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

Triple quantum (TQ)-filtered ²³Na 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 ²³Na 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.