Cardiac MRS studies in rodents and other animals

© 2015 John Wiley & Sons, Ltd. We describe MR spectroscopy techniques that have been used over the past 40 years, first in the isolated, beating rodent heart and, more recently, the in situ heart. Initially, 31P MRS was used to follow changes in myocardial phosphocreatine, ATP, and Pi during ischemia. From the spectra, changes in intra- and extracellular pH (pHi and pHo) could be calculated, as could the concentration of free magnesium, ADP and AMP, the cytosolic phosphorylation potential, and the free energy of ATP hydrolysis. Subsequently, attempts were made to use 2-deoxyglucose to measure pHi and glucose uptake, while magnetization transfer was used to measure myocardial creatine kinase flux. Making the same measurements in vivo has proved difficult, yet 31P and 1H MRS of the in vivo mouse heart have been achieved by several groups, who have measured myocardial energetics, creatine, and lipids. 13C MRS has been used to follow cardiac glycogen, lipids, and TCA cycle flux and, more recently, hyperpolarized 13C MRS has been used to measure pyruvate dehydrogenase flux, pHi, and short-chain fatty acid and ketone metabolism in vivo. Finally, MRS has been used to measure the intra- and extracellular cation concentrations and thereby trans-sarcolemmal cation fluxes in the rodent heart.