scholarly journals Gluconeogenesis in the amphibian retina. Lactate is preferred to glutamate as the gluconeogenic precursor

1988 ◽  
Vol 254 (2) ◽  
pp. 359-365 ◽  
Author(s):  
S S Goldman
Keyword(s):  
Energy Metabolism ◽  
Cyclic Amp ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Lactate Production ◽  
Glycogen Metabolism ◽  
Hepatic Tissue ◽  
Ionophore A23187 ◽  
Fructose 1,6 Bisphosphatase ◽  
Full Complement

The capacity for gluconeogenesis in the isolated amphibian retina was found to be approx. 70-fold greater with lactate than with glutamate as the gluconeogenic precursor, 1426 versus 21 pmol of glucose incorporated into glycogen/h per mg of protein. It was also found that 11-15% of the glucosyl units in glycogen are derived from C3 metabolites of the glycolytic pathway, suggesting that lactate is recycled within the retina. In concert with these metabolic observations, a full complement of the gluconeogenic enzymes was detected in retinal homogenates. These included: glucose-6-phosphatase, fructose-1,6-bisphosphatase, acetyl-CoA-dependent pyruvate carboxylase and phosphoenolpyruvate carboxykinase. Agents that regulate the rate of gluconeogenesis in hepatic tissue were tested on the retina. At concentrations of glutamate and lactate that are presumed to be relevant physiologically, it was found that vasoactive intestinal peptide, ionophore A23187 and elevated [K+] each enhanced the rate of gluconeogenesis in Ringer containing 50 microM-glutamate, whereas in Ringer containing 8.5 mM-lactate these agents inhibited the rate of gluconeogenesis. Further, it was found that the classic gluconeogenic hormone glucagon inhibited gluconeogenesis in both glutamate- and lactate-containing Ringer. Retinal energy metabolism was found to be altered in lactate-containing Ringer, in that lactate production was suppressed completely. In addition, glycogen metabolism appeared to be dependent on increased cytosolic Ca2+ and was insensitive to increased retinal cyclic AMP.

scholarly journals Metabolic control of hepatic gluconeogenesis during exercise

1983 ◽  
Vol 212 (3) ◽  
pp. 633-639 ◽  
Author(s):  
G L Dohm ◽  
E A Newsholme
Keyword(s):  
Metabolic Control ◽  
Pyruvate Kinase ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Prolonged Exercise ◽  
Allosteric Effectors ◽  
Fructose 1,6 Bisphosphatase ◽  
Metabolite Concentrations ◽  
Fructose 1,6 Bisphosphate ◽  
Hexose Phosphates

Prolonged exercise increased the concentrations of the hexose phosphates and phosphoenolpyruvate and depressed those of fructose 1,6-bisphosphate, triose phosphates and pyruvate in the liver of the rat. Since exercise increases gluconeogenic flux, these changes in metabolite concentrations suggest that metabolic control is exerted, at least, at the fructose 6-phosphate/fructose 1,6-bisphosphate and phosphoenolpyruvate/pyruvate substrate cycles. Exercise increased the maximal activities of glucose 6-phosphatase, fructose 1,6-bisphosphatase, pyruvate kinase and pyruvate carboxylase in the liver, but there were no changes in those of glucokinase, 6-phosphofructokinase and phosphoenolpyruvate carboxykinase. Exercise changed the concentrations of several allosteric effectors of the glycolytic or gluconeogenic enzymes in liver; the concentrations of acetyl-CoA, ADP and AMP were increased, whereas those of ATP, fructose 1,6-bisphosphate and fructose 2,6-bisphosphate were decreased. The effect of exercise on the phosphorylation-dephosphorylation state of pyruvate kinase was investigated by measuring the activities under conditions of saturating and subsaturating concentrations of substrate. The submaximal activity of pyruvate kinase (0.5 mM-phosphoenolpyruvate), expressed as percentage of Vmax., decreased in the exercised animals to less than half that found in the controls. These changes suggest that hepatic pyruvate kinase is less active during exercise, possibly owing to phosphorylation of the enzyme, and this may play a role in increasing the rate of gluconeogenesis.

Response of Hepatic Carbohydrate and Cyclic AMP Metabolism to Cadmium Treatment in Rats

1975 ◽  
Vol 53 (1) ◽  
pp. 174-184 ◽  
Author(s):  
Z. Merali ◽  
S. Kacew ◽  
R. L. Singhal
Keyword(s):  
Cyclic Amp ◽  
Carbohydrate Metabolism ◽  
Cadmium Chloride ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Additional Treatment ◽  
Hepatic Tissue ◽  
Phosphodiesterase Activity ◽  
Metabolic Alterations ◽  
Acute Dose ◽  
Cadmium Treatment

Daily intraperitoneal injection of cadmium chloride (0.25 or 1 mg/kg) for 21 or 45 days into rats significantly stimulated the activities of hepatic pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-diphosphatase, and glucose-6-phosphatase, increased the concentrations of glucose and urea in the blood, and decreased the levels of glycogen in the liver. Whereas chronic cadmium treatment failed to alter adenosine-3′,5′-monophosphate phosphodiesterase (phosphodiesterase) activity, the endogenous levels of cyclic AMP (cAMP) and the activity of basal- and fluoride-stimulated forms of hepatic adenylate cyclase (AC) were markedly increased in cadmium-injected animals. Treatment with the higher dose (1.0 mg/kg) of cadmium chloride for 45 days produced greater metabolic alterations in hepatic tissue than those seen with the lower dose (0.25 mg/kg) given for a shorter period of time (21 days). Discontinuation of cadmium administration for 14 days in rats previously injected with cadmium chloride (1 mg/kg per day) for 21 days, failed to reverse the observed changes in hepatic cAMP or carbohydrate metabolism. A similar persistence of metabolic alteration was noted in rats treated with cadmium (1 mg/kg per day) for 45 days and subsequently maintained without additional treatment for 28 days. Administration of an acute dose of cadmium chloride (60 mg/kg) decreased hepatic phosphodiesterase activity and glycogen content 1 h after the injection. In addition, acute cadmium exposure increased blood glucose, serum urea, and hepatic cAMP levels, and produced an augmentation of basal- and fluoride-activated AC. However, the activities of various hepatic gluconeogenic enzymes remained unaffected in animals given an acute dose of cadmium chloride (60 mg/kg). Data provide evidence that suggests that the gluconeogenic potential of liver is markedly enhanced following chronic exposure to cadmium and that the cadmium-induced changes in carbohydrate metabolism may be associated with an enhanced synthesis of cAMP. In addition, the present study shows that the cadmium-induced metabolic alterations persist even after the cessation of cadmium treatment for a period of 28 days.

Effect of Endurance Training and Fasting on Renal Gluconeogenic Enzymes in the Rat

2004 ◽  
Vol 14 (3) ◽  
pp. 323-332 ◽  
Author(s):  
Ken D. Sumida ◽  
Jeff H. Garrett ◽  
William T. Mcjilton ◽  
Andrea L. Hevener ◽  
Casey M. Donovan
Keyword(s):  
Enzyme Activities ◽  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Training Status ◽  
Chronic Exercise ◽  
Fed State ◽  
Fasted State ◽  
Significant Difference ◽  
Fructose 1,6 Bisphosphatase ◽  
Gluconeogenic Enzyme

The purpose of this study was to examine the effects of chronic exercise training (running 30 m/min, 10% grade, 90 min/d for 8–10 weeks) on specific renal enzyme activities involved with the gluconeogenic pathway in the fed and 24-hr fasted state in rats. A portion of the kidney (containing the cortex and medulla) was homogenized from which cytosolic (c) and mitochondrial (m) fractions were separated. Maximal gluconeogenic enzyme activities were assessed for: phosphoenolpyruvate carboxykinase (cPEPCK), fructose 1,6-bisphosphatase (cFBP), pyruvate carboxylase (mPC), aspartate aminotrans-ferase (cAspAT), alanine aminotransferase (cAlaAT), and lactate dehydroge-nase (cLDH). In the fed state, there was no significant difference between groups in any of the enzymes examined (nmoles/min × mg protei n–1): cPEPCK (25.8 ± 1.7), cFBP(106.8 ± 7.1), mPC (20.7 ± 1.8), cAspAT( 1047.1 ±38.6), cAlaAT (52.3 ±4.3), and cLDH(1728.6± 163.2). After the 24-hr fast, there was a significant increase in cPEPCK (52.4 ± 2.9 and 52.0 ± 2.1) and mPC (44.6 ± 4.3 and 47.6 ± 4.9), control and trained, respectively. These results suggest that the maximal enzyme activities for cPEPCK and mPC can be augmented as a result of fasting that was independent of the training status.

scholarly journals The existence of a glyconeogenic pathway in rat skin

1976 ◽  
Vol 156 (2) ◽  
pp. 465-468 ◽  
Author(s):  
R F Peters ◽  
A M White
Keyword(s):  
Pyruvate Carboxylase ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Rat Skin ◽  
Fructose 1,6 Bisphosphatase

The existence of a glyconeogenic pathway in rat skin has been demonstrated by measurement of three of the key glyconeogenic enzymes, fructose 1,6-bisphosphatase, pyruvate carboxylase and phosphoenolpyruvate carboxykinase, and by studies on the incorporation in vitro of carbon from pyruvate and alanine into skin glycogen.

scholarly journals Glycogenolytic effects of the calcium ionophore A23187, but not of vasopressin or angiotensin, in foetal-rat hepatocytes

1984 ◽  
Vol 220 (2) ◽  
pp. 441-445 ◽  
Author(s):  
M Freemark ◽  
S Handwerger
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Glycogen Synthesis ◽  
Calcium Ionophore ◽  
Rat Hepatocytes ◽  
Glycogen Metabolism ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Foetal Rat ◽  
20 Nm

Vasopressin, angiotensin and phenylephrine stimulate glycogenolysis in postnatal rat liver by a Ca2+-mediated mechanism not involving cyclic AMP. To determine whether these hormones promote glycogenolysis in foetal liver, we have examined their effects, and those of the Ca2+ ionophore A23187, on glycogen metabolism in cultured foetal-rat hepatocytes. Vasopressin and angiotensin (0.1 nM-0.1 microM) had no effects on either glycogen synthesis (as assessed by [14C]glucose incorporation into glycogen) or phosphorylase a activity. However, A23187 at 1 and 10 microM inhibited glycogen synthesis by 31.3 and 89.1% respectively (both P less than 0.001) and stimulated phosphorylase a activity by 66.9 and 184.1% respectively (both P less than 0.01). Incubation of cells in Ca2+-deficient medium attenuated the effects of 10 microM-A23187 on glycogen synthesis and abolished the effects of 1 microM-A23187. As in postnatal liver, glucagon (1 and 20 nM) and isoprenaline (1 and 10 microM), which activate adenylate cyclase, inhibited glycogen synthesis and stimulated phosphorylase a activity in foetal hepatocytes. The minimal effective concentration of phenylephrine was 10 times that of isoprenaline. These results indicate striking differences in the ontogeny of cyclic AMP-mediated and Ca2+-mediated processes which regulate hepatic glycogenolysis. Since increases in cytosolic Ca2+ induce glycogenolysis in foetal-rat liver, the weak or absent responses to vasopressin, angiotensin and the alpha-adrenergic agonists may result from defects in hormone-receptor binding or in post-receptor events leading to the mobilization of intracellular Ca2+ stores.

scholarly journals POST-EXERCISE LACTATE PRODUCTION AND METABOLISM IN THREE SPECIES OF AQUATIC AND TERRESTRIAL DECAPOD CRUSTACEANS

1994 ◽  
Vol 186 (1) ◽  
pp. 215-234 ◽  
Author(s):  
R. P. Henry ◽  
C. E. Booth ◽  
F. H. Lallier ◽  
P. J. Walsh
Keyword(s):  
Pyruvate Carboxylase ◽  
Energy Production ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Lactate Production ◽  
Specific Pattern ◽  
Turnover Rates ◽  
Decapod Crustaceans ◽  
Anaerobic Energy ◽  
Cardisoma Guanhumi ◽  
Species Specific

Aquatic and terrestrial crustaceans are dependent on both aerobic and anaerobic metabolism for energy production during exercise. Anaerobic energy production is marked by an accumulation of lactate in both muscle tissue and haemolymph, but the metabolic fate of lactate is not clear. Lactate recycling via gluconeogenesis and the potential role of carbonic anhydrase (CA) in supplying bicarbonate for the carboxylation of pyruvate were investigated in three species of decapod crustaceans: Callinectes sapidus (aquatic), Cardisoma guanhumi (semi-terrestrial) and Gecarcinus lateralis (terrestrial). CA activity was found in mitochondria and cytoplasmic fractions of gill, hepatopancreas and muscle of all three species. Significant activities of key enzymes of gluconeogenesis (e.g. pyruvate carboxylase, phosphoenolpyruvate carboxykinase and fructose bisphosphatase), however, could not be detected. Exercise to exhaustion produced a species-specific pattern of accumulation and clearance of lactate in tissue and haemolymph, indicating a differential degree of reliance on anaerobic energy production. Treatment with acetazolamide, a CA inhibitor, did not significantly alter the pattern of lactate dynamics in animals given repeated bouts of exhaustive exercise interspersed with periods of recovery. Injection of [U-14C]lactate resulted in the appearance of label in both muscle glycogen and excreted carbon dioxide, suggesting multiple metabolic fates for lactate. Lactate turnover rates for G. lateralis were similar to those reported for fish. In these animals, gluconeogenesis possibly proceeds via the reversal of pyruvate kinase, or via the typical Cori cycle but so slowly that the uncatalysed supply of bicarbonate is sufficient to keep pace with the low activities of pyruvate carboxylase and the subsequent low rates of pyruvate carboxylation.

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