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Extraction of Long-Chain Fatty Acids in Isolated Rat Heart During Acute Low-Flow Ischemia

Clinic for Nuclear Medicine, University Hospital Charité, Humboldt University of Berlin, Berlin, Germany

Although ß-oxidation of fatty acids is suppressed rapidly during ischemia, the behavior of fatty acid extraction at different flow rates is incompletely understood. This study assessed the relationship between flow and extraction of ¹²³I-iodophenylpentadecanoic acid (IPPA) in the isolated heart model, especially at low flow. Methods: Isolated hearts from male Wistar rats (n = 15) were subjected to retrograde perfusion with constant flow (Krebs Henseleit solution containing 10 mmol/L glucose). A latex balloon in the left ventricle allowed isovolumetric contractions and ventricular pressure measurements. The extraction of ¹²³I-IPPA was assessed with the indicator dilution technique and ^99mTc-albumin as the intravascular reference. The flow was either increased from the control flow (8 mL/min) until 300% or reduced until 10%. ¹²³I-IPPA extraction was measured three times before and 10 min after flow alteration. The tracer uptake was estimated from the product of net extraction and flow. Results: The mean ¹²³I-IPPA extraction at the control flow (third measurement) was 51.6% ± 2.8%. Between flow rates of approximately 25% and 300%, ¹²³I-IPPA extraction increased exponentially at decreasing flow rates. At flow rates 25% of the control flow, ¹²³I-IPPA extraction was exponentially higher than predicted. ¹²³I-IPPA uptake and flow changed largely in parallel. During low flow, the rate–pressure product showed the expected decline (perfusion–contraction matching). Conclusion: The extraction of ¹²³I-IPPA is preserved and slightly increased (relative to flow) during acute low-flow ischemia.

Key Words: ¹²³I-iodophenylpentadecanoic acid • myocardial metabolism • low-flow ischemia • fatty acid extraction