ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

In anesthetized curarized cats with their chests open, we recorded the activity of type B right atrial vagal stretch receptors, right atrial pressure, and instantaneous dimensional changes of the right atrium. The nervous activity was analyzed during alterations in atrial dynamics produced by acute volume loading of the right atrium under control conditions and during sympathetic and vagal stimulations. Our results demonstrated that the mean frequency of discharge in the burst was dependent on the absolute tension and the rate of change in tension developed in atrial muscles during filling. The responses of different receptors to changes in atrial dynamics were qualitatively similar but characteristic for each receptor studied. In some experiments nervous activity was recorded after the cats had been killed: static and dynamic changes in atrial tension were then produced by injecting blood into the right atrium. Under these conditions dynamic stimuli always activated the receptors at tensions below the threshold for static stimuli. During dynamic stimuli the instantaneous firing rate was always higher than it was during static stimuli applied at the same level of tension. This study indicates that the nervous activity of type B atrial vagal receptors is closely dependent on static and dynamic changes in atrial wall tension.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The genotype of homograft kidneys plays the primary role in determining chronic blood pressure levels in two strains of rats with opposite genetically controlled propensities for hypertension. In hypertensive rats from the hypertension-prone (S) strain, a renal homograft from the same strain resulted in a slight rise in blood pressure to a level that was equivalent to that in appropriate uninephrectomized S controls. In contrast, a renal homograft from the hypertension-resistant (R) strain led to a sharp fall in blood pressure in hypertensive S recipients. Opposite results were found when the host came from the R strain: R homografts maintained the same low pressure as that seen in controls, whereas S homografts resulted in hypertension. We concluded that genetically controlled factors operating through the kidney can chronically modify the blood pressure up or down. The central role of the kidney in hypertension is thus further documented.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The relationship between regional blood flow and epicardial S-T segment elevation was studied in 26 open-chest anesthetized dogs with left anterior coronary artery ligations. Changes in myocardial blood flow, measured with 15 ± 5μ (diameter) microspheres labeled with14lCe,85Sr, and169Yb, were correlated with summated S-T segment elevations 15 minutes, 1 hour, and 2 hours after coronary artery occlusion. In normal areas, myocardial blood flow was 113 ± 5 ml/min 100 g−1and summated S-T segment elevation was 0.3 ± 0.2 mv. Fifteen minutes after coronary artery occlusion in 26 dogs, S-T segment elevation was 5.7 ± 0.7 mv over the center of the infarct and myocardial blood flow was 10 ± 1 ml/min 100 g−1; over the border zone, myocardial blood flow was 63 ± 4 ml/min 100g−1and S-T segment elevation was 3.1 ± 0.1 mv. One third of the areas with a myocardial blood flow of 10 ml/min 100 g−1or less had no S-T segment elevation. In the center and border zones of the infarct in 9 dogs, myocardial blood flow increased from 11 ± 2 and 67 ± 8 ml/min 100g−115 minutes after occlusion to 20 ± 4 and 84 ± 12 ml/min 100 g−1respectively, 2 hours after coronary artery occlusion. These increases were not associated with a significant reduction in summated S-T segment elevation. The results do not suggest a simple quantitative relationship between epicardial S-T segment elevation and myocardial blood flow following acute coronary artery occlusion.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Changes in perfusion pressure in response to graded doses of prostaglandin F2α(PGF22α) were measured during both forward and retrograde perfusion of isolated cat lungs perfused at a constant flow rate. During forward perfusion, PGF2αproduced a dose-dependent increase in pulmonary artery pressure and a decrease in lung fluid volume. During retrograde perfusion, PGF2αalso produced a dose-dependent increase in perfusion pressure; however, the dose required was fivefold greater than that needed to produce an identical change in pressure during forward perfusion. In addition, during retrograde perfusion, the lung fluid volume increased in response to PGF2αThese results suggest that the major site of activity of PGF22αis on the arterial side of the pulmonary vascular bed and that inactivation of PGF2αby the lung occurs primarily distal to this arterial site of vasomotion. The changes in perfusion pressure in response to PGF2αwere markedly dependent on pH and oxygen tension (Po2), being abolished by severe alkalosis and potentiated by both acidosis and hypoxia. In contrast, neither serotonin nor norepineph-rine exhibited such a pH or Po2dependency. Since the ratio of the forward response to the retrograde response was not decreased by alterations of pH or Po2, their influence on the responses appears to be through interaction at the site of vascular activity rather than through alteration of the rate of prostaglandin inactivation.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effects of Mn2+-containing solutions on the mechanical and electrical responses of myocardial tissue were studied on guinea pig ventricular strips. At a concentration of 10 mM, Mn2+abolished the twitch responses and caused the development of a contracture in stimulated preparations but not in resting or in Ca2+-depleted preparations. The duration of action potentials was shortened, and dV/dtma]lwas decreased. In Ca2+-depleted (0.1 mM), Mg2+-free medium, Mn2+also increased the amplitude of the overshoot; the increase was due to a slow phase of depolarization. Measurement of the Mn2+uptake showed an increased influx of these ions in stimulated preparations compared with that in quiescent preparations. These results suggest that Mn2+(1) generates a transmembrane current in guinea pig myocardial cells and (2) interferes with the excitation-contraction coupling process at two levels: the cell membrane and an intracellular site.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effect of angiotensin on the action of tyramine was studied in isolated rabbit left atria paced by point and field stimulation to more clearly define the interaction of angiotensin with the sympathetic nervous system. Administration of angiotensin resulted in similar increases in contractility in both point- and field-stimulated atria. In point-stimulated preparations only the muscle is stimulated to contract, whereas in field-stimulated preparations both nerve and muscle are stimulated. l-Sar-8-Ala-angiotensin II completely blocked the direct inotropic effect of angiotensin in a molar dose ratio of 3:1 in both point- and field-stimulated preparations. However, angiotensin (0.05–10 ng/ml) potentiated the inotropic effect of tyramine in field-stimulated atria only. This facilitatory effect was not inhibited by l-Sar-8-Ala-angiotensin II at a molar dose ratio of 3:1; indeed, a ratio of 500:1 was necessary for complete blockade of this angiotensin-induced potentiation. This antagonist in doses of 0.1–1000 ng/ml was without contractile effect in any preparation, regardless of whether tyramine was present. The data suggest the presence of (1) a presynaptic angiotensin receptor that, in the presence of sympathetic nerve stimulation, modulates the release of norepinephrine and (2) a second angiotensin receptor in cardiac tissue that directly influences myocardial contractility.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effects of changes in the calcium ion concentration in the medium bathing single beating cultured chick embryo ventricular cells were determined using an electro-optical monitoring technique for measuring the amplitude and velocity of cell wall motion. Although single cells showed significant decreases in the amplitude and velocity of cell wall motion during contraction when the calcium ion concentration was lowered from 1.8 mM to 0.9 raM, there were no significant changes in these parameters when the concentration was increased from 1.8 mM to 3.6 mM. Ventricular strips obtained from embryos of the same age showed positive inotropic responses to an increase in the external calcium ion concentration from 1.8 mM to 3.6 mM, and the magnitude of this response increased with increasing embryonic age. These results suggest that there is a reduced positive inotropic responsiveness in young chick embryo ventricular cells, which is particularly marked in the single cultured cell preparation because of the tendency of culturing techniques to select out immature cell populations.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Stenoses were artificially induced in 13 large mongrel dogs by implanting small hollow cylindrical plugs in their femoral arteries. The instantaneous pressure drop across the stenosis and the flow rate were measured for a series of stenoses varying in severity from 52.3 to 92.2%. Mean pressure drops ranged from approximately 2 to 30 mm Hg with peak pressure drops ranging from 9 to 53 mm Hg. The pressure drop could be estimated from a relatively simple equation that was originally developed for flow through model stenoses. With this equation, the effects of several factors that contribute to the pressure drop, including stenosis size and shape, artery lumen diameter, blood density, blood viscosity, and velocity and acceleration of flow, could be clearly delineated. For severe stenoses, unsteady flow effects were small, and flow could be treated as quasi-steady. Calculations based on data obtained from the dog experiments revealed that the mean pressure drop across a stenosis increased nonlinearly with percent stenosis and showed quantitatively that the value of critical stenosis decreased with increasing demand for blood flow.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The rat heart demonstrates marked alterations in its responses to ouabain and increased frequencies of stimulation and in the duration of its action potential during the initial 21 days of life. At an age of 6.2 days 5 × 10−5m ouabain produced a 158.2% increase in dP/dt compared with a 17.2% increase at 21.1 days (P< 0.001). At 6.2 days dP/dt increased by 53.4% when the heart rate was accelerated from 30 to 90 beats/min compared with an increase of 12.2% at 21.1 days (P≪ 0.005). The positive glycoside and staircase responses at the younger age were virtually eliminated when the hearts were perfused with a solution containing 50% [Na+]oand 25% [Ca2+]o([Ca2+]o/[Na+]02maintained constant). The duration of the ventricular action potential progressively decreased from 350–400 msec at birth to 100–150 msec at 21 days of life. This decrease was due to a shortening and a decrease in the potential level of the plateau phase. The prominent plateau typical of the early neonatal period was significantly diminished by perfusion with 50% [Na+]o. The results suggest that Na+flux through a slow membrane channel plays a significant role in the positive staircase and glycoside responses of the early neonatal rat heart. As the heart matures and becomes functionally anomalous relative to other mammalian species, the slow channel progressively closes.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID