ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The influence of tonic sympathetic and parasympathetic nervous system activity on ventricular refractory period duration was studied in 13 mongrel dogs. Strength-interval curves were obtained from the apex of the right ventricular endocardium with a transvenous bipolar catheter. The effects of sympathetic activity were assessed by unilateral and bilateral stellectomies and tonic vagal effects were studied by inducing cholinergic blockade with atropine (0.2 mg/kg) and by sectioning the cervical vagi bilaterally. Right stellectomy shifted the strength-interval curve 3-5 msec earlier (P< 0.005). In contrast, left stellectomy shifted the strength-interval curve 4-7 msec later (P< 0.001). Thus, right and left unilateral stellectomy produced opposite effects. However, when the contralateral ganglion was removed, right and left stellectomy produced qualitatively similar effects, increasing refractoriness. The net effect of bilateral stellectomy was to shift the strength-interval curve 8-10 msec later (P< 0.001) and this was primarily dependent on left stellectomy. Blockade of vagal efferent activity with atropine shifted the strengthinterval curve 3-6 msec earlier (P= 0.001). Removal of vagal afferent activity by vagotomy during atropine blockade shifted the strength-interval curve 2-3 msec earlier (P= 0.03). It is concluded that both stellate ganglia exert qualitatively similar effects on cardiac refractoriness; however, the left ganglion dominates and unilateral right stellectomy produces a paradoxical decrease in refractoriness. The sympathetic effects are tonically antagonized by vagal activity.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The effect of histamine on coronary blood flow (CBF) was studied in anaesthetized greyhounds. CBF and systemic blood pressure were measured using electromagnetic flow transducers and catheters in the aorta during infusions of drugs into the left circumflex coronary artery. Histamine infusions (5, 10, and 20 μg/min) produced dose-related increases in CBF without changing heart rate or blood pressure. Metiamide (100 μg/min) given simultaneously produced a parallel displacement of the histamine dose-response curve to the right (P< 0.05) with a dose ratio of 2. Mepyramine (100 μg/min) produced a larger parallel displacement of the dose-response curve (dose ratio = 4). Together, metiamide and mepyramine greatly reduced the histamine response (dose ratio = 16), showing that the metiamide blockade is augmented in the presence of mepyramine. Similarly, mepyramine blockade is augmented in the presence of metiamide. The increase in CBF produced by histamine infusion (20 μg/ min) was similar to the peak flow response of reactive hyperemia following 8-second occlusions. However, mepyramine and metiamide together had no effect on the peak flow response, duration, or total repayment of flow debt in reactive hyperemia. These results show that histamine-induced coronary vasodilation is mediated by both H, and H, receptors. However, the vasodilation of reactive hyperemia after brief coronary artery occlusions does not appear to involve histamine.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

On the basis of an electrical analog, open circuit impedance functions were used to analyze the microcirculation. No specific structure need be assumed except a two-port, two-terminal network in which the major artery and vein supplying the tissue represent the input port and the two ends of the microvessel under study are the output port. The open circuit measurements were made by occluding microvessels in the exteriorized omenturn of anesthetized rabbits. The pressure upstream and downstream to the occlusion defines the source pressure of a Thévenin's equivalent circuit. The equivalent resistance value was calculated by plotting the flow through a given microvessel against the pressure developed during a gradual occlusion. The changes in pressure vs. the changes in flow during a progressive occlusion were found to be linearly related. The Thévenin's equivalent resistance was maximum downstream to an occluded artery and upstream to the occluded vein. Within the capillary network, source pressures consistently were within a narrow range. Topically applied norepinephrine resulted in marked changes in source resistance and no changes in source pressures. Threshold doses of norepinephrine given intravenously resulted in changes in source pressures, but minimal changes in source resistance, even though a substantial change in vascular resistance was indicated when calculated on the basis of arterial pressure minus micropressure divided by microvessel flow. The present method defines the functional characteristics of the distributing vessels in terms of two pressures and two equivalent resistances and is relatively easy to perform. The technique can be used to determine the vascular components involved in the response to particular stimuli.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Fetal and maternal glomerular filtration rate (GFR), renal plasma flow (RPF), urine volume, sodium excretion, and fractional sodium reabsorption were measured in a chronically instrumented sheep preparation. Fetal GFR was essentially stable between 110 and 135 days of gestation (term = 147 days). There was a significant increase in GFR after 135 days. After the infusion of 50 ml of normal saline over a 30-minute period, fetal GFR and sodium excretion increased significantly. Fractional sodium reabsorption was significantly decreased. Thus, the fetus is capable of responding to volume expansion with saline with an increase in GFR and a decrease in fractional sodium reabsorption. After the infusion of 1000 ml of normal saline into the ewe in 1 hour, maternal GFR and RPF rose significantly. Sodium excretion rose 6-fold and fractional sodium reabsorption fell significantly. After the infusion of saline into the ewe, there was no change in fetal GFR, RPF, sodium excretion, urine volume, or fractional sodium reabsorption. Since there were no changes in fetal renal function after maternal volume expansion with saline there was no evidence for the transplacental passage of a natriuretic factor from ewe to fetus.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

Dopamine shifted the voltage-dependence of the slow outward current that underlies spontaneous diastolic depolarization to a more positive voltage range and increased the rate constants of inactivation of this current at voltages negative to −80 mV. Dopamine increased the magnitude of the slow inward current and the delayed outward current. Dopamine had an inconsistent effect on the positive dynamic current and the timeindependent potassium current. These effects were consistent with effects on the slope of diastolic depolarization, plateau voltage, and action potential duration and are similar to those of epinephrine. The effects of dopamine on the slow inward current and on the delayed outward current were abolished by verapamil, a slow channel blocker. This finding substantiates that outward potassium currents are modulated by intracellular calcium.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

In an attempt to determine the mechanism by which hyaluronidase reduces myocardial injury following coronary artery occlusion, myocardial blood flow was studied in 20 open-chest dogs with occlusion of the left anterior descending coronary artery. Ten dogs served as controls, and 10 received hyaluronidase (500 NF units/kg) intravenously 20 minutes after occlusion. At 15 minutes and at 6 hours after occlusion, regional myocardial blood flow in the epicardial and endocardial halves of both ischemic and nonischemic zones were determined with radiolabeled microspheres. Mean arterial pressure, heart rate, and cardiac output were similar in the untreated and treated dogs through the 6 hours of the experiment. Moreover, regional blood flow to nonischemic myocardium (areas without epicardial S-T segment elevation 15 minutes after occlusion) was similar in the two groups 15 minutes and 6 hours after occlusion. Fifteen minutes after occlusion, the flow to the ischemic myocardium subjacent to sites with S-T segment elevation exceeding 2 mV) in the untreated group was: transmural, 28.1 ± 2.2 (mean ± SE) ml/min per 100 g; endocardial, 20.7 ± 1.8; and epicardial, 38.5 ± 3.1. The endocardial-epicardial flow ratio was 0.56 ± 0.04. Six hours after occlusion, the untreated group demonstrated a further decrease in blood flow to the ischemic myocardium: transmural, 15.2 ± 1.4 ml/min per 100 g; endocardial, 6.8 ± 1.1; and epicardial, 24.3 ± 1.9. The endocardial-epicardial flow ratio fell to 0.28 ± 0.04. In contrast, the hyaluronidase-treated dogs showed no further reduction in blood flow to ischemic myocardium 6 hours after occlusion: transmural, 30.3 ± 3.1 ml/min per 100 g; endocardial, 21.3 ± 2.5; and epicardial, 38.8 ± 3.8. These regional myocardial flows were significantly higher than those of the untreated dogs 6 hours after occlusion. Thus, salvage of damaged myocardium by hyaluronidase might be explained by its beneficial effect on collateral blood flow to the ischemic tissue, though this effect on collateral flow could be the consequence rather than the cause of this salvage.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

The influence that the pressure-sensitive receptors in the cardiovascular system have on renal nerve activity and on heart rate was compared in normotensive rats (NTR) and spontaneously hypertensive rats (SHR). The cardiovascular receptors were stimulated by raising the blood pressure (BP) with intravenous phenylephrine. The duration of silence in the record of renal sympathetic nerve activity produced by a number of different rises in BP was measured. We found that the pressure that was just able to produce a silence in the nerve activity (threshold pressure) was higher in the SHR (170 mm Hg) than in the NTR (130 mm Hg). Also, comparable rises in BP above the threshold pressure in the SHR and NTR were less effective in the SHR in producing a complete inhibition of sympathetic nerve activity as judged by the short duration of inhibition. In contrast, we found that the changes in heart rate produced by rises in BP above threshold pressure were similar in NTR and SHR although the threshold pressure was somewhat higher in the latter. It was, therefore, concluded that the cardiovascular pressure receptors, apart from being reset to operate at a higher pressure level in the SHR, are less able to inhibit ongoing sympathetic activity than in the NTR. It is suggested that this is most likely due to a high sympathetic activity in the SHR.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

To examine the influence of preexistent diabetes mellitus on left ventricular performance and coronary blood flow responses to acute ischemia, mild normoglycemic diabetes was induced in nine mongrel dogs after three doses of alloxan, (20 mg/kg, iv), at monthly intervals. Hemodynamic measurements and coronary blood flow (85Kr clearance) were obtained before and after the onset of ischemia. This was produced by occlusion of the proximal left anterior descending coronary artery via a balloon-type catheter in nine intact anesthetized diabetic dogs and 10 nondiabetic dogs. During the 1st hour of ischemia in the diabetic group, the end-diastolic pressure rose from 7 ± 1.1 (mean ± SE) mm Hg to 23.8 ± 2.3 without a significant increase of end-diastolic volume. In controls end-diastolic pressure rose from 8.6 ± 1.1 mm Hg to 15.3 ± 1.4, and end-diastolic volume was significantly increased, so that the ratio of end-diastolic pressure and volume was significantly higher in the diabetic group (P< 0.005). Although indices of contractility did not differ, stroke volume and work reductions were significantly greater in diabetics, despite the fact that coronary blood flow was reduced to a similar extent. Size of the ischemic areas appeared comparable as judged by distribution of dye injected distal to the occlusion. Since potassium loss and sodium gain in the inner and outer layers of ischemic tissue did not differ between the two groups, the intensity of ischemia seemed similar. Glycogenolysis was unimpaired in the diabetic ischemic muscle but triglyceride levels remained elevated. Morphologically the diabetic myocardium was characterized by a diffuse accumulation of periodic acid-Schiffpositive glycoprotein in the interstitium, which was thought to limit diastolic filling of the ischemic ventricle and to contribute to the substantial reduction of ventricular performance.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID

摘要:

We measured the characteristics of the decline in tension during isometric relaxation of canine papillary muscle. In the intact heart, relaxation begins with the isovolumic phase, but in experiments on papillary muscle previously reported the isotonic phase preceded the isometric phase during the course of relaxation. In our experiments, however, the isotonic bar was locked at the instant the muscle reached the end-systolic fiber length in order to hold the fiber at that length during the succeeding relaxation process. Therefore, we obtained a relaxation process similar to that occurring in an intact heart. The major results of these experiments are: (1) Maximum rate of the decline in tension (-dT/dtmax) is linearly related to the magnitude of total load. (2)' -dT/dtmaxis augmented by positive inotropic interventions and diminished by negative inotropic interventions. (3) An increase in preload results in only a slight increase in -dT/dtmax. (4) End-systolic fiber length itself is not a principal determinant of -dT/dtmax. (5) -dT/dtmaxdivided by total load is independent of the amount of muscle shortening. We, therefore, suggest that -dT/dtmaxdivided by total load can be a useful index of the relaxation characteristics of cardiac muscle.

ISSN:0009-7330    

出版商:OVID    

年代:1977

数据来源: OVID