DECREASED MYOCARDIAL CALCIUM-UPTAKE AFTER ISOPROTERENOL IN STREPTOZOTOCIN-INDUCED DIABETIC RATS - STUDIES IN THE INVITRO PERFUSED HEART

  • 1 January 1983
    • journal article
    • research article
    • Vol. 48  (2) , 156-161
Abstract
Myocardial Ca uptake in response to isoproterenol (ISO, 10-4 M) was investigated in control and streptozotocin-induced diabetic rats using an in vitro heart perfusion model. An initial labeling with 45Ca added to the perfusate (with or without ISO) was followed by a cold Ca-free washout, clearing the myocardial interstitium of 45Ca. In this way the remaining 45Ca was an estimate of the myocardial Ca uptake during the labeling period. In control rats ISO induced a statistically significantly increase in myocardial Ca uptake within the first 5 min, as well as from the 5th to the 15th min after exposure to this strong .beta.-receptor agonist. In contrast to this, diabetic hearts showed no increase in Ca uptake during any of these periods. The toxic effect of ISO was expressed by a leak of creatinine phosphokinase to the perfusate. In control rats the concentration of creatinine phosphokinase increased after ISO with a statistically significant correlation to the Ca uptake, while no enzymatic leak was seen after perfusion of the diabetic hearts. This abnormal response to strong .beta.-receptor stimulation in experimental diabetes is in accordance with earlier in vivo finding of a myocardial protection against toxic doses of ISO. A decreased catacholamine-induced Ca transport through the myocardial sarcolemma in streptozotocin-induced diabetic rats was indicated. This might hypothetically have relevance for diabetic heart disease as well as diabetic neuropathy.