摘要:

The effects of tetrodotoxin on sinus node activity were studied by direct perfusion through its nutrient artery. Tetrodotoxin suppresses action potentials by blocking sodium entry into the cell. In the open-chest anesthetized dog, direct perfusion of the sinus node artery with tetrodotoxin, 1.0 μg/ml, caused immediate sinus slowing lasting 12 to 60 minutes. This slowing was not affected by intranodal atropinization. Tetrodotoxin also produced complete blockade of sinus node response to vagal stimulation. Blockade of sinus node responses to stellate stimulation was less profound. Tetrodotoxin had no effect on chronotropic responses to intranodal acetylcholine and norepinephrine. These findings suggest that blockade of transmembrane sodium transport (or the rapid entry channel) has a negative chronotropic effect which is not cholinergic and during which response to neurotransmitter substances is normal. Concomitant with this effect there is blockade of neurotransmitter release (or synthesis) in the sinus node.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

Granules of the submaxillary gland of the white mouse contain both kallikrein and renin. The granules were separated and concentrated in sequential centrifugation procedures. They were more stable at room temperature and in hypertonic sucrose solutions than in the cold or in isotonic solution. The amylase, acid phosphatase, renin, kallikrein, and benzoyl-L-arginine ethyl ester esterase contents of the granules were determined. Kallikrein and renin showed a similar distribution pattern after fractionation. Granular renin released the equivalent of 9.6 μg angiotensin II amide/mg enzyme protein/min from swine serum angiotensinogen. Granular kallikrein liberated from human kininogen the equivalent of 8.4 μg bradykinin/mg enzyme protein/min.Electron micrographs of the isolated granules showed various forms; some were spherical and symmetrical, and others were amorphous.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

To explore the sequence of metabolic, mechanical, and electrocardiographic (ECG) events during myocardial anoxia, isolated rat hearts were paced from the atrium. Anoxic and recovery periods were studied. Adenosine triphosphate (ATP) and creatine phosphate (CP) declined to 50% of control during the first minute and remained at that level for the 5-minute anoxic period. ATP and CP returned to control values after 10 and 20 seconds of recovery. Lactate and potassium efflux from the myocardium closely followed the highenergy phosphate changes. During anoxia, left ventricular systolic pressure increased initially, then fell below the control level after 2 minutes, and recovered within 20 seconds of reoxygenation. In catecholamine-depleted hearts, it fell immediately with anoxia, and recovery was incomplete. The conduction time for the pacing stimulus to reach the ventricle increased with anoxia and decreased with reoxygenation. S-T alterations in the ECG also lagged behind high-energy phosphate reduction and recovery.The study demonstrates that in the isolated heart, ECG evidence of myocardial hypoxia may be absent when high-energy phosphate levels in the myocardium are very low. Mechanical changes are more closely related temporally to high-energy phosphate alterations than are ECG changes. The release of endogenous catecholamines is important to maintain mechanical function in the hypoxic heart.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

The renal excretion of renin infused intravenously was studied in anesthetized rats. The renin in the urine was adsorbed onto DEAE cellulose and selectively eluted for separate assay on the rat blood pressure preparation. The influence of saline loading, furosemide, mercuric chloride, and maleic acid was determined by following the changes in renin excretion. Both mercuric chloride and maleic acid led to a sixfold increase in the amount of renin appearing in the urine. Among the various factors which might have led to this result, an effect on renal tubular reabsorption after glomerular filtration of the renin is the most likely.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

A method was developed to determine the elastic behavior of large blood vessels in terms of their transmission characteristics for small sinusoidal pressure signals. The method is new insofar as it utilizes transient signals of the form of finite trains of sine waves that are superimposed on the naturally occurring pressure fluctuations and are generated by an electrically driven impactor or by a pump. Its application to the thoracic aortas of 18 mature mongrel dogs anesthetized with pentobarbital has shown that dispersion and attenuation data for frequencies between 40 and 200 cps can be obtained without requiring either Fourier transform computations or resolution of reflection interference. For the frequency range considered, the descending aorta is only mildly dispersive but exhibits strong attenuation that must be attributed primarily to dissipative mechanisms in the vessel wall. At normal blood pressure levels, the wave speed during diastole can have a value between 4 and 6 m/sec. For all frequencies tested the amplitude ratio of the waves exhibits the same exponential decay pattern with distance measured in wavelengths. A marked increase in wave speed observed from diastole to systole can be associated with an increase in mean flow and with a stiffening of the aortic wall due to the rise in pressure. This phenomenon implies that the aortas of anesthetized dogs should exhibit nonlinear properties with respect to large amplitude pulse waves such as those generated by the heart.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

摘要:

Tetrodotoxin given to cats in doses of 1 to 10 μg/kg iv caused profound cardiovascular depression characterized by decreases in systolic and diastolic blood pressures, pulse pressure, heart rate, force of myocardial contraction, cardiac output and peripheral resistance. These effects were associated with marked inhibition of the responses to stimulation of nerves to the adrenal medulla and the sympathetic nerves to heart and blood vessels. Sinus bradycardia due to toxin did not occur after acute cardiac sympathetic denervation. In isolated sympathetic nerve-right atrium preparations, tetrodotoxin at 1 to 2 × 10−8g/ml abolished the positive inotropic and chronotropic responses to nerve stimulation without effect on spontaneous rate or force, or transmitter release by tyramine. Toxin-produced vasodilation in perfused hindlimbs was associated with marked inhibition of the normal vasoconstrictor responses to sympathetic vasomotor nerve stimulation. Vasodilation was not due to a direct action on vascular smooth muscle, since it was not seen after α-receptor blockade with phenoxybenzamine, after sympathetic denervation, or after blockade of adrenergic transmitter release by guanethidine or β-TM 10 accompanied by adrenalectomy. Vasodilators such as acetylcholine, histamine and isoproterenol consistently produced additional vasodilation under these conditions. The hypotensive effect of the toxin was also observed in spinal cats. It is concluded that the potent hypotensive action of tetrodotoxin, in the cat, is primarily due to blockade of conduction in peripheral sympathetic nerves and nerve fibers innervating the adrenal medulla.

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:1968

数据来源: OVID