摘要:

The effects of frequency of contraction and of external calcium and sodium concentration on the inotropic actions of acetylcholine (ACh) on isolated mammalian myocardium were examined. In stimulated left atria of cats, ACh reduced tension development, i.e. exerted a negative inotropic effect, which became more striking as the frequency of contraction was increased and was inhibited by atropine. In cat papillary muscles studied at a low frequency (<42/min), high concentrations of ACh augmented tension development, i.e. produced a positive inotropic effect, which was enhanced by atropine. At high frequencies (>72/min) this positive effect of ACh was abolished. Moreover, at high frequencies, ACh consistently further reduced the normal increment in tension associated with increasing frequency. The magnitude of the positive inotropic action of ACh on papillary muscle was abolished by lowering the extracellular [Na+] and varied inversely with the extracellular [Ca2+]. These findings were interpreted in terms of a dual action of ACh on the myocardium: (1) an action on the muscarinic receptor that reduces contractility and may be blocked with atropine, and (2) a direct effect on cellular membrane permeability to Ca2+that stimulates contractility and may be reduced by prior elevation of intracytoplasmic [Ca2+].

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The storage and release of3H-norepinephrine in the hearts of rats made hypertensive by desoxycorticosterone and NaCl is reported. The initial uptake of the labeled catecholamine was similar in hypertensive and normotensive groups. After an intravenous injection of3H-norepinephrine, there was a greater and more prolonged fall in specific activity of cardiac norepineph-rine in the first few hours in the hypertensive animals. Subcellular distribution studies showed that in the hearts from hypertensive rats a greater proportion of the labeled amine was present in the soluble-cytoplasmic fraction than in the granular-storage fraction. In control rats an equilibrium between soluble and granular fractions was reached by 1 hr, while in the hypertensives it was not achieved within 24 hr. In the first few hours there was a 45% fall in specific activity in the granular fraction of the hypertensive rats, but only a small re-deuction in the controls. There was an elevation in the fraction of deaminated metabolites in the hearts of the hypertensive animals, while in the kidneys all3H-metabolites were increased. These observations are consistent with the concept that there is a defect in the storage and retention of norepinephrine by granules in sympathetic nerves in this type of experimental hypertension. Such an abnormality might permit increased amounts of physiologically active cate-cholamine to be available to the receptor.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The synthesis of lipid by rabbit atherosclerotic intima incubated in vitro has been investigated and compared with that of foam cells isolated from intimal lesions. In the atherosclerotic arterial intima,14C-labeled acetate is readily incorporated into the lipid fraction, most of the label being found in the phos-pholipid and cholesterol ester fatty acid fractions. Minimal incorporation into triglyceride, fatty acid, and cholesterol occurred. The major phospholipid synthesized was lecithin but significant incorporation into phosphatidyl inositol, phosphatidyl ethanolamine, and sphingomyelin also took place. The fatty acids synthesized were predominantly saturated in the phospholipid fraction. More monounsaturated fatty acids were present in the cholesterol ester fatty acids, but in both moieties little polyunsaturated fatty acids were labeled by the acetate. Isolated foam cells were also shown to incorporate14C-labeled acetate into both phospholipid and cholesterol ester fatty acids. The foam cells, however, incorporated a significantly higher proportion of acetate into cholesterol ester than did the whole intima. The fatty acids synthesized by the foam cells were more polyunsaturated in both the phospholipid and the cholesterol ester fraction than was the case with the whole intima. The relevance of these findings to the origin of lipid in the atherosclerotic lesion is discussed.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Very weak, 60-cps alternating current applied directly to the heart can cause ventricular fibrillation; greater current strength is required to induce ventricular fibrillation with a single shock delivered during the vulnerable period of the cardiac cycle. The present experiments were designed to examine the basis of this difference. The studies were performed in anesthetized open-chest dogs. The current strength required to induce ventricular fibrillation was 0.52± 0.16 ma with 60 cps for 5 sec, and 15.0±4.3 ma with a single square-wave pulse of 10 msec. However, when the duration of 60 cps was reduced to produced only 4, 3, 2, or1 ventricular response, the threshold for ventricular fibrillation after the last response was 0.4, 2, 18, or 24 ma respectively. After any given number of successive premature ventricular responses, the fibrillation threshold was comparable with either 60 cps or a single pulse. We concluded that, if an accelerating ventricular tachycardia that is produced by 60-cps stimulation is of sufficient duration (5 or 6 beats), the VF threshold is reduced progressively after each premature ventricular response, thus making it possible to include VF with very weak current.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The effects of variations in external K+and Ca2+concentrations on electrical and mechanical activity of the isolated rat portal vein were studied using a sucrose-gap technique. Spontaneous activity in normal Krebs solution consists of bursts of action potentials accompanied by phasic contractions. Moderate reduction in [K+]oresults in slight hyperpolarization with decreased discharge frequency. Greater reduction or total removal of extracellular K causes a temporary increase in burst frequency. Graded increases in [K+]ofrom 6 up to 128 mM cause depolarization with an increase in discharge frequency and in contraction amplitude until [K+]oreaches a level of 6 to 7 times normal when spike potentials are abolished and a contracture develops. The relationship between membrance potential and log [K+]oindicates a relatively low permeability to K+. Increasing [Ca2+]ocauses slight hyperpolarization, decreased burst frequency, increased burst duration and increased contraction amplitude. Reducing [Ca2+]ocauses increased frequency of discharge and shortening of bursts, until single spikes appear, each preceded by a prepotential; thus the activity resembles that in cardiac pacemaker cells. In Ca2+-free solution, electrical and mechanical activity ceases within 10 to 15 min. Calcium is essential for activation of the contractile mechanism and for maintenance of spontaneous spike discharge.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Effects of norepinephrine (NE) and isoproterenol on simultaneously recorded electrical and contractile activity in rat portal vein were studied using a sucrose-gaps technique. This vascular smooth muscle shows spontaneous phasic contractions correlated with bursts of action potentials. Norepinephrine (10-99 to 10-7w/v) increases the duration of the bursts and shortens the interval between after an initial period of continuous spike discharge. The tension response is greater than can be accounted for by the increase in electrical activity. High NE concentrations (10–5) produce depolarization, decrease of spike amplitude, or even abolition of spikes and maintained contractions. Norepinephrine increases contracture tension of K+-depolarized portal vein without changing membrane potential. Electrical and mechanical activity is reinitiated in preparations inactivated by elimination of Ca2+this may be due to release of bound calcium. Phenoxybenzamine abolishes the above NE responses. The typical response to isoproterenol (109to 107) in a normal ionic environment consists of moderate depolarization, decreased burst duration, but increased frequency of bursts and inhibition of tension development which is not simply correlated with the change in electrical activity. This pattern resembles that produced by lowering [Ca2+]o. Contracture tension in high [K+]ois reduced by isoproterenol without changes in membrane potential. These responses to isoproterenol are abolished by propranolol. At high concentrations of isoproterenol (10-5) the inhibitory responses are not sustained, but revert to a pattern of activity resembling that induced by NE.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

Cardiac enlargement was produced in three groups of male rats by maintaining them on a diet low in iron. Hearts from anemic rats increased approximately 100% in weight compared to hearts from normal rats. When compared to control cardiac tissue, no consistent significant changes in theconcentrationof DNA, RNA, or protein occurred in any of the groups. Thetotalamount of all three constituents increased significantly in the enlarged hearts; this increase was proportional to the degree of cardiac enlargement. The data indicate that nuclear and cytoplasmic material increased equally in cardiac enlargement due to nutritional anemia. This and other observations in the literature suggest hyperplasia as the most likely explanation.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID

摘要:

The effect of reducing the force of right atrial contraction on right ventricular stroke volume was determined in anesthetized open-chest dogs. Atrial contractile force, measured directly with a strain-gauge arch, was decreased by electrical stimulation of the right vagus nerve; right ventricular stroke volume was measured with an electro-magnetic flowmeter. Heart rate was maintained constant by electrical stimulation of the right atrium.Vagal stimulation decreased atrial contractile force by an average of 47±2.6 (SEM)% of the control, and stroke volume fell by 4.0±0.9%. During vagal stimulation, no change was observed in right ventricular contractile force. In addition, no consistent change was noted in mean right atrial or right ventricular pressures. The relation between the decrease in atrial force and stroke volume was not altered significantly by the rate of right atrial pacing. In 7 of 10 experiments, increasing the inhibition of atrial force produced a further decrease in stroke volume.Since neural, mechanical, and humoral factors modify atrial contractile force in the intact animal, the present study provides more definitive evidence that the ability to alter atrial force represents another adaptive mechanism in the regulation of cardiac performance.

ISSN:0009-7330    

出版商:OVID    

年代:1967

数据来源: OVID