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Resolving the sources of plasma glucose excursions following a glucose tolerance test in the rat with deuterated water and [U-13C]glucose.

Delgado TC, Barosa C, Nunes PM, Cerdán S, Geraldes CF, Jones JG - PLoS ONE (2012)

Bottom Line: Plasma water (2)H-enrichment attained isotopic steady-state within 2-4 minutes following the load.Between 15 and 120 minutes, the load contribution fell whereas the gluconeogenic contribution remained constant.In rats that were placed on high-fat diet, the development of glucose intolerance was associated with a significantly higher gluconeogenic contribution to plasma glucose levels after the load.

View Article: PubMed Central - PubMed

Affiliation: Intermediary Metabolism Group, Center for Neurosciences and Cell Biology, Coimbra, Portugal.

ABSTRACT
Sources of plasma glucose excursions (PGE) following a glucose tolerance test enriched with [U-(13)C]glucose and deuterated water were directly resolved by (13)C and (2)H Nuclear Magnetic Resonance spectroscopy analysis of plasma glucose and water enrichments in rat. Plasma water (2)H-enrichment attained isotopic steady-state within 2-4 minutes following the load. The fraction of PGE derived from endogenous sources was determined from the ratio of plasma glucose position 2 and plasma water (2)H-enrichments. The fractional gluconeogenic contributions to PGE were obtained from plasma glucose positions 2 and 5 (2)H-positional enrichment ratios and load contributions were estimated from plasma [U-(13)C]glucose enrichments. At 15 minutes, the load contributed 26±5% of PGE while 14±2% originated from gluconeogenesis in healthy control rats. Between 15 and 120 minutes, the load contribution fell whereas the gluconeogenic contribution remained constant. High-fat fed animals had significant higher 120-minute blood glucose (173±6 mg/dL vs. 139±10 mg/dL, p<0.05) and gluconeogenic contributions to PGE (59±5 mg/dL vs. 38±3 mg/dL, p<0.01) relative to standard chow-fed controls. In summary, the endogenous and load components of PGE can be resolved during a glucose tolerance test and these measurements revealed that plasma glucose synthesis via gluconeogenesis remained active during the period immediately following a glucose load. In rats that were placed on high-fat diet, the development of glucose intolerance was associated with a significantly higher gluconeogenic contribution to plasma glucose levels after the load.

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13C NMR spectrum of monoacetone glucose (MAG) derived from plasma glucose 120 minutes after an intra-peritoneal glucose load enriched with [U-13C]glucose (1.5 mg/g body weight) (A) in a) healthy control and b) HFD fed-animals.The singlet (C1) corresponding to the natural abundance and [U-13C]glucose isotopomer (the quartet Q1–Q4) are represented in the inset. The doublet signals (D1 and D2) are due to 13C-13C coupling between carbons 1 and 2 (but not carbon 5) and represent the sum of [1,2,3-13C3]glucose and [1,2-13C2]glucose isotopomers. 2H NMR spectrum of MAG from pooled samples (B) from a) control and b) HFD-fed animals 120 min after an intraperitonral glucose load (1.5 mg/g body weight) enriched with deuterated water (2H2O). Seven MAG aliphatic hydrogens derived from plasma glucose are shown and identified respectively.
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pone-0034042-g002: 13C NMR spectrum of monoacetone glucose (MAG) derived from plasma glucose 120 minutes after an intra-peritoneal glucose load enriched with [U-13C]glucose (1.5 mg/g body weight) (A) in a) healthy control and b) HFD fed-animals.The singlet (C1) corresponding to the natural abundance and [U-13C]glucose isotopomer (the quartet Q1–Q4) are represented in the inset. The doublet signals (D1 and D2) are due to 13C-13C coupling between carbons 1 and 2 (but not carbon 5) and represent the sum of [1,2,3-13C3]glucose and [1,2-13C2]glucose isotopomers. 2H NMR spectrum of MAG from pooled samples (B) from a) control and b) HFD-fed animals 120 min after an intraperitonral glucose load (1.5 mg/g body weight) enriched with deuterated water (2H2O). Seven MAG aliphatic hydrogens derived from plasma glucose are shown and identified respectively.

Mentions: The contribution of the i.p. glucose load to PGE was estimated from plasma [U-13C]glucose enrichment levels as previously described [9], [10], [11], [12] and a representative 13C NMR spectrum of plasma glucose sampled at 120 min from a control rat is shown in Figure 2A a). In control healthy rats, blood glucose peaked at 15 min after the glucose load and decreased gradually thereafter, returning to pre-load levels after 120 min (Figure 3A). While total blood glucose levels crested at above 300 mg/dL at 15 minutes post-load, the load glucose only accounted for about one third of this excursion (Figure 3B), indicating that the initial surge in plasma glucose levels following the glucose tolerance test is only partly accounted for by absorption of the glucose load. Thereafter, the absolute contribution of the load glucose to PGE decreased slowly. Recycled glucose isotopomers from Cori cycle activity were undetectable until about 15 minutes after the glucose load. From 15 to 60 minutes after the glucose load, the amount of recycled glucose rose gradually and then remained constant up to 120 minutes (Figure 3C). Recycled glucose contributions to PGE increased over time from 2% at 15 minutes to 75% at 120 minutes.


Resolving the sources of plasma glucose excursions following a glucose tolerance test in the rat with deuterated water and [U-13C]glucose.

Delgado TC, Barosa C, Nunes PM, Cerdán S, Geraldes CF, Jones JG - PLoS ONE (2012)

13C NMR spectrum of monoacetone glucose (MAG) derived from plasma glucose 120 minutes after an intra-peritoneal glucose load enriched with [U-13C]glucose (1.5 mg/g body weight) (A) in a) healthy control and b) HFD fed-animals.The singlet (C1) corresponding to the natural abundance and [U-13C]glucose isotopomer (the quartet Q1–Q4) are represented in the inset. The doublet signals (D1 and D2) are due to 13C-13C coupling between carbons 1 and 2 (but not carbon 5) and represent the sum of [1,2,3-13C3]glucose and [1,2-13C2]glucose isotopomers. 2H NMR spectrum of MAG from pooled samples (B) from a) control and b) HFD-fed animals 120 min after an intraperitonral glucose load (1.5 mg/g body weight) enriched with deuterated water (2H2O). Seven MAG aliphatic hydrogens derived from plasma glucose are shown and identified respectively.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3316706&req=5

pone-0034042-g002: 13C NMR spectrum of monoacetone glucose (MAG) derived from plasma glucose 120 minutes after an intra-peritoneal glucose load enriched with [U-13C]glucose (1.5 mg/g body weight) (A) in a) healthy control and b) HFD fed-animals.The singlet (C1) corresponding to the natural abundance and [U-13C]glucose isotopomer (the quartet Q1–Q4) are represented in the inset. The doublet signals (D1 and D2) are due to 13C-13C coupling between carbons 1 and 2 (but not carbon 5) and represent the sum of [1,2,3-13C3]glucose and [1,2-13C2]glucose isotopomers. 2H NMR spectrum of MAG from pooled samples (B) from a) control and b) HFD-fed animals 120 min after an intraperitonral glucose load (1.5 mg/g body weight) enriched with deuterated water (2H2O). Seven MAG aliphatic hydrogens derived from plasma glucose are shown and identified respectively.
Mentions: The contribution of the i.p. glucose load to PGE was estimated from plasma [U-13C]glucose enrichment levels as previously described [9], [10], [11], [12] and a representative 13C NMR spectrum of plasma glucose sampled at 120 min from a control rat is shown in Figure 2A a). In control healthy rats, blood glucose peaked at 15 min after the glucose load and decreased gradually thereafter, returning to pre-load levels after 120 min (Figure 3A). While total blood glucose levels crested at above 300 mg/dL at 15 minutes post-load, the load glucose only accounted for about one third of this excursion (Figure 3B), indicating that the initial surge in plasma glucose levels following the glucose tolerance test is only partly accounted for by absorption of the glucose load. Thereafter, the absolute contribution of the load glucose to PGE decreased slowly. Recycled glucose isotopomers from Cori cycle activity were undetectable until about 15 minutes after the glucose load. From 15 to 60 minutes after the glucose load, the amount of recycled glucose rose gradually and then remained constant up to 120 minutes (Figure 3C). Recycled glucose contributions to PGE increased over time from 2% at 15 minutes to 75% at 120 minutes.

Bottom Line: Plasma water (2)H-enrichment attained isotopic steady-state within 2-4 minutes following the load.Between 15 and 120 minutes, the load contribution fell whereas the gluconeogenic contribution remained constant.In rats that were placed on high-fat diet, the development of glucose intolerance was associated with a significantly higher gluconeogenic contribution to plasma glucose levels after the load.

View Article: PubMed Central - PubMed

Affiliation: Intermediary Metabolism Group, Center for Neurosciences and Cell Biology, Coimbra, Portugal.

ABSTRACT
Sources of plasma glucose excursions (PGE) following a glucose tolerance test enriched with [U-(13)C]glucose and deuterated water were directly resolved by (13)C and (2)H Nuclear Magnetic Resonance spectroscopy analysis of plasma glucose and water enrichments in rat. Plasma water (2)H-enrichment attained isotopic steady-state within 2-4 minutes following the load. The fraction of PGE derived from endogenous sources was determined from the ratio of plasma glucose position 2 and plasma water (2)H-enrichments. The fractional gluconeogenic contributions to PGE were obtained from plasma glucose positions 2 and 5 (2)H-positional enrichment ratios and load contributions were estimated from plasma [U-(13)C]glucose enrichments. At 15 minutes, the load contributed 26±5% of PGE while 14±2% originated from gluconeogenesis in healthy control rats. Between 15 and 120 minutes, the load contribution fell whereas the gluconeogenic contribution remained constant. High-fat fed animals had significant higher 120-minute blood glucose (173±6 mg/dL vs. 139±10 mg/dL, p<0.05) and gluconeogenic contributions to PGE (59±5 mg/dL vs. 38±3 mg/dL, p<0.01) relative to standard chow-fed controls. In summary, the endogenous and load components of PGE can be resolved during a glucose tolerance test and these measurements revealed that plasma glucose synthesis via gluconeogenesis remained active during the period immediately following a glucose load. In rats that were placed on high-fat diet, the development of glucose intolerance was associated with a significantly higher gluconeogenic contribution to plasma glucose levels after the load.

Show MeSH
Related in: MedlinePlus