K+, MG2+-aspartate (KMg-ASP)--mediated prevention of isoproterenol(ISO)-induced metabolic changes in the myocardium.

Isoproterenol (ISO) in a single dose of 7.5 mg/kg b.w. i.v was found to produce alterations of cardiac metabolism in dogs. After 2 h, high energy phosphate stores and glycogen were reduced, whereas the levels of lactate, pyruvate, the lactate/pyruvate ratio and myofibrillar ATPase activity were elevated. Ca2+ -accumulation by sarcoplasmic reticulum (SR) and mitochondria were increased (P less than 0.01). After 24 h, a partial recovery in the parameters followed could be observed. Only myofibrillar ATPase activity and the Ca2+ -uptake by SR and mitochondria were lowered. When K,Mg-ASP was administered, i.v. concurrently with ISO, myofibrillar ATPase and Ca2+ -accumulation by SR did not differ from controls 2 h after ISO application. Also the other parameters exhibited a tendency to improve (P less than 0.01), but did not reach control levels. 24 h after ISO application we could observe a similar effect of K,Mg-ASP in the prevention of Ca2+ -overload accompanying metabolic changes.