Glucose inhibits phenobarbital-induced δ-aminolevulinate synthase expression in normal but not in diabetic rat hepatocytes

1996 ◽  
Vol 74 (2) ◽  
pp. 271-281 ◽  
Author(s):  
Cecilia L. Varone ◽  
Eduardo T. Cánepa ◽  
Elena B. C. Llambías ◽  
Moisés Grinstein
Keyword(s):  
Phosphodiesterase Inhibitor ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Diabetic Rat ◽  
Glucose Effect ◽  
Camp Content ◽  
Aminolevulinate Synthase ◽  
Abnormal Metabolism ◽  
Normal Rat ◽  
Mrna Half Life

In the present work, we demonstrate the presence of a glucose inhibitory effect on the phenobarbital-mediated induction of the δ-aminolevulinate synthase mRNA in normal rat hepatocytes, consistent with the results obtained with the δ-aminolevulinate synthase activity previously reported. This "glucose effect" can be prevented by adding cAMP, adenylate cyclase activators, or a phosphodiesterase inhibitor. δ-Aminolevulinate synthase mRNA half-life is not modified in the presence of phenobarbital or glucose. When the same experiments are performed using diabetic cells, no glucose effect is observed, even when the endogenous cAMP content is lowered to normal levels. The results obtained in this study suggest that glucose decreases δ-aminolevulinate synthase biosynthesis by acting at a pretranslational step. Assuming that the glucose effect operates by a repression mechanism exerted by metabolites derived from or related to glucose, the present results may reflect a derangement in the formation of these metabolites as a result of the abnormal metabolism operating in the diabetic state.Key words: glucose, δ-aminolevulinate synthase expression, diabetic rat hepatocytes, phenobarbital, cAMP.

Regulation of phenobarbital-induced ferrochelatase mRNA activity by dibutyryl cAMP and glucose in normal and diabetic rat hepatocytes

1992 ◽  
Vol 70 (1) ◽  
pp. 26-33 ◽  
Author(s):  
Eduardo T. Cánepa ◽  
Marcelo Páez Pereda ◽  
Elena B. C. Llambías ◽  
Moïses Grinstein
Keyword(s):  
Experimental Evidence ◽  
Rat Hepatocytes ◽  
Diabetic Rat ◽  
Dibutyryl Camp ◽  
Glucose Effect ◽  
Normal Cells ◽  
Camp Content ◽  
Normal Rat ◽  
Increased Activity

The induction of ferrochelatase activity by phenobarbital and its potentiation by dibutyryl cAMP assayed in normal rat hepatocytes are associated with increased activity of ferrochelatase mRNA. Glucose inhibits this stimulatory effect. This inhibition can be reversed with increasing concentrations of dibutyryl cAMP. The inducing effect exerted by phenobarbital on the activity of ferrochelatase mRNA in diabetic hepatocytes is greater than that observed in normal cells. This enhanced response in diabetic rat hepatocytes is neither potentiated by adding dibutyryl cAMP nor repressed by glucose. The absence of a glucose effect persists even when the endogenous cAMP content is lowered to normal levels. The results obtained in this study are consistent with those reported in other published studies of ferrochelatase activity. This adds more experimental evidence to support the concept that ferrochelatase is inducible. The results obtained suggest that ferrochelatase is more susceptible to induction with phenobarbital in diabetic rat hepatocytes than in normal rat hepatocytes.Key words: ferrochelatase mRNA activity, phenobarbital, cAMP, glucose, diabetic rat hepatocytes.

Studies on regulatory mechanisms of heme biosynthesis in hepatocytes from normal and experimental-diabetic rats. Role of insulin

1990 ◽  
Vol 68 (6) ◽  
pp. 914-921 ◽  
Author(s):  
Eduardo T. Cánepa ◽  
Elena B. C. Llambías ◽  
Moisés Grinstein
Keyword(s):  
Aminolevulinic Acid ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Inhibitory Effect ◽  
Diabetic Rats ◽  
Significant Inhibition ◽  
Diabetic Rat ◽  
Experimental Conditions ◽  
Cytochrome P 450

In the present work we demonstrate that insulin decreases the phenobarbital-induced activities of δ-aminolevulinic acid synthase and ferrochelatase in isolated hepatocytes from normal and experimental-diabetic rats. Insulin concentrations required to produce significant inhibition in diabetic hepatocytes were higher than in normal cells. Under similar experimental conditions, insulin decreased the basal activities of δ-aminolevulinic acid synthase and ferrochelatase in hepatocytes from normal rats; no inhibitory effect was observed on the basal activity of δ-aminolevulinic acid synthase in hepatocytes from diabetic rats. Cytochrome P-450 content of both normal and diabetic cells was not affected by insulin in absence or presence of phenobarbital. The inhibitory action of insulin was exerted even when effective concentrations of glucagon, dexamethasone, or 8-(p-chlorophenylthio)-cAMP were present.Key words: δ-aminolevulinic acid synthase, ferrochelatase, cAMP, insulin, diabetic rat hepatocytes.

Studies on regulatory mechanisms of heme biosynthesis in hepatocytes from normal and experimental-diabetic rats. Role of cAMP

1989 ◽  
Vol 67 (11-12) ◽  
pp. 751-758 ◽  
Author(s):  
Eduardo T. Cánepa ◽  
Elena B. C. Llambías ◽  
Moisés Grinstein
Keyword(s):  
Aminolevulinic Acid ◽  
Rat Hepatocytes ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Intracellular Camp ◽  
Induction Effect ◽  
Isolated Rat Hepatocytes ◽  
Camp Content ◽  
Cytochrome P 450 ◽  
Phenobarbital Induction

In the present work we have been able to demonstrate the existence of some interrelationship between intracellular level of cAMP content and phenobarbital induction of δ-aminolevulinic acid synthase, ferrochelatase, and cytochrome P-450 biosynthesis in isolated rat hepatocytes. The increase of the level of intracellular cAMP produced by activators of adenylate cyclase, inhibitors of phosphodiesterase, or added cyclic nucleotides is reflected by an increase of the phenobarbital induction effect. The greater induction observed in hepatocytes of diabetic rats may be due to a higher level of the intracellular cAMP. The lack of potentiation of added cAMP in diabetic cells is mainly due to the fact that the maximum induction that could be attained is already achieved by the effect of the preexisting high level of the endogenous cAMP.Key words: δ-aminolevulinic acid synthase, ferrochelatase, cytochrome P-450, cAMP, diabetic rat hepatocytes.

cAMP regulation of phenobarbital-mediated induction of δ-aminolevulinate synthase mRNA in hepatocytes from normal and experimental diabetic rats

1994 ◽  
Vol 72 (9-10) ◽  
pp. 381-390 ◽  
Author(s):  
Cecilia L. Varone ◽  
Eduardo T. Canépa ◽  
Elena B. C. Llambías ◽  
Moisés Grinstein
Keyword(s):  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Dibutyryl Camp ◽  
Dependent Protein Kinase ◽  
Normal Cells ◽  
Aminolevulinate Synthase ◽  
Maximum Activation ◽  
Dependent Protein

We examined the mechanism underlying the effect of cAMP on δ-aminolevulinate synthase mRNA biosynthesis in isolated hepatocytes from normal and experimental diabetic rats. We have demonstrated that the potentiation by dibutyryl cAMP of the phenobarbital-mediated induction of δ-aminolevulinate synthase enzyme activity, observed in our previously reported studies, reflects an increased amount of its mRNA. The inducing effect exerted by phenobarbital on the biosynthesis of δ-aminolevulinate synthase mRNA in diabetic hepatocytes is greater than that observed in normal cells. This enhanced response to the increased level of endogenous cAMP in diabetic hepatocytes is apparently sufficient for a maximum activation of the cAMP-dependent protein kinase. The present results suggest that in rat liver dibutyryl cAMP modulates δ-aminolevulinate synthase mRNA biosynthesis by acting predominantly, if not exclusively, at the level of gene transcription.Key words: δ-aminolevulinate synthase mRNA, phenobarbital, cAMP, diabetic rat hepatocytes.

Pentoxifylline inhibits Ca2+-dependent and ATP proteasome-dependent proteolysis in skeletal muscle from acutely diabetic rats

2007 ◽  
Vol 292 (3) ◽  
pp. E702-E708 ◽  
Author(s):  
Amanda Martins Baviera ◽  
Neusa Maria Zanon ◽  
Luiz Carlos Carvalho Navegantes ◽  
Renato Hélios Migliorini ◽  
Isis do Carmo Kettelhut
Keyword(s):  
Protein Degradation ◽  
Muscle Protein ◽  
Phosphodiesterase Inhibitor ◽  
Inhibitory Effect ◽  
Diabetic Rats ◽  
Camp Phosphodiesterase ◽  
Camp Content ◽  
Muscle Protein Degradation ◽  
Vitro Effect

Previous studies from this laboratory have shown that catecholamines exert an inhibitory effect on muscle protein degradation through a pathway involving the cAMP cascade. The present work investigated the systemic effect of pentoxifylline (PTX; cAMP-phosphodiesterase inhibitor) treatment on the rate of overall proteolysis, the activity of proteolytic systems, and the process of protein synthesis in extensor digitorum longus muscles from normal and acutely diabetic rats. The direct in vitro effect of this drug on the rates of muscle protein degradation was also investigated. Muscles from diabetic rats treated with PTX showed an increase (22%) in the cAMP content and reduction in total rates of protein breakdown and in activity of Ca2+-dependent (47%) and ATP proteasome-dependent (23%) proteolytic pathways. The high content of m-calpain observed in muscles from diabetic rats was abolished by PTX treatment. The addition of PTX (10−3 M) to the incubation medium increased the cAMP content in muscles from normal (22%) and diabetic (51%) rats and induced a reduction in the rates of overall proteolysis that was accompanied by decreased activity of the Ca2+-dependent and ATP proteasome-dependent proteolytic systems, in both groups. The in vitro addition of H-89, an inhibitor of protein kinase A (PKA), completely blocked the effect of PTX on the reduction of proteolysis in muscles from normal and diabetic rats. The present data suggest that PTX exerts a direct inhibitory effect on protein degradative systems in muscles from acutely diabetic rats, probably involving the participation of cAMP intracellular pathways and activation of PKA, independently of tumor necrosis factor-α inhibition.

Mechanism of the Antiplatelet Action of Dipyridamole in Whole Blood: Modulation of Adenosine Concentration and Activity

1986 ◽  
Vol 55 (01) ◽  
pp. 012-018 ◽  
Author(s):  
Paolo Gresele ◽  
Jef Arnout ◽  
Hans Deckmyn ◽  
Jos Vermylen
Keyword(s):  
Platelet Aggregation ◽  
Adenosine Receptor ◽  
Whole Blood ◽  
Blood Cells ◽  
Inhibitory Action ◽  
Phosphodiesterase Inhibitor ◽  
Inhibitory Effect ◽  
Adenosine Concentration ◽  
Pharmacological Studies

SummaryDipyridamole inhibits platelet aggregation in whole blood at lower concentrations than in plasma. The blood cells responsible for increased effectiveness in blood are the erythrocytes. Using the impedance aggregometer we have carried out a series of pharmacological studies in vitro to elucidate the mechanism of action of dipyridamole in whole blood. Adenosine deaminase, an enzyme breaking down adenosine, reverses the inhibitory action of dipyridamole. Two different adenosine receptor antagonists, 5’-deoxy-5’-methylthioadenosine and theophylline, also partially neutralize the activity of dipyridamole in blood. Enprofylline, a phosphodiesterase inhibitor with almost no adenosine receptor antagonistic properties, potentiates the inhibition of platelet aggregation by dipyridamole. An inhibitory effect similar to that of dipyridamole can be obtained combining a pure adenosine uptake inhibitor (RE 102 BS) with a pure phosphodiesterase inhibitor (MX-MB 82 or enprofylline). Mixing the blood during preincubation with dipyridamole increases the degree of inhibition. Lowering the haematocrit slightly reduces the effectiveness.Although we did not carry out direct measurements of adenosine levels, the results of our pharmacological studies clearly show that dipyridamole inhibits platelet aggregation in whole blood by blocking the reuptake of adenosine formed from precursors released by red blood cells following microtrauma. Its slight phosphodiesterase inhibitory action potentiates the effects of adenosine on platelets.

Effects of extracellular ATP on hepatic fatty acid metabolism

1996 ◽  
Vol 270 (4) ◽  
pp. G701-G707 ◽  
Author(s):  
M. Guzman ◽  
G. Velasco ◽  
J. Castro
Keyword(s):  
Fatty Acid ◽  
De Novo ◽  
Specific Inhibitor ◽  
Rat Hepatocytes ◽  
Inhibitory Effect ◽  
Extracellular Atp ◽  
Acid Oxidation ◽  
A 23187 ◽  
Malonyl Coa ◽  
Cpt I

Incubation of rat hepatocytes with extracellular ATP inhibited acetyl-CoA carboxylase (ACC) activity and fatty acid synthesis de novo, with a concomitant decrease of intracellular malonyl-CoA concentration. However, both carnitine O-palmitoyltransferase I (CPT-I) activity and ketogenesis from palmitate were inhibited in parallel by extracellular ATP. The inhibitory effect of extracellular ATP on ACC and CPT-I activities was not evident in Ca2+ -depleted hepatocytes. Incubation of hepatocytes with thapsigargin, 2,5-di-(t-butyl)-1,4-benzohydroquinone (BHQ), or A-23187, compounds that increase cytosolic free Ca2+ concentration ([Ca2+]i), depressed ACC activity, whereas CPT-I activity was unaffected. The phorbol ester 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) increased ACC activity, whereas it decreased CPT-I activity in a nonaddictive manner with respect to extracellular ATP. The inhibitory effect of extracellular ATP on ACC activity was also evident in the presence of bisindolyl-maleimide, a specific inhibitor of protein kinase C (PKC), whereas this compound abolished the extracellular ATP-mediated inhibition of CPT-I. In addition, the PMA-induced inhibition of CPT-I was not potentiated by thapsigargin, BHQ, or A-23187. Results thus show 1) that the intracellular concentration of malonyl-CoA is not the factor responsible for the inhibition of hepatic long-chain fatty acid oxidation by extracellular ATP, and 2) that the inhibition of ACC by extracellular ATP may be mediated by an elevation of [Ca2+]i, whereas CPT-I may be inhibited by extracellular ATP through a PKC-dependent mechanism.

scholarly journals 3-oxo acid coenzyme A-transferase in normal and diabetic rat muscle

1976 ◽  
Vol 158 (2) ◽  
pp. 509-512 ◽  
Author(s):  
A Fenselau ◽  
K Wallis
Keyword(s):  
Skeletal Muscle ◽  
Coenzyme A ◽  
Substrate Inhibition ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Functional Parameters ◽  
Rat Muscle ◽  
Coa Transferase ◽  
Normal Rat ◽  
Streptozotocin Diabetic Rats

The amounts of succinyl-CoA--3-oxo acid CoA-transferase (EC 2.8.3.5) decrease progressively in skeletal muscle in streptozotocin-diabetic rats, reaching after 10 days about 50% of the value in normal rat muscle. Electrofocusing studies indicate the occurrence of partial proteolysis of the enzyme in diabetic muscle. However, several functional parameters relating to acetoacetate utilization, including substrate inhibition, are quite similar for muscle transferase preparations from normal and diseased rats. The development of pathological ketoacidosis is discussed in the light of these observations.

STEADY STATE OXIDATION OF GLUCOSE IN THE HYPOTHYROID DIABETIC RAT: A ROLE FOR THE ADRENAL CORTEX IN GLUCOSE OXIDATION

1963 ◽  
Vol 41 (5) ◽  
pp. 1293-1305
Author(s):  
Dorothy S. Dow ◽  
C. E. Allen
Keyword(s):  
Steady State ◽  
Glucose Oxidation ◽  
Tricarboxylic Acid Cycle ◽  
Critical Factor ◽  
Inhibitory Effect ◽  
Reduced Form ◽  
Diabetic Rat ◽  
Hexose Monophosphate ◽  
Hexose Monophosphate Pathway ◽  
Oxidation Of Glucose

A steady state between the specific activities of blood glucose and expired CO2in the hypothyroid diabetic rat was maintained for extended periods of time following a single intraperitoneal injection of glucose-1-C14or glucose-6-C14. Rates of oxidation of the labelled sugars were measured during the steady state.Glucose oxidation by way of glycolysis and the tricarboxylic acid cycle in the hypothyroid diabetic rat paralleled the decrease in expired CO2but glucose oxidation by way of the hexose monophosphate pathway was completely suppressed.It is suggested that the observed inhibitory effect on the hexose monophosphate pathway is due to the maintenance of diphosphopyridine nucleotide in the reduced form as the result of goitrogen inhibition of steroid-catalyzed transhydrogenation.The results suggest that steroid concentration may be a critical factor in regulation of glucose oxidation by way of the hexose monophosphate pathway.

Sign in / Sign up

Export Citation Format

Share Document