NMR studies of tissue metabolism

During the past six or seven years, high resolution nuclear magnetic resonance (NMR) has been established as a powerful tool for the study of cellular metabolism in isolated cells and organs. The non-invasive nature of the measurement offers many advantages over conventional analytical techniques, but limitations on sensitivity restrict the method to the observation of molecules present in the cell at relatively high concentrations (in the order of 0.5-1 mM). Inevitably, many of the initial investigations tended to confirm existing knowledge, but this was important in establishing the validity of the NMR method. In the last few years, NMR has contributed new and interesting information on several aspects of metabolism and metabolic regulation. The majority of reports deal with 31P, 13C, and, to a lesser extent, 1H NMR. The particular areas of interest include measurements of metabolic fluxes in the steady state and transport processes, observations of cellular pH and H+ ion distribution, and compartmentation and spatially resolved NMR of whole animals. The ability to directly observe the intracellular milieu is perhaps the major single advantage of NMR. A very large number of different systems can be studied, but it is important to keep in mind that NMR is simply an additional method for studying metabolism and must always be combined with carefully designed biochemical experiments.