Phase 1 trial of dichloroacetate (DCA) in adults with recurrent malignant brain tumors.

BACKGROUND: Recurrent malignant brain tumors (RMBTs) carry a poor prognosis. Dichloroacetate (DCA) activates mitochondrial oxidative metabolism and has shown activity against several human cancers. DESIGN: We conducted an open-label study of oral DCA in 15 adults with recurrent WHO grade III - IV gliomas or metastases from a primary cancer outside the central nervous system. The primary objective was detection of a dose limiting toxicity for RMBTs at 4 weeks of treatment, defined as any grade 4 or 5 toxicity, or grade 3 toxicity directly attributable to DCA, based on the National Cancer Institute's Common Toxicity Criteria for Adverse Events, version 4.0. Secondary objectives involved safety, tolerability and hypothesis-generating data on disease status. Dosing was based on haplotype variation in glutathione transferase zeta 1/maleylacetoacetate isomerase (GSTZ1/MAAI), which participates in DCA and tyrosine catabolism. RESULTS: Eight patients completed at least 1 four week cycle. During this time, no dose-limiting toxicities occurred. No patient withdrew because of lack of tolerance to DCA, although 2 subjects experienced grade 0-1 distal parasthesias that led to elective withdrawal and/or dose-adjustment. All subjects completing at least 1 four week cycle remained clinically stable during this time and remained on DCA for an average of 75.5 days (range 26-312). CONCLUSIONS: Chronic, oral DCA is feasible and well-tolerated in patients with recurrent malignant gliomas and other tumors metastatic to the brain using the dose range established for metabolic diseases. The importance of genetic-based dosing is confirmed and should be incorporated into future trials of chronic DCA administration.

A NOVEL INTRINSIC UNSCENTED KALMAN FILTER FOR TRACTOGRAPHY FROM HARDI*

The unscented Kalman filter (UKF) was recently introduced in literature for simultaneous multi-tensor estimation and tractography. This UKF however was not intrinsic to the space of diffusion tensors. Lack of this key property leads to inaccuracies in the multi-tensor estimation as well as in tractography. In this paper, we propose an novel intrinsic unscented Kalman filter (IUKF) in the space of symmetric positive definite matrices, which can be used for simultaneous recursive estimation of multi-tensors and tractography from diffusion weighted MR data. In addition to being more accurate, IUKF retains all the advantages of UKF for instance, multi-tensor estimation is only performed in the places where it is needed for tractography, which would be much more efficient than the two stage process involved in methods that do tracking post diffusion tensor estimation. The accuracy and effectiveness of the proposed method is demonstrated via real data experiments.

Evidence of separate pathways for lactate uptake and release by the perfused rat heart.

The simultaneous release and uptake of lactate by the heart has been observed both in vivo and ex vivo; however, the pathways underlying these observations have not been satisfactorily explained. Consequently, the purpose of this study was to test the hypothesis that hearts release lactate from glycolysis while simultaneously taking up exogenous lactate. Therefore, we determined the effects of fatty acids and diabetes on the regulation of lactate uptake and release. Hearts from control and 1-wk diabetic animals were perfused with 5 mM glucose, 0.5 mM [3-(13)C]lactate, and 0, 0.1, 0.32, or 1.0 mM palmitate. Parameters measured include perfusate lactate concentrations, fractional enrichment, and coronary flow rates, which enabled the simultaneous, but independent, measurements of the rates of 1) uptake of exogenous [(13)C]lactate and 2) efflux of unlabeled lactate from metabolism of glucose. Although the rates of lactate uptake and efflux were both similarly inhibited by the addition of palmitate, (i.e., the ratio of lactate uptake to efflux remained constant), the ratio of lactate uptake to efflux was significantly higher in the controls compared with the diabetic group (1.00 +/- 0.14 vs. 0.50 +/- 0.07, P < 0.002). These data, combined with heterogeneous (13)C enrichment of tissue lactate, pyruvate, and alanine, suggest that glycolytically derived lactate production and oxidation of exogenous lactate operate as functionally separate metabolic pathways. These results are consistent with the concept of an intracellular lactate shuttle.

MR imaging measurement of compartmental water diffusion in perfused heart slices.

Myocardial tissue slices were isolated from the left ventricular free wall (7 slices) and left ventricular papillary muscle (3 slices) of New Zealand White male rabbits (n = 4) and were subsequently superfused with a modified St. Thomas' Hospital cardioplegic solution at 19 degrees C. The diffusion-weighted images were obtained with a 600-MHz nuclear magnetic resonance spectrometer using diffusion gradient b-values that ranged from 166 to 6,408 s/mm(2); the apparent diffusion coefficient of water in the tissues were subsequently calculated. All of the tissue samples that were studied exhibited nonmonoexponential diffusion. Data from seven slices were mathematically fitted by a biexponential expression with a fast diffusion component of 0.72 +/- 0.07 x 10(-3) mm(2)/s, and a slow diffusion component of 0.060 +/- 0.033 x 10(-3) mm(2)/s. The fast component dominated the calculated apparent diffusion coefficient of the tissue, composed of 82 +/- 3% of the overall diffusion-dependent signal decay. Thus myocardial tissue exhibits characteristics consistent with multiple compartments of diffusion. This work has important implications for myocardial diffusion tensor imaging, as well as the changes in diffusion that have been reported following myocardial ischemia.

Two-component diffusion tensor MRI of isolated perfused hearts.

Nonmonoexponential MR diffusion decay behavior has been observed at high diffusion-weighting strengths for cell aggregates and tissues, including the myocardium; however, implications for myocardial MR diffusion tensor imaging are largely unknown. In this study, a slow-exchange-limit, two-component diffusion tensor model was fitted to diffusion-weighted images obtained in isolated, perfused rat hearts. Results indicate that there are at least two distinct components of anisotropic diffusion, characterized by a "fast" component whose principal diffusivity is comparable to that of the perfusate, and a highly anisotropic "slow" component. It is speculated that the two components correspond to tissue compartments and have a general agreement with the orientations of anisotropy, or fiber orientations, in the myocardium. Moreover, consideration of previous studies of myocardial diffusion suggests that the presently observed fast component may likely be dominated by diffusion in the vascular space, whereas the slow component may include the intracellular and interstitial compartments. The implications of the results for myocardial fiber orientation mapping and limitations of the current two-component model used are also discussed.

Preferential inhibition of lactate oxidation relative to glucose oxidation in the rat heart following diabetes.

OBJECTIVE: Alterations in myocardial metabolism occur early after the onset of diabetes suggesting that they may play a role in the development of cardiac dysfunction. Inhibition of myocardial pyruvate dehydrogenase (PDH), glucose transport and glycolysis have all been reported following diabetes. In vivo lactate is also a potential source of energy for the heart and its oxidation should not be affected by changes in glucose transport and glycolysis. Therefore, the objective of this study, was to test the hypothesis that following diabetes the inhibition of glucose oxidation would be greater than the inhibition of lactate oxidation. METHODS: Hearts from control and one-week-old diabetic rats were perfused with [1-13C]glucose (11 mmol/l) alone, [1-13C]glucose plus lactate (0.5 mmol/l) or glucose plus [3-13C]lactate (0.5 or 1.0 mmol/l) as substrates. Glucose and lactate oxidation rates were determined by combining 13C-NMR glutamate isotopomer analysis of tissue extracts with measurements of oxygen consumption. RESULTS: In diabetic hearts perfused with glucose alone, glucose oxidation was decreased compared to controls (0.31 +/- 0.08 vs. 0.71 +/- 0.11 mumoles/min/g wet weight; p < 0.05). Surprisingly, in hearts perfused with glucose plus 0.5 mmol/l lactate, there was no difference in glucose oxidation between control and diabetic groups (0.20 +/- 0.05 vs. 0.16 +/- 0.04 mumoles/min/g wet weight respectively). However, under these conditions lactate oxidation was markedly reduced in the diabetic group (0.89 +/- 0.18 vs. 0.24 +/- 0.05 mumoles/min/g wet weight; p < 0.05). At 1.0 mmol/l lactate oxidation was still significantly depressed in the diabetic group. CONCLUSION: There was a greater decrease in lactate oxidation relative to glucose oxidation in hearts from diabetic animals. These results demonstrate that diabetes leads to a specific inhibition of lactate oxidation independent of its effects on pyruvate dehydrogenase.

Simultaneous noninvasive determination of regional myocardial perfusion and oxygen content in rabbits: toward direct measurement of myocardial oxygen consumption at MR imaging.

PURPOSE: To determine whether myocardial arterial perfusion and oxygen concentration can be quantified simultaneously from the same images by using spin labeling and the blood oxygenation level-dependent (BOLD) effect with fast spin-echo (SE) imaging. MATERIALS AND METHODS: A T2-weighted fast SE pulse sequence was written to image isolated, arrested, blood-perfused rabbit hearts (n = 6) at 4.7 T. Perfusion images with intensity in units of milliliters per minute per gram that covered the entire left ventricle with 0.39 x 0.39 x 3.00-mm resolution were obtained in less than 15 minutes with a 32-fold reduction in imaging time from that of a previous study. Estimates of oxygen concentration were made from the same images acquired for calculation of perfusion images. RESULTS: Estimates of regional myocardial oxygen content could be made from the perfusion images; this demonstrated the feasibility of three-dimensional calculation of regional oxygen consumption, which requires concomitant measurement of both oxygen content and flow. Fast SE imaging was shown to be as sensitive to hemoglobin desaturation as standard SE imaging. Perfusion abnormalities and oxygen deficits were easily identified and verified qualitatively with gadopentetate dimeglumine on both perfusion and BOLD images obtained after coronary arterial ligation. CONCLUSION: T2-weighted fast SE imaging combined with perfusion-sensitive spin labeling can be used to measure myocardial arterial perfusion and oxygen concentration. This provides the groundwork for calculation of regional myocardial oxygen consumption.

Impact of 1 wk of diabetes on the regulation of myocardial carbohydrate and fatty acid oxidation.

The aim of this study was to investigate the effect of increasing exogenous palmitate concentration on carbohydrate and palmitate oxidation in hearts from control and 1-wk diabetic rats. Hearts were perfused with glucose, [3-(13)C]lactate, and [U-(13)C]palmitate. Substrate oxidation rates were determined by combining (13)C-NMR glutamate isotopomer analysis of tissue extracts with measurements of oxygen consumption. Carbohydrate oxidation was markedly depressed after diabetes in the presence of low (0.1 mM) but not high (1.0 mM) palmitate concentration. Increasing exogenous palmitate concentration 10-fold resulted in a 7-fold increase in the contribution of palmitate to energy production in controls but only a 30% increase in the diabetic group. Consequently, at 0.1 mM palmitate, the rate of fatty acid oxidation was higher in the diabetic group than in controls; however, at 1.0 mM fatty acid oxidation, it was significantly depressed. Therefore, after 1 wk of diabetes, the major differences in carbohydrate and fatty acid metabolism occur primarily at low rather than high exogenous palmitate concentration.

Lactic acid and protein interactions: implications for the NMR visibility of lactate in biological systems.

The addition of bovine serum albumin (BSA) to a solution of lactate and alanine resulted in the disappearance of the 1H-NMR resonances from lactate but not alanine. As temperature is increased lactate becomes increasingly NMR visible and after heating above 65 degreesC and cooling to 25 degreesC lactate binding is reduced. With a concentration of 0.2 mM BSA, there was a linear relationship between NMR visible lactate versus total lactate over a range of lactate concentrations of 0.2-35 mM (slope 0.384+/-0.003) indicating that approx. 60% of the added lactate is not visible in the 1H-NMR spectrum. With a 0.1 mM BSA solution, however, the slope was markedly higher indicating that under these conditions only 25-30% of the lactate was NMR invisible. The results from this study indicate that decreased NMR visibility of lactate in proteinaceous solutions is due to non-specific binding which is dependent on the tertiary structure of the protein. This has important implications not only for the interpretation of in vivo 1H-NMR experiments but also for 13C, and 14C studies of metabolism.

Delayed reduction of tissue water diffusion after myocardial ischemia.

The apparent diffusion coefficient (ADC) of water after regional myocardial ischemia was measured in isolated, perfused rabbit hearts by using magnetic resonance imaging (MRI) techniques. After ligation of the left anterior descending coronary artery, the ADC of the nonperfused region showed a gradual but significant decreasing trend over time, whereas that of the normally perfused myocardium remained constant. Morphological analysis revealed that the ADC decrease reflected the expansion of a subregion of reduced ADC within the nonperfused myocardium. The dynamics of the diffusion change and the morphological progression of the affected tissue suggest that the ADC decrease may be linked to the onset of myocardial infarction, which is known to involve myocyte swelling. The ADC reduction provides a potentially valuable MRI tissue-contrast mechanism for noninvasively determining the viability of the ischemic myocardium and assessing the dynamics of acute myocardial infarction.

Relationship between cardiac function and substrate oxidation in hearts of diabetic rats.

The effects of streptozotocin-induced diabetes on myocardial substrate oxidation and contractile function were investigated using 13C nuclear magnetic resonance (NMR) spectroscopy. To determine the consequences of diabetes on glucose oxidation, hearts were perfused with [1-13C]glucose (11 mM) alone as well as in the presence of insulin (to stimulate glucose transport) and dichloroacetate (to stimulate pyruvate dehydrogenase). The contribution of glucose to the tricarboxylic acid (TCA) cycle was significantly decreased in hearts from diabetic animals compared with controls, with glucose alone and with insulin; however, the addition of dichloroacetate significantly increased the contribution of glucose to the TCA cycle. Contractile function in hearts from diabetic animals was significantly depressed with glucose as the sole substrate, regardless of the presence of insulin or dichloroacetate (P < 0.0005). To determine whether diabetes had any direct effects on beta-oxidation and the TCA cycle, hearts were perfused with glucose (11 mM) plus [6-13C]hexanoate (0.5 mM) as substrates. In control hearts, with glucose plus hexanoate as substrates, hexanoate contributed 98.9 +/- 2% of the substrate entering the TCA cycle; this was significantly decreased to 90.7 +/- 0.6% in the diabetic group (P < 0.02). The addition of hexanoate to the perfusate resulted in a significant increase in peak systolic pressure in the diabetic group (P < 0.001) such that contractile function was indistinguishable from controls.

Acute L-triiodothyronine administration potentiates inotropic responses to beta-adrenergic stimulation in the isolated perfused rat heart.

OBJECTIVE: Acute inotropic effects of triiodothyronine (T3) have been reported, employing both in vivo experimental animal models and in vitro isolated heart perfusions. However, the mechanisms responsible for these acute inotropic effects remain unclear. The aim of this study, therefore, was to delineate the role of the beta-adrenergic receptor system in these acute responses. METHODS: The hearts from both euthyroid and hypothyroid (treated with 0.05% PTU in drinking water) male Sprague-Dawley rats were used in 5 experimental study protocols. Hearts from euthyroid rats were perfused with buffer containing either T3(10(-7) M) or control while continuously recording left ventricular function for 10 min ('acute effects'). Two-hour perfusions ('subacute effects') and cardiac responses following increasing doses of isoproterenol (10(-10) to 10(-6) M) in the presence or absence of T3-containing buffer (acute interaction) were also determined. In hypothyroid rats, the subacute responses and the acute interactions were investigated. RESULTS: In the presence of T3, an acute, significant potentiation of the inotropic responses following beta-adrenergic stimulation with isoproterenol was observed in both rat cohorts, which was more pronounced in hearts from euthyroid rats. An acute (< 40 s), but transient (79 +/- 8 s), direct inotropic response was observed in hearts from euthyroid rats. No cardiac responses were seen during a 2-h perfusion in hearts from either euthyroid or hypothyroid rats. CONCLUSIONS: The acute inotropic effects of T3 in non-ischemic myocardium probably result from an acute interaction between T3 and catecholamines rather than through a direct inotropic effect of T3 alone.

Quantitative cardiac perfusion: a noninvasive spin-labeling method that exploits coronary vessel geometry.

PURPOSE: To quantitate myocardial arterial perfusion with a noninvasive magnetic resonance (MR) imaging technique that exploits the geometry of coronary vessel anatomy. MATERIALS AND METHODS: MR imaging was performed with a spin-labeling method in six arrested rabbit hearts at 4.7 T. Selective inversion of magnetization in the short-axis imaging section along with all myocardium apical to that section produces signal enhancement from arterial perfusion. A linescan protocol was used for validation of flow enhancement. Flow was quantitated from two images and validated with spin-echo (SE) imaging. Regional perfusion defects were created by means of coronary artery ligation and delineated with gadolinium-enhanced imaging. RESULTS: Linescan estimates of T1 obtained at physiologic flows agreed with model predictions. Flow-induced signal enhancement measured on SE images also agreed with expected values. Finally, perfusion abnormalities created by means of coronary artery ligation were detected. CONCLUSION: This spin-labeling method provides quantitative estimates of myocardial arterial perfusion in this model and may hold promise for clinical applications.

A versatile oxygenator and perfusion system for magnetic resonance studies.

A compact, reusable membrane oxygenator has been constructed for the perfusion of cultured cells and isolated organs. While the oxygenator was designed to be compatible with nuclear magnetic resonance (NMR) spectroscopy studies, it can also be used for any experiment which requires warming and oxygenation of perfusates. For the NMR studies, the oxygenator can be positioned at the opening of the magnet bore which allows oxygenation and warming of the perfusate immediately prior to delivery to the tissue, therefore eliminating problems with heat or oxygen loss which may occur with the long perfusion lines. (c) 1996 John Wiley & Sons, Inc.

Metabolic compartmentation of lactate in the glucose-perfused rat heart.

Several studies using exogenous pyruvate as substrate have suggested that there are separate intracellular pyruvate pools in cardiac cells. Such heterogeneity in intracellular pyruvate has important implications for our understanding of both oxidative and nonoxidative glucose metabolism. Because pyruvate is not a major substrate for the heart in vivo, we wished to determine if there was pyruvate compartmentation with glucose as substrate. Hearts were isolated from male Sprague-Dawley rats and retrogradely perfused (Langendorff) with a modified Krebs-Henseleit buffer containing [1-13C[glucose for 5-115 min. At the end of each experiment, hearts were freeze-clamped and extracted for determination of the fractional enrichment of alanine, lactate, and acetyl CoA using 1H- and 13C-nuclear magnetic resonance spectroscopy. The fractional enrichment of alanine at the C-3 position was significantly higher than that for lactate at 55 min [43.6 +/- 2.8 vs. 27.2 +/- 4.6% (SD), n = 5, P < 0.003]. The differences in steady-state enrichment between lactate and alanine were not due to differences in the rate of labeling of these metabolites. The mean steady-state lactate enrichment was higher in the perfusate samples compared with the tissue samples from the same experiments (46.6 +/- 2.2 vs. 30.5 +/- 2.5%, n = 3, P < 0.005). Because fractional enrichment of alanine, acetyl CoA, and perfusate lactate are similar, we suggest that there is a separate nonexchanging pool of lactate rather than cytosolic compartmentation of pyruvate that has been previously proposed.

Blood oxygenation dependence of T1 and T2 in the isolated, perfused rabbit heart at 4.7T.

An MR line scan protocol has been used to measure relaxation parameters (T1 and T2) in isolated, blood perfused rabbit hearts at various blood oxygenations. Hearts were retrogradely perfused at 37 degrees C with a cardioplegic solution (modified St. Thomas' solution) containing sheep red blood cells and adenosine (1 mM) to maximally vasodilate the coronary vascular bed. Arresting the hearts eliminated motion complications and minimized arteriovenous oxygenation differences. The authors have found that under conditions of stable flow, there is a strong correlation between T2 in myocardial septa and hemoglobin (Hb) saturation, while tissue T1 is virtually independent of blood oxygenation. These effects are believed to be due to the paramagnetic agent deoxyhemoglobin.

Calculation of absolute metabolic flux and the elucidation of the pathways of glutamate labeling in perfused rat heart by 13C NMR spectroscopy and nonlinear least squares analysis.

Absolute metabolic fluxes in isolated perfused hearts have been determined by a nonlinear least squares analysis of glutamate labeling kinetics from [1-13C]glucose, [4-13C]beta-hydroxybutyrate, or [2-13C]acetate using 13C NMR spectroscopy. With glucose as substrate, the malate-aspartate shuttle flux was too slow to account for the reducing equivalents generated by glycolysis and to predict the observed oxygen consumption rate. For acetate and beta-hydroxybutyrate, the malate-aspartate shuttle had to be reversed for the network to agree with the observed oxygen consumption and glutamate labeling. Thus, an additional redox shuttle was required to reoxidize the NADH produced by cytoplasmic malate dehydrogenase. Using this model there was good agreement between the experimentally determined oxygen consumption and glutamate labeling and the calculated values of these parameters from the model for all substrates. The contribution of exogenous substrate to the overall tricarboxylic acid (TCA) cycle flux, 89.6 +/- 6.5% (mean +/- S.D.) as measured in the tissue extracts compared well with 91.4 +/- 4.2% calculated by the model. The ratio of TCA cycle flux to oxygen consumption for acetate, was 2.2 +/- 0.1, indicating that NADH production is principally accounted for by TCA cycle flux. For glucose or beta-hydroxybutyrate, this ratio was 2.9 +/- 0.2, consistent with the existence of other NADH producing reactions (e.g. glycolysis, beta-hydroxybutyrate oxidation).

Quantitative proton spectroscopy of canine brain: in vivo and in vitro correlations.

Quantitative, single-voxel proton NMR spectroscopy of normal brain was performed in five adult beagle dogs using the cerebral water signal as an internal intensity reference. The same brain regions were then rapidly isolated and frozen using a pneumatic biopsy drill, perchloric acid extracted, and analyzed by biochemical assay and high-resolution NMR spectroscopy. The concentrations of the major resonances in the in vivo and in vitro spectra were compared, and good agreement was found between the different measurements. The in vivo spectra contained three peaks at 3.21, 3.04, and 2.02 ppm, which are usually assigned to trimethylamines (TMA), creatines, and N-acetyl derivatives (NAc), which corresponded to be the following metabolite concentration values: 1.7 +/- 0.6, 7.7 +/- 2.1, and 10.9 +/- 2.7 mumol/g wet weight respectively. In vitro, the following metabolite concentrations were measured: glycerophosphocholine (GPC) 1.3 +/- 0.2, phosphocholine (PC) 0.5 +/- 0.1, phosphocreatine (PCr) 2.6 +/- 0.4, creatine (Cr) 5.9 +/- 1.4, and N-Acetyl aspartate (NAA) 8.9 +/- 1.8 mumol/g wet weight. Therefore, the 3.21 ppm resonance observed in the in vivo spectrum is predominantly GPC and PC in a ratio of 2.6:1, the 3.04 ppm resonance is Cr and PCr in a ratio of 2.3:1, and the 2.02 ppm resonance is predominantly (approximately 80%) NAA with small contributions from N-acetylaspartylglutamate (NAAG) and glutamate. The data presented here validate the technique of water referencing as a simple and convenient means of quantitating single-voxel in vivo proton NMR spectra of the brain.

Oxygenation in the rabbit myocardium: assessment with susceptibility-dependent MR imaging.

PURPOSE: To determine the feasibility of using hemoglobin (Hb) desaturation as an indicator of myocardial oxygenation. MATERIALS AND METHODS: High-resolution gradient-echo nuclear magnetic resonance (MR) images of isolated, blood-perfused rabbit hearts were obtained at various blood oxygenation levels. The hearts were perfused at 37 degrees C with a Langendorff apparatus modified for nuclear MR imaging. The perfusate contained bovine red blood cells in a cardioplegic solution that eliminated motion artifacts and minimized arteriovenous oxygenation differences. Hb saturation was varied (7%-100%) randomly. Perfusion pressure was continuously monitored, and blood samples were obtained. RESULTS: There was a substantial correlation between image signal intensity in the myocardium and Hb saturation in the blood, believed to be due to susceptibility effects of the paramagnetic species deoxyhemoglobin. CONCLUSION: Direct and noninvasive determination of regional Hb saturation with susceptibility-dependent MR imaging may provide information regarding regional myocardial O2 content.

A 13C-NMR study of glucose oxidation in the intact functioning rat heart following diabetes-induced cardiomyopathy.

A causative factor in the development of diabetes-induced heart dysfunction may be abnormalities in myocardial energy metabolism. Using 13C-NMR spectroscopy, we investigated the effects of experimentally induced diabetes (streptozotocin 65 mg/kg, i.v.) on glucose metabolism and contractile function in the isolated perfused rat heart. Hearts from streptozotocin-treated and untreated control rats were perfused with 11 mM [1-13C]glucose as substrate and 1H-decoupled 13C-spectra recorded for up to 90 min. Incorporation of label from [1-13C]glucose into lactate and glutamate was observed in hearts from control animals, consistent with metabolism through glycolysis and TCA cycle, respectively. Diabetic hearts did not incorporate label into lactate or glutamate. Addition of insulin (0.05 U/ml) to the buffer resulted in the appearance of [3-13C]lactate, although glutamate labeling was not observed. Addition of insulin plus dichloroacetate (2 mM) resulted in incorporation of label from [1-13C]glucose into 2-, 3- and 4-13C-glutamate, indicating glucose entry into the TCA cycle. Addition of insulin, or insulin plus dichloroacetate to control hearts did not alter labeling of either lactate or glutamate. Cardiac function in hearts from the diabetic group was depressed compared to controls and declined significantly over the duration of the experiment. These studies show that concomitant with a decrease in cardiac function, glucose oxidation is profoundly inhibited following the induction of diabetes with streptozotocin. These observations are consistent with a combination of decreased glucose transport and a decrease in pyruvate dehydrogenase activity.