ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Cardiac myosin obtained from rats and mice (smaller animals) had a higher adenosinetriphosphatase (ATPase) activity in the presence of calcium ions (Ca2+) than did cardiac myosin from rabbits and dogs (larger animals). Structural differences between the two types of cardiac myosin were suggested by the lower apparent activation energy of the Ca2+activated ATPase reaction catalyzed by cardiac myosin from the smaller animals and by the lower rate of inactivation of ATPase at pH 9.0. No evidence for activators of myosin ATPase was found in heart muscle or cardiac myosin from rats and mice. The cardiac myosin from these animals was also distinctive with respect to the pattern of activation and inhibition of ATPase by salts and sulfhydryl reagents. ATPase activity of cardiac myosin from the smaller animals was less sensitive to the inhibitory effect of KCl in the presence of Ca2+and was not activated byN-ethylmaleimide, suggesting a difference in the myosin molecule at or near the active site. When sodium dodecyl sulfate-polyacrylamide gel electrophoresis was performed, no difference was observed in the molecular weight or the proportion of the light chains between the two types of cardiac myosin. ATPase activity of skeletal myosin was approximately the same in all animals and showed a pattern similar to that of the cardiac myosins from rabbits and dogs. The structural difference in the cardiac myosin from rats and mice suggested by these experiments appears to account for the enhanced myocardial contractility found in these animals.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

This investigation attempted to determine whether stimulation of intrathoracic receptors, including those in the left atrium, is associated with changes in renal vascular resistance. In 19 dogs, the left kidney was perfused at constant pressure and the right hind limb was perfused at constant flow. A partial obstruction of the mitral orifice that increased left atrial pressure by less than 20 cm H2O caused tachycardia, hypotension, renal vasodilatation (5% increase in flow), and hind-limb vasoconstriction (10% increase in pressure). A partial obstruction of the orifice that raised left atrial pressure more than 20 cm H2O caused tachycardia, hypotension, and more hind-limb vasoconstriction (20% increase in pressure), but renal vascular resistance did not change. After bilateral vagotomy in either the thorax or the neck, partial obstruction of the mitral orifice caused constriction in both the renal and the hind-limb vascular beds. In 10 dogs, localized distention of three pulmonary vein-left atrial junctions caused an increase in heart rate and a small but significant increase in renal blood flow but had no effect on hind-limb vascular resistance. At least a part of the reflex renal dilatation caused by mitral obstruction probably resulted from stimulation of left atrial receptors.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The effect of prolonged administration of alcohol on calcium binding and uptake by sarcoplasmic reticulum and mitochondria and on respiratory function of mitochondria was investigated in heart muscle of dogs. Dogs were paired and maintained with and without alcohol for 6 months; alcohol was administered by adding it to drinking water and food with vitamin supplements. Measurements were made after alcohol had been temporarily withheld for 2 days. Prolonged alcohol ingestion resulted in a decline in calcium binding and uptake by sarcoplasmic reticulum and mitochondria, suggesting a diminished affinity of the reticular and mitochondrial membranes for calcium ions. The endogenous calcium content of mitochondria and sarcoplasmic reticulum decreased. Prolonged alcohol administration failed to alter cardiac contractility, although contraction and relaxation tended to diminish following the administration of angiotensin. The results illustrate that one link in the regulation of the state of contraction or relaxation involving myofibrillar calcium transport is weakened in dogs maintained on alcohol for prolonged periods of time.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Effects of changes in atrial compliance on cardiac performance were analyzed using a circulatory analog model. The atrium was assumed to be a noncontracting chamber with a constant compliance. It connected the venous return system, which was represented by mean circulatory filling pressure and a venous return resistance in accordance with Guyton's concept, with the ventricle, which was characterized by a time-varying elasticity. Atrial compliance was increased from near zero to a value at which atrial volume was twice ventricular stroke volume, while the parameters of ventricular contractility were kept unchanged. Cardiac output increased from 2,400 to 3,240 ml/min with increases in atrial compliance from 0.1 to 20 ml/mm Hg (venous return resistance 0.1 mm Hg sec/ml), whereas mean atrial pressure simultaneously decreased from 3.0 to 2.2 mm Hg. This result indicates that cardiac performance in terms of the cardiac output-mean atrial pressure relationship was markedly improved by increases in atrial compliance in spite of constant ventricular contractility. The analysis of the model strongly suggests that natural atrial compliance in situ, by pooling venous return flow during systole and supplying it to the ventricle during diastole, facilitates the transformation of the continuous venous return flow into the intermittent ventricular filling flow.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Cats subjected to coronary artery occlusion were used to study the effect of methylprednisolone on the release of lysosomal acid hydrolases and creatine phosphokinase (CPK) from ischemic myocardial tissue. Plasma CPK activity was increased significantly 2 hours after occlusion and increased eightfold 5 hours after ligation in vehicle-treated cats. Intravenous administration of methylprednisolone (30 mg/kg) 30 minutes before or 60 minutes after occlusion significantly limited the increases in plasma CPK activity to values only slightly greater than those observed in sham-operated cats. Plasma activities of the lysosomal hydrolases, β-glucuronidase and cathepsin D, were comparable in all groups of cats and did not change during the 5-hour observation period. Nevertheless, cathepsin D and β-glucuronidase activities were reduced 41% and 33%, respectively, in the ischemic portion of the myocardium of untreated cats subjected to coronary artery ligation. The CPK activity of the ischemic myocardium was reduced 43% in these cats. Pre- or posttreatment of cats with methylprednisolone prevented the decline in CPK and lysosomal hydrolase activity of ischemic myocardium. These data indicate that lysosomal disruption is a consequence of myocardial ischemia and that pre- or posttreatment with methylprednisolone prevents the leakage of myocardial lysosomal and cellular enzymes. Moreover, the methylprednisolone-induced stabilization of myocardial membranes appears to be related to the ability of glucocorticoid to limit infarct size following myocardial ischemia.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

The reaction between hog renin and rat angiotensinogen followed Michaelis-Menten kinetics. A Kmvalue of 1,109 ng angiotensin/ml was determined for the rate of angiotensin formation at pH 7.4 and 37°C. The pH optimum for the reaction of hog renin with rat angiotensinogen was between 6.8 and 7.0. Pepstatin inhibited the reaction in a noncompetitive way. The maximum inhibitory effect occurred at approximately pH 6; at values above pH 8.0, pepstatin had no inhibitory effect. The effect of pepstatin was reversible, since renin activity could be restored by 24 hours of dialysis against distilled water. A 50% inhibition of the enzymatic activity of 0.01 dog units of hog renin was obtained with 0.45 μg pepstatin/ml.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Large changes in stroke volume and peripheral vascular resistance were induced by varying the heart rate and by intra-aortically infusing acetylcholine or angiotensin II in six dogs with heart block and electromagnetic flowmeters chronically implanted around their ascending aortas. Changes in stroke volume, aortic and atrial pressures, and systemic resistance were monitored continuously for 3–6 hours under morphine-pentobarbital anesthesia. The characteristics of diastolic pressure decay at heart rates ranging from 60 beats/min to 200 beats/min and during transient periods of asystole were studied, especially with reference to the distortions caused by reflected pressure waves. The diastolic phase of pressure pulses recorded over a segment of the thoracic aorta several centimeters long centered about 4 cm cephalad to the dorsal insertion of the diaphragm could be closely approximated by a straight line on a semilogarithmic scale. Under the conditions of these experiments, changes in the slope of that line and of its reciprocal, the time constant, correlated well with concomitant variations in peripheral vascular resistance. This relationship appears to be of practical value for continuous monitoring of systemic resistance directly from the diastolic segments of pressure pulses recorded from the lower thoracic aorta.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Determination of the copper (Cu) content of rat, rabbit, and mouse hearts proved to be a sensitive microassay for mitochondrial content and membrane area of mitochondrial cristae per unit myocardial cell volume. The direction of variations in Cu content correlated well with variations in membrane area of mitochondrial cristae determined by morphometry of electron micrographs during normal postnatal growth, ventricular hypertrophy after aortic constriction, and thyroxin-stimulated myocardial cell growth. Right and left ventricular and interventricular septal Cu contents per unit dry weight were the same, did not vary during postnatal growth, and significantly exceeded atrial Cu content. Among different mammalian species, ventricular Cu content per unit dry weight tended to vary inversely with adult animal size and thus with adult resting heart rate. The existence of mechanisms for transport of67Cu across the myocardial cell plasma membrane and for incorporation of67Cu into mitochondrial cristae from an intracellular precursor pool was demonstrated by injecting67Cu-labeled blood serum into rats.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID

摘要:

Measurements were made of filtration coefficients (Lp), area per unit path length (A/Δx), and equivalent pore radius (rp) in the control state and following severe ischemia (arrested blood flow) for periods of 30 minutes, 1 hour, and 3 hours. The value ofAs/Δxfor diffusion of all lipid-insoluble substances was not changed after 30 minutes of ischemia, but it was increased after 1 and 3 hours of ischemia. The value ofrpcalculated from the theory of restricted diffusion yielded values of 34–35 Å for both the control period and after all three periods of ischemia. Combination of hydrodynamic data (Lp) and diffusion data (Aω/Δx) yielded values forrpof 23 Å for control and ischemic periods. Measurements of plasma-protein osmotic pressure, tissue-protein osmotic pressure, tissue hydrostatic pressure, and capillary hydrostatic pressure supported the conclusion that extended periods of arrested blood flow did not affect muscle capillary membrane porosity. In 5 of 16 hind limbs, there appeared to be a porosity change following 3 hours of arrested blood flow. This change was demonstrated by a net decrease in plasma-protein osmotic pressure and an increase inrpfrom 34 Å to 54 Å.Lpwas not changed after 30 minutes but was increased after 1 hour of ischemia; the increase was associated solely with an increase in capillary surface area. After 3 hours of ischemia, the primary change in 11 of 16 hind limbs was an increase in capillary surface area, although an increase in the size of the pores per unit membrane area could not be rigorously excluded. In 5 hind limbs after 3 hours of ischemia, an increase inrpwas the primary change and an increase in capillary surface area was of secondary importance. The data indicate that the edema which occurs subsequent to reperfusion of the vasculature after moderately long periods of severe ischemia results from an increase in capillary hydrostatic pressure augmented by an increase in capillary surface area not associated with an increase in membrane porosity. The rise in capillary pressure for any given arterial or venous pressure involves a decrease in precapillary resistance, but postcapillary resistance does not change for any given flow.

ISSN:0009-7330    

出版商:OVID    

年代:1974

数据来源: OVID