ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

In dogs under pentobarbital anesthesia, the administration of KCl in single intra-atrial doses of 1 mg/kg produced varying effects on intraventricular conduction depending upon the initial potassium concentration of systemic blood. At normal and moderately increased systemic K concentrations, single injections of KCl improved intraventricular conduction, but at higher systemic K concentrations a negative dromotropic effect appeared. Following injection into the right atrium, the effect appeared immediately in the right ventricle, followed after some delay by an appreciably lesser effect in the left ventricle. Injection of potassium into the left atrium altered conduction in the left ventricle without affecting the right ventricle. The results indicate that transient alterations of [K] in the blood of the ventricular cavity can act directly on the specialized conduction network to alter the rate of intraventricular conduction.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The anterior leaflet of the mitral valve of the dog contains blood vessels, nerve fibers, and cardiac muscle in addition to elastic fibers and collagen. When studied in a myograph, the electrically stimulated mitral valve actively developed tension and shortened. Active tension was found to be a function of initial length of the valve and was increased by norepinephrine and decreased by acetylcholine. The presence of neuronally releasable norepinephrine stores in the valve was indicated by responsiveness to tyramine. The negative inotropic response of the mitral valve to acetylcholine was consistent with an atrial origin of the tissue. Possible functional roles for mitral valve muscle and the potential significance of its neural control are discussed.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Preliminary observations in patients undergoing open-heart surgery have suggested that the lysosomes in the right atrium are increased in patients with atrial septal defects. This increase in lysosomes per myocardial cell appears to be directly related to the size of the left to right shunt. The following experiments were performed to see if similar findings could be produced in an experimental model. Atrial septal defects were produced in seven dogs. The biopsy specimens were prepared for ultrastructural examination and viewed with an electron microscope. Lysosomes were counted in representative sections and an estimate of the lysosomes per square micron of heart tissue obtained. The number of lysosomes per square micron of myocardium increased significantly following the creation of atrial septal defects in dogs, with the most marked increase occurring in the right ventricle. Several small atrial septal defects closed spontaneously, as proved by cardiac catheterization, and in these animals the elevated lysosome counts present initially returned toward normal after obliteration of the left to right shunt at the atrial level. Control dogs showed no significant increase in myocardial lysosomes over the 18-month period despite repeated thoracotomies and myocardial biopsy. These studies add further evidence to support the role of the lysosome as an important intracellular organelle which is related to cellular stress.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Several factors affecting K+transport by rabbit heart mitochondria were examined, using a K+-sensitive electrode. The histone fractions f2a and β-7 produced an energy-dependent efflux of K+. Inorganic phosphate was required for optimal activity; Kmfor phosphate was 60 μM. Both rate and extent of K+efflux decreased as K+concentration in the reaction medium was increased. The direction of valinomycin-induced K+movements was shown to depend on the net resultant of an active transport mechanism and increased membrane permeability. The detergent triton X-100 produced a nonspecific increase in membrane permeability that led to a rapid efflux of K+. Evidence is presented for competition between ion transport and ATP formation for some common energy intermediate. Possible mechanisms of action of histones and other agents affecting heart mitochondrial K+transport are considered.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

A method of examining a small (50 to 100 μ o.d.) strand of living cardiac muscle containing several fibers with a high power optical system is described. When the strand was stretched so that it was just taut, the muscle fibers within were found to be slack and severely buckled. An extension of 40 to 60% of this initial length was required before the fibers became straightened and aligned with the long axis of the strand. This finding can account for the fact that cardiac muscle, unlike skeletal muscle, must be subjected to considerable passive tension before its maximum active tension can develop. The resting sarcomere length (that observed when the fiber is just straightened) was 2.0 to 2.2μ. Overall strand length and sarcomere length were measured and had no accurately predictable relation. Rabbit papillary muscle fixed at a length at which the passive tension was just zero showed similar buckling of the muscle fibers. The collagen content (in the form of hydroxyproline analysis) of heart muscle was approximately 6 times that of skeletal muscle. The significance of these findings and their relation to some previously reported mechanical properties of cardiac muscle are discussed.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The role of adrenergic mechanisms for the development of ventricular fibrillation during induced hypothermia was studied in cats. Prenylamine (60 mg/kg) caused a disappearance of the adrenergic transmitter in the muscular nerves; those to the vessels were only slightly affected. Thus pretreated, animals can be cooled to 17.8 to 17°C rectal temperature, and subsequently rewarmed, without developing ventricular fibrillation. Blood pressure was maintained with metaraminol. Without pretreatment the animals constantly develop ventricular fibrillation at 23 to 18.6°C. When prenylamine was given in a dose (20 mg/kg) that does not overtly affect the norepinephrine content of the cardiac adrenergic nerves, ventricular fibrillation was not prevented. In one group of animals receiving 60 mg/kg of prenylamine, norepinephrine instead of metaraminol was infused to maintain the blood pressure during cooling. These animals developed ventricular fibrillation (or cardiac standstill). Fluorescence microscopy showed that the infusion had restored the norepinephrine content in the cardiac nerves previously depleted of their endogenous transmitter by prenylamine. The incidence of ventricular fibrillation seems to be related to the number of intact adrenergic nerves present in relation to the cardiac muscles. Hypothermia caused a distinct release of transmitter from the cardiac adrenergic nerves.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The amount and state of binding of three lysosomal acid hydrolases, acid phosphatase, cathepsin, and β-glucuronidase, were studied in canine cardiac muscle following severe asphyxia and deep hypothermia. The studies were done on adult mongrel dogs anesthetized with sodium pentobarbital. Asphyxia was produced by tracheal occlusion, and was maintained until the onset of cardiac arrest (6 to 10 min). Hypothermic conditions were achieved by placing the heart on partial bypass through a heat exchanger. The heart was cooled to 6 to 10°C and held at this temperature for 30 min while circulation and respiration were maintained by artificial means. Control dogs were subjected to similar surgical procedures. Immediately following the experiments, the whole hearts were removed, cooled to 0 to 4°C, homogenized, and fractionated into supernatant and lysosomal fractions. The levels of bound and free acid hydrolases were estimated in the whole homogenates and fractions. Asphyxia produced a large shift of acid hydrolase activity from a bound form to a free form, as evidenced by elevated ratios of free to bound activity in the whole homogenates and elevated ratios of supernatant to lysosomal activity with respect to the fractions. Hypothermia did not alter the binding status of the lysosomal enzymes. These findings suggest that lysosomal enzymes play a major role in asphyxic damage to the heart.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Distribution of coronary flow to the inner and outer layers of the left ventricle of the anesthetized, open chest dog was estimated by the myocardial uptake of86Rb chloride infused into the cannulated common left coronary artery. With normal relationship of coronary perfusion pressure and left intra-ventricular pressure, there was no significant underperfusion of the endocardium. When left intraventricular pressure was raised and coronary perfusion pressure was held at levels sufficient to provide normal coronary flow, endocardial distribution remained equal to or slightly greater than that to the epicardium. However, when coronary perfusion pressure was lowered, particularly to levels causing obvious signs of myocardial hypoxia, maintenance of a normal left intraventricular pressure resulted in marked underperfusion of the endocardium. The coronary vasoactive drugs, dipyridamole, norepinephrine, vasopressin, and the β-adrenergic receptor blocking agent, propranolol, increased the flow distribution to the endocardium of both the normotensive and hypertensive left ventricle. It is concluded that the systolic tissue pressure which increases from epicardium to endocardium does not cause significant underperfusion of the endocardium in either the normotensive or hypertensive left ventricle as long as normal coronary perfusion pressure and flow are maintained.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Both α- (vasoconstrictor) and β- (vasodilator) receptor activity was demonstrated in the coronary arteries of the unanesthetized dog independent of adrenergic receptors in the myocardium. In the β-receptor blocked animal, α-adrenergic receptor activity was demonstrated after intravenous and intracoronary injections of epinephrine and norepinephrine by the occurrence of coronary vasoconstriction which could be eliminated by blocking α-adrenergic receptors as well. Coronary vasoconstriction was also seen prior to β-receptor blockade after intravenous phenylephrine and, on occasion, after intracoronary injections of norepinephrine. β-adrenergic receptor activity was demonstrated in several instances after intravenous or intracoronary injections of catecholamines by an initial vasodilatation which could be eliminated by β-adrenergic receptor blockade and which occurred before there was any change in myocardial or systemic hemodynamics. The role of this independent adrenergic receptor activity in the control of the coronary circulation remains to be determined.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID