Effect of D-600 on ischemic and reperfused rabbit myocardium: relation with timing and modality of administration

In this study we have investigated the possibility that D-600, a phenylalkylamine calcium antagonist, protects the isolated rabbit heart against ischemia and reperfusion-induced damage. D-600 was either subcutaneously injected (2mg/kg, twice daily for 5 to 6 days) in the rabbit before isolation of the heart, or delivered to the isolated hearts in the perfusate (10(-7) M), either at the onset of ischemia and during reperfusion, or only during post-ischemic reperfusion. Ischemia (90 min) was induced by reducing coronary flow from 25 to 1 ml/min, followed by 30 min of reperfusion. Myocardial damage was determined in terms of mechanical function, release of creatine phosphokinase (CPK) and noradrenaline, mitochondrial function, calcium homeostasis, and endogenous stores of ATP and creatine phosphate (CP). Administration of D-600 to the rabbits or to the isolated hearts at the time of ischemia exerted protection. There are four groups of evidence in support of this conclusion: 1) the rise in diastolic pressure during ischemia was diminished with greater recovery of developed pressure during reperfusion; 2) CPK and noradrenaline release during reperfusion were reduced; 3) the oxygen consumption and ATP generating capacities of mitochondria were better maintained; and 4) associated with this preservation of mitochondrial function was the maintenance of near normal calcium homeostasis and of endogenous ATP and CP stores. The two different modalities of administration did not produce substantially different results. When administered to the isolated hearts after the ischemic period, D-600 failed to improve mechanical recovery and release of endogenous substances. However, it reduced mitochondrial calcium overload and improved ATP production. The mechanism of the protective effect of D-600 seems to be multiple: energy-sparing effect, reduction of the toxicity mediated by endogenous catecholamines, and direct inhibition of mitochondrial calcium transport.