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

Abstract

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 μg/kg) were used. Maximal changes in the phosphomonoesters (PME), inorganic phosphate (P i) and β-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. P i was unaltered at 2.8 mmol/kg but increased by 28.8% ( P<0.01) at 5.6 mmol/kg alanine+glucagon. β-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. 31P-NMR analysis of liver extracts revealed that PME increases were partly due to 3-phosphoglycerate and corroborated reductions in β-NTP and γ-NTP: β-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.