Differing mechanisms of hepatic glucose overproduction in triiodothyronine-treated rats vs. Zucker diabetic fatty rats by NMR analysis of plasma glucose.

The metabolic mechanism of hepatic glucose overproduction was investigated in 3,3'-5-triiodo-l-thyronine (T3)-treated rats and Zucker diabetic fatty (ZDF) rats (fa/fa) after a 24-h fast. 2H2O and [U-13C3]propionate were administered intraperitoneally, and [3,4-13C2]glucose was administered as a primed infusion for 90 min under ketamine-xylazine anesthesia. 13C NMR analysis of monoacetone glucose derived from plasma glucose indicated that hepatic glucose production was twofold higher in both T3-treated rats and ZDF rats compared with controls, yet the sources of glucose overproduction differed significantly in the two models by 2H NMR analysis.

Impaired tricarboxylic acid cycle activity in mouse livers lacking cytosolic phosphoenolpyruvate carboxykinase.

Liver-specific phosphoenolpyruvate carboxykinase (PEPCK) null mice, when fasted, maintain normal whole body glucose kinetics but develop dramatic hepatic steatosis. To identify the abnormalities of hepatic energy generation that lead to steatosis during fasting, we studied metabolic fluxes in livers lacking hepatic cytosolic PEPCK by NMR using 2H and 13C tracers. After a 4-h fast, glucose production from glycogenolysis and conversion of glycerol to glucose remains normal, whereas gluconeogenesis from tricarboxylic acid (TCA) cycle intermediates was nearly absent.

Glucose production pathways by 2H and 13C NMR in patients with HIV-associated lipoatrophy.

Patients with HIV taking protease inhibitors were selected for the presence (five subjects) or absence (five subjects) of lipoatrophy. Following an overnight fast, subjects were given oral (2)H(2)O in divided doses (5 mL/kg body water), [U-(13)C(3)] propionate (10 mg/kg), and acetaminophen (1000 mg). Glucose (from plasma) or acetaminophen glucuronide (from urine) were converted to monoacetone glucose for (2)H NMR and (13)C NMR analysis.

Glucose production, gluconeogenesis, and hepatic tricarboxylic acid cycle fluxes measured by nuclear magnetic resonance analysis of a single glucose derivative.

A triple-tracer method was developed to provide absolute fluxes contributing to endogenous glucose production and hepatic tricarboxylic acid (TCA) cycle fluxes in 24-h-fasted rats by (2)H and (13)C nuclear magnetic resonance (NMR) analysis of a single glucose derivative. A primed, intravenous [3,4-(13)C(2)]glucose infusion was used to measure endogenous glucose production; intraperitoneal (2)H(2)O (to enrich total body water) was used to quantify sources of glucose (TCA cycle, glycerol, and glycogen), and intraperitoneal [U-(13)C(3)] propionate was used to quantify hepatic anaplerosis, pyruvate cycling, and TCA cycle flux. Plasma glucose was converted to monoacetone glucose (MAG), and a single (2)H and (13)C NMR spectrum of MAG provided the following metabolic data (all in units of micromol/kg/min; n = 6): endogenous glucose production (40.

Sources of plasma glucose by automated Bayesian analysis of 2H NMR spectra.

Sources of blood glucose can be determined after oral ingestion of (2)H(2)O followed by isolation of plasma glucose and measurement of the relative (2)H enrichments in select positions within the glucose molecule. Typically, (2)H enrichments are obtained by mass spectrometry but (2)H NMR offers an alternative. Here it is demonstrated that the entire analysis may be automated by Bayesian analysis of a (2)H free induction decay signal of monoacetone glucose to obtain a direct readout of the relative contributions of glycogenolysis, glycerol, and phosphoenol pyruvate to plasma glucose production.

Increased hepatic fructose 2,6-bisphosphate after an oral glucose load does not affect gluconeogenesis.

The generally accepted metabolic concept that fructose 2,6-bisphosphate (Fru-2,6-P2) inhibits gluconeogenesis by directly inhibiting fructose 1,6-bisphosphatase is based entirely on in vitro observations. To establish whether gluconeogenesis is indeed inhibited by Fru-2,6-P2 in intact animals, a novel NMR method was developed using [U-13C]glucose and 2H2O as tracers. The method was used to estimate the sources of plasma glucose from gastric absorption of oral [U-13C]glucose, from gluconeogenesis, and from glycogen in 24-h fasted rats.

Noninvasive evaluation of liver metabolism by 2H and 13C NMR isotopomer analysis of human urine.

Mammalian liver disposes of acetaminophen and other ingested xenobiotics by forming soluble glucuronides that are subsequently removed via renal filtration. When given in combination with the stable isotopes 2H and 13C, the glucuronide of acetaminophen isolated from urine provides a convenient "chemical biopsy" for evaluating intermediary metabolism in the liver. Here, we describe isolation and purification of urinary acetaminophen glucuronide and its conversion to monoacetone glucose (MAG).

13C isotopomer analysis of glutamate by tandem mass spectrometry.

Tandem mass spectrometry allows a compound to be isolated from the rest of the sample and dissociated into smaller fragments. We show here that fragmentation of glutamate mass isotopomers yields additional mass spectral data that significantly improve the analysis of metabolic fluxes compared to full-scan mass spectrometry. In order to validate the technique, tandem and full-scan mass spectrometry were used along with (13)C NMR to analyze glutamate from rat hearts perfused with three substrate mixtures (5 mM glucose plus 5 mM [2-(13)C]acetate, 5 mM [1-(13)C]glucose plus 5 U/L insulin, and 5 mM glucose plus 1 mM [3-(13)C]pyruvate).

Effect of exercise on (23)Na MRI and relaxation characteristics of the human calf muscle.

The acute affect of voluntary muscle contractions performed by healthy volunteers was evaluated using (23)Na nuclear magnetic resonance (NMR). Three-dimensional gradient-echo (23)Na images, pulse-acquired spectra, and transverse relaxation times were obtained before and after ankle flexion-extension exercise. The muscle sodium concentration was calculated from (23)Na images using a 40 mM NaCl standard and the measured T(2) values.

Use of a single (13)C NMR resonance of glutamate for measuring oxygen consumption in tissue.

A kinetic model of the citric acid cycle for calculating oxygen consumption from (13)C nuclear magnetic resonance (NMR) multiplet data has been developed. Measured oxygen consumption (MVO(2)) was compared with MVO(2) predicted by the model with (13)C NMR data obtained from rat hearts perfused with glucose and either [2-(13)C]acetate or [3-(13)C]pyruvate. The accuracy of MVO(2) measured from three subsets of NMR data was compared: glutamate C-4 and C-3 resonance areas; the doublet C4D34 (expressed as a fraction of C-4 area); and C-4 and C-3 areas plus several multiplets of C-2, C-3, and C-4.

Ion-Pairing Interactions between Co(en)(3)(3+) and the (23)Na NMR Frequency Shift Reagent TmDOTP(5)(-).

Three new formulations of TmDOTP(5)(-) (DOTP(8)(-) = 1,4,7,10-tetraazacyclododecane-1,4,7,11-tetrakis(methylenephosphonate)) have been prepared in an effort to develop a low-osmolality form of the (23)Na frequency shift reagent (SR). Equally concentrated (0.32 M) solutions of (MegH)(4)HTmDOTP (Meg = N-methylglucamine or meglumine), Na(4)HTmDOTP, and [Co(en)(3)](4/3)HTmDOTP have solution osmolalities of 1245, 1040, and 707 mOsm/kg, respectively, comparable to the ionic and non-ionic gadolinium-based MRI contrast agent preparations in clinical use.