Depletion of lactate by dichloroacetate reduces cardiac efficiency after hemorrhagic shock

Lactate infusion elevates cardiac output through increased heart rate and decreased vascular resistance: a randomised, blinded, crossover trial in a healthy porcine model

BACKGROUND

Lactate is traditionally recognized as a by-product of anaerobic metabolism. However, lactate is a preferred oxidative substrate for stressed myocardium. Exogenous lactate infusion increases cardiac output (CO). The exact mechanism underlying this mechanism has yet to be elucidated. The aim of this study was to investigate the cardiovascular mechanisms underlying the acute haemodynamic effects of exogenous lactate infusion in an experimental model of human-sized pigs.

METHODS

In this randomised, blinded crossover study in eight 60-kg-pigs, the pigs received infusions with one molar sodium lactate and a control infusion of tonicity matched hypertonic saline in random order. We measured CO and pulmonary pressures using a pulmonary artery catheter. A pressure-volume admittance catheter in the left ventricle was used to measure contractility, afterload, preload and work-related parameters.

RESULTS

Lactate infusion increased circulating lactate levels by 9.9 mmol/L (95% confidence interval (CI) 9.1 to 11.0) and CO by 2.0 L/min (95% CI 1.2 to 2.7). Afterload decreased as arterial elastance fell by  -1.0 mmHg/ml (95% CI  -2.0 to  -0.1) and systemic vascular resistance decreased by  -548 dynes/s/cm5 (95% CI  -261 to  -835). Mixed venous saturation increased by 11 percentage points (95% CI 6 to 16), whereas ejection fraction increased by 16.0 percentage points (95% CI 1.1 to 32.0) and heart rate by 21 bpm (95% CI 8 to 33). No significant changes in contractility nor preload were observed.

CONCLUSION

Lactate infusion increased cardiac output by increasing heart rate and lowering afterload. No differences were observed in left ventricular contractility or preload. Lactate holds potential as a treatment in situations with lowered CO and should be investigated in future clinical studies.

Regulating mitochondrial metabolism by targeting pyruvate dehydrogenase with dichloroacetate, a metabolic messenger

Dichloroacetate (DCA) is a naturally occurring xenobiotic that has been used as an investigational drug for over 50 years. Originally found to lower blood glucose levels and alter fat metabolism in diabetic rats, this small molecule was found to serve primarily as a pyruvate dehydrogenase kinase inhibitor. Pyruvate dehydrogenase kinase inhibits pyruvate dehydrogenase complex, the catalyst for oxidative decarboxylation of pyruvate to produce acetyl coenzyme A. Several congenital and acquired disease states share a similar pathobiology with respect to glucose homeostasis under distress that leads to a preferential shift from the more efficient oxidative phosphorylation to glycolysis. By reversing this process, DCA can increase available energy and reduce lactic acidosis. The purpose of this review is to examine the literature surrounding this metabolic messenger as it presents exciting opportunities for future investigation and clinical application in therapy including cancer, metabolic disorders, cerebral ischemia, trauma, and sepsis.

Lactate and Myocadiac Energy Metabolism

The myocardium is capable of utilizing different energy substrates, which is referred to as “metabolic flexibility.” This process assures ATP production from fatty acids, glucose, lactate, amino acids, and ketones, in the face of varying metabolic contexts. In the normal physiological state, the oxidation of fatty acids contributes to approximately 60% of energy required, and the oxidation of other substrates provides the rest. The accumulation of lactate in ischemic and hypoxic tissues has traditionally be considered as a by-product, and of little utility. However, recent evidence suggests that lactate may represent an important fuel for the myocardium during exercise or myocadiac stress. This new paradigm drives increasing interest in understanding its role in cardiac metabolism under both physiological and pathological conditions. In recent years, blood lactate has been regarded as a signal of stress in cardiac disease, linking to prognosis in patients with myocardial ischemia or heart failure. In this review, we discuss the importance of lactate as an energy source and its relevance to the progression and management of heart diseases.

Arterial Lactate in Cardiogenic Shock: Prognostic Value of Clearance Versus Single Values

OBJECTIVES

This study sought to compare single lactate values at admission (L1) and after 8 h (L2) with lactate clearance (LC) for mortality prediction in cardiogenic shock (CS).

BACKGROUND

Early estimation of prognosis in CS complicating acute myocardial infarction is crucial for tailored treatment selection. Arterial lactate is the most widely used point-of-care parameter in CS. In septic shock, lactate reduction over time-LC-has been extensively investigated. However, in CS, only limited data exist, and the prognostic value of LC is unknown.

METHODS

This study is a subanalysis of the IABP-SHOCK II (Intraaortic Balloon Pump in Cardiogenic Shock II) trial and the corresponding registry. Lactate levels were prospectively collected. All-cause mortality at 30 days was assessed as primary endpoint.

RESULTS

For 671 of 783 (85.7%) patients, L1 and L2 values were available. The area under the receiver-operating characteristic curve (L1: 0.69; L2: 0.76; LC: 0.59) showed no difference between L1 and LC (p = 0.20). In contrast, L2 was a significantly better predictive parameter than L1 or LC (p < 0.001 for both). In multivariable stepwise Cox regression analysis, L2 ≥3.1 mmol/l (best cutoff value by Youden index) and LC <-3.45%/h remained independently predictive for time to death (p < 0.001 for both), with L2 showing the highest chi-square test score (42.1) and hazard ratio (2.89; 95% confidence interval: 2.10 to 3.97).

CONCLUSIONS

Arterial lactate after 8 h is superior in mortality prediction in comparison with baseline lactate and LC. A cutoff value of 3.1 mmol/l for lactate after 8 h showed the best discrimination for assessing early prognosis in CS and may serve as new treatment goal. (Intraaortic Balloon Pump in Cardiogenic Shock II [IABP-SHOCK II]; NCT00491036).

Lactic Acidosis and the Role of Sodium Bicarbonate: A Narrative Opinion

Lactic acidosis occurs commonly and can be a marker of significant physiologic derangements. However what an elevated lactate level and acidemia connotes and what should be done about it is subject to inconsistent interpretations. This review examines the varied etiologies of lactic acidosis, the physiologic consequences, and the known effects of its treatment with sodium bicarbonate. Lactic acidosis is often assumed to be a marker of hypoperfusion, but it can also result from medications, organ dysfunction, and sepsis even in the absence of malperfusion. Acidemia causes deleterious effects in almost every organ system, but it can also have positive effects, increasing localized blood flow and oxygen delivery, as well as providing protection against hypoxic cellular injury. The use of sodium bicarbonate to correct severe acidemia may be tempting to clinicians, but previous studies have failed to show improved patient outcomes following bicarbonate administration. Bicarbonate use is known to decrease vasomotor tone, decrease myocardial contractility, and induce intracellular acidosis. This suggests that mild to moderate acidemia does not require correction. Most recently, a randomized control trial found a survival benefit in a subgroup of critically ill patients with serum pH levels <7.2 with concomitant acute kidney injury. There is no known benefit of correcting serum pH levels ≥ 7.2, and sparse evidence supports bicarbonate use <7.2. If administered, bicarbonate is best given as a slow IV infusion in the setting of adequate ventilation and calcium replacement to mitigate its untoward effects.

Activation of Pyruvate Dehydrogenase Activity by Dichloroacetate Improves Survival and Neurologic Outcomes After Cardiac Arrest in Rats

No pharmacological interventions are currently available to provide neuroprotection for patients suffering from cardiac arrest. Dichloroacetate (DCA) is a pyruvate dehydrogenase kinase inhibitor, which activates pyruvate dehydrogenase (PDH), and increases cell adenosine triphosphate (ATP) production by promoting influx of pyruvate into the Krebs cycle. In this study, we investigated the effects of DCA on post-resuscitation neurological injury in an asphyxial cardiac arrest rat model. Asphyxial cardiac arrest was established by endotracheal tube clamping. A total of 111 rats were randomized into three groups: Sham group, Control group, and DCA intervention group. Animals in DCA intervention group were intraperitoneally administered DCA with a loading dose of 80 mg/kg at 15 min after return of spontaneous circulation (ROSC), whereas rats in the Control group received equivalent volume of saline. DCA treatment increased 3-day survival time, and reduced neurologic deficit scores at 24, 48, and 72 h after ROSC. It also attenuated cellular apoptosis and neuronal damage in the hippocampal cornuammonis one region by hematoxylin-eosin staining and TdT-mediated dUTP nick-end labeling assay. In addition, DCA reduced the messenger RNA expression of tumor necrosis factor α and interleukin 1β in brain hippocampus and cortex after ROSC. Furthermore, DCA treatment significantly increased ATP production, PDH activity, and decreased blood glucose, lactate, and brain pyruvate levels after ROSC. Our results suggested that DCA has neuroprotective effects on brain injury after cardiac arrest, and its salutary effects were associated with an increase of mitochondrial energy metabolism in the brain through activation of PDH activity.

Clinical use of plasma lactate concentration. Part 2: Prognostic and diagnostic utility and the clinical management of hyperlactatemia

OBJECTIVE

To review the current literature pertaining to the use of lactate as a prognostic indicator and therapeutic guide, the utility of measuring lactate concentrations in body fluids other than blood or plasma, and the clinical management of hyperlactatemia in dogs, cats, and horses.

DATA SOURCES

Articles were retrieved without date restrictions primarily via PubMed, Scopus, and CAB Abstracts as well as by manual selection.

HUMAN AND VETERINARY DATA SYNTHESIS

Increased plasma lactate concentrations are associated with increased morbidity and mortality. In populations with high mortality, hyperlactatemia is moderately predictive in identifying nonsurvivors. Importantly, eulactatemia predicts survival better than hyperlactatemia predicts death. Consecutive lactate measurements and calculated relative measures appear to outperform single measurements. The use of lactate as a therapeutic guide has shown promising results in people but is relatively uninvestigated in veterinary species. Increased lactate concentrations in body fluids other than blood should raise the index of suspicion for septic or malignant processes. Management of hyperlactatemia should target the underlying cause.

CONCLUSION

Lactate is a valuable triage and risk stratification tool that can be used to separate patients into higher and lower risk categories. The utility of lactate concentration as a therapeutic target and the measurement of lactate in body fluids shows promise but requires further research.

Mitochondrial targeting by dichloroacetate improves outcome following hemorrhagic shock

Hemorrhagic shock is a leading cause of death in people under the age of 45 and accounts for almost half of trauma-related deaths. In order to develop a treatment strategy based on potentiating mitochondrial function, we investigated the effect of the orphan drug dichloroacetate (DCA) on survival in an animal model of hemorrhagic shock in the absence of fluid resuscitation. Hemorrhagic shock was induced in rats by withdrawing 60% of the blood volume and maintaining a hypotensive state. The studies demonstrated prolonged survival of rats subjected to hemorrhagic injury (HI) when treated with DCA. In separate experiments, using a fluid resuscitation model we studied mitochondrial functional alterations and changes in metabolic networks connected to mitochondria following HI and treatment with DCA. DCA treatment restored cardiac mitochondrial membrane potential and tissue ATP in the rats following HI. Treatment with DCA resulted in normalization of several metabolic and molecular parameters including plasma lactate and p-AMPK/AMPK, as well as Ach-mediated vascular relaxation. In conclusion we demonstrate that DCA can be successfully used in the treatment of hemorrhagic shock in the absence of fluid resuscitation; therefore DCA may be a good candidate in prolonged field care following severe blood loss.

Comparison of fluid balance and hemodynamic and metabolic effects of sodium lactate versus sodium bicarbonate versus 0.9% NaCl in porcine endotoxic shock: a randomized, open-label, controlled study

BACKGROUND

Sodium lactate has been shown to improve hemodynamics and avoid fluid overload. The objective of this study was to confirm a beneficial effect on fluid balance with sodium lactate infusion and to specify whether the advantage of lactate is related to a negative chloride balance, its particular metabolism, or simply its energy load.

METHODS

This was an interventional, randomized, open-label, controlled experimental study. Fifteen female "large white" pigs (2 months old) were challenged with intravenous infusion of Escherichia coli endotoxin. Three groups of five animals were randomly assigned to receive different fluids: a treatment group received sodium lactate 11.2% (SL group); an isotonic control group received 0.9% NaCl (NC group); and a hypertonic control group, with the same amount of osmoles and sodium as the SL group, received sodium bicarbonate 8.4% (SB group). In order to provide the same energy load in the three groups, control groups were perfused with an equivalent energy supply. Statistical analysis was performed with non-parametric tests and the Dunn correction for multiple comparisons at p < 0.05.

RESULTS

Fluid and chloride balance, hemodynamics, oxygenation markers, and microcirculatory parameters were measured over a 5-h period. Cumulative fluid balance was significantly lower in the SL group (550 (415-800) mL; median (interquartile range)) compared to the NC group (1100 (920-1640) mL, p = 0.01) and the SB group (935 (790-1220) mL, p = 0.03). Hemodynamics, cardiac efficiency, and microcirculation were significantly enhanced in the SL group, resulting in a significant improvement in oxygen delivery (SL group 417 (305-565) mL/min/m² at 300 min versus the NC (207 (119-272) mL/min/m², p = 0.01) and the SB (278, (211-315) mL/min/m², p = 0.03) groups). Oxygenation markers (arterial oxygen partial pressure (PaO₂)/inspired oxygen fraction (FiO₂), mixed venous oxygen saturation (SvO₂), and venoarterial carbon dioxide tension difference (Pv-aCO₂) were enhanced with sodium lactate infusion. Chloride balance was equivalent in both hypertonic groups and significantly reduced compared to the NC group.

CONCLUSION

Sodium lactate infusion improves fluid balance and hemodynamics. The advantage of lactate does not seem to be explained by its energy load or by the induced negative chloride balance with subsequent water movements.

Clinical significance of lactate in acute cardiac patients

Lactate, as a metabolite of easy and quick assessment, has been studied over time in critically ill patients in order to evaluate its prognostic ability. The present review is focused on the prognostic role of lactate levels in acute cardiac patients (that is with acute coronary syndrome, cardiogenic shock, cardiac arrest, non including post cardiac surgery patients). In patients with ST-elevation myocardial infarction treated with mechanical revascularization, hyperlactatemia identified a subset of patients at higher risk for early death and in-hospital complications, being strictly related mainly to hemodynamic derangement. The prognostic impact of hyperlactatemia on mortality has been documented in patients with cardiogenic shock and in those with cardiac arrest even if there is no cut-off value of lactate to be associated with worse outcome or to guide resuscitation or hemodynamic management. Therapeutic hypothermia seems to affect per se lactate values which have been shown to progressively decrease during hypothermia. The mechanism(s) accounting for lactate levels during hypothemia seem to be multiple ranging from the metabolic effects of reduced temperatures to the hemodynamic effects of hypothermia (i.e., reduced need of vasopressor agents). Serial lactate measurements over time, or lactate clearance, have been reported to be clinically more reliable than lactate absolute value also in acute cardiac patients. Despite differences in study design, timing of lactate measurements and type of acute cardiac conditions (i.e., cardiogenic shock, cardiac arrest, refractory cardiac arrest), available evidence strongly suggests that higher lactate levels can be observed on admission in non-survivors and that higher lactate clearance is associated with better outcome.

Hypertonic sodium lactate improves fluid balance and hemodynamics in porcine endotoxic shock

Introduction

Based on the potential interest in sodium lactate as an energy substrate and resuscitative fluid, we investigated the effects of hypertonic sodium lactate in a porcine endotoxic shock.

Methods

Fifteen anesthetized, mechanically ventilated pigs were challenged with intravenous infusion of E. coli endotoxin. Three groups of five animals were randomly assigned to receive 5 mL/kg/h of different fluids: a treatment group received hypertonic sodium lactate 11.2% (HSL group); an isotonic control group receiving 0.9% NaCl (NC group); a hypertonic control group with the same amount of osmoles and sodium than HSL group receiving hypertonic sodium bicarbonate 8.4% (HSB group). Hemodynamic and oxygenation variables, urine output and fluid balance were measured at baseline and at 30, 60, 120, 210 and 300 min. Skin microvascular blood flow at rest and during reactive hyperemia was obtained using a laser Doppler flowmetry technique. Results were given as median with interquartile ranges.

Results

Endotoxin infusion resulted in hypodynamic shock. At 300 min, hemodynamics and oxygenation were significantly enhanced in HSL group: mean arterial pressure (103 [81–120] mmHg vs. 49 [41–62] in NC group vs. 71 [60–78] in HSB group), cardiac index (1.6 [1.2–1.8] L/min/m² vs. 0.9 [0.5–1.1] in NC group vs. 1.3 [0.9–1.6] in HSB group) and partial pressure of oxygen (366 [308–392] mmHg vs. 166 [130–206] in NC group vs. 277 [189–303] in HSB group). At the same time, microvascular reactivity was significantly better in HSL group with a lower venoarterial CO₂ tension difference (5.5 [4–10] mmHg vs. 17 [14–25] in NC group vs. 14 [12–15] in HSB group). The cumulative fluid balance was lower in HSL group (-325 [-655; -150] mL) compared to NC (+560 [+230; +900] mL, p = 0.008) and HSB (+185 [-110; +645] mL, p = 0.03) groups.

Conclusions

In our hypodynamic model of endotoxic shock, infusion of hypertonic sodium lactate improves hemodynamic and microvascular reactivity with a negative fluid balance and a better oxygenation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0467-3) contains supplementary material, which is available to authorized users.

Stress hyperlactataemia: present understanding and controversy

An increased blood lactate concentration is common during physiological (exercise) and pathophysiological stress (stress hyperlactataemia). In disease states, there is overwhelming evidence that stress hyperlactataemia is a strong independent predictor of mortality. However, the source, biochemistry, and physiology of exercise-induced and disease-associated stress hyperlactataemia are controversial. The dominant paradigm suggests that an increased lactate concentration is secondary to anaerobic glycolysis induced by tissue hypoperfusion, hypoxia, or both. However, in the past two decades, much evidence has shown that stress hyperlactataemia is actually due to increased aerobic lactate production, with or without decreased lactate clearance. Moreover, this lactate production is associated with and is probably secondary to adrenergic stimulation. Increased lactate production seems to be an evolutionarily preserved protective mechanism, which facilitates bioenergetic efficiency in muscle and other organs and provides necessary substrate for gluconeogenesis. Finally, lactate appears to act like a hormone that modifies the expression of various proteins, which themselves increase the efficiency of energy utilisation and metabolism. Clinicians need to be aware of these advances in our understanding of stress hyperlactataemia to approach patient management according to logical principles. We discuss the new insights and controversies about stress hyperlactataemia.

Effect of hyperosmolar sodium lactate infusion on haemodynamic status and fluid balance compared with hydroxyethyl starch 6% during the cardiac surgery

Background and Aim:

No solution has been determined ideal for fluid therapy during cardiac surgery. Previous studies have shown that hyperosmolar sodium lactate (HSL) infusion has improved cardiac performance with smaller volume infusion, which resulted in negative fluid balance. This study compared the effects between a patent-protected HSL infusion and hydroxyethyl starch (HES) 6% on haemodynamic status of the patients undergoing cardiac surgery.

Methods:

In this open-label prospective controlled randomized study, patients were randomly assigned to receive loading dose of either HSL or HES 6%, at 3 mL/kgBW within 15 min, at the beginning of surgery. Haemodynamic parameters and fluid balance were evaluated, while biochemical parameters and any adverse effect were also recorded. Haemodynamic and laboratory parameters were analyzed through repeated measures analysis of variance. Statistical assessment of fluid management was carried out through Student t-test. All statistical analyses were performed using the statistical package for the social sciences^® version 15, 2006 (SPSS Inc., Chicago, IL).

Results:

Out of 100 enrolled patients in this study (50 patients in each arm), 98 patients were included in analysis (50 in HSL group; 48 in HES group). Cardiac index increased higher in HSL group (P = 0.01), whereas systemic vascular resistance index decreased more in HSL than HES group (P = 0.002). Other haemodynamic parameters were comparable between HSL and HES group. Fluid balance was negative in HSL group, but it was positive in HES group (−445.94 ± 815.30 mL vs. +108.479 ± 1219.91 mL, P < 0.009).

Conclusion:

Administration of HSL solution during the cardiac surgery improved cardiac performance and haemodynamic status better than HES did.

Physiological effects of hyperchloraemia and acidosis

The advent of balanced solutions for i.v. fluid resuscitation and replacement is imminent and will affect any specialty involved in fluid management. Part of the background to their introduction has focused on the non-physiological nature of 'normal' saline solution and the developing science about the potential problems of hyperchloraemic acidosis. This review assesses the physiological significance of hyperchloraemic acidosis and of acidosis in general. It aims to differentiate the effects of the causes of acidosis from the physiological consequences of acidosis. It is intended to provide an assessment of the importance of hyperchloraemic acidosis and thereby the likely benefits of balanced solutions.

Myocardial lactate deprivation is associated with decreased cardiovascular performance, decreased myocardial energetics, and early death in endotoxic shock

OBJECTIVE

We examined whether lactate availability is a limiting factor for heart function during endotoxic shock, and whether lactate deprivation thus induces heart energy depletion, thereby altering cardiovascular performance. The study goals were to determine whether muscle lactate production is linked to beta(2)-stimulation and to ascertain the effects of systemic lactate deprivation on hemodynamics, lactate metabolism, heart energetics, and outcome in a lethal model of rat's endotoxic shock.

INTERVENTIONS

We modulated the adrenergic pathway in skeletal muscle using microdialysis with ICI-118551, a selective beta(2)-blocker. Muscle lactate formation in endotoxic shock was further inhibited by intravenous infusion of ICI-118551 or dichloroacetate (DCA), an activator of pyruvate dehydrogenase (DCA) and their combination.

RESULTS

Muscle lactate formation was decreased by ICI-118551. During endotoxic shock both ICI-118151 and DCA decreased circulating and heart lactate concentrations in parallel with a decrease in tissue ATP content. The combination ICI-118551-DCA resulted in early cardiovascular collapse and death. The addition of molar lactate to ICI-1185111 plus DCA blunted the effects of ICI-118551+DCA on hemodynamics. Survival was markedly less with ICI-118551 than with endotoxin alone.

CONCLUSION

Systemic lactate deprivation is detrimental to myocardial energetics, cardiovascular performance, and outcome.

Lactate metabolism in acute uremia

Lactate is a key metabolite that is produced by every cell and oxidized by most of them, provided that they do contain mitochondria. Its metabolism is connected to energetic homeostasis and the cellular redox state. It is well recognized as an indicator of severe outcome in severely ill patients, however, it is not a detrimental factor per se. Conversely, some recent data tend even to indicate a beneficial effect in several metabolic disorders. Although the liver has long been recognized as a key organ in lactate homeostasis, the kidney also plays a major role as a gluconeogenic organ significantly involved in the glucose-lactate cycle. In acute renal failure, sodium lactate is widely used as a buffer in replacement fluids because the anion (lactate - ) is metabolized and the cation (Na + ) remains, leading to decreased water dissociation and proton concentration. The metabolic disorders related to acute renal failure or associated with it, such as liver failure, may affect lactate metabolism, and therefore they are often regarded as limiting factors for the use of lactate-containing fluids in such patients. By investigating endogenous lactate production in severe septic patients with acute renal failure, we found that an acute exogenous load of lactate did not affect the basal endogenous lactate production and metabolism. This indicates that exogenous lactate is well metabolized even in patients suffering from acute renal failure and severe sepsis with a compromised hemodynamic status.

Ethanol intoxication and lactated Ringer's resuscitation prolong hemorrhage-induced lactic acidosis

Ethanol (EtOH) blunts the respiratory and metabolic compensation during hemorrhage, resulting in a more severe lactic acidemia. We hypothesized that lactated Ringer's (LR) resuscitation may exacerbate this lactic acidemia. Male guinea pigs were implanted with arterial and venous catheters. Two days after catheter placement, conscious animals were injected intraperitoneally with 1 g/kg EtOH, 0.3 g/kg EtOH, or an equal volume of water 30 min before hemorrhage (60% of estimated blood volume). After 30 min of hemorrhagic shock, animals were resuscitated with isotonic saline (S) or LR at 1 mL/min (three times shed blood volume). Mean arterial blood pressure (MABP) was not affected by pretreatment with either dose of EtOH, but was significantly decreased by hemorrhage in all groups. Both S and LR resuscitation slightly increased MABP, but neither restored it to prehemorrhage values. Blood lactate levels increased in all groups during hemorrhage and remained elevated for 3 h in animals pretreated with 1 g/kg EtOH. In the group pretreated with 0.3 g/kg EtOH, pH decreased during shock but returned to prehemorrhage levels during the resuscitation period. Resuscitation with S returned pH to prehemorrhage values in animals pretreated with 1.0 g/kg EtOH. Resuscitation with LR did not exacerbate, but did prolong, the lactic acidemia after shock in animals pretreated with 1.0 g/kg EtOH. Administration of additional lactate during intoxication and hypovolemia for hemodynamic stabilization before blood transfusion may exacerbate a metabolic stress.

Differential modulation of glucose, lactate, and pyruvate oxidation by insulin and dichloroacetate in the rat heart

Despite the fact that lactate and pyruvate are potential substrates for energy production in vivo, our understanding of the control and regulation of carbohydrate metabolism is based principally on studies where glucose is the only available carbohydrate. Therefore, the purpose of this study was to determine the contributions of lactate, pyruvate, and glucose to energy production in the isolated, perfused rat heart over a range of insulin concentrations and after activation of pyruvate dehydrogenase with dichloroacetate (DCA). Hearts were perfused with physiological concentrations of [1-13C]glucose, [U-13C]lactate, [2-13C]pyruvate, and unlabeled palmitate for 45 min. Hearts were freeze clamped, and 13C NMR glutamate isotopomer analysis was performed on tissue extracts. Glucose, lactate, and pyruvate all contributed significantly to myocardial energy production; however, in the absence of insulin, glucose contributed only 25-30% of total pyruvate oxidation. Even under conditions where carbohydrates represented >95% of substrate entering the tricarboxylic acid (TCA) cycle, we found that glucose contributed at most 50-60% of total carbohydrate oxidation. Despite being present at only 0.1 mM, pyruvate contributed between approximately 10% and 30% of total acetyl-CoA entry into the TCA cycle. We also found that insulin and DCA not only increased glucose oxidation but also exogenous pyruvate oxidation; however, lactate oxidation was not increased. The differential effects of insulin and DCA on pyruvate and lactate oxidation provide further evidence for compartmentation of cardiac carbohydrate metabolism. These results may have important implications for understanding the mechanisms underlying the beneficial effects of increasing cardiac carbohydrate metabolism.

Pyruvate prevents poly-ADP ribose polymerase (PARP) activation, oxidative damage, and pyruvate dehydrogenase deactivation during hemorrhagic shock in swine

The inadequate availability of fuel substrates and sharp decline in cellular ATP have been implicated in a cascade of events associated with cell death and organ failure during hemorrhagic shock (HS). In this in vivo swine model of severe prolonged HS, the effect of exogenous pyruvate administration on various markers of cell damage in brain and liver was examined. Thirty minutes after the start of controlled arterial hemorrhage, 30% sodium pyruvate, 10% saline, or 0.9% saline was administered via jugular vein. Four hours after the initiation of hemorrhage, tissue samples from brain and liver were obtained and examined for the cellular and molecular markers of cellular damage. Results of our study suggest that pyruvate prevents loss of total NAD content, cleavage of poly-ADP ribose polymerase (PARP), and inhibits lipid peroxidation in both the brain and liver of swine during prolonged severe HS. We conclude that there are multiple mechanisms by which pyruvate can possibly prevent cell damage caused during HS.

Metabolic and hemodynamic effects of hypertonic solutions: sodium-lactate versus sodium chloride infusion in postoperative patients

Although hypertonic saline has been proposed as an intravenous resuscitation fluid, the beneficial effects of the sodium load are associated with potentially deleterious effects of chloride. Since the physiological lactate anion is well metabolized, hypertonic lactate solution could represent an interesting alternative. The aim of this study was to compare metabolic and hemodynamic effects of hypertonic infusion of sodium lactate versus sodium chloride in three groups of surgical patients who underwent elective coronary artery bypass grafting (CABG). Hypertonic lactate solution was infused to patients 14 to 16 h after surgery either involving a cardiopulmonary bypass (CPB-Lac, n = 20) or on-off pump (OPCAB-Lac, n = 20), whereas the third group consisted of patients undergoing cardiopulmonary bypass but receiving hypertonic saline solution (CPB-NaCl, n = 20). An equal fluid and sodium load (2.5 mL/2.5 mmol x kg(-1)) was infused in all patients over 15 min. Plasma glucose and sodium increased after infusion in the three groups, but the changes, although significant, were small. As expected, lactate rose only in CPB-Lac and OPCAB-Lac groups, the changes being more marked in CPB-Lac, indicating a slower lactate metabolism in this group compared with OPCAB-Lac. Although both solutions produced significant increases in cardiac index and oxygen delivery, there was a significant decrease in oxygen extraction only in groups receiving sodium lactate (CPB-Lac and OPCAB-Lac) and not in CPB-NaCl. Finally, hypertonic NaCl infusion induced a modest, although significant, decrease in arterial pH and bicarbonate, whereas hypertonic lactate infusion increased these two parameters in both CPB-Lac and OPCAB-Lac. This study demonstrates that hypertonic lactate infusion is safe and well tolerated in patients undergoing elective cardiac surgery.