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C Morand

Publications and source records attributed to C Morand.

At least 55 records · Page 3Linked to original sources
PubMed1992

Control of glycogen metabolism by gluconeogenic and ketogenic substrates in isolated hepatocytes from fed rats.

1. This study was conducted to examine the effects of gluconeogenic and ketogenic substrates on the activities of the glycogen-metabolizing enzymes and on glycogenolysis in isolated hepatocytes from fed rats. 2. Gluconeogenic substrates like fructose, dihydroxyacetone or lactate turned out to stimulate the glucose-induced activation of glycogen synthase and this effect may be linked, to some extent, to the increase of the cellular glucose 6-phosphate concentration. 3. The effect of fructose was accompanied by the onset of glycogen synthesis. 4. Energetic substrates like fatty acids were also potent activators of glycogen synthase, especially in the presence of glucose. 5. When fatty acids were added alone or together with a physiological concentration of glucose, they induced or potentiated the inhibition of glycogen phosphorylase-a. 6. This inhibitory effect was mediated by a decrease of lactate release. 7. The stimulatory effect of amino acids on glycogen synthase seemed to be direct, non mediated by an inhibition of the phosphorylase-a activity although hepatic glycogenolysis markedly decreased. 8. Moreover, the amino acid action could be linked to their capacities to induce cell swelling and/or to limit proteolysis.

Amino Acids↗
PubMed1992

Replacement of digestible wheat starch by resistant cornstarch alters splanchnic metabolism in rats.

Splanchnic metabolism was investigated in rats fed either a diet containing highly digestible wheat starch (DS diet) or amylase-resistant cornstarch (RS diet). In rats fed the latter diet, there was a considerable enlargement of the cecum and an increase in the production and absorption of volatile fatty acids (VFA), chiefly acetic and propionic acids. As a result, the major substrates absorbed from the digestive tract were glucose in rats fed the DS diet and both glucose and VFA in rats fed the RS diet. The liver removed about one-third of the absorbed glucose in rats fed the DS diet, whereas there was a slight release of glucose by the liver in rats fed the RS diet. Plasma insulin was higher in rats fed the DS diet, and there were smaller fluctuations of plasma insulin and liver glycogen between the fed and postabsorptive periods in rats adapted to the RS diet. In these animals, propionate was the major VFA taken up by the liver and approximately 50% of absorbed acetate was also removed by the liver. During the postabsorptive period, there was still a substantial contribution of VFA, especially propionate, to liver metabolism. A depressive effect of the RS diet on plasma triglycerides, cholesterol and free fatty acids was observed only during the postabsorptive period. Replacement of a large part of absorbed glucose by VFA apparently allows time for absorption of energy fuels to be extended and dampens the fluctuations of glucose metabolism during the light: dark cycle.

Alanine↗
PubMed1992

[Regulation of glycogen metabolism in liver].

Glycogen metabolism in the liver is subject to complex regulations in which substrates or hormones may interact in different ways according to the nutritional conditions. Activation of glycogen synthesis strongly depends on the availability of glucose, gluconeognic substrates and amino acids. These factors act mainly by a direct or indirect activation of the synthase phosphatase. On the other hand, cAMP or Ca(2+)-dependent glycogenolytic agents cause glycogen degradation by the mean of specific protein kinases which may inactivate the glycogen synthase or activate the glycogen phosphorylase. The active form of glycogen phosphorylase is a potent allosteric inhibitor of the synthase phosphatase. Insulin increases glycogen synthesis by counteracting the action of glycogenolytic hormones and by enhancing the glucose induced activation of glycogen synthase. The respective importance of these different regulations is discussed in this article.

Animals↗
PubMed1991

Interactions between propionate and amino acid metabolism in isolated sheep hepatocytes.

The purpose of the present study was to evaluate the contribution of various substrates to glucose synthesis in isolated sheep hepatocytes, and more specifically to quantify the contribution of propionate to gluconeogenesis. Liver cells from fed sheep have a very high capacity for propionate utilization and conversion into glucose. The gluogenicity of lactate or amino acids was very low in hepatocytes from fed sheep, but was significantly increased in hepatocytes from starved animals. Amino acids such as alanine or glutamine were characterized by a substantial utilization towards ureogenesis; whereas their conversion to glucose was very low. Propionate utilization and conversion into glucose was inhibited by butyrate, ammonia and especially ethanol (by up to 80%). Ethanol promoted a striking accumulation of intracellular malate in hepatocytes incubated with propionate (reaching 14.9 mumol/g cell) and led to a depletion of phosphoenolpyruvate; ethanol inhibition could be counteracted by pyruvate. Propionate and butyrate enhanced ureogenesis from ammonia in ruminant liver cells but their effects were not additive. Propionate also elicited a marked increase in cellular concentrations of phosphoserine and serine, particularly in the presence of ammonia; such effects could influence phospholipid metabolism in the liver. These findings emphasize the contribution of propionate, compared with the other glucogenic substrates, to glucose synthesis in ruminants and point to the possibilities of modulation of the glucogenicity of propionate by various substrates which may be present in portal blood.

Amino Acids↗
PubMed1990

Non-hormonal and hormonal control of glycogen metabolism in isolated sheep liver cells.

1. Control of glycogen metabolism by various substrates and hormones was studied in ruminant liver using isolated hepatocytes from fed sheep. 2. In these cells glucose appeared uneffective to stimulate glycogen synthesis whereas fructose and propionate activated glycogen synthase owing to (i) a decrease in phosphorylase a activity and (ii) changes in the intracellular concentrations of glucose 6-phosphate and adenine nucleotides. 3. The activation of hepatic glycogenolysis by glucagon and alpha 1-adrenergic agents was associated with increased phosphorylase a and decreased glycogen synthase activities. 4. The simultaneous changes in these two enzyme activities suggest that in sheep liver, activation of phosphorylase a is not a prerequisite step for synthase inactivation. 5. In sheep hepatocytes, in the presence of propionate and after a lag period, insulin activated glycogen synthase without affecting phosphorylase a. 6. This latter result suggests that the direct activation of glycogen synthase by insulin is mediated by a glycogen synthase-specific kinase or phosphatase. Insulin also antagonized glucagon effect on glycogen synthesis by counteracting the rise of cAMP.

Animals↗
PubMed1988

Modulation of glucagon effects by changes in extracellular pH and calcium.

We have examined the influence of extracellular pH and calcium concentration on the action of glucagon on isolated rat hepatocytes, perfused liver or plasma membrane preparations. Incubation of rat hepatocytes with 10 nM glucagon at pH 7.4 caused an immediate increase in cAMP concentrations (8-fold), and this rise was almost 50% lower at acidic extracellular pH (6.9). This effect of pH could not be explained by an alteration of the hormone binding to its receptor for glucagon concentrations higher than 1 nM. The effect of acidosis on cAMP production was still present with non-hormonal effectors, such as 10 microM Gpp[NH]p, 30 microM forskolin or 10 mM NaF. This suggests a direct action of acidosis on the regulatory component Ns and/or on the catalytic subunit of adenylate cyclase. Acidic pH also depressed mitochondrial processes responsive to glucagon (NAD(P)H fluorescence, glutamine breakdown). Whatever the experimental model, calcium appeared to be required for maximal stimulation of cAMP production by glucagon. On perfused rat liver, glycogenolysis was depressed in the absence of extracellular calcium in the perfusate. In isolated hepatocytes, the stimulation of phosphorylase alpha activity by glucagon was modulated by extracellular calcium concentrations lower than 0.2 mM. This suggests that, although glucagon action is chiefly cAMP-mediated, its effect on calcium mobilization (affecting various cellular process, including cAMP production itself) should also be taken into account. This work also confirmed the importance of calcium in the stimulation of mitochondrial metabolism of glutamine by glucagon.

Adenylyl Cyclases↗
PubMed1988

Control of hepatic utilization of glutamine by transport processes or cellular metabolism in rats fed a high protein diet.

The hepatic metabolism of glutamine in rats adapted to a 15% casein high carbohydrate (HC) diet was compared to that in rats adapted to a 70% casein high protein (HP) diet. Portal glutamine concentrations in rats fed the HP diet were twice as high as those in rats fed the HC diet and glutamine was very efficiently extracted (40%) by the liver of rats fed the HP diet. From experiments of intraportal infusion of glutamine, it appeared that higher capacities of glutamine uptake develop in vivo in rats adapted to an HP diet. Hepatocytes isolated from such animals displayed higher capacities to metabolize glutamine to urea, even at physiological concentrations. This resulted from an increase of mitochondrial glutamine hydrolysis (observed in both intact and disrupted mitochondria) and from enhanced Na+-dependent glutamine transport (+50%, as measured by plasma membrane vesicles). In hepatocytes from rats fed the HC diet, glutamine breakdown was more efficiently stimulated by glucagon (and cAMP) than by vasopressin or epinephrine. In hepatocytes from rats fed the HP diet, this process was very responsive to both cAMP and Ca-dependent hormones. Metabolic adaptation to an HP diet results in the liver becoming a major site of glutamine utilization caused by adaptations of membrane transport, cell metabolism and tissue responsiveness to hormones.

Animals↗
PubMed1988

Characterization of glucagon and catecholamine effects on isolated sheep hepatocytes.

The purpose of this study was to characterize the glycogenolytic response to catecholamines and glucagon in isolated sheep hepatocytes. In this species, epinephrine appeared to exert its action on hepatic glycogenolysis by altering the cytosolic concentrations of both adenosine 3',5'-cyclic monophosphate (cAMP) and Ca2+. In contrast to results obtained in rat hepatocytes, glucagon failed to induce a rise in free cytosolic Ca2+ in sheep liver. Experiments on isolated hepatocytes or on liver plasma membranes showed that in sheep, glucagon was more efficient than epinephrine in promoting the production of cAMP. In the presence of glucagon or epinephrine, the activation of the glycogen phosphorylase a always appeared greater in sheep than in rat liver cells, whereas the variations in cellular cAMP were quite limited in sheep. The alpha 1- and beta-agonists (phenylephrine and isoproterenol) were alone as efficient as epinephrine in promoting phosphorylase a activation in sheep hepatocytes. All these results indicate the existence in sheep liver of a glycogen phosphorylase highly responsive to hormones.

1-Methyl-3-isobutylxanthine↗