Effect of hormones on hepatocyte gluconeogenesis in different models of acute uraemia

Hepatocytes isolated from the livers of starved, sham-operated, bilaterally nephrectomised and ureter-ligated rats as well as rats with ischaemic acute renal failure were used for a comparative study of the effects of different hormones on gluconeogenesis. In all tested groups dibutyryl-3':5'-adenosine monophosphate inhibits glucose synthesis from pyruvate whereas this process is not affected by glucagon and only slightly activated by adrenalin. In contrast, gluconeogenesis from dihydroxyacetone was stimulated by all three hormones at the expense of the conversion of dihydroxyacetone to lactate. In the presence of l-serine adrenalin, glucagon and dibutyryl cAMP also stimulate glucose synthesis, which is more marked in bilaterally nephrectomised and ureter-ligated animals. In half of the experiments with bilaterally nephrectomised rats (group BN 2), lack of sensitivity of hepatocytes to all tested hormones on gluconeogenesis from serine or dihydroxyacetone was observed. The beta-adrenergic antagonist propranolol reduced the stimulatory effect of adrenalin on glucose synthesis from serine and abolished the influence of catecholamines in the presence of dihydroxyacetone and pyruvate. This suggests that both alpha- and beta-receptors are involved in the activation of hepatic gluconeogenesis. Insulin and parathyroid hormone did not change the rate of glucose synthesis in any of the experimental groups.     

Role of energy charge and redox state for hepatocyte gluconeogenesis of acutely uremic rats

Hepatocytes were isolated from rats following bilateral nephrectomy, ureter ligation or sham operation under sodium pentobarbital (Nembutal) anesthesia to investigate the potential role of energy charge and redox state for the gluconeogenetic ability of liver cells. Ketogenesis from l-serine, sodium pyruvate or dihydroxyacetone was significantly higher in hepatocytes of acutely uremic rats indicating higher concentration of reducing equivalents in the mitochondria. During incubation, the mitochondrial redox state characterized by beta-hydroxybutyrate/acetoacetate ratio moved into direction of reduction in all experimental groups, whereas cytosolic redox state characterized by lactate/pyruvate ratio shifted to the oxidative state indicating lack of cytosolic reducing equivalents. Hepatocyte ATP and oxoglutarate production of ureter-ligated rats were significantly higher compared with binephrectomized or sham-operated animals independent of the substrates used. Simultaneously, energy charge showed values higher than 0.85 only in hepatocytes of ureter-ligated animals indicating high energy supply for energy requiring processes. We conclude that hepatic gluconeogenesis and ketogenesis of acutely uremic rats are limited by a lack of cytosolic reducing equivalents independent of cell energy supply.     

Effect of cyclosporin A,azathioprine, and prednisolone on carbohydrate metabolism of rat hepatocytes

The effect of different immunosuppressive drugs (prednisolone, azathioprine, cyclosporin A) on liver carbohydrate metabolism in the rat was investigated. Daily administration of prednisolone (3 mg/kg body weight) and azathioprine (2 mg/kg body weight) intraperitoneally for 2 weeks caused significantly lower liver glycogen content than that in NaCl-treated controls. Liver glucose and lactate content, as well as plasma glucose, glucagon, and serum insulin concentration of these animals, remained unchanged. There were no differences in any of these parameters between cyclosporin A (15 mg/kg body weight)-treated and vehicle (olive oil/ethanol)-treated animals. Prednisolone caused significantly lower glucose production in isolated rat hepatocytes using Na-pyruvate as the substrate, whereas glucose production was unchanged in hepatocytes of azathioprine-treated rats using pyruvate or l-serine as substrates. Glucose production from pyruvate or serine was significantly inhibited by cyclosporin A compared to the vehicle, but did not differ from the effects of azathioprine and prednisolone. Lactate production was significantly lower in cyclosporin-treated animals than in those given either the vehicle or azathioprine. Cyclosporin A completely reversed the inhibition of hepatocyte glycogen consumption caused by the vehicle. However, glycogen production in the presence of cyclosporin A was comparable to the effects of prednisolone and azathioprine. Finally, hepatocyte ketone body production using pyruvate as the substrate was higher in the presence of all immunosuppressive drugs. In the presence of serine, acetoacetate production increased in rats treated with 50 mg/kg body weight cyclosporin A, and -hydroxybutyrate production in animals receiving 15 and 50 mg/kg body weight cyclosporin A.This article is dedicated to Professor K. Kochsiek, Chief of the Medical Department, University of Würzburg, FRG, on the occasion of his 60th birthday     

Regulation of gluconeogenesis in hepatocytes from fasted alloxan-diabetic rats

Hepatocytes from fasted, alloxan-diabetic rats were incubated in the absence of gluconeogenic substrates to deplete residual glycogen stores. Glucose production from lactate and pyruvate was enhanced in cells from diabetic rats relative to similarly treated hepatocytes from fasted, nondiabetic control rats. Gluconeogenesis from dihydroxyacetone, fructose, or glycerol was not increased but the formation of lactate plus pyruvate from dihydroxyacetone was decreased. The stimulation of gluconeogenesis by exogenous fatty acids was decreased by diabetes. The rates of gluconeogenesis in the presence of lactate plus pyruvate plus oleate were equal in hepatocytes from diabetic and control rats and indicate that the maximal rate of gluconeogenesis was not increased. With lactate plus pyruvate as substrates, stimulation of gluconeogenesis by norepinephrine or dibutyryl-cAMP was not altered by diabetes. The catecholamine stimulation of gluconeogenesis from glycerol also was unaffected. In contrast, diabetes decreased the maximal stimulation of gluconeogenesis from dihydroxyacetone by dibutyryl-cAMP, glucagon, or norepinephrine and this decrease was proportional to the decreased production of lactate plus pyruvate. The concentrations of glucagon or norepinephrine required for half-maximal stimulation were not altered by diabetes. Thus, the hormonal stimulation of gluconeogenesis from dihydroxyacetone is decreased by diabetes, probably because of decreased pyruvate kinase activity, but the interaction of glucagon and norepinephrine with hepatocytes and the subsequent stimulation of gluconeogenesis from physiologic substrates is not impaired.     

Evidence for aerobic glycolysis in lambda-carrageenan-wounded skeletal muscle

Classically, increased lactate production in wounded tissue is ascribed to anaerobic glycolysis although its oxygen consumption has been found to be similar to normal tissue. This apparent inconsistency was studied in a standardized isolated perfused wound model. Male Sprague-Dawley rats were wounded (group W) with intramuscular injections of lambda-carrageenan and fed ad lib.; not wounded and pair fed to the decreased food intake of the wounded animals (group PFC); or not wounded and fed ad lib. (group ALC). After 5 days, the hindlimbs of animals from each group were either perfused using a standard perfusate with added [U-14C]glucose or [1-14C]pyruvate or assayed for the tissue content of lactate and pyruvate. In addition, the effect of a 30% hemorrhage on the tissue lactate and pyruvate concentration was examined. Wounding increased glucose uptake and lactate production by 100 and 96%, respectively, above that seen in ALC animals. Oxygen consumption was unchanged by wounding (5.74, 5.14, and 5.83 mumole/min/100 g in W, PFC, and ALC, respectively). Glucose and pyruvate oxidation were also unaltered among the groups. Hemorrhage resulted in a comparable increase in lactate and pyruvate in tissue from wounded and pair-fed control animals (above those concentrations found in tissue harvested without preexisting hemorrhage). As a consequence, the same relationship in L/P ratio was maintained after hemorrhage. Taken together, these results confirm the presence of aerobic glycolysis in wounded tissue (unchanged oxygen consumption, glucose, and pyruvate oxidation). In addition, pyruvate dehydrogenase activity in the wound was apparently the same as that found in muscle from pair-fed control animals.     

Glycogen synthesis from serine in isolated perfused hindquarters of acutely uraemic rats

Isolated hindquarters of bilaterally nephrectomized and sham-operated rats were perfused in the presence and absence of 14C-labelled serine, respectively. After a perfusion period of 30 min 14C-serine was 4,074 +/- 270 dpm/ml in the perfusion medium of sham-operated animals and decreased to 2,800 +/- 190 dpm/ml in the medium of acutely uraemic rats. Muscle glycogen concentration in sham-operated animals was 1.10 +/- 0.04 mg/g wet weight in the absence and 1.03 +/- 0.11 mg/g in the presence of serine. In contrast, in acutely uraemic rats there was a glycogen concentration of 0.57 +/- 0.09 mg/g in the absence of serine. Glycogen was increased in the presence of serine in the perfusion medium, the value being 1.50 +/- 0.13 mg glycogen/g wet weight. Incorporation of labelled serine into skeletal muscle glycogen was significantly higher in acutely uraemic animals (15 +/- 0.5 mumol/g glycogen) than in sham-operated animals (10 +/- 0.4 mumol/g). The results are compatible with the hypothesis that serine increases muscle glycogen synthesis in acute uraemia.     

Kidney independent serine synthesis in the rat. Effect of dietary serine and glycine restriction

The potential role of the kidney in renal serine synthesis was elucidated in rats following dietary serine as well as serine and glycine depletion for 6 weeks. Serine deficient diet caused a significant rise in blood serine and glycine values. In contrast, blood glycine concentration decreased significantly following serine and glycine depletion, whereas blood serine levels remained unchanged. Bilateral nephrectomy caused a significant decrease of blood serine values of control and serine deficient rats. Serine concentration, however, was not affected by bilateral nephrectomy following serine and glycine deficiency indicating kidney-independent serine synthesis under these conditions. There was a significant increase of blood lactate and pyruvate levels under serine and serine/glycine deficient diet compared with control animals, whereas blood ketone bodies fell. In contrast, 24 h after bilateral nephrectomy blood ketone bodies rose and blood lactate and pyruvate concentrations decreased significantly. 24 h after bilateral nephrectomy there was a marked rise in blood citrate values of female rats compared with male animals indicating sex dependency of kidney citrate metabolism in the rat.     

Activation by vanadate of glycolysis in hepatocytes from diabetic rats

In hepatocytes from starved streptozocin-induced diabetic rats, vanadate increases the glycolytic flux because it raises the levels of fructose-2,6-bisphosphate (Fru-2,6-P2), the main regulatory metabolite of this pathway. This effect of vanadate on Fru-2,6-P2 levels is time and dose dependent, and it remains in cells incubated in a calcium-depleted medium. Vanadate is also able to counteract the decrease on Fru-2,6-P2 levels produced by glucagon, colforsin, or exogenous cAMP. However, vanadate does not modify 6-phosphofructo-2-kinase and pyruvate kinase activities, but it does counteract the inactivation of these enzymes induced by glucagon. Likewise, Fru-2,6-P2ase activity is also not affected by vanadate. In addition, vanadate is able to increase the production of both lactate and CO2 in hepatocytes from streptozocin-induced diabetic rats incubated in the presence of glucose in the medium. Vanadate behaves as a glycolytic effector in these cells, and this effect may be related to its ability to normalize blood glucose levels in diabetic animals.     

Carbohydrate metabolism in potassium-depleted rats

Carbohydrate metabolism was examined in different organs of rats with dietary potassium deprivation for 4 weeks. Thereafter, a 24- or 48-hour starvation period caused a significant decrease of skeletal muscle and liver glycogen content in K+-depleted (KD) rats, whereas kidney glycogen concentration increased and heart glycogen remained unchanged. In contrast, liver glucose concentration was significantly higher in starved KD animals without changes in muscle, heart, and kidney glucose concentrations. Potassium depletion caused a highly significant decrease of plasma and muscle potassium concentrations, metabolic alkalosis, reduced plasma insulin, and increased creatine phosphokinase levels. Blood lactate, pyruvate, and oxoglutarate levels were significantly enhanced in fasted KD rats, whereas blood citrate, beta-hydroxybutyrate, and glucose concentrations were unchanged. Blood acetoacetate level, however, was significantly reduced following potassium depletion. Therefore, beta-hydroxybutyrate/acetoacetate ratio increased significantly, whereas lactate/pyruvate ratio was not influenced. Our results clearly indicate impaired carbohydrate metabolism in potassium-depleted rats.     

Effects of benfluorex on fatty acid and glucose metabolism in isolated rat hepatocytes: from metabolic fluxes to gene expression

The effects of benfluorex and two of its metabolites (S 422-1 and S 1475-1) on fatty acid and glucose metabolic fluxes and specific gene expression were studied in hepatocytes isolated from 24-h fasted rats. Both benfluorex and S 422-1 (0.1 or 1 mmol/l) reduced beta-oxidation rates and ketogenesis, whereas S 1475-1 had no effect. At the same concentration, benfluorex and S 422-1 were more efficient in reducing gluconeogenesis from lactate/pyruvate than S 1475-1. Benfluorex inhibited gluconeogenesis at the level of pyruvate carboxylase (45% fall in acetyl-CoA concentration) and of glyceraldehyde-3-phosphate dehydrogenase (decrease in ATP/ADP and NAD(+)/NADH ratios). Accordingly, neither benfluorex nor S 422-1 inhibited gluconeogenesis from dihydroxyacetone, but both stimulated gluconeogenesis from glycerol. In hepatocytes cultured in the presence of benfluorex or S 422-1 (10 or 100 micromol/l), the expression of genes encoding enzymes of fatty acid oxidation (carnitine palmitoyltransferase [CPT] I), ketogenesis (hydroxymethylglutaryl-CoA synthase), and gluconeogenesis (glucose-6-phosphatase, PEPCK) was decreased, whereas mRNAs encoding glucokinase and pyruvate kinase were increased. By contrast, Glut-2, acyl-CoA synthetase, and CPT II gene expression was not affected by benfluorex or S 422-1. In conclusion, this work suggests that benfluorex mainly via S 422-1 reduces gluconeogenesis by affecting gene expression and metabolic status of hepatocytes.     

Hepatic glucose cycling does not contribute to the development of hyperglycemia in Zucker diabetic fatty rats.

Hepatic glucose cycling, whereby glucose is taken up by the liver, partially metabolized, then recycled to glucose, makes a substantial contribution to the development of hyperglycemia in IDDM. This stimulation of glucose cycling appears to be associated with elevated rates of fatty acid oxidation. Whether hepatic glucose cycling also contributes to the development of hyperglycemia in NIDDM is unclear. Using a model of NIDDM, the Zucker diabetic fatty (ZDF) rat, we determined whether glucose cycling was enhanced. Hepatocytes from ZDF rats exhibited higher rates of glucose phosphorylation and glycolysis, but there was no increase in the rate of cycling between glucose and glucose-6-phosphate or between glycolytically derived pyruvate and glucose. Despite the increased rates of glycolysis, the production of CO2 in liver cells from ZDF rats was no different from rates measured in cells from control animals. Instead, there was a large increase in the accumulation of lactate and pyruvate in the ZDF liver cells. The addition of 2-bromopalmitate, an inhibitor of fatty acid oxidation that inhibited glucose cycling in hepatocytes from IDDM rats, had no effect on glucose cycling in cells from ZDF rats. We therefore conclude that, unlike in IDDM, hepatic glucose cycling does not contribute to the development of hyperglycemia in the NIDDM Zucker rat.     

Effect of starvation on the local and systemic metabolic effects of the lambda-carrageenan wound

The contribution that starvation makes to the altered glucose metabolism in injured rats was evaluated. Food intake, weight change, nitrogen balance, and muscle tissue concentrations of glycogen, glucose, and the glycolytic intermediates were determined in these animals. This study concluded that the wounded and pair fed control groups presented adequately represent the metabolic states associated with injury and semistarvation in experimental animals, decreased food intake plays a major role in the weight loss and nitrogen balance in this wound model, wounding overrides two of the controlling steps of glycolysis (hexokinase and phosphofructokinase) in skeletal muscle during starvation, the finding of similar pyruvate dehydrogenase activity after wounding and starvation as demonstrated by tissue lactate to pyruvate ratios and lactate and pyruvate concentrations suggest that lactate production in wounded tissue may not be simply a manifestation of an altered redox state secondary to anaerobic conditions.     

Adverse effects of sucrose-rich diets on uraemic rats

The nature of carbohydrate may affect the tolerance and progression of uraemia. The effects of three diets differing only in their carbohydrate source: namely corn starch (C), glucose (G) or sucrose (S) were examined. Study 1 examined the effects of the three carbohydrate diets on unilaterally nephrectomised control rats and severely uraemic rats. The three carbohydrates produced similar nutritional effects in uninephrectomised rats, whereas sucrose rapidly induced anorexia, stunting and slightly accelerated renal damage in uraemia. Study 2 examined the long-term effects of the three carbohydrates in moderate uraemia under conditions of high and identical carbohydrate intakes. Hyperphagic Zucker uraemic rats (F rats) received a daily allotment of each diet plus pure carbohydrate. Lean uraemic rats (L rats) received the same dietary allotment without the carbohydrate supplement. The F rats fed sucrose showed greater morbidity and mortality but little renal deterioration. Their plasma triglycerides increased dramatically. The L rats fed sucrose had the greatest urinary protein, the least creatinine clearance and the most severe renal damage. Thus, sucrose-rich but not glucose-rich diets have two adverse effects in uraemia: a deterioration in nutritional status, perhaps related to abnormal fructose utilisation, and a long-term effect on the kidney, resulting in accelerated renal deterioration.     

Role of excess glycogenolysis in fasting hyperglycemia among pre-diabetic and diabetic Zucker (fa/fa) rats

Sources of plasma glucose and glucose turnover were investigated in 8-week-old (pre-diabetic) and 13-week-old (diabetic) Zucker (fa/fa) rats after a 24-h fast. Intraperitoneal (2)H(2)O was administered and [3,4-(13)C(2)]glucose and [U-(13)C(3)]propionate were infused into conscious active rats. (13)C nuclear magnetic resonance analysis of monoacetone glucose derived from blood glucose indicated that glucose production was increased significantly in 8- and 13-week-old fa/fa rats compared with age-matched Zucker (+/+) rats, and hepatic glycogen was dramatically higher among fa/fa animals regardless of age. Glycogenolysis, essentially 0 in +/+ rats after a 24-h fast, was significant in fa/fa rats (11 +/- 6 and 17 +/- 7% of glucose production in 8- and 13-week-old rats, respectively), even after a 24-h fast. Tricarboxylic acid (TCA) cycle flux and efflux of carbon skeletons from the cycle (cataplerosis) were both significantly higher in fa/fa rats compared with controls, but net gluconeogenesis from the TCA cycle was not higher because products leaving the cycle were returned to the cycle via a pyruvate cycling pathway. Thus, pyruvate cycling flux increased in proportion to TCA cycle flux, leaving net gluconeogenesis unchanged in fa/fa animals compared with control animals. The distribution of (2)H in skeletal muscle glycogen suggested that at least a fraction of glucose molecules entering glycogen pass through phosphomannose isomerase.     

Decreases in myocardial glucose and increases in pyruvate but not ischaemia are observed during porcine endotoxaemia

Background: Myocardial dysfunction occurs commonly in septic shock. It is not known whether this is due to local ischaemia and metabolic disturbances. Our hypothesis was that endotoxaemic myocardial dysfunction may be associated with interstitial ischaemic and metabolic changes, measured using interstitial microdialysis (MD).
Methods: Eighteen pigs were randomized to control ( n =6) or endotoxin infusion ( n =12). MD catheters were inserted into the myocardium for measurement of interstitial glucose, pyruvate and lactate concentrations. Plasma glucose and lactate concentrations and systemic haemodynamic parameters were measured simultaneously.
Results: Compared with the control group, the endotoxaemic animals had significantly decreased left ventricular stroke work and venous oxygen saturation (SvO2), and increased mean pulmonary artery pressure and plasma lactate. In the endotoxaemic group, decreases in interstitial glucose were observed, occurring simultaneously with increases in interstitial pruvate. Interstitial lactate : pyruvate ratios decreased with time in all animals.
Conclusions: Despite severe systemic and pulmonary haemodynamic changes, interstitial MD measurements revealed no evidence of anaerobic metabolism in the myocardium of endotoxaemic pigs. There were, however, changes in glucose and pyruvate concentrations, suggesting local energy metabolic disturbances.     

Modifications of citric acid cycle activity and gluconeogenesis in streptozotocin-induced diabetes and effects of metformin.

To better define the modifications of liver gluconeogenesis and citric acid cycle, or Krebs' cycle, activity induced by insulin deficiency and the effects of metformin on these abnormalities, we infused livers isolated from postabsorptive or starved normal and streptozotocin-induced diabetic rats with pyruvate and lactate (labeled with [3-13C]lactate) with or without the simultaneous infusion of metformin. Lactate and pyruvate uptake and glucose production were calculated. The 13C-labeling pattern of liver glutamate was used to calculate, according to Magnusson's model, the relative fluxes through Krebs' cycle and gluconeogenesis. These relative fluxes were converted into absolute values using substrate balances. In normal rats, starvation increased gluconeogenesis, the flux through pyruvate carboxylase-phosphoenolpyruvate carboxykinase (PC-PEPCK), and the ratio of PC to pyruvate dehydrogenase (PDH) flux (P < 0.05); metformin induced only a moderate decrease in the PC:PDH ratio. Livers from postabsorptive diabetic rats had increased lactate and pyruvate uptakes (P < 0.05); their metabolic fluxes resembled those of starved control livers, with increased gluconeogenesis and flux through PC-PEPCK. Starvation induced no further modifications in the diabetic group. Metformin decreased glucose output from the liver of starved diabetic rats (P < 0.05). The flux through PC-PEPCK and also pyruvate kinase were decreased (P < 0.05) by metformin in both groups of diabetic rats. In conclusion, insulin deficiency increased in this model of diabetes gluconeogenesis through enhanced uptake of substrate and increased flux through PC-PEPCK; metformin decreased glucose production by reducing the flux through PC-PEPCK.     

Glucose metabolism in injured tissue: a longitudinal study

Injured tissue is characterized by increased glucose uptake and increased lactate production as compared to normal tissue. These metabolic changes have been attributed to the presence of inflammatory cells in injured tissues. To correlate these metabolic changes with changes in the inflammatory cell population at various times after injury, we studied the lambda-carrageenan hindlimb wound model in anesthetized rats. Perfusion studies demonstrated that at 3 and 5 days after injury glucose uptake was increased in injured hindlimbs, compared with hindlimbs from pair-fed control animals. At 3, 5, and 10 days after injury, lactate production from glucose was increased in injured hindlimbs, compared with hindlimbs from pair-fed control animals. These metabolic changes were not related to differences in body weight or food intake. There was no difference in glucose oxidation or in oxygen consumption in injured hindlimbs, compared with hindlimbs from pair-fed control animals. The increased glucose uptake and increased lactate production from glucose was coincident with the presence of inflammatory cells--predominantly macrophages--at the site of injury. It is suggested that the glucose metabolism in injured tissue reflects the metabolism of the inflammatory cells at the site of injury.     

大鼠胆源性脓毒症时的肝脏糖异生功能及相关激素环境的改变

急性胆源性肝损害所致多系统器官功能不全的机理尚不完全清楚。作者采用肝脏原位灌注法测定了大鼠急性胆道感染（AOC）所致脓毒症时肝脏糖异生功能的改变，并对AOC后机体重要理糖激素环境的变化及其对精异生功能的影响进行了探讨。结果表明：AOC后24小时大鼠肝脏糖异生功能明显降低，血乳酸和促糖激素水平明显升高，胰岛素显著降低，血糖约维持在正常水平的2．5倍。AOC48小时，大鼠肝脏糖异生功能进一步降低，血乳酸浓度继续增加，但促糖激素无继续升高或明显下降，胰岛素显著上升，血糖水平较AOC24小时明显下降。提示AOC早期大鼠肝脏糖异生功能即有明显降低，此时机体可通过增加糖异生基质和改变理糖激素环境维持应激所需要的高血糖水平；后期肝脏糖异生功能进一步受损，机体代偿功能明显紊乱，血糖浓度明显降低，这可能是胆源性多系统辞官功能不全发生发展的病理生理机理之一。     

Ischaemic pre-conditioning means an increased adenosine metabolism with decreased glycolytic flow in ischaemic pig myocardium

Background: Ischaemic pre‐conditioning (IP) is a potent protective mechanism for limiting the myocardial damage due to ischaemia. It is not fully known as to how IP protects. The metabolism of adenosine may be an important mechanistic component. We study the role of adenosine turnover together with glycolytic flow in ischaemic myocardium subjected to IP. Methods: An acute myocardial ischaemia pig model was used, with microdialysis sampling of some metabolites (lactate, adenosine, glucose, glycerol, taurine) of ischaemic myocardium. An IP group was compared with a control group before and during a prolonged ischaemia. ¹⁴C‐labelled adenosine and glucose were infused through microdialysis probes, and lactate, ¹⁴C‐labelled lactate, glucose, taurine and glycerol were analysed in the effluent. The glycogen content in myocardial biopsies was determined. Results: The ¹⁴C‐adenosine metabolism was higher as there was a higher production of ¹⁴C‐lactate in IP animals compared with the controls. The glycolytic flow, measured as myocardial lactate formation, was retarded during prolonged ischaemia in IP animals. Myocardial free glucose and glycogen content decreased during the prolonged ischaemia in both groups, with higher free glucose in the IP group. We confirmed the protective effects of IP with lower myocardial concentrations of markers for cellular damage (glycerol). Conclusions: This association between increased adenosine turnover and decreased glycolytic flow during prolonged ischaemia in response to IP can possibly be explained by the competitive effect for the metabolites from both glucose and adenosine metabolism for entering glycolysis. We conclude that this study provides support for an energy‐metabolic explanation for the protective mechanisms of IP.     

Reduction in spinal cord postischemic lactic acidosis and functional improvement with dichloroacetate

Pyruvate dehydrogenase complex (PDHC) is a major enzyme of glucose metabolism. Dichloroacetate (DCA) is a noncompetitive inhibitor of PDHC kinase, an enzyme that inactivates PDHC. We examined the effects of DCA on extracellular lactate and pyruvate concentration changes and spinal somatosensory evoked potentials (SSEP) in ischemic rabbit spinal cords. In the first group of 26 animals, the aorta was occluded until postsynaptic SSEP waves were completely suppressed for 10 min, a period of ischemia that causes neurologic deficits in 50% of untreated animals. DCA (25 mg/kg) was given to 13 of these animals before ischemia. In the second group of 24 animals, the aorta was occluded until the postsynaptic SSEP waves were absent for 20 min, a period of ischemia that produces paraplegia in 100% of untreated animals. DCA (25 mg/kg) was given to 16 of these animals just before the aortic occlusion was released. After occlusion, extracellular spinal lactate concentrations increased abruptly while pyruvate concentrations fell. Both lactate and pyruvate concentrations reached a plateau during the ischemic period but increased when the aortic balloon was deflated. DCA-treated animals had lower lactate and pyruvate peak concentrations during reperfusion, as well as more rapid and greater recovery of SSEP at 2 h after reperfusion. DCA did not alter spinal metabolism during the ischemia but appeared to produce a more rapid shift to glucose metabolism on reperfusion. Thus, DCA treatment resulted in better electrophysiological recovery after both moderate and severe ischemia, either by reducing lactic acidosis or by increasing the recovery rate of aerobic energy production.