摘要:

We have investigated the effects of sudden changes in the load against which the left ventricle contracts in healthy conscious dogs. During a steady state, initial responses were assessed by comparing the beat before with the beat after such a change. Flow was measured by electromagnetic flowmeters and pressure usually by a catheter-tip transducer.Results show that under the conditions of these experiments the curves relating external work and power to load are consistent with the parabolic relationship shown for isolated hearts and muscle strips and that in each case the left ventricle normally functions near the peak of the curve.When an increased load was maintained until a new steady state was reached the left ventricle still functioned on the descending limbs of what presumably were different work-load and power-load curves. It was concluded from this that either the increase in load was too great or the time too short for reflex humoral and intrinsic mechanisms to readjust and permit the ventricle to function again at the peak of each curve, or that the circulatory system does not make relatively rapid adaptations in this way to an increase in systemic load.The immediate effects of changes in load on left ventricular stroke volume were similar to those seen in isolated preparations. Stroke volume varied inversely with the load. Stroke volume changes were accompanied by changes in the duration, rate, and velocity of ejection. The duration of the isovolumetric phase was affected little but the period from valve closure to the end of ventricular relaxation varied with the load so that the total duration of contraction and relaxation of the ventricle was relatively unchanged, though an increase in load did tend to prolong it.Before the onset of the baroreceptor response the right ventricle was not affected, the two ventricles acting independently in relation to all these changes.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

Determinations of left ventricular oxygen consumption were made in the isolated heart of a dog while the ventricle performed work by compressing air. In the described preparation the air compressed by the ventricle could be rapidly released and the ventricular pressure pulse repeatedly interrupted at specific points during its cycle. Upon interrupting the pressure pulse at its peak there was a 10% increase in peak pressure that appeared in the subsequent four to five beats. When the intraventricular pressure was released at various points during its ascent to peak pressure, left ventricular oxygen consumption could be correlated with both the pressure, at which it was interrupted, and the area under the pressure pulse. When the oxygen consumed by a ventricle developing a full pressure pulse was compared to that of a ventricle in which the intraventricular pressure was released at its peak-land when the peak systolic pressure of the two compared pulses were equal-then the oxygen consumed by the ventricle when the pulse was interrupted averaged 91% of that when the pulse was full. These studies indicate that by the time the pressure pulse has reached its peak, myocardial oxygen consumption has been largely determined, and that the oxygen cost of the ventricular relaxation is small.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

Electrical stimulation of the left stellate ganglion of the dog is associated with an increase in urine flow, in electrolyte and total solute excretion, and in the renal clearance of inulin. These changes appear rapidly, are well maintained during prolonged stimulation, and stop soon after stimulation has ceased. The hemodynamic responses associated with these changes are an increase in arterial pulse pressure, an increase or no change in mean arterial blood pressure, and a decline in mean left atrial pressure. The diuretic response to stellate ganglion stimulation is diminished, but not abolished, by bilateral cervical vagotomy as are the changes in electrolyte excretion, total solute excretion, and the renal clearance of inulin. However, the hemodynamic responses are not greatly modified by cervical vagotomy. Vagotomy just above the diaphragm does not appear to modify these responses. The effect of vagotomy on the renal responses to stellate stimulation appears to be a result of sectioning baroreceptor afferent nerves which traverse the vagus nerves. The rapidity of the renal response to stellate stimulation, its temporal relation to the hemodynamic changes, and the effect of cervical vagotomy indicate that the diuresis is, to a large degree, secondary to withdrawal of renal sympathetic vasoconstrictor nerve discharge. The similarities between the renal responses to stellate stimulation and to intravenous infusions indicate that infusion diuresis may be mediated, at least in part, by the same mechanism.When renal blood flow is measured directly in the perfused kidney, carotid occlusion is associated with little change or with a decrease in renal blood flow at a time when renal arterial pressure increases. When renal blood flow is maintained constant in the perfused kidney, carotid artery occlusion is associated with an increase in renal arterial pressure. The intrarenal administration of the adrenergic blocking agent, phenoxybenzamine, can prevent the increase in renal vascular resistance during carotid occlusion indicating that it is due to an adrenergic mechanism. The renal pressure-flow curve is displaced down and to the right during carotid occlusion; autoregulation of renal blood flow is still observed, although at a lower level of blood flow. All these changes indicate that the primary renal response to carotid occlusion is vasoconstriction mediated by the renal sympathetic nerves.It is well-known that urine flow increases when renal arterial pressure is increased independent of a change in the activity of the renal vasoconstrictor nerves and independent of a change in renal blood flow. Consequently, the rise in arterial pressure associated with carotid occlusion can contribute directly to the response of the kidney to carotid occlusion. The variability of the changes in water and electrolyte excretion by the kidney during carotid occlusion may represent a varying contribution of direct and reflex mechanisms to the total response.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

In dogs with denervated hearts intravenous infusions of epinephrine (1.0 to 3.0 μg/kg/min) caused marked acceleration of the heart rate and a significant reduction of intraventricular conduction time. Equal doses infused into the descending thoracic aorta increased the heart rate only slightly, but exerted undiminished effects upon conduction time.Evisceration did not modify the intraventricular dromotropic effect of epinephrine so long as the hepatic arterial supply was preserved. Occlusion of the hepatic artery abolished the dromotropic effect of epinephrine without modifying its chronotropic action.The time course of the dromotropic effect and of the kalemic action of epinephrine was approximately the same.Intravenous infusions of KCl matching the hyperkalemic effect of epinephrine caused similar dromotropic actions.Isoproterenol even in high doses (up to 2.0 μg/kg/min) did not decrease intraventricular conduction time and had only a slight hyperkalemic effect.After the administration of SY28 (1.0 mg/kg) epinephrine caused neither hyperkalemia nor decreased intraventricular conduction time.It is concluded that in the heart in situ the effect of epinephrine on intraventricular conduction is the result of an indirect action mediated through the liberation of K+ions from the liver.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

A massive infusion test has been devised to evaluate the functional capacity of the heart.In five dogs extensive surgical procedures followed by episodes of arterial hypotension at 30 mm Hg and lasting 90 minutes caused severe cardiac incapacity, which was demonstrated by failure of rate of cardiac work to increase throughout the infusion together with a large rise in left atrial pressure. This incapacity was not evident in tests made immediately after the hypotensive episode. The damage became more and more severe in tests performed 90 and 150 minutes after the end of the hypotension even though mean arterial pressure was maintained at 100 mm Hg. Operated control dogs did not show cardiac deterioration in tests timed as above. The rate of cardiac work continued to increase throughout the infusion with a relatively small rise of left atrial pressure.In a series of five dogs, flow to the coronary arteries and to those supplying the head and forelimbs was maintained by normal blood pressure while the rest of the animal was made hypotensive for 90 minutes. The arterial pressure in the whole animal was then returned to an average level of 100 mm Hg. Tests made at intervals after the hypotension showed equivocal evidence of cardiac deterioration.In another series of four dogs, prepared as above, the partial hypotension lasted 150 minutes before the arterial pressure was returned to normal. Tests at intervals after hypotension showed cardiac damage in all the animals and severe damage in three. Evidence is presented indicating that the peripheral vascular bed had deteriorated functionally as a result of 150 minutes of partial hypotension.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

Synthetic angiotensin a has pronounced inotropic effects on isometrically contracting, isolated papillary muscles of kittens. The response increases with drug concentration over the range from 10−10M to 10−5M. The mean maximum increase in tension development is 120%. Contractility is raised by angiotensin through an increase in the degree of activation of the contractile elements with no significant change in the duration of their active state. Low concentrations of angiotensin have a greater inotropic action than equimolar concentrations ofl-norepinephrine; but the maximum inotropic effect obtainable withl-norepinephrine is almost twice that of angiotensin.The inotropic effects of angiotensin on cat atrial muscle are slight, and the drug is inactive on frog ventricular myocardium. It has no effect on the resting length-tension relationship of mammalian atrial or ventricular muscle. The frequency of impulse formation in the SA node is not significantly changed by concentrations of angiotensin up to 10−5M. In marked contrast to levarterenol, angiotensin does not cause ectopic impulse formation in atrial or ventricular muscle.It is suggested that the positive inotropic effect of angiotensin on ventricular myocardium is of importance for the pressor action of the drug in the intact circulation. The increase in myocardial contractility tends to minimize or prevent decreases in cardiac output in the face of increased resistance to cardiac ejection and thus supports the elevation of arterial pressure.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

The number and reactivity of the sulfhy-dryl groups of cardiac and skeletal actin preparations have been examined, using material from dogs and rabbits. The number of sulfhy-dryl groups of all actins was approximately six per mole, two of which could be characterized as fast-reacting and were not essential for polymerization. The time course of the reaction of the sulfhydryl groups of heart and skeletal actins with -pmercuribenzoate were identical, and the effects of Ca++Mg++and adenosinetriphosphate upon this reaction were similar for actins from the two tissues. In accord with previous structural comparisons, no difference between cardiac and skeletal actin has been detected.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

The general and regional circulatory effects of synthetic bradykinin were investigated in 19 healthy volunteers. During intravenous infusion of bradykinin (25 μg/min) mean arterial pressure decreased initially, but returned to control levels within a few minutes. Heart rate increased during the hypotensive period, but subsequently returned toward preinfusion levels. Cardiac output increased, mainly as a result of increased stroke volume, and systemic vascular resistance decreased. Blood flow to hand increased during such infusions of bradykinin, but blood flow to forearm was not altered significantly. Intravenous infusions of 40 μg/min produced an increase in blood flow to the forearm, resulting solely from cutaneous vasodilatation in most subjects. The distensibility of hand veins increased both during intravenous infusions of 25 μg/min and during infusions of 0.2 μg/min into the brachial artery. Renal clearance of inulin was slightly decreased during infusion of 25 μg/ min bradykinin; there was no detectable change of PAH clearance.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

It has been suggested that lipoprotein lipase (LPL) activity may play a role in the etiology of atherosclerosis. To determine whether there is an inverse relationship between arterial LPL activity and the tendency for arteries to become atherosclerotic, determinations were made of the activities of the enzyme in homogenates of the aortas of animals under conditions associated with a greater or lesser tendency for atherosclerosis to develop. It was found that the LPL activities of the aortas of old rats and rabbits were significantly lower than those of young animals of the same species, respectively. Rats, which are resistant to the development of atherosclerosis, manifested about twice the aortic LPL activities that rabbits did, the latter animals being notorious for the ease with which they develop the disease. This was true regardless of the age and sex of the animals compared. These results support the hypothesis that low arterial LPL activity may be associated with increased atherogenesis. Aortas of female rats or rabbits, however, showed no greater LPL activities than did aortas of males of the same species. Renal and desoxycorticosterone-salt hypertensions were accompanied by significant increases rather than decreases in aortic LPL activity. The latter results are not consonant with the aforementioned hypothesis.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID

摘要:

The endogenous oxygen consumption of aorta and of diaphragmatic muscle have been studied in female rats and correlated with different phases of estrus. Cyclic changes of oxygen consumption were demonstrated in the aorta but not in the diaphragm. Estradiol in vitro depressed the endogenous Qo2of the aorta from diestrous animals. Possible implications of this work are discussed.

ISSN:0009-7330    

出版商:OVID    

年代:1964

数据来源: OVID