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Natural abundance carbon-13 nuclear magnetic resonances (NMR) from human arm and rat tissues have been observed in vivo. These signals arise primarily from triglycerides in fatty tissue. Carbon-13 NMR was also used to follow, in a living rat, the conversion of C-1-labeled glucose, which was introduced into the stomach, to C-1-labeled liver glycogen. The carbon-13 sensitivity and resolution obtained shows that natural abundance carbon-13 NMR will be valuable in the study of disorders in fat metabolism, and that experiments with substrates labeled with carbon-13 can be used to study carbohydrate metabolism in vivo.

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High-resolution phosphorous (31P)-NMR spectra of biological molecules provide detailed information about the metabolism of living systems. Although the NMR method is non-destructive, all studies so far, with two exceptions, have been carried out on excised, perfused organs and tissues or have required some form of surgery for in situ measurements. The use of 'surface' radiofrequency coils does not require surgery, but is best suited for tissues close to the surface of the animals. We describe here 'topical magnetic resonance'--a new, non-surgical method for acquiring 31P-NMR spectra from a selected, localized place deep within an animal by modifying the main magnetic field, B0, using only static-field gradients. The method is conceptually similar to one spin-imaging method but primarily provides biochemical rather than spatial information. This new technique can be used in fundamental investigations into living systems, clinical diagnosis and the estimation of the efficacy of drug therapy.

The 31P-NMR spectra of living tumours (Walker 256 carcinosarcomas) have been obtained using surface coils and found to be unlike those of normal tissues. Contrary to expectations, their intracellular pH (measured from the chemical shift of the inorganic phosphate peak) was only slightly more acid than that of normal rat muscle, and glucose infusion did not depress it. However, when deoxyglucose was infused, the tumour intracellular pH measured from the chemical shift of the deoxyglucose-6-phosphate peak was much lower (6.44 +/- 0.02) than that measured from the phosphate peak (7.14 +/- 0.01).