Technetium-99m glucarate uptake in a swine model of limited flow plus increased demand

Abstract

Background. Glucarate is a 6-carbon dicarboxylic acid shown to be taken up by necrotic myocytes, binding to nuclear histones in animal models of coronary occlusion, resulting in infarction. This study investigated glucarate uptake in a model of severe ischemia. Methods and Results. Thirty-five experiments were performed, in which a catheter-mounted stenosis (reducing lumen dimensions by 80%) was placed in the left anterior descending coronary artery (LAD) of an anesthetized, instrumented domestic swine and technetium-99m glucarate (GLU) was injected during the last minute of 5 minutes of pacing. Hemodynamic and blood flow measurements were performed at control, during pacing, and during recovery. The animals were killed; their hearts were stained with fluorescein dye and triphenyl tetrazolium chloride (TTC). Electron micography (EM; n = 6) and cell centrifugation (n = 7) were also performed. On the basis of net lactate production and severe blood flow reduction in the risk region (RR), ischemia with pacing developed in 25 animals. Fifteen of 25 animals showed tracer uptake in the RR on in vivo and ex vivo imaging (scan positive), and 10 were scan negative in the RR. Endocardial blood flow in the RR during pacing was 0.28 ± 0.16 mL/g/min for scan-positive and 0.30 ± 0.17 mL/g/min for scan-negative experiments (P = not significant [NS]). Transmyocardial net lactate extraction during pacing was −63% ± 44% for scan-positive and −53% ± 60% for scan-negative experiments (P = NS). Control and recovery heart rates were higher in scan-positive experiments (108 ± 14 vs 92 ± 17, and 125 ± 24 vs 104 ± 18,P < .02). Lactate extraction was lower during control and recovery in scan-positive animals (2 ± 29 vs 30 ± 19, P = .03). Scan-positive animals had a more proximal stenosis position. Minimal necrosis was documented by means of TTC negative staining in 8 of 15 scan-positive experiments (comprising 10% ± 4.3% of RR area). EM or cell fractionation was performed in 5 of the 7 remaining scan-positive and TTC-positive hearts, and in those 5 experiments, necrosis was documented by means of EM in 2 and by means of cell fractionation in 3. Conclusions. Uptake of Tc-99m glucarate was seen in the RR in a swine model of ischemia severe enough to produce myocyte injury and early cell death. (J Nucl Cardiol 2000;7:590-8.)