摘要:

Cardiac contractile protein ATPase activity was studied in cats 10 days after adrenalectomy at a time when the mean arterial blood pressure was 27% lower than that of control cats. The Ca2+-dependent, azide-insensitive ATPase activity of myofibrils isolated from the ventricles of adrenalectomized cats was 63% of the activity of control preparations (P<0.025). Similarly, the specific activities of cardiac actomyosin (myosin B) and myosin from adrenalectomized cats had decreased to 54 and 75% of control values, respectively (P<0.005). The percent reductions in ATPase activities in the three protein preparations from adrenalectomized animals were not significantly different, suggesting that the depression was associated with myosin per se. The reduction in the myosin ATPase activity in adrenal insufficiency was prevented by dexamethasone treatment adequate to prevent the decline in mean arterial blood pressure of the adrenalectomized cats. The reduction in cardiac performance in frank adrenal insufficiency may reflect a decrease in the rate of conversion of chemical to mechanical energy by the myocardial contractile proteins.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

The isolated rat heart perfused without substrate provides a good model in which to study biochemical changes in the failing myocardium. In this preparation, there is a decline in the ability of both the mitochondria and the sarcoplasmic reticulum to accumulate calcium in the absence of oxalate after 30 minutes of perfusion. Calcium binding by mitochondria fell from control levels of 47 ± 8 mμmoles/mg protein to 17.5 ± 4.9 mμmoles/mg protein and that by microsomes from 29.8 ± 5.1 mμmoles/mg protein to 15.2 ± 4.8 mμmoles/mg protein. This drop coincided with die start of the decline in myocardial contractility. The calcium uptake by the sarcoplasmic reticulum in the presence of oxalate decreased from control levels of 534.1 ± 32.0 to 160.5 ± 27.2 mμmoles/mg protein after 2 hours of perfusion, at which time the myocardial contractility had dropped to below 10% of control levels. This change in the calcium uptake by the sarcoplasmic reticulum is associated with an increase in its ATPase activity from 1.91 ± 0.21 to 3.00 ± 0.31 μmoles P1/mg protein/min over 2 hours of perfusion without substrate. This suggests that there is an uncoupling of the microsomal ATP-dependent calcium pump in these late stages of heart failure due to substrate lack. The change in calcium binding to reticulum occurred in association with the onset of contractile failure, whereas changes in calcium uptake in the presence of oxalate were delayed and probably represent irreversible disorganization of the intracellular membranes.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

Rat papillary muscles were used to study the influence of glucose (5 mM), linoleate (1 to 1.75 mM), octanoate (0.5 to 1.75 mM) and pent-4-enoic acid (1 to 5 mM) on mechanical performance under oxygenated, hypoxic and anoxic conditions. The buffer solution contained 0.3 mM albumin. Free fatty acids (FFA) (1.0 to 1.75 mM) did not alter mechanical performance under oxygenated conditions. During hypoxia or anoxia, FFA (0.5 to 1.75 mM) depressed contractility and increased resting force; glucose improved mechanical performance and modified the depressant effects of FFA. The depressant effect of the nonmetabolized FFA, pentenoic acid, was similar to that of other FFA. This suggests that the effect was mediated directly by FFA or acyl CoA derivatives rather than their metabolic products, and that it might be due to a detergent effect or calcium binding by FFA present in excess of intracellular FFA binding capacity at low pH. Force development during anoxia could be augmented by calcium, implying that the reduced ability of the myofilaments to contract could not be attributed entirely to a reduction of high energy stores.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

The closest analog to propagated excitation of the heart is an electromotive surface. The width of the cardiac electromotive surface was 0.9 ± 0.1 mm and was remarkably constant. The mean epicardial surface component of voltage across the electromotive surface was 62.4 ± 7.2 mv with the chest closed and 74.1 ± 8.3 mv with the chest open. This 18.7% increase is significant (P< .001) and suggests a shunting effect of the lungs and thorax. Fortuitous measurement of voltage across the electromotive surface yielded nine values in excess of 80 mv and two above 90 mv, suggesting that the true voltage across the electromotive surface is of about the same magnitude as the transmembrane action potential. Cross-fiber activation resulted in a 29.5% reduction in voltage, a 51.8% reduction in conduction velocity and notched QRS complexes.A closed electromotive surface has no external electrical field, suggesting that its voltage is uniform. The voltage between two electrodes, both in advance or toward the rear of a normally propagated open electromotive surface, is caused by an extracardiac current path, since removal of the lung from the epicardial surface greatly reduces this voltage and augments that across the electromotive surface.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

The overall dimensions of the carotid sinus, the thicknesses of the individual layers within its wall, and the tissue composition of the tunica media were measured on histological sections of the carotid bifurcation fixed in vivo in anesthetized dogs, cats, and rabbits. The outstanding dimensional features of the carotid sinus as compared to the adjoining carotid segments are its thinned media-intima layer and increased ratio of internal radius to media-intima thickness. These differences carry a high level of significance statistically. There appears to be no marked increase in the ratio of radius to whole-wall thickness in the sinus portion of the carotid tree. The tunica media in the carotid sinus wall contains more than twice as much elastic tissue per unit volume (mean value 62.3% elastin) as the media in the carotid vessels adjoining the sinus; reciprocally, smooth muscle constitutes 16.4% of the tunica media in the sinus wall but approximately 50% or more of the media in the common, internal, and external carotid arteries caudal and cranial to the sinus (mean values in percent of total volume). Results are discussed in relation to the position of the baroreceptors within the sinus wall and mechanisms of stimulating them.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

Renal lymph was collected from single hilar lymphatics in 58 anesthetized dogs (1) to study the mechanism by which lymph production is affected during diuresis and (2) to determine whether a medullary contribution to renal lymph could be defined by changes in the electrolyte concentration of hilar lymph with concomitant alterations in the concentration gradient of the renal medulla. When diuresis was induced by a solute load (mannitol), lymph flow increased by 25 to 300%. On the other hand, when diuresis was induced without such a solute load, lymph flow was either unaffected (mersalyl) or slightly reduced (furosemide). It was concluded that the effect of mannitol on renal lymph flow was mediated primarily through its general effect on extracellular fluid rather than through any specific intrarenal consequence of the diuresis itself.Control hilar lymph-to-plasma concentration ratios for Na+(1.057 ± 0.040), Cl−(1.129 ± 0.040) and Ca2+(0.770 ± 0.046) but not K+(0.0986 ± 0.086) were found to be significantly different from 1.0. Failure of mannitol diuresis to alter significantly the lymph-plasma ratios of Na+and Cl−provided evidence that the high electrolyte concentrations of the inner medulla were not reflected in hilar lymph. The finding that furosemide abolished the lymph-plasma concentration difference for Na+and significantly reduced that for Cl−was taken as evidence that the outer medulla was a significant source of renal hilar lymph.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID

摘要:

The influence of stimulation on the healing-over of myocardial cells of the toad was investigated. The rate of sealing was markedly increased in beating muscles. This effect of stimulation on the healing process varied with the frequency of the stimulus and depended on the extracellular Ca concentration. Low sodium solutions increased the rate of sealing in stimulated muscles but not at rest. Some evidence is presented that the increased Ca influx which accompanies stimulation activates the reactions involved in the sealing process.

ISSN:0009-7330    

出版商:OVID    

年代:1970

数据来源: OVID