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Biomedical subjects

J G Papp

Publications and source records attributed to J G Papp.

At least 109 records · Page 6Linked to original sources
PubMed1988

Electrophysiological effects of GYKI-23 107, a new antiarrhythmic compound, in isolated rabbit and canine cardiac preparations.

The cellular cardiac electrophysiological effects of GYKI-23 107 (1-/2,6-dimethylamino/-2-dimethylaminopropane dihydrochloride), a new investigational antiarrhythmic drug, were studied in rabbit and canine ventricular muscle and Purkinje fibers. For comparison, mexiletine was used. GYKI-23 107, like mexiletine, did not affect the resting membrane potential and slightly reduced the action potential amplitude in both fiber types. The time for repolarization was shortened, but the ratio of effective refractory period to action potential duration was increased by both drugs. The maximum rate of depolarization (Vmax) was depressed by the drugs in a frequency-dependent ("use-dependent") manner. GYKI-23 107 slowed the recovery kinetics of Vmax in the canine ventricular muscle (Tc = 229.9 +/- 5.6 ms; n = 7) and Purkinje fiber (Tc = 149.6 +/- 33.8 ms; n = 7) in the same way as mexiletine. The kinetics of restitution of action potential duration during premature and postmature stimulation were slowed to similar degrees in the presence of both GYKI-23 107 and mexiletine in canine Purkinje fibers. It is concluded that, on the basis of its cardiac cellular electrophysiological effects, GYKI-23 107 can be categorized as a class Ib antiarrhythmic agent.

Animals↗
PubMed1987

[Prenatal effect of fenoterol (Partusisten) on the heart in the presence of verapamil].

The effect of fenoterol and fenoterol + verapamil on fetal hearts obtained from termination of pregnancy and surviving in nutrient solution was investigated. In 10--20-week-old fetal hearts, under the influence of fenoterol, a concentration-dependent increase was observed in spontaneous rate and contractility. A close linear correlation was found between the fetal age and the tachycardiac effect of the drug. The positive chronotropic and inotropic effect of fenoterol was significantly decreased by a therapeutically meaningful concentration (20 micrograms/l) of verapamil. The results are in favour of the suggestion that the inhibition by verapamil of the in utero fetal tachycardiac effect of fenoterol might occur, at least in part, in the fetal heart itself.

Dose-Response Relationship, Drug↗
PubMed1987

[Effect of caffeine on the contractility of the fetal heart muscle].

The caffeine-induced changes in contractility of early human fetal hearts obtained from termination of pregnancy and surviving in nutrient solution was studied. Three concentrations of caffeine (0.01; 0.1 and 1 mMol/l) were applied. In the presence of caffeine there was a significant age- and concentration-dependent increase in the contractility of fetal hearts. On the basis of this positive inotropic and the previously observed tachycardiac effect of caffeine the authors call attention to the potential harmful effect of the drug on the fetal heart.

Caffeine↗
PubMed1986

Interaction of calcium antagonists with beta-adrenoceptor blocking agents.

Responsiveness to verapamil, the best studied calcium antagonist, was examined in cardiac preparations of rabbits pretreated with beta-adrenoceptor blockers (propranolol 2 mg/kg or oxprenolol 4 mg/kg s.c.) twice daily for either one or six weeks. Using this dose-regimen, the degree of cardiac beta-adrenoceptor blockade in conscious rabbits was substantial and similar for propranolol and oxprenolol. When administered for one week, neither propranolol nor oxprenolol affected to any marked extent the electrical and mechanical response to verapamil, diltiazem or fendiline in tissues isolated from various parts of the heart. In contrast, pretreatment with propranolol for six weeks resulted in a significant aggravation of the negative inotropic effect of verapamil in both atrial and ventricular muscle, and the verapamil-induced delay in atrio-ventricular and intra-ventricular conduction also became more pronounced. The same long-term administration of oxprenolol, one of the beta-blockers with "intrinsic" sympathomimetic activity, did not alter the atrial or ventricular contractile response to verapamil and did not significantly increase the lengthening of atrio-ventricular conduction time occurring in the presence of verapamil. It is concluded that from the point of view of adverse direct cardiac interactions with verapamil prolonged administration of oxprenolol appears to be less dangerous than chronic treatment with propranolol. It is also assumed that in those cases in which acute administration of verapamil may be necessary, concomitant chronic blockade of cardiac beta-adrenoceptors is less dangerous if drugs known to possess not only beta-adrenoceptor blocking properties, but also some "intrinsic" sympathomimetic activity are applied.

Adrenergic beta-Antagonists↗
PubMed1985

[Effect of caffeine on fetal heart rate and caffeine consumption habits in pregnant patients].

Responsiveness to caffeine was studied in early human fetal hearts surviving in nutrient solution. Alterations of the spontaneous contraction rate were followed. Three concentrations (0.01, 0.1 and 1 mmol/l) were applied. In the presence of caffeine there was a significant age- and concentration-dependent increase in fetal heart rate in the period of the 6th to 17th weeks of gestation. Concerning the caffeine consumption habits of pregnant women a questionaire investigation was carried out in 686 cases. 69 per cent of the pregnants regularly drink coffee; 10.7 per cent of them consumes more than 300 mg per day. The authors call attention to the potential harmful effect of caffeine on the fetal heart.

Caffeine↗
PubMed1984

Investigations on the chemistry of berbanes. 10. Synthesis of raunescinone analogues with hypotensive and antihypertensive activity.

The pharmacologically active (methylenedioxy)- and diethoxyepialloberbane keto esters I have been synthesized with use of the readily available keto esters 2 as starting material. By choice of the appropriate reaction sequence both antipodes of keto ester 2a can be employed to provide any enantiomer of the desired raunescinone analogue 1a. Hypotensive, antihypertensive, and central depressant effects of 1a are described. The principle effect observed for 1a was a potent hypotensive and antihypertensive effect of long duration without depression of the central nervous system.

Animals↗
PubMed1984

Effects of hypoxia on the guinea-pig myocardium following inhibition of adenosine deaminase by coformycin.

The effect of moderate and severe hypoxia on the electrical and mechanical activity of isolated left atria of guinea-pigs was compared in the presence and absence of coformycin, a highly specific and tight-binding inhibitor of adenosine deaminase. The myocardial actions of hypoxia (reduction in the duration of intracellularly recorded action potentials and decrease in isometric tension, maximum velocity of contraction and relaxation as well as in time to peak tension) were significantly enhanced by coformycin, when applied in a concentration of 7 mumol/l producing nearly complete inhibition of adenosine deaminase in atrial muscle. These effects of coformycin were moderate during early hypoxia (0-5 min) and became pronounced during the late phase of oxygen deprivation (5-16 min). The results are in favour of the previous assumption that under hypoxic conditions the increased tissue level of adenosine might contribute to the functional impairment of the guinea-pig myocardium.

Action Potentials↗
PubMed1984

[Increase in weight and changes in the heart weight/body weight quotient of the embryonic heart in early pregnancy].

On the basis of measuring heart weight and body weight of 73 embryos it is shown that there is a close linear correlation between growth of the heart, increase of heart weight and body weight and age of pregnancy. The increase in heart weight, however, is not proportional to that of the increase in body weight during intrauterine development. There is a considerable shift in the heart weight/body weight ratio (i.e. a change in the cardio-fetal index: (formula; see text) In early pregnancy (5-7th weeks) the cardio-fetal index varies from 1.5 to 2.5 and in the course of pregnancy it decreases gradually. In the 12th-14th weeks it falls below 1, and following the 14th week it stays on a relatively constant level of 0.5-0.8. In early embryonic phase heart weight in relation to body weight is 2-5 times bigger than in the period following the 14th week. The significance of these findings is discussed.

Body Weight↗
PubMed1983

[The effect of temperature changes on the spontaneous heart rate of the isolated surviving human embryonal heart].

The effect of changes in temperature on the spontaneous fetal heart rate (FHR) of 17 isolated human hearts obtained from early pregnancy was investigated. A slow increase in the temperature of the nutrient solution provoked a 10/min FHR increase pro every 1 degrees C change from 32 to 38 degrees C, and this change did not depend on weight and age of the hearts and the basic FHR. At 40 degrees C the tendency of FHR decrease could be observed especially in case of bigger hearts. As result of the decrease in the temperature of the nutrient solution the fetal hearts stopped beating between 22 and 12 degrees C.

Fetal Heart↗
PubMed1982

Potentiation of the myocardial actions of adenosine in the presence of coformycin, a specific inhibitor of adenosine deaminase.

The effects of coformycin, a highly potent and specific inhibitor of the intracellular enzyme adenosine deaminase and the influence of dipyridamole, an inhibitor of the cellular adenosine uptake mechanism, were studied on the adenosine-induced changes in the electrical and mechanical activity of isolated electrically driven left atria of guinea-pig hearts. Adenosine (0.1 mumol/l-1 mmol/l) by itself elicited a concentration-dependent decrease in the action potential duration and contractile force of atrial preparations. Coformycin, when applied in a concentration inducing a nearly complete inhibition of adenosine deaminase activity in intact atrial myocardium (7 mumol/l), enhanced the adenosine-induced reduction both in the duration of the intracellularly recorded action potential and in the contractile force of the atria, preferentially at higher concentrations of adenosine (10 mumol/l-1 mmol/l). The calculated half recovery time during wash-out (t1/2) was found to be about 6 times longer than that of controls (317.5 +/- 47 and 51.3 +/- 4.3 sec, respectively). In contrast with adenosine, the action of 2-chloroadenosine (an adenosine deaminase resistant purine derivative) on the atrial contractile force was not affected in the presence of coformycin. Dipyridamole (0.3 mumol/l) was capable of significantly potentiating the adenosine-induced depression of atrial mechanical activity, mainly at lower concentrations of adenosine (0.1-10 mumol/l). Preincubation of atrial preparations with a combination of coformycin and dipyridamole produced a strong enhancement in the adenosine-induced decrease of mechanical activity at all concentrations of adenosine. It is suggested that adenosine might exert its myocardial actions not only through the known extracellular, but also via possible intracellular purinoceptors.

Action Potentials↗
PubMed1982

[Method for determination of mechanical activity and electrophysiological properties of isolated human embryonal heart].

The authors have invented a complex method by which to examine surviving hearts of early human embryos. The method enables testing of mechanical activity of the heart as well as of many electrophysiological parameters, such as spontaneous heart rate, electrical threshold of stimuli, stimulus conduction time, effective refractory phase, and intracellular action potential. --A special transport device was designed for storage and movement of embryonic hearts which were all obtained from cases of legal abortion. A contractility recorder was devised to follow up mechanical heart activity. A variant of the standard micro-electrode technique was developed to measure electrophysiological parameters. This technique has worked extremely well in recording the membrane potential at rest and the intracellular action potential in cells of small embryonic hearts. Also developed was a differentiation unit for direct and convenient measurement of depolarisation velocity of heart cells. The complex method has proved to be particularly suitable to study physiological characteristics relating to the responsiveness of the early human foetal heart to pharmaceuticals.

Abortion, Legal↗
PubMed1982

[Action of acetylcholine and carbamylcholine on spontaneous rates of hearts isolated from human embryos].

Fifty-eight early human foetal hearts, which had been obtained from cases of legal termination of pregnancy, were studied for their sensitivity to acetylcholine. Acetylcholine action was found to cause moderate decline in spontaneous human embryonic heart rate around the fifth and sixth weeks of development. The sensitivity to acetylcholine of the embryonic heart, aged between five and eight weeks, was found to go up along with growing age. The action of carbamylcholine, another cholinergic stimulant, was studied in some of the cases. Bradycardic action of carbamylcholine upon hearts aged between nine and ten weeks was found to be much stronger than that on hearts aged between five and six weeks. --The findings recorded from these studies have produced evidence to the effect that parasympathetic innervation in human embryonic hearts was preceded by the appearance of cholinergic receptors. They have also shown that in a very early phase of ontogenesis considerable change is undergone also by the cholinergic receptors of the heart.

Abortion, Legal↗
PubMed1982

[Effect of adrenaline, noradrenaline, isoproterenol and tyramine on the isolated surviving human fetal heart].

Studies were conducted by the authors into the action of adrenergic stimulants on isolated surviving hearts of 64 foetuses obtained from termination of pregnancies. They found that under the direct impact of stimulating catecholamines (adrenaline, noradrenalinee, and isoproterenol) the adrenergic receptors caused increase in spontaneous frequency of heart contractions, as early as in the fifth to ninth weeks of development, that is before adrenergic innervation of the heart. Such tachycardic effects were increasingly pronounced between the fifth and 24th week, along with growing age. Reactions produced by early and somewhat developed hearts were different with significance. Convincing effects were not detectable until hearts were ten or eleven weeks of developmental age, when tyramine was used which acted through release of noradrenalin. The latter date was in approximate coincidence with the appearance of adrenergic nerve elements for growth into the cardiac substance. In the 17th week of development, tyramine was used with good success to produce numerous effects which were characteristic of catecholamines, such as higher irritability and contractility of the myocardium and decrease of the effective refractory phase.

Abortion, Induced↗
PubMed1980

Effect of adenosine on sinoatrial and ventricular automaticity of the guinea pig.

In isolated spontaneously beating right ventricular strips and right atrial preparations of guinea pigs adenosine was found to exert a concentration-dependent suppressing effect on the pacemaker activity. Responsiveness to adenosine was approximately 30-fold higher in ventricular than in atrial preparations. A decrease in the rate of slow diastolic (phase 4) depolarization of Purkinje and sinoatrial nodal fibers proved to be a major determinant of the adenosine-induced alteration in pacemaker activity. It is suggested that adenosine might exert its depressant effect on ventricular automaticity via direct excitation of purine receptors located in the specialized pacemaker fibres of the ventricular tissue.

Action Potentials↗
PubMed1979

[Normal values of fetal heart rate in the 5th to 18th weeks of pregnancy (in vivo and in vitro studies)].

The normal values of the foetal heart rate (FHR) in early pregnancy were determined in utero by Doppler ultrasound technique and in vitro on isolated, in nutrient solution surviving, foetal hearts obtained from termination of pregnancy. The early heart rate was found to be surprisingly high in 354 successful ultrasonic examinations. In the eighth week the average FHR was 178 min-1. In the course of pregnancy there was a gradual decrease in FHR and in the 17th-18th week it reached 140 min-1 characteristic of the human foetus. Similar data were obtained under in vitro conditions.

Doppler Effect↗