scholarly journals The stimulation of mitochondrial pyruvate carboxylation after dexamethasone treatment of rats

1984 ◽  
Vol 219 (1) ◽  
pp. 107-115 ◽  
Author(s):  
A D Martin ◽  
E H Allan ◽  
M A Titheradge
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Active Form ◽  
Specific Inhibitor ◽  
Hormone Treatment ◽  
Dexamethasone Treatment ◽  
Pyruvate Metabolism ◽  
Glucocorticoid Treatment ◽  
Pyruvate Carboxylation ◽  
Liver Homogenates ◽  
Stimulation Of

Treatment of rats for 3 h with dexamethasone was shown to stimulate both pyruvate carboxylation and decarboxylation in the subsequently isolated mitochondria. The effect of hormone treatment on pyruvate carboxylation was also apparent in liver homogenates assayed within minutes of killing the animal and was independent of the temperature at which the assay was performed, suggesting that it was not an artifact of the mitochondrial preparation procedure. The stimulation of both aspects of pyruvate metabolism in the intact organelle was independent of the induction of either pyruvate carboxylase or pyruvate dehydrogenase. Similarly, there was no change in the percentage of pyruvate dehydrogenase in the active form, indicating that the effect of steroid treatment on pyruvate oxidation was not via changes in the degree of phosphorylation of the enzyme. Adrenalectomizing the animals for a period of 14 days before the experiment had no effect on either parameter. Glucocorticoid treatment of the animals increased the rate of pyruvate uptake into the mitochondria, as measured by the titration of pyruvate metabolism with alpha-cyano-4-hydroxycinnamate, a specific inhibitor of the pyruvate translocator. It also increased the intramitochondrial concentrations of acetyl-CoA and ATP and led to an elevated [ATP]/[ADP] ratio within the mitochondria. It is suggested that both enzymes of pyruvate metabolism exist in the mitochondria under considerable restraint and that glucocorticoids act to relieve this restraint by alterations in substrate supply and the intramitochondrial concentrations of effector molecules.

Glucocorticoid inhibition of Na-SO4 transport by chick renal brush-border membranes

1989 ◽  
Vol 256 (6) ◽  
pp. R1176-R1183 ◽  
Author(s):  
J. L. Renfro ◽  
N. B. Clark ◽  
R. E. Metts ◽  
M. A. Lynch
Keyword(s):  
Brush Border ◽  
Renal Tubule ◽  
Hormone Treatment ◽  
Sulfate Transport ◽  
Dexamethasone Treatment ◽  
Glucocorticoid Treatment ◽  
Renal Brush Border Membranes ◽  
Electrical Gradient ◽  
22Na Uptake ◽  
Renal Brush Border

To examine the effect of glucocorticoids on sulfate transport by the chick (domestic Gallus gallus) renal tubule we dosed 3-wk-old animals with 60 micrograms dexamethasone/100 g body wt at 24 and 6 h before isolation of renal brush-border (BBM) and basolateral membranes (BLM). Dexamethasone treatment significantly reduced Na-dependent sulfate transport by BBM and had no effect in paired membranes on bicarbonate, proton, or electrical gradient-driven sulfate transport. The glucocorticoid treatment had no statistically significant effect on HCO3-SO4 exchange in the BLM. Kinetic analysis of the dexamethasone effect on the Na-SO4 transport process showed that apparent Vmax was significantly decreased to almost one-half that seen in controls (from 676 to 348 pmol.mg protein-1.5 s-1). The Km in control BBM was 0.40 +/- 0.095 mM and was not significantly different in dexamethasone-treated membranes (0.53 +/- 0.094 mM). To determine whether the dexamethasone-induced decrease in Na-SO4 transport by BBM was indirectly caused by stimulation of Na-H exchange and more rapid dissipation of the initial Na gradient used to drive sulfate uptake, we examined the effect of 0.1 mM amiloride on Na-SO4 uptake by BBM. With amiloride present, dexamethasone treatment caused Vmax to significantly drop from 1,102 to 660 pmol.mg protein-1.5 s-1. Amiloride had no statistically significant effect on the Km. The extent to which amiloride increased Na-SO4 transport and blocked 22Na uptake by BBM did not appear to be related to hormone treatment. The data indicate that glucocorticoids may participate in the regulation of sulfate excretion.

scholarly journals Stimulation of mitochondrial functions by glucagon treatment. Evidence that effects are not artifacts of mitochondrial isolation

1983 ◽  
Vol 210 (3) ◽  
pp. 819-827 ◽  
Author(s):  
C B Jensen ◽  
F D Sistare ◽  
H C Hamman ◽  
R C Haynes
Keyword(s):  
Phosphoenolpyruvate Carboxykinase ◽  
Treatment Result ◽  
Direct Result ◽  
Differential Centrifugation ◽  
Hormonal Stimulation ◽  
Pyruvate Carboxylation ◽  
Mitochondrial Functions ◽  
Liver Homogenates ◽  
Citrulline Synthesis ◽  
Stimulation Of

(1) Activation of rat liver mitochondrial functions following glucagon treatment was demonstrated in mitochondria that had not been isolated by the conventional technique of differential centrifugation and washing in sucrose solutions. Crude liver homogenates in 0.3 M-sucrose or 0.15 M-KCl prepared from rats treated with glucagon showed stimulation of State-3 and uncoupled respiration, carboxylation of pyruvate, and citrulline synthesis comparable with those previously reported in isolated mitochondria. (2) During the isolation procedure of mitochondria the hormonal stimulations of pyruvate carboxylation and citrulline formation were shown not to be enhanced by sequential washing. (3) Mitochondria isolated from glucagon-treated rats by differential centrifugation and washing in 0.3 M-mannitol/1 mM-EGTA, pH 7.0, exhibited a mean rate of citrulline synthesis that was greater than twice that of the control. Liver homogenates prepared in 0.3 M-sucrose or 0.3 M-mannitol showed identical rates of State-3 respiration and percentage stimulations of respiration by glucagon treatment. (4) Addition of glucagon led to a rapid accumulation of malate and aspartate and decreased the amounts of glutamate and citrate in isolated hepatocytes incubated with L-lactate. When gluconeogenesis was inhibited at the phosphoenolpyruvate carboxykinase (EC 4.1.1.32) reaction these phenomena were accentuated, lending support to the interpretation that they are the direct result of stimulation of carboxylation and oxidation reactions in the mitochondria. These results do not support the proposal [Siess, Fahimi & Wieland (1981) Hoppe-Seyler's Z. Physiol. Chem. 362. 1643-1651] that the mitochondrial effects of glucagon treatment result from a stabilization of mitochondria to detrimental effects of sucrose during their isolation. (5) The mean hormonal stimulation of pyruvate carboxylation in mitochondria isolated in 0.3 M-sucrose was shown to be approx. 2.5-fold when assayed either at 37 degrees C or 25 degrees C. In contrast, on the basis of similar experiments, Siess et al. (1981) concluded that the effects of glucagon on hepatic mitochondria are not characteristic of a true hormonal stimulation. Our data indicate this conclusion to be unjustified.

Parallel stimulation by Ca2+ of inotropism and pyruvate dehydrogenase in perfused heart

1984 ◽  
Vol 247 (1) ◽  
pp. C45-C52 ◽  
Author(s):  
R. Bunger ◽  
B. Permanetter
Keyword(s):  
Pyruvate Dehydrogenase ◽  
Work Performance ◽  
Channel Blocker ◽  
Pyruvate Dehydrogenase Complex ◽  
Active Form ◽  
Cardiac Mechanics ◽  
Energy Utilization ◽  
Perfused Heart ◽  
Pyruvate Oxidation ◽  
Stimulation Of

The effects of extracellular Ca2+ (0.375-;3.75 mM) on pyruvate oxidation and active form of the pyruvate dehydrogenase complex (PDCa) were quantitated in perfused guinea pig hearts in relation to inotropism, hydraulic work performance, and myocardial oxygen uptake (MVO2). The effects of afterload and norepinephrine (NE), alone or combined with the Ca2+ channel blocker D 600, were also examined. Hearts utilized 1-5 mM pyruvate in presence of 5 mM DL-3-hydroxybutyrate as substrates. Pyruvate oxidation and MVO2 increased essentially in parallel regardless of whether inotropism and energy metabolism were stimulated by increasing the Ca2+ concentration [( Ca2+]), the NE concentration [( NE]), or the afterload. PDCa activity was also directly related to [Ca2+], [NE], and afterload, respectively. Elevated [Ca2+] failed, however, to stimulate pyruvate oxidation and PDCa activity when MVO2 was held constant by an appropriate decrease in afterload at constant preload. Compound D 600, theophylline, and dibutyryl adenosine 3',5'-cyclic monophosphate also produced parallel alterations in cardiac mechanics, pyruvate oxidation, and MVO2. The striking proportionality between PDCa parameters, MVO2, and cardiac mechanics during the various alterations in cellular Ca2+ metabolism seemed to suggest that the observed Ca2+ stimulation of the PDC might be mainly secondary to increased myocardial energy utilization and myocyte respiration. Evidence for an additional direct effect of Ca2+ on the intact PDC system was not obtained.

scholarly journals Stimulation of mitochondrial pyruvate metabolism and citrulline synthesis by dexamethasone. Effect of isolation and incubation media

1984 ◽  
Vol 222 (2) ◽  
pp. 379-387 ◽  
Author(s):  
A D Martin ◽  
M A Titheradge
Keyword(s):  
Adenine Nucleotides ◽  
Isolation Procedure ◽  
Mitochondrial Matrix ◽  
Pyruvate Metabolism ◽  
Pyruvate Carboxylation ◽  
Matrix Volume ◽  
The Matrix ◽  
Citrulline Synthesis ◽  
Stimulation Of

Hepatic mitochondria isolated in 0.3 M-sucrose or 0.3 M-mannitol from rats treated for 3h with dexamethasone displayed stimulated rates of pyruvate carboxylation and decarboxylation and citrulline synthesis when compared with organelles from control animals. Mitochondria isolated in mannitol also displayed elevated rates of pyruvate carboxylation and decarboxylation when compared with those isolated in sucrose, and this stimulation was shown to be independent of the lengthy isolation procedure. Citrulline synthesis proceeded at similar rates in mitochondria isolated in either sugar. The concentration of exchangeable adenine nucleotides was identical in mitochondria isolated in sucrose or mannitol, suggesting that those prepared in the former sugar are not more permeable to metabolites than those prepared in the latter. The matrix volume of mitochondria isolated in mannitol was greater than that of mitochondria isolated in sucrose, and the effect of mannitol on pyruvate metabolism was mimicked by swelling the organelles in hypo-osmotic sucrose. Measurements of the extra-matrix volume by using [14C]sucrose or [14C]mannitol suggest that mannitol can permeate mitochondria to a greater extent than can sucrose. The possibility that mannitol elicits its effect by entering the mitochondrial matrix and so initiating swelling is discussed.

Glucocorticoid effects on respiration and metabolism by rat liver homogenates

1962 ◽  
Vol 202 (2) ◽  
pp. 343-346 ◽  
Author(s):  
Dennis D. Goetsch ◽  
L. E. McDonald
Keyword(s):  
Lactic Acid ◽  
Oxygen Uptake ◽  
Rat Liver ◽  
Inorganic Phosphate ◽  
Chronic Administration ◽  
Glucocorticoid Treatment ◽  
Carbohydrate Utilization ◽  
Protein Levels ◽  
Liver Homogenates ◽  
And Control

The effects of glucocorticoid administration on oxygen uptake, glucose and glycogen disappearance, lactic acid formation, and inorganic phosphate and protein levels in rat liver homogenates have been studied. A single injection of hydrocortisone, prednisolone, or 9 α-fluoroprednisolone 5 hr before sacrifice resulted in a highly significant increase in oxygen uptake by rat liver homogenates, whereas chronic administration of prednisolone daily for 7 days caused a marked inhibition in homogenate respiration. Glycolytic rate did not appear to be affected by single injections since endogenous carbohydrate utilization was similar in liver homogenates prepared from control and treated animals. Incubation of liver homogenates under aerobic conditions disclosed that inorganic phosphate levels were decreased in homogenates from corticoid-treated rats, whereas these levels were similar in treated and control liver homogenates incubated under nitrogen. Under anaerobic conditions, liver homogenates from treated rats accumulated lactic acid more rapidly than untreated liver homogenates. Glucocorticoid treatment did not appear to affect protein disappearance since no differences between protein levels in treated and untreated rat liver homogenates were detected following incubation.

scholarly journals The activity of the pyruvate dehydrogenase complex in heart and liver from mice during the development of obesity and insulin resistance

1987 ◽  
Vol 243 (2) ◽  
pp. 549-553 ◽  
Author(s):  
I D Caterson ◽  
L D Astbury ◽  
P F Williams ◽  
M A Vanner ◽  
G J Cooney ◽  
...  
Keyword(s):  
Insulin Resistance ◽  
Pyruvate Dehydrogenase ◽  
Serum Insulin ◽  
Pyruvate Dehydrogenase Complex ◽  
Active Form ◽  
Whole Body ◽  
Acid Oxidation ◽  
Mitochondrial Fatty Acid Oxidation ◽  
Gold Thioglucose ◽  
Mitochondrial Fatty Acid

The amount of pyruvate dehydrogenase in the active form (PDHa) was increased 1.7-fold compared with controls in heart muscle of mice 1 week after induction of obesity with a single injection of gold-thioglucose. At 4 weeks post injection, the amount of PDHa was decreased to 32% of control, a value which was observed in later stages of the obesity syndrome. In contrast, liver PDHa was increased and remained at an increased activity during the development of obesity. Despite normal post-prandial serum insulin contents, liver membrane insulin-receptor numbers were decreased 1 week after gold-thioglucose injection, and there was no change in receptor affinity. The decrease in heart PDHa in the obese animals was reversed by a single dose of 2-tetradecylglycidic acid, but this inhibitor of mitochondrial fatty acid oxidation did not affect liver PDHa in these animals. These early and diverse changes in PDHa argue for a multifactorial aetiology in the development of the whole-body insulin resistance seen in older gold-thioglucose-treated obese animals.

Cholesterol Metabolism and Vitamin B6. III. The Stimulation of Hepatic Cholesterogenesis in the Vitamin B6-Deficient Rat

1971 ◽  
Vol 49 (8) ◽  
pp. 933-935 ◽  
Author(s):  
C. M. Hinse ◽  
P. J. Lupien
Keyword(s):  
Vitamin B6 ◽  
Cholesterol Metabolism ◽  
Krebs Cycle ◽  
Pool Size ◽  
Liver Slices ◽  
Liver Homogenates ◽  
The Difference ◽  
Hepatic Cholesterogenesis ◽  
Stimulation Of

The rate of incorporation of labeled acetate into cholesterol by liver slices of pyridoxine-deficient rats was found to be three times that of control rats; with liver homogenates the difference between the two groups was even greater. Using the CO2 trapping technique, a 30% decrease in the hepatic acetate pool size was observed in pyridoxine-deficient rats and a 20% increase in pair-fed rats. Activity of the Krebs cycle was decreased by a third in the pair-fed rats.

Skeletal muscle pyruvate dehydrogenase activity during maximal exercise in humans

1995 ◽  
Vol 269 (3) ◽  
pp. E458-E468 ◽  
Author(s):  
C. T. Putman ◽  
N. L. Jones ◽  
L. C. Lands ◽  
T. M. Bragg ◽  
M. G. Hollidge-Horvat ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Pyruvate Dehydrogenase ◽  
Maximal Exercise ◽  
Vastus Lateralis ◽  
Active Form ◽  
Lactate Production ◽  
Glycolytic Flux ◽  
Muscle Lactate ◽  
Mitochondrial Oxidation ◽  
Exercise In Humans

The regulation of the active form of pyruvate dehydrogenase (PDHa) and related metabolic events were examined in human skeletal muscle during repeated bouts of maximum exercise. Seven subjects completed three consecutive 30-s bouts of maximum isokinetic cycling, separated by 4 min of recovery. Biopsies of the vastus lateralis were taken before and immediately after each bout. PDHa increased from 0.45 +/- 0.15 to 2.96 +/- 0.38, 1.10 +/- 0.11 to 2.91 +/- 0.11, and 1.28 +/- 0.18 to 2.82 +/- 0.32 mmol.min-1.kg wet wt-1 during bouts 1, 2, and 3, respectively. Glycolytic flux was 13-fold greater than PDHa in bouts 1 and 2 and 4-fold greater during bout 3. This discrepancy between the rate of pyruvate production and oxidation resulted in substantial lactate accumulation to 89.5 +/- 11.6 in bout 1, 130.8 +/- 13.8 in bout 2, and 106.6 +/- 10.1 mmol/kg dry wt in bout 3. These events coincided with an increase in the mitochondrial oxidation state, as reflected by a fall in mitochondrial NADH/NAD, indicating that muscle lactate production during exercise was not an O2-dependent process in our subjects. During exercise the primary factor regulating PDHa transformation was probably intracellular Ca2+. In contrast, the primary regulatory factors causing greater PDHa during recovery were lower ATP/ADP and NADH/NAD and increased concentrations of pyruvate and H+. Greater PDHa during recovery facilitated continued oxidation of the lactate load between exercise bouts.

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