Naunyn-Schmiedeberg's Archives of Pharmacology

, Volume 273, Issue 3, pp 283–293 | Cite as

A postsynaptic effect of tyramine in ventricular muscle

  • W. Brandt
  • M. Reiter
  • K. Seibel
Article

Summary

Tachyphylaxis and susceptibility to pretreatment with reserpine demonstrate that tyramine increases contractility of the guinea-pig papillary muscle in concentrations up to 10−4 M by means of an indirect sympathomimetic effect.

In higher concentrations (up to 3×10−3 M) tyramine causes an increase in force of contraction which is characterized by a slowing of relaxation of the isometric contraction curve. Pretreatment with reserpine reveals that this positive inotropic effect is composed of an indirect sympathomimetic and a direct post-synaptic effect; the latter is not subject to tachyphylaxis and produces by itself (at 3×10−3 M) an increase in force of contraction which amounts to about 50% of the maximum of the indirectly produced inotropic effect.

The postsynaptically-induced positive inotropic effect of tyramine is not antagonized by propranolol (5×10−6 M). It is unlikely, therefore, that it is brought about by stimulation of adrenergic β-receptors.

The height of the isometric contraction curve in reserpine-pretreated muscles is increased by tyramine as a result of an increase in the rate of force development despite a marked concentration-dependent increase in relaxation time (t2).

The direct inotropic effect of tyramine is correlated with a prolongation of the duration of the action potential (AP) which amounts to 70% at 3×10−3 M. In addition to its influence on the duration of the AP, tyramine slows the rate of depolarization and decreases the membrane resting potential.

Key words

Tyramine Postsynaptic Effect Cardiac Muscle Prolongation of Action Potential Retardation of Relaxation 

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Copyright information

© Springer-Verlag 1972

Authors and Affiliations

  • W. Brandt
    • 1
    • 2
  • M. Reiter
    • 1
    • 2
  • K. Seibel
    • 1
    • 2
  1. 1.Institut für Pharmakologie und Toxikologie der Technischen Universität MünchenMunichGermany
  2. 2.Abteilung für experimentelle Pharmakologie der GSFNeuherberg

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