bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution of Plastoelasticity to the Tone of the Cat Portal Vein
Authors: ALEXANDER ROBERT S.
Published: June 2012

Isolated helical strips of cat portal vein were subjected to sudden stresses to produce immediate elastic extension followed by a slow plastoelastic extension or "creep". Recovery from this creep was evaluated by restretching with varying intervals between stretches. In appropriately stimulated vessels, significant creep recovery continues for periods in excess of 20 minutes. Both the rate and the ultimate magnitude of the creep recovery were substantially increased by contractile activity produced by norepinephrine or electrical stimulation. The rate and ultimate magnitude of creep recovery were decreased by dilator drugs, although some recovery persisted. The only factors found capable of blocking creep recovery were complete inactivation of the contractile machinery by removal of calcium from the system or maintainence of tension on the tissue during the recovery period. This behavior is explained by a model in which contracted elements are capable of slowly converting into a stable shortened configuration capable of passively maintaining venous tone until mechanical stress causes a plastoelastic extension to the longer configuration.
Reflex Effects of Stimulation of Carotid Sinus and Aortic Baroreceptors on Hindlimb Vascular Resistance in Dogs
Authors: Dampney Roger A. L. , Taylor Michael G. , McLachian Elspeth M.
Published: June 2012

Two series of experiments were performed on anesthetized dogs whose hindlimbs were perfused at constant flow and the blood pressures in the femoral artery, aortic arch, and carotid sinus recorded. The reflex changes in hindlimb vascular resistance were determined in response to changes in pressure in the aortie arch in the first series, and in the carotid sinus in the second. In each series, when one baroreceptor area was stimulated, the other area was eliminated-in the first series, by perfusing the carotid sinuses at constant pressure, and in the second, by vagotomy. The quantitative relationships between hindlimb vascular resistance and pressure at each of the two baroreceptor sites were determined over the low frequency range (0.001-0.1 Hz). The average estimated steady-state gain of the carotid sinus baroreceptor system was 2.22±0.19 (
SE
) and that of the aortic baroreceptor system 1.06±0.13. The time courses of response for both systems were similar but the aortic baroreceptors were about half as sensitive as the carotid sinus baroreceptors over the entire frequency range.
Reflex Apnea, Bradycardla, and Hypotension Produced by Serotonin and Phenyldiguanidecting on the Nodose Ganglia of the Cat
Authors: Jacobs Louise , Comroe Julius H.
Published: June 2012

Five to 20 µg of phenyldiguanide or serotonin (5-HT) injected into the common carotid arteries of cats (anesthetized with chloralose and urethan) elicited an immediate apnea, usually accompanied by bradycardia and hypotension. The response persisted after ligation of the external carotid and lingual arteries. Since the internal carotid is occluded in the cat, the receptors must be in the distribution of the occipital or ascending pharyngeal arteries. Denervation of the carotid sinus and carotid body, removal of the superior cervical ganglion, section of the vagosympathetic trunk below the nodose ganglion, and extracranial section of cranial nerves IX, XI, and XII did not diminish the response. Section or procaine block of the extracranial supranodose vagus or removal of the nodose ganglion usually abolished the apnea and bradycardia; hypotension still occurred in many cats. Examination of the nodose ganglion by fluorescence microscopy revealed nests of intensely fluorescent cells similar to type 1 carotid body cells. Although previous investigators have reported that veratrnm alkaloids or acetylstrophanthidin causes vomiting or bradycardia by an action on the nodose ganglion, this is the first demonstration that a naturally occurring substance (5-HT) stimulates receptors in the nodose ganglion, causing reflex apnea and hypotension in addition to bradycardia.
Effects of Cyclic AMP, Sympathomimetic Amines, and Adrenergic Receptor Antagonists on Renin Secretion
Authors: Winer Nathaniel , Chokshi Deenbandhu S. , Walkenhorst Walter G.
Published: June 2012

Renal vein renin activity was measured by bioassay of plasma obtained from anesthetized dogs during renal arterial infusion of sympathomimetic amines, cyclic AMP, and other nucleotides. Renin secretion was calculated as the product of renal blood flow and the arterial-renal venous renin difference. Infusion of cyclic AMP significantly increased renin secretion, while administration of ATP, ADP, 5'AMP, and adenosine in quantities equimolar to cyclic AMP had no effect. Phentolamine, an
α
-receptor antagonist, and
dl-
propranolol, a
β
-receptor blocker, abolished the cyclic AMP-induced rise in renin secretion. Paradoxically, the increase in renin production induced by infusion of norepinephrine, a predominantly
α
-receptor agonist, was suppressed by propranolol administration, and the renin-stimluating effect of isoproterenol, a
β
-receptor stimulator, was blocked by phentolamine administration. In addition, the
d
- and
l
-isomers of propranolol were equipotent in suppressing the isoproterenol-induced rise in renin secretion. Administration of AY-21,O11, a
β
-receptor antagonist which lacks local anesthetic properties, also prevented the isoproterenol-induced rise in renin secretion, but lidocaine had no suppressive effect. The effects on renin secretion of cyclic AMP and sympathomimetic amines alone and in combination with adrenergic receptor antagonists were independent of changes in glomerular filtration rate, sodium excretion, urine flow, systemic blood pressure, and heart rate. The data suggest that cyclic AMP acts within the kidney as an intracellular mediator of renin secretion, and that phentolamine and propranolol suppress ream secretion at a site distal to cyclic AMP production, rather than by blockade of plasma membrane adrenergic receptors or inhibition of adenyl cyclase.
Effect of Altering Potassium Concentration on the Action of Lidocaine and Diphenylhydantoin on Rabbit Atrial and Ventricular Muscle
Authors: Singh B. N. , Williams E. M. Vaughan
Published: June 2012

All previously studied antiarrhythmic drugs which also have local anaesthetic properties reduce the maximum rate of depolarization (MRD) of cardiac muscle. Recent evidence suggested that lidocaine and diphenylhydantoin (DPH) might have a different mode of action, because they did not reduce MRD except at high concentration. The latter evidence, however, was obtained from tissues nourished by solutions containing 2.7-3 m
M
potassium. In the present experiments, the effects of lidocaine and DPH were studied in solutions with 5.6 and 3 mM KCl. In the former, both drugs reduced MRD at concentrations similar to those found in the blood of treated patients, but in low [KCl] higher concentrations were necessary. It was concluded that there was no reason to suppose that the mode of action of lidocaine and DPH on the cardiac membrane is fundamentally different from that of quinidine, procaine, procainamide and other compounds which interfere directly with depolarization.
The Two Components of the Human Atrial Action Potential
Authors: Fabiato Alexandre , Fabiato Fran$$$oise
Published: June 2012

Action potentials studied in 36 human atrial strips at 27°C were found to be separated into two components. Simultaneous recordings with two microelectrodes demonstrated an independent conduction of the second component through selective and variable pathways. Increased separation of the two components was elicited by higher rate and lower intensity of stimulation, high K
+
, low Ca
2+
hypertonic solutions as well as by low temperature. Opposite procedures resulted in a more homogeneous and less variable excitation. Consequently, low rate and high intensity of stimulation allowed the study of the membrane permeabilities related to the two successive depolarizations. The first was suppressed by tetrodotoxin, the second by MnCl
2
and both by low Na
+
solutions. Hence, it was concluded that the separation was related to a nonhomogeneous excitation of the preparation and that the two components are triggered by two relatively independent depolarizations using different channels. Furthermore, the small amplitude of the first depolarization, without overshoot, and its modifications with stimulation intensity suggest that it might be due to an electrotonic spread or to a junctional mechanism.
Determination of the True Phase Velocity of Arterial Pressure Waves in Vivo
Authors: Cox Robert H.
Published: June 2012

Results of simultaneously recorded pressure, diameter, flow, and differential pressure from an arterial segment were studied by Fourier analysis. The method was applied to pressure propagation in the femoral artery of anesthetized dogs. Experimental values of phase velocity compared favorably with values predicted from a theoretical wave propagation model. The phase velocity was generally constant for frequencies over 35 rad/sec. At frequencies below 20 rad/sec, it decreased rapidly with decreasing frequency. The frequency variations of the true and apparent phase velocities were significantly different. The characteristic impedance of the femoral artery was a weak function of frequency arid nearly independent of the mean arterial pressure. High frequency values of the local fluid impedance above 50 rad/sec were significantly lower than those of the characteristic impedance. It was concluded that the method can be used to obtain reliable values of phase velocity in the physiological frequency range from in vivo measurements.
Effects on the Canine P Wave of Discrete Lesions in the Specialized Atrial Tracts
Authors: Waldo Albert L. , Bush Harry L. , Gelband Henry , Zorn George L. , Vitikainen Kari J. , Hoffman Brian F.
Published: June 2012

The role of the specialized atrial tracts in determining the polarity, morphology, and duration of normal and ectopic P waves in the canine heart was studied by producing discrete surgical lesions in selected portions of these tracts. Effects of these lesions were correlated with changes in the polarity, morphology, and duration of the P waves and with conduction time to selected atrial sites when the atria were paced from the sinoatrial (SA) node, the left atrial portion of Bachmann's bundle, the low interatrial septum near the atrioventricular (AV) node, and the posterior-inferior left atrium. A lesion in the anterior internodal tract where it leaves the head of the SA node prolonged conduction time between the SA and AV nodes and significantly increased P wave duration when the atria were paced from the SA node and low interatrial septum sites. A lesion in the branch of the anterior internodal tract running through Bachmann's bundle significantly changed P wave polarity, morphology, and duration when the atria were paced from the SA node, Bachmann's bundle, and low interatrial septum sites. A lesion in the posterior internodal tract failed to change P wave polarity, morphology, or duration. When the atria were paced from the posterior-inferior left atrium, the lesions had no significant effect on P-wave polarity, morphology, or duration. It is concluded that specialized atrial tracts play a functionally important role in the sequence of atrial activation during many normal and ectopic rhythms.
Sympathetic Control of Pulmonary Vascular Impedance in Anesthetized Dogs
Authors: Pace John B.
Published: June 2012

The effects of left stellate ganglion stimulation on pulmonary hydraulic input impedance was evaluated in 21 experiments on open-chest dogs anesthetized with chloralose. The stellate ganglion was stimulated at 1, 2, 5, 10, and 20 cps, and impedance spectra were generated at each frequency. Control spectra were characterized by frequency-dependent oscillations in impedance magnitude. Generally, impedance minimums occurred between 2 and 3 cps and maximums between 4 and 6 cps. Stellate ganglion stimulation caused elevations in impedance magnitude and shifted the impedance curve upward. The average control impedance magnitude at the minimum was 4780 dyne sec cm
-5
kg ± 262 SE and was increased to 82.80 ± 452 during stimulation at 20 cps, while the frequency of the first harmonic in the control averaged 2.50 ± 0.08 SE cps and was 3.10 ± 0.08 during stimulation at 20 cps. Maximum activation of sympathetic outflows (10-20 cps) caused the impedance curve to flatten, attenuating frequency dependent oscillations characteristic of control spectra. The administration of propranolol attenuated cardiogenic increases in pulmonary pressure and flow during stellate ganglion stimulation, but elevations in pulmonary vascular impedance still occurred, indicating that this was not dependent on changes in harmonic content of the flow pulse that attended changes in heart rate and stroke volume. Frequency dependent oscillations in impedance magnitude were usually enhanced during left stellate ganglion stimulation following propranolol. The results indicate that sympathetic nerve stimulation increases the opposition to pulsatile flow; since pulmonary vascular resistance was relatively less affected, the input impedance becomes a greater fraction of the total opposition that must be overcome in moving blcod through the lungs.
A Noninvasive Technique for the Determination of Velocity of Circumferential Fiber Shortening in Man
Authors: Poraskos John A. , Grossman William , Saltz Stephen , Dalen James E. , Dexter Lewis
Published: June 2012

Velocity of circumferential fiber shortening (V as determined by analysis of left ventricular cineangiocardiograms has been proposed as a measure of left ventricular myocardial contractility. In this study, a noninvasive ultrasonic technique was used to measure the rate of shortening of the left ventricular internal minor axis throughout ejection in 61 patients. These measurements permitted calculation of mean Vcr. In 23 patients with normal left ventricular function, mean V
CF
averaged 1.45 ± 0.08 circumferences/sec (mean SE). Tn contrast, mean V in 38 patients with impaired left ventricular function was significantly depressed (0.91 ±0.09 circumferences/see, P <0.001). In 17 patients, adequate resolution of septal and posterior wall thicknesses permitted measurement of midwali radius at 50-msec intervals throughout the cardiac cycle. These measurements permitted computation of instantaneous and peak V Values for peak V
CF
at the midwall were generally similar to those observed for mean V at the internal axis. In patients with normal left ventricular function, peak V
CF
averaged 1.58 ± 0.23 circumferences/sec. This study has demonstrated the feasibility of measuring the velocity of left ventricular circumferential fiber shortening in man by a noninvasive method. Initial studies indicate that this approach may prove useful in the detection and serial evaluation of left ventricular performance in patients with heart disease.
Differentiation of Certain Platelet Factors Related to Blood Coagulation
Authors: DEUTSCH ERWIN , JOHNSON SHIRLEY A. , SEEGERS WALTER H.
Published: June 2012

Study of the platelets from the viewpoint of the blood coagulation mechanisms seems likely to be helpful for increasing our knowledge of thrombosis, and bleeding tendencies in thrombasthenias and thrombopathias. A logical approach to their study is the differentiation of their properties and where possible to ascribe those properties to individual components. Platelet factors 1, 3 and 4 are considered from that viewpoint. The first accelerates the formation of thrombin in a manner analogous to serum Ac-globulin. Factor 3 is required for the development of threone activity, and factor 4 has antiheparin properties.
A Study of Defibrillating Agents on Perfused Rabbit Hearts
Authors: DIRKEN M. N. J. , GEVERS F. , HEEMSTRA H. , HUIZING E. H.
Published: June 2012

Cooling the myocardium is an effective method for abolishing ventricular fibrillation. Using this method as a reference a comparison between five other methods for cardiac resuscitation is made using the Langendorff preparation of the rabbit's heart.
A Square Wave Electromagnetic Flowmeter for Application to Intact Blood Vessels
Authors: DENISON ADAM B. , SPENCER MERRILL P. , GREEN HAROLD D.
Published: June 2012

A new type electromagnetic flowmeter which utilizes an alternating square wave magnetic field applied to the unopened blood vessel is described. It attains stability of baseline and sensitivity not possible with older D.C. and A.C. meters and therefore puts measurement of blood flow through the unopened vessel on a practical basis.
Vulnerability of the Dog Ventricle and Effects of Defibrillation
Authors: HOFFMAN BRIAN F. , SUCKLING E. E. , BROOKS CHANDLER McC.
Published: June 2012

Vulnerability to ventricular fibrillation has been studied in 20 dogs by means of test stimuli of known strength and duration in order to ascertain the relationship between the vulnerable period and the recovery of excitability and to determine the effects of countershock defibrillation. The relative refractory period is found to be the only portion of the cycle during which fibrillation could be produced by this technique. Defibrillation was accomplished without producing significant changes in vulnerability or excitability.
Protein-Lipid Relationships in Normal Dog Plasma
Authors: Russ ELLA M. , RAYMUNT JULIE
Published: June 2012

Although Cohn's microfractionation method number 10 was specifically devised to meet the conditions of protein concentration and distribution in human plasma, it is shown in this contribution that it may be applied to studies of canine plasma. Essentially all of the lipids of plasma are recovered in Fractions IV + V + VI and I + III. Only negligible amounts appear in Fraction II. Electrophoretic studies proved that the lipoproteins of Fraction IV + V + VI have the mobility of alpha globulins and those in Fraction I + III have the mobility of beta globulins.
Absolute Quantitative Comparison of Instantaneous QRS Equipotentials on a Normal Subject with Dipole Potentials on a Homogeneous Torso Model
Authors: FRANK ERNEST
Published: June 2012

Quantitative results of a critical experiment designed to determine influence of human-body inhomogeneity and applicability of fixed-location dipole hypothesis for ventricular depolarization are presented. Results reflect in pictorial form, conclusions that the fixed-location dipole representation is approximately 95 per cent accurate for the QRS complex at any body-surface point; influence of inhomogeneities on surface potentials is roughly ±10 per cent.
Comparison of Spatial Instantaneous ECG Vectors, Measured with the SVEC, with Mean Vectors Derived from Conventional ECG Leads
Authors: SIMONSON ERNST , SCHMITT OTTO H. , LEVINE RAPHAEL B.
Published: June 2012

Two approaches to the analysis of spatial electrocardiographic vectors are currently being used: construction from the conventional ECG leads, and measurements from oscilloscopic recordings of spatial loops. There are several fundamental differences between the approaches, and there is no
a priori
certainty that equivalent or even similar phenomena are being investigated. This study presents a statistical comparison between mean spatial vectors, constructed from the conventional ECG, and instantaneous maximum spatial vectors, determined with the stereovector electro-cardiographic technic.
The Immediate Influence of Increased Venous Pressure Upon Resistance to Flow in the Dog's Hind Leg
Authors: PHILLIPS FRED A. , BRIND SHIRLEY H. , LEVY MATTHEW N.
Published: June 2012

Variations in flow in the presence of a constant arteriovenous pressure difference can only occur when vascular dimensions have been altered, irrespective of the rheological properties of the liquid being perfused. When the vascular bed of the hind leg is subjected to parallel changes in arterial and venous pressures, higher absolute values of pressure result in an enhancement of flow. This constitutes convincing evidence to indicate that certain vessels which offer a significant resistance to blood flow are distensible.
Auricular Fibrillation Induced and Maintained in Animals by Acetylcholine or Vagal Stimulation
Authors: LOOMIS TED A. , KROP STEPHEN
Published: June 2012

Animals pretreated with appropriate doses of anticholinesterase agents develop auricular flutter and fibrillation following injection of acetylcholine or vagal stimulation. Depression of normal sinoauricular nodal function facilitates induction of fibrillation. During fibrillation, additional injections of acetylcholine, or vagal stimulation, increase the rate of fibrillation. Atropine in small doses reverts the fibrillation to normal sinus rhythm.
Arterial Hypertension in Hemidecorticate Rats
Authors: COVIAN M. R. , HOUSSAY H. E. J.
Published: June 2012

Hemidecortication usually caused arterial hypertension in rats for one or two months. Sympathicolytic drugs caused a transient reduction in blood pressure. Release of subcortical centers from the modulating action of the cerebral cortex seems to be the best explanation.
Intra-Aneurysmal Hemodynamics--Jet Action
Authors: GERMAN WILLIAM J. , BLACK SAMUEL P. W.
Published: June 2012

Jet action from experimental "berry" aneurysms was evaluated as part of a long-range study of stress-strain-time relations of aneurysmal rupture. It was apparent that free jet action was a potent stress agent upon matter in its path. Calculated velocities of free jets ranged up to 477 cm. per sec. Supplementary observations were made upon jets from glass-model aneurysms, including the jet effects upon gelatin blocks cast about the models. Coefficients of velocity were determined for the various jets studied and the results were correlated with theoretic hydraulics.
Interrelationships Between Cardiac Effects of Ouabain, Hypocalcemia and Hyperkalemia
Authors: PAGE ERNEST , REAL JACK D.
Published: June 2012

In dogs anesthetized with pentobarbital, ventricular arrhythmias induced by ouabain were consistently reverted to sinus rhythm by acute lowering of the serum calcium. In ouabain-in-toxicated dogs, the depressed and shortened S-T segment was elevated and lengthened by induced hypocalcemia. Potassium administered concomitantly with ouabain exerted a protective effect against ouabain intoxication. Lowering of the serum calcium in animals showing moderately advanced potassium effects in their ECG precipitated acute, fatal potassium poisoning. Ouabain was capable of reversing the tachycardia and pulsus alternans due to hypocalcemia in the face of persistent hypocalcemic tetany.
A Spectrophotometric Study of Actomyosin
Authors: ROBB JANE S. , GRUBB MARLIN , BRAUNFELDS HELENA
Published: June 2012

It is known that when actomyosin and adenosine triphosphate (ATP) interact, the ultraviolet absorption is no longer that characteristic either of actomyosin or of ATP. This report deals with a spectrophotometric study of interactions of various chemicals and/or drugs with actomyosin. The intention was to discover whether these agents alter the absorption, i.e., optical density (O.D.) of actomyosin solutions and if so, whether all the agents produce similar changes.
Comparison of Simultaneously Recorded Central and Peripheral Arterial Pressure Pulses During Rest, Exercise and Tilted Position in Man
Authors: KROEKER EDWIN J. , WOOD EARL H.
Published: June 2012

Central (aortic or subclavian), brachial, radial and femoral pressure pulses were recorded simultaneously in 12 healthy subjects during conditions of rest, exercise and 70 degree head-up tilt. Peripheral systolic pressure at rest uniformly exceeded the central systolic pressure generated by the same heartbeat. The average radial pulse pressure was 146, 146 and 165 per cent of central pulse pressure during rest, exercise and tilt while radial mean pressures were 94, 93 and 98 per cent of central mean pressures respectively. Summation of the incident pulse wave with reflected waves from the periphery and resonance effects in the peripheral arterial systems may produce these changes in pressure and contour.
Slow Conduction and Reentry in the Ventricular Conducting System
Authors: WIT ANDREW L. , HOFFMAN BRIAN F. , CRANEFIELD PAUL F.
Published: June 2012

Depression of excitability and responsiveness provoked by the action of high K
+
and epinephrine on short bundles of excised canine Purkinje fibers yields reentrant excitation. An impulse entering a depressed area undergoes marked slowing of conduction; the impulse then may continue forward while also returning through the pathway by which the initiating impulse entered the depressed area. The impulse may be delayed or blocked in either the forward or the retrograde direction. The reentrant excitation can occur in the absence of premature excitation. Various methods of depression of excitability produce return extrasystoles in Purkinje fibers. The common factor is very slow conduction which depends upon the abolition of the fast upstroke and the appearance of a low-voltage, slowly propagated action potential that is readily blocked.
Slow Conduction and Reentry in the Ventricular Conducting System
Authors: WIT ANDREW L. , CRANEFIELD PAUL F. , HOFFMAN BRIAN F.
Published: June 2012

Closed loops of fibers of the ventricular conducting system of canine or bovine hearts were used to study circus movement of excitation. Action potentials were recorded at three sites with intracellular microelectrodes. Discrete segments were depressed by application of K
+
-rich agar or the entire loop was depressed by modified Tyrode's solution containing 15-17 mM K
+
and 1 to 5 x 10
-6
M epinephrine. The loops were 12-35 mm long and the effective conduction velocity was 0.02-0.08 m/sec. Impulses entering some loops traveled in one direction only, circling around the loop and returning to produce a second response at one or more sites (single circus movement). In other loops the impulse traveled around the circuit repeatedly (sustained circus movement). Circus movement around short loops requires a low conduction velocity and must be initiated by an impulse that travels around the loop in only one direction. Single circus movement can cause extrasystoles. Sustained circus movement can cause idioventricular rhythms and ventricular tachycardia.
Relation of V
max
to Different Models of Cardiac Muscle
Authors: PARMLEY WILLIAM W. , CHUCK LEONARD , SONNENBLICK EDMUND H.
Published: June 2012

The present study was undertaken to reevaluate the effects of preload on maximum velocity of shortening at zero load, V
max
, relative to the length-tension curve. Force-velocity relations were measured from afterloaded isotonic contractions and were calculated from isometric contractions of isolated cat papillary muscles. Results were interpreted in the light of three alternative mechanical models of muscle. V
max
was obtained by mathematical extrapolation of each force-velocity relation to zero load using a hyperbolic least-squares analysis performed on an IBM 360 computer. With the application of all three muscle models to isotonic force-velocity relations, V
max
was relatively constant at low preloads but was reduced substantially as muscle length approached L
max
(the length at the peak of the active length-tension curve). In force-velocity relations from isometric contractions, similar results were obtained with the two-element and Voigt models of muscle. With the Maxwell model, V
max
remained more nearly constant near L
max
. Peak developed force (isometric contraction), maximum dP/dt, peak calculated velocity of the contractile element (V
CE
), and V
max
were compared in terms of their dependence on preload and length over the entire length-tension curve (using the Maxwell model). Peak V
CE
and V
max
were similar and were less dependent on preload than maximum dP/dt or developed force.
Autoregulation of Directly Measured Blood Flows in the Superficial and Deep Venous Drainage Areas of the Cat Kidney
Authors: GALSKOV Åge , NISSEN OLE I.
Published: June 2012

The renal arterial pressure was changed in steps of 25 mm Hg, or it was successively varied between two levels (100 and 150 mm Hg) to obtain four or five stable flow recordings at each level. Statistical calculations indicated that the blood flows in the two drainage areas of the cat kidney were autoregulated with equal effectiveness (whether judged from inflow or outflow rates). The flows at 100 mm Hg were approximately 95% of the flows at 150 mm Hg. To establish whether the accuracy of the method was sufficient to detect a possible nonautoregulated fraction of the arcuate flow similar in magnitude to that traversing the medulla, the flow data were compared with the flows calculated from a simple mathematical model consisting of three homogeneous compartments (outer cortical, inner cortical, and medullary), each with its own pressure-flow relationship. If the flows through all cortical glomeruli are similarly autoregulated, the experimental results are incompatible with a flow through juxtamedullary glomeruli which is proportional to pressure and constitutes 5-;7%, or more, of the total renal blood flow.
Potassium Efflux from Amphibian Atrium during the Cardiac Cycle: A REEXAMINATION
Authors: JUNCKER DAVID F. , GREENE ERNEST A. , STISH RICHARD , LORBER VICTOR
Published: June 2012

Fine fibers from amphibian atrium were mounted in a microperfusion chamber and loaded with
42
K, followed by a rapid, nonisotopic wash during which the preparation was stimulated electrically. The stimulus was triggered and the "cold" effluent collected by a high-speed rotary fraction collector. Thus effluent corresponding to the same time interval in the cardiac cycle was always collected in the same tube. Large numbers of cycles were thus summed, decreasing the error in the tracer assay. Mechanical systole, previously shown to produce an artifact in the tracer efflux profile, was suppressed or prevented by various means. Under these conditions, a prolonged decrease in
42
K efflux was observed, corresponding in time to the plateau of the action potential. Experiments were also carried out with
22
Na,
45
Ca, and
82
Br, all of which showed primarily a single, positive efflux peak with its maximum within the first 50 msec of the action potential. Cell membrane permeability to K
+
appears to be markedly voltage dependent; and a diminished membrane permeability to K
+
apparently plays an important part in the generation of the plateau of the cardiac action potential.
Experimental Unilateral Renal Artery Constriction in the Dog
Authors: LUPU ANDREI N. , MAXWELL MORTON H. , KAUFMAN JOSEPH J. , WHITE FRED N.
Published: June 2012

Chronic hypertension caused by unilateral constriction of the renal artery in the presence of the opposite untouched kidney can be produced in the dog by progressive plication of the renal artery over a period of several hours. Twenty-three female dogs were studied. Mean arterial blood pressure was measured in the unanesthetized recumbent dog by direct puncture of the femoral artery. Reproducible control blood pressure readings were obtained only after daily training of the animals for at least 2 months. Mean arterial blood pressure for the whole group of animals was 98.25 ± 7.45 (SD) mm Hg prior to constriction. Three months after constriction, the mean arterial blood pressure of the group of dogs with a 50-63% reduction in renal blood flow was 132.4 ± 5.51 (SD) mm Hg (
P
< 0.001); for the group with a 78-86% reduction in renal blood flow it was 144.68 ± 10.68 (SD) mm Hg (
P
< 0.001). Six dogs from these two groups underwent ipsilateral nephrectomies 4-16 months after constriction, and their elevated arterial blood pressures returned to preconstriction normal values. It was concluded that this type of experimental hypertension in the dog is renal dependent in both the acute and the chronic stages.
Regional Circulatory Adjustments to Moderate and Severe Chronic Anemia in Conscious Dogs at Rest and during Exercise
Authors: VATNER STEPHEN F. , HIGGINS CHARLES B. , FRANKLIN DEAN , MCKOWN DANIEL P.
Published: June 2012

The successive changes in regional blood flows and resistances due to moderate and severe anemia were studied serially in nine conscious dogs after they recovered from implantation of ultrasonic Doppler transducers or electromagnetic flow probes on the left circumflex coronary, the mesenteric, the renal, and the iliac arteries and pressure gauges or catheters in the aorta. Anemia was induced by progressive phlebotomy and volume replacement over a period of 2-4 weeks. In moderate anemia (average hematocrit 22%) heart rate increased from 73 beats/min to 105 beats/min, and mean arterial pressure fell from 98 mm Hg to 94 mm Hg. Flow increased to the coronary bed by 75% and to the iliac bed by 45%, but flow to the mesenteric bed was not significantly affected and renal flow fell by 9%. Coronary and iliac resistances fell by 45% and 32%, respectively, but mesenteric and renal resistances were not significantly affected. In severe anemia (hematocrit 14%) heart rate increased to 129 beats/min, and mean arterial pressure was at control levels; coronary flow increased by 227%, iliac flow by 102%, mesenteric flow by 29%, and renal flow by 20%. Resistance decreased in the coronary bed by 69%, in the iliac bed by 52%, in the mesenteric bed by 23%, and in the renal bed by 19%. Exercise during severe anemia increased heart rate to 224 beats/min, mean arterial pressure to 114 mm Hg, coronary flow by 34%, and iliac flow by 215%; it reduced mesenteric flow by 59% and renal flow by 48%. Thus, blood flow increased and resistance decreased to all beds studied, indicating that in the resting conscious dog compensatory reduction of visceral flow is not a feature of the cardiovascular response to severe anemia at rest, although a redistribution of regional blood flow does occur. However, the added stress of exercise during severe anemia results in substantial reductions in mesenteric and renal blood flows.
Release of Blood from the Splanchnic Circulation in Dogs
Authors: Brooksby Gerald A. , Donald David E.
Published: June 2012

In dogs anesthetized with α-chloralose, passive alterations in splanchnic blood flow over a range of flows between 10 ml/kg min
-1
and 50 ml/kg min
-1
produced by a blood flow pump or by a change in perfusion pressure were associated with changes in splanchnic blood volume of 0.19 ± 0.1 (SD) ml/kg and 0.43 ± 0.15 ml/kg, respectively, for a change in flow of 1 ml/kg min
-1
. Mechanical increase in splanchnic outflow resistance raised portal venous pressure from a control mean of 6.9 ± 4.1 mm Hg to 15.4 ± 3.5 mm Hg and increased splanchnic blood volume by 8.1 ± 2.2 ml/kg. Of the total change in splanchnic blood volume during an 18-second supramaximal stimulation of the thoracic splanchnic nerves, an estimated 65% was released "passively." The magnitude of this passive release was related linearly to splanchnic blood flow. During increased resistance to splanchnic outflow, the passive release was absolutely and relatively reduced, but the volume of blood actively released by constriction of capacitance elements was absolutely and relatively increased. During hemorrhage (7.2 ml/kg body weight), an average of 4.7 ± 0.6 ml/kg of blood (21% of the calculated splanchnic blood volume) was mobilized, and arterial blood pressure decreased an average of 5%. Repetition of the bleeding after bilateral splanchnicectomy passively mobilized 3.25 ± 0.9 ml/kg of blood (68% of the innervated value), but arterial blood pressure declined by an average of 20%.
Studies on Renin
Authors: Haas Erwin , Goldblatt Harry , Lewis LaVera , Gipson Edwin C.
Published: June 2012

Dog renin was produced with a yield of 1.1 Goldblatt units (GU)/g renal tissue and with a specific activity of 1.3 GU/mg protein, i.e., a specific activity 10-16 times higher than that of previous preparations. This renin, free of angiotensinase and of anaphylactoid substances, was used to study the effects of prolonged infusion of renin in normal conscious dogs and as a standard for the bioassay of renin. A simplified method was designed for the indirect assay of canine renin. After prolonged incubation, the angiotensin produced was determined by bioassay in the rat, and the final estimate was expressed as the concentration of renin, in terms of GU, with an accuracy of ± 12.8%. The lower sensitivity of the assay is 1.0 x 10
-5
GU/ml; this limit permits an estimate of the endogenous renin in 0.1 ml of normal dog serum or in 0.005 mg of normal canine renal tissue. The sensitivity of this bioassay is, therefore, within the range found in seven radioimmunoassays (0.26 x 10
-5
GU/ml to 6.2 x 10
-5
GU/ml), and compared with the previous direct bioassay of renin in the dog the sensitivity is approximately 100,000-fold greater. By reference to an internationally accepted unit of renin, the Goldblatt unit, it was possible to recalculate and compare directly the results obtained in seven laboratories on the concentration of renin in blood, renal lymph, and various other tissues. This unified method for the evaluation of renin assays has made possible the determination of the rate of release of renin from the kidneys and the minimum rate of infusion of renin capable of producing persistent appreciable elevation of blood pressure.
Pressures in the Pial Arterial Microcirculation of the Cat during Changes in Systemic Arterial Blood Pressure
Authors: Stromberg Don D. , Fox James R.
Published: June 2012

Dynamic arterial blood pressures were recorded by micropuncture of 99 cortical surface arteries and arterioles in cats anesthetized with pentobarbital or chloralose and urethane, using the Wiederhielm servocontrolled micropipette pressure system incorporating pipette tips less than 0.5µ in diameter. During these measurements, systemic blood pressure was varied by supplemental intravenous administration of barbiturate, by intravenous administration of norepinephrine, or by arterial hemorrhage and reinfusion. Pial arterial blood pressure varied systematically with the changes in systemic blood pressure, forming a basis for analysis and synthesis of the results. Measurements in individual vessels indicated that the range of pressures and of pressure responses of the cortical surface vessels was variable with both vessel size and prevailing end-expiratory gas CO
2
content. Pooled data indicated that 39% of the loss in pressure head occurred in arteries upstream from the largest (300µ or more in diameter) surface arteries, 21% between these arteries and surface arterioles 50µ or less in diameter, and 40% downstream from the surface arterioles at a systemic blood pressure of 50 mm Hg. At a systemic blood pressure of 180 mm Hg the upstream loss decreased to 33%, loss across the pial vessels decreased to 15%, and the downstream loss increased to 52%. Thus, the results indicated that the cerebrovascular response to changes in systemic blood pressure occurred predominantly downstream from the surface arterial vasculature.
Perivascular Potassium and pH as Determinants of Local Pial Arterial Diameter in Cats
Authors: Kuschinsky W. , Wahl M. , Bosse O. , Thurau K.
Published: June 2012

The effects of and the interaction between local perivascular variation in potassium and bicarbonate concentration on the diameter of pial arteries were studied in cats by the microapplication technique. At 11 mEq/liter of bicarbonate, a direct correlation existed between vascular diameter and K
+
concentrations between 0 and 10 mEq/liter. At K
+
concentrations between 10 and 20 mEq/liter, no further increase in vascular diameter was observed. At a K
+
concentration of 5 mEq/liter, an inverse relationship existed between pial arterial diameter and perivascular bicarbonate concentrations between 0 and 22 mEq/liter. At K
+
concentrations of 0 and 10 mEq/liter, the pial arterial diameter was determined strongly by the K
+
concentration and was only slightly, if at all, influenced by bicarbonate concentrations between 5 and 22 mEq/liter. At lower bicarbonate concentrations the local acidity induced a marked vasodilation. The results indicate that the diameter of pial arterioles in cats is affected by periarteriolar concentrations of K
+
and H
+
; the degree of the vasoreaction induced by H
+
is modulated by K
+
.
Unresponsiveness of Pial Precapillary Vessels to Catecholamines and Sympathetic Nerve Stimulation
Authors: Raper A. Jarrell , Kontos Hermes A. , Wei Enoch P. , Patterson John L.
Published: June 2012

A systematic analysis of the possible existence of neurogenic control of precapillary pial vessels was made in three species (cat, dog, and rabbit). In all of these animals, pial vessels failed to respond to externally applied isoproterenol or norepinephrine in high concentrations (up to 100 µg/ml), although the vessels did dilate in response to externally applied histamine. Adrenergic nerve endings on the pial vessels were demonstrated by fluorescent histochemical techniques specific for catecholamines. However, in the absence of changes in arterial blood pressure and arterial blood carbon dioxide tension, pial precapillary vessels showed no change in caliber in response to stimulation of the ipsilateral superior cervical ganglion. These results show that pial precapillary vessels are not subject to vasoconstriction probably because they lack sufficient receptors for the catecholamine neurotransmitter.
Microvascular Responses to Alterations in Oxygen Tension
Authors: Duling Brian R.
Published: June 2012

The changes in microvascular diameter and perivascular oxygen tension resulting from alterations in suffusion solution Po
2
were investigated in a study of the participation of oxygen in the regulation of blood flow. Diffusion gradients for oxygen were altered by changing the Po
2
of a solution covering the surface of the hamster cheek pouch. As the solution Po
2
was raised from a low of 11 mm Hg, perivascular Po
2
of the large arterioles initially decreased to a minimum at approximately 40 mm Hg and then increased progressively as solution Po
2
was elevated further. Arterial capillary and tissue Po
2
remained relatively constant over a range of solution oxygen tensions between 11 and 40 mm Hg, suggesting that either the precapillary sphincters or the terminal arterioles were active in regulating tissue Po
2
as the input of O
2
from the solution was increased. The arterioles constricted as solution Po
2
was elevated. Average arteriolar diameter decreased by 13% as solution Po
2
increased from 11 to 47 mm Hg. A more pronounced constriction of 20% occurred when solution Po
2
was increased from 11 to 84 mm Hg. These experiments indicated that the response of large and small arterioles was not mediated by a direct effect of oxygen on the vascular smooth muscle, since decreases in perivascular oxygen tension were coincident with decreases in vascular diameter in these vessels over a range of solution Po
2
between 11 and 47 mm Hg. The data did not distinguish between a direct and an indirect effect of oxygen on the vascular smooth muscle of the terminal arterioles and precapillary sphincters. However, the oxygen tensions measured at these sites (18-30 mm Hg) required that the vascular smooth muscle cells respond to altered oxygen tension at levels higher than those which have been demonstrated experimentally.
Electrophysiological Properties of the Rabbit Sinoatrial Perinodal Fibers
Authors: Strauss Harold C. , Bigger J. Thomas
Published: June 2012

In the rabbit, the sinus node is surrounded by a group of cells which we have termed perinodal fibers. Since sinus node impulses preferentially proceed to the crista terminalis and then spread to the rest of the atrium, we selected the zone of perinodal fibers lying between the sinus node and the crista terminalis for study. Values of transmembrane potentials and the maximum rate of rise (Vmax) of phase 0 in these perinodal fibers were intermediate between those in sinus node and crista terminalis fibers. Values of phase-0 amplitude and Vmax obtained from perinodal fibers near the crista terminalis were greater than those values from perinodal fibers near the sinus node. Membrane responsiveness was determined using premature stimulation or potassiuminduced depolarization. In perinodal fibers, recovery of phase-0 Vmax of premature responses to peak value showed a strong time dependence outlasting full repolarization and extending throughout diastole. The increasing values of Vmax during diastole occurred despite spontaneous diastolic depolarization. When time was minimized as a variable, using potassium-induced depolarization, Vmax was also shown to be dependent on membrane activation voltage. In addition, recovery of phase-0 amplitude of premature responses to peak value was shown to be somewhat time dependent. The resistance of phase-0 amplitude and Vmax to the depolarizing effects of increased external potassium concentration was greater in perinodal fibers than it was in ordinary a trial fibers. We were able to show that premature responses capable of exciting the crista terminalis blocked in the zone of perinodal fibers.
Comparison of Afferent Activity of Canine Aortic and Sinus Nerves
Authors: Pelletier Conrad L. , Clement Denis L. , Shepherd John T.
Published: June 2012

Pressure-dependent changes in afferent activity in the aortic and the sinus nerves were studied in 17 anesthetized dogs that were artificially ventilated with oxygen. Systemic arterial blood pressure was varied either continuously or in steps over the range of mean aortic blood pressure from 220 to 50 mm Hg with a pressurized reservoir connected to the abdominal aorta. Multifiber preparations from 20 aortic and 8 sinus nerves were used, and stimulusresponse curves were defined by measuring the mean impulse frequency at the various levels of pressure. Heart rate and pulse pressure were similar during recordings from both nerves. The two curves were S-shaped, with that for the aortic nerve being to the right of that for the sinus nerve. The change in activity was approximately linear from 200 to 120 mm Hg (mean aortic blood pressure) in the aortic nerve and from 180 to 80 mm Hg in the sinus nerve; there was no significant change in impulse frequency below mean blood pressures of 100 and 70 mm Hg, respectively. The threshold systolic blood pressure was 95 ± 3 (SE) mm Hg for the aortic receptors and 62 ± 4 mm Hg for the carotid sinus receptors. Thus, in the dog, the aortic baroreceptors are involved mainly in the control of high blood pressure, whereas at lower pressures the major control occurs through the carotid sinus baroreflex.
Effects of Added or Substituted Potassium Ion on
45
Ca Movements in Rabbit Aortic Smooth Muscle
Authors: GOODMAN FRANK R. , WEISS GEORGE B. , WEINBERG MICHAEL N. , POMARANTZ STANLEY D.
Published: June 2012

The effects of elevated potassium ion (K
+
) concentration on radioactive calcium (
45
Ca) movements and distribution were investigated in media-intimal strips prepared from rabbit aortic smooth muscle.
45
Ca uptake was measured in either normal (1.5 mM Ca
2+
) or low-Ca (0.1 mM Ca
2+
) solutions. In low-Ca solutions, elevating the K
+
concentration either by substituting equimolar (165.4 mM) K
+
for sodium (Na
+
) (substituted-K solution) or by increasing K
+
concentration to 80 mM (added-K solution) increased the
45
Ca uptake. Exposure of the muscle strips to high K
+
concentrations during washout of
45
Ca decreased the
45
Ca efflux into either zero-Ca or low-Ca bathing solutions. Moreover, increased K
+
concentration elicited its effects in the presence or the absence of Na
+
. The decrease in
45
Ca efflux induced by substituted-K solution was also obtained in the presence of ethylenediaminetetraacetic acid (EDTA), but prior incubation of muscles with 1.5 mM strontium (Sr
2+
) plus
45
Ca prevented this decrease in
45
Ca efflux. It would appear that the
45
Ca affected by high K
+
concentrations is at Sr-sensitive sites which are inaccessible to EDTA. If
45
Ca at these sites contributes directly to
45
Ca efflux, a shift of some of this
45
Ca to less superficial cellular sites might be responsible for the decreased efflux of
45
Ca observed in the presence of increased K
+
concentration.