ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effects of neurotransmitters injected into the posterior and the anterior septal artery on the automaticity of the atrioventricular (AV) junctional area were examined in the excised, blood-perfused canine AV node preparation. An AV rhythm of 57.4 ± 2.8 beats/min (N = 28) developed after the destruction of the sinoatrial node.l-Norepinephrine injected into the anterior septal artery increased the frequency of AV rhythm, butl-norepinephrine injected into the posterior septal artery caused a pacemaker shift from the anterior septal artery area to the posterior septal artery area. Acetylcholine injected into the posterior septal artery blocked retrograde conduction but did not decrease the frequency of AV rhythm; however, acetylcholine injected into the anterior septal artery decreased AV rhythm but did not affect retrograde conduction. Destruction of the posterior septal artery area failed to change AV rhythm. The surgically separated anterior septal artery preparation had the same rate as did the AV node preparation. The posterior septal artery preparation had a definitely lower rate and responded to smaller doses ofl-norepinephrine than did the AV node preparation. The results of the present study indicate that AV rhythm in the AV node originates in the area supplied by the anterior septal artery and that the area supplied by the posterior septal artery, which has extremely low automaticity, is highly responsive tol-norepinephrine, resulting in nodal tachycardia.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The relationship of P-wave polarity and morphology in leads II, III, and aVF to the sequence of atrial activation was studied in the canine heart when the atria were paced from the region of the sinus node or the posterior-inferior left atrium and when retrograde activation of the atria occurred with right ventricular epicardial pacing. Deeply negative P waves in leads II, III, and aVF which occurred when the posterior-inferior left atrium was paced were associated with true retrograde activation of the atria. Positive P waves recorded in leads II, III, and aVF during retrograde atrial capture with right ventricular pacing were associated with rapid retrograde spread of the impulse in the interatrial septum to the region of Bachmann's bundle from which site the impulse spread to depolarize significant portions of both atria in a manner similar to that demonstrated during pacing from the region of the sinus node. When the atria were paced from a site just anterior to the coronary sinus ostium, positive P waves recorded in leads II, III, and aVF were associated with early activation in the vicinity of Bachmann's bundle and later activation of the posterior-inferior left atrium. When the atria were paced from a site just posterior to the coronary sinus ostium, negative P waves in leads II, III, and aVF were associated with early activation of the posterior-inferior left atrium and later activation in the vicinity of Bachmann's bundle. It was concluded that the time of arrival of the impulse at Bachmann's bundle relative to that at the posterior left atrium and the direction of spread of the impulse from and within Bachmann's bundle are critical in determining P-wave polarity and morphology.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The effect of arterial hypertension on cerebral blood flow was studied by the intracarotid133Xe clearance method in baboons. The arterial blood pressure was raised in gradual steps with angiotensin. Baboons with renal hypertension of 8–12 weeks duration were studied along with normotensive baboons. In initially normotensive baboons, cerebral blood flow remained constant until the mean arterial blood pressure had risen to the range of 140 to 154 mm Hg; thereafter cerebral blood flow increased with each rise in mean arterial blood pressure. In the chronically hypertensive baboons, cerebral blood flow remained constant until the mean arterial blood pressure had been elevated to the range of 155 to 169 mm Hg. Thus, in chronic hypertension it appears that there are adaptive changes in the cerebral circulation which may help to protect the brain from further increases in arterial blood pressure.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The question regarding the existence of an alpha-adrenergic component of pial arterial tone was investigated using a microapplication technique combined with the measurement of vascular diameter. Concentration-response curves for the alpha-receptor blocker, phentolamine, revealed no vascular reaction for a concentration range from 2.5 x 10−11to 2.5 x 10−7M. At higher concentrations (up to 1.3 x 10−3M) concentration-dependent dilations were observed. Constrictions of pial arteries induced by perivascular injection of 2.5 x 10−6M norepinephrine could be reduced by 38% and 73% when phentolamine was applied simultaneously in concentrations of 2.5 x 10−7and 2.5 x 10−6M, respectively, whereas constrictions due to 2.5 x 10−4M norepinephrine were not reduced by 2.5 x 10−6M phentolamine, indicating a competitive antagonism between norepinephrine and phentolamine for pial arteries. Stimulation of the cervical sympathetic chain (90 seconds, 10 v, 1.4 msec, 20 Hz) induced constrictions of pial arteries (mean 12%) which could be reduced by two-thirds during the simultaneous application of 2.5 x 10−7M phentolamine. Since the constriction induced by norepinephrine applied exogenously or released endogenously could be reduced by a concentration of phentolamine which had no vascular effect per se, we conclude that the resting tone of the pial arteries is not influenced by an alpha-adrenergic component under our experimental conditions. The dilations induced by high concentrations of phentolamine are believed to be nonspecific.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Veratrum alkaloids injected into the coronary circulation stimulate myocardial receptors to produce reflex bradycardia and arterial hypotension (the Bezold-Jarisch reflex). This study investigated the hypothesis that parasympathetic coronary vasodilation occurs as part of the Bezold-Jarisch reflex. Blood flow in the circumflex coronary artery was measured in chloralose-anesthetized, closed-chest dogs with a newly developed cannula-tip flow transducer. Alpha-receptor blockade with Dibozane (2 mg/kg) was used to prevent peripheral vasodilation, and beta-receptor blockade with propranolol (1 mg/kg) was used to prevent adrenergic cardiac effects. Electrical pacing was used to maintain a constant heart rate. Under these conditions, veratridine injected into the anterior descending coronary artery but not into the circumflex coronary artery produced a 63% increase in circumflex coronary blood flow and an 88% increase in diastolic coronary conductance. The effect was abolished when the reflex arc was interrupted by either vagotomy or atropine administration. It is concluded that a cardiocoronary reflex parasympathetic coronary vasodilation can be elicited by stimulating cardiac receptors with veratridine.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Vessel dimensions and characteristic responses to norepinephrine were measured in various arteries and veins of the rabbit made hypertensive by partial constriction of the upper abdominal aorta. The ear, radial, and basilar arteries taken from the circulation proximal to the ligature (the hypertensive arteries) were thickened in proportion to the rise in arterial blood pressure. The water, sodium, and potassium contents of these and all other vessels were not significantly changed in the hypertensive rabbits. The maximum response to norepinephrine in the ear artery, a representative vessel from the hypertensive part of the rabbit, was increased, whereas the sensitivity of this vessel to norepinephrine expressed as the ED50did not alter with changes in the arterial blood pressure. In contrast, the thickness and the maximum response to norepinephrine of the saphenous artery, representative of vessels distal to the ligature (normotensive vessels) and of the saphenous and cephalic veins were unaltered. The sensitivity as indicated by the norepinephrine ED50of the veins, but not of the saphenous artery, increased with a rise in carotid artery blood pressure. These results suggest that the increased responsiveness to norepinephrine of arteries proximal to the ligature is due to changes in muscle mass and that the increased responsiveness of the veins is due to increased sensitivity to norepinephrine.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

To determine whether significant regional differences in shortening exist in the canine left ventricle, the shortening characteristics of small segments of the circumferentially oriented hoop axis fibers and the more longitudinally oriented fibers near the epicardium were examined using pairs of ultrasound crystals placed at three levels of the left ventricular free wall in the open-chest dog. Mean control shortening of the hoop axis fibers near the apex of the left ventricle averaged 20% of the end-diastolic length, significantly greater than shortening at the midventricular (13%) or basal (14%) levels. During transient periods of aortic constriction, end-diastolic length increased significantly and the extent of shortening was maintained for the hoop axis fibers at the apical and midventricular levels; end-diastolic length did not change and shortening decreased at the basal level. The epicardial fibers shortened an average of 5.6% of their end-diastolic length during control conditions at all three sites and showed small, parallel changes in shortening and end-diastolic length during aortic constriction. We conclude that significantly greater hoop axis shortening occurs near the apex of the left ventricle and that at this level a uniformly contracting model is inappropriate. In addition, the response of the hoop axis fibers to increased aortic impedance is not homogeneous, with a significant reduction in shortening occurring only at the base of the left ventricle where end-diastolic length does not increase.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

Reflex control of hind-limb and renal resistance vessels by cardiac and pulmonary receptors was studied by interrupting afferent vagal nerve traffic when only the heart or only the lungs were in situ in anesthetized dogs with sinoaortic denervation. During normocapnia, interruption of cardiac and of pulmonary vagal traffic decreased hind-limb blood flow (constant-pressure perfusion) by 23% and 21%, respectively. Corresponding decreases in renal blood flow were 23% and 33%. Hypercapnia augmented the decreases in renal blood flow due to the vagal block. Thus, the inhibitions exerted by the heart and lung receptors on these two beds were similar during normocapnia but were greater on the renal vessels during hypercapnia. In closed-chest dogs with their aortic nerves sectioned and their carotid sinus pressure controlled, combined withdrawal of carotid and cardiopulmonary inhibition decreased hind-limb and renal blood flow by about 80% and 40%, respectively, during both normovolemia and hypervolemia. Interruption of cardiopulmonary inhibition was responsible for 17% and 31% of the decrease in hind-limb blood flow at normal and increased blood volumes, respectively; values for the decreases in renal blood flow were 50% and 65%. Thus, cardiopulmonary receptors oppose the vasoconstriction due to carotid sinus hypotension more effectively in the kidney than they do in the hind limb.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID

摘要:

The organization within the descending sympathetic pathways on the surface of the dorsolateral funiculus of the spinal cord was investigated in anesthetized dogs. Changes in heart rate and carotid, renal, and femoral resistances were calculated during electrical stimulation of the descending spinal sympathetic pathways; the location within the pathway of the maximum change in each of these parameters was then determined. Blood pressure increased at each stimulation point with the maximum increase at 3–3.5 mm ventrolateral to the dorsolateral sulcus (DLS). The maximum increases in carotid, renal, and femoral resistances occurred with stimulation at 0.5–1.5, 2, and 3 mm ventrolateral to the DLS, respectively. Maximum heart rate responses were elicited by stimulation 2 mm ventrolateral to the sulcus. These data demonstrate that the pathway is organized in a dorsal-to-ventral manner, with the most rostral parts of the body being represented most dorsally and the more caudal parts being represented more ventrally.

ISSN:0009-7330    

出版商:OVID    

年代:1975

数据来源: OVID