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Biomedical subjects

J G Papp

Publications and source records attributed to J G Papp.

At least 127 records · Page 7Linked to original sources
PubMed1979

On the possible role of adenosine in the hypoxia-induced alterations of the electrical and mechanical activity of the atrial myocardium.

The effects of adenosine on transmembrane potential and myocardial contractility were compared with those of hypoxia in electrically driven left atrial preparations of guinea-pigs. The amplitude and duration of action potential, contractile force and maximum rate of rise of tension development were decreased by both adenosine and hypoxia. Both the adenosine- and hypoxia-induced changes could readily be prevented by aminophylline, a competitive antagonist of adenosine. Serious changes of transmembrane atrial potential due to long-lasting hypoxia could also be reversed by aminophylline. On the basis of the present results it is assumed that in acute myocardial hypoxia the increased tissue level of adenosine might contribute to the functional impairment of the atrial myocardium.

Action Potentials↗
PubMed1978

[Effect of atropine on fetal heart rate].

The effect of atropine on the foetal heart rate (FHR) was examined in 56 normal pregnancies. 40 mcg/kg atropine was administered. According to the results of the examinations the FHR was not effected by atropine in the 8.--13. weeks of gestation. The FHR was effected by the applied dose of atropine only after the 17th week increasing over the physiological oscillation. In the course of pregnancy FHR was increased by atropine in every case it nearly raised to FHR values observed in the 8.--13 weeks still not effected by atropine.

Atropine↗
PubMed1976

Cardiac actions of arachidonic acid.

The cardiac actions of arachidonic acid (AA, C 20:4), the precursor of prostaglandin E2 (PGE2) and F2 alpha (PGF2 alpha) were studied in isolated atria and papillary muscles of guniea-pigs as well as canine Purkinje fibers. In contrast to the cardio-depressant actions of some short and long-chain fatty acids (octanoate, oleate) AA (10(-6)-10(-4) M) increased sinoatrial rate and contractility in guinea-pig atrial preparations. This cardio-stimulant action of AA was accompanied by an increase in the amplitude and maximum rate of rise of the intracellularly recorded atrial action potential. Some increase in the resting membrane potential and a slight prolongation of the action potential duration could also be observed. AA did not induce any pace-maker activity in isolated papillary muscle of guinea pigs or in isolated Purkinje fibers. Similarly to AA, PGE2 and PGF2 alpha (2.1-10(-8)12.1-10(-5) M) were also found to increase atrial rate and contractile force. The stimulating actions of AA were reduced by application of high concentrations of indomethacin (5-10(-5) M).

Action Potentials↗
PubMed1970

The effect of altered thyroid state on atrial intracellular potentials.

1. A group of rabbits was made hypothyroid by thyroidectomy, and another group was injected daily with L-thyroxine. After an appropriate interval respective alterations in thyroid state were confirmed by measurement of heart weight and of plasma iodine, and the animals' atria were isolated for recording.2. Measurements were made of atrial contractions, conduction velocity, spontaneous heart rate and maximum driven frequency, and action potentials were recorded with intracellular micro-electrodes.3. The resting potential and action potential heights were not affected by differences of thyroid state.4. Atrial arrhythmias are common in hyperthyroidism, rare in myxoedema. The possibility that hypothyroidism might reduce the rate of rise of the action potential, as do anti-arrhythmic drugs, and hyperthyroidism increase it, was investigated. Although the rate of rise was slower in hypothyroid atria at some driving frequencies, this could not alone account for an anti-arrhythmic effect, because at frequencies near the spontaneous heart rate the rate of rise of the action potential was not reduced.5. The duration of the repolarization phase of the action potential was greatly prolonged in atria from thyroidectomized rabbits, and was shortened in hyperthyroid atria. These changes could account for a reduced probability of arrhythmias in hypothyroidism, and the converse in hyperthyroidism.

Action Potentials↗
PubMed1969

A comparison of the anti-arrhythmic actions of I.C.I. 50172 and (--)-propranolol and their effects on intracellular cardiac action potentials and other features of cardiac function.

1. I.C.I. 50172 had marked quinidine-like effects on intracellular cardiac action potentials at concentrations above 20 mg/l. (6.61 x 10(-5)M). The rate of rise and overshoot of the action potential, conduction velocity and contractions were decreased. (-)-Propranolol had similar effects at less than 1/30 this concentration.2. I.C.I. 50172 had 1/100 the activity of (-)-propranolol as a local anaesthetic. Since this is also the ratio of their in vitro beta-receptor blocking activities, I.C.I. 50172 provides no net increase in specificity of beta-receptor blockade.3. In contrast, the in vivo activity of I.C.I. 50172 in protecting anaesthetized guinea-pigs against ouabain-induced ventricular fibrillation was 40% that of (-)-propranolol.4. Structure-activity relations of beta-receptor blocking drugs are discussed.

Acetanilides↗
PubMed1969

The effect of bretylium on intracellular cardiac action potentials in relation to its anti-arrhythmic and local anaesthetic activity.

1. The initial effect of bretylium tosylate on isolated rabbit atria was to increase conduction velocity, contraction heights, spontaneous frequency and maximum driven frequency, and to reduce electrical threshold. At concentrations of 200 mg/l. or less, these were the only effects, and were consistent with the known sympathomimetic actions of bretylium.2. At extremely high concentrations, 1,200 and 2,400 mg/l., the initial actions were succeeded by weak quinidine-like effects; reduced conduction velocity, spontaneous and maximum driven frequencies, and rate of rise of action potential. The electrical threshold was raised, but contraction heights were not reduced.3. The local anaesthetic activity of bretylium, measured by reductions in the frog nerve action potential, was 1/90 that of procaine and 1/300 that of propranolol, on a molar basis.4. Acute pretreatment with bretylium, 20 mg/kg intravenously, significantly increased the amount of infused ouabain required before the appearance of the first signs of atrial arrhythmia in anaesthetized guinea-pigs, but did not prevent ventricular arrhythmias.5. Pretreatment with bretylium 30 mg/kg subcutaneously 24 hr, and again 4 hr before ouabain infusion, increased the dose of ouabain inducing atrial irregularity and slightly but significantly reduced the incidence of ventricular fibrillation.

Action Potentials↗