Abstract

The ability of reserpinization and dichloro-isoproterenol (DCI) to modify the production of ouabain-induced augmentation on mammalian myocardium has been re-evaluated on the isolated cat papoillary muscle prepamation.

Employing this preparation, it was found that pretreatment with either DCI or reserpine significantly reduced or abolished ouabain-induced augmentation, depending on the concentration of ouabain used. Combined treatment with reserpine and DCI reduced ouabain-induced augmentation still further. Moreover, the ability of reserpinized or DCI-treated muscles to respond to double the concentration of calcium was unaltered.

On tht basis of these results, two possible mechanisms have been proposed to explain the apparent relationship between ouabain-induced augmentation and the availability of endogenous catecholamines in the heart. The fimst proposes that ouabain may act directly to increase cardiac contractile force by releasing catecholamines from storage sites located within the heart; and the second, that ouabain-induced augmentation is dependent upon the presence of a certain level of catecholamines which would be analogous to a permissive action.