Abstract

These results are presented as evidence that certain corticosteroids and some congeners act directly upon the cat papillary muscle preparation producing a positive inotropic action. This action is characterized by two components. The first component is a transient response, the magnitude of which may be related to a substance's mineralocorticoid structure. Thus, the addition of DOCA (0.5 µg/ml) and 9α-FF (1 µg/ml) results in a pronounced positive inotropic action, whereas the addition of glucocorticoids, such as cortisone (1 µg/ml) and prednisone (20 µg/ml), produces no marked inotropic action in comparison to the controls. The first component is sometimes followed by a second one which is characterized by a prolonged elevation. The addition of ouabain (0.02 µg/ml), Sc-8109 (1 µg/ml) and Sz-600 (2 µg/ml) results in a marked positive inotropic response and prolonged duration of action which can apparently be correlated with the presence of a C-17 lactone or C-14 OH.

It should also be pointeti out that, although the production of a positive inotropic action on the papillary muscle preparation results from those steroids lacking a ketone at C-11, this action does not necessarily parallel mineralocorticoid potency. Moreover, these experiments do not permit us to conclude that steroids and cardiac glycosides have a similar mechanism of action upon cardiac tissue.