摘要:

Cross-circulation through normal recipient dogs of blood from saline-loaded donor dogs that had escaped from desoxycorticosterone acetate (DCA) resulted in a sixfold rise in renal sodium excretion in the recipients. The change occurred without a detectable alteration in filtered sodium (FNa). To investigate the locus of secretion of a humoral factor responsible for the natriuresis, a series of ablational procedures was performed in DCA-escaped, saline-loaded donors. Nephrectomy, hepatectomy, or decapitation before saline loading and cross-circulation failed to block the increase in renal sodium excretion in the recipients. Analysis of periods during cross-circulation with a decrease in FNalower than the lowest control value showed that sodium excretion was elevated significantly above control levels in experiments with normal, hepatectomized, and decapitated donors. In contrast, with nephrectomized donors the increase in sodium excretion in the recipients was negligible. This finding points to the need for further study of the kidney as a possible source of a humoral factor in the control of renal salt excretion.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The sodium salts of stearic, oleic, linoleic and linolenic acids were added to human washed platelet suspensions and platelet-rich citrated plasma. Aggregation of the platelets was measured microscopically and with a turbidimetric method. All of the fatty acids had the ability to produce aggregation when added to washed platelets, but stearic acid, a long-chain saturated fatty acid, was more potent than were the unsaturated acids when added to platelet-rich plasma. Aggregation of platelets by fatty acids required the presence of calcium ions and the aggregation was irreversible. The addition of albumin diminished the aggregating effects of fatty acids, but microscopic aggregates still formed in most instances. Subnormal aggregation was noted when sodium stearate was added to platelet-rich plasma from a patient with a severe deficiency of factor XII (Hageman factor). Thus, fatty acids are now known to have two potential thrombogenic effects: platelet aggregation and the activation of clotting factors involved in the early stages of blood coagulation.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The cholinergic innervation of the rabbit heart was studied in vitro and in vivo. An isolated preparation, which included the combined atria, S-A node, A-V node and bundle of His, was mounted so that microelectrodes could be placed in either the specialized or nonspecialized tissues. Using a roving monopolar electrode, local transmural electrical stimulation of intracardiac nerves (nerve stimulation) was applied at the A-V or the S-A node. At the A-V node it induced hyperpolarization, reduced the duration and amplitude of action potentials recorded from three regions of the A-V node and the His bundle, whether the preparation was spontaneously beating or electrically driven in either the forward or retrograde direction, and blocked membrane excitation in the nodal and nodal-His regions and to downstream structures. The depressant effects of nerve stimulation were augmented by physostigmine and antagonized by atropine. Addition of acetylcholine to the bath reduced the frequency at which the A-V node conducted, but in the concentrations used did not duplicate the effects of nerve stimulation. The behavior of the S-A node is qualitatively similar to that of the A-V node. In the presence of a sinus rhythm, nerve stimulation applied at the A-V node did not affect the activity of the S-A node, and during artificial atrial drive, nerve stimulation of the S-A node did not affect A-V nodal function, indicating that little or no neural communication exists between the two regions in the isolated preparation. Locally released acetylcholine appears to depress excitability of specialized cells in the central node, independently of the direction of propagation.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The effects of variation in calcium concentration on the action potential of Purkinje fibers isolated from the dog heart were studied. Action potentials recorded during perfusion with Tyrode solution containing 2.7 mM calcium chloride were compared with those recorded during subsequent perfusion with solutions containing 0.675 (1/4X), 1.35 (1/2X), 5.4 (2X), or 10.8 (4X) mM calcium chloride. In both 1/2X and 1/4X solutions, the time required to repolarize to minus 60 mv and the duration of the action potential were increased. There were significant decreases in the slopes of phases 2 and 3 and the terminal phase of repolarization, while the slope of phase 1 increased. In 2X or 4X solutions, repolarization was speeded mainly by an earlier onset of phase 3. As a result the time to repolarize to minus 60 mv and the duration of the action potential were decreased significantly. The slope of phase 1 decreased significantly in 4X solution. In both high calcium solutions the rate and magnitude of diastolic depolarization increased. It was shown that the rate of the calcium-enhanced diastolic depolarization was dependent on the stimulus rate. The possible role of these changes in transmembrane potential in causing the ventricular arrhythmias following CaCl2infusion in intact animals is discussed.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The rate of formation of angiotensin was investigated for the reaction of angiotensinase-free human renin, at various states of purity, with angiotensinogen, in pooled, angiotensinase-free human serum. The velocity constant of this reaction and the Michaelis constant of the renin-substrate complex were determined. The concentration of angiotensinogen and of endogenous renin in human serum was also determined and, on the basis of these results, a procedure was designed for the indirect assay of human renin. This was carried out under a wide range of experimental conditions, for periods of incubation ranging from 10 min to 18 hours, for various concentrations of substrate, and for renin concentrations varying from 0.000025 to 0.20 unit/ml. The absence of angiotensinase made possible the prolonged incubation (18 hours) of a minute quantity of renin with a large amount of the renin substrate. The resultant formation of large amounts of angiotensin permitted its accurate assay in the dog.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Atrioventricular (A-V) conduction and the functional refractory period (FRP) of the A-V system were studied in 13 dogs chronically infected by T. cruzi that had ECG disturbances indicative of myocarditis. Histopathologic findings at the A-V node and the bundle of His were correlated with the FRP and with conduction times of the A-V propagation system. Retarded conduction was related to inflammatory and fibrotic processes localized at the bundle of His. At relatively slow rates of stimulation, conduction time was prolonged, but the ventricle was capable of following high atrial rates. With augmented FRP, mononuclear cell infiltrates were observed in the A-V node or in the septal muscle around the node. This suggests that the node was included in the inflammatory process. No correlation was found between inflammatory infiltrates of the bundle of His and changes in the FRP. At relatively slow rates of stimulation, normal A-V conduction time corresponded to prolonged FRP. A-V conduction became slow as the atrial rate increased. A point was reached when the ventricle could not follow the moderately increased atrial rates.Excitability of cardiac tissues was so markedly altered in 5 dogs with severe inflammatory infiltrates that a similar study of the A-V system could not be made.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Intrapericardial pressures were recorded via a saline-filled Teflon catheter (o. d., 1.3 mm) in 11 anesthetized dogs studied without thoracotomy. Seven animals were studied before, during, and after 1-min exposures to transverse accelerations that ranged from 1G (normal gravitational environment) to 7G when in the supine (+Gj), prone (−Gx), left decubitus (+Gv), and right decubitus (−Gy) positions. Four additional animals were studied at 1G only, while in these same body positions. Pressures also were recorded from both atria, right ventricle, aorta, esophagus, and the potential pleural space. Mean end-expiratory intrapericardial pressure varied directly with the vertical height of the recording site in the thorax during all conditions studied, as would be expected in a hydrostatic system. Transpericardial pressures were not significantly different from zero at all levels of acceleration studied. Transmural left and right atrial pressures were independent of the height of the recording site in the thorax and were unchanged during exposures to transverse accelerations that ranged from plus to minus 7Gx.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Severe myocardial necrosis was produced in virgin Sprague-Dawley rats without preexisting arteriosclerosis and in breeder Sprague-Dawley rats with various degrees of arteriosclerosis by giving two subcutaneous injections of isoproterenol; the virgin rats received 50 mg/100 g and the breeder rats 25 mg/100 g body weight. Breeder rats withstood the stress and shock of myocardial necrosis with fewer untoward effects than the virgin animals. Changes in the thymus and adrenal glands also indicated that the arteriosclerotic breeder rats responded with a different pattern of adrenocortical activity. There were marked differences between the nonarteriosclerotic and arteriosclerotic rats in the fluctuation of serum transaminases and lactic dehydrogenase levels during the stress of myocardial necrosis. During the acute stages of myocardial necrosis there was intense activation of lipid metabolism with gross and microscopic evidence of intense fatty infiltration of the liver; during myocardial repair this lipid was removed concomitantly with reduction of hypercholesteremia. The dichotomy of response has been ascribed to the possibility that the preexisting arteriosclerosis in the breeder rats led to the development of increased collateral coronary artery circulation which afforded some degree of protection to the myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Retrograde concealment of serially evoked premature ventricular responses was studied in an isolated preparation of rabbit atria and ventricles. Transmembrane potentials were recorded simultaneously from single cells within the atrioventricular (A-V) node and ventricular specialized conduction system, together with atrial and ventricular bipolar electrograms. In these experiments, retrograde conduction delays and block occurred within the ventricles, between ventricular muscle and the Purkinje-bundle branch system, between the bundle branch and His bundle, and within the A-V node.The ventricular specialized conduction system was found to be a major location of retrograde conduction delays and block. Many examples of retrograde concealment and block, previously interpreted as due to A-V nodal mechanisms, almost certainly result instead from mechanisms operating within the ventricular specialized conduction system.Antegrade and retrograde block of sequentially evoked premature responses occurred within the A-V node. Reentry “echo” responses occurred in many experiments following premature stimulation of the atria, the ventricles, or both.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The close association of elastin, collagen, and smooth muscle in the mammalian aortic media results in viscoelastic properties that account for many of its static and dynamic mechanical features. The structural components of the media are precisely oriented in concentric layers, or lamellar units, of fairly uniform composition. A comparative study of the adult thoracic aorta in 10 mammalian species, including 15 canine breeds, showed that the number of lamellar units in the media of adult mammalian aortas is very nearly proportional to aortic radius regardless of species or variations in measured wall thickness. Estimated wall tensions ranged from 7,820 dynes/cm in a 28-g mouse to 203,000 dynes/cm in a 200,000-g sow, but the average tension per lamellar unit of an aortic media was remarkably constant regardless of species, ranging from 1,090 to 3,010 dynes/cm. The findings suggest that the elastin lamella and the contents of its adjacent interlamellar zone represent the unit of structure and function of the mammalian aortic wall.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID