[Catecholamines--therapeutic and adverse effects on the heart]

Catecholamine activation enhances the inotropy of the heart by increasing the sarcolemmal influx of Ca2+. This increased influx is counteracted by an increased sarcolemmal efflux and sarcoplasmic reticulum uptake of Ca2+. Thus the intracellular milieu is protected against a gradual rise in Ca2+ concentration. However, under conditions of continuous, excessive catecholamine release, the heart's potential to remove Ca2+ from the cytosol might become exhausted. This might be caused by a Ca2+-dependent exhaustion of high-energy phosphates. As a result of this, Ca2+ overload of the myocytes and eventually a decrease in the pump function of the heart might occur. This paradox has implications for the clinical management of ischaemic heart disease.