bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in cardiac output and total peripheral resistance during development of renal hypertension in the rabbit: lack of confomity with the autoregulation theory.
Authors: Fletcher P J , Korner P I , Angus J A , Oliver J R
Published: June 2012

Serial measurements of cardiac output (CO), mean arterial pressure (MAP), heart rate, and total peripheral resistance (TPR), were made on unanesthetized rabbits with previously implanted Doppler flowmeters. After 2 days of control measurements the rabbits were subjected alternatively to bilateral renal cellophane wrapping (wrap group) or to sham operation and additional measurements were made 1, 2, 4, 8, 16, 25, and 32 days after operation. During the 1st week after operation changes in CO were identical in the wrap and sham-operated groups, with an overall increase to a value of 110% of control on day 4 (P less than 0.05). Thereafter CO fell gradually, reaching 75% of control by day 32 in the wrap group, but only 95% of control in the sham-operated group. When CO was expressed per unit of body weight the latter differences were somewhat reduced, but still were significant. In wrap animals MAP and TPR rose progressively to 155% and 194% of control by day 32. In the sham-operated group the corresponding increases to 108% and 118% of control were significantly smaller. The MAP and TPR of the renal wrap rabbits exceeded the values in sham-operated rabbits, even over the 1st week after operation, by an average for MAP of 8.6 +/- 1.4% (P less than 0.001), and for TPR of 8.0 +/- 2.5% (P = 0.01). The results suggest that the changes in CO during the 1st week were a nonspecific consequence of the preceding wrap or sham operation. They bore no apparent relationship to the subsequent development of the hypertension which was "resistance-mediated" from the earliest stages. We conclude that the present findings for the rabbit differ from those reported for other species and do not conform to the changes predicted by the autoregulation theory of the pathogenesis of hypertension.
Changes in coronary and collateral flows and adequacy of perfusion in the dog following one and three months of circumflex occlusion.
Authors: Scheel K W , Galindez T A , Cook B , Rodriguez R J , Ingram L A
Published: June 2012

We investigated changes in circumflex, left anterior descending (LAD), and right coronary artery flows as well as changes in collateral flows to these vessels after long-term circumflex occlusion. Coronary and collateral flows of each vessel were determined simultaneously in an isolated heart preparation in which the vasculature was maximally dilated with dipyridamole. The resistances as related to total heart weight of the circumflex, LAD, and right coronary arteries of 16 control dogs were found to be 0.59 +/- 0.06, 0.93 +/- 0.09, and 2.37 +/- 0.17 (mean +/- SEM) mm Hg/[(ml/min)/100 g], respectively. Total minimal coronary resistance was 0.21 +/- 0.01. In 10 dogs subjected to occlusion for 1 month no significant change in circumflex coronary resistance was observed, but the resistance of the unimpaired vessels decreased significantly. The resistances of the LAD and right coronary arteries were 0.66 +/-0.04 and 1.72 +/- 0.13, respectively. Both values were considerably less (P less than 0.01) than control. In nine dogs subjected to occlusion for 3 months the resistance of the unimpaired LAD and right arteries, as well as the circumflex coronary resitance, were not significantly different from control. We also found that retrograde flows for all vessels increased 7-fold after 1 month and 10.5-fold (relative to control) after 3 months of occlusion. From these data we conclude that vascular adaptations, which occurred in response to an ischemic stimulus, are responsible for the long-term regulation of the metabolic needs of the myocardium.
Quantification of human atrioventricular nodal concealed conduction utilizing S1S2S3 stimulation.
Authors: Wu D , Denes P , Dhingra R C , Wyndham C R , Rosen K M
Published: June 2012

We studied antegrade concealed conduction of atrial extrastimuli (A2) that blocked in the atrioventricular (AV) node in eight subjects, using a third extrastimulus (A3), coupled at decreasing coupling intervals to A2. Three A1-A2 intervals were tested in each subject: late (just shorter than AV nodal effective refractory period), intermediate, and early (just longer than atrial functional refractory period). The curves relating the following variables were constructed for each A2: A1-A3, H1-H3 and A2-A3, A3-H3. The former was compared to the control A1-A2, H1-H2 curve. Concealment of A2 was demonstrated in all eight subjects at the three tested values of A1-A2. The A2-A3, A3-H3 curve allowed analysis of AV nodal conduction time (A3-H3) and AV nodal recovery time (defined as the shortest A2-A3 at which the impulse conducted to the His bundle) at identical values of A2-A3. In all subjects the timing of blocked A2 had minimal effect on both AV nodal conduction time and recovery time. In five of the eight subjects a late A2 sporadically conducted to the His bundle. Conduction of A2 to the His bundle resulted in marked lengthening of both AV nodal conduction and recovery times. Concealed conduction of A2 was always demonstrated, but the degree of concealment was relatively fixed, whether A2 was an early, intermediate, or late blocked premature beat. Slow conduction of A2 had a much greater effect than concealment of A2 on subsequent impulse conduction.
Reflex vascular capacity reduction in the dog.
Authors: Rothe C F
Published: June 2012

The maximum degree and time course of active reflex venoconstriction in chloralose-anesthetized dogs was studied. The mean circulatory filling pressure (Pmc) was measured by fibrillating the heart and rapidly pumping blood from the aorta to the vena cava until the systemic arterial pressure equaled the central venous pressure. Ventricular fibrillation was continued for 1 minute and was assumed to induce maximal sympathetic discharge to the capacity vessels. Blood was removed to maintain the Pmc constant at the level determined at 8 seconds after the start of fibrillation. It was necessary to remove 13.8 ml/kg by the end of 1 minute. After autonomic nervous system blockade by hexamethonium only 4.8 ml/kg were removed to hold the Pmc constant. Thus, in conclusion, the maximal degree of active venoconstriction induced by circulatory arrest was 9.0 ml/kg during the 1st minute of cardiac fibrillation. A basal capacity vessel tone was present, equivalent to 10 ml/kg under the experimental conditions used.
Quantification of baroreceptor influence on arterial pressure changes seen in primary angiotension-induced hypertension in dogs.
Authors: Cowley A W , DeClue J W
Published: June 2012

We studied the role of the sino-aortic baroreceptors in the gradual development of hypertension induced by prolonged administration of small amounts of angiotensin II (A II) in intact dogs and dogs with denervated sino-aortic baroreceptors. Short-term 1-hour infusions of A II(1.0-100 ng/kg per min) showed that conscious denervated dogs had twice the pressor sensitivity of intact dogs. Long-term infusions of A II at 5.0 ng/kg per min (2-3 weeks) with continuous 24-hour recordings of arterial pressure showed that intact dogs required 28 hours to reach the same level of pressure attained by denervated dogs during the 1st hour of infusion. At the 28th hour the pressure in both groups was 70% of the maximum value attained by the 7th day of infusion. Both intact and denervated dogs reached nearly the same plateau level of pressure, the magnitude being directly related both the the A II infusion rate and the daily sodium intake. Cardiac output in intact dogs initially decreased after the onset of A II infusion, but by the 5th day of infusion it was 38% above control, whereas blood volume was unchanged. Heart rate returned to normal after a reduction during the 1st day of infusion in intact dogs. Plasma renin activity could not be detected after 24 hours of A II infusion in either intact or denervated dogs. The data indicate that about 35% of the hypertensive effect of A II results from its acute pressor action, and an additional 35% of the gradual increase in arterial pressure is in large measure a result of baroreceptor resetting. We conclude that the final 30% increase in pressure seems to result from increased cardiac output, the cause of which may be decreased vascular compliance. since the blood volume remains unaltered.
Hierarchy of ventricular pacemakers.
Authors: Hope R R , Scherlag B J , El-Sherif N , Lazzara R
Published: June 2012

To characterize the pattern of pacemaker dominance in the ventricular specialized conduction system (VSCS), escape ventricular pacemakers were localized and quantified in vivo and in virto, in normal hearts and in hearts 24 hours after myocardial infarction. Excape pacemaker foci were localized in vivo during vagally induced atrial arrest by means of electrograms recorded from the His bundle and proximal bundle branches and standard electrocardiographic limb leads. The VSCS was isolated using a modified Elizari preparation or preparations of each bundle branch. Peacemakers were located by extra- and intracellular recordings. Escape pacemaker foci in vivo were always in the proximal conduction system, usually the left bundle branch. The rate was 43+/-11 (mean+/-SD) beats/min. After beta-adrenergic blockade, the mean rate fell to 31+/-10 beats/min, but there were no shifts in pacemaker location. In the infarcted hearts, pacemakers were located in the peripheral left bundle branch. The mean rate was 146+/-20 beats/min. In isolated normal preparations, the dominant pacemakers usually were in the His bundle, firing at a mean rate of 43+/-10 beats/min. The rates of pacemakers diminished with distal progression. In infarcted hearts, the pacemakers invariably were in the infarct zone. The mean firing rates were not influenced by beta-adrenergic blockade. The results indicate that the dominant pacemakers are normally in the very proximal VSCS, but after myocardial infarction pacemaker dominance is shifted into the infarct. Distribution of pacemaker dominance is independent of sympathetic influence.
Oxygen Consumption of the Completely Isolated Dog Heart In Fibrillation
Authors: JARDETZKY OLEG , GREENE ERNEST A. , LORBER VICTOR
Published: June 2012

Evidence is presented, that in the completely isolated nonworking dog heart oxygen consumption is higher during a period of electrically induced fibrillation than during a period of rhythmical contraction and that this increase is not due to the electric stimulus per se.
The Effect of Potassium on the Occurrence of Petechial Hemorrhages in Renal Hypertensive Rabbits
Authors: GORDON DAVID B. , DRURY DOUGLAS R.
Published: June 2012

Administration of extra potassium to rabbits with renal hypertension reduces the incidence and severity of petechial hemorrhages. It also enables the animals to sustain higher blood pressure levels. Potassium apparently protects the vascular system to some extent against the damage caused by hypertension.
Estimation of the Residual Volume of the Ventricle of the Dog's Heart by Two Indicator Dilution Technics
Authors: HOLT J. P.
Published: June 2012

A dye dilution and an electric conductivity method for measuring end-diastolic volume and stroke volume of the left ventricle are described, and equations for the calculation of stroke volume are given. When dye is injected "instantaneously" into the left ventricle during diastole, the aortic dye concentration-time curve obtained is a step-like curve and not a smooth curve. The ventricle empties itself in a "fractional" manner, approximately 46 per cent of its end-diastolic volume being ejected with each stroke and 54 per cent remaining in the ventricle at the end of systole.
An Experimental Study of Burger Triangles Constructed From Toad Hearts in Situ
Authors: ZAO ZANG Z.
Published: June 2012

The present paper presents a method of constructing Burger triangles directly from living toad hearts in situ. Depolarization and repolarization Burger triangles from same toads were almost identical. It was shown, that the Burger triangle is more accurate than the Einthoven triangle. The two expedients of Brody, which simplify the use of the Burger triangle, are illustrated. Burger triangular shapes from toads approximate those of Wilson, constructed from human subjects with a current dipole on thorax.
Effect of a Cardiac Glycoside (Cedilanid) on the Sodium and Potassium Balance of the Human Heart
Authors: GONLUBOL F. , SIEGEL A. , BING R. J.
Published: June 2012

Previous studies on the isolated heart have demonstrated that digitalis glycosides can mobilize potassium from the heart muscle. Using catheterization of the coronary sinus of dogs' hearts, it could also be shown that the injection of acetyl strophanthidin results in negative myocardial balances of potassium and in positive balances of sodium. The results described in this report, using Cedilanid in therapeutic dosages, indicate that this glycoside has no effect on the sodium and potassium balance of the human heart. A significant increase in potassium concentration in arterial and coronary sinus blood occurred. The findings suggest that Cedilanid, in therapeutic doses, causes potassium liberation primarily from extracardiac tissues.
Effects of Beta-Sitosterol on Regression of Cholesterol Atherosclerosis in Rabbits
Authors: BEHER WILLIAM T. , ANTHONY WILLIAM L. , BAKER GIZELLA D.
Published: June 2012

Feeding β-sitosterol to atherosclerotic rabbits slightly increased the regression of plasma and liver cholesterol. However, β-sitosterol had no effect on aorta lipid, cholesterol or plaque regression.
Partial Separation of an Oxytocic Principle from Preparations of Angiotonin
Authors: BUMPUS F. MERLIN , SCHWARZ HANS , PAGE IRVINE H.
Published: June 2012

Partially purified angiotonin preparations have been shown to contain both oxytocic and pressor activity. However, they do not parallel each other in samples of differing purity. Methods for their partial separation and purification are described.
The Image Tetrahedron in Man Determined by Reciprocal Stimulation of a Tridimensional Esophageal Electrode
Authors: HIRSCH JACOB I. , BRILLER STANLEY A. , KOSSMANN CHARLES E. , Marchand Nathan
Published: June 2012

The anatomic apices of a tetrahedron were located on the image surface of living man by reciprocal stimulation of an electrode placed in the esophagus at the assumed electric center of the heart. The rectilinear components of the three-dimensional electrode were not oriented with respect to the axes of the body. Therefore, it was possible to determine the shape of the image tetrahedron but not its orientation in the body. The method is applicable to living man with the electrode placed at any assumed electric center of the heart.
Left Ventricular Dimensions Recorded by Sonocardiometry
Authors: RUSHMER ROBERT F. , FRANKLIN DEAN L. , ELLIS RICHARD M.
Published: June 2012

A new technic for continuously recording the dimensions of internal organs in intact unanesthetized animals has been developed as a modification of sonar technics. A sound is emitted by a small barium titanate crystal mounted on one side of the left ventricle, and the time required for the sound waves to pass through the chamber to another crystal on the opposite side is monitored 1,000 to 2,500 times/sec. Such crystals have continued to function reliably for more than 3 months after installation in the animal. Changes in left ventricular diameter have been recorded during spontaneous cardiac responses to various conditions including physical exertion on a treadmill.
Effect of Ganglionic Blocking Agents Upon Blood Flow and Resistance in the Superior Mesenteric Artery of the Dog
Authors: TRAPOLD JOSEPH H. , Sullivan Joan G.
Published: June 2012

The response of the mesenteric vascular circuit of anesthetized dogs to a group of ganglionic blocking agents has been studied. The results demonstrate that these agents produce a decrease in blood pressure, blood flow and vasomotor activity of the mesenteric bed and either no change or a decrease in mesenteric resistance. When the perfusing pressure to the mesenteric artery was maintained at control levels an increase in flow with a concomitant decrease in mesenteric resistance followed the injection of the blocking agents. The present report presents experimental evidence that our preliminary report was in error.
Ventricular Suction in the Turtle
Authors: KRANER JAMES C. , OGDEN ERIC
Published: June 2012

In two different experimental environments the isolated turtle ventricle was found to fill and eject blood in the absence of a positive filling pressure. It is concluded that the ventricle can "suck" fluid using energy liberated from its wall during diastole.
Separation of primary and secondary cardiovascular events in systemic anaphylaxis.
Authors: Zavecz J H , Levi R
Published: June 2012

The purpose of this investigation was to differentiate primary cardiac participation in systemic anaphylaxis from a cardiac reaction secondary to respiratory distress. Hemocyaninsensitized guinea pigs were anesthetized with sodium pentobarbital and artifically ventilated. The chest was opened and the left ventricle cannulated. The electrocardiogram, bronchial resistance, arterial blood pressure, and left ventricular pressure and its first derivative were recorded. Following intravenous administration of antigen, the sinus rate increased by about 50-60 beats/min, left ventricular dP/dt increased by a factor of 3, and mean arterial pressure doubled. Conduction disturbances occurred in all of the experiments and ventricular fibrillation in four of six. These changes were concomitant with a 4-fold rise in bronchial resistance. To separate the cardiac and respiratory components, antigen was administered directly into the left ventricle to expose the heart to antigen before the lungs. The intracardiac challenge resulted in increases in sinus rate and left ventricular and arterial pressure quantitatively similar to changes recorded from guinea pigs after the intravenous challenge. However, all these changes preceded the rise in bronchial resistance by 60 seconds. Arrhythmias occurred as frequently as with the intravenous challenge. Our findings show that by use of an appropriate route for administration of antigen, cardiovascular and respiratory components of systemic anaphylaxis can be separated. Our data also indicate that anaphylactic cardiovascular changes can be dissociated temporally into two sets of events: an initial primary cardiac reaction caused by intracardiac release of histamine and a subsequent cardiovascular reaction secondary to systemic release of mediator.
The intrinsic innervation of the canine heart: a functional study.
Authors: Priola D V , Spurgeon H A , Geis W P
Published: June 2012

The intrinsic innervation of the heart has been described anatomically but seldom, functionally. These experiments were designed to verify and to evaluate the influence of intrinsic neural activation on the contractility of the atria and ventricles. Nine mongrel dogs underwent total cardiac denervation using the Geis two-stage technique. Following recovery, they were placed on total cardiopulmonary bypass. Balloons were inserted into each cardiac chamber, filled with saline, and used to record atrial and ventricular isovolumic pressures in response to intracoronary drug injections. The hearts were paced to avoid rate changes. Acetylcholine (ACh) (0.05-1.0 mug) was given to assess direct effects on the myocardium; nicotine (NIC) (25-200 mug) was used to produce indirect inotropic effects. d-Tubocurare (dTC) (1.0-2.5 mg) and tetrodotoxin (TTX) (10-30 mug) were used to differentiate the direct and the indirect effects. Both ACh and NIC produced qualitatively similar negative inotropic responses in both atria and ventricles. dTC usually produced a significantly greater blockade of responses to NIC than toACh. TTX administered to 12 other denervated dogs to differentiate direct and neurally mediated responses, completely blocked NIC-induced negative inotropy but did not change responses to ACh. The data show that (1) the intrinsic cardiac innervation can exert significant negative inotropic effects on atria and ventricles (10 to greater than 30%); (2) there is no functional evidence of participation by chromaffin cells in the inotropic responses to intrinsic nerve activation; (3) the negative inotropy produced by NIC is sensitive to dTC and, especially, TTX blockade. This is consistent with the mechanism of action being intrinsic neural stimulation.
Quantification of apolipoprotein B in grossly normal human aorta.
Authors: Hoff H F , Heideman C L , Gaubatz J W , Gotto A M , Erickson E E , Jackson R L
Published: June 2012

A quantitiative electroimmunodiffusion (EID) assay was developed for apolipoprotein B (apoB), the major apoprotein of human plasma low density lipoproteins (LDL) and very low density lipoproteins (VLDL). Specificity, sensitivity (30-200 ng) and reproducibility (11%) were established. We used this system to determine the amount of buffer-soluble apoB in supernatant fractions from homogenates of the intima from grossly normal human aortas. Assays of whole tissue minces yielded only one-third of the apoB in supernatant fractions. Intimal homogenates contained 0.34-18.45 mug of apoB/mg of tissue, dry weight (mean 5.42 +/- 3.95 SD). We also found that no apoB was detected in the homogenates of adjacent tunica media. Furthermore, most of the intimal apoB was found in the LDL density (d) fraction (d 1.006-1.063) after differential ultracentrifugation, while the VLDL (d less than 1.006) fraction contained only negligible amounts of apoB. By electron microscopy, it was determined that the LDL density fraction contained particles 200-250 A in diameter which were similar in size to plasma LDL. These results suggest that grossly normal aortas contain significant quantities of intact LDL.
Hemodynamic effects of rapid atrial stimulation in adult and young dogs.
Authors: Truccone N J , Krongrad E
Published: June 2012

We evaluated the use of rapid atrial stimulation (RAS) to produce 2:1 atrioventricular (AV) block as a method for treating supraventricular tachycardias. We studied the cardiovascular hemodynamic changes before and after block in eight adult dogs and nine young dogs (3-4 1/2 weeks old). In each dog an electrocardiogram; cardiac index; aortic, pulmonary, and left ventricular (LV) systolic and end-diastolic pressures; and LV (dp/dt) p were recorded simultaneously and pulmonary ans systemic resistances were calculated. Measurements were obtained during (1) the control state, (2) RAS with maximal 1:1 AV conduction, (3) RAS with 2:1 AV block, and (4) RAS with 1:1 AV conduction at 50% of the rate which resulted in 2:1 AV block. Comparison of the hemodynamic effect of RAS with maximal 1:1 AV conduction and hemodynamics in the control state showed that there was a significant decrease in cardiac index and aortic mean pressure of 39% and 15%, respectively. When hemodynamic changes during RAS with 2:1 AV block were compared with those during RAS with maximal 1:1 AV conduction, cardiac index, LV systolic pressure, and aortic mean pressure increased by 52%, 17%, and 22%, respectively. LV (dp/dt) p increased by 20% and was significantly higher during RAS with 2:1 AV block than at higher ventricular rates obtained with RAS and maximal 1:1 AV conduction. We found that in this acute study the hemodynamic findings for the young dogs were similar to those for adult dogs. The data suggest that (1) significant hemodynamic improvement is obtained by RAS causing 2:1 AV block when compared to higher ventricular rates associated with 1:1 AV conduction; (2) in addition to increasing the diastolic filling period, reducing the very high ventricular rates improves the cardiac contractile state, and (3) RAS and 2:1 AV block may provide a useful technique for the management of some patients with intractable supraventricular tachycardia.
Effect of physical training on calcium transport by rat cardiac sarcoplasmic reticulum.
Authors: Penpargkul S , Repke D I , Katz A M , Scheuer J
Published: June 2012

Cardiac microsomes enriched in fragmented sarcoplasmic reticulum (SR) were isolated from hearts of physically trained rats and were compared to those from sedentary rats. Preparations from conditioned rats were found to transport calcium to a greater extent than those from sedentary rats both in the absence and in the presence of 1 mM oxalate. Higher oxalate concentrations abolished the differences in calcium accumulation by cardiac microsomes from conditioned and sedentary rats and indicated a qualitative change in SR from conditioned hearts. We conclude that the increased transport by SR from hearts of conditioned rats may provide one mechanism for enhanced contractile reserve in these hearts.
Stimulation of cholesterol esterification in rhesus monkey arterial smooth muscle cells.
Authors: St Clair R W , Smith B P , Wood L L
Published: June 2012

The influence of homologous high density lipoprotein (HDL) and low density lipoprotein (LDL) and of whole hypercholesterolemic serum on the esterification of oleic acid and cholesterol was studied in rhesus monkey arterial smooth muscle cells. Whole hypercholesterolemic serum and isolated LDL stimulated cholesterol esterification as much as 10-fold using either cholesterol-1,2-3H or oleate-1-14C as substrate. At the same concentrations of cholesterol, HDL stimulated cholesterol esterification to a lesser extent, to a maximum of 3-fold. Associated with the stimulation of cholesterol esterification by LDL or whole hypercholesterolemic serum was a greater than 10-fold increase in the cholesteryl ester content of the arterial smooth muscle cells. Esterification to cholesterol reached a maximum after 8-12 hours of culture with either hypercholesterolemic serum or LDL. The stimulation of esterification was specific for esterification to cholesterol because there was little change in incorporation of fatty acid into triglycerides and phospholipids. These studies provide further evidence that a major consequence of the interaction of plasma LDL with the cellular elements of the arterial wall is a stimulation of cholesterol esterification. These studies, coupled with the observation that cholesteryl esters, more than any other single component, increase in the atherosclerotic artery, suggest an important role of a stimulation in cholesterol esterification in the pathogenesis of atherosclerosis.
Inhibition of sympathetic neurotransmission in canine blood vessels by adenosine and adenine nucleotides.
Authors: Verhaeghe R H , Vanhoutte P M , Shepherd J T
Published: June 2012

Adenosine and the adenine nucleotides caused a greater relaxation of strips of canine saphenous vein and tibial artery when they had been contracted by nerve stimulation than by exogenous norepinephrine. An infusion of adenosine into the dogs' lateral saphenous vein, perfused at constant flow, caused a greater relaxation of this vein when constricted by electrical stimulation of the lumbar sympathetic chain than by exogenous norepinephrine. That this difference was due to inhibition by these compounds of the output of neurotransmitter from the sympathetic nerve endings was demonstrated by column chromatographic analysis of the radioactivity in the superfusion fluid of vein strips, previously incubated with tritiated norepinephrine. Both adenosine and adenosine triphosphate (10(-5) M) reduced the efflux of 3H-norepinephrine during nerve stimulation with electrical impulses. Adenosine also reduced the efflux caused by potassium (30 mM), but not that caused by tyramine (6 X 10(-6) M). Theophylline antagonized the inhibitory effect of adenosine on the sympathetic neurotransmission. We found that at 4 X 10(-4) M adenosine triphosphate still caused a decreased efflux of neurotransmitter during electrical stimulation, but with adenosine the 3H-norepinephrine efflux no longer decreased and the overflow of deaminated compounds increased. Furthermore, the same concentration of adenosine increased the efflux of 3H-norepinephrine and deaminated compounds in unstimulated strips, and the increase of 3H-norepinephrine was enhanced after monoamine oxidase inhibition. Thus, we conclude that at higher concentrations adenosine increases the intraneuronal leakage of norepinephrine out of the storage vesicles.
Characteristics of rat aortic baroreceptors with nonmedullated afferent nerve fibers.
Authors: Thorén P , Saum W R , Brown A M
Published: June 2012

Nervous activity was recorded from nonmedullated afferent baroreceptor fibers in the left aortic nerve of normotensive rats. The aortic arch was perfused in vitro with oxygenated Krebs-Henseleit solution. Two different patterns of aortic C fiber discharge were found. One type (5 of 29 fibers) had a regular discharge at constant pressure whereas the other type had an irregular discharge. The differences between the two types were independent of the mean steady state rates of discharge. The average threshold pressure for the receptors with the regular discharge was 87 mm Hg (range, 65-125); it was 152 mm Hg (range, 85-260) for the irregularly discharging receptors. During a pressure step the receptors in either group normally showed an initial high frequency burst of activity and a sustained discharge which had a lower frequency. Furthermore, the peak discharge and the sustained discharge were lower on the average in the receptors with the irregular type of firing. We also found that addition of norepinephrine to the perfusate lowered threshold. Since unmyelinated axons are the predominant fiber type in the rat aortic nerve and since some receptors are activated at physiological pressures they may contribute to the tonic control of blood pressure. Their effects should be particularly important when the blood pressure is increased.
On the mechanism underlying the action of D-600 on slow inward current and tension in mammalian myocardium.
Authors: Nawrath H , Eick R E , McDonald T F , Trautwein W
Published: June 2012

D-600 the methoxy derivative of verapamil, is said to affect the force of cardiac contraction and the slow inward current (LSi) specifically by reducing the membrane conductance for Ca2+ (gsi). However, it is apparent that many effects of D-600 cannot be adequately explained solely by an effect on gsi. We studied the effects of D-600 on membrane current and tension of cat papillary muscle, using a conventional single sucrose gap voltage clamp technique. The results indicate that D-600 not only reduces the maximal Ca conductance but also, depending on concentration and duration of exposure, alters both the kinetics of the Ca-carrying system and the amplitude of the steady state outward current. No changes in the steady state activation and inactivation variables or in the rate of Isi inactivation were found. However, a substantial increase in the time to peak Lsi, as much as 7 times normal, was observed after exposure to D-600 (0.5 X 10(-6) to 2.0 X 10(-6) M) for at least 20 minutes. Because approximately only 75% of the reduction in Lsi induced by D-600 could be attributed to change in the maximum value of gsi (gsi), we conclude that the change in time to peak and about 25% of the reduction in Isi must be due to a change in the activation kinetics of the Ca-carrying system, Calculations suggest that the time to 70% activation of gsi can be prolonged to as much as 10 times normal by prolonged exposure to negatively inotropic concentrations of D-600.
Beneficial effect of arachidonic acid during hemorrhagic shock in the dog.
Authors: Flynn J T , Lefer A M
Published: June 2012

Arachidonic acid (AA), precursor of the bisenoic prostaglandins was infused at a rate of 120 mug/kg per min into the vena cava of dogs subjected to hemorrhagic shock to assess the effects of stimulation of the prostaglandin (PG) synthetase system on the shock state. Hemorrhagic shock was induced by bleeding to a mean arterial blood pressure (MABP) of 40 mm Hg for 150 minutes followed by reinfusion of all remaining shed blood. In sham shock dogs receiving AA vehicle (0.1 M Na2C03), there were no significant changes in MABP, superior mesenteric artery flow (SMAF), renal artery flow (RAF), PGF2 or PGF2alpha concentrations, or in cathepsin D or myocardial depressant factor (MDF) activities during a 260-minute experimental period. During oligemia, untreated hemorrhagic shock dogs exhibited dramatic reductions in MABP, SMAF, and RAF which were transiently restored following reinfusion, but markedly decreased 100 minutes after reinfusion. Cathepsin D, MDF, PGE2, and PGF2alpha values increased significantly in these dogs. AA given during oligemia did not prevent changes in SMAF or RAF, but maintained MABP at near-normal values after reinfusion. AA also significantly protected against the plasma accumulation of both cathepsin D an MDF is hemorrhagic shock dogs. Circulating PGF2alpha and PGE2 values increased rapidly in AA-treated dogs and plateaued at 3.6 and 4.8 times control values, respectively, during oligemia. Hemorrhagic shock dogs receiving AA plus Na meclofenamate, a PG synthetase inhibitor, were not significantly different from shock dogs receiving vehicle except that the circulating PG concentrations did not increase. Thus, products of the PG synthetase system appear to prevent the plasma accumulation of lysosomal hydrolases nand of MDF, and may significantly preserve MABP after hemorrhagic shock in the dog.
Development of left ventricular hypertrophy in young spontaneously hypertensive rats after peripheral sympathectomy.
Authors: Cutilletta A F , Erinoff L , Heller A , Low J , Oparil S
Published: June 2012

The effects of peripheral sympathectomy with nerve growth factor antiserum (NGFAS) on blood pressure, systemic hemodynamics, myocardial function, myocardial hypertrophy, and renin were studied in male spontaneously hypertensive (SH) rats of the Okamoto strain and normotensive control Kyoto-Wistar (WKY) rats. NGFAS prevented the developing of hypertension in the SH rats but did not alter blood pressure in the WKY rats. The NGFAS-treated SH rats developed the same hemodynamic abnormalities as the sham-treated rats, including increased peripheral vascular resistance and depressed cardiac output; Indices of left ventricular performance, including peak flow velocity, stroke power, stroke work, dP/dtmax, and flow acceleration (dF/dt), were diminished in the SH rats compared to the WKY rats. NGFAS treatment further depressed ventricular function in the SH rats, but had little effect on the WKY rats; Plasma renin activity in both the SH and WKY rats was unaffected by NGFAS treatment. Although NGFAS treatment effectively prevented the development of hypertension in the SH rats, it did not influence the development of left ventricular hypertrophy as reflected by increases in left ventricular mass, RNA, DNA, and hydroxyproline content. The data suggest that the development of myocardial hypertrophy and myocardial dysfunction in the SH rat is in part independent of hypertension and plasma renin activity.
Effects of intermittent pressure loading on the development of ventricular hypertrophy in the cat.
Authors: Marcus M L , Eckberg D L , Braxmeier J L , Abboud F M
Published: June 2012

Although the effects of persistent pressure loading on the development of ventricular hypertrophy have been studied extensively, the effects of intermittent pressure loading have not been examined. To study the effects of intermittent pressure loading we subjected the right ventricle of cats to intermittent pulmonary artery constriction over a 2-week period. Two intermittent pressure loading schedules were employed. The first consisted of a right ventricular systolic pressure of 60 mm Hg for 3.5 days and normal right ventricular pressure for 3.5 days; and the second consisted of a right ventricular systolic pressure of 60 mm Hg for 2.3 days and normal right ventricular pressure for 4.7 days. The intermittent pressure-loaded cats were compared with normal unoperated controls, sham-operated controls, and cats with persistent right ventricular pressure load for either 1-week or 1- to 2-month duration. The data indicate that intermittent pressure loading caused significant right ventricular hypertrophy. Since significant residual ventricular hypertrophy was present in both intermittent pressure loading groups, regression of ventricular hypertrophy involves a slower process than the progression of hypertrophy.
Partition of xenon and iodoantipyrine among erythrocytes, plasma, and myocardium.
Authors: Carlin R , Chien S
Published: June 2012

A new method was developed for determining directly the distribution of 133Xe between red cells and plasma in vitro without an air-fluid interface; the partitioning of 133Xe and 133-i-iodantipyrine between blood and myocardium was investigated in the dog in situ. The red cell-plasma partition coefficient for 133Xe (lambdacpX, unit: ml/ml) at 37 degrees C was 2.27 +/- 0.07 (mean +/- SD) for human blood and 3.31 +/- 0.06 for dog blood. The red cell-plasma partition coefficient for 131I-iodantipyrine (lambdacpI, ml/ml) was 0.75 +/- 0.04 for human blood and 0.97 +/- 0.03 for dog blood. lambdacpX and lambdacpI did not change significantly after the intravenous administration of sodium pentobarbital (30 mg/kg) into the dog. lambdacpX of dog blood varied inversely with temperature, whereas lambdacpI showed very little change with temperature. The blood-left ventricle partition coefficient for 133Xe (lambda'btX, corrected for trapped blood) varied directly with directly with red cell volume fraction (H): lambda'btX = 1.32 + 2.00 H. Blood-left ventricle partition coefficient for 131I-iodoanitpyrine did not vary significantly with H. The results support the concept of a three-compartment partition of the indicator among erythrocytes, plasma, and myocardium. The mean values (+/- SD) of the hematocrit-independent plasma-tissue partition coefficient in the left ventricle for 133Xe and 131I-iodoantipyrine were 1.08 +/- 0.16 and 1.54 +/- 0.20 g/ml, respectively.
Histamine receptors in the coronary circulation of the dog. Effects of mepyramine and metiamide on responses to histamine infusions.
Authors: Giles R W , Heise G , Wilcken D E
Published: June 2012

The effect of histamine on coronary blood flow (CBF) was studied in anaesthetized grayhounds. CBF and systemic blood pressure were measured using electromagnetic flow transducers and catheters in the aorta during infusions of drugs into the left circumflex coronary artery. Histamine infusions (5, 10, and 20 microng/min) produced dose-related increases in CBF without changing heart rate or blood pressure. Metiamide (100 microng/min) given simultaneously produced a parallel displacement of the histamine dose-response curve to the right (P less than 0.05) with a dose ratio of 2. Mepyramine (100 microng/min) produced a larger parallel displacement of the dose-response curve (dose ratio = 4). Together, metiamide and mepyramine greatly reduced the histamine response (dose ratio = 16), showing that the metiamide blockade is augmented in the presence of mepyramine. Similarly, mepyramine blockade is augmented in the presence of metiamide. The increase in CBF produced by histamine infusion (20 microng/min) was similar to the peak flow response of reactive hyperemia following 8-second occlusions. However, mepyramine and metiamide together had no effect on the peak flow response, duration, or total repayment of flow debt in reactive hyperemia. These results show that histamine-induced coronary vasodilation is mediated by both H1 and H2 receptors. However, the vasodilation of reactive hyperemia after brief coronary artery occlusions does not appear to involve histamine.
Reflex regulation of sympathetic activity in the spontaneously hypertensive rat.
Authors: Coote J H , Sato Y
Published: June 2012

The influence that the pressure-sensitive receptors in the cardiovascular system have on renal nerve activity and on heart rate was compared in normotensive rats (NTR) and spontaneously hypertensive rats (SHR). The cardiovascular receptors were stimulated by raising the blood pressure (BP) with intravenous phenylephrine. The duration of silence in the record of renal sympathetic nerve activity produced by a number of different rises in BP was measured. We found that the pressure that was just able to produce a silence in the nerve activity (threshold pressure) was higher in the SHR (170 mm Hg) than in the NTR (130 mm Hg). Also, comparable rises in BP above the threshold pressure in the SHR and NTR were less effective in the SHR in producing a complete inhibition of sympathetic nerve activity as judged by the short duration of inhibition. In contrast, we found that the changes in heart rate produced by rises in BP above threshold pressure were similar in NTR and SHR although the threshold pressure was somewhat higher in the latter. It was, therefore, concluded that the cardiovascular pressure receptors, apart from being reset to operate at a higher pressure level in the SHR, are less able to inhibit ongoing sympathetic activity than in the NTR. It is suggested that this is most likely due to a high sympathetic activity in the SHR.
Maximum rate of tension fall during isometric relaxation at end-systolic fiber length in canine papillary muscle.
Authors: Tamiya K , Kikkawa S , Gunji A , Hori M , Sakurai Y
Published: June 2012

We measured the characteristics of the decline in tension during isometric relaxation of canine papillary muscle. In the intact heart, relaxation begins with the isovolumic phase, but in experiments on papillary muscle previously reported the isotonic phase preceded the isometric phase during the course of relaxation. In our experiments, however, the isotonic bar was locked at the instant the muscle reached the end-systolic fiber length in order to hold the fiber at the length during the succeeding relaxation process. Therefore, we obtained a relaxation process similar to that occurring in the intact heart. The major results of these experiments are: (1) Maximum rate of the decline in tension (-dT/dtmax) is linearly related to the magnitude of total load. (2) -dT/dtmax is augmented by positive inotropic interventions and diminished by negative inotropic interventions. (3) An increase in preload results in only a slight increase in -dT/dtmax. (4) End-systolic fiber length itself is not a principal determinant of -dT/dtmax. (5) -dT/dtmax divided by total load is independent of the amount of muscle shortening. We, therefore, suggest that -dT/dtmax divided by total load cand be a useful index of the relaxation characteristics of cardiac muscle.
Contribution of prostaglandins to the renal circulation in conscious, anesthetized, and laparotomized dogs.
Authors: Terragno N A , Terragno D A , McGiff J C
Published: June 2012

The effects of an inhibitor of prostaglandin (PG) synthetase, indomethacin, were studied on renal blood flow (RBF) and mean aortic blood pressure (MABP) and related to changes in concentrations of PGs in renal venous blood under widely different experimental conditions. Although levels of PGE-like material ("PGE") in renal venous blood of the chloralose-anesthetized-laparotomized dog were 8-fold greater than in conscious dogs, viz., 0.39 vs. 0.05 ng/ml of blood, respectively, RBF and MABP were similar for each group. Indomethacin in doses as high as 10 mg/kg, iv, affected neither RBF, MABP, nor PG levels either in the conscious dog or in the anesthetized dog. However, in the anesthetized-laparotomized dog, smaller doses of indomethacin (2 mg/kg, iv) decreased RBF by more than 40% and increased MABP by 15%. This was associated with a decline in concentration of renal venous PGs to those levels observed in conscious dogs. The principal renal PG varied according to the experimental conditions. The venous levels of "PGF" were greater than "PGE" in conscious dogs, whereas in acutely stressed dogs the renal venous concentrations of "PGE" were more than 2-fold those of "PGF". Plasma renin activity was highly correlated with "PGE" levels in renal venous blood, but not with "PGF" levels. Thus, in the acutely stressed dog, the renal circulation is supported by a major PG component, withdrawal of which results in a decline in RBF. In contrast, in the conscious dog at rest, renal PGs do not appear to contribute significantly to RBF. The significance of the small basal release of PGs into the renal venous effluent of the conscious dog, which is not affected by indomethacin, remains to be determined.
The aortic bodies supplied by coronary arteries in the dog. Their contribution to the hypertensive response that follows serotonin injection.
Authors: Eckstein R W
Published: June 2012

I assessed the role of the chemoreceptors (aortic bodies) supplied by the coronary arteries in the hypertensive response induced by left atrial injection of (200 microgram serotonin) in adult anesthetized dogs. I compared the pressor response induced by serotonin during normal coronary circulation with that during exclusion of the central coronary segments from which the coronary blood supply to the aortic bodies arises. Exclusion of the central segments reduced the pressor response significantly from the control responses. Exclusion of the coronary blood supply of the aortic bodies resulted in a reduction of the control response of more than 50% in only two of the 21 dogs. I conclude that although the aortic bodies supplied by the coronary arteries play a significant role in the total hypertensive response to injected serotonin, their role usually is not predominant.
Use of calcium ionophores to determine the effects of intracellular calcium on the action potential of canine cardiac Purkinje fibers.
Authors: Gelles J M
Published: June 2012

The effects of calcium ionophores X-537A, A23187, and PR-47 on the action potential of canine cardiac Purkinje fibers were studied using standard microelectrode techniques. The ionophores hyperpolarize the membrane potential, eliminate the notch on the action potential plateau, decrease action potential duration, decrease plateau amplitude and duration, decrease spontaneous diastolic depolarization and excitability, and decrease the rate effect on action potential duration. These effects were shown to be independent of catecholamines, membrane-bound calcium, and the patency of the slow inward current channel. The effects of the ionophores depended on the presence of calcium in the external solution. A plausible interpretation of the data is that an ionophore-mediated increase in intracellular calcium shifts the voltage dependence of transmembrane potassium currents to more negative levels.
Angiotensin (A I, A II, A III) receptor characterization. Correlation of prostaglandin release with peptide degradation.
Authors: Blumberg A L , Nishikawa K , Denny S E , Marshall G R , Needleman P
Published: June 2012

We examined the ability of the angiotensins (A I, A II, A III) to release a prostaglandin E (PGE)-like substance in the isolated Krebs' perfused kidney and mesenteric vasculature of the rabbit by parallel bioassay. In the kidney, the order of potency for PGE release was A II greater than A III greater than A I with ED50's of 36, 100, and 500 pmol, respectively. In the mesenteric preparation, on the other hand, the order of potency was A III greater than A II greater than A I with ED50's of 75, 125, and 500 pmol, respectively. During one transit through the kidney 72-76% of bioassayable A I and A II was degraded. A III was 89% metabolized. In contrast, the mesenteric vasculature inactivated only 27% of A II and 23% of A III. This data suggests an inverse relationship between renal peptide degradation and PGE release. For characterization of the renal angiotensin receptor-mediating PGE release, dissociation constants (KB) of the competitive angiotensin antagonists [IIe7]-A III and [Sar1, IIe3]-A II were determined with each angiotensin. KB values of the individual antaganists were not significantly different with A I, A II, or A III; this finding suggests that one renal angiotensin receptor is involved with PGE release.