scholarly journals Uptake and metabolism of propionate in the liver isolated from sheep treated with glucagon

1997 ◽  
Vol 77 (5) ◽  
pp. 783-793 ◽  
Author(s):  
Abdulhamid Mohamed Ali ◽  
Markandeya Jois
Keyword(s):  
Jugular Vein ◽  
Isolated Hepatocytes ◽  
Maximal Rate ◽  
Caudal Lobe ◽  
Sterile Saline ◽  
Sheep Liver ◽  
Net Uptake ◽  
Perfusion Experiment ◽  
Uptake And Metabolism ◽  
Stimulation Of

The uptake and metabolism of propionate in the isolated perfused caudal lobe of the liver and in isolated hepatocytes were examined following treatment of sheep with glucagon or saline. Glucagon or sterile saline was infused at 9·8 µg/min for 3 h into the jugular vein and then the caudal lobe of the liver was removed surgically under anaesthesia. The caudal lobe was used either to prepare hepatocytes or in a non-recirculating perfusion experiment. Uptake and metabolism of propionate were studied using [2-14C]propionate. In studies using the non-recirculation perfusion of the caudal lobe of the sheep liver it was shown that the treatment of sheep with glucagon resulted in an increased rate of gluconeogenesis from propionate and in an increased net uptake of propionate by the caudal lobe. The uptake of propionate into the hepatocytes was saturable, concentrative and exhibited a Km for propionate of 0·24 (SE 0·07) mM and a maximal rate of uptake (Vmax) of 6·7 (SE 0·6) nmol/mg dry cells per min and was unaffected by glucagon treatment of sheep. After incubation of cells in medium containing 0·5 mM-[2-14C]propionate for 10 min, the rate of gluconeogenesis from propionate was 22 % higher in the hepatocytes isolated from glucagon-treated sheep. Concentrations in the medium of 1·35 mM butyrate and 1 mM-caproate inhibited propionate uptake by about 50 % and abolished the glucagon-induced stimulation of gluconeogenesis from propionate. The results are consistent with a regulatory role for glucagon in the gluconeogenesis from propionate in the sheep liver.

scholarly journals Long-term maintenance of low concentrations of fructose for the study of hepatic glucose phosphorylation

1999 ◽  
Vol 337 (3) ◽  
pp. 497-501 ◽  
Author(s):  
John W. PHILLIPS ◽  
Debra C. HENLY ◽  
Michael N. BERRY
Keyword(s):  
Isolated Hepatocytes ◽  
Maximal Rate ◽  
Prolonged Incubation ◽  
Low Concentrations ◽  
Hepatic Glucose ◽  
Incubation Periods ◽  
Glucose Phosphorylation ◽  
Term Maintenance ◽  
Stimulation Of

The stimulation of glucose phosphorylation in isolated hepatocytes by low fructose concentrations is transient due to the rapid metabolism of fructose. To prolong this stimulatory effect fructose was enzymically generated in the incubation medium from either sucrose with invertase or inulin with inulinase. A maximal rate of glucose phosphorylation was achieved when fructose was formed at at least 0.01 µmol/min, which maintained a concentration of 70 µM fructose in the medium. In the presence of a fructose concentration of 70 µM, the rate of phosphorylation with 5 mM glucose was doubled and remained constant over a 2.5 h period. Under these conditions the rate of glycolysis was increased more than 3-fold. The stimulation of flux through glucokinase by low concentrations of fructose decreased the proportion of glucose phosphorylated, which was cycled between glucose and glucose 6-phosphate, and increased the proportion that was glycolysed. The method described for maintaining the stimulation of glucose phosphorylation by isolated hepatocytes over prolonged incubation periods is especially suited to the further study of the control of glucokinase activity, in particular how the variation of flux through glucokinase affects the flux through all the pathways that utilize the product, glucose 6-phosphate.

scholarly journals Dependence of the adaptive capacity of liver mitochondria on preparation method

2020 ◽  
pp. 177-185
Author(s):  
H. Mazur ◽  
◽  
V. Merlavsky ◽  
B.O. Manko ◽  
V.V. Manko ◽  
...  
Keyword(s):  
Adaptive Capacity ◽  
Respiration Rate ◽  
Functional State ◽  
Liver Perfusion ◽  
Isolated Hepatocytes ◽  
Liver Mitochondria ◽  
Optimal Concentration ◽  
Maximal Rate

When conducting studies on isolated hepatocytes, it is important to obtain cells that retain the functional properties that are characteristic of the whole organ. Increased blood viscosity during liver perfusion, decreased perfusion pressure in blood vessels, and hence hypoxia, are among the factors that may affect the functional state of isolated hepatocytes. The functional state of cells can be estimated by the adaptive capacity of mitochondria, by inducing maximal respiration rate by uncoupling respiration and oxidative phosphorylation due to the addition of FCCP. The research aimed to investigate the adaptive capacity of mitochondria of isolated hepatocytes using in situ and in vitro liver perfusion. Hepatocytes were isolated by the two-staged Seglen method by in situ and in vitro liver perfusion. Isolated hepatocytes, after 15-minute incubation in the medium without addition or with respective oxidative substrate – glutamine, pyruvate, succinate, monomethyl succinate, α-ketoglutarate, dimethyl-α-ketoglutarate (at a concentration of 2 mM) or glucose (10 mM) – were added into the respiratory chamber and FCCP was added in increasing concentrations. It was established that at in situ liver perfusion maximal rate of uncoupled respiration and the optimal concentration of FCCP was higher than at in vitro liver perfusion. Addition of exogenous substrates to a medium increased the respiration rate of hepatocytes. Upon in situ liver perfusion maximal uncoupled respiration rate increased at all causes except glucose, and at in vitro liver perfusion – only when dimethyl-α-ketoglutarate, succinate and monomethyl succinate were used. The optimal concentration of FCCP at in vitro liver perfusion increased due to the addition of glutamine, pyruvate and monomethyl succinate to the medium, and at in situ liver perfusion – only upon glucose oxidation. In both perfusion methods, the highest maximal rate of uncoupled respiration is with the use of monomethyl succinate and the optimal FCCP concentration – upon pyruvate oxidation. Therefore, in situ liver perfusion is better method to obtain stable and metabolically active hepatocytes in support respiratory processes at a high level then in vitro perfusion.

scholarly journals Regulation of mitochondrial pyruvate carboxylation in isolated hepatocytes by acute insulin treatment

1983 ◽  
Vol 214 (2) ◽  
pp. 451-458 ◽  
Author(s):  
A B Chisholm ◽  
E H Allan ◽  
M A Titheradge
Keyword(s):  
Insulin Treatment ◽  
Second Messengers ◽  
Isolated Hepatocytes ◽  
Carboxylase Activity ◽  
Effector Molecules ◽  
Pyruvate Carboxylation ◽  
Isolated Mitochondria ◽  
Glucose Synthesis ◽  
Important Site ◽  
Stimulation Of

The effect of acute insulin treatment of hepatocytes on pyruvate carboxylation in both isolated mitochondria and cells rendered permeable by filipin was examined. Challenging the cells with insulin alone had no effect on either the basal rate of pyruvate carboxylation or gluconeogenesis, although it did suppress the responses to both glucagon and catecholamines. Insulin treatment was unable to antagonize the enhanced rate of pyruvate carboxylation caused by stimulation of the cells with either angiotensin or vasopressin. Neither insulin nor the gluconeogenic hormones altered the total extractable pyruvate carboxylase activity in the isolated mitochondria, suggesting that the effect of hormones at the level of the isolated intact organelle was mediated via alterations in the intramitochondrial concentrations of effector molecules, notably ATP and the [ATP]/[ADP] ratio and substrate availability. The alterations in pyruvate carboxylation correlate well with glucose synthesis in terms of sensitivity to effector molecules, putative second messengers and time of onset of the response, indicating that alterations in the flux through this enzyme are compatible with it being an important site in the control of gluconeogenesis from C3 precursors.

Effect of norepinephrine on consumption of oxygen in perfused skeletal muscle from cold-exposed rats

1988 ◽  
Vol 254 (4) ◽  
pp. E482-E489 ◽  
Author(s):  
M. Shiota ◽  
S. Masumi
Keyword(s):  
Skeletal Muscle ◽  
Beta Adrenergic ◽  
Control Muscle ◽  
Exposure To Cold ◽  
Net Uptake ◽  
Increased Activity ◽  
Net Release ◽  
Stimulation Of

The effect of norepinephrine on the consumption of O2 was studied in the skeletal muscle in the perfused hindlimbs of rats that had been kept at 4 degrees C for 5-25 days. 1) Basal rates of consumption of O2 and release of lactate were not affected by exposure to cold. 2) The stimulation of consumption of O2 by norepinephrine increased in the perfused hindlimbs of rats exposed to cold for 10-25 days, with a maximum stimulation at 20 days. The response to norepinephrine decreased markedly in hindlimbs perfused with propranolol or phentolamine. Phenylephrine, in the presence of 0.5 nM isoproterenol, stimulated the consumption of O2 at concentrations as low as 0.5 microM, with a maximum at 5 microM, in hindlimbs from the group exposed to cold for 20 days. 3) Ouabain inhibited the stimulation of consumption of O2 by norepinephrine. Norepinephrine caused a net release of K+ in control muscle but a net uptake of K+ by muscle from the group exposed to cold for 20 days. The results suggest that the calorigenic responsiveness to norepinephrine increases in skeletal muscle during acclimation of the rat to the cold, both alpha- and beta-adrenergic actions are involved in the calorigenic effects of norepinephrine, and the increased activity of the Na+-K+ ATPase under the influence of norepinephrine may be involved in the calorigenic action of norepinephrine on the skeletal muscle of cold-acclimated rats.

Progressive potentiation of peptide release during a neuronal discharge

1990 ◽  
Vol 63 (4) ◽  
pp. 738-744 ◽  
Author(s):  
K. J. Loechner ◽  
E. M. Azhderian ◽  
R. Dreyer ◽  
L. K. Kaczmarek
Keyword(s):  
Time Course ◽  
External Medium ◽  
Egg Laying ◽  
Maximal Rate ◽  
Peptide Release ◽  
Acidic Peptide ◽  
Neuroactive Peptides ◽  
Connective Tissue Sheath ◽  
Bag Cell Neurons ◽  
Stimulation Of

1. In response to electrical stimulation, the bag cell neurons of Aplysia generate an afterdischarge that lasts 20-40 min. During this afterdischarge several neuroactive peptides are released. We have now studied the time course of release of two of these peptides, egg-laying hormone (ELH) and acidic peptide (AP). For the collection of released peptides, the artery to the bag cell clusters was perfused. The medium surrounding the clusters (artificial seawater, ASW) was completely exchanged at 5-min intervals before, during, and after stimulation of an afterdischarge. Peptides released into the external medium were analyzed with the use of high-pressure liquid chromatography. 2. Before stimulation, no detectable ELH and AP were found in the external medium. After the onset of an afterdischarge, the amount of ELH and AP released increased progressively until 15-20 min of firing. Toward the conclusion of an afterdischarge, the release of ELH and AP returned to control levels. 3. In contrast to the pattern of release of the peptides, the firing rate of the bag cell neurons is maximal within the first minute of afterdischarge and thereafter declines. 4. Release of the peptides from axonal varicosities occurs within the vascularized connective-tissue sheath that covers the clusters of bag cell neurons. Experiments were therefore carried out to establish whether the observed time course of release is affected by diffusion of the peptides through the vasculature into the external medium and, in particular, to determine whether the maximal rate of release at 15-20 min into the afterdischarge could be accounted for by a delay in transport of peptides from the neurites.(ABSTRACT TRUNCATED AT 250 WORDS)

Cortical Spreading Depression Does Not Result in the Release of Calcitonin Gene-Related Peptide into the External Jugular Vein of the Cat: Relevance to Human Migraine

Cephalalgia ◽  
1993 ◽  
Vol 13 (3) ◽  
pp. 180-183 ◽  
Author(s):  
Richard D Piper ◽  
Lars Edvinsson ◽  
Rolf Ekman ◽  
Geoffrey A Lambert
Keyword(s):  
Migraine With Aura ◽  
Cortical Spreading Depression ◽  
Spreading Depression ◽  
Jugular Vein ◽  
Calcitonin Gene Related Peptide ◽  
External Jugular Vein ◽  
Related Peptide ◽  
Calcitonin Gene ◽  
Vasoactive Peptide ◽  
Stimulation Of

There is circumstantial evidence that cortical spreading depression (SD) may account for the scotoma and the “spreading cortical oligemia” seen during migraine with aura. It has been shown that calcitonin gene-related peptide (CGRP) is increased in blood taken from the external jugular vein (EJV) in humans during migraine and after stimulation of the trigeminal ganglion. To test the hypothesis that cortical SD may elevate the concentration of this vasoactive peptide in the EJV during migraine, we have measured its concentration in the external jugular vein of cats during cortical SD. This study demonstrates that SD has no effect on the concentration of CGRP either during the passage of a wave of spreading depression across the cortex or, 60 min later, during the period of post-SD cortical oligemia.

scholarly journals Development of an Improved Technique for the Perfusion of the Isolated Caudal Lobe of Sheep Liver

2000 ◽  
Vol 85 (5) ◽  
pp. 469-478
Author(s):  
A. M. Ali ◽  
H. C. Rossouw ◽  
M. Silove ◽  
J. G. Van Der Walt
Keyword(s):  
Caudal Lobe ◽  
Sheep Liver ◽  
Improved Technique
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