Acute Hormonal Regulation of Cyclic AMP Content and Glycogen Phosphorylase Activity in Fetal Liver in Organ Culture

Endocrinology ◽  
1974 ◽  
Vol 94 (4) ◽  
pp. 935-939 ◽  
Author(s):  
PETER SHERLINE ◽  
HOWARD EISEN ◽  
WALTER GLINSMANN
Keyword(s):  
Cyclic Amp ◽  
Organ Culture ◽  
Hormonal Regulation ◽  
Glycogen Phosphorylase ◽  
Fetal Liver ◽  
Phosphorylase Activity ◽  
Glycogen Phosphorylase Activity

scholarly journals Hormonal stimulation of cyclic AMP accumulation and glycogen phosphorylase activity in calcium-depleted hepatocytes from euthyroid and hypothyroid rats

1980 ◽  
Vol 188 (3) ◽  
pp. 593-599 ◽  
Author(s):  
C C Malbon ◽  
H R Gilman ◽  
J N Fain
Keyword(s):  
Cyclic Amp ◽  
Glycogen Phosphorylase ◽  
Female Rats ◽  
Phosphorylase Activity ◽  
Response Curves ◽  
Hormonal Stimulation ◽  
Low Concentrations ◽  
Cyclic Amp Accumulation ◽  
Adrenergic Antagonist ◽  
Glycogen Phosphorylase Activity

Activation of glycogen phosphorylase by hormones was examined in hepatocytes isolated from euthyroid and hypothyroid female rats and incubated by Ca2+-free buffer containing 1 mM-EGTA. Basal glycogen phosphorylase activity was decreased in Ca2+-free buffer. However, the activation of hepatocyte glycogen phosphorylase, in the absence of extracellular Ca2+, in response to adrenaline, glucagon or phenylephrine was slightly lower, whereas that by vasopressin was abolished. The activation of glycogen phosphorylase by phenylephrine, adrenaline or isoproterenol (isoprenaline) in hepatocytes from euthyroid rats incubated in the absence of Ca2+ was not accompanied by any detectable increase in total cyclic AMP. The log-dose/response curves for activation of phosphorylase by phenylephrine or low concentrations of adrenaline were the same in hepatocytes from hypothyroid as compared wit euthyroid rats, whereas the response to isoproterenol was greater in hepatocytes from hypothyroid rats. However, the increases in total cyclic AMP accumulation caused by adrenaline or isoproterenol were greater in hepatocytes from hypothyroid rats than in hepatocytes from euthyroid rats. The increases in cyclic AMP accumulation caused by adrenaline or isoproterenol in Ca2+-depleted hepatocytes from hypothyroid rats were blocked by propranolol, a beta-adrenergic antagonist. In contrast, propranolol was only partially effective asan inhibitor of the activation of glycogen phosphorylase by phenylephrine or adrenaline in hepatocytes from hypothyroid rats and ineffective on phosphorylase activation in cells from euthyroid rats. These data indicate that the alpha-adrenergic activation of glycogen phosphorylase is not affected by the absence of extracellular Ca2+, and the extent to which total cyclic AMP was increased by adrenergic amines did not correlate with glycogen phosphorylase activation.

Regulation of muscle glycogen phosphorylase activity following short-term endurance training

1996 ◽  
Vol 270 (2) ◽  
pp. E328-E335 ◽  
Author(s):  
A. Chesley ◽  
G. J. Heigenhauser ◽  
L. L. Spriet
Keyword(s):  
Endurance Training ◽  
Muscle Glycogen ◽  
Glycogen Phosphorylase ◽  
Citrate Synthase ◽  
Phosphorylase Activity ◽  
Short Term ◽  
Mitochondrial Potential ◽  
Before And After ◽  
Glycogen Phosphorylase Activity ◽  
Muscle Biopsies

The purpose of this study was to examine the regulation (hormonal, substrate, and allosteric) of muscle glycogen phosphorylase (Phos) activity and glycogenolysis after short-term endurance training. Eight untrained males completed 6 days of cycle exercise (2 h/day) at 65% of maximal O2 uptake (Vo2max). Before and after training subjects cycled for 15 min at 80% of Vo2max, and muscle biopsies and blood samples were obtained at 0 and 30 s, 7.5 and 15 min, and 0, 5, 10, and 15 min of exercise. Vo2max was unchanged with training but citrate synthase (CS) activity increased by 20%. Muscle glycogenolysis was reduced by 42% during the 15-min exercise challenge following training (198.8 +/- 36.9 vs. 115.4 +/- 25.1 mmol/kg dry muscle), and plasma epinephrine was blunted at 15 min of exercise. The Phos a mole fraction was unaffected by training. Muscle phosphocreatine utilization and free Pi and AMP accumulations were reduced with training at 7.5 and 15 min of exercise. It is concluded that posttransformational control of Phos, exerted by reductions in substrate (free Pi) and allosteric modulator (free AMP) contents, is responsible for a blunted muscle glycogenolysis after 6 days of endurance training. The increase in CS activity suggests that the reduction of muscle glycogenolysis was due in part to an enhanced mitochondrial potential.

Regulation of glycolytic enzymes during anoxia in the turtle Pseudemys scripta

1989 ◽  
Vol 257 (2) ◽  
pp. R278-R283 ◽  
Author(s):  
S. P. Brooks ◽  
K. B. Storey
Keyword(s):  
Heart Muscle ◽  
Glycogen Phosphorylase ◽  
White Muscle ◽  
Fold Increase ◽  
Glycolytic Enzymes ◽  
Phosphorylase Activity ◽  
Enzyme Form ◽  
Red Muscle ◽  
Km Value ◽  
Glycogen Phosphorylase Activity

The glycolytic enzymes glycogen phosphorylase, phosphofructokinase (PFK), and pyruvate kinase (PK) were assessed in liver, heart, red muscle, and white muscle of aerobic and 5-h anoxic turtles (Pseudemys scripta) for changes in total activity and kinetic parameters. Anoxia induced statistically significant changes in these glycolytic enzymes in each of the four organs assayed. Compared with normoxic controls, anoxic liver showed a 3.3-fold increase in glycogen phosphorylase activity, a 1.5-fold increase in the PFK I50 value for citrate (concentration that inhibits initial activity by 50%), a 1.5-fold increase in the PFK Michaelis constant (Km) value for fructose 6-phosphate (P), and an increased maximal activity of PK. Anoxic heart muscle showed a 2.6-fold decrease in glycogen phosphorylase activity and, for PFK, a 1.7-fold decrease in the Km value for ATP and a twofold increase in the I50 value for citrate. In anoxic white muscle, PFK showed a fivefold lower Km value for fructose-6-P and a threefold lower activator concentration producing half-maximal activation (A50) for potassium phosphate than the aerobic enzyme form. Changes in anoxic white muscle PK included a twofold increase in the Km value for ADP and a 1.7-fold decrease in the I50 value for alanine. In red muscle, anoxia affected only the Km value for ATP, which was 50% higher than the value for the aerobic enzyme form. Fructose 2,6-diphosphate (P2) levels also decreased in heart muscle and increased in red and white muscle during anoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Axotomy increases glycogen phosphorylase activity in motoneurones

Neuroscience ◽  
1984 ◽  
Vol 12 (4) ◽  
pp. 1261-1269 ◽  
Author(s):  
C.J. Woolf ◽  
M.S. Chong ◽  
A. Ainsworth
Keyword(s):  
Glycogen Phosphorylase ◽  
Phosphorylase Activity ◽  
Glycogen Phosphorylase Activity
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