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Biomedical subjects

K Greeff

Publications and source records attributed to K Greeff.

At least 37 records · Page 2Linked to original sources
PubMed1981

Inotropic effects and Na+,K+-ATPase inhibition of ouabain in isolated guinea-pig atria and diaphragm.

Effects of ouabain on force of contraction were compared in electrically driven isolated tissue preparations of guinea-pig left atria and diaphragm. A distinct and steady positive inotropic effect of ouabain was observed in atrial preparations, whereas in diaphragm preparations, ouabain produced only a slight and transient positive inotropic effect, followed by the negative inotropic phase. The transient positive inotropic effect of ouabain was observed even in the absence of extracellular calcium, but was markedly dependent on the extracellular sodium concentration. In vitro [3H]ouabain binding studies revealed that the affinity of Na+,K+-ATPase for ouabain was about eight times higher and tissue concentration of the enzyme was significantly lower in diaphragm than in cardiac tissue. The Ki value for ouabain inhibition of the cardiac Na+,K+-ATPase was also approximately ten times higher than for the diaphragm enzyme. Ouabain-sensitive 86Rb uptake, an estimate of sodium pump activity, was inhibited by ouabain at a time when it produced its transient positive inotropic effect in diaphragm preparations. These results indicate that the lack of a distinct and steady positive inotropic effect of ouabain in diaphragm was due neither to the difference in the ouabain-Na+,K+-ATPase interaction between diaphragm and cardiac tissues nor the failure of sodium pump inhibition by ouabain in diaphragm.

Animals↗
PubMed1981

The positive inotropic action of triamterene in isolated heart tissues. Its interaction with beta-adrenergic agonists and electrophysiological investigations.

Triamterene (20--80 mumol/l) inhibits the positive inotropic action of orciprenaline in guinea-pig left atria. 200 mumol/l triamterene completely suppress the effect of orciprenaline (10(-8)--10(-4) mol/l). But if orciprenaline is applied first and triamterene afterwards no antagonism can be seen; triamterene shows an additional positive inotropic effect. A mathematical model is presented which allows a quantitative description of the interaction if two different sites of action are accepted for triamterene: a stimulating effect mediated via inhibition of phosphodiesterase and leading to an increase in slow inward current and an inhibition of the orciprenaline-adenylcyclase complex. The additional increase in contractile force by triamterene after pretreatment with orciprenaline can be explained by the model if the blocking site of triamterene is not considered. Triamterene increases force of isometric contraction and broadens action potential in all repolarization phases in guinea-pig left atria to a greater extent than in papillary muscles. 100 mumol/l triamterene increases action potential duration at 30% repolarization in atria by 109 +/- 13% (n = 4) and in papillary muscles by 28 +/- 4% (n = 4). These effects also occur to a similar degree when the animals have been pretreated with reserpine 2 mg/kg on 2 days prior to the experiment. Maximum upstroke velocity of atrial and ventricular action potentials is not changed up to 100 mumol/l triamterene, indicating its lack of influence on cardiac fast sodium channels.

Action Potentials↗
PubMed1981

Analysis of the positive-inotropic activity of the benzimidazole derivative AR-L 115 BS in isolated guinea pig atria.

When comparing the positive-inotropic effect of 2-[(2-methoxy-4-methylsulfinyl)phenyl]-1H-imidazo[4,5-b]pyridine (AR-L 115 BS) on the isolated guinea pig atria with those of theophylline, orciprenaline and strophanthin G, the following results were obtained: 1. In left atria the maximum effective concentration of AR-L 115 BS is 3.16 x 10(-4), of theophylline 10(-3), of strophanthin G 6.81 x 10(-7) and of orciprenaline 10(-5) mol/l. The increase in the contractile force thereby obtained was 192, 111, 158 and 277%, respectively (extracellular calcium concentration 1.2 mmol/l). Therefore AR-L 115 BS is somewhat less effective than orciprenaline but more effective than theophylline and strophanthin G. 2. AR-L 115 BS is also effective in atria isolated from animals pretreated with reserpine and its effect is not reduced in the presence of bupranolol. 3. Contrary to strophanthin G, AR-L 115 BS has a shorter time of onset of activity and is less dependent on the extracellular calcium concentration. 4. Similar to theophylline, AR-L 115 BS inhibits the positive-inotropic effect of orciprenaline dose-dependently, while strophanthin G increases the positive-inotropic effect of orciprenaline. 5. The effect of AR-L 115 BS differs from that of orciprenaline in having only little effect on the contraction rate in isolated right atrial preparations.

Animals↗
PubMed1979

Lack of influence of histamine antagonists on digitalis cardiotoxicity.

Experiments were carried out in order to study the interaction between cardioactive glycosides and histamine or histamine H1- AND/OR H2-receptor antagonists in anaesthetized cats or guinea pigs. The toxicity of ouabain or digoxin was tested by infusing the glycosides until idioventricular rhythm or death occurred. Histamine increased the toxicity of ouabain, but the histamine H1- and/or H2-receptor antagonists (metiamide and mepyramine)did not influence the toxicity of digitalis. In cats the increase in pulmonary arterial blood pressure caused by digoxin was not affectedby histamine H1- and/or H2-receptor antagonism in spite of the fact that the increase of pulmonary blood pressure caused by histamine could be abolished by H1-receptor antagonists. Our results indicate that histamine is not involved in the toxic effect of cardiac glycosides.

Animals↗
PubMed1979

[On the mechanism of the positive inotropic effect of triamterene on the myocardium (author's transl)].

The influence of triamterene on the contractile force and the cellular electrolyte content and exchange was studied in isolated, electrically stimulated guinea-pig atria. 1. Triamterene (40 to 200 mumol/l) produces a positive inotropic effect which is most pronounced when the extracellular calcium concentration is reduced (1.2 to 0.6 mmol/l) or the contractile force is diminished by pentobarbital (400 mumol/l). The inotropic action of triamterene was shown to be independent of the rate of stimulation (1--2 Hz). 2. By pretreatment with the adrenergic beta-receptor blocking drugs bupranolol and pindolol or by reserpinization the positive inotropic effect of triamterene was not significantly altered. 3. After incubating the atrial preparations with 45calcium for 30 min the intracellularly exchangeable calcium fraction was significantly enhanced by triamterene (100 mumol/l). If triamterene was added to the bathing medium after the 45calcium exchange process had already reached a steady-state, no further increase in the extent of the intracellular calcium exchange was observed during an additional 30-min period of incubation. Since the cellular total calcium content shows remained unchanged it is postulated that the increase in calcium influx is balanced by a simultaneous elevation of calcium efflux. In addition, triamterene did not show any influence on the intracellular potassium, sodium and magnesium content as well as on the extracellular space volume.

Adrenergic beta-Antagonists↗
PubMed1979

[Comparison of the cardiac effects of triamterene and its phase II metabolite p-hydroxytriamterene sulphuric acid ester (author's transl].

The positive inotropic action of triamterene (TA) on isolated, electrically stimulated left atria was compared with that of its phase II metabolite, p-hydroxytriamterene sulphuric acid ester (OH-TA-ester). It was found that the metabolite also possesses a positive inotropic action, its potency, however, is about 10 times lower than that of triamterene.

Animals↗
PubMed1978

The effect of chronic administration of digitoxin on the activity of the myocardial (Na + K)-ATPase in guinea-pigs.

When guinea-pigs were treated for 24 days with digitoxin 0.3 mg/kg s.c., the activity of the (Na + K)-ATPase of the heart muscle increased by about 30% compared to controls, whereas the enzymes prepared from kidney and brain showed no significant alteration in their activity. In animal species treated with digitoxin for 1 to 5 days, no increase of enzyme activity was observed. Only after 10 to 15 days of treatment, a significant increase of the (Na + K)-ATPase activity was noted which increased no further with treatment up to 24 days. There was no significant difference in the kinetic properties of the (Na + K)-ATPase prepared from digitoxin-treated animals compared to those from control animals; the KM-values for ATP remained unchanged, and there was the same dependence of the activity on the K+-concentration and the same sensitivity towards digitoxin. As there appears to be no significant change in the specific properties of the enzyme, the increase in activity may possibly be caused by an increase in the amount of enzyme as a result of an adaptive enzyme regulation.

Adenosine Triphosphatases↗
PubMed1978

[A method for radio-immunological determination of g-strophanthin (author's transl)].

For the purpose of estimating g-strophanthin radio-immunologically the following steps are described: the preparation of g-strophanthin antigen, the production of antibodies in the rabbit, the presentation of calibration curves, and the possibility of a quantitative determination of heterogenous glycosides. According to Malaprades reaction, g-strophanthin adheres to human albumin. With this antigen thus obtained antibodies are produced in rabbits. For the presentation of calibration curves, the addition of antiserum and g-strophanthin have to be matched in quantity; the calibration curves correspond to mathematical data. An increased sensitivity of the method is possible to attain by reducing the amount of labelled antigen and antiserum. The slight cross-reactivity of antibodies can be used to determine other glycosides when these are incubated labelled with tritium instead of 3H-g-strophanthin.

Animals↗