Abstract
Recently, the function of the myocardium has been explained by means of the classification of adrenergic receptors proposed by Ahlquist (1). The presence of beta adrenergic receptors in the myocardium was already established by Nickerson and Chan (2), Moran and Perkins (3), and Moran et al. (4), while that of alpha adrenergic receptors was reported on the isolated rabbit's atria by Govier et al. (5-7). Hence, this investigation has been prompted by interests to re-evaluate the existance of myocardial alpha and beta adrenergic receptors in the isolated papillary muscle of the cat, and to study the location of these two receptors. During the experiments of the action of dibenamine on adrenergic receptors, it was unexpectedly found that dibenamine has two different actions, either a short-reversible effect or a long-lasting effect, according to the duration of the administration.
