COMPARISON OF FATTY-ACID TRACERS FTHA AND BMIPP DURING MYOCARDIAL-ISCHEMIA AND HYPOXIA

To study the sensitivity of two fatty acid tracers to changes in beta- oxidation, the myocardial retention kinetics of odine-15-(p-iodophenyl )-3(R,S)-methylpentadecanoic acid (BMIPP) and 14-F-18-fluoro-6-thia-he ptadecanoic acid (FTHA) were compared in states of oxygen deprivation due to ischemia and hypoxia. Methods: Nineteen swine were studied by e xtracorporeal perfusion of the three coronary arteries. Fatty acid bet a-oxidation rates were determined by infusion of tritiated palmitate i nto the left anterior descending artery (LAD) and by measurement of la beled water production in the LAD perfusion bed. After a baseline peri od of 30 min, animals were divided into three groups and subjected to a 50-min intervention period. For the control group, there was no chan ge in perfusion; for the ischemia group, there was a 60% decrease in L AD perfusion; and for the hypoxia group, the perfusion rate was unchan ged, but venous blood was used as the LAD perfusate. Continuous infusi on of FTHA and BMIPP into the LAD started 10 min into the intervention period and continued until the end of the intervention period. Retent ion rates of the two tracers were compared between the LAD and circumf lex perfusion beds. Results: No difference in beta-oxidation rate occu rred from the baseline to the intervention period in the control group . A 50% reduction in beta-oxidation occurred in the ischemia group, an d an 80% reduction occurred in the hypoxia group. No difference in ret ention of BMIPP or FTHA occurred in the control group. In the ischemia group, reduction in retention of both tracers occurred. However, in t he hypoxia group. FTHA uptake was unchanged, whereas BMIPP retention i ncreased compared to the circumflex arterial bed. Conclusion: Decrease d retention of both BMIPP and FTHA occurred with ischemia, despite the known differences in metabolism of the two tracers. This difference i n metabolism was further highlighted in the setting of hypoxia with in creased BMIPP uptake. Thus, these results suggest that uptake of both FTHA and BMIPP tracks reduction of fatty acid utilization in myocardia l ischemia but fails in tracking reduction of fatty acid oxidation dur ing hypoxia.