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Related Experiment Videos

Effect of digitalis on left ventricular function in exercising dogs

L D Horwitz, J M Atkins, M Saito

    Circulation Research
    |December 1, 1977
    PubMed
    Summary

    Ouabain's positive effect on heart function is minimal during intense exercise due to high sympathetic stimulation. However, it does enhance contractility during exercise when beta-adrenergic blockade is present.

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    Area of Science:

    • Cardiology
    • Pharmacology
    • Exercise Physiology

    Background:

    • Ouabain is a cardiac glycoside known to increase myocardial contractility.
    • The impact of ouabain on cardiac function during physiological stress, like exercise, is not fully understood.

    Purpose of the Study:

    • To investigate the effects of ouabain on left ventricular function in healthy hearts during graded treadmill exercise.
    • To determine if sympathetic stimulation during exercise attenuates the inotropic effects of ouabain.
    • To examine ouabain's effects during exercise under beta-adrenergic blockade.

    Main Methods:

    • 14 chronically instrumented dogs were subjected to graded treadmill exercise.
    • Measurements included left ventricular pressure, dp/dtmax, stroke volume, heart rate, and running speed.

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  • Experiments involved administration of ouabain alone, ouabain with atropine, and ouabain with propranolol.

    • Main Results:

    • At rest, ouabain increased dp/dtmax and stroke volume.
    • During exercise, ouabain did not alter dp/dtmax or stroke volume and limited exercise capacity.
    • Ouabain increased contractility during exercise with beta-blockade, unlike during normal exercise or with atropine.

    Conclusions:

    • The inotropic effect of ouabain is significantly diminished during strenuous exercise due to high sympathetic nervous system activity.
    • Ouabain can still increase myocardial contractility during exercise when beta-adrenergic pathways are blocked.