Evaluation of triple quantum‐filtered 23 Na NMR spectroscopy in the in situ rat liver

Triple quantum (TQ)‐filtered 23 Na NMR spectroscopy and the shift reagent, TmDOTP 5‐ , have been used to evaluate the contributions of intra‐ (Na i + ) and extracellular (Na e + ) sodium to the TQ‐filtered signal in the rat liver, in situ. Na e + contributed significantly to the total TQ‐filtered signal in live animals, and the intensity of this signal did not change postmortem. The TQ‐filtered Na i + signal increased by approximately 380% over a period of 1 h postmortem, whereas the single quantum (SQ) Na i + increased by 90%. The constancy of the TQ‐filtered Na e + signal indicates that changes in total TQ‐filtered 23 Na signal intensity in liver (without a shift reagent) may accurately reflect changes in TQ‐filtered Na i + signal intensity. The large percent increase in the TQ‐filtered Na i + signal as compared to the SQ signal suggests that the fraction of Na i + interacting with macromolecules increases after death.