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.