Lactate Gradient Research Articles

Differential effects of defibrillation on systemic and cardiac sympathetic activity

ObjectiveTo assess the effect of defibrillation shocks on cardiac and circulating catecholamines.DesignProspective examination of myocardial catecholamine balance during dc shock by simultaneous determination of arterial and coronary sinus plasma concentrations....

An in vitro System for the Analysis of Changes in Depth Distribution of Diffusates in Bacterial Films

No suitable technique exists which allows simultaneous analysis of time- and depth-dependent concentrations of all components of interest in single samples of intercellular fluid from dental plaque biofilms. We have developed an in vitro model which allows detailed study of these interactions by analysis of intercellular fluid and pH measurement at the film base. Compact, defined-depth films of Streptococcus mutans were formed in a micrometer-controlled, variable-depth well and bathed in synthetic saliva. Films exposed to synthetic saliva containing glucose for 2 min followed by clearance with glucose-free synthetic saliva gave typical ‘Stephan-type’ pH profiles. Intercellular fluid isolated from successive 200-μm-thick sections of 600-μm-deep films was analysed by ion chromatography. A concentration gradient of lactate, falling with depth, was measured. The experimental system described here, the first of its type to be described, can easily be used to analyse pH changes and the depth-dependent distribution of diffusates in a model bacterial film. Although this bacterial film is far removed from a natural biofilm, the apparatus has potential for the study of grown biofilms and is an important advance towards position-dependence analysis of diffusates in biofilms.

Short-chain fatty acids have polarized effects on sodium transport and intracellular pH in rabbit proximal colon

Background & Aims: Short-chain fatty acids (SCFAs) stimulate colonic Na + absorption, presumably by acidification of colonocytes and activation of apical Na +/H + exchangers. It is unclear whether this effect depends on SCFA gradients across the colonic epithelium, and, if so, why. The aim of this study was to determine (1) whether SCFAs added unilaterally to either the apical or basolateral border of the cell have similar effects on intracellular pH (pH i); (2) whether SCFA gradients alter Na + transport and; (3) what regulatory factors are involved in gradient-induced Na + transport. Methods: pH i was measured in intact epithelial rabbit proximal colon using the pH-sensitive indicator 2',7'-bis(carboxyethyl)-5-(6)-carboxyfluorescein, and Na + transport was measured under short-circuit conditions. Results: Apical and basolateral SCFAs had equivalent effects on decreasing pH i, but the recovery toward baseline was more vigorous after apical SCFAs. Gradients of both propionate and lactate (50 mmol/L [mucosal], 0 mmol/L [serosal]) stimulated electroneutral Na + absorption, which was inhibited by bicarbonate, mucosal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and Cl − removal. However, it was not blocked by amiloride. The differential response to a series of pharmacological agents showed that gradient-stimulated transport is distinct from epinephrine-stimulated electroneutral Na + absorption. Conclusions: A physiological gradient of SCFAs across the colonic epithelium elicits polarized effects on both pH i and Na + absorption that may be important determinants of colonic fluid transport. GASTROENTEROLOGY 1998;114:737-747

Thermodynamic significance of the lactate gradient.

The theory that some bacteria can save energy by an energy-recycling process, in which protons are excreted with metabolic end-products with variable stoichiometry, has been examined by 1H-NMR. A method has been developed that utilises observed differences in the Hahn T2 relaxation of metabolites in the intracellular and extracellular compartments to distinguish and quantify metabolite signals originating from both compartments. It was found that the lactate electrochemical-potential gradient calculated from the fraction of lactate that is sufficiently mobile to contribute to the NMR signal was in exact balance with the proton electrochemical-potential gradient over a wide range of pH values. The conclusion was reached that previous reports of variable stoichiometry were due to 'bound' lactate at high intracellular pH that could neither contribute neither to the NMR signal nor to the lactate electrochemical-potential gradient.

Open-chest cardiac massage without major thoracotomy: metabolic indicators of coronary and cerebral perfusion

Objective: to compare the coronary and cerebral perfusion achieved using a novel method of minimally-invasive, direct cardiac massage to that obtained using bimanual, open-chest cardiac massage. Design: prospective, controlled animal study with repeated measures. Setting: university research laboratory. Subjects: large domestic swine. Interventions: aortic, coronary sinus, jugular venous and pulmonary artery catheters were placed. Following an equilibration period, ventricular fibrillation was induced. After 4 min of untreated ventricular fibrillation, animals underwent bimanual, open-chest cardiac massage ( N=6) or minimally-invasive, direct cardiac massage using a novel device for direct cardiac compression ( N=6). Adrenaline was administered at a dose of 1 mg intravenously every 5 min. Measurements: systemic metabolic parameters, (arterial P O 2 , P CO 2 and lactate concentration) and coronary sinus and jugular venous metabolic parameters (pH, PV O 2 , SV O 2 , PV CO 2 and lactate concentration) were measured and calculated (coronary sinus/jugular-arterial SV O 2 , coronary sinus/jugular-arterial P CO 2 and lactate differences) at baseline and at 10, 20 and 30 min following induction of ventricular fibrillation. Animals were euthanised after 30 min with no attempt at defibrillation. Main Results: oxygen tension and oxygen saturation of coronary sinus blood declined significantly during the experimental period, but no differences were noted between treatment groups. The coronary sinus-arterial oxygen saturation difference increased during the study with no significant differences between groups. Coronary sinus P CO 2 and the coronary sinus-arterial P CO 2 difference increased significantly in both experimental groups during cardiac massage. No inter-group differences were noted. A similar relationship was noted in coronary sinus lactate values. The coronary sinus-arterial lactate difference displayed a positive balance at all intervals with no differences noted between group values. The oxygen tension and oxygen saturation of jugular venous blood, were reduced from baseline levels with both treatments. The jugular-arterial oxygen saturation difference increased in both groups compared to baseline values. Between group values were significantly different only at the 20 min interval. Both the jugular venous P CO 2 and the jugular-arterial P CO 2 gradient were elevated at all intervals, but no inter-group differences were noted. Jugular venous lactate concentration rose steadily with time in both groups. No significant increase in the jugular-arterial lactate gradient was noted at any time point. Conclusions: minimally-invasive, direct cardiac massage provides coronary and cerebral perfusion similar to that achieved using standard open-chest cardiac massage. This method may provide a more effective substitute for standard, closed-chest cardiac massage in cases of refractory cardiac arrest.

Systemic and regional effects of experimental gradual splanchnic ischemia

Purpose: We evaluated the effects of gradual intestinal ischemia on systemic and regional haemodynamics and oxygen transport. Materials and Methods: Superior mesenteric artery (SMA) blood flow was decreased by 40%, 70%, and 100% for 60-minute periods and thereafter released in 12 pigs. Hemodynamic changes were monitored continuously, and the intestinal perfusion was evaluated by changes in portal vein-arterial lactate gradient, intramucosal pH, tonometric Pco 2, tonometric-portal vein Pco 2 gradient, and regional oxygen extraction. Results: Local signs of intestinal hypoperfusion developed during the SMA occlusion. Intramucosal pH and portal vein pH decreased from 7.18 ± 0.04 to 6.81 ± 0.04 ( P < .01) and from 7.36 ± 0.01 to 7.25 ± 0.03 ( P < .05), respectively. Intramucosal Pco2 and tonometric-portal vein Pco2 gradient increased from 12.4 ± 1.3 to 21.2 ± 1.8 kPa ( P < .01) and from 6.0 ± 1.3 to 14.0 ± 1.9 kPa ( P < .05), respectively. Portal vein-arterial lactate gradient and splanchnic oxygen extraction increased from 0.02 ± 0.07 to 2.32 ± 0.47 mmol/L ( P < .01) and from 0.44.-k 0.03 to 0.60 ± 0.03 ( P < .05), respectively. Systemic changes observed during the SMA occlusion were reduction of cardiac index (161 ± 12 to 114 ± 8 mL/min/kg, P < .01) and pulmonary capillary wedge pressure (4 ± 1 to 3 ± 1 mm Hg) and increase in heart rate (124 ± 5 to 173 ± 11 beats/ min, P < .01) and mean arterial pressure (79 ± 3 to 104 ± 5 mm Hg, P < .01). Systemic oxygen extraction increased ( P < .05), arterial pH increased ( P < .05), and arterial lactate decreased ( P < .01) during the SMA occlusion. Splanchnic ischemia defined as an increase in portal vein-arterial lactate gradient above mean +2 SD of the baseline occurred at 93 ± 15 minutes corresponding 70% SMA occlusion. Conclusion: We conclude that signs of tissue hypoperfusion started to develop at 70% SMA occlusion and that regional tissue hypoperfusion in the splanchnic region may develop without any systemic signs of oxygen supply/demand mismatch.

Release of Lactate by the Lung in Acute Lung Injury

The pathogenesis of hyperlactatemia during sepsis is poorly understood. We have previously described an increase in lactate concentration across the lung in the dog during early endotoxemia. Accordingly, we sought to determine if the lung releases lactate in humans and what relation this has with lung injury. We measured lactate concentrations across the lung and lung injury scores (LIS) in two groups of patients. Group 1 consisted of nine patients with acute lung injury (LIS > or = 2.0) and elevated lactate concentrations (> 2.0 mmol/L). Group 2 contained 12 patients with no acute lung injury (LIS scores < or = 1.5), with or without increased lactate concentrations. Simultaneous measurements of plasma lactate and blood gases were obtained from indwelling arterial and pulmonary artery catheters. Measurements of cardiac output were also obtained. Lactate measurements were done using a lactate analyzer (YSI; Yellow Springs, Ohio). For each patient with acute lung injury and hyperlactatemia, an arterial-venous lactate gradient existed demonstrating release of lactate by the lung. This gradient persisted after correction for changes in hemoconcentration across the lung. The lactate gradient across the lung was 0.4 +/- 0.2 mmol/L for group 1 vs 0.05 +/- 0.1 mmol/L for group 2 (p = 0.001). This corresponded to a mean pulmonary lactate flux of 231.3 +/- 211.3 vs 5.0 +/- 37.2 mmol/h (p = 0.001). The lactate flux and the arterial-venous lactate difference correlated with LIS both for the entire sample and for the subgroup with hyperlactatemia (r = 0.69, p < 0.01). Pulmonary lactate flux was not related to arterial lactate levels (r = 0.25). In patients with acute lung injury and hyperlactatemia, the lung is a major source of lactate and lactate flux correlates with LIS. This lactate flux could explain some of the hyperlactatemia seen in sepsis.

Ischemic preconditioning in cardiac surgery: A word of caution

Objective: Ischemic preconditioning is now established as an effective means of reducing infarct size. However, it remains uncertain whether preconditioning can improve the myocardial protection afforded by cardioplegia. The present study was designed to address this issue. Methods: After the institution of cardiopulmonary bypass, 10 patients were preconditioned with 3 minutes of aortic crossclamping followed by 2 minutes of reperfusion before the onset of retrograde continuous warm cardioplegic arrest. Ten case-matched patients served as controls. Three blood samples were drawn simultaneously from the radial artery and the coronary sinus before bypass, at the end of the 5-minute preconditioning protocol or after 5 minutes of bypass in control patients, and at the end of cardioplegic arrest. These samples were assayed for creatine kinase MB isoenzyme and lactate. Right atrial biopsy specimens taken at the same time points were processed by Northern blotting for the expression of messenger ribonucleic acid of both c- fos and heat shock protein 70. Results: At the end of arrest, the release of creatine kinase MB from the myocardium was markedly greater in preconditioned patients than in the controls. The transmyocardial lactate gradient was shifted toward production in the preconditioned group (+0.22 ± 0.13 mmol/L) and toward extraction in the control group (-0.06 ± 0.21 mmol/L). Molecular biology data did not suggest a protective effect of preconditioning. There were no clinical adverse events related to preconditioning. Conclusions: Preconditioning does not enhance cardioplegic protection and might even be deleterious. These results do not dismiss its use in cardiac operations. They rather emphasize the need for identifying pharmacologic mediators that could safely and effectively duplicate the cardioprotective effects of ischemic preconditioning. (J THORAC CARDIOVASC SURG 1996;112:1378-86)

Scalp blood lactate: a new test strip method for monitoring fetal wellbeing in labour.

To determine fetal scalp blood lactate with a new test strip method in parturients with normal and abnormal cardiotocograms during labour and to describe the relation to maternal lactate, fetal scalp blood pH, cord artery lactate and acid-base balance. Labour wards at the University Hospitals of Huddinge and Lund and at the County Hospital of Ostersund, Sweden. Fetal scalp blood was sampled for lactate (n = 269) and pH (n = 285) determination in 177 parturients with abnormal intrapartum CTG. Lactate and pH were also analysed in a group of 64 women with normal pregnancies and with a reactive fetal heart rate tracing prior to sampling of fetal scalp blood. At fetal blood sampling lactate was also determined in maternal capillary blood, while at birth lactate and acid-base balance in cord artery blood was performed in almost all cases. Medians and percentiles (lactate and acid-base balance). Correlation between fetal scalp blood lactate (dependent) and scalp blood pH, cord artery blood lactate and acid-base parameters and labour time prior to fetal blood sampling. In the group with abnormal cardiotocograms, fetal scalp and umbilical artery blood lactate and acid-base parameters differed significantly from the same parameters in the normal group. The fetal-maternal lactate gradient changed from negative in the normal group to positive in the fetal distress group. Multiple regression analysis, with scalp lactate as the dependent parameter, revealed a significant correlation with fetal scalp blood pH (P < 0.001) and umbilical artery lactate (P < 0.01). Intrapartum scalp blood lactate was significantly correlated with pH and cord artery lactate. The results indicate that increased lactate levels in fetal blood sampling describes fetal lactacidosis. The new disposable test strip requiring only 5 microliters of blood for lactate determination may be better than traditional methods for monitoring fetal wellbeing in labour.

Lactate and H+ uptake in inactive muscles during intense exercise in man.

1. The present study examined how uptake of lactate and H+ in resting muscle is affected by blood flow, arterial lactate concentration and muscle metabolism. 2. Six males subjects performed intermittent arm exercise in two separate 32 min periods (Part I and Part II) and in one subsequent 20 min period in which one leg knee-extensor exercise was also performed (Part III). The exercise was performed at various intensities in order to obtain different steady-state arterial blood lactate concentrations. In the inactive leg, femoral venous blood flow (draining about 7.7 kg of muscles) was measured and femoral arterial and venous blood was collected frequently. Biopsies were taken from m. vastus lateralis of the inactive leg at rest and 10 and 30 min into both Part I and Part II as well as 10 min into recovery from Part II. 3. The arterial plasma lactate concentrations were 7, 9 and 16 mmol l-1 after 10 min of Parts I, II and III, respectively, and the corresponding arterial-venous difference (a-vdiff) for lactate in the resting leg was 1.3, 1.4 and 2.0 mmol l-1. The muscle lactate concentration was 2.8 mmol (kg wet wt)-1 after 10 min of Part I and remained constant throughout the experiment. During Parts I and II, a-vdiff lactate decreased although the arterial lactate concentration and plasma-muscle lactate gradient were unaltered throughout each period. Thus, membrane transport of lactate decreased during each period. 4. Blood flow in the inactive leg was about 2-fold higher during arm exercise compared to the rest periods, resulting in a 2-fold higher lactate uptake. Thus, lactate uptake by inactive muscles was closely related to blood flow. 5. Throughout the experiment a-vdiff for actual base excess and for lactate were of similar magnitude. Thus, in inactive muscles lactate uptake appears to be coupled to the transport of H+.

Tissue oxygenation with graded dissolved oxygen delivery during cardiopulmonary bypass

Background: Intravascular perfluorochemical emulsions together with a high oxygen tension may increase the delivery of dissolved oxygen to useful levels. The hypothesis of this study is that increasing the dissolved oxygen content of blood with incremental doses of a perfluorochemical emulsion improves tissue oxygenation during cardiopulmonary bypass in a dose-related fashion. Methods and Results: Oxygen utilization was studied in a profoundly anemic canine model of hypothermic cardiopulmonary bypass. Forty-two dogs (mean ± standard error of the mean). Cardiopulmonary bypass was begun and resulted in a hematocrit of 9.4% + 0.6%. A standard primng solution was used in the control group ( n = 12), and the test groups received 1.35 gm perfluorochemical · kg -1 ( n = 10 dogs), or 5.4 gm perfluorochemical · kg -1 ( n = 10 dogs), 2.7 gm perfluorochemical · kg -1(n = 10 dogs) through the venous return cannula. Each animal underwent a series of randomized pump flows (0.25,0.5, 1.0, 1.5, 2.0, and 3.0 L · min -1 · m -2 ) at 32° C. After the randomized flows were completed at 32° C, the temperature was raised to 38° C and cardiopulmonary bypass was discontinued. Mortality from cardiac failure on separation from cardiopulmonary bypass was 42% in the control group and 20% in perfluorochemical-treated groups. The mean perfluorochemical dose was higher in surviviors than in nonsurvivors (2.9 + 0.4 versus 1.3 + 0.5 gm perfluorochemical · kg -1; p < 0.05). No differences in oxygen consumption or transbody lactate gradient were found between groups during cardiopulmonary bypass. Analysis of mixed venous oxygen tension (a surrogate measure for tissue oxygenation) as a function of cardiopulmonary bypass flow normalized to body surface area showed that the control group had significantly lower mixed venous oxygen tension ( p < 0.05) than the perfluorochemical emulsion-treated groups. Furthermore, the differences were related to the perfluorochemical emulsion dose. These differences in mixed venous oxygen tension continued after termination of cardiopulmonary bypass. The coronary sinus oxygen tension and cardiac arterial-venous oxygen content differences during and after cardiopulmonary bypass were similar among the control and perfluorochemical emulsion-treated animals. Dissolved oxygen consumption during and after cardiopulmonary bypass was calculated. Dissolved oxygen consumption increased in the perfluorochemical-treated animals in a perfluorochemical dose-related manner and was significantly higher in perfluoro-chemical-treated animals than in the control animals ( p < 0.05). Conclusions: Graded increases in mixed venous oxygen tension during cardiopulmonary bypass were observed in response to graded increases in the dissolved oxygen delivery. These data suggest that enhancing oxygenation with perfluorochemical-dissolved oxygen is an effective temporary substitute for the use of hemoglobin-bound oxygen during cardiopulmonary bypass. Perfluorochemical-dissolved oxygen may be particularly beneficial in the setting of multiple hypoxic stresses. (J T HORAC C ARDIOVASC S URG 1995;110: 774-85) J T HORAC C ARDIOVASC S URG 1995;110:1-85.

Myocardial metabolic changes during reperfusion of ventricular fibrillation: a 31P nuclear magnetic resonance study in swine.

Myocardial metabolic requirements during reperfusion of ventricular fibrillation are poorly understood. The objective of this study was to determine if controlled reperfusion after a clinically relevant global ischemia period of 10 mins was sufficient to prevent or reverse myocardial ischemia as indicated by changes in myocardial high energy phosphates, myocardial intracellular pH, and great cardiac vein lactate. Prospective laboratory study with controlled reperfusion. Research laboratory at a university medical center. Five swine weighing 19 +/- 3 kg. Ten minutes of nonperfused ventricular fibrillation followed by reperfusion with cardiopulmonary bypass (flow 30 mL/kg/min) for 50 mins. Myocardial adenosine triphosphate (ATP), phosphocreatine, and intracellular pH were determined using in vivo 31P nuclear magnetic resonance. Myocardial blood flow, measured by 15-mu radiolabeled microspheres, was significantly increased above baseline during reperfusion. Phosphocreatine was depleted during the 10 mins of nonperfused ventricular fibrillation, but recovered to 122 +/- 18% of baseline with reperfusion and was 112 +/- 18% at 60 mins (p < .005). ATP concentrations decreased to 51 +/- 16% of baseline after 10 mins of nonperfused ventricular fibrillation, improved to 67 +/- 9% of baseline with early reperfusion, and were 65 +/- 9% of baseline at 60 mins (p < .02). Myocardial intracellular pH improved from 6.11 +/- 0.18 after 10 mins of nonperfused ventricular fibrillation, to 6.89 +/- 0.20 with early reperfusion, and then decreased to 6.85 +/- 0.35 at 60 mins ventricular fibrillation (p < .001). Despite myocardial blood flows higher than baseline during the reperfusion period, great cardiac vein/aortic lactate gradient increased over the reperfusion period. Prolonged reperfusion with supranormal myocardial blood flow does not restore normal myocardial aerobic metabolism in the fibrillating myocardium after a 10-min nonperfused ventricular fibrillation period.

Emprego de uma nova emulsão de perfluorocarbonos (OxygentMR) em circulação extracorpórea: estudo experimental em cães

Testou-se uma nova emulsão de perfluorocarbonos (OxygentMR, Alliance Pharmaceutical, San Diego, CA 92121, EUA) em circulação extracorpórea (CEC) com hipotermia de 32ºC e hematócrito de 12%. Estudaram-se 42 cães, 12 dos quais não receberam a droga e serviram de controle (Grupo 1), enquanto os demais constituíram 3 grupos de 10 animais cada, tratados com doses de Oxygent de 1,5 ml/kg (Grupo 2), 3 ml/kg (Grupo 3) e 6 ml/kg (Grupo 4) as quais geraram fluorocritos de, respectivamente, 1 %, 2% e 3%. Foram analisadas variáveis do metabolismo do oxigênio (O2) em 6 diferentes fluxos de perfusão (Q), ordenados ao acaso. Reaqueceram-se os cães, interrompeu-se a CEC e acompanharam-se os animais por 1 hora. Diferenças intergrupos foram analisadas pelo teste das médias dos quadrados mínimos e pelo teste de Duncan, considerando-se significantes os valores de p< 0,05. Embora algo maiores no Grupo 4, a pressão parcial bem como o conteúdo arterial de oxigênio (CaO2) foram estatisticamente semelhantes ao grupo controle. A pressão parcial de O2 no sangue venoso misto (PvO2) do Grupo 4, em função do Q, mostrou-se significativamente maior (p < 0,03) que a do grupo controle, conquanto isto não tenha se repetido ao ser analisada em função da oferta tecidual de O2 . Também não houve diferença quanto ao consumo de O2 total e dissolvido, nem quanto aos gradientes sistêmico e miocárdico de lactato, porém a maior dose da emulsão (Grupo 4) expressa efeito dose-dependente benéfico, ainda que de natureza especulativa, do Oxygent sobre o metabolismo do oxigênio.

Tuberculous Peritonitis: Diagnostic Value of Ascitic Fluid pH and Lactate

The analytical pattern of ascitic fluid in peritoneal tuberculosis is frequently similar to that found in other causes of ascites. The diagnostic value of the ascitic fluid pH and lactate in cases of tuberculous peritonitis has not yet been established. Ascitic fluid pH, lactate, total proteins, cell count, lactate dehydrogenase, glucose, and their blood-ascitic gradients were determined in 10 patients with tuberculous peritonitis (group I). These results were compared with those obtained from 40 patients with cirrhotic sterile ascites (group II), 16 patients with spontaneous bacterial peritonitis (group III), and 18 patients with malignant ascites (group IV). A decreased pH and an elevated lactate level in ascitic fluid were found in patients in group I in comparison with those in group II (p < 0.001). No significant differences were found between group I and groups III and IV. The arterial blood-ascitic fluid pH gradient was more than 0.10 (p < 0.001), and the ascitic fluid-serum lactate gradient was greater than 15 mg/dl (p < 0.001) in group I when compared with group II. No significant differences were found between group I and groups III and IV. Ascitic fluid pH and lactate are useful markers in differentiating tuberculous peritonitis from cirrhotic sterile ascites. However, these variables lack specificity, as they are also decreased and increased, respectively, in cases of malignant ascites and spontaneous bacterial peritonitis.

Lactate transport mechanisms at apical and basolateral membranes of bovine retinal pigment epithelium

The isolated bovine retinal pigment epithelium actively transports lactate from the apical to the basal bath. Net short-circuit [14C]lactate flux in 20 mM lactate was 0.46 +/- 0.09 mu eq.cm-2.h-1 (n = 8). In open circuit, with a physiological lactate gradient, net [14C]lactate flux was 0.66-1.31 mu eq.cm-2.h-1 (n = 3). Lactate in the apical bath caused intracellular acidifications that were saturable, apparently stereospecific, and reduced in magnitude by several H-lactate cotransport inhibitors. In the basal bath, lactate caused intracellular alkalinizations that were dependent on the presence of Na. In short circuit, 20 mM lactate in both baths reversed the direction of net transepithelial 22Na transport from secretion to absorption, suggesting the presence of basolateral Na-lactate cotransport moving lactate out of the cells. Outwardly directed Na-lactate cotransport requires a lactate:Na stoichiometry > 1.4:1, consistent with the coupled movement of Na, lactate, and net negative charge across the basolateral membrane. Intracellular microelectrode recordings showed that basal lactate hyperpolarized and apical lactate depolarized the basolateral membrane. For lactate absorption, this is a novel arrangement of membrane proteins:luminal H-lactate cotransport and serosal electrogenic Na:(n)lactate cotransport. Lactate transport across the retinal pigment epithelium may play an important role in regulating retinal metabolism and subretinal space volume and composition.

Duration of asystolic reperfusion and reperfusate electrolyte composition influence postcardioplegia ventricular fibrillation

The conditions of postcardioplegia reperfusion that influence cardiac electrophysiologic recovery have not yet been fully elucidated. Studies of postcardioplegia electrophysiologic recovery and reperfusion-induced arrhythmias, particularly reperfusion-induced ventricular fibrillation, are useful for improving our understanding of reperfusion injury since reperfusion-induced arrhythmias are sensitive indicators for reperfusion injury. The purpose of this study was to determine the effects of asystolic reperfusion and reperfusate electrolyte composition on postcardioplegia electrophysiologic recovery of the heart. The hypothesis tested is that the duration of asystolic reperfusion produced by a hyperkalemic reperfusate is a primary determinant for the return of cardiac electrical activity without reperfusion-induced ventricular fibrillation and that reperfusion with a hypocalcemic-hyperkalemic solution further reduces the prevalence of reperfusion-induced ventricular fibrillation by limiting myocyte calcium exposure during initial postischemic recovery. Fifty-six pigs were supported by cardiopulmonary bypass and subjected to identical conditions of hypothermic cardioplegic arrest. Reperfusion was initiated with unmodified pump blood, a hypocalcemic-normokalemic cardioplegic solution, a hyperkalemic-normocalcemic cardioplegic solution, or a hyperkalemic-hypocalcemic cardioplegic solution. The hyperkalemic-normocalcemic solution was administered at a dose of 500 ml/m2 or 1500 ml/m2. The hyperkalemic-hypocalcemic and hypocalcemic-normokalemic solutions were given only at a dose of 500 ml/m2. All cardioplegic reperfusion solutions were followed by infusion of unmodified pump blood for the remainder of the 15-minute period of controlled reperfusion. Reperfusion-induced ventricular fibrillation was less prevalent in the high-dose hyperkalemic solution group (4/12) than in the low-dose hyperkalemic solution (9/10) or unmodified pump blood (12/12) groups (p < 0.05). The transmyocardial lactate gradient at the time of initial postreperfusion electrical activity was positive (0.21 +/- 0.04 mmol/L) in the high-dose hyperkalemic group and negative (-0.05 +/- 0.09 mmol/L) in the low-dose hyperkalemic group (p < 0.05). Fibrillation was less prevalent in the hypocalcemic-hyperkalemic group (8/12) than in the other groups reperfused with cardioplegic solution at a dose of 500 ml/m2 (hypocalcemic-normokalemic, 10/10; hyperkalemic-normocalcemic, 9/10) or in the group reperfused with unmodified pump blood (12/12) (p < 0.05, hypocalcemic-hyperkalemic group versus other reperfusate groups). Reperfusion-induced ventricular fibrillation is an indicator of reperfusion injury, and in this study the conditions of reperfusion influenced the prevalence of reperfusion-induced ventricular fibrillation. Recovery of aerobic metabolism during hyperkalemia-induced asystolic reperfusion was associated with a lower prevalence of reperfusion-induced ventricular fibrillation. Combining hypocalcemia with hyperkalemia decreased the prevalence of reperfusion-induced ventricular fibrillation.

Lactate and H+ effluxes from human skeletal muscles during intense, dynamic exercise.

1. Lactate and H+ efflux from skeletal muscles were studied with the one-legged knee extension model under conditions in which blood flow, arterial lactate and the muscle-blood lactate concentration gradient were altered. Subjects exercised one leg twice to exhaustion (EX1, EX2), separated by a 10 min recovery and a period of intense intermittent exercise. After 1 h of recovery the exercise protocol was repeated with the other leg. Low-intensity exercise was performed with one leg during the recovery periods, while the other leg was passive during its recovery periods. 2. Prior to, and immediately after, EX1 and EX2 and then 3 and 10 min after EX1, a biopsy was taken from the vastus lateralis of the exercised leg for lactate, pH, muscle water and fibre-type determinations. Measurements of leg blood flow and venous-arterial differences for lactate (whole blood and plasma), pH, partial pressure of CO2 (PCO2), haemoglobin, saturation and base excess (BE) were performed at the end of exercise and regularly during the recovery period after EX1. 3. The lactate release was linearly related (r = 0.96; P < 0.05) to the muscle lactate gradient over a range of muscle lactate from 0 to 45 mmol (kg wet wt)-1. The muscle lactate transport was evaluated from the net femoral venous-arterial differences (V-Adiff) for lactate. This rose with increases in the muscle lactate gradients, but as the gradient reached higher levels the V-Adiff lactate responded less than at smaller gradients. Thus, the lactate transport over the muscle membrane appears to be partly saturated at high muscle lactate concentrations. 4. The percentage of slow twitch (%ST) fibres was inversely related to the muscle lactate gradient, but it was not correlated to the lactate release at the end of the exercises. In spite of a significantly higher blood flow during active recovery, the lactate release was the same whether the leg was resting or performed low-intensity exercise in the recovery periods. In several other conditions the muscle lactate and H+ gradients would have predicted that the V-Adiff lactate would have been greater than it actually was. Thus, a variety of factors affect muscle lactate transport, including arterial lactate concentration, muscle perfusion, muscle contraction pattern and muscle morphology. 5. The muscle and femoral venous pH declined during EX1 to 6.73 and 7.14-7.15, respectively, and they increased to resting levels during 10 min of either passive or active recovery.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional differentiation and primary metabolism of mouse mammary epithelial cells in extended-batch and hollow-fiber culture

Growth, expression of functional differentiation (as characterized by synthesis and secretion of milk proteins), and primary metabolism were studied for a mouse mammary epithelial cell line, COMMA-1D, in extended-batch and hollow-fiber reactor cultures. Batch cultures were performed on Costar polycarbonate membrane inserts, allowing basal and apical exposure to medium. Protein production was induced in both batch and hollow-fiber cultures in hormone-supplemented medium. In batch cultures, high levels of protein production and secretion were maintained for 18 days. Once differentiation was induced, the rate of deinduction was low, even in medium containing epidermal growth factor (EGF) and serum; cells continued to express and secrete proteins for at least 12 days after prolactin and hydrocortisone were removed. Cells in both batch and hollow-fiber cultures were highly glycolytic and exhibited low rates of glutaminolysis. In batch culture on membrane inserts, cells showed polarized metabolism between the apical and basal side, maintaining significant gradients of glucose and lactate. Medium hormonal composition and subsequent differentiation affected both glucose uptake and lactate yield for COMMA-1D in batch culture.

Glyconeogenic and oxidative lactate utilization in skeletal muscle.

In this article we present a synthesis of recent information concerning the fate of lactate in skeletal muscle. This is important since lactate is continuously produced by skeletal muscle at rest and at all levels of exercise. Therefore, the disposal of lactate as an 'intermediary' metabolite is discussed. The two primary fates of lactate in skeletal muscle are (1) oxidation and (2) glycogen synthesis (glyconeogenesis). From recent evidence it seems relatively clear that glycogen formation in muscle is primarily dependent on glucose, although in fast twitch muscles a considerable proportion of lactate can account for muscle glycogen formation, especially immediately after exercise when circulating lactate levels are elevated. Exactly how lactate is converted to glycogen is not known yet, but an extramitochondrial pathway that is divergent from the hepatic gluconeogenic pathway seems likely. Oxidation of lactate is quantitatively the most important means of disposing of lactate, whether in exercising or nonexercising muscle. The lactate gradient between muscle and blood may be an important factor dictating whether lactate is taken up or released by muscle, independent of whether the muscle is active or not. Finally a novel role for epinephrine is considered that may be important for the mitochondrial oxidation of lactate.

Is fetal acidosis in the human fetus maternogenic during labor? A reanalysis

The purpose of this study was to investigate whether maternogenic fetal acidosis can occur at the time of labor and delivery and to evaluate the extent of the possible maternal contribution to fetal acidosis. We have therefore determined fetal and maternal lactate concentrations and acid-base status under various conditions in 589 women at the end of gestation and during labor. The results show that metabolic acidosis develops in all fetuses because of increased production of lactic acidosis is primarily of fetal origin: 1) the umbilical arteriovenous lactate differences were positive and large in steady-state conditions as well as in depressed newborns; 2) the conditions that could produce a net transfer of lactate from the mother to the fetus, namely a positive maternofetal gradient of lactate and proton, were rarely observed; and 3) the correlation between fetal and maternal lactate levels was very weak, with regression coefficients decreasing from near steady-state conditions to acute stress conditions, indicating that the increase in lactate in the fetus and mother occurs independently. This correlation indicates also that increased maternal lactate production under conditions of labor and delivery can make a contribution by affecting the rate of net transfer from fetus to mother. This is possible in approximately 6% of the fetuses.