Acid-base regulation: has 31P NMR any answers?

In vivo assessment of metabolic perturbations following alanine and glucagon administration using 31P-MRS in the rat

This study set out to validate the use of 31P-NMR spectroscopy together with alanine +/- glucagon infusions to assess hepatic gluconeogenic flux in vivo. Bolus infusions of alanine (2.8 or 5.6 mmol/kg) +/- glucagon (250 microg/kg) were used. Maximal changes in the phosphomonoesters (PME), inorganic phosphate (Pi) and beta-NTP occurred 40 mins post infusion. PME increased 13.1% (p < 0.02) and 20.8% (P < 0.01) at 2.8 mmol/kg + glucagon and 5.6 mmol/kg +/- glucagon, respectively. Pi was unaltered at 2.8 mmol/kg but increased by 28.8% (P < 0.01) at 5.6 mmol/kg alanine + glucagon. beta-NTP decreased by 14.4% (P < 0.02) and 16.1% (P < 0.02) at 5.6 mmol/kg -/+ glucagon, respectively. This latter infusion showed slower recovery rates of NTP which remained 12.3% (P < 0.05) lower 70 min post infusion compared with pre-infusion values. 31 P-NMR analysis of liver extracts revealed that PME increases were partly due to 3-phosphoglycerate and corroborated reductions in beta-NTP and gamma-NTP: beta-NDP ratio upon infusion of 5.6 mmol/kg alanine +/- glucagon. Hepatic glucose output from perfused liver experiments showed no difference between alanine concentrations indicating maximal glucose output at the lower concentration. This study has shown that in vivo 31P-NMR in combination with alanine infusion, can be used to determine metabolic changes associated with gluconeogenesis.

Acid/base may be more variable than previously thought

Organ systems in the human body may not be homogeneous in regard to pH. Possibly specific organ systems under certain conditions maintain a pH level significantly different than the systemic pH.

Controlled ventilation during NMR spectroscopic studies: hemodynamic and biochemical consequences

The effects of different ventilation methods on cardiac output measured by the indicator-dilution method, liver blood flow measured by a deuterium washout technique using 2H nuclear magnetic resonance (NMR) and liver concentrations of ATP and intracellular pH determined with 31P NMR were compared in anesthetized rats. No differences in mean arterial blood pressure were demonstrable with the different modes of ventilation. However, significant drops in cardiac output were observed between freely breathing and animals ventilated with positive pressure but not the high frequency oscillatory method (407 +/- 46 and 520 +/- 88 vs. 633 +/- 86 ml/min/kg, p less than 0.05 and p = NS, respectively). Moreover, liver blood flow was significantly reduced during positive pressure but not high frequency oscillatory ventilation compared with free breathing rats (32 +/- 4 and 43 +/- 10 vs. 46 +/- 8 ml/100 g, p less than 0.05 and p = NS, respectively). 31P NMR spectroscopy revealed no effects of either ventilation method on tissue ATP or intracellular pH as estimated by the chemical shift of inorganic phosphate. These data suggest that controlled ventilation in normal rats accomplished with standard positive pressure methods is associated with major decreases in cardiac output and liver blood flow despite maintenance of normal blood pressure. High frequency oscillatory ventilation appears to effect less compromise of cardiac output and hepatic perfusion than positive pressure ventilation and may, therefore, be preferable for some biological studies.