scholarly journals Development of gluconeogenesis from dihydroxyacetone in rat hepatocytes during a feeding cycle and starvation

1984 ◽  
Vol 218 (3) ◽  
pp. 975-981 ◽  
Author(s):  
B Azzout ◽  
J Peret
Keyword(s):  
Catalytic Activity ◽  
Pyruvate Kinase ◽  
Kinase Activity ◽  
Activity Ratio ◽  
Rat Hepatocytes ◽  
Equal Proportion ◽  
Pyruvate Kinase Activity ◽  
Nocturnal Feeding ◽  
Feeding Cycle ◽  
Fructose 1,6 Bisphosphate

Pyruvate kinase activity and the rates of gluconeogenesis and glycolysis in rat hepatocytes were evaluated by production of glucose and lactate + pyruvate from dihydroxyacetone during a feeding cycle or progressive starvation. In fed rats, during daylight (low food intake) and until darkness, gluconeogenesis progressively increased and glycolysis decreased slightly, but gluconeogenesis never exceeded glycolysis. During nocturnal feeding, gluconeogenesis and glycolysis returned to their morning rates. After 8 h starvation, an equal proportion of dihydroxyacetone was converted into glucose and into lactate + pyruvate. When glycogen was depleted (11 h of starvation), gluconeogenesis was maximal and glycolysis minimal. In fed and starved rats, the concentration of fructose 1,6-bisphosphate was the same. The activity ratio of pyruvate kinase (ratio of velocity at 0.5 mM-phosphoenolpyruvate to the maximum catalytic activity obtained with 4mM-phosphoenolpyruvate) was high in crude extracts of cells incubated with dihydroxyacetone and low in (NH4)2SO4-treated extracts, but remained unchanged during the whole experiment. There was no correlation between the rates of gluconeogenesis and glycolysis from dihydroxyacetone and the activity ratio of pyruvate kinase.

scholarly journals Insulin regulation of pyruvate kinase activity in cultured rat hepatocytes, in the presence of vasopressin, ionophore A23187 or 4β-phorbol 12β-myristate 13α-acetate

1988 ◽  
Vol 252 (3) ◽  
pp. 717-721 ◽  
Author(s):  
R A Pittner ◽  
J N Fain
Keyword(s):  
Cyclic Amp ◽  
Pyruvate Kinase ◽  
Kinase Activity ◽  
Primary Cultures ◽  
Rat Hepatocytes ◽  
Ionophore A23187 ◽  
Short Term ◽  
Pyruvate Kinase Activity ◽  
Cultured Rat Hepatocytes ◽  
Early Inhibition

The short-term interactions of insulin and vasopressin on pyruvate kinase (PK) activity were studied in primary cultures of rat hepatocytes. (1) Vasopressin inhibited PK activity by approx. 30% within 15 s, but activity returned to control values by 5 min. The transient inhibition by vasopressin was mimicked by either 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) or ionophore A23187. (2) Insulin alone transiently inhibited PK activity at 1 min, but stimulated PK activity at 5 and 15 min. (3) Insulin completely antagonized the early inhibition by vasopressin, PMA or A23187 of PK activity at 15 s. (4) Insulin inhibited PK activity in the presence of vasopressin, PMA or A23187 at 5 min. (5) 8-Bromo cyclic AMP inhibited PK activity within 15 s, and this inhibition was maintained for at least 5 min. Insulin did not antagonized the inhibition by the cyclic AMP analogue. These results show that insulin under appropriate conditions can act as an inhibitor or activator of PK.

scholarly journals Acute regulation of pyruvate kinase activity in rat epididymal adipose tissue by insulin

1979 ◽  
Vol 180 (3) ◽  
pp. 523-531 ◽  
Author(s):  
R M Denton ◽  
N J Edgell ◽  
B J Bridges ◽  
G P Poole
Keyword(s):  
Pyruvate Kinase ◽  
Kinase Activity ◽  
Covalent Modification ◽  
Epididymal Adipose Tissue ◽  
Pyruvate Kinase Activity ◽  
Marked Diminution ◽  
Fructose 1,6 Bisphosphate ◽  
Fat Pads

1. Evidence is presented that exposure of epididymal fat-pads from fed rats to insulin leads to a marked diminution in the Km for phosphoenolpyruvate of pyruvate kinase. Effects of insulin may be readily demonstrated in experiments both in vivo and in vitro and are not secondary to the activation by the hormone of glucose transport. No effect of insulin is apparent in tissues from 48 h-starved animals. 2. The mechanism of the effect of insulin on pyruvate kinase was not established. The observed changes in Km do not appear to be the result of alterations in the amounts of bound effectors such as fructose 1,6-bisphosphate and alanine. Rather, as the effect persists in incubated extracts, it appears that a change in the degree of phosphorylation or some other covalent modification of the enzyme may be involved.

Red blood cell age, pyruvate kinase activity, and insulin receptors. Evidence that monocytes and RBCs may behave differently

Diabetes ◽  
1983 ◽  
Vol 32 (11) ◽  
pp. 1017-1022 ◽  
Author(s):  
A. Camagna ◽  
R. De Pirro ◽  
L. Tardella ◽  
L. Rossetti ◽  
R. Lauro ◽  
...  
Keyword(s):  
Blood Cell ◽  
Pyruvate Kinase ◽  
Red Blood Cell ◽  
Kinase Activity ◽  
Insulin Receptors ◽  
Pyruvate Kinase Activity ◽  
Cell Age

Red Blood Cell Age, Pyruvate Kinase Activity, and Insulin Receptors: Evidence that Monocytes and RBCs May Behave Differently

Diabetes ◽  
1983 ◽  
Vol 32 (11) ◽  
pp. 1017-1022 ◽  
Author(s):  
A. Camagna ◽  
R. D. Pirro ◽  
L. Tardella ◽  
L. Rossetti ◽  
R. Lauro ◽  
...  
Keyword(s):  
Blood Cell ◽  
Pyruvate Kinase ◽  
Red Blood Cell ◽  
Kinase Activity ◽  
Insulin Receptors ◽  
Pyruvate Kinase Activity ◽  
Cell Age

scholarly journals The glucagon-induced activation of pyruvate dehydrogenase in hepatocytes is diminished by 4β-phorbol 12-myristate 13-acetate. A role for cytoplasmic Ca2+ in dehydrogenase regulation

1987 ◽  
Vol 241 (3) ◽  
pp. 729-735 ◽  
Author(s):  
J M Staddon ◽  
R G Hansford
Keyword(s):  
Dehydrogenase Activity ◽  
Phorbol Ester ◽  
Pyruvate Dehydrogenase ◽  
Kinase Activity ◽  
Rat Hepatocytes ◽  
Pyruvate Kinase Activity ◽  
Isolated Rat Hepatocytes ◽  
Intact Cells ◽  
Subsequent Addition ◽  
Isolated Rat

Phenylephrine, vasopressin and glucagon each increased the amount of active (dephospho) pyruvate dehydrogenase (PDHa) in isolated rat hepatocytes. Treatment with 4 beta-phorbol 12-myristate 13-acetate (PMA) opposed the increase in PDHa caused by both phenylephrine and glucagon, but had no effect on the response to vasopressin: PMA alone had no effect on PDHa. As PMA is known to prevent the phenylephrine-induced increase in cytoplasmic free Ca2+ concentration ([Ca2+]c) and to diminish the increase [Ca2+]c caused by glucagon, while having no effect on the ability of vasopressin to increase [Ca2+]c, these data are consistent with the notion that in intact cells an increase in [Ca2+]c results in an increase in the mitochondrial free Ca2+ concentration, which in turn leads to the activation of PDH. In the presence of 2.5 mM-Ca2+, glucagon caused an increase in NAD(P)H fluorescence in hepatocytes. This increase is taken to reflect an enhanced activity of mitochondrial dehydrogenases. PMA alone had no effect on NAD(P)H fluorescence; it did, however, compromise the increase produced by glucagon. When the extracellular free [Ca2+] was decreased to 0.2 microM, glucagon could still increase NAD(P)H fluorescence. Vasopressin also increased fluorescence under these conditions; however, if vasopressin was added after glucagon, no further increase in fluorescence was observed. Treatment of the cells with PMA resulted in a smaller increase in NAD(P)H fluorescence on addition of glucagon: the subsequent addition of vasopressin now caused a further increase in fluorescence. Changes in [Ca2+]c corresponding to the changes in NAD(P)H fluorescence were observed, again supporting the idea that [Ca2+]c indirectly regulates intramitochondrial dehydrogenase activity in intact cells. PMA alone had no effect on pyruvate kinase activity, and the phorbol ester did not prevent the inactivation caused by glucagon. The latter emphasizes the different mechanisms by which the hormone influences mitochondrial and cytoplasmic metabolism.

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