[Catecholamine-antagonistic effects of propranolol and the mechanical function of ventricular myocardium]

The catecholamine-propranolol antagonism was studied on guinea-pig papillary muscles. 1. A competition between propranolol and catecholamine, the latter subject to saturable elimination from the extracellular space, for a homogeneous populations of beta-adrenoceptors of the cellular surface does not suffice to explain the influence on the inotropic effects. 2. The antagonism was differentiated into a "surmountable" and an "unsurmountable" component by means of the stereospecific influence of propranolol on maximal catecholamine effects in regard to velocity of contraction and acceleration of relaxation. The "unsurmountable" component was explained by a competition for intracellular beta-adrenoceptors, in addition to the competition at the beta-adrenoceptors of the cellular surface ("surmountable" component).