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Differences in the inotropic cardiac effects of noradrenaline and dihydro-ouabain

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Summary

  1. 1.

    The positive inotropic effects of noradrenaline and of dihydro-ouabain on guinea-pig papillary muscles were compared by analyzing the isometric contraction curves in regard to height (F C ), time to peak force (t 1), relaxation time (t 2), and mean velocities of force development (S 1) and relaxation (S 2).

  2. 2.

    The maximum inotropic effect (Δ F C ) obtained with dihydro-ouabain is 20% greater than that of noradrenaline (p<0.02). The difference is even greater between the maximal klinotropic effects (Δ S 1): i.e., the mean velocity of S 1 reaches a maximum with dihydro-ouabain which lies 50% above that obtained with noradrenaline.

  3. 3.

    Time to peak force (t 1) is shortened by dihydro-ouabain (−25%) more than by noradrenaline (−7%). Relaxation time (t 2) at the end of the concentration-effect curve is reduced 30% by noradrenaline whereas dihydro-ouabain prolongs t 2 by 12%.

  4. 4.

    The opposite effects of dihydro-ouabain and noradrenaline on t 2 reflect their differring influences upon relaxation velocity. The increase in S 2 by the maximally effective concentration of noradrenaline surpasses by about 50% the maximal increase obtained with dihydro-ouabain.

  5. 5.

    The increase in relaxation velocity (Δ S 2) by noradrenaline in a maximally effective concentration exceeds its klinotropic effect (Δ S 1) by about 60%. The effect of noradrenaline on ventricular muscle, therefore, predominantly enhances relaxation, as at β-adrenoceptors of smooth muscle. The enhancement of the relaxation by noradrenaline probably limits the positive inotropic effect of this drug and leads to the flatness of the concentration-effect curves in regard to Δ F C and Δ S 1, and to a characteristic bending in the slope of the isometric contraction curve.

  6. 6.

    Dihydro-ouabain causes a relative retardation in relaxation velocity: the increase in S 2 by maximally effective concentrations in 34% less than its positive klinotropic effect. This suggest an interference with the relaxation process by high concentrations of the glycoside which thus might contribute to its positive inotropic effect.

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Authors and Affiliations

  1. Institut für Pharmakologie und Toxikologie der Technischen Universität München, München, Germany

    Melchior Reiter

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  1. Melchior Reiter
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Supported by funds from Deutsche Forschungsgemeinschaft.

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Reiter, M. Differences in the inotropic cardiac effects of noradrenaline and dihydro-ouabain. Naunyn-Schmiedeberg's Arch. Pharmacol. 275, 243–250 (1972). https://doi.org/10.1007/BF00500053

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  • DOI: https://doi.org/10.1007/BF00500053

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