Triple-quantum-filtered 23Na NMR spectroscopy of subcutaneously implanted 9L gliosarcoma in the rat in the presence of TmDOTP5-

The utility of triple-quantum (TQ)-filtered Na-23 NMR spectroscopy for discriminating between intra- and extracellular Na+(Na-i(+) and Na-e(+) respectively) in a solid tumor in vivo was evaluated using TmDOTP5- as a Na-23 shift reagent. Infusion of 80 mM TmDOTP5- without added Ca2+ produced baseline-resolved Na and Na-e(+) peaks in both single-quantum (SQ) and TQ-filtered Na-23 spectra. The Na-i(+) signal represented 22 +/- 4% of the SQ spectrum, but 59 +/- 10% of the TQ-filtered spectrum. Therefore, the Nat contribution in TQ-filtered spectra is much higher than in SQ spectra. Both SQ and TQ-filtered Na-i(+) signals increased by about 75% 1 h after sacrificing the animal. The TQ-filtered relaxation times did not change during this time, indicating that changes observed in TQ-filtered spectra collected with a preparation time of 3 ms represent changes in the concentration of sodium ions contributing to the TQ-filtered signal. Similar experiments were conducted without TmDOTP5- to determine changes in the Na-e(+) signal in the absence of the shift reagent. The changes in total SQ and TQ-filtered signals 1 h after sacrificing the animal showed that the SQ Na-e(+) signal decreased by approximately 35%, while the TQ-filtered Na-e(+) signal did not change significantly. This demonstrates that the TQ-filtered Na-23 signal is relatively insensitive to changes in Na-e(+) content. TO our knowledge, this work represents the first evaluation of multiple- quantum-filtered Na-23 spectroscopy to discriminate between intra- and extracellular Na+ in a solid tumor in vivo. (C) 2001 Academic Press.