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Biomedical subjects

M G Udel'nov

Publications and source records attributed to M G Udel'nov.

At least 19 recordsLinked to original sources
PubMed1985

[Possible participation of slow Na+--Ca++ channels in realizing cholinergic effects on the cardiac pacemaker].

The effect of the Ca++-permeability inhibitors (Mn ions, Verapamil, D-600) on the bioelectrical activity and cholinergic responses of isolated sinus node involved reduction of the pacemaker rhythm within 30-40 min and a complete inhibition of the bioelectrical discharge as well as a diminished amplitude of the AP and a reduced slope of the slow diastolic and the fast depolarization. The findings seem to be due to an inhibiting of the slow Na+-Ca++ influx by Ca++-antagonists. The prolonged APs and the reduced rate of terminal repolarization might be due to effect of the inhibition on potassium permeability. After electrical stimulation of the efferent nerve or acetylcholine application, the cholinergic reactions were markedly reduced with Mn++ D-600 and Verapamil. The participation of slow Na+-Ca++ channels in cholinergic reactions of pacemaker cells is discussed.

Acetylcholine↗
PubMed1984

[Mechanical action of the atria during stimulation on the work of the sinus node].

The cardiac pacemaker and atria were removed from the frog heart and placed into a chamber with Ringer solution. Atrial pacing was performed at a suprathreshold milliamperage. The mechanism of changes in the cardiac pacemaker during atrial pacing was studied both under the conditions of the blockade of the intracardiac nervous system and elimination of the bioelectrical and mechanical effects of the atria on the cardiac pacemaker. It is inferred that the change in the rate of pacemaker stimulation during atrial pacing is largely determined by the mechanical activity of the atria.

Animals↗
PubMed1984

[Relation between intracardiac reflex effects on the rate of atrioventricular conduction and parameters of neural pathway stimulation].

Intracardiac nerves of the frog isolated heart were cut and the central or the peripheral end was stimulated. The atrioventricular (a-v) conduction was measured. The data showed that the intracardiac parasympathetic nervous system could induce both acceleration and deceleration of the a-v conduction, depending on the parameters of stimulation. Atropine blocked both the positive and the negative dromotropic effects whereas beta-adrenoblocking agent inderal was ineffective. The possible mechanism of the dromotropic effects observed are discussed.

Animals↗
PubMed1983

[Intracardiac neurogenic regulation of the rate of excitation conduction in the atrioventricular area of the heart. I. Dependence of the effect on the moment of stimulus application in spontaneous and artificially stabilized rhythms of the heart beat].

The influence of the intracardiac reflectory system on the atrioventricular propagation in the experiments on the isolated frog's heart has been investigated. The ability of the intracardiac reflectory cholinergic activation to accelerate or reduce the atrioventricular propagation was confirmed. Both effects remain on the background of the artificially stabilized heart rhythm. The dromotropic effect direction was shown not to be connected with the electrocardiogram (ECG) phase at which the stimulus has been given; the positive or negative dromotropic effect can appear giving the stimulus at the same phase of the ECG. But there is a strong correlation between the moment of the stimulation and the dromotropic effect intensity. The most high degree of the acceleration and inhibition appears when the stimulus is given near the P component of the ECG.

Action Potentials↗
PubMed1983

[Role of the atrium in the functional organization of the sinoatrial node].

The automatic activity of the venous sinus was studied in respect to the atrial bioelectrical activity in frogs. Each of the two parts of the divided venous sinus had different rhythms. Extra-cellular recording revealed that the APs of both parts of the sinus were closely synchronized if the parts were connected with the atrium. The data obtained suggests that this synchronization was due to atrial bioelectrical activity.

Action Potentials↗
PubMed1983

[Characteristics of the vascular reactions of rabbits to prolonged stimulations in experimental atherosclerosis].

The constrictory reactions to long electrostimulation of renal, pulmonary femoral arteries and distal aorta segments of intact rabbits getting 200 mg/kg of holesterine during 4-12 months have been compared. It has been established that all artherosclerotic vessels exhibit higher initial amplitude of constriction using as indicator of phasic reactions. the tetanus stability increases, that expresses in longer conservation of initial constriction amplitude on relatively high level; this is evidence of vessels capacity to long tonic reactions. These changes of aorta and pulmonary vessels were more distinct.

Animals↗
PubMed1982

[Changes in the rate of sinoatrial node after high-frequency stimulation of the heart atrium].

Variations in the sinus node rate of the frog heart isolated together with the atria were studied during suprathreshold atrial stimulation at a frequency exceeding the intrinsic sinus node rate. If the stimulation frequency surpassed the intrinsic sinus node rate by 20%, the sinus node rate became equal to the pacing rate. Provided the pacing rate was increased, the sinus node rhythm became irregular. If the pacing rate exceeded the sinus node rate more than two-fold, the latter became half the pacing rate. Variations in the sinus node rate during suprathreshold atrial stimulation were also observed after blockade of possible retrograde conduction by application of the necrotic tissue on the sinoatrial border. The results allow the conclusion that variations in the sinus node rate seen during high-frequency suprathreshold atrial stimulation are not connected with retrograde conduction.

Action Potentials↗
PubMed1982

[Changes in the activity of the intracardiac postganglionic apparatus during the interaction of the regulatory sympathetic and parasympathetic effects on the pacemaker rhythm].

Chronotropic effect on the isolated sinus node of the frog heart and postganglionic impulse activity of the intracardiac pathways were studied during separate and joint stimulation of extracardiac sympathetic and parasympathetic nerves. The joint stimulation attenuated or augmented the impulse activity. This effect depended on the "energy" of initial parasympathetic and/or sympathetic activity. beta-Adrenoblocking inderal abolished the parasympathetic impulse activity augmentation. A possible role of intracardiac ganglionic system in the sympathetic-parasympathetic interaction is discussed.

Animals↗
PubMed1982

[Hypothalamic participation in regulating parasympathetic reflexes to the heart in unanesthetized cats].

The influences of electrical stimulation of different hypothalamic areas on cardiac parasympathetic reflexes were studied in unanesthetized unrestrained cats. Cardiac reflexes were induced by imitation of venous input increase to the heart or by stimulation of cervical part of the vagus. The hypothalamus exerted two-way effects on cardiac reflexes: they were either increased or decreased during hypothalamic stimulation. This suggests that the hypothalamus renders facilitating as well as inhibitory influences on cardiac reflex bradycardia. The forebrain is supposed to participate in cardiac regulation by modulating cardiac reflexes both in unanesthetized cats and anesthetized ones.

Animals↗
PubMed1981

[Effect of iontophoretic application of acetylcholine on the discharge rate and action potential shape of pacemaker cells].

A study was made of the action of iontophoretic application of acetylcholine to the limited number of pacemaker cells with a simultaneous recording of the activity of one of them. It was shown that both generalized and strictly localized action of acetylcholine is capable of exerting different chronotropic effects. Acceleration of the rhythm was normally accompanied by an increase in the rate of accretion of slow diastolic depolarization (SDD) and by a decrease in the action potential. The same pacemaker cell was demonstrated to modulate the direction of the chronotropic reaction for an opposite one depending on acetyl-choline concentration. Low concentration of the mediator induced rhythm acceleration and an increase in the accretion rate of SDD whereas high concentration led to rhythm deceleration and SDD lowering.

Acetylcholine↗
PubMed1980

[Interaction of parasympathetic and sympathetic neurohumoral influences in regulating the heart rate of cod].

Chronotropic effects on the cod heart in case of the parasympathetic stimulation alone were initially negative and rather small; the joint stimulation of parasympathetic and sympathetic nerves or the vagus stimulation after noradrenaline administration augmented the initial bradycardia. In case of initial marked parasympathetic negative chronotropic effect, catecholamines diminished the parasympathetic inhibition. The sympathetic innervation and its transmitter seem to be able to increase the cholinergic effect.

Animals↗
PubMed1979

[Bioelectrical analysis of the regulatory interaction of sympathetic and parasympathetic nervous influences on the heart rhythm].

The changes of chronotropic effect on the isolated sinus node of the frog heart were studied during the separate and simultaneous stimulation of the sympathetic and intracardiac reflex parasympathetic pathways. Intracellular activity of the pacemaker cells was recorded. The separate stimulation of the intracardiac reflex system resulted in bradycardia (in winter) or tachycardia (in summer). Stimulation of sympathetic chain supervening the activation of the intracardiac pathways induced an intensification of both the parasympathetic bradycardia and tachycardia; these effects were cholinergic in nature. The recording of the intracellular pacemaker activity showed the existence of the complicated interaction between the sympathetic and parasympathetic pulse-mediator actions on the heart pacemaker both on the prepulase process and on the membrane polarization and other action potential parameters. Possible mechanisms of this interaction are discussed.

Animals↗