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Figure 4 Examples of [¹⁸F]-2-deoxy-2-fluoro-D-glucose (FDG) time-activity curves obtained in isolated heart perfusion, using external coincidence detectors. This approach allows the evaluation of insulin-stimulated myocardial FDG uptake without the influence of systemic factors. (A) Short-term insulin effect: compared with the initial portion of the curve (baseline), an increase of the FDG uptake rate (slope of the curve segment) is seen in the wild-type mouse heart shortly after insulin is added to the perfusion buffer (arrow). Conversely, no change is observed in the GLUT4-null mouse heart after the addition of insulin (arrow). (B) Long-term insulin stimulation: hearts were perfused with insulin containing buffer 60 min after in vivo administration of insulin/glucose. In this condition, both GLUT4-null and wild-type hearts had an increased FDG uptake rate compared with the corresponding baseline value. GLUT = glucose transporter.