Myocardial lesions induced by natural catecholamines in vitro

Isolated rat hearts were perfused using a retrograde technique under constant pressure head or constant coronary flow. The addition of 1-epinephrine or 1-norepinephrine (1 microgram/ml) to the perfusion medium for 1 h caused visible and irreversible morphological changes which usually became apparent after 4 h of perfusion in the form of small, pale, opaque spots or streaks gradually enlarging on the surface or on the cross-section area of the myocardium. Light- and electron-microscopic examination showed a disintegration process analogous to that of myocardial infarction but without the infiltration with blood elements. The structural changes were preceded by an increased release of lactate dehydrogenase into the effluent, the most characteristic metabolic change accompanying myocardial injury. Nevertheless, the underlying mechanism of the cardiotoxic action of catecholamines remains to be clarified; several factors under consideration could be eliminated: hyperlipidemia, trombogenic process, acidity due to enhanced production of lactate, reduced total coronary inflow rate and toxicity of oxidation products of catecholamines.