THE MODIFICATION OF INOTROPIC ACTION OF OUABAIN BY 6-HYDROXYDOPAMINE AND α-METHYL-P-TYROSINE IN DOGS

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Abstract
The action of ouabain on myocardial inotropsin pretreated with 6-hydroxydopamine and .alpha.-methyl-p-tyrosine was studied. Inotropic action of ouabain was not changed by depletion of catecholamines in the brain, in which the central sympathetic neurons were destroyed by an intraventricular administration of 6-hydroxydopamine. Systemic administration of 6-hydroxydopamine and .alpha.-methyl-p-tyrosine reduced ventricular catecholamines to 5.3% and 20.8% of the control, respectively. Percent increase of contractility of ouabain after the pretreatment of 6-hydroxydopamine and .alpha.-methyl-p-tyrosine was reduced to 16.7% and 50.2% of the control, respectively. Catecholamines in the myocardium may play an important role in producing cardiotonic action of cardiac glycosides. Brain catecholamines or the sympathetic CNS do not appear to participate in the exertion of the positive inotropic action of cardiac glycosides.

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