摘要:

The experimental design which most closely reproduces clinical renovascular hypertension is constriction of one renal artery, with the other renal artery and kidney left intact. To test the role of renin and angiotensin in the pathogenesis of renovascular hypertension, attempts were made to induce such hypertension in rats previously immunized with angiotensin. In 29 highly immunized and 33 control rats, one renal artery was partially constricted and the other kidney and renal artery left intact. Preoperative blood pressures were equal in all rats (means: immunized, 118 ± SE 0.95; controls, 117 ± 0.70 mm Hg). Both groups developed hypertension during the 13 days following operation (means: immunized, 173 ± 3.42; controls, 169 ± 4.65 mm Hg). The high blood pressures persisted throughout the observation period (56 days). Immune sera completely inactivated large amounts of angiotensin (mean, 1130 ± SD 887 ng/ml antiserum; range 200−4000), and high intravenous doses of renin and angiotensin had no effect on the blood pressure of immunized rats. These data provide strong evidence that the direct pressor effect of circulating angiotensin is not essential for the development of hypertension evoked by constricting one renal artery in the rat.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

We studied the reflex changes in myocardial contractility elicited by electrical stimulation of afferent cardiac sympathetic nerve fibers or chemical stimulation of their cardiac endings. Veratridine injected directly into the left coronary artery was the chemical stimulus. The maximum rate of rise of left ventricular pressure, dP/dt max, was used as an index of myocardial contractility. The stimuli evoked increases in dP/dt max in vagotomized cats with or without spinal transection (C1). Electrical stimulation provoked the same effect in vagotomized dogs. Increases in dP/dt max occurred which were independent of changes in heart rate, preload, or afterload. They were reflex in nature since they were abolished by section of the upper thoracic sympathetic rami or cardiac sympathetic nerves. These results are the first demonstration of a cardiocardiac reflex which can be mediated entirely by the spinal cord. Electrical stimulation in vagotomized cats and dogs also produced a reflex increase in arterial blood pressure partly due to sympathetic vasoconstriction.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Spontaneous changes in ventricular automaticity were determined from changes in idioventricular rate in eight dogs with heart block. The mediating effects of imposed rate were assessed in terms of (1) changes in post-pacing depression after ventricular pacing in 14 dogs and (2) changes in vagally induced ventricular escape time after atrial pacing in five dogs with intact AV conduction. Spontaneous ventricular automaticity decreased throughout the major portion of digitalization. The transition to a ventricular tachycardia was late and abrupt. Transient increases in rate transiently enhanced ventricular automaticity throughout digitalization. In animals with heart block, this was recognized at 38 ± 3% (SE) of the toxic dose of ouabain as blunting of postpacing depression, i.e., a significant decrease in the depression of the first post-pacing beat. Blunting was progressive and was replaced at 72 ± 3% of the toxic dose by post-pacing acceleration, i.e., the cycle length of the first post-pacing beat became shorter than the average pre-pacing cycle length. In vagal stimulation experiments ventricular escape time decreased earlier during atrial pacing at 180−190 beats/min (74 ± 3% of the toxic dose) than during atrial pacing at 140−150 beats/min (92 ± 3%). Early ventricular escape was not seen after pacing at 100 beats/min. These findings indicate that heart rate is a critical determinant of early increases in ventricular automaticity during digitalization.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The reflex bradycardia produced by a transient phenylephrine-induced rise of arterial pressure was investigated in man during rest and supine exercise, before and after autonomic blockade of the heart. Reflex bradycardia diminished proportionally to the tachycardia of exercise. Propranolol slowed the heart at rest and during exercise, but increased the reflex response only at rest, having no effect during exercise. Atropine, or atropine with propranolol, blocked the reflex during rest and exercise. The tachycardia following hypotension induced by amyl nitrite was similarly affected by the two drugs. Tachycardia induced by standing up and by isoprenaline also diminished the reflex bradycardia. It is concluded that reflex heart rate changes following sudden changes of arterial pressure are predominantly parasympathetic, and diminish during exercise in parallel with the decrease of parasympathetic tone. The reflex response is determined partly by the interaction of parasympathetic and sympathetic impulses at the sinoatrial node, shown by the effects of peripheral sympathetic stimulation and blockade at rest. During exercise central depression of the reflex may also occur.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The effect of the timing of discrete bursts of efferent vagal impulses on heart rate was determined in anesthized dogs. Two modes of stimulation were employed. In the first mode, one stimulus burst was delivered per cardiac cycle. As the time from the beginning of the P wave to the vagal stimulus (P-St interval) was progessively increased, there was first a progressive lengthening of the cardiac cycle (P-P interval), then a rapid decrease in P-P interval, and finally a gradual augmentation of the P-P interval. The amplitudes of curves of P-P interval as a function of P-St interval increased as the number of stimuli per burst was augmented, with 10 stimuli/burst yielding nearly maximal effects. Vagal stimuli applied at P-St intervals which coincided with the negative-slope (d[P-P]/d[P-St]) region of such curves tended to evoke sinus arrhythmias. With 5 stimuli/burst or more, these arrhythmias were pronounced and consisted of alternate short and long P-P intervals. In the second mode of stimulation, bursts of stimuli were delivered to the vagus nerve at a frequency independent of heart rate. The cardiac pacemaker tended to become synchronized in some fixed ratio of vagal stimuli to P waves, and this tendency became greater the larger the number of stimuli per burst of impulses. Within any range of synchronization, a paradoxical effect was manifest–increasing frequencies of vagal stimulation produced increasing rather than decreasing heart rates.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The effects of several inotropic agents were investigated in papillary muscle preparations from normal cats and cats that had undergone previous total extrinsic cardiac denervation. The papillary muscles were bathed in a modified Krebs-Ringer's solution which was equilibrated with 95% O2-5% CO2for the control drug studies or 5% O2-5% CO2-90% N2for the hypoxia studies. This degree of hypoxia produced a 32 ± 3% decrease in tension in papillary muscles from normal cats and a 14 ± 4% decrease in catecholamine-depleted papillary muscles. During hypoxia there was depression of the maximum response to ouabain and norepinephrine with otherwise unchanged dose-response curves. Deterioration of the hypoxic muscles occurred after exposure to norepinephrine concentrations of 5 × 10−7M and greater. The dose-response curve for angiotensin II was unchanged by hypoxia. However, during hypoxia, the dose-response curves for two heptapeptide analogues of angiotensin II, 1-des-5-Valand 1-des-5-Ile-angiotensin II, were augmented. The inotropic effects of these analogues under control and hypoxic conditions were the same in the normal and catecholamine-depleted muscles. The potentiation by hypoxia of the inotropic effects of the angiotensin II analogues is unique among the agents studied.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Cardiac hypertrophy was produced in rats by constricting the abdominal aorta subdiaphragmatically. The weight of the left ventricle was significantly elevated 2 days after aortic constriction and was 19% higher than in shamoperated animals at 11 days. The activity of protocollagen proline hydroxylase (PPH), an enzyme participating in collagen biosynthesis, and the hydroxyproline content of the heart muscle were determined. PPH activity was increased at 2 days after aortic constriction and declined thereafter, being still above the control level at 11 days. The hydroxyproline content of the left ventricle was significantly increased at 11 days in hypertrophied heart muscle compared to controls. The present results suggest that in cardiac hypertrophy an early connective tissue activation occurs. Later, this leads to connective tissue accumulation. The increased collagen content may give support to the cardiac muscle contracting against systolic overload.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

Conventional intracellular recordings from the bundle of His and right bundle branch of the canine heart demonstrated that the slope of diastolic depolarization is markedly depressed by superfusion with relatively small concentrations (4−8 μg/ml) of acetylcholine. As the cells become less automatic, take-off potential increases, rise time of phase 0 is reduced, action potential amplitude increases, and conduction proceeds more rapidly.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

The sequence of conduction through the intraventricular conducting system and endocardial muscle was studied by microelectrode mapping of large areas of isolated canine ventricular tissue. We found that most of the endocardium of the right ventricular free wall is activated simultaneously whereas the left endocardial muscle is activated in an apex-to-base sequence. Right septal activation is from apex to base, and the left septum is activated first at the junction of the middle and lower thirds of the septum and then as a bidirectional wave front toward the apex and the base. These right-left differences occur because the sites of impulse input into muscle on the right encompass the entire free wall, base of the papillary muscle, and the lowermost septum, and on the left are primarily limited to the lower ventricular cavity, lower septum, and bases of the papillary muscles. These patterns of left ventricular excitation relate to the presence of a functionally continuous ring of conducting tissue formed by a merger of the major divisions of the left bundle branch on the upper left ventricular free wall. The “ring” itself is electrophysiologically isolated from muscle, but connects to a network of subendocardial conducting tissue extending to the apex and having input to muscle only in its lower portions.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID

摘要:

A finite-element model is used to analyze the mechanical behavior of the left ventricle. The ventricle is treated as a heterogeneous, linearly elastic, thickwalled solid of revolution. The inner third of the ventricular wall is assumed to be transversely isotropic with a longitudinal Young's modulus, transverse modulus, and shear modulus of 60 g/cm2, 30 g/cm2, and 15.5 g/cm2, respectively. In the outer two-thirds of the ventricular wall the myocardium is assumed to be isotropic with a Young's modulus of 60 g/cm2. Polsson's ratio is assumed to be equal to 0.45 throughout the ventricular wall. The valvular ring at the base of the ventricle is simulated by a homogeneous layer cf collagen. The model appears to predict gross free-wall deformation in the left ventricle of the potassium-arrested rat heart fixed in situ. The presence of a relatively compliant transversely isotropic region near the endocardial surface results in significantly lower axial and circumferential stresses in this region than are present in a homogeneous, isotropic model. The presence of a simulated valvular ring results in a concentration ofrelatively large stresses near the base of the ventricle.

ISSN:0009-7330    

出版商:OVID    

年代:1972

数据来源: OVID