ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The distribution of renal blood flow was measured in isolated blood-perfused dog kidneys using radioactive labeled microspheres. The kidneys were perfused at a constant systolic pressure of 140 mm Hg. For the first 50 minutes of perfusion, flow to the outer zones of the renal cortex was 79±2% (SE) of the total renal blood flow, and inner cortical blood flow accounted for 21±2%. With continued perfusion, inner cortical blood flow increased progressively, reaching 34±3% by 150 minutes—a time when renin substrate was depleted in the perfusates. Infusions of the tetradecapeptide renin substrate (5–50 μg/min) reestablished the fractional distribution of renal blood flow observed in the initial 50 minutes of perfusion, i.e., inner cortical blood flow was reduced significantly from 36±2% to 23±4% (P< 0.05). In contrast, infusions of angiotensin II (1–10 μg/min) did not reduce the fractional distribution of renal blood flow to the inner cortex. These data provide evidence to support the hypothesis that angiotensin might be formed as an intrarenal hormone which participates in the regulation of deep cortical and medullary vascular resistances. Circulating angiotensin II does not appear to serve a similar function.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

The smooth muscle of the rat portal vein which supports propagation becomes supersensitive to exogenousl-norepinephrine after elimination of the vessel's intramural neuronal uptake mechanism. Such supersensitivity is generally associated with intimate neuromuscular connections. Since the adrenergic vasomotor fibers in the portal vein do not enter the muscle tissue, it has been proposed that muscle cells close to the nerve terminals must determine the response to norepinephrine. With the aim of elucidating the mechanism behind the prejunctional supersensitivity, the total uptake of labeled norepinephrine in the portal vein was analyzed and its distribution within the vessel wall was evaluated directly using isotopically labeled frozen sections. The total uptake of the portal vein, related to its endogenous norepinephrine content, was comparable with that in other vascular and nonvascular tissues. The3H-uptake profile of the vessel wall showed that the neurogenic uptake was confined to the narrow adrenergic plexus between the longitudinal and the circular muscle layers. The neuronal uptake mechanism therefore could only influence the concentration of exogenous norepinephrine at muscle cells close to the nerve terminals. These results support the hypothesis that the prejunctional supersenstivity in the rat portal vein indicates that the alpha receptors are located on muscle cells in the vicinity of the adrenergic nerve terminals.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Normal and sinoaortic baroreceptor–denervated dogs were monitored continuously (24 hours a day) to quantify the role of the baroreceptors in determining the average level and the variability of arterial blood pressure, heart rate, cardiac output, and total peripheral resistance. The frequency of occurrence over 24-hour periods was obtained for each variable using a fiber optic curve-scanning system to read the variables from continuously recorded charts and a digital computer system to plot curves. The results indicate that the degree of hypertension previously reported for this preparation has been highly exaggerated, presumably due to the methods of study. The average 24-hour mean arterial blood pressure was 101.6 mm Hg in normal dogs and only 112.7 mm Hg in baroreceptor-denervated dogs. The normal dogs exhibited narrowly distributed 24-hour frequency distribution curves for blood pressure; in contrast the denervated dogs exhibited curves with twice the 24-hour standard deviation. Similar analysis indicated that the baroreceptors exerted less influence on the daily stabilization of heart rate than they did on arterial blood pressure and that they had very little if any influence on the daily stabilization of cardiac output and total peripheral resistance. Hemodynamic variables during postural changes were studied along with diurnal rhythms. We concluded that the primary function of the baroreceptor reflex is not to set the chronic level of arterial blood pressure but, instead, to minimize variations in systemic arterial blood pressure, whether these variations are caused by postural changes of the animal, excitement, diurnal rhythm, or even spontaneous fluctuations of unknown origin.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

In this paper we presented a method for determining the distribution of circumferential (SΘ), longitudinal (Sz), and radial (Sr) stress and of strain-energy density (W) in canine aortic segments under physiological loading. Aortic segments from 13 dogs were studied in vitro. Intraluminal pressure and longitudinal force were varied over ranges of 25 to 200 cm H2O and 0 to 100 g, respectively, and the external radius and the segment length were measured at each step. A nonlinear theory of large deformation of the aortic tissue based on the assumptions of incompressibility and curvilinear orthotropy was applied to the data. The 3, 7, or 12 constitutive constants of the theory were calculated without using the usual thin-wall assumption. These constants were then used to calculate the distribution of stresses and ofW. The results indicated that (I)SΘ,Sz,Sr, andWwere largest in magnitude at the endothelial surface and decreased toward the adventitial surface, (2) the decrease was most marked in the inner third of the vessel wall, (3) in generalSΘ>Sz>W>Sr, and (4) at a given longitudinal stretch an increase in intraluminal pressure increasedSΘ,Sz, |Sr|, andW, with the effect being most marked onSΘ.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Bilateral electrolytic lesions of the nucleus tractus solitarii in the rat at the level of the obex abolished baroreceptor reflexes and resulted in an immediate, marked elevation in systemic blood pressure without a change in heart rate. In unanesthetized rats the hypertension was associated with a marked increase in total peripheral resistance, a reduction in blood flow in the abdominal aorta, and an increase in central venous pressure. The cardiac output was reduced to 62% of control as a consequence of reduced stroke volume, which was reflected, in turn, by increased end-diastolic pressure. The hypertension was abolished and the end-diastolic pressure lowered by blockade of alpha receptors with phentolamine. The hypertension was not due to changes in blood gases or to release of agents from the kidneys or the adrenal glands; it was very sensitive to anesthetics and was abolished or aborted by midcollicular decerebration. Within hours after lesioning, the rats developed progressive congestive heart failure and died in shock, often in association with pulmonary edema. We concluded that the fulminating hypertension evoked by lesions of the nucleus tractus solitarii was due to the increased vasoconstriction caused by the augmented discharge of sympathetic nerves in response to central deafferentation of baroreceptor reflexes; the hypertension was mediated by alpha receptors and depended on the integrity of structures lying above the midbrain.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Serum dopamine-β-hydroxylase activity varied from 3 to 581 units/ml in a group of 168 untreated adults (90 normals, 78 with borderline or overt hypertension). Levels did not correlate with blood pressure or age, but mean values were significantly lower in blacks than they were in whites. Subjects with exceptionally low levels of serum dopamine-β-hydroxylase activity showed normal cardiovascular function and normal β-hydroxylation of an administered synthetic substrate, hydroxyamphetamine. Pronounced blood pressure reduction by antihypertensive drugs did not change serum dopamine-β-hydroxylase activity, and intensive bicycle exercise produced only small and variable increases. Two subjects with severe sympathetic dysfunction, i.e., orthostatic hypotension, showed normal levels of dopamine-β-hydroxylase activity (89–123 units/ml). Serum dopamine-β-hydroxylase activity varied from 450 to 950 units/ml in five subjects with pheochromocytomas and decreased to one-tenth the preoperative level in one subject who underwent curative surgery. Therefore, serum dopamine-β-hydroxylase activity is not a satisfactory index of sympathetic function; moreover, activity levels do not correlate with prevailing blood pressure. Subjects with pheochromocytomas, however, may show increased serum levels of the enzyme, which demonstrates that such tumors can release dopamine-β-hydroxylase.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Transmembrane activity was recorded from canine false tendons bathed with Tyrode's solution at 37°C. Stimulus patterns provided a 3-second pause after every ten beats. Acetylstrophanthidin was infused at concentrations up to 2×10−7g/ml. One or two transient depolarizations (TDs) followed the last driven response of each series. The appearance of TDs was associated with depression of normal phase-4 depolarization. The peak of the earliest TD (TD-1) occurred at an interval approximately equal to the basic cycle length. The later TD (TD-2) occurred at about twice the basic cycle length. Coupling intervals were determined primarily by the last cycle length. The amplitude of TD-1 was maximal when the basic cycle length was 600 msec, but TD-2 continued to increase as the basic cycle length diminished further. The amplitude of both TDs increased with the number of beats in the train. Either or both could reach threshold and induce single extrasystoles or trains of extrasystoles. TDs could be induced to reach threshold after each driven response, resulting in sustained bigeminal rhythms with fixed coupling. Possibly TDs provide a mechanism for various clinically observed arrhythmias induced by cardiac glycosides.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Transient depolarizations (TDs) appeared in canine Purkinje tissue but not in cardiac muscle during exposure to 1–2 × 10−7g/ml of acetylstrophanthidin. At low levels of toxicity, the TDs were associated with a decrease in threshold and an increase in automaticity. As intoxication progressed, the TDs coincided with transient periods of increased threshold and conduction block. Propagation from muscle to Purkinje tissue was blocked during, but not before or after, the crest of the TDs. As a result of the interaction between temporal and spatial (electrotonic) factors, various patterns of block, including unidirectional block, were observed. At moderate frequencies 2:1 block was demonstrated, but at faster rates 1:1 transmission occurred. At a later stage of toxicity, repetitive stimulation led to progressive depolarization in Purkinje tissue followed by a period of block during which slow repolarization eventually restored excitability and conductivity. In the whole heart, conduction block could permit reentry and could be responsible for the ultimate transition from ventricular tachycardia to ventricular fibrillation.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID

摘要:

Isolated preparations of atrial specialized conduction fibers (“plateau” fibers) qualitatively resembled ventricular Purkinje fibers (false tendons) in their response to acetylstrophanthidin. Acetylstrophanthidin in concentrations of 1–3 ×10−7g/ml caused coupled, frequency-dependent transient depolarizations (TDs) in both types of fiber. In free-running strands of plateau fibers the TDs could reach threshold and generate coupled action potentials, but TDs and automatic responses did not occur in ordinary atrial muscle fibers. TDs were suppressed by elevation of the external potassium concentration. Automatic activity and TDs in atrial plateau fibers were abolished by acetylcholine. Automatic activity was also sometimes suppressed in false tendons by acetylcholine, but TDs and related coupled responses were not influenced.

ISSN:0009-7330    

出版商:OVID    

年代:1973

数据来源: OVID