scholarly journals Inhibition of ureagenesis by valproate in rat hepatocytes. Role of N-acetylglutamate and acetyl-CoA

1983 ◽  
Vol 216 (1) ◽  
pp. 233-236 ◽  
Author(s):  
F X Coude ◽  
G Grimber ◽  
P Parvy ◽  
D Rabier ◽  
F Petit
Keyword(s):  
Rat Hepatocytes ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Acetyl Coa ◽  
Isolated Rat Hepatocytes ◽  
Cellular Concentration ◽  
Acetylglutamate Synthase ◽  
Ornithine Transcarbamoylase

Valproate (0.5-5 mM) strongly inhibited urea synthesis in isolated rat hepatocytes incubated with 10 mM-alanine and 3 mM-ornithine. Valproate at the same concentrations markedly decreased concentrations of N-acetylglutamate, an essential activator of carbamoyl-phosphate synthetase I (EC 6.3.4.16), in parallel with the inhibition of urea synthesis by valproate. This compound also lowered the cellular concentration of acetyl-CoA, a substrate of N-acetylglutamate synthase (EC 2.3.1.1); glutamate, aspartate and citrulline were similarly decreased. Valproate in a dose up to 2 mM did not significantly affect the cellular concentration of ATP and had no direct effect on N-acetylglutamate synthesis, carbamoyl-phosphate synthetase I and ornithine transcarbamoylase (EC 2.1.3.3) activities.

scholarly journals NADP-specific isocitrate dehydrogenase in regulation of urea synthesis in rat hepatocytes

1980 ◽  
Vol 190 (3) ◽  
pp. 581-592 ◽  
Author(s):  
L G Petcu ◽  
G W E Plaut
Keyword(s):  
Isocitrate Dehydrogenase ◽  
Reductive Amination ◽  
Rat Hepatocytes ◽  
Urea Synthesis ◽  
Isolated Rat Hepatocytes ◽  
Lactate And Pyruvate ◽  
Rate Limiting ◽  
Isolated Rat ◽  
Reducing Equivalents

The effect of inhibition of NADP-specific isocitrate dehydrogenase (EC 1.1.1.42) by DL-threo-alpha-methylisocitrate (3-hydroxy-1,2,3-butanetricarboxylase) on urea synthesis was studied in isolated rat hepatocytes. alpha-Methylisocitrate substantially inhibited the rate of urea synthesis (35—84%) with substrates requiring net reductive amination of 2-oxoglutarate to glutamate for aspartate synthesis (i.e., L-serine, D-alanine, or NH4Cl + L-lactate). alpha-Methylisocitrate did not inhibit synthesis of urea from substrates not requiring reductive formation of glutamate (i.e. L-alanine, L-glutamine, L-asparagine, or NH4Cl + L-ornithine). The rate-limiting role of NADPH in urea synthesis was correlated with the decrease in NADPH content that occurred upon addition of NH4Cl or of alpha-methylisocitrate to hepatocytes incubated with lactate and pyruvate, indicating utilization of NADPH for reductive amination of 2-oxoglutarate and inhibition of NADPH generation via NADP-isocitrate dehydrogenase, respectively. Similar results were obtained with D-alanine and L-serine; however, alpha-methylisocitrate or NH4Cl did not substantially decrease NADPH content when L-alanine was the substrate. Inhibitors or ornithine—2-oxo acid transaminase (L-canaline or gabaculine) decreased the uptake of ornithine by hepatocytes and inhibited the alpha-methylisocitrate insensitive urea synthesis from ornithine and NH4Cl. Canaline did not inhibit urea synthesis from lactate, ornithine, and NH4Cl but the inhibition by alpha-methylisocitrate of urea formation from this combination was appreciably larger with canaline (approx. 82%) than without canaline (approx. 48%). Inhibition of urea synthesis from NH4Cl + lactate by alpha-methylisocitrate was partially prevented by oleate, octanoate, or 3-hydroxybutyrate. When the NADH content of hepatocytes was increased by 3-hydroxybutyrate, the addition of NH4Cl and/or alpha-methylisocitrate caused a decline in NADH (and NADPH) content, suggesting that reducing equivalents from NADH as well as from NADPH can support net reductive amination of 2-oxoglutarate when required for urea synthesis.

scholarly journals Adaptative increase of ornithine production and decrease of ammonia metabolism in rat colonocytes after hyperproteic diet ingestion

2004 ◽  
Vol 287 (2) ◽  
pp. G344-G351 ◽  
Author(s):  
Béatrice Mouillé ◽  
Véronique Robert ◽  
François Blachier
Keyword(s):  
Cell Metabolism ◽  
Carbamoyl Phosphate Synthetase ◽  
Carbamoyl Phosphate ◽  
Ammonia Metabolism ◽  
Ornithine Carbamoyl Transferase ◽  
Urea Production ◽  
Colonic Lumen ◽  
Isocaloric Diets ◽  
The One

Chronic high-protein consumption leads to increased concentrations of NH4+/NH3 in the colon lumen. We asked whether this increase has consequences on colonic epithelial cell metabolism. Rats were fed isocaloric diets containing 20 (P20) or 58% (P58) casein as the protein source for 7 days. NH4+/NH3 concentration in the colonic lumen and in the colonic vein blood as well as ammonia metabolism by isolated surface colonic epithelial cells was determined. After 2 days of consumption of the P58 diet, marked increases of luminal and colonic vein blood NH4+/NH3 concentrations were recorded when compared with the values obtained in the P20 group. Colonocytes recovered from the P58 group were characterized at that time and thereafter by an increased capacity for l-ornithine and urea production through arginase ( P < 0.05). l-Ornithine was mostly used in the presence of NH4Cl for the synthesis of the metabolic end product l-citrulline. After 7 days of the P58 diet consumption, however, the ammonia metabolism into l-citrulline was found lower ( P < 0.01) when compared with the values measured in the colonocytes recovered from the P20 group despite any decrease in the related enzymatic activities (i.e., carbamoyl-phosphate synthetase I and ornithine carbamoyl transferase). This decrease was found to coincide with a return of blood NH4+/NH3 concentration in colonic portal blood to values close to the one recorded in the P20 group. In response to increased NH4+/NH3 concentration in the colon, the increased capacity of the colonocytes to synthesize l-ornithine is likely to correspond to an elevated l-ornithine requirement for the elimination of excessive blood ammonia in the liver urea cycle. Moreover, in the presence of NH4Cl, colonocytes diminished their synthesis capacity of l-citrulline from l-ornithine, allowing a lower cellular utilization of this latter amino acid. These results are discussed in relationship with an adaptative process that would be related to both interorgan metabolism and to the role of the colonic epithelium as a first line of defense toward luminal NH4+/NH3 concentrations.

scholarly journals Acute effects of glucagon on citrulline biosynthesis

1982 ◽  
Vol 206 (3) ◽  
pp. 627-631 ◽  
Author(s):  
D Rabier ◽  
P Briand ◽  
F Petit ◽  
P Parvy ◽  
P Kamoun ◽  
...  
Keyword(s):  
High Protein Diet ◽  
High Protein ◽  
Protein Diet ◽  
Carbamoyl Phosphate Synthetase ◽  
Acute Effects ◽  
Carbamoyl Phosphate ◽  
Carbohydrate Diet ◽  
Acetylglutamate Synthase

Mitochondria isolated from livers of rats fed on different diets showed altered capacity to synthesize citrulline. Glucagon, 15 min after injection, increases citrulline biosynthesis, except after the high-protein diet. A significant correlation between citrulline biosynthesis and N-acetylglutamate content with and without glucagon treatment was shown when rats were fed on a standard or a carbohydrate diet. Different diets modified carbamoyl phosphate synthetase I (EC 6.3.4.16) and N-acetylglutamate synthase (acetyl-CoA:L-glutamate N-acetyltransferase, EC 2.3.1.1) activities. Glucagon did not modify these activities.

P413 ROLE OF KINASES EGFR AND SRC IN ESTRADIOL 17β-GLUCURONIDE (E17G) INDUCED CHOLESTASIS IN ISOLATED RAT HEPATOCYTES COUPLETS (IRHC)

2014 ◽  
Vol 60 (1) ◽  
pp. S205-S206
Author(s):  
I.R. Barosso ◽  
A.E. Zucchetti ◽  
G.S. Miszczuk ◽  
M.G. Roma ◽  
F.A. Crocenzi ◽  
...  
Keyword(s):  
Rat Hepatocytes ◽  
Isolated Rat Hepatocytes ◽  
Estradiol 17Β ◽  
Isolated Rat

scholarly journals Evidence that Ca2+-release-activated Ca2+ channels in rat hepatocytes are required for the maintenance of hormone-induced Ca2+ oscillations

2003 ◽  
Vol 370 (2) ◽  
pp. 695-702 ◽  
Author(s):  
Roland B. GREGORY ◽  
Gregory J. BARRITT
Keyword(s):  
High Selectivity ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Cation Channels ◽  
Isolated Rat Hepatocytes ◽  
Pharmacological Agents ◽  
Crac Channels ◽  
Kinetics Of ◽  
Ca2 Channels

Store-operated Ca2+ channels in liver cells have been shown previously to exhibit a high selectivity for Ca2+ and to have properties indistinguishable from those of Ca2+-release-activated Ca2+ (CRAC) channels in mast cells and lymphocytes [Rychkov, Brereton, Harland and Barritt (2001) Hepatology 33, 938—947]. The role of CRAC channels in the maintenance of hormone-induced oscillations in the cytoplasmic free Ca2+ concentration ([Ca2+]cyt) in isolated rat hepatocytes was investigated using several inhibitors of CRAC channels. 2-Aminoethyl diphenylborate (2-APB; 75μM), Gd3+ (1μM) and 1-{β-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl}-1H-imidazole hydrochloride (SK&F 96365; 50μM) each inhibited vasopressin- and adrenaline (epinephrine)-induced Ca2+ oscillations (measured using fura-2). The characteristics of this inhibition were similar to those of inhibition caused by decreasing the extracellular Ca2+ concentration to zero by addition of EGTA. The effect of 2-APB was reversible. In contrast, LOE-908 {(R,S)-(3,4-dihydro-6,7-dimethoxy-isochinolin-1-yl)-2-phenyl-N,N-di[2-(2,3,4-trimethoxyphenyl)ethyl]acetamidemesylate}(30μM), used commonly to block Ca2+ inflow through intracellular-messenger-activated, non-selective cation channels, did not inhibit the Ca2+ oscillations. In the absence of added extracellular Ca2+, 2-APB, Gd3+ and SK&F 96365 did not alter the kinetics of the increase in [Ca2+]cyt induced by a concentration of adrenaline or vasopressin that induces continuous Ca2+ oscillations at the physiological extracellular Ca2+ concentration. Ca2+ inflow through non-selective cation channels activated by maitotoxin could not restore Ca2+ oscillations in cells treated with 2-APB to block Ca2+ inflow through CRAC channels. Evidence for the specificity of the pharmacological agents for inhibition of CRAC channels under the conditions of the present experiments with hepatocytes is discussed. It is concluded that Ca2+ inflow through CRAC channels is required for the maintenance of hormone-induced Ca2+ oscillations in isolated hepatocytes.

Sign in / Sign up

Export Citation Format

Share Document