence suggests that the degree of increase in the arterial diameters, relative to the increase in ventricular muscle mass, is similar in both newborn and adult animals. However, the results suggest also that the capacity to respond to pressure loads, in terms of increased muscle mass, is relatively greater in the newborn animals than in the adults.
Distribution of Blood Flow within the Skin of the Rabbit with Particular Reference to Hair Growth
Authors: Thorburn Geoffrey D. , Casey Brian H. , Molyneux Geoffrey S.
Published: June 2012

Previous work using a Kr
85
clearance technique demonstrated the existence in rabbit thigh skin of a bimodal distribution of blood flow which was consistent with the presence of two distinct vascular compartments with markedly different flow rates. These observations on the rabbit thigh have been extended to compare flow patterns during the inactive phase of the hair growth cycle and during active hair growth.

Resting areas and hair-growing areas of rabbit skin have been examined histologically and the vascular pattern has been demonstrated after perfusion of the vessels with India ink. The results provide an anatomical basis for the two-compartment model derived from analysis of the clearance curves.

The mean rate of blood flow for the fast compartment during the inactive phase was 29.7 ml/100 g tissue/min and 4.3 ml/100 g tissue/min for the slow compartment; these did not change significantly with active hair growth. However the relative size of the fast compartment altered markedly with active hair growth, the relative size of the fast compartment increasing from 21 to 67% of the tissue mass. The mean cutaneous blood flow was more than doubled during the active phase.

Histological studies demonstrated a marked increase in the size of the follicles during the active phase and a concomitant increase in the extent of the vascular bed around the follicles. This would indicate that the fast compartment represents the follicular tissue and its associated blood supply; its flow rate was a measure of nutrient blood flow to the hair follicle. The flow rate of the slow compartment was then a measure of nutrient blood flow in the rest of the skin. These conclusions were supported by observations in areas of skin with sparse hair growth. The effect of body heating and cooling on cutaneous blood flow distribution was also noted.
Correlation of Visco-elastic Properties of Large Arteries with Microscopic Structure
Authors: APTER JULIA T. , RABINOWITZ MURRAY , CUMMINGS DOROTHY H.
Published: June 2012

The media of 14 regions of the aorta and 3 regions of the pulmonary artery of dogs were subjected to a step-function circumferential stretch taking 20 msec to complete. The tension rose synchronously with the increase in circumference, then dropped exponentially to a reasonably steady state within 2 sec. A mathematical model, developed consistent with this stress-relaxation curve, showed how to use the tension curves to measure a viscous, a serieselastic, and a parallel-elastic constant unique for a given curve. These constants were compared with the microscopic structure of the same or similar segments; collagen was determined as hydroxyproline in a water soluble fraction, elastin as hydroxyproline in the residue and from the width and number of elastic lamellae, and muscle from the nitrogen content of a nonfibrous fraction, from cell counts and from contractility. The constituents varied widely and independently enough to permit correlating viscous and elastic constants with microscopic structure. The viscous and series-elastic constants were higher where muscle content was high, and increased markedly when the muscle was tonically contracted. The parallel-elastic constant was high when elastin was high and in the presence of contracted muscle, but seemed independent of collagen content, at the moderate tensions tested.
Circulatory Responses to Electrical and Reflex Activation of the Nervous System after Cardiac Denervation
Authors: PEISS CLARENCE N. , COOPER THEODORE , WILLMAN V. L. , RANDALL WALTER C.
Published: June 2012

Rigorous testing procedures assessed the extent of extrinsic cardiac denervation in three groups of animals subjected to cardiac extirpation and reimplantation (E&R), mediastinal neural ablation (MNA) or thoracic ganglionectomy (BSTG). After E&R, all dogs were completely denervated. Evidence for vagal reinnervation appeared as early as 26 days and for both vagal and sympathetic reinnervation in 74 days. After one, two and three years, the functional responses to reflex and electrical activation of the nervous system were similar to those in normal dogs. After MNA, only one animal of eight was totally denervated. Seven showed varying degrees of cardiac activation in response to diencephalic stimulation or stimulation of the cardiac sympathetic nerves. Thus MNA, though surgically feasible, cannot be assumed to be successful without rigorous testing. After BSTG, four of eight dogs showed complete separation of sympathetic cardiac outflow from the CNS; in all eight, moderate to large cardio-accelerator responses were elicited from the distal vagosympathetic trunk after atropinization. There is little correlation between the over-all cardiac responses persisting in all operated animals and total cardiac catecholamine content, or between cardio-accelerator responses and right atrial catecholamine content.
Loss of Baroreflex Bradycardia in Renal Hypertensive Rabbits
Authors: ALEXANDER NATALIE , DECUIR MARJORIE
Published: June 2012

The degree of reflex bradycardia elicited by a sudden, brief rise in arterial pressure was used as an index of sino-aortic reflex activity in conscious rabbits with early renal hypertension. Change in heart rate was measured every 6 seconds after injected angiotensin which caused a rise in blood pressure of 15 to 60 mm Hg. Ninety-one tests for reflex bradycardia were made in 30 normal rabbits; 14 of them were tested intermittently during the 1 to 40 day period following unilateral nephrectomy and latex encapsulation of the opposite kidney. A total of 62 tests were made after arterial pressure had risen 10 to 80 mm Hg, average 35, above control values. Average decrease in heart rate was significantly less and frequency of negligible reflex bradycardia was much higher in hypertensives than controls. Individual rabbits showed no tendency for reflex bradycardia to return toward normal magnitude. However, the vasomotor component of the sino-aortic reflex mechanism in renal hypertensive rabbits buffered the pressor response to angiotensin in a normal manner. Resetting of sino-aortic reflex activity under hypertensive conditions is discussed.
Effect of Changing Heart Rate on Cardiovascular Function in the Conscious Dog
Authors: NOBLE MARK I. M. , TRENCHORD DIANA , GUZ ABRAHAM
Published: June 2012

The effect of heart rate on the cardiovascular system of the conscious dog was studied by pacing the heart with an implanted right atrial electrode. Left ventricular outflow was measured by an electromagnetic flowmeter with a chronically implanted transducer on the ascending aorta. As heart rate increased, stroke volume fell, and this was linearly related to heart rate over the entire range studied. Peak flow rate and maximum acceleration decreased as heart rate increased, but the change was small compared with that in stroke volume. The decrease in stroke volume resulted principally from a loss of volume ejected in late systole. An increase in heart rate sometimes resulted in a rise of cardiac output, and when this occurred mean arterial pressure rose; when cardiac output did not increase, mean arterial pressure also remained unchanged. The data suggest that there is a pressure for the systemic circulation analogous to the "critical closing pressure" of peripheral vascular beds. It was shown that in these circumstances changes in calculated systemic resistance may not reflect any real alterations in the peripheral vascular beds.
Spontaneous Aortic Lesions in Rabbits I. Morphologic Characteristics
Authors: SCHENK ERIC A. , GAMAN ELIZABETH , FEIGENBAUM A. S.
Published: June 2012

A number of morphologically distinct, spontaneously occurring lesions are present in the rabbit aorta. Intimal atheromata occur in newborn rabbits, decrease in incidence as the rabbit becomes weaned, and are a rarity in the adult. Intimal mesenchymal thickening is first seen in weanling rabbits and is almost universally present in the adult. Medial sclerotic changes involving exclusively the inner one-half of the media and termed "type A" lesions are present in weanling and adult, but not in newborn rabbits.

Type A lesions have a variable gross appearance, but a fairly uniform microscopic appearance, which shows principally fragmentation and calcification of elastic lamina and accumulation of acid mucopolysaccharides.

"Type B" lesions, medial sclerosis involving exclusively the outer half of the media, usually occur throughout the entire aorta, and only in adult rabbits.
Repolarization Phase at Various Sites of the Right Atrium
Authors: IRISAWA HIROSHI , NINOMIYA ISHIO , SEYAMA ISSEI
Published: June 2012

By means of a suction electrode method, the time course of depolarization and repolarization was observed in the in situ exposed right atrium of dogs. Under normal conditions the end of repolarization at various sites on the atrium occurred after the QRS spikes, and therefore, the T
a
wave should be inscribed after and not during the QRS spikes. The concentric spread of activation originating from the S-A node has been confirmed. The region of inital excitation does not become the initial focus of repolarization. The initial focus of repolarization is different from animal to animal, and this focus cannot be associated with any special cardiac tissue. The process of repolarization occurs concentrically from an initial focus that is not limited to any specific region of the atrium.
Myocardial High Energy Phosphate Stores in Acutely Induced Hypoxic Heart Failure
Authors: POOL PETER E. , COVELL JAMES W. , CHIDSEY CHARLES A. , BRAUNWALD EUGENE
Published: June 2012

In order to determine the relation between depression of myocardial function and the myocardial high energy phosphate stores during acute hypoxia, a technique for serial evaluation of these stores was developed. Acute hypoxia was induced in 18 anesthetized dogs and serial determinations of adenosine triphosphate (ATP) and creatine phosphate (CP) were made while myocardial function was continuously measured. Myocardial concentrations of ATP were maintained even in the presence of severe hypoxia and myocardial failure. There was a small depression of the average myocardial CP concentration during early heart failure. However, in more than one-third of the dogs there was no significant depression of CP concentration at this time. It is concluded that hypoxic depression of myocardial function is not initiated by a decrease in the total myocardial high energy phosphate stores. The possibility could not be excluded that a particular fraction of the high energy phosphate store is decreased when myocardial failure is induced by hypoxia.
Cardiac Myosin Adenosinetriphosphatase Activity
Authors: LUCHI ROBERT J. , KRITCHER EVE Marie
Published: June 2012

Cardiac myosin prepared by any one of a number of modifications of the basic Szent-Gyorgyi method and cardiac myosin prepared by the lithium chloride-ammonium sulfate technique differ in two important respects: 1) Szent-Gyorgyi-prepared myosin solutions are inhomogeneous by both chemical and immunologic criteria; 2) the ATPase activity of Szent-Gyorgyi-prepared myosin is low in comparison to lithium chloride-ammonium sulfate prepared cardiac myosin. Evidence is presented in this paper showing that the reduced ATPase activity of Szent-Gyorgyi-prepared cardiac myosin is the result of inhibition of the enzyme, possibly by a nucleotide contaminant, and a "diluting" effect of other nitrogen-containing contaminants of low specific activity.

Many earlier studies indicate that cardiac and skeletal muscle myosin prepared by the Szent-Gyorgyi method differed strikingly in their ATPase activities. Comparison of lithium chloride-ammonium sulfate prepared cardiac and skeletal muscle myosin shows that skeletal muscle myosin has a slightly but significantly higher ATPase activity than canine cardiac myosin. A methodologic error was not excluded as the cause of this discrepancy. In a number of other characteristics, canine cardiac and skeletal muscle myosin ATPase activity was virtually identical.
Measurement of Left Ventricular Volume by Biplane Angiocardiography and Indicator-Washout Techniques: A Comparison in the Canine Heart
Authors: BARTLE STUART H. , SANMARCO MIGUEL E.
Published: June 2012

Left ventricular volumes were determined sequentially in 31 dogs and simultaneously in 12 by biplane angiocardiography and a dye-dilution, thermal washout technique.

The mean ejected fraction (SV/EDV; systolic volume/end diastolic volume) was significantly higher when measured by angiocardiography (.53 ± .03) than by the washout method (.27 ± .02). The end diastolic volume measured by angiocardiography was lower, 21.1 ± 1.5 ml/10 kg versus 34.4 ± 3.6, as was the end systolic volume, 11.3 ± 1.3 ml/10 kg versus 25.5 ± 3.2. Mean stroke volume by angiocardiography was 10.9 ml/10 kg, or 1.8 ml greater than by dye dilution (the average amount of contrast material injected per beat was 1.9 ml/10 kg).

No difference was found between the washout fractions calculated from early and from late beats. There was a significant inverse correlation between the observed heart rate and washout SV/EDV. There was no correlation between heart rates and the discrepancy in measuring the various volumes.

Technical difficulties and theoretical considerations are discussed and it is concluded that in dogs the angiographic method gives more accurate calculations of end diastolic and end systolic volumes than the washout technique. The latter method appears to underestimate SV/EDV systematically, probably because of incomplete mixing of indicator in the ventricle. This leads to falsely high values for EDV and ESV.
Demonstration of a Dual A-V Nodal Conduction System in the Isolated Rabbit Heart
Authors: MENDEZ CARLOS , MOE GORDON K.
Published: June 2012

The intranodal propagation of atrial and ventricular echoes in in-vitro preparations of the rabbit heart was traced from microelectrode records at many puncture sites. Composite records indicate that the upper part of the node can be functionally and spatially dissociated into two pathways (α and β), which communicate with a final common pathway (FCP) about halfway between the atrium and the His bundle.

Atrial echoes, induced by premature atrial stimulation, traverse the α pathway and return to the atrium from the middle part of the node over the β route; echoes can occur without propagation of the premature response to the ventricle.

Ventricular echoes, induced by premature stimulation of the His bundle, pass from the FCP to the atrium over the α route, and back to the FCP over the β route.

Repetitive reciprocation, in the nature of an intranodal circus movement, was commonly observed.

The results completely substantiate previous conclusions based on indirect observations in the dog heart.
Control of Heart Rate by the Autonomic Nervous System
Authors: ROBINSON BRIAN F. , EPSTEIN STEPHEN E. , BEISER G. David , BRAUNWALD EUGENE
Published: June 2012

The control of heart rate by the autonomic nervous system was investigated in conscious human subjects by observing the effects of β-adrenergic blockade with propranolol, of parasympathetic blockade with atropine, and of combined sympathetic and parasympathetic blockade. The increase in heart rate with mild exercise in supine men was mediated predominantly by a decrease in parasympathetic activity; at higher levels of work, however, sympathetic stimulation also contributed to cardiac acceleration. When the response to 80° head-up tilt was compared with the response to exercise in the same subject supine, it appeared that the attainment of an equivalent heart rate was associated with a significantly greater degree of sympathetic activity during tilting than during exercise. Although heart rate was always higher at any given pressure during exercise than it had been at rest, the changes in heart rate that followed alterations in arterial pressure were found to be of similar magnitudes at rest and during exercise; it was therefore concluded that the sensitivity of the baroreceptor system was not altered during exercise. Investigation of the efferent pathways concerned in mediating the baroreceptor-induced changes in heart rate suggested that the relative roles of the sympathetic and parasympathetic systems were nearly equal in the resting state. During exercise, on the other hand, changes in sympathetic activity appeared to be the predominant mechanism by which speeding and slowing of the heart was achieved. It thus appears that baroreceptor-induced alterations in heart rate may be mediated by increased or decreased activity of either efferent system; the ultimate balance, however, is critically dependent on the preexisting level of background autonomic activity.
Effect of Adrenergic Antagonists on the Peripheral Constrictor Action of Kinekard, A Cardioactive Plasma Fraction
Authors: NAYLER WINIFRED G. , ROSENBAUM MAURICE , MCLNNES IAN E. , RACE DAVID , LOWE THOMAS E.
Published: June 2012

The possibility that endogenous epinephrine, norepinephrine or angioten-sin is involved in the response of the peripheral circulation to kinekard, a plasma pressor fraction of relatively low molecular weight, was investigated in anesthetized dogs on heart-lung bypass and isolated perfused gracilis muscle preparations. The prior administration of bretylium tosylate, guanethidine or the β-adrenergic antagonist, propranolol, failed to modify the pressor action of kinekard. This pressor action was blocked by the prior addition of the α-adrenergic antagonist, phenoxybenzamine. These results have been interpreted to mean that kinekard acts on the α-receptor sites in the peripheral circulation to cause constriction and that this response does not involve or depend on the release of stored catecholamines.
Transthoracic Ventricular Defibrillation with Triangular and Trapezoidal Waveforms
Authors: SCHUDER JOHN C. , RAHMOELLER GLENN A. , STOECKLE HARRY
Published: June 2012

From 7, 200 fibrillation-defibrillation episodes in anesthetized dogs, the effectiveness of 6 classes of unidirectional shocks in reversing ventricular fibrillation of 30-sec duration was determined. The shocks lasted for 1 to 256 msec. Three waveforms (ascending ramp triangular, descending ramp triangular, and trapezoidal) were studied at peak currents of 10 amp and 20 amp. Families of curves of per cent success vs. energy were derived from the data for the 6 classes of waveforms studied and from corresponding curves for 3 classes of unidirectional square-wave shocks previously studied by our group. The families of curves were used as a basis for an analysis of the influence of various parameters on the effectiveness of shocks. We conclude that an appropriate energy content is a necessary, but not sufficient condition for effective ventricular defibrillation, that long, low-amplitude tails on shocks are detrimental and that excessive energy content is detrimental.
In Vitro Studies of Phospholipid Synthesis in Experimental Atherosclerosis
Authors: PARKER FRANK , ORMSBY JOHN W. , PETERSON NORMAN F. , ODLAND GEORGE F. , WILLIAMS ROBERT H.
Published: June 2012

Using in vitro techniques and labeled linoleic acid and glucose, alterations in phospholipid synthesis in the aorta were correlated with electron microscopic studies at various intervals of time after feeding rabbits cholesterol. After 4 to 8 weeks of feeding, more phospholipid precursors were incorporated into the phospholipids of atherosclerotic blood vessels than of normal vessels. Concomitant with the metabolic alterations, the following ultrastructural changes occur. Smooth muscle cells of the plaque (myo-intimal cells) evolve into highly vacuolated cells containing a profusion of cytoplasmic organelles. The increase in membranous organelles suggests that the increase in phospholipid synthesis may be the result of a cellular requirement for increased intracytoplasmic structural phospholipid.
Ventricular Response in Atrial Fibrillation
Authors: HOOPEN M. TEN
Published: June 2012

The data on durations of the intervals between successive R-R waves in the ECG from patients during atrial fibrillation, reported by Horan and Kistler (Circulation Research 9: 305, 1961) show that the larger the mean and modal value in a record the larger were the shortest and longest durations. The finding that the latter extreme was usually a few times larger than the former has been used in an attempt to organize the data with the help of a probabilistic model. It is assumed that a sequence of intervals is generated, the durations of which are symmetrically distributed, but in fibrillation the process is distorted from time to time and larger intervals occasionally occur. The effects of atrial impulses on conduction through the A-V node are discussed. A mathematical expression describing this phenomenon is derived.
Effect of Catecholamines and Adrenergic Blocking Agents on Oxidative Phosphorylation in Rat Heart Mitochondria
Authors: SOBEL BURTON , JEQUIER ERIC , SJOERDSMA ALBERT , LOVENBERG WALTER
Published: June 2012

Polarographic methods were used to examine oxidative phosphorylation in mitochondria isolated from hearts of rats treated with 5 mg/kg epinephrine, norepinephrine, or isoproterenol in oil given subcutaneously. Uncoupling of oxidative phosphorylation occurred (P/O ratio 2.1 ± .04 compared to P/O ratio of controls, 2.9 ± .03). Other indices of mitochondrial function, including oxygen consumption, respiratory control, adenosinetriphosphatase activity, and swelling were normal. The time course of depression of P/O ratio was parallel to that of myocardial catecholamine uptake, yet normal mitochondria were not affected by catecholamines in vitro (10
-3
M). Adrenergic blocking agents in vitro did not improve the function of mitochondria from catecholamine-treated animals. No free fatty acids were detectable in extracts of mitochondria from either group by gas liquid chromatography, and the lipid profiles of extracts from each were similar by thin layer chromatography. The data indicate a means by which large quantities of exogenous or endogenous catecholamines could lead to increased oxygen consumption in vivo, or contribute to impairment of myocardial function.
Some Characteristics of Transmembrane Potentials of AV Nodal Cells during Propagation of Premature Beats
Authors: MENDEZ CARLOS , MOE GORDON K.
Published: June 2012

Transmembrane potentials of AV nodal cells in isolated rabbit hearts were recorded during propagation of premature responses. With selected patterns of stimulation it was possible to obtain conduction block at different levels inside the AV node. When block occurred, action potentials recorded just proximal to the sites of block were brief. When propagation was barely successful, action potentials obtained from the same cells were prolonged and showed a hump in the repolarizing limb. Assuming that the AV node behaves as a functional syncytium, these phenomena can be explained as follows. (1) When conduction block occurs, local circuits established between active and inactive regions provide repolarizing current to the distal active region. This current will shorten the action potential of such cells. (2) When propagation is barely successful, the impulse may stop and resume its travel after a delay. While the impulse is arrested,
repolarizing
current will tend to shorten the action potential of the active region, but when propagation starts again, the newly excited tissue will provide
depolarizing
current to the previously active region, causing a delay in repolarization. Parallel changes in the refractory phase were also demonstrated.
Myokinase Activity of Coronary Arteries
Authors: CARR C. JELLEFF , BELL FREDERICK K. , HURST J. NEIL , KRANTZ JOHN C.
Published: June 2012

In exploring the mechanism of action of vasodilating drugs an attempt has been made to study the enzyme systems of the blood vessels. A transphosphatase of the myokinase type has been found to be present in the coronary arteries of the steer. The activity has been studied under the optimal conditions for this enzyme system. Coronary arterial tissue may be maintained at the temperature of dry ice for a number of days without significant loss of enzyme activity. This will permit an investigation of the effects of drugs upon the activity of these enzymes.
Input Impedance of the Systemic Circulation
Authors: O'ROURKE MICHAEL F. , TAYLOR MICHAEL G.
Published: June 2012

The hydraulic load presented to the left ventricle by the systemic circulation was characterized by expressing pressure-flow relationships in the ascending aorta as input impedance. This was determined by spectral or Fourier analysis of simultaneously recorded pressure and flow waves in 1 unanesthetized and 27 anesthetized dogs. Impedance modulus fell steeply from its value at zero frequency (the peripheral resistance) and its value was lowest (less than 1/20th of the peripheral resistance) over that band of frequencies (usually between 1.5 and 10 cycle/sec) which contained most of the energy of the left ventricular ejection (flow) wave. The patterns of modulus and phase of ascending aortic impedance were found to result from the presence of two functionally discrete reflecting sites in the systemic circulation, one in the upper part of the body and the other in the lower. The presence of these two sites appears to be an important factor in maintaining a low impedance modulus between 1.5 and 10 cycle/sec, and so in providing a favorable impedance to pulsatile flow from the heart. Both modulus and phase of impedance in the ascending aorta showed changes similar to those seen in other arteries when blood pressure was altered and when vasodilation occurred in the vascular bed.
Observations on Concealed Conduction in Atrial Fibrillation
Authors: MOORE E. NEIL
Published: June 2012

The mechanism of the ventricular dysrhythmia associated with atrial fibrillation in isolated rabbit heart was studied by recording electrograms from right atrium and ventricle simultaneously with transmembrane action potentials recorded from single fibers within the A-V node and right bundle branch. In most experiments, the variation in ventricular cycle length during experimentally initiated atrial fibrillation resulted from concealed conduction within the A-V node. The most frequently recorded ventricular interval during atrial fibrillation was found when a single response was concealed within the A-V node. In several experiments, as many as seven to nine consecutively concealed responses were recorded from the A-V node. When repetitive A-V nodal concealment occurred, the resulting ventricular cycle lengths were prolonged accordingly. In only a few experiments were conduction delay and block observed within the ventricular specialized conduction system (VSCS) during atrial fibrillation. Subsidiary pacemakers were never observed within the A-V node but were noted occasionally within the VSCS following epinephrine administration. Multiple A-V nodal concealments were usually associated with rapid atrial rates.
Post-Countershock Arrhythmias in Untreated and Digitalized Dogs
Authors: EICK ROBERT E. TEN , WYTE STEVEN R. , ROSS SAMUEL M. , HOFFMAN BRIAN F.
Published: June 2012

Recent studies suggest that countershock can stimulate cardiac autonomic nerves and that the resulting release of norepinephrine contributes to post-countershock (PCS) arrhythmias. β-Adrenergic receptor blocking agents, reserpine, cocaine, and cardiac-denervated preparations were used to evaluate this hypothesis in dogs under pentobarbital anesthesia. The suitability of the dog as an experimental system was examined. In the normal dog, the duration of PCS arrhythmia caused by a countershock of given energy was increased 100% by ouabain (0.05 mg/kg iv). In both normal dogs and dogs given ouabain (0.05 mg/kg iv), dichloroisoproterenol, pronethalol, and propranolol reduced the duration of PCS arrhythmia; reserpine, a norepinephrine depletor, reduced the duration of PCS arrhythmia; cocaine, a norepinephrine-uptake inhibitor possessing antiarrhythmic properties, increased the duration of PCS arrhythmia; denervation of the heart reduced the duration of PCS arrhythmia. Ouabain (0.05 mg/kg iv) reduced the duration of PCS arrhythmia in dogs with denervated hearts. These findings indicate that PCS arrhythmia in dogs is norepinephrine dependent. Evidence indicated that ouabain has an anti-adrenergic action on the heart also is presented.
Uptake of Calcium by Glycerinated Cardiac Slices
Authors: FAIRHURST ALAN S. , PALUS DONALD A. , JENDEN DONALD J.
Published: June 2012

Partially glycerinated cardiac slices have been used to assess the effects of ryanodine and of mitochondrial and other inhibitors on calcium transport in systems that appear to retain a high degree of functional integrity. Strips of rabbit ventricle were extracted in 50% (w/v) glycerol for 24 hr at 4°C and slices 100 µ thick were cut on the freezing microtome. Such slices can bind 30 to 40 µmole of calcium/g of protein when incubated in medium containing
45
Ca in the form of a Ca-EGTA buffer, binding being decreased with increasing times of glycerination. The concentrations of ATP and of Ca
2+
required for halfmaximal activity are 5 x 10
-5
M and 10
-7
M respectively; both ATP and creatine phosphate must be present to elicit maximal uptake. Calcium accumulation appears to be attributable to the sarcoplasmic reticulum rather than to mitochondria, and is inhibited by caffeine, Salyrgan and ryanodine. Uptake is stimulated by oligomycin, but is not affected by azide, ouabain, carbachol, eserine, epinephrine or norepinephrine.
Effect of Respiratory Alkalosis on Survival in Hemorrhagic Shock
Authors: BRANDFONBRENER MARTIN , WHANG ROBERT
Published: June 2012

The effect of respiratory alkalosis on survival in hemorrhagic shock was studied in pentobarbital-anesthetized dogs. Since cell membranes are relatively poorly permeable to bicarbonate ion, production of alkalosis by hyperventilation may influence intracellular pH more than by bicarbonate infusion. Hyperventilation was produced by increasing tidal volume in one group of dogs. Spontaneously breathing dogs served as controls. Another control group in which ventilation was maintained with a respirator to produce normal blood gas values was also studied. Shock was produced by arterial bleeding at a fixed rate to maintain blood pressure at 50 mm Hg for 90 min, then at 30 mm Hg for 45 min. The blood was then reinfused. In the hyperventilation group 7 of 9 animals survived 480 min with a blood pressure greater than 75 mm Hg, while none of 8 in the control group and none of 7 in which ventilation was maintained at the normal level survived with these criteria. Arterial pH was higher in the hyperventilation than the other groups, while differences in Pao
2
were not significant throughout most of the experiment. Hyperventilation improved survival and hemorrhagic shock, probably related to the changes in pH.
Influence of the lonic Environment on Spontaneous Electrical and Mechanical Activity of the Rat Portal Vein
Authors: AXELSSON JOHANN , WAHLSTROöm BO , JOHANSSON Börje , JONSSON OLOF
Published: June 2012

The effects of variations in external K
+
and Ca
2+
concentrations on electrical and mechanical activity of the isolated rat portal vein were studied using a sucrose-gap technique. Spontaneous activity in normal Krebs solution consists of bursts of action potentials accompanied by phasic contractions. Moderate reduction in [K+]
o
results in slight hyperpolarization with decreased discharge frequency. Greater reduction or total removal of extracellular K causes a temporary increase in burst frequency. Graded increases in [K+]
o
from 6 up to 128 mM cause depolarization with an increase in discharge frequency and in contraction amplitude until [K+]
o
reaches a level of 6 to 7 times normal when spike potentials are abolished and a contracture develops. The relationship between membrance potential and log [K
+
]
o
indicates a relatively low permeability to K
+
. Increasing [Ca
2+
]
o
causes slight hyperpolarization, decreased burst frequency, increased burst duration and increased contraction amplitude. Reducing [Ca
2+
]
o
causes increased frequency of discharge and shortening of bursts, until single spikes appear, each preceded by a prepotential; thus the activity resembles that in cardiac pacemaker cells. In Ca
2+
-free solution, electrical and mechanical activity ceases within 10 to 15 min. Calcium is essential for activation of the contractile mechanism and for maintenance of spontaneous spike discharge.
Electrical and Mechanical Characteristics of Vascular Smooth Muscle Response to Norepinephrine and Isoproterenol
Authors: JOHANSSON BöJRE , JOHSSON OLOF , AXELSSON JOHANN , WAHLSTRöm BO
Published: June 2012

Effects of norepinephrine (NE) and isoproterenol on simultaneously recorded electrical and contractile activity in rat portal vein were studied using a sucrose-gaps technique. This vascular smooth muscle shows spontaneous phasic contractions correlated with bursts of action potentials. Norepinephrine (10
-9
9 to 10
-7
w/v) increases the duration of the bursts and shortens the interval between after an initial period of continuous spike discharge. The tension response is greater than can be accounted for by the increase in electrical activity. High NE concentrations (10-5) produce depolarization, decrease of spike amplitude, or even abolition of spikes and maintained contractions. Norepinephrine increases contracture tension of K
+
-depolarized portal vein without changing membrane potential. Electrical and mechanical activity is reinitiated in preparations inactivated by elimination of Ca
2+
this may be due to release of bound calcium. Phenoxybenzamine abolishes the above NE responses. The typical response to isoproterenol (10
9
to 10
7
) in a normal ionic environment consists of moderate depolarization, decreased burst duration, but increased frequency of bursts and inhibition of tension development which is not simply correlated with the change in electrical activity. This pattern resembles that produced by lowering [Ca
2+
]
o
. Contracture tension in high [K
+
]
o
is reduced by isoproterenol without changes in membrane potential. These responses to isoproterenol are abolished by propranolol. At high concentrations of isoproterenol (10
-5
) the inhibitory responses are not sustained, but revert to a pattern of activity resembling that induced by NE.
Relationship between the Metabolic and Vasodilator Effects of Epinephrine in Human Forearm Muscle
Authors: KONTOS HERMES A. , RICHARDSON DAVID W. , PATTERSON JOHN L.
Published: June 2012

The effect of intra-arterial and intravenous epinephrine on skeletal muscle blood flow and metabolism were studied in the human forearm following complete suppression of the circulation to forearm skin by epinephrine inotophoresis. Epinephrine by either route of administration increased blood flow, O
2
consumption and CO
2
production, and decreased arteriovenous differences of O
2
and CO
2
across the forearm. The increments in blood flow did not correlate with the increments in O
2
consumption or CO
2
production. In the intact forearm intravenous epinephrine increased deep forearm venous Po
2
but not venous PCo
2
. Hypocapnia, induced by voluntary hyperventilation, did not alter the response of forearm blood flow to intravenous epinephrine. These results show that the vasodilator response of skeletal muscle vessels to epinephrine is not dependent on decrease in Po
2
or increase in PCO
2
in the environment of the high resistance vessels. They also suggest that the calorigenic effect of the hormone is not a dominant factor in its vasodilator effect in skeletal muscle.
A Technique for the Microscopic Study of Blood Vessels in Living Striated Muscle (Cremaster)
Authors: MAJNO GUIDO , GILMORE VIRGINIA , LEVENTHAL MONIKA
Published: June 2012

A technique is described whereby it is possible to study the vessels of a striated muscle (the rat cremaster) in vivo. In the anesthetized rat, a part of the scrotal skin is excised; the cremaster muscle is exposed and studied by epi-illumination. To improve the optical conditions, a white reflecting surface is brought behind the cremaster through the inguinal canal. Twitching of the muscle may be prevented by the use of a neuromuscular blocking agent. It is also possible to study the blood vessels of the fascia overlying the cremaster. The method may also be applied to the rabbit; it is recommended for short-term studies in which topographic requirements prevail. Its advantages and limitations are discussed.
Effect of Beta-Adrenergic Receptor Blockade on Racing Performance of Greyhounds with Normal and with Denervated Hearts
Authors: DONALD DAVID E. , FERGUSON DAVID A. , MILBURN SIDNEY E.
Published: June 2012

A field study was made of the effect of β-adrenergic receptor blockade (propranolol; Kö 592) on the racing performance of six normal greyhounds and three with chronic extrinsic cardiac denervation. Records were made of the time to race a 5/16-mile course before and after blockade; the heart rate was recorded by telemetry. After the administration of the β-adrenergic receptor-blocking agent to the normal greyhound, racing time was slightly increased, and maximal heart rate was slighdy decreased. After blockade in the cardiac denervated greyhounds, racing time was prolonged, cardiac acceleration was severely limited, and the animals finished running in a state of collapse. The data indicated diat die cardiostimulant action of both sympathetic nerves and circulating catecholamines was necessary for maximal performance. After blockade of one or the other of these mechanisms, racing performance was slightly reduced from normal. Withdrawal of both adjuvants severely limited the performance of maximal exercise.