ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

This study was designed to quantitate transmural myocardial blood flow when coronary arterial inflow was limited to systole and during the subsequent reactive hyperemic response. Studies were performed in 10 awake dogs chronically prepared with electromagnetic flowmeters and pneumatic occluders on the left circumflex coronary artery. Intermittent coronary perfusion, confined to the interval of left ventricular systole or an equivalent period during diastole, was effected by an R wave-triggered solenoid valve connected to the occluder. To measure regional myocardial blood flow we injected radionuclide labeled microspheres, 7–10μ fim in diameter, into the left atrium. When arterial inflow was limited to systole, flow was normal in the subepicardial layers and was decreased as a linear function of tissue depth in the subendocardial layers. When coronary arterial inflow was limited to an equivalent interval in diastole, the transmural distribution of flow was uniform. When coronary flow was confined to systole for more than 20 seconds, the blood flow debt incurred elicited a reactive hyperemia similar to that following a total occlusion of equivalent blood flow debt. However, regional myocardial blood flow during the peak of reactive hyperemia following systolic perfusion was preferentially directed to the subendocardium, where underperfusion was most marked, whereas reactive hyperemia flow following a total occlusion of equivalent blood flow debt was distributed more evenly across the left ventricular wall. Thus, when coronary in-flow was limited to systole, ventricular contraction produced a transmural gradient in myocardial blood flow resulting in subendocardial underperfusion.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

The discharge characteristics of type B left atrial receptors were analyzed during alterations in heart rate. Recordings were made from single-fiber preparations of the left cervical vagus of pentobarbital-anesthetized, open-chest dogs. The heart was paced following a sinoatrial crush at frequencies ranging from 60 to 240 beats/min. Left atrial transmural pressure was varied at each heart rate by the intravenous infusion of warm isotonic NaCl. As heart rate was increased there was a progressive decrease in the level of peak “v” wave left atrial pressure. Concomitantly with the decrease in left atrial pressure, the number of spikes per cardiac cycle decreased as did the maximal instantaneous frequency of discharge. A significant positive relationship could be demonstrated with either the discharge per minute [(spikes per cycle) x heart rate] or discharge per cycle vs. the peak “v” wave of the left atrial pressure, regardless of heart rate. The number of impulses that entered the central nervous system per unit of time remained relatively constant at heart rates between 90 and 240/min. It is concluded from these data that the reflex effects which have been attributed in the past to atrial stretch receptor stimulation during clinical episodes of atrial tachyarrhythmias may be better correlated with some aspect of receptor discharge other than frequency or the number of discharges per cycle.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

This study was performed to determine whether stimulation of the carotid chemoreceptors increases total or regional cerebral blood flow and whether activation of arterial chemoreceptors contributes to cerebral vasodilation during systemic hypoxemia. In anesthetized and ventilated dogs, carotid chemoreceptors were stimulated with nicotine or hypoxic and hypercapnic blood. To measure total and regional cerebral blood flow, we used labeled 15-μ microspheres. Stimulation of chemoreceptors did not increase cerebral blood flow or produce significant redistribution of cerebral blood flow, even though the chemoreflex was intact in these animals (as manifested by vasoconstriction in muscle, kidney, and small bowel) and the cerebral vessels dilated in response to systemic hypercapnia. In other studies in anesthetized, ventilated dogs and rhesus monkeys, cerebral vasodilator responses to systemic hypoxemia were observed before and after denervation of carotid and aortic chemoreceptors. Systemic hypoxemia produced large and equivalent increases in cerebral blood flow before and after chemodenervation. We conclude that stimulation of carotid chemoreceptors does not produce cerebral vasodilation and that chemoreceptors do not contribute significantly to cerebral vasodilation during systemic hypoxemia.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

When studied on isolated rat mesenteric arteries perfused with Tyrode's solution, angiotensin I and angiotensin 11(1 ng/ml), a synthetic tetradecapeptide renin substrate, and a purified hog renin substrate (50–100 ng/ml) potentiated vasoconstrictor responses to sympathetic nerve stimulation and to injected norepinephrine without altering basal pressure. These agents produced a greater augmentation of the vasoconstrictor responses to nerve stimulation than to injected norepinephrine. The potentiation of vasoconstrictor responses to sympathetic nerve stimulation and injected norepinephrine which was elicited by renin substrate and angiotensin I was abolished by an inhibitor of angiotensin I-converting enzyme, SQ 20,881, and by an angiotensin II receptor antagonist, [Sar1-Ile8]angiotensin II. In contrast, the potentiating effect of angiotensin II was blocked only by the latter compound. We conclude that utilization of renin substrate within the vascular wall by renin or renin-like enzymes results in the formation of angiotensin I, which is converted to angiotensin II. Angiotensin in turn potentiates the vasoconstrictor responses to adrenergic stimuli presumably by augmenting release of the adrenergic transmitter and inhibiting its neuronal reuptake as well as by increasing vascular reactivity to norepinephrine.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Renal hemodynamics and renal function were evaluated in rats at 3, 24. and 48 hours and at 7 days after the induction of acute renal failure (ARF) by glycerol injection. Three hours after induction of ARF, creatinine clearance was 0.04 ml/min/lOOg; renal blood flow (RBF), 1.99 ml/min/IOOg; and filtration fraction, 3.7Z. All were abnormally low. Although the administration of isotonic saline (total dose, 3% of body weight) to rats 3 hours after glycerol injection significantly improvedcreatinine clearance (0.17 ml/min/100 g), RBF (2.54 ml/min/100 g), and filtration fraction (12.9%), these values still were significantly lower than those of controls (creatinine clearance = 0.50 ml. ml/min/100 g, RBF = 4.92 ml/min/100 g, filtration fraction = 20 .0%, all P values <0.001). Serum creatinine concentrations were significantly elevated at 24 hours (3.72 gm/100 ml), 48 hours (4.69 mg/100 ml), and 7 days (0.66 mg/100 ml) after glycerol injection compared to control (0.46 mg/100 ml, all P <0.01). RBF during these phases was not different from normal (4.41 ml/min/100 g). RBF 3 hours after bilateral ureteral obstruction was measured to determine the effects of tubular obstruction on renal hemodynamics. The RBF of rats with ureteral obstruction (4.12 ml/min/IOOg) was not significantly different from controls (4.41 ml/min/100 g), suggesting that tubular obstruction in this model of ARF is probably not the cause of decreased RBF. The depressed glomerular filtration, as reflected by the decreased creatinine clearance that occurs during glycerol-induced ARF, is probably related to altered intrarenal vascular resistance or to changes in glomerular capillary permeability, or both.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

A variety of estrogen- and progestin-containing oral contraceptive agents reduced renal blood flow (RBF) significantly in 23 healthy, nonhypertensive young women, to a mean of 75 ± 3.3% of the value expected for their age and dietary sodium intake (P < 0.001). There was also significant activation of the renin-angiotensin system: renin substrate was increased approximately 3-fold in association with a striking increase in the circulating renin activity and angiotensin II levels in relation to sodium intake and excretion. Two observations suggest that the RBF reduction was directly mediated by angiotensin II. A correlation was demonstrable between circulating angiotensin II and RBF (P < 0.01), and renal vascular responsiveness to angiotensin II infused into the renal artery was reduced significantly (P < 0.001). Moreover, the oral contraceptive agents modified the basic relationship between sodium balance and vascular responsiveness to angiotensin II, suggesting that the agents acted through some mechanism other than alteration in the state of sodium balance. These observations provide further evidence for an important role of angiotensin 11 as a determinant of RBF. Renal vasoconstriction may contribute to the genesis of a number of complications, such as sodium retention and hypertension, associated with oral contraceptive use.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID

摘要:

Depolarization of the atrioventricular junctional tissues and of the atrial septum was examined in the perfused dog heart before and during ventricular fibrillation by (1) recording the potentials from the junctional tissues in the regions of the interatrial and interventricular septum and examining the relationship of activity at these sites to atrial depolarization, (2) computing histograms and autocorrelograms of atrial firing intervals to study atrial rhythmicity, and (3) plotting the sequence of atrial septaldepolarization. The junctional tissue was generally randomly depolarized by the fibrillating ventricles. The histograms and autocorrelograms indicate that during ventricular fibrillation the atrial depolarization intervals do not remain constant, but vary widely. This seems to be due to the retrograde excitation from the junctional tissues. Plots of the depolarization sequences of the interatrial septum also indicate that retrograde depolarization takes place. The junctional tissues decrease the number of impulses that can pass from ventricle to atrium, and they similarly decrease the number of impulses that pass in an antegrade direction during atrial fibrillation.

ISSN:0009-7330    

出版商:OVID    

年代:1976

数据来源: OVID