The metabolic effects of sodium dichloroacetate in the starved rat

1. Sodium dichloroacetate (300mg/kg body wt. per h) was infused in 24h-starved rats for 4h. 2. Blood glucose decreased significantly, an effect that had previously only been noted in diabetic animals 3. Plasma insulin concentration decreased by 63%; blood lactate and pyruvate concentrations decreased by 50 and 33%, whereas concentrations of 3-hydroxybutyrate and acetoacetate increased by 81 and 73% respectively. 4. Livers were freeze-clamped at the end of the 4h infusion. There were significant decreases in hepatic [glucose], [glucose 6-phosphate], [2-phosphoglycerate], the [lactate]/[pyruvate] ratio, [citrate] and [malate], and also [alanine], [glutamate] and [glutamine], suggesting a diminished supply of gluconeogenic substrates. 5. Animals subjected to a functional hepatectomy at the end of 2h infusions showed no difference in blood-glucose disappearance but a highly significant decrease in the rate of accumulation of lactate, pyruvate, glycerol and alanine, compared with control animals. Dichloroacetate decreased ketone-body clearance. 6. After functional hepatectomy an increase in glutamine accumulation appeared to compensate for the decrease in alanine accumulation. 7. It is concluded that dichloroacetate causes hypoglycaemia by decreasing the net release of gluconeogenic precursors from extrahepatic tissues while inhibiting peripheral ketone-body uptake. 8. These findings are consistent with the activation of pyruvate dehydrogenase (EC 1.2.4.1) in rat muscle by dichloroacetate previously described by Whitehouse & Randle (1973).     

Effect of insulin on ketogenesis and fatty acid synthesis in rat hepatocytes incubated with dichloroacetate

In parenchymal liver cells isolated from fed rats, insulin increased the formation of 14CO2 from [1-14C]pyruvate (and presumably the flux through pyruvate dehydrogenase) by 14%. Dichloroacetate, an activator of the pyruvate dehydrogenase complex, stimulated this process by 133%. As judged from the conversion of [2-14C]pyruvate to 14CO2, the tricarboxylic acid cycle activity was not affected by insulin, but it was depressed by dichloroacetate. In hepatocytes from fed rats, incubated with glucose as the only carbon source, dichloroacetate caused a stimulation (31%) of fatty acid synthesis, measured as 3H incorporation from 3H2O into fatty acid, and an increased (134%) accumulation of ketone bodies (acetoacetate + D-3-hydroxybutyrate). Dichloroacetate did not affect ketone body formation from [14C]palmitate, suggesting that the increased accumulation of ketone bodies resulted from acetyl-CoA derived from pyruvate. Insulin stimulated fatty acid synthesis in hepatocytes from fed rats. In the combined presence of insulin plus dichloroacetate, fatty acid synthesis was more rapid than in the presence of either insulin or dichloroacetate, whereas the accumulation of ketone bodies was smaller than in the presence of dichloroacetate alone. Although pyruvate dehydrogenase activity, which is rate-limiting for fatty acid synthesis in hepatocytes from fed rats, is stimulated both by insulin and by dichloroacetate, the reciprocal changes in fatty acid synthesis and ketone body accumulation brought about by insulin in the presence of dichloroacetate suggest that insulin is also involved in the regulation of fatty acid synthesis at a mitochondrial site after pyruvate dehydrogenase, possibly at the partitioning of acetyl-CoA between citrate and ketone body formation.     

Effects of dichloroacetate on the metabolism of glucose, pyruvate, acetate, 3-hydroxybutyrate and palmitate in rat diaphragm and heart muscle in vitro and on extraction of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo

1. The extractions of glucose, lactate, pyruvate and free fatty acids by dog heart in vivo were calculated from measurements of their arterial and coronary sinus blood concentration. Elevation of plasma free fatty acid concentrations by infusion of intralipid and heparin resulted in increased extraction of free fatty acids and diminished extractions of glucose, lactate and pyruvate by the heart. It is suggested that metabolism of free fatty acids by the heart in vivo, as in vitro, may impair utilization of these substrates. These effects of elevated plasma free fatty acid concentrations on extractions by the heart in vivo were reversed by injection of dichloroacetate, which also improved extraction of lactate and pyruvate by the heart in vivo in alloxan diabetes. 2. Sodium dichloroacetate increased glucose oxidation and pyruvate oxidation in hearts from fed normal or alloxan-diabetic rats perfused with glucose and insulin. Dichloroacetate inhibited oxidation of acetate and 3-hydroxybutyrate and partially reversed inhibitory effects of these substrates on the oxidation of glucose. In rat diaphragm muscle dichloroacetate inhibited oxidation of acetate, 3-hydroxybutyrate and palmitate and increased glucose oxidation and pyruvate oxidation in diaphragms from alloxan-diabetic rats. Dichloroacetate increased the rate of glycolysis in hearts perfused with glucose, insulin and acetate and evidence is given that this results from a lowering of the citrate concentration within the cell, with a consequent activation of phosphofructokinase. 3. In hearts from normal rats perfused with glucose and insulin, dichloroacetate increased cell concentrations of acetyl-CoA, acetylcarnitine and glutamate and lowered those of aspartate and malate. In perfusions with glucose, insulin and acetate, dichloroacetate lowered the cell citrate concentration without lowering the acetyl-CoA or acetylcarnitine concentrations. Measurements of specific radioactivities of acetyl-CoA, acetylcarnitine and citrate in perfusions with [1-(14)C]acetate indicated that dichloroacetate lowered the specific radio-activity of these substrates in the perfused heart. Evidence is given that dichloroacetate may not be metabolized by the heart to dichloroacetyl-CoA or dichloroacetylcarnitine or citrate or CO(2). 4. We suggest that dichloroacetate may activate pyruvate dehydrogenase, thus increasing the oxidation of pyruvate to acetyl-CoA and acetylcarnitine and the conversion of acetyl-CoA into glutamate, with consumption of aspartate and malate. Possible mechanisms for the changes in cell citrate concentration and for inhibitory effects of dichloroacetate on the oxidation of acetate, 3-hydroxybutyrate and palmitate are discussed.     

Mechanism responsible for the hypoglycemic actions of dichloroacetate and 2-chloropropionate

Dichloroacetate, an activator of the pyruvate dehydrogenase complex, is known to lower blood glucose, lactate, pyruvate, and alanine when given to diabetic and 24 h fasted rats. Under certain conditions, especially when pyruvate carboxylase is made rate limiting for want of bicarbonate, dichloroacetate effectively inhibits glucose synthesis from lactate by isolated hepatocytes. 2-Chloropropionate also activates the pyruvate dehydrogenase complex, lowers blood glucose, lactate, and pyruvate in 24 h fasted rats, but stimulates gluconeogenesis from lactate or alanine by isolated hepatocytes. Dichloroacetate is catabolized to glyoxylate and thence to oxalate by liver cells, whereas 2-chloropropionate cannot be catabolized to these products. Glyoxylate and oxalate are potent inhibitors of glucose synthesis from lactate, pyruvate, and alanine, but not from dihydroxyacetone. Inhibition is much more pronounced in a bicarbonate-deficient medium, in which pyruvate carboxylase is probably rate limiting for gluconeogenesis. It seems likely, therefore, that the inhibition of lactate gluconeogenesis by dichloroacetate is actually caused by oxalate, which inhibits pyruvate carboxylation. Nevertheless, the major effect of dichloroacetate, and probably the sole effect of 2-chloropropionate, on blood glucose concentration is to limit substrate availability in the blood for hepatic gluconeogenesis. Since oxalic acid stone formation and renal dysfunction may prove to be side effects of any therapeutic application of dichloroacetate, we suggest that further studies on the treatment of hyperglycemia and lactic acidosis with pyruvate dehydrogenase activators be carried out with 2-chloropropionate rather than dichloroacetate.     

A possible mechanism for the anti-ketogenic action of alanine in the rat

1. The anti-ketogenic effect of alanine has been studied in normal starved and diabetic rats by infusing l-alanine for 90min in the presence of somatostatin (10μg/kg body wt. per h) to suppress endogenous insulin and glucagon secretion. 2. Infusion of alanine at 3mmol/kg body wt. per h caused a 70±11% decrease in [3-hydroxybutyrate] and a 58±9% decrease in [acetoacetate] in 48h-starved rats. [Glucose] and [lactate] increased, but [non-esterified fatty acid], [glycerol] and [3-hydroxybutyrate]/[acetoacetate] were unchanged. 3. Infusion of alanine at 1mmol/kg body wt. per h caused similar decreases in [ketone body] (3-hydroxybutyrate plus acetoacetate) in 24h-starved normal and diabetic rats, but no change in other blood metabolites. 4. Alanine [3mmol/kg body wt. per h] caused a 72±9% decrease in the rate of production of ketone bodies and a 57±8% decrease in disappearance rate as assessed by [3-¹⁴C]acetoacetate infusion. Metabolic clearance was unchanged, indicating that the primary effect of alanine was inhibition of hepatic ketogenesis. 5. Aspartate infusion at 6mmol/kg body wt. per h had similar effects on blood ketone-body concentrations in 48h-starved rats. 6. Alanine (3mmol/kg body wt. per h) caused marked increases in hepatic glutamate, aspartate, malate, lactate and citrate, phosphoenolpyruvate, 2-phosphoglycerate and glucose concentrations and highly significant decreases in [3-hydroxybutyrate] and [acetoacetate]. Calculated [oxaloacetate] was increased 75%. 7. Similar changes in hepatic [malate], [aspartate] and [ketone bodies] were found after infusion of 6mmol of aspartate/kg body wt. per h. 8. It is suggested that the anti-ketogenic effect of alanine is secondary to an increase in hepatic oxaloacetate and hence citrate formation with decreased availability of acetyl-CoA for ketogenesis. The reciprocal negative-feedback cycle of alanine and ketone bodies forms an important non-hormonal regulatory system.     

The effects of inhibition of gluconeogenesis on ketogenesis in starved and diabetic rats.

Experiments were performed in which the effects of inhibiting gluconeogenesis on ketone-body formation were examined in vivo in starved and severely streptozotocin-diabetic rats. The infusion of 3-mercaptopicolinate, an inhibitor of gluconeogenesis (DiTullio et al., 1974), caused decreases in blood [glucose] and increases in blood [lactate] and [pyruvate] in both normal and ketoacidotic rats. Patterns of liver gluconeogenic intermediates after 3-mercaptopicolinate infusion suggested inhibition at the level of phosphoenolpyruvate carboxykinase. This was confirmed by measurement of hepatic oxaloacetate concentrations which were increased 5-fold after 3-mercaptopicolinate administration. The infusion of 3-mercaptopicolinate caused a decrease in total ketone-body concentrations of 30% in starved rats and 73% in the diabetic animals. Blood glycerol and hepatic triglyceride concentrations remained unchanged. The decreases in ketone-body concentrations were associated with increases in the calculated hepatic cytosolic and mitochondrial [NADH]/[NAD+] ratios. The decrease in ketogenesis seen after inhibition of gluconeogenesis may have resulted from an inhibition of hepatic fatty acid oxidation by the more reduced mitochondrial redox state. It was concluded that gluconeogenesis may stimulate ketogenesis by as much as 30% in severe diabetic ketoacidosis.     

Likely individuality of the enzymes catalyzing the phosphorylation of choline and ethanolamine.

Dichloroacetate has effects upon hepatic metabolism which are profoundly different from its effects on heart, skeletal muscle, and adipose tissue metabolism. With hepatocytes prepared from meal-fed rats, dichloroacetate was found to activate pyruvate dehydrogenase, to increase the utilization of lactate and pyruvate without effecting an increase in the net utilization of glucose, to increase the rate of fatty acid synthesis, and to decrease slightly [1-¹⁴C]oleate oxidation to ¹⁴CO₂ without decreasing ketone body formation. With hepatocytes isolated from 48-h-starved rats, dichloroacetate was found to activate pyruvate dehydrogenase, to have no influence on net glucose utilization, to inhibit gluconeogenesis slightly with lactate as substrate, and to stimulate gluconeogenesis significantly with alanine as substrate. The stimulation of fatty acid synthesis by dichloroacetate suggests that the activity of pyruvate dehydrogenase can be rate determining for fatty acid synthesis in isolated liver cells. The minor effects of dichloroacetate on gluconeogenesis suggest that the regulation of pyruvate dehydrogenase is only of marginal importance in the control of gluconeogenesis.     

Impaired sensitivity to insulin of rat livers perfused with blood of diminished haematocrit.

1. In livers from fed rats perfused with homologous whole blood of a haematocrit value of 37%, insulin decreased the perfusate concentrations of glucose and amino acids, production of ketone bodies (3-hydroxybutyrate + acetoacetate) and increased bile flow. 2. Perfusion with blood diluted with buffer to a haematocrit value of 17% decreased hepatic O2 consumption by 40-50%. Perfusate concentrations of glucose and lactate, the rate of ketogenesis and the ratios [lactate]/[pyruvate] and [3-hydroxybutyrate]/[acetoacetate] were all increased. 3. In livers perfused with blood of diminished haematocrit, effects of insulin on perfusate glucose an amino acids, ketogenesis and bile flow were abolished.     

Ketone-body metabolism in tumour-bearing rats.

During starvation for 72 h, tumour-bearing rats showed accelerated ketonaemia and marked ketonuria. Total blood [ketone bodies] were 8.53 mM and 3.34 mM in tumour-bearing and control (non-tumour-bearing) rats respectively (P less than 0.001). The [3-hydroxybutyrate]/[acetoacetate] ratio was 1.3 in the tumour-bearing rats, compared with 3.2 in the controls at 72 h (P less than 0.001). Blood [glucose] and hepatic [glycogen] were lower at the start of starvation in tumour-bearing rats, whereas plasma [non-esterified fatty acids] were not increased above those in the control rats during starvation. After functional hepatectomy, blood [acetoacetate], but not [3-hydroxybutyrate], decreased rapidly in tumour-bearing rats, whereas both ketone bodies decreased, and at a slower rate, in the control rats. Blood [glucose] decreased more rapidly in the hepatectomized control rats. Hepatocytes prepared from 72 h-starved tumour-bearing and control rats showed similar rates of ketogenesis from palmitate, and the distribution of [1-14C] palmitate between oxidation (ketone bodies and CO2) and esterification was also unaffected by tumour-bearing, as was the rate of gluconeogenesis from lactate. The carcinoma itself showed rapid rates of glycolysis and a poor ability to metabolize ketone bodies in vitro. The results are consistent with the peripheral, normal, tissues in tumour-bearing rats having increased ketone-body and decreased glucose metabolic turnover rates.     

A double-isotope method for the measurement of ketone-body turnover in the rat. Effect of L-alanine.

The synthesis of 4-3H-labelled ketone bodies, and their use along with 14C-labelled ketone-body precursors, is employed using an 'in vivo' rat infusion model to measure ketone-body turnover. The use of two isotopes is necessary to measure ketone-body turnover when ketogenesis may occur from more than one precursor such as glucose and fatty or amino acids. Requirements of isotopic equivalence in terms of metabolic similarity, valid stoichiometry and the lack of differences in the kinetics of relevant enzymes is demonstrated for the 4-3H- and 14C-labelled ketone bodies. The hypoketonaemic effect of L-alanine is shown by two distinct phases after the administration of L-alanine. During the first 12 min after alanine administration ther was a 50% decrease in acetoacetate and a 30% decrease in 3-hydroxybutyrate production, with no significant change in the utilization of either compound. The hypoketonaemic action of alanine during the following 16 min was primarily associated with an uptake of 3-hydroxybutyrate that was somewhat greater than the increase in its production. There were essentially equivalent decreases in production and utilization of acetoacetate, resulting in no significant net change in the level of this ketone body in the blood.     

Effect of dichloroacetate and glucagon on the incorporation of labeled substrates into glucose and on pyruvate dehydrogenase in hepatocytes from fed and starved rats

Dichloroacetate (2 mm) stimulated the conversion of [1-¹⁴C]lactate to glucose in hepatocytes from fed rats. In hepatocytes from rats starved for 24 h, where the mitochondrial $\text{NADH}\text{NAD}{}^{\mathrm{+}}$ ratio is elevated, dichloroacetate inhibited the conversion of [1-¹⁴C]lactate to glucose. Dichloroacetate stimulated ¹⁴CO₂ production from [1-¹⁴C]lactate in both cases. It also completely activated pyruvate dehydrogenase and increased flux through the enzyme. The addition of β-hydroxybutyrate, which elevates the intramitochondrial $\text{NADH}\text{NAD}{}^{\mathrm{+}}$ ratio, changed the metabolism of [1-¹⁴C]lactate in hepatocytes from fed rats to a pattern similar to that seen in hepatocytes from starved rats. Thus, the effect of dichloroacetate on labeled glucose synthesis from lactate appears to depend on the mitochondrial oxidation-reduction state of the hepatocytes. Glucagon (10 nm) stimulated labeled glucose synthesis from lactate or alanine in hepatocytes from both fed and starved rats and in the absence or presence of dichloroacetate. The hormone had no effect on pyruvate dehydrogenase activity whether or not the enzyme had been activated by dichloroacetate. Thus, it appears that pyruvate dehydrogenase is not involved in the hormonal regulation of gluconeogenesis. Glucagon inhibited the incorporation of 10 mm [1-¹⁴C]pyruvate into glucose in hepatocytes from starved rats. This inhibition has been attributed to an inhibition of pyruvate dehydrogenase by the hormone (Zahlten et al., 1973, Proc. Nat. Acad. Sci. USA70, 3213–3218). However, dichloroacetate did not prevent the inhibition of glucose synthesis. Nor did glucagon alter the activity of pyruvate dehydrogenase in homogenates of cells that had been incubated with 10 mm pyruvate in the absence or presence of dichloroacetate. Thus, the inhibition by glucagon of pyruvate gluconeogenesis does not appear to be due to an inhibition of pyruvate dehydrogenase.     

Metabolic effects of vasopressin infusion in the starved rat. Reversal of ketonaemia.

The effects of vasopressin on the metabolism of starved rats were investigated by using a constant-infusion regimen (50 pmol/kg body wt. per min, after an initial loading dose of 150 pmol/kg body wt.). 2. Blood ketone bodies decreased by 50% in 10 min, and this was accompanied by a 60% decrease in the plasma non-esterified fatty acids. 3. Blood glucose increased by 0.9 mM within 5 min and decreased to control values over the 40 min infusion. Small increases in lactate and pyruvate also occurred. 4. Plasma insulin was not increased by vasopressin infusion. 5. The net decrease in blood ketone bodies caused by vasopressin was similar when somatostatin was infused simultaneously (1 nmol/kg body wt. per min). 6. Hepatic ketone bodies were significantly decreased by vasopressin, as was the 3-hydroxybutyrate/acetoacetate ratio. A small increase in the hepatic concentration of several glycolytic intermediates also occurred. 7. Vasopressin did not decrease the ketonaemia produced by infusions of octanoate or long-chain triacylglycerol in rats that had been pre-treated with the anti-lipolytic agent 3,5-dimethylpyrazole. 8. In comparison with vasopressin, the infusion of adrenaline or glucose had much smaller effects in decreasing the ketonaemia of starvation, despite the 4-fold increase in plasma insulin, at 10 min, with the glucose infusion. 9. The primary metabolic effect of vasopressin in the starved rat appears to be that of decreased supply of non-esterified fatty acid to the liver. It is suggested that vasopressin has a direct anti-lipolytic effect in adipose tissue.     

Mechanism of activation of pyruvate dehydrogenase by dichloroacetate and other halogenated carboxylic acids

1. Monochloroacetate, dichloroacetate, trichloroacetate, difluoroacetate, 2-chloropropionate, 2,2'-dichloropropionate and 3-chloropropionate were inhibitors of pig heart pyruvate dehydrogenase kinase. Dichloroacetate was also shown to inhibit rat heart pyruvate dehydrogenase kinase. The inhibition was mainly non-competitive with respect to ATP. The concentration required for 50% inhibition was approx. 100mum for the three chloroacetates, difluoroacetate and 2-chloropropionate and 2,2'-dichloropropionate. Dichloroacetamide was not inhibitory. 2. Dichloroacetate had no significant effect on the activity of pyruvate dehydrogenase phosphate phosphatase when this was maximally activated by Ca(2+) and Mg(2+). 3. Dichloroacetate did not increase the catalytic activity of purified pig heart pyruvate dehydrogenase. 4. Dichloroacetate, difluoroacetate, 2-chloropropionate and 2,2'-dichloropropionate increased the proportion of the active (dephosphorylated) form of pyruvate dehydrogenase in rat heart mitochondria with 2-oxoglutarate and malate as respiratory substrates. Similar effects of dichloroacetate were shown with kidney and fat-cell mitochondria. Glyoxylate, monochloroacetate and dichloroacetamide were inactive. 5. Dichloroacetate increased the proportion of active pyruvate dehydrogenase in the perfused rat heart, isolated rat diaphragm and rat epididymal fat-pads. Difluoroacetate and dichloroacetamide were also active in the perfused heart, but glyoxylate, monochloroacetate and trichloroacetate were inactive. 6. Injection of dichloroacetate into rats starved overnight led within 60 min to activation of pyruvate dehydrogenase in extracts from heart, psoas muscle, adipose tissue, kidney and liver. The blood concentration of lactate fell within 15 min to reach a minimum after 60 min. The blood concentration of glucose fell after 90 min and reached a minimum after 120 min. There was no significant change in plasma glycerol concentration. 7. In epididymal fatpads dichloroacetate inhibited incorporation of (14)C from [U-(14)C]glucose, [U-(14)C]fructose and from [U-(14)C]lactate into CO(2) and glyceride fatty acid. 8. It is concluded that the inhibition of pyruvate dehydrogenase kinase by dichloroacetate may account for the activation of pyruvate dehydrogenase and pyruvate oxidation which it induces in isolated rat heart and diaphragm muscles, subject to certain assumptions as to the distribution of dichloroacetate across the plasma membrane and the mitochondrial membrane. 9. It is suggested that activation of pyruvate dehydrogenase by dichloroacetate could contribute to its hypoglycaemic effect by interruption of the Cori and alanine cycles. 10. It is suggested that the inhibitory effect of dichloroacetate on fatty acid synthesis in adipose tissue may involve an additional effect or effects of the compound.     

Effects of adrenaline on ketogenesis from long- and medium-chain fatty acids in starved rats.

1. Injection of adrenaline into 24 h-starved rats caused a 69% decrease in blood [ketone-body] (3-hydroxybutyrate plus acetoacetate), accompanied by a decreased [3-hydroxybutyrate]/[acetoacetate] ratio. Blood [glucose] and [lactate] increased, but [alanine] was unchanged. 2. Adrenaline also decreased [ketone-body] after intragastric feeding of both long- and medium-chain triacylglycerol. The latter decrease was observed after suppression of lipolysis with 5-methylpyrazole-3-carboxylic acid, indicating that the antiketogenic action of adrenaline was not dependent on the chain length of the precursor fatty acid. 3. The actions of adrenaline to decrease blood [ketone-body] and to increase blood [glucose] were not observed after administration of 3-mercaptopicolinate, an inhibitor of gluconeogenesis. This suggests that these effects of the hormone are related. 4. The possible clinical significance of the results is discussed with reference to the restricted ketosis often observed after surgical or orthopaedic injury.     

Metabolic effects of propionate in normal and vitamin B12-deficient rats

1. Administration of propionate caused a twofold increase in the concentrations of lactate and pyruvate in the blood of vitamin B(12)-deficient rats, whereas there was a slight decrease in lactate and a 50% increase in pyruvate in normal rats. 2. Concentrations of total ketone bodies in the blood of normal rats were not significantly altered by propionate administration but the [3-hydroxybutyrate]/[acetoacetate] ratio decreased from 3.0 to 2.0. In the vitamin B(12)-deficient rats there was a 40% decrease in total ketone bodies and a change in the ratio from 3.4 to 1.2. 3. The changes in the concentration of ketone bodies in freeze-clamped liver preparations were similar in pattern to those observed in blood. 4. Propionate administration caused a decrease in the concentration of acetyl-CoA in the livers of both groups of animals, but the absolute decrease was greater in the vitamin B(12)-deficient group. The decrease in the concentration of CoA was similar in both groups. 5. As in blood, there were threefold increases in the concentrations of lactate and pyruvate in the livers of the vitamin B(12)-deficient rats after propionate administration, whereas there was no significant change in the concentrations of these metabolites in the normal rats. 6. There was a 50% inhibition of glucose synthesis in perfused livers from vitamin B(12)-deficient rats when lactate and propionate were substrates as compared with lactate alone. 7. It is concluded that the conversion of lactate into glucose is inhibited in vitamin B(12)-deficient rats after propionate administration, and that this effect is due to inhibition of the pyruvate carboxylase step resulting from a decrease in acetyl-CoA concentration and a postulated increase in methylmalonyl-CoA concentration.     

Effect of dichloroacetate on lactate concentration in exercising humans

The precise mechanism responsible for the increase in plasma lactate concentration during exercise in humans is not known. We have used dichloroacetate to test the hypothesis that a limitation in pyruvate dehydrogenase activity is responsible for the rise in plasma lactate. Dichloroacetate stimulates the activity of pyruvate dehydrogenase, which is normally the regulatory enzyme in the oxidation of glucose when tissue oxygenation is adequate. Six subjects were studied twice according to a randomized, crossover protocol, involving one test with saline infusion and another with dichloroacetate infusion. Exercise load on a bicycle ergometer was increased progressively until exhaustion. Blood samples were drawn each minute throughout exercise and periodically throughout 120 min of recovery. Dichloroacetate significantly lowered the lactate concentration during exercise performed at less than 80% of the average maximal O2 consumption. The peak concentration of lactate at exhaustion was not affected by dichloroacetate treatment, but dichloroacetate did lower lactate concentration throughout recovery. These results suggest that a limitation in pyruvate dehydrogenase activity contributes to the increase in plasma lactate during submaximal exercise and recovery.     

Metabolic effects of bicarbonate in the treatment of diabetic ketoacidosis.

The effect of intravenous bicarbonate on the changes in intermediary metabolites during the initial treatment of diabetic ketoacidosis was examined in 16 patients. The results were compared with the changes seen in 16 patients receiving intravenous saline. Infusion of 150 mmol (mEq) bicarbonate significantly delayed the fall in blood lactate, lactate:pyruvate ratio, and total ketone bodies observed in the saline treated group. No difference in the rate of fall of blood glucose concentration was found. There is no metabolic indication for the use of intravenous bicarbonate in the treatment of diabetic ketoacidosis.     

Glucose metabolism in perfused skeletal muscle. Effects of starvation, diabetes, fatty acids, acetoacetate, insulin and exercise on glucose uptake and disposition.

1. The regulation of glucose uptake and disposition in skeletal muscle was studied in the isolated perfused rat hindquarter. 2. Insulin and exercise, induced by sciatic-nerve stimulation, enhanced glucose uptake about tenfold in fed and starved rats, but were without effect in rats with diabetic ketoacidosis. 3. At rest, the oxidation of lactate (0.44 mumol/min per 30 g muscle in fed rats) was decreased by 75% in both starved and diabetic rats, whereas the release of alanine and lactate (0.41 and 1.35 mumol/min per 30 g respectively in the fed state) was increased. Glycolysis, defined as the sum of lactate+alanine release and lactate oxidation, was not decreased in either starvation or diabetes. 4. In all groups, exercise tripled O2 consumption (from approximately 8 to approximately 25 mumol/min per 30 g of muscle) and increased the release and oxidation of lactate five- to ten-fold. The differences in lactate release between fed, starved and diabetic rats observed at rest were no longer apparent; however, lactate oxidation was still several times greater in the fed group. 5. Perfusion of the hindquarter of a fed rat with palmitate, octanoate or acetoacetate did not alter glucose uptake or lactate release in either resting or exercising muslce; however, lactate oxidation was significantly inhibited by acetoacetate, which also increased the intracellular concentration of acetyl-CoA. 6. The data suggest that neither that neither glycolysis nor the capacity for glucose transport are inhbitied in the perfused hindquarter during starvation or perfusion with fatty acids or ketone bodies. On the other hand, lactate oxidation is inhibited, suggesting diminished activity of pyruvate dehydrogenase. 7. Differences in the regulation of glucose metabolism in heart and skeletal muscle and the role of the glucose/fatty acid cycle in each tissue are discussed.     

Plasmodium berghei: lactic acidosis and hypoglycaemia in a rodent model of severe malaria; effects of glucose, quinine, and dichloroacetate

Fulminant malaria infections are characterised by hypoglycaemia and potentially lethal lactic acidosis. In young adult Wistar rats (n = 26) infected with Plasmodium berghei (ANKA strain), hyperparasitaemia (greater than 50%), anaemia (PCV 19.6 +/- 5.3%; mean +/- SD) hypoglycaemia (1.04 +/- 0.74 mmol/litre), hyperlactataemia (13.2 +/- 2.20 mmol/litre), hyperpyruvicaemia (0.51 +/- 0.12 mmol/litre) and metabolic acidosis (arterial pH 6.96 +/- 0.11) developed after approximately 14 days of infection. Hypoglycaemia was associated with appropriate suppression of plasma insulin concentrations. In a second series of experiments the metabolic effects of treatment with glucose (500 mg/kg/hr), quinine (5 mg/kg bolus followed by 10 mg/kg over 1 hr) and a potent activator of pyruvate dehydrogenase, dichloroacetate (300 mg/kg) were studied over a 1-hr period. In control animals quinine had no measurable effects, but dichloroacetate significantly reduced arterial blood lactate (74%) and pyruvate (80%). In infected animals, glucose infusion attenuated the rise in lactate (38% compared with 82%; P less than 0.01) but quinine had no additional metabolic effects. Dichloroacetate further attenuated the rise in lactate (14%; P less than 0.01).     

Brain energy metabolism in streptozotocin-diabetes.

Regional brain glucose use was measured in rats with streptozotocin-induced diabetes (65 mg/kg intravenously) of 1 or 4 weeks duration, by using [6-14C]glucose and quantitative autoradiography. The concentrations of several metabolites were measured in plasma and brain. Results were compared with those from normal untreated rats. Glucose concentrations were increased in both plasma and brain, to similar degrees in both diabetic groups. Plasma ketone-body concentrations were 0.25, 1.0, and 3.15 mumol/ml in the control, 1-week and 4-week groups respectively (sum of acetoacetate and 3-hydroxybutyrate). Glucose use was increased throughout the brain (differences were statistically significant in 55 of 59 brain areas) after 1 week of diabetes, with an increase of 25% for the brain as a whole. In contrast, normal rates were found throughout the brain after 4 weeks of diabetes. None of the brain areas was affected significantly differently from the others, in either diabetic group. There was no significant loss of 14C as lactate or pyruvate during the experimental period, nor was there any indication of net production of lactate in any of the groups. Other methodological considerations that could have affected the results obtained in the diabetic rats were likewise ruled out. Because the ketone bodies are expected to supplement glucose as a metabolic fuel for the brain, our results indicate that brain energy consumption is increased during streptozotocin-diabetes.