STRUCTURAL STUDIES OF NMR DETECTED LIPIDS IN MYOCARDIAL-ISCHEMIA

Lipid-induced abnormalities in myocardial function have been implicate d in a number of ischemic events including the accumulation of lipids in human myocardium following myocardial infarction. Although animal m odels have shown the source of these lipids to be triglycerides, the s pecific species involved has not been identified. In order to better u nderstand the mechanism(s) defining this lipid accumulation, it follow s that the identification of the lipids involved may be important in a chieving this aim. Therefore, this study examined the use of NMR probe s for delineating the biochemical makeup of the increased H-1 NMR obse rved lipid signal following myocardial infarction. Specifically, the p resent study demonstrated the utility of the spin-echo pulse sequence for the study of alterations in myocardial lipids following ischemic i njury. Spin-echo spectra allowed the analysis of subsets of lipids wit hin the large lipid pool inherent in most myocardium. The analyses of the chemical shifts of the lipid resonances provided a simple yet powe rful means for deducing lipid class associated with the ischemic injur y and suggested the species arises predominantly from saturated lipids . The examination of the CH2/CH3 NMR ratio provided additional informa tion regarding the species involved, however, because the spin-echo te chnique was utilized, which may distort certain signal intensities, ca ution must be exercised in interpreting the specific species involved. With this in mind, a tentative assignment has been given to octanoic acid. Finally, a temperature dependence of the lipid signals was noted and determined to be unique for spin-echo lipid. Although this depend ence did not provide the necessary information regarding the gel-to-li quid crystal phase transition temperature which might aid in understan ding the origin of the lipid species, it did determine that the specie s involved was only the spin-echo observed lipid and that the dependen ce was reversible. Finally, the increase in signal intensity associate d with the spin-echo lipid signal at physiologic temperature may provi de the necessary means to observe such species utilizing chemical shif t imaging methods.