Natural abundance Carbon-13 nuclear magnetic resonance spectroscopy of liver and adipose tissue of the living rat.

We have employed the topical magnetic resonance (TMR) technique to obtain natural abundance 13C nuclear magnetic resonance (NMR) spectra from liver and adipose tissue in the living rat. Experiments were performed in a TMR magnet (20-cm diameter) with a two-turn radio-frequency coil ("surface" coil) combined with a focused static magnetic field. The in vivo spectra that were obtained at 20.2 MHz have been assigned by comparison with those from excised organs obtained in a conventional spectrometer operating at 90.5 MHz. Signals in the TMR spectra corresponding to carbons of the carbohydrates, glucose and glycogen, and of the lipids, triglycerides and phospholipids, have been resolved in vivo and assigned. The effects of chronic modification of dietary fat and carbohydrate on the in vivo spectra have been investigated. The levels of carbohydrates and of saturated and unsaturated fats in the liver as measured by 13C TMR reflect the relative amounts of these compounds in the long-term diet.