Pharmacological induction of delayed and prolonged cardiac protection: The role of prostanoids.
In 1983, a delayed and prolonged cardioprotection induced by drugs was described. This pharmacologically induced adaptation to stress represents a new trend in cardioprotection as opposed to the classical drug treatment that was based on the presence of drug-receptor binding. Such a long-lasting, delayed adaptation can be induced by non-injurious pharmacological stimuli (eg, prostacyclin and its stable analogues, catecholamines and other substances) and manifests as a marked protection against the severe consequences of ischemia; attenuation of early morphological changes (limitation in infarct size) and reduction in ventricular arrhythmias as results of coronary artery occlusion and reperfusion or ouabain toxication. The protection is time- and dose-dependent; the maximum effects occur 24 h and 48 h after drug treatment. These effects can be prolonged for a longer period by the periodic administration of maintenance doses. Concerning the mechanism of this marked delayed protection, the findings show that these adaptive stresses stimulate the adenylate cyclase/cyclic AMP (cAMP) system and result in elevation in cardiac cAMP level. This triggers the induction of Na(+)/K(+)-ATPase and activates phosphodiesterase (PDE) isoforms, most likely PDE1 and PDE4. The increased amount of PDE isoforms and activated Na(+)/K(+)-ATPase moderates ischemic myocardial potassium loss, and reduces sodium and calcium accumulation during myocardial ischemia. This also attenuates ouabain toxicity. Induction of PDE isoforms may lead to a reduction in the accumulation of excess cAMP and contribute to a lessened response to beta-adrenergic stimuli. The antiarrhythmic effects can be explained by electrophysiological changes, such as prolongations of the effective refractory period and the action potential duration during ischemia and reperfusion. The advantages of pharmacologically induced adaptation to stress in preventive therapy are that an exact dosage can be applied, the risk of the harmful effects is minimal, the protection can be prolonged, and it can be induced under pathological conditions (eg, atherosclerosis, hypercholesterolemia). Pharmacologically induced long-term protection may represent a new approach in the therapy of cardiovascular diseases.
Szekeres
László
L
Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical Center, University of Szeged, Szeged, Hungary.