Indirect monitoring of carbon-13 metabolism with NMR: analysis of perfusate with a closed-loop flow system.

NMR studies of living cells and of perfused organs almost invariably require a major effort in the design of either the probe or the support system. For enriched 13C studies of metabolism, it is sometimes possible to use a simpler approach, one amenable to use in narrow-bore high-resolution NMR spectrometers. Since some of the metabolic changes are reflected by changes in the chemical composition of the media, it may be necessary to provide only for NMR measurements of the perfusate. A simple apparatus is described which allows NMR measurement of the perfusate. A commercially available concentric NMR tube, modified to incorporate flow, is inserted in the flow loop and placed in the spectrometer. An example is given of the metabolism of 13C-enriched glucose to lactate by chick embryo fibroblasts grown in a hollow fiber bundle assembly.