Function and energy metabolism of isolated rats hearts as influenced by Sr++

Effect of adenosine and AICAR on ATP content and regional contractile function in reperfused canine myocardium

We investigated whether the postischemic acceleration of adenosine triphosphate (ATP) synthesis by means of precursor infusion is beneficial for the contractile function of reperfused myocardium. A coronary artery was occluded for 45 min in 21 dogs to produce a marked but reversible ischemia. During the following 3 hours of reperfusion either adenosine (n = 6) or AICAR (5-amino-imidazole-4-carboxamide-riboside) (n = 6) was infused intracoronarily by a small transfemoral catheter positioned in the LAD. ATP repletion by adenosine was nearly 50% of the deficit caused by the previous ischemia, the effect of AICAR on steady-state tissue ATP concentration was insignificant. Regional systolic function of these both groups was compared to that of a control group (n = 9) receiving only a saline infusion. We measured the regional function by subendocardially implanted ultrasound transducers using the transit time method. All three groups showed a reduction to about 25% of the initial segment shortening at the end of ischemia, followed by a quick recovery to half of the preocclusion segment shortening after reopening of the vessel. No further changes were observed in the control series during the 3 hours of reperfusion (50 +/- 10% SE segment shortening at the end). With adenosine infusion - in spite of the resulting considerable ATP elevation - no significant change of segmental contractile function occurred (44 +/- 5% SE segment shortening). Only the AICAR treated group differed from control. It produced a continuous deterioration during reflow resulting in a holosystolic bulging of -20% +/- 10% SE at the end of 3 hours of reperfusion. Our results show that there is no correlation between different ATP tissue levels achieved by adenosine infusion and systolic function in reperfused myocardium after regional reversible ischemia. We hypothesize that reperfusion dyskinesia is caused by a failure of energy utilisation rather than of energy supply.

Myocardial high energy phosphates and function as influenced by di- or trivalent cations and isoproterenol or DBcAMP

The effects of Mn++, La+++ and Co++ (2 mM) with and without ISO or DBcAMP were investigated in isolated perfused rat hearts concerning mechanical and metabolic parameters. Mn++ and La+++ produce cardiac arrest accompanied by unchanged content of high energy phosphates. ISO or DBcAMP resp. administered together with these cations do not exhibit characteristic effects. Co++ induces cardiac arrest as well, but in addition severe reduction of high energy phosphate stores and O2-consumption. The effects of Co++ can be partly prevented by administration of ISO and elevated extracellular Ca++ concentration concerning mechanical parameters and oxygen consumption, whereas high energy phosphate stores remain low. The results obtained demonstrated that the Ca++ antagonistic ions studied show the expected metabolic consequences of EC-uncoupling only in the case of Mn++ and La+++. Co++ ions induce in additions to cardiac arrest and low O2-consumption severe reduction of high energy phosphate stores indicating disturbance of respiratory control of mitochondria.