Tissue Concentrations Of Pyruvate Research Articles

Control of d-octopine formation in scallop adductor muscle as revealed through thermodynamic studies of octopine dehydrogenase

Octopine dehydrogenase (OcDH) from the adductor muscle of the great scallop, Pecten maximus (Linné, 1758), catalyses the NADH-dependent condensation of l-arginine and pyruvate to d-octopine, NAD(+) and water during escape swimming and subsequent recovery. During exercise, ATP is mainly provided by the transphosphorylation of phospho-l-arginine and to some extent by anaerobic glycolysis. NADH resulting from the glycolytic oxidation of 3-phosphoglyceraldehyde to 1,3-bisphosphoglycerate is reoxidized during d-octopine formation. In some scallops d-octopine starts to accumulate during prolonged, strong muscular work, whereas in other species d-octopine formation commences towards the end of swimming and continues to rise during subsequent recovery. The activity of OcDH is regulated by a mandatory, consecutive mode of substrate binding in the order NADH, l-arginine and pyruvate, as demonstrated by isothermal titration calorimetry. The first regulatory step in the forward reaction comprises the binding of NADH to OcDH with a dissociation constant K(d) of 0.014±0.006 mmol l(-1), which reflects a high affinity and tight association of the apoenzyme with the co-substrate. In the reverse direction, NAD(+) binds first with a K(d) of 0.20±0.004 mmol l(-1) followed by d-octopine. The binary OcDH-NADH complex associates with l-arginine with a K(d) of 5.5±0.05 mmol l(-1). Only this ternary complex combines with pyruvate, with an estimated K(d) of approximately 0.8 mmol l(-1) as deduced from pyruvate concentrations determined in the muscle of exhausted scallops. At tissue concentrations of pyruvate between 0.5 and 1.2 mmol l(-1) in the valve adductor muscle of fatigued P. maximus, binding of pyruvate to OcDH plays the most decisive role in initiating OcDH activity and, therefore, in controlling the onset of d-octopine formation.

Is subdiaphragmatic aortic cross-clamping a suitable model for spinal cord ischemia/reperfusion injury study in rats?

To evaluate the efficacy of subdiaphragmatic aortic cross-clamping in an experimental model of ischemia/reperfusion injury of the spinal cord in albino rats. Thirty-six male Wistar rats were randomized in two groups (n=18): G-1 (Sham) and G-2 (Ischemia/Reperfusion, I/R). G-2 rats were submitted to 30 min subdiafragmatic aortic cross-clamping. G-1 rats served as controls and were submitted to surgical trauma (laparotomy) without ischemia. Samples (spinal cord and arterial blood) were collected at the end of ischemic period and 10 (T-10) and 20 (T-20) min later in G-2 rats. Sham rats (G-1) samples were collected at the same time-points. Blood and tissue metabolites concentrations of pyruvate, lactate, glucose and medullary adenosine triphosphate (ATP) were assayed. Blood and tissue concentrations of pyruvate and glucose as well as lactate and medullary ATP were not different when comparing G1 to G2. Lactacemia was significantly elevated in G-2 compared with G-1 rats during reperfusion (T-10). Subdiaphragmatic aortic cord cross-clamping is not a suitable rat model for spinal cord ischemia/reperfusion injury study as it does not ensure changes in in vivo tissue metabolites concentrations similar to those found in tissues subjected to ischemia/reperfusion.

Lactate Production, Tissue Distribution, and Elimination following Exhaustive Exercise in Larval and Adult Bullfrogs Rana catesbeiana

The time course following exhaustive exercise of changes in lactate in blood, muscle, skin, kidney, urine, and branchial exhaled water in larval Rana catesbeiana, and in blood and muscle of adult R. catesbeiana, has been investigated. Tissue concentrations of pyruvate, lactate dehydrogenase (LDH) activity, and whole-animal V̇o2 and V̇co2 were also measured. Resting levels of blood and muscle lactate in tadpoles were not significantly different from those of adults. Muscle lactate concentrations, determined immediately following exhaustive exercise, were the same in tadpoles and adults and increased six times above resting levels in both forms. Blood lactate in adults was maximal within 1 min following exercise in adults but did not peak for 30 min in tadpoles. Blood lactate in tadpoles and adults returned to resting values 4 and 6 h, respectively, following exercise. The major difference between tadpoles and adults was thus the time course of blood lactate changes during recovery from exhaustive exercise. In tadpoles, 7% of total lactate produced during exercise was eliminated via the gills (80% of eliminated lactate), skin (13%), and urine (6%). Prevention of gill ventilation (responsible for less than one-half of total oxygen uptake) resulted in a 140% increase in blood and muscle lactate concentration during the first 2 h after exercise. Gill lactate elimination probably is important to acid-base regulation by tadpoles during recovery from exercise. The LDH activity in both larvae and adults can be summarized as follows: muscle ≫ kidney > liver ≫ heart ∼ lung. Muscle concentrations of pyruvic acid decreased following exercise in tadpoles and adults, even though blood pyruvate increased two times and remained elevated for more than 2 h. Pyruvate concentration of kidney and of whole-body homogenates of tadpoles increased two times and five times, respectively, immediately following exhaustive exercise. Low pyruvate and high LDH activity, conditions favoring reconversion of lactate to pyruvate, were thus most evident within the muscle itself. The rapid decrease in muscle lactate following exercise, which was not paralleled by an increase in blood lactate, suggests that reconversion of lactate to pyruvate may occur in muscle. Oxygen uptake remained significantly elevated after exercise for 10 h in tadpoles and 4 h in adults, partially reflecting O₂ consumed in the metabolism of lactate produced during the exercise bout. The respiratory quotient in both stages remained depressed for several hours after exercise, possibly because of acid-base imbalances incurred during and after exercise.

Androgenic control of glycolysis, the pentose cycle and pyruvate dehydrogenase in the rat ventral prostate

Androgenic control of glucose metabolism was studied in the rat ventral prostate. Rats were castrated 48 h, and treated with testosterone 6–24 h before being killed. Glucose utilization was increased 12 h after testosterone, which accounted for the elevated formation of lactate from glucose. The pentose cycle activity, pyruvate oxidation in vitro and the proportion of active pyruvate dehydrogenase in situ were increased 6–12 h after testosterone independently of glucose utilization. Total pyruvate dehydrogenase did not change. Hormonal activation of pyruvate dehydrogenase was not mediated by the changes in the tissue concentrations of pyruvate, ATP and ADP, known to be effectors of the enzyme complex. Inhibition of protein synthesis for 1–2 h led to a decrease in the proportion of active pyruvate dehydrogenase in the prostate of normal, testosterone-maintained rats, whereas total pyruvate dehydrogenase, glucose utilization and the pentose cycle were not affected. Cycloheximide had no effect on glucose metabolism and pyruvate dehydrogenase in testosterone-free castrated rats. Previous studies provided evidence that testosterone increases glucose oxidation by inducing the synthesis of a protein activator with a rapid turnover. The present study suggests that the proposed protein (s) are involved in the hormonal regulation of the interconversion of pyruvate dehydrogenase between its active and inactive forms.

Circulatory and metabolic effects in the brain induced by amphetamine sulphate.

Cerebral circulatory and metabolic effects of amphetamine sulphate (0.25-25 mg.kg-1 i.v. or 5-10 mg.kg-1 i.p.) were studied in anesthetized, paralyzed and artifically ventilated rats. Cerebral blood flow (CBF) was measured with a modification of the Kety and Schmidt (1948) technique, and oxygen consumption (CMRO2) was calculated from CBF and arteriovenous differences in oxygen content. Regional CBF was evaluated from the uptake of 14C-ethanol. Cortical metabolites were analysed following freezing of tissue in situ. Amphetamine administration gave rise to a marked increase in CBF that was doubled following 0.25 mg.kg-1 and increased 4-fold following 15 mg.kg-1. However, such excessive increases in flow were confined to frontoparietal cortical regions, while other cortical or subcortical areas showed more moderate hyperemia. The increase in CBF was unrelated to changes in arterial PCO2, blood pressure, or tissue lactate content. CMRO2 increased by 30% to 95% depending on dose and rat strain used. At all doses employed, amphetamine gave rise to glycogenolysis in cerebral cortex but, in animals studied within the first 30 min after 5 mg.kg-1, or less, the only other changes were increases in glucose-6-phosphate and alpha-ketoglutarate concentrations. When the dose was increased to 15 mg.kg-1, there were moderate increased in lactate concentration and lactate/pyruvate ratio. Sixty min after 5 mg.kg-1 there were increases in tissue concentrations of pyruvate, citric acid cycle intermediates and alanine, as well.

The role of chemical equilibria in organ function

The point is made and illustrated by examples that it is useful in the biochemical analysis of organ function to separate those component processes which require a supply of energy (ATP) from those which occur spontaneously because of the tendency to establish equilibrium. The stoichiometric formation of aspartate and carbamoyl phosphate in the synthesis of urea can be accounted for by the fact that the concentration of aspartate is determined by the equilibrium in the aspartate aminotransferase system. This fixes the hepatic aspartate concentration at about 0.7 m m. Any excess of nitrogen becomes available for the carbamoyl phosphate synthesis reaction, and any aspartate removed by interaction with citrulline is automatically replaced. The glutamate dehydrogenase reaction—as an equilibrium system—working in both directions plays a role in mediating the stoichiometry of carbamoyl phosphate and aspartate. The function of alanine as a nitrogen carrier from peripheral tissues to the liver can be accounted for by the tendency of the alanine aminotransferase in peripheral tissues to move toward equilibrium. Any glutamate formed, especially by transamination from branched-chain amino acids, is bound to form alanine at the given tissue concentrations of pyruvate and α-oxoglutarate. As alanine, in contrast to glutamate, readily passes through cell membranes it is discharged into the circulation. The role of glutamine as a second nitrogen carrier is discussed. In ammonia excretion by the acidotic kidney the main energy requiring process is the excretion of H + ions. The transfer of ammonia and the release of ammonia from glutamine and glutamate can be understood on the basis of equilibrium relations. The main point is the fact that the glutamate dehydrogenase system is at near-equilibrium in renal cortex. Withdrawal of ammonia and a fall of the α-oxoglutarate concentration (due according to Alleyne to increased activity of phosphoenolpyruvate carboxykinase) therefore causes glutamate to be dehydrogenated. Glutamate is an inhibitor of glutaminase and the fall in the glutamate concentration relieves the inhibition. The formation of lactate from alanine in the perfused rat liver or isolated hepatocytes is the result of equilibrium relations in the lactate dehydrogenase and alanine aminotransferase systems. Key factors determining the occurrence of equilibrium reactions are the metabolic concentrations within the cell or cell compartment. The question of how tissue metabolite concentrations may be regulated is discussed.