摘要:

The contractile state of the left ventricle in man was analyzed by correlating left ventricular (LV) dimensional changes during contraction determined from cineangiograms, with simultaneous measurements of LV pressure. The mechanical characteristics of ventricular contraction were expressed quantitatively by deriving the extent and velocity of circumferential fiber shortening at the midwall and the time course of LV wall tension (stress); the instantaneous relations between tension, velocity, and length were then examined. In 6 patients without LV disease, wall tension became maximal soon after the onset of ejection, then declined rapidly; in 9 patients with LV disease, tension fell only slightly with continued ejection. The extent of shortening of the minor LV circumference was consistently less in patients with LV disease than in those without such disease. Velocity of circumferential fiber shortening throughout contraction ranged from 0.22 to 1.11 circumferences/sec in patients with LV disease and from 1.66 to 2.71 circumferences/sec in patients without LV disease, at comparable levels of wall tension (137 to 467 g/cm2, and 175 to 409 g/cm2, respectively). The initial rate of change of velocity of the circumferential fibers at the onset of ejection also was less than in the group without LV disease. The velocity of shortening of the contractile elements at maximum wall tension was 0.11 to 0.87 circumferences/sec in patients with LV disease and 1.46 to 2.04 circumferences/sec in patients without LV disease.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The aim of this study was to evaluate utilization of chemical energy in relation to myocardial mechanics in variably afterloaded contractions of cardiac muscle by determining total energy utilization (∼P) in the absence of energy production. Right ventricular papillary muscles of cats were equilibrated at 26°C in a myograph in Krebs' solution while contracting isometrically (12/min). Following treatment with iodoacetate and N2to inhibit completely ATP production from glycolytic and aerobic metabolism, the muscles were stimulated to contract isotonically 20 to 75 times with varying after loads. They were then rapidly frozen in liquid N2-cooled isopentane, and concentrations of ATP, creatine phosphate, inorganic phosphate and creatine were measured.The efficiency of energy utilization for the performance of internal work was 0.0067 μmoles ∼P/g-cm of work and for external work was 0.0031 μmoles ∼P/g-cm. In addition, resting energy utilization was 0.662 μmoles/g/min and activation energy was estimated to be 0.040 μmoles/g/contraction. These findings provide a demonstration of the Fenn effect in cardiac muscle and explain the well-known discrepancy in energy cost when cardiac work is increased by increasing pressure load as opposed to increasing volume load.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The relations between renin release and renal hemodynamics, renal sodium load, and sodium and water balance were studied during hyponatremia, hypernatremia, mercurial natriuresis, norepinephrine infusion, and reduction in renal perfusion pressure. Significant reciprocal relations were found between renin secretory activity and the renal arterial plasma sodium concentration, the filtered sodium load, and urinary sodium excretion; however, no significant, or even consistent, relations were found between renin release and any hemodynamic parameter or sodium or water balance. During bilateral stimulation of renin release, unilateral restoration of the filtered sodium load inhibited ipsilateral renin release, without demonstrable changes in hemodynamics, while renin release from the contralateral kidney continued unabated. However, this inhibition was not seen unless the filtered sodium load and urinary sodium excretion rose to control levels even though renal venous plasma sodium concentrations exceeded 170 mEq/liter. Thus, renin release can be dissociated from hemodynamics and sodium and water balance, but not from some function of the filtered sodium load. We propose that renin secretory activity is controlled by an intrarenal, but extravascular, sodium-sensitive mechanism and that the stimulus is a function of the sodium flux across the macula densa into the interstitium surrounding the contiguous juxtaglomerular cells.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

Renal adaptation to anemia was studied in dogs that had been bled repeatedly during a week to produce hematocrit values of between 12 and 21%. Total renal blood flow was unaltered despite a significant increase in cardiac output. Total renal oxygen consumption was within normal limits, but the Po2of cortical tissue was significantly reduced. Glomerular filtration rate and therefore filtered sodium load were reduced. These alterations were interpreted as resulting from preglomerular vasoconstriction together with a decrease in postglomerular vascular resistance, the latter perhaps a consequence chiefly of the diminished blood viscosity. Sodium reabsorption in relation to filtered sodium load was unimpaired in anemic animals; actually the sodium excretion factor was lower than in normal animals. It is concluded that the maintenance of normal renal function in the anemic animal is obtained by a decrease in work load (i.e. reduced glomerular filtration rate) and more efficient oxygen extraction related to increased blood tissue Po2gradient. Increased titers of erythropoiesis-stimulating substance could be demonstrated in these anemic animals. It is suggested that the low cortical tissue Po2is responsible for the release of this factor.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The effect of emetine hydrochloride on protein synthesis in rat myocardium was studied. Emetine inhibited incorporation of tritiated leucine into soluble proteins and actomyosin in an in vitro system using minced rat myocardium in a supporting medium. Fifty percent inhibition of incorporation of the isotope into soluble proteins and actomyosin occurred at an emetine concentration of 5 × 10-7M. Incorporation was also significantly inhibited when animals were treated with emetine for three days. The data suggest that emetine toxicity in the myocardium may be mediated through its effects on protein biosynthesis.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The effect on left ventricular performance of electrical stimulation of the cut central end of the quadriceps nerve was studied in open-chest dogs. Stimulation of the nerve at 2 to 4 times threshold for the flexion reflex, which presumably activated intermediate-sized afferent fibers, caused a decrease in heart rate and arterial pressure. Stimulation at 5 to 25 times threshold, which presumably activated small-sized, high-threshold afferent fibers, increased heart rate, arterial pressure, and cardiac output. When heart rate, arterial pressure, and cardiac output were controlled, activation of high-threshold afferent fibers caused a significant increase in the maximal rate of pressure rise, stroke power, and mean rate of ejection of the left ventricle without an increase in the end-diastolic pressure. These same fibers may in some way be activated during muscular exercise and be partially responsible for the increase in left ventricular contractility that occurs during that time.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

Cardioglobulin is a protein system in mammalian plasma, assayed by its effect on contractility of isolated frog heart. Gel filtration was employed to separate individual components, called cardioglobulin-A, -B and -C, from rat and human plasma: Cardioglobulin-A of both rat and human is a small globulin. Biological activity is abolished by heparin. A part of rat plasma cardioglobulin-A probably exists as a readily dissociable complex with another protein and is not inactivated by heparin. Rat cardioglobulin-C is a large globulin, contains calcium essential for biological activity, and binds strongly to the frog heart. The human protein that corresponds functionally to rat cardioglobulin-C is a much smaller globulin and does not bind. Both rat and human cardioglobulin-B are sensitive to heparin at concentrations recommended for collection of plasma but are stable in tenfold lower concentrations that still prevent clotting. Human cardioglobulin-B separates into two fractions on G-200 Sephadex. It is not known whether they exist as a complex in plasma or as individual proteins. Rat cardioglobulin-B has not been isolated, but preliminary data indicate it is chemically distinct from human cardioglobulin-B. As a result of this work, assay of individual Cardioglobulin components can be reliably performed.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID