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Unlabelled: We previously reported that uptake of 123I-labeled 15-iodophenyl 3-methyl pentadecanoic acid (BMIPP) was lower than that of thallium in ischemic myocardium. Such discordant findings between BMIPP and thallium were compared with those of PET using 18F-deoxyglucose (FDG) and 11C-acetate to assess metabolic alterations in such segment., Methods: Sixteen patients with coronary artery disease underwent both BMIPP SPECT and PET. Relative FDG uptake (% FDG uptake) and the clearance rate constant (% Kmono) of 11C-acetate from the myocardium were calculated as markers of glucose and oxidative metabolism, respectively., Results: Relative FDG uptake of the myocardial segments with reduced BMIPP uptake and normal thallium uptake (discordant segments) was similar (85.3 +/- 10.3) to that of the normal segments (86.5 +/- 11.7) but higher than that of segments with reduced uptake of both BMIPP and thallium (67.5 +/- 19.9). Similarly, the discordant segments showed a higher % Kmono value (77.8 +/- 13.1 versus 70.0 +/- 19.1) and FDG-to-perfusion ratio (1.15 +/- 0.08 versus 1.01 +/- 0.22) than in the concordantly reduced segments., Conclusion: BMIPP uptake appears to provide metabolic information independent of thallium uptake. Combined imaging of BMIPP and thallium may potentially identify ischemic but viable myocardium.

Unlabelled: Radiolabeled fatty acids such as 15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP) have unique metabolic properties of potential use as myocardial perfusion tracers. Accordingly, we compared the in vivo pattern of uptake of BMIPP and 201Tl in hypoperfused rabbit myocardium., Methods: Animals were intubated, ventilated and their arterial pressures monitored. A left thoracotomy was performed. After ligation of a major branch of the circumflex artery, an intravenous injection of BMIPP or BMIPP/201TI was given. Radiolabeled microspheres were used to document the area of risk. After the circulation period, the animals were killed. Tracer deposition within the hearts was determined by either dual-tracer autoradiography (Protocol I) or by segmental tissue analysis (Protocol II)., Results: Dual-tracer autoradiographic activity profiles for BMIPP were comparable to those of 201TI. Moreover, the two tracers yielded similar values for normal-to-defect contrast and defect size. The myocardial activity concentration of BMIPP for both protocols correlated strongly with coronary blood flow and compared favorably with 201TI., Conclusion: BMIPP and 201TI accurately delineate areas of hypoperfusion distal to a coronary occlusion. Therefore, differences in the myocardial distribution of BMIPP and 201TI in clinical studies may be related to cellular fatty acid metabolism.

Unlabelled: Increased clinical use of 123I-labeled 15-(p-iodophenyl)-3-(R,S)-methyl- pentadecanoic acid ([123I]BMIPP) revealed discordance between BMIPP uptake and that of perfusion agents, which was inexplicable due to the uncertainty of its myocardial metabolism. This study clarifies the metabolic fate of BMIPP and its relation to substrates in isolated rat hearts., Methods: Rat hearts were perfused with 5 mmole/liter HEPES buffer containing various energy substrates and 1% bovine serum albumin. The buffer was recirculated for 4 hr after bolus injection of [123I]BMIPP. Heart time-activity curves were monitored externally. After perfusion, the radioactivity in the heart and recirculated buffer was measured. The metabolites in the buffer were then extracted and analyzed by HPLC and TLC., Results: when 0.4 mmole/liter oleate was the energy substrate, more than eight radioactive BMIPP metabolites were detected. The metabolites in the coronary effluent depended on the energy substrate in the buffer. The radioactivity in the heart at the end of the perfusion period was significantly higher when 0.4 mmole/liter oleate (28.0% +/- 1.2% ID/g, mean +/- s.e.m.) or 10 mmole/liter glucose with 25 U/liter insulin (43.9% +/- 2.2% ID/g) were the substrates compared to when 5 mmole/liter acetate (8.5% +/- 0.4% ID/g) or 0.4 mmole/liter cold BMIPP (6.2% +/- 0.3% ID/g) were the substrates. The distribution of metabolites suggests that oleate stimulated both alpha and beta oxidations, whereas glucose with insulin inhibited both. Acetate also stimulated alpha oxidation but not beta oxidation. Cold BMIPP strongly inhibited both alpha- and beta-oxidations, and little alpha oxidation occurred compared to beta-oxidation., Conclusion: These results suggest that [123I]BMIPP is metabolized in the myocardium and the metabolism is closely related to myocardial carbohydrate utilization.