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Biomedical subjects

D L Rothman

Publications and source records attributed to D L Rothman.

At least 109 records · Page 6Linked to original sources
PubMed1995

Impaired net hepatic glycogen synthesis in insulin-dependent diabetic subjects during mixed meal ingestion. A 13C nuclear magnetic resonance spectroscopy study.

Hepatic glycogen concentration was measured in six subjects with insulin-dependent diabetes mellitus (IDDM) and nine weight-matched control subjects using 13C nuclear magnetic resonance spectroscopy during a day in which three isocaloric mixed meals were ingested. The relative fluxes of the direct and indirect (3 carbon units-->-->glycogen) pathways of hepatic glycogen synthesis were also assessed using [1-13C]glucose in combination with acetaminophen to noninvasively sample the hepatic UDP-glucose pool. Mean fasting hepatic glycogen content was similar in the two groups. After each meal, hepatic glycogen content increased, peaking 4-5 h after the meal in both groups. By 11:00 p.m. the IDDM subjects had synthesized only 30% of the glycogen that was synthesized by the control group [IDDM subjects, net increment = 44 +/- 20 (mean +/- SE) mM; control subjects, net increment = 144 +/- 14 mM; P < 0.05]. After breakfast the flux through the gluconeogenic pathway relative to the direct pathway of hepatic glycogen synthesis was 1.7-fold greater in the IDDM subjects (59 +/- 4%) than in the control subjects (35 +/- 4%, P < 0.0003). In conclusion, under mixed meal conditions, subjects with poorly controlled IDDM have a major defect in net hepatic glycogen synthesis and augmented hepatic gluconeogenesis. The former abnormality may result in an impaired glycemic response to counterregulatory hormones, whereas both abnormalities may contribute to postprandial hyperglycemia.

Adult↗
PubMed1995

In vivo measurement of phenylalanine in human brain by proton nuclear magnetic resonance spectroscopy.

Disorders of the CNS are the major causes of morbidity and mortality observed in untreated subjects with phenylketonuria (PKU). A method to measure cerebral concentrations of phenylalanine (Phe) in vivo would greatly enhance the ability to investigate both the pathophysiology and the efficacy of therapy of this aminoacidopathy. Twelve image-guided localized proton nuclear magnetic resonance spectroscopic studies were performed in seven subjects with PKU using pulse sequences optimized to detect the aromatic protons of Phe. Ten control studies were also performed using a 2.1-Tesla Bruker Biospec spectrometer. Plasma Phe was measured at the time of the spectroscopic examination in the PKU patients. A Phe signal was observed in all 12 studies performed on the group with PKU, and in five studies cerebral Phe concentrations were measured to be 480 to 780 mumol/g. Plasma Phe concentrations were 0.7 to 3.3 mM (10.8 to 54.8 mg/dL) in the subjects with PKU. Human cerebral Phe concentrations can be measured noninvasively using proton nuclear magnetic resonance spectroscopy. A simultaneous measure of Phe and several other cerebral metabolites is obtained with this innovative technology. Adaptations of this technique can be used to investigate PKU and other neurometabolic disorders with modifications of current clinical magnetic resonance imaging systems.

Adolescent↗
PubMed1995

Contribution of hepatic glycogenolysis to glucose production in humans in response to a physiological increase in plasma glucagon concentration.

The contribution of net hepatic glycogenolysis to overall glucose production during a physiological increment in the plasma glucagon concentration was measured in six healthy subjects (18-24 years, 68-105 kg) after an overnight fast. Glucagon (approximately 3 ng.kg-1.min-1), somatostatin (0.1 microgram.kg-1.min-1), and insulin (0.9 pmol.kg-1.min-1) were infused for 3 h. Liver glycogen concentration was measured at 15-min intervals during this period using 13C-labeled nuclear magnetic resonance spectroscopy, and liver volume was assessed from magnetic resonance images. The rate of net hepatic glycogenolysis was calculated from the decrease in liver glycogen concentration over time, multiplied by the liver volume. The rate of glucose appearance (Ra) was calculated from [3-3H]glucose turnover data using a two-compartment model of glucose kinetics. Plasma glucagon concentration rose from 136 +/- 18 to 304 +/- 57 ng/l and plasma glucose concentration rose from 5.6 +/- 0.1 to 10.4 +/- 0.9 mmol/l on initiation of the infusions. Mean baseline Ra was 11.8 +/- 0.4 mumol.kg-1.min-1, increased rapidly after the beginning of the infusions, reaching its highest value after 20-40 min, and returned to baseline by 140 min. Liver glycogen concentration decreased almost linearly (from 300 +/- 19 mmol/l liver at baseline to 192 +/- 20 mmol/l liver at t = 124 min) during 2 h after the beginning of the infusions, and the calculated mean rate of net hepatic glycogenolysis was 21.7 +/- 3.6 mumol.kg-1.min-1. Mean Ra during the same time period was 22.8 +/- 2.3 mumol.kg-1.min-1. Thus, net hepatic glycogenolysis accounted for 93 +/- 9% of Ra.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1994

Validation of 13C NMR measurements of liver glycogen in vivo.

The natural abundance 13C NMR intensity of the glycogen C1 resonance was measured in the surgically exposed liver of rabbits in vivo (n = 17) by integration from 98 to 104 ppm and compared double blindedly to the subsequent biochemical measurement. Coil loading was measured each time from a reference sphere at the coil center and the NMR intensity was normalized accordingly. For quantification, the normalized NMR intensity was calibrated using aqueous glycogen solutions ranging from 110 to 1100 mumol glucosyl units/g (n = 14). An in vivo range from 110 to 800 mumol glucosyl units/g wet weight was measured with a highly linear correlation with concentration (r = 0.85, P < 0.001). The in vivo NMR concentration was 0.95 +/- 0.05 (mean +/- standard error, n = 17) of the concomitant enzymatic measurement of glycogen content. We conclude that the 13C NMR signal of liver glycogen C1 is essentially 100% visible in vivo and that natural abundance 13C NMR spectroscopy can provide reliable noninvasive estimates of in vivo glycogen content over the physiological range of liver glycogen concentrations when using adequate localization and integration procedures.

Animals↗
PubMed1994

Analysis of macromolecule resonances in 1H NMR spectra of human brain.

Macromolecule resonances underlying metabolites in 1H NMR spectra were investigated in temporal lobe biopsy tissue from epilepsy patients and from localized 1H spectra of the brains of healthy volunteers. The 1H NMR spectrum of brain tissue was compared with that of cytosol and dialyzed cytosol after removal of low molecular weight molecules (< 3500 daltons) at 8.4 and 2.1 Tesla. The assignment of specific resonances to macromolecules in 2.1 Tesla, short-TE, localized human brain 1H NMR spectra in vivo was made on the basis of a J-editing method using the spectral parameters (delta, J) and connectivities determined from 2D experiments in vitro. Two prominent connectivities associated with macromolecules in vitro (0.93-2.05 delta and 1.6-3.00 delta) were also detected in vivo by the J-editing method. Advantage was taken of the large difference in measured T1 relaxation times between macromolecule and metabolite resonances in the brain spectrum to acquire 'metabolite-nulled' macromolecule spectra. These spectra appear identical to the spectra of macromolecules isolated in vitro.

Adult↗
PubMed1994

Proton spectroscopy of human stroke: assessment of transverse relaxation times and partial volume effects in single volume steam MRS.

Proton T2 relaxation times were measured in 13 stroke patients and 13 aged-matched normal subjects at 2.1 T. Spectra were acquired from an 8-cc volume using the STEAM sequence with echo times (TE) of 30.4 ms and 270.0 ms and repetition time of 2.8 s. Transverse relaxation times were estimated using two-point calculations. Percentage volume of infarct in the STEAM voxel was measured on spin-echo MRI encompassing the infarct and correlated with the peak amplitude of N-acetylated compounds (NA). T2 values of NA, creatine, and choline resonances showed no significant difference between patients and controls. T2 for lactate in patients was 780 +/- 257 ms, respectively (mean +/- SE, n = 7). In stroke patients, high inverse correlation was found between the absolute NA signal and partial volume of normal brain contributing to each spectrum (p < .001, r = 0.97). Together with unchanged T2, this suggests that NAA largely disappears from infarcted tissue within 24 hr postinfarct.

Aged↗
PubMed1994

NMR studies of human brain function.

Recent advances in magnetic resonance imaging and spectroscopy make it possible to measure localized changes in human brain activity and metabolism in single subjects during sensory stimulation and cognition. Differences between stimulated and unstimulated subjects can be visualized to a resolution of mm3 in less than 1s, a significant improvement over the more established method, positron emission tomography. Magnetic resonance spectroscopy of the human brain, measuring fluxes in several cm3, has followed changes in metabolic rates during visual stimulation.

Biological Transport↗
PubMed1994

Localized 13C NMR spectroscopy in the human brain of amino acid labeling from D-[1-13C]glucose.

Cerebral metabolism of D[1-13C]glucose was studied with localized 13C NMR spectroscopy during intravenous infusion of enriched [1-13C]glucose in four healthy subjects. The use of three-dimensional localization resulted in the complete elimination of triacylglycerol resonance that originated in scalp and subcutaneous fat. The sensitivity and resolution were sufficient to allow 4 min of time-resolved observation of label incorporation into the C3 and C4 resonances of glutamate and C4 of glutamine, as well as C3 of aspartate with lower time resolution. [4-13C]Glutamate labeled rapidly reaching close to maximum labeling at 60 min. The label flow into [3-13C]glutamate clearly lagged behind that of [4-13C]-glutamate and peaked at t = 110-140 min. Multiplets due to homonuclear 13C-13C coupling between the C3 and C4 peaks of the glutamate molecule were observed in vivo. Isotopomer analysis of spectra acquired between 120 and 180 min yielded a 13C isotopic fraction at C4 glutamate of 27 +/- 2% (n = 4), which was slightly less than one-half the enrichment of the C1 position of plasma glucose (63 +/- 1%), p < 0.05. By comparison with an external standard the total amount of [4-13C]glutamate was directly quantified to be 2.4 +/- 0.1 mumol/ml-brain. Together with the isotopomer data this gave a calculated brain glutamate concentration of 9.1 +/- 0.7 mumol/ml, which agrees with previous estimates of total brain glutamate concentrations. The agreement suggests that essentially all of the brain glutamate is derived from glucose in health human brain.

Adult↗
PubMed1994

Liver glycogen turnover in fed and fasted humans.

Whether liver glycogen synthesis and breakdown occur simultaneously during net glycogen synthesis was assessed in fed and fasted healthy humans. The peak intensity of the carbon-1 (C1) resonance of the glycosyl units of glycogen was monitored with 13C nuclear magnetic resonance spectroscopy during [1-13C]glucose infusion followed by unlabeled glucose infusion. The C1 peak intensity increased almost linearly during the [1-13C]glucose infusion, reflecting a near linear rate of glycogen synthesis. When switched to unlabeled glucose, the C1 peak intensity reached a plateau in the fasted subjects and declined in the fed subjects, reflecting active glycogenolysis during a time of net glycogen synthesis. We conclude that liver glycogen synthesis and degradation occur simultaneously in humans under conditions of net glycogen synthesis. The relative turnover rate was significantly higher in the fed (57 +/- 3%) than in the fasted state (31 +/- 8%; P < 0.01). The results indicate that glycogen may regulate its rate of breakdown and that liver glycogen turnover may be an important factor in limiting the accumulation of liver glycogen in humans.

Adult↗
PubMed1994

Human muscle glycogen resynthesis after exercise: insulin-dependent and -independent phases.

To study the effects of glycogen depletion and insulin concentration on glycogen synthesis, gastrocnemius glycogen was measured with 13C-nuclear magnetic resonance at 4.7 T after exercise. Subjects performed single-leg toe raises to deplete gastrocnemius glycogen to 75, 50, or 25% of resting concentration (protocol I). Insulin dependence of glycogen synthesis was assessed after depletion to 25% with (protocol II) and without (protocol III) infusion of somatostatin to inhibit insulin secretion. After depletion to 75 and 50%, glycogen resynthesis rates were similar (2.4 +/- 0.7 and 2.8 +/- 0.6 mM/h, respectively). When glycogen was depleted to 25% (< 30 mM), the resynthesis rate was significantly higher (P < 0.02) at 33 +/- 7 mM/h, and it declined to 3.5 +/- 0.9 mM/h at > 35 mM glycogen. At < 35 mM glycogen, synthesis was not affected by low insulin (24 +/- 4 mM/h, protocol vs. 19 +/- 3 mM/h, protocol III), whereas at > 35 mM glycogen, synthesis ceased without insulin (-0.07 +/- 0.19 mM/h, protocol II). After depletion to 25% (protocol III), plasma lactate transiently increased (0.81 mM at rest, 1.82 mM 0 h after exercise, and 0.76 mM 2 h after exercise), whereas other plasma constituents did not significantly change. We conclude that after depletion to < 30 mM initial glycogen resynthesis is insulin independent and glycogen dependent, which suggests local control.

Adult↗
PubMed1994

13C-nuclear magnetic resonance spectroscopy studies of hepatic glucose metabolism in normal subjects and subjects with insulin-dependent diabetes mellitus.

To determine the effect of insulin-dependent diabetes mellitus (IDDM) on rates and pathways of hepatic glycogen synthesis, as well as flux through hepatic pyruvate dehydrogenase, we used 13C-nuclear magnetic resonance spectroscopy to monitor the peak intensity of the C1 resonance of the glucosyl units of hepatic glycogen, in combination with acetaminophen to sample the hepatic UDP-glucose pool and phenylacetate to sample the hepatic glutamine pool, during a hyperglycemic-hyperinsulinemic clamp using [1-13C]-glucose. Five subjects with poorly controlled IDDM and six age-weight-matched control subjects were clamped at a mean plasma glucose concentration of approximately 9 mM and mean plasma insulin concentrations approximately 400 pM for 5 h. Rates of hepatic glycogen synthesis were similar in both groups (approximately 0.43 +/- 0.09 mumol/ml liver min). However, flux through the indirect pathway of glycogen synthesis (3 carbon units-->-->glycogen) was increased by approximately 50% (P < 0.05), whereas the relative contribution of pyruvate oxidation to TCA cycle flux was decreased by approximately 30% (P < 0.05) in the IDDM subjects compared to the control subjects. These studies demonstrate that patients with poorly controlled insulin-dependent diabetes mellitus have augmented hepatic gluconeogenesis and relative decreased rates of hepatic pyruvate oxidation. These abnormalities are not immediately reversed by normalizing intraportal concentrations of glucose, insulin, and glucagon and may contribute to postprandial hyperglycemia.

Acetaminophen↗
PubMed1994

Turnover of human muscle glycogen with low-intensity exercise.

To determine whether glycogen turnover occurs during prolonged low-intensity exercise, five subjects performed plantar flexion of the right leg at 15% MVC for 5 h. At rest and during the initial 2.5 h of exercise gastrocnemius glycogen was monitored in both legs with natural abundance 13C NMR. At 2.5 h exercise, a step-up infusion of 99% enriched 1-13C glucose was begun and maintained over the next 1.5 h of continued exercise to monitor 1-13C glucose incorporation into the exercising muscle's glycogen pool. Exercise was continued for an hour following the infusion, and NMR scans were performed throughout the session. During the first 2 h of exercise, glycogen 1-13C signal amplitudes dropped approximately 30% and remained there at 2.5 h, indicating that glycogen concentration had leveled. Following infusion, glycogen signal amplitudes rose to 123% of resting values, remaining there during an hour of subsequent exercise. There was no change of glycogen 1-13C signal in the nonexercising leg. Venous glucose levels remained stable until the infusion was begun and then rose < 7% (5.57-5.96 mmol.l-1) during the infusion. Venous insulin and C-peptide levels did not change during the infusion. We conclude that the human gastrocnemius can degrade and synthesize glycogen simultaneously during prolonged low-intensity exercise.

Adult↗
PubMed1993

Localized 1H NMR measurement of glucose consumption in the human brain during visual stimulation.

Spatially localized 1H NMR spectroscopy has been applied to measure changes in brain glucose concentration during 8-Hz photic stimulation. NMR spectroscopic measurements were made in a 12-cm3 volume centered on the calcarine fissure and encompassing the primary visual cortex. The average maximum change in glucose levels was 0.34 mumol.g-1 (n = 5) at 15 min; glucose level had turned toward resting level at 25 min. The glucose change was used to calculate the increase of glucose cerebral metabolic rate in the visual cortex region for individual subjects by using the Michaelis-Menten model of glucose transport on the assumption of constant transport kinetics. The glucose cerebral metabolic rate was calculated to increase over the nonstimulated rate by 22% during the first 15 min of photic stimulation. A model in which the glucose metabolic rate gradually decreases during stimulation was proposed as a possible explanation for the recovery of brain glucose and previously measured lactate concentrations to prestimulus values after 15 min.

Blood Glucose↗
PubMed1993

Localized 1H NMR measurements of gamma-aminobutyric acid in human brain in vivo.

Localized 1H NMR spectroscopy in conjunction with J editing was used to measure the concentration of gamma-aminobutyric acid (GABA) in the occipital lobe of four control human volunteers and four epileptic volunteers who were receiving the drug vigabatrin. The GABA concentration measured in four nonepileptic subjects was 1.1 +/- 0.1 mumol/cm3 of brain, which is in good agreement with previous values measured in surgically removed human cortex. A dose-dependent elevation of GABA concentration was measured in patients receiving the GABA transaminase inhibitor vigabatrin, with the maximum measured level of 3.7 mumol/cm3 of brain measured at the highest dose (6 g per day) studied. 1H NMR measurements of GABA in those patients receiving GABA-elevating agents such as vigabatrin will be of importance in establishing the relationship between seizure suppression and the concentration of brain GABA.

4-Aminobutyrate Transaminase↗
PubMed1993

Echo-planar magnetic resonance imaging studies of frontal cortex activation during word generation in humans.

Nine subjects were studied by high-speed magnetic resonance imaging while performing language-based tasks. Subjects were asked either to repeat or to generate verbs associated with nouns read by an experimenter while magnetic resonance images were obtained of the left inferior frontal lobe. The echo-planar imaging sequence was used with a gradient echo time of 70 ms to give an apparent transverse relaxation time weighting (T2* that is sensitive to local hemoglobin levels. Images were acquired every 3 s (repetition time) in series of 32. In plane resolution was 6 x 4.5 mm and slice thickness was 10 mm. An increase in signal accompanied performance of the tasks, with significantly more activation for verb generation than for repeating. The activation effect occurred within 3 s after task onset and could be observed in single images from individual subjects. The primary focus of activation appeared in gray matter along a sulcus anterior to the lateral sulcus that included the anterior insula, Brodmann's area 47, and extending to area 10. Little or no activation of this region was found for a passive listening, covert generation, or mouth-movement control tasks. Significant activation was also found for a homologous region in the right frontal cortex but not for control regions in calcarine cortex. These results are consistent with prior studies that have used positron emission tomography imaging with 15O-labeled water as a blood flow tracer.

Brain Mapping↗
PubMed1993

Nuclear magnetic resonance imaging and spectroscopy of human brain function.

The techniques of in vivo magnetic resonance (MR) imaging and spectroscopy have been established over the past two decades. Recent applications of these methods to study human brain function have become a rapidly growing area of research. The development of methods using standard MR contrast agents within the cerebral vasculature has allowed measurements of regional cerebral blood volume (rCBV), which are activity dependent. Subsequent investigations linked the MR relaxation properties of brain tissue to blood oxygenation levels which are also modulated by consumption and blood flow (rCBF). These methods have allowed mapping of brain activity in human visual and motor cortex as well as in areas of the frontal lobe involved in language. The methods have high enough spatial and temporal sensitivity to be used in individual subjects. MR spectroscopy of proton and carbon-13 nuclei has been used to measure rates of glucose transport and metabolism in the human brain. The steady-state measurements of brain glucose concentrations can be used to monitor the glycolytic flux, whereas subsequent glucose metabolism--i.e., the flux into the cerebral glutamate pool--can be used to measure tricarboxylic acid cycle flux. Under visual stimulation the concentration of lactate in the visual cortex has been shown to increase by MR spectroscopy. This increase is compatible with an increase of anaerobic glycolysis under these conditions as earlier proposed from positron emission tomography studies. It is shown how MR spectroscopy can extend this understanding of brain metabolism.

Brain↗
PubMed1993

NMR-spectroscopic investigation of cerebral reanimation after prolonged ischemia.

The severity of brain injury following interruption of blood flow depends on a number of ischemic and post-ischemic variables. The most important ischemic variables are the duration of ischemia, the amount of residual blood flow, the type and depth of anesthesia, brain glucose content and temperature. Among the post-ischemic factors the no-reflow phenomenon, edema and a variety of biochemical disturbances are of particular importance. Due to the complex interaction of these factors irreversible brain injury usually occurs after less than 10 min cerebrocirculatory arrest in normothermia. However, the safe ischemia time of the brain can be substantially extended when appropriate therapeutic measures are used to alleviate post-ischemic injury. NMR-spectroscopy is particularly suited for the analysis of this process. Recording of 31P, 1H and 19F spectra allow the continuous non-invasive assessment of such basic parameters as brain energy state, tissue pH, the content of lactate and blood flow (using Freon-23 as an inert tracer). In addition, information is obtained about changes in the content of phosphomonoesters and -diesters, glutamate, glutamine, aspartate and N-acetyl aspartate. These measurements can be combined with in vivo electrophysiological and post-mortem biochemical investigations for the further refinement of functional/metabolic monitoring. We have used this approach to study the potentials of post-ischemic resuscitation after one hour complete ischemia of the normothermic cat brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid-Base Equilibrium↗