Possible involvement of indirect mechanism in cardiovascular action of dobutamine in dogs.

Possible mechanisms of dobutamine effects on adrenoceptors were investigated in comparison with tyramine, dopamine and noradrenaline after depletion of noradrenaline stores by ephedrine in dogs. Dobutamine, like other amines, induced pressor and positive chronotropic effects. After repeated treatment with ephedrine (total 40 mg/kg), both effects of dobutamine were markedly depressed. However, after ephedrine, the effects of tyramine were eliminated while those of noradrenaline were slightly decreased. Pressor responses to dopamine were reversed to depressor and positive chronotropic responses were abolished. The results suggest that dobutamine differs from other catecholamines in its mode of action and that its cardiovascular actions may be mediated in part through an indirect action on adrenoceptors.