scholarly journals The cytosolic concentration of phosphate determines the maximal rate of glycogenolysis in perfused rat liver

1990 ◽  
Vol 266 (1) ◽  
pp. 207-212 ◽  
Author(s):  
F Vanstapel ◽  
M Waebens ◽  
P Van Hecke ◽  
C Decanniere ◽  
W Stalmans
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Glycogen Phosphorylase ◽  
Perfused Rat Liver ◽  
Maximal Rate ◽  
Free Medium ◽  
Progressive Decrease ◽  
Dibutyryl Cyclic Amp ◽  
Initial Value ◽  
Contrast Exposure

Glycogenolysis was studied in glycogen-rich perfused livers in which glycogen phosphorylase was fully converted into the a form by exposure of the livers to dibutyryl cyclic AMP. We monitored intracellular Pi by 31P n.m.r. Perfusion with Pi-free medium during 30 min caused a progressive decrease of the Pi signal to 50% of its initial value. In contrast, exposure of the livers to KCN and/or 2,4-dinitrophenol resulted in a rapid doubling of the Pi signal. Alterations in the intracellular Pi coincided with proportional changes in the rate of hepatic glycogenolysis (measured as the output of glucose plus lactate). The results indicate that the rate of glycogenolysis catalysed by phosphorylase a depends linearly on the hepatic Pi concentration. Hence the Km of phosphorylase a for its substrate Pi must be considerably higher than the concentrations that occur in the cytosol, even during hypoxia.

scholarly journals Hepatic thiol and glutathione efflux under the influence of vasopressin, phenylephrine and adrenaline

1985 ◽  
Vol 226 (2) ◽  
pp. 545-549 ◽  
Author(s):  
H Sies ◽  
P Graf
Keyword(s):  
Plasma Membrane ◽  
Cyclic Amp ◽  
Rat Liver ◽  
Isolated Perfused Rat Liver ◽  
Peripheral Inflammation ◽  
Perfused Rat Liver ◽  
Dibutyryl Cyclic Amp ◽  
Hormone Dependence ◽  
Experimental Shock ◽  
Hormone Effects

Thiol and glutathione (GSH) efflux across the sinusoidal plasma membrane in isolated perfused rat liver was stimulated by addition of hormones such as vasopressin, phenylephrine and adrenaline, whereas glucagon or dibutyryl cyclic AMP were without effect. Phenylephrine and adrenaline effects were sensitive to prazosin and phentolamine, respectively. The increase in thiol efflux was largely accounted for by an increase in GSH efflux. Thiol efflux and the hormone effects were abolished in GSH-depleted liver. Biliary GSH efflux was diminished upon hormone addition. The newly discovered hormone-dependence of GSH release across the sinusoidal plasma membrane may explain the known loss of GSH during conditions of experimental shock (traumatic or endotoxin) and stress and peripheral inflammation.

scholarly journals Hepatic inositol release upon hormonal stimulation of perfused rat liver

1988 ◽  
Vol 251 (3) ◽  
pp. 843-848 ◽  
Author(s):  
S vom Dahl ◽  
P Graf ◽  
H Sies
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Radioactive Material ◽  
Perfused Rat Liver ◽  
Dibutyryl Cyclic Amp ◽  
Hormonal Stimulation ◽  
Metabolic Difference ◽  
Basal Release ◽  
Stimulation Of ◽  
Sustained Increase

A sustained increase in the hepatic release of 3H radioactivity was shown to occur upon hormonal stimulation of perfused rat liver 15-20 h after intraperitoneal injection of 100 microCi of myo-[2-3H]inositol. Hormone-released radioactive material was analysed by t.l.c. and was found to consist predominantly of [3H]inositol, without further metabolites. Vasopressin (14 nM), phenylephrine (1.7 microM), angiotensin II (15 nM), glucagon (0.5 nM) and dibutyryl cyclic AMP (5 microM) exert maximal effects on hepatic inositol efflux after 10-15 min of stimulation. Omission of Ca2+ from the perfusion medium abolishes the hormone-dependent inositol release. LiCl (10 mM) does not significantly affect the basal release of [3H]inositol, but suppresses vasopressin- and angiotensin-triggered inositol release. Inositol efflux induced by glucagon, dibutyryl cyclic AMP and phenylephrine, however, remains essentially unchanged by LiCl infusion. This establishes a further metabolic difference between these two groups of agonists in that stimuli that act through cyclic AMP produce a stimulated outflow of inositol, but apparently without a Li+-sensitive phosphatase being involved in the overall process.

scholarly journals Factors that prevent the premature appearance of glucokinase in neonatal rat liver

1980 ◽  
Vol 186 (3) ◽  
pp. 817-826 ◽  
Author(s):  
M J O Wakelam ◽  
M B Allen ◽  
D G Walker
Keyword(s):  
Angiotensin Ii ◽  
Cyclic Amp ◽  
Insulin Release ◽  
Rat Liver ◽  
Neonatal Rat ◽  
Oral Glucose ◽  
Dibutyryl Cyclic Amp ◽  
Simultaneous Treatment ◽  
Physiological Factors ◽  
Glucose Administration

1. The physiological factors that prevent the precocious appearance of glucokinase activity in the 13-day-old rat that can be induced by oral glucose administration were explored. 2. Evidence is presented that the galactose component of milk sugar is inhibitory. In the absence of this inhibitory galactose, the amount of glucose necessary to effect appreciable induction is greater than that present in milk. 3. The induction is prevented both by administration of mannoheptulose, which inhibits insulin release, and by excess insulin; the amount of insulin available therefore seems to be critical. 4. The inhibition of induction by galactose does not appear to be via competition with glucose but by enhancing insulin release and thereby making this excessive. The relative amounts of glucose and insulin appear to be important in regulating glucokinase induction. 5. The precocious induction of glucokinase by glucose is inhibited by simultaneous treatment with approriate amounts of adrenaline, glucagon, dibutyryl cyclic AMP or isoprenaline but not by vasopressin or angiotensin II. 6. No single cause of glucokinase induction in neonatal rat liver can be recognized. The process is subject to regulation by many factors at a time subsequent to when competence to synthesize the enzyme has been established.

Effect of epinephrine and dibutyryl cyclic AMP on Δ5-desaturation activity of rat liver microsomes

Lipids ◽  
1980 ◽  
Vol 15 (12) ◽  
pp. 1064-1066 ◽  
Author(s):  
I. N. T. de Gomez Dumm ◽  
M. J. T. de Alaniz ◽  
R. R. Brenner
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Liver Microsomes ◽  
Rat Liver Microsomes ◽  
Dibutyryl Cyclic Amp ◽  
Desaturation Activity

Production, Uptake, and Metabolic Effects of Cyclic AMP in the Bivascularly Perfused Rat Liver

1997 ◽  
Vol 54 (10) ◽  
pp. 1115-1125 ◽  
Author(s):  
Jorgete Constantin ◽  
Fumie Suzuki-Kemmelmeier ◽  
Nair Seiko Yamamoto ◽  
Adelar Bracht
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Metabolic Effects ◽  
Perfused Rat Liver
Sign in / Sign up

Export Citation Format

Share Document