Flexibility of the hepatic zonation of carbon and nitrogen fluxes linked to lactate and pyruvate transformations in the presence of ammonia

2007 ◽  
Vol 293 (4) ◽  
pp. G838-G849 ◽  
Author(s):  
Jurandir Fernando Comar ◽  
Fumie Suzuki-Kemmelmeier ◽  
Écio Alves Nascimento ◽  
Adelar Bracht
Keyword(s):  
Alanine Aminotransferase ◽  
Current View ◽  
Urea Synthesis ◽  
Direct Products ◽  
Carbamoyl Phosphate ◽  
Carbon And Nitrogen ◽  
Lactate And Pyruvate ◽  
Alanine Synthesis ◽  
A Minor ◽  
Alanine Aminotransferase Activity

It has been proposed that key enzymes of ureagenesis and the alanine aminotransferase activity predominate in periportal hepatocytes. However, ureagenesis from alanine, when measured in the perfused liver, did not show periportal predominance and even the release of the direct products of alanine transformation, lactate and pyruvate, was higher in perivenous cells. An alternative way of analyzing the functional distributions of alanine aminotransferase and the urea cycle along the hepatic acini would be to measure alanine and urea production from precursors such as lactate or pyruvate plus ammonia. In the present work these aspects were investigated in the bivascularly perfused rat liver. The results of the present study confirm that gluconeogenesis and the associated oxygen uptake tend to predominate in the periportal region. Alanine synthesis from lactate and pyruvate plus ammonia, however, predominated in the perivenous region. Furthermore, no predominance of ureagenesis in the periportal region was found, except for conditions of high ammonia concentrations plus oxidizing conditions induced by pyruvate. These observations corroborate the view that data on enzyme activity or expression alone cannot be extrapolated unconditionally to the living cell. The current view of the hepatic ammonia-detoxifying system proposes that the small perivenous fraction of glutamine synthesizing perivenous cells removes a minor fraction of ammonia that escapes from ureagenesis in periportal cells. However, since urea synthesis occurs at high rates in all hepatocytes with the possible exclusion of those cells not possessing carbamoyl-phosphate synthase, it is probable that ureagenesis is equally important as an ammonia-detoxifying mechanism in the perivenous region.

scholarly journals Selective inhibition of alanine aminotransferase and aspartate aminotransferase in rat hepatocytes

1984 ◽  
Vol 220 (3) ◽  
pp. 707-716 ◽  
Author(s):  
N W Cornell ◽  
P F Zuurendonk ◽  
M J Kerich ◽  
C B Straight
Keyword(s):  
Aspartate Aminotransferase ◽  
Alanine Aminotransferase ◽  
Rat Hepatocytes ◽  
Selective Inhibition ◽  
Enoic Acid ◽  
Urea Synthesis ◽  
Aminotransferase Activity ◽  
Glucose Synthesis ◽  
Alanine Aminotransferase Activity

Experiments were conducted with intact rat hepatocytes to identify inhibitors and incubation conditions that cause selective inhibition of alanine aminotransferase or aspartate aminotransferase. Satisfactory results were obtained by preincubating cells with L-cycloserine or L-2-amino-4-methoxy-trans-but-3-enoic acid in the absence of added substrates. When cells were incubated for 20 min with 50 microM-L-cycloserine, alanine aminotransferase activity was decreased by 90%, whereas aspartate aminotransferase was inhibited by 10% or less. On subsequent incubation, synthesis of glucose and urea from alanine was strongly inhibited, but glucose synthesis from lactate was unaffected. L-2-Amino-4-methoxy-trans-but-3-enoic acid (400 microM) in hepatocyte incubations caused 90-95% inactivation of aspartate aminotransferase, but only 15-30% loss of alanine aminotransferase activity. After preincubation with the inhibitor, glucose synthesis from lactate was almost completely blocked; with alanine as the substrate, gluconeogenesis was unaffected, and urea synthesis was only slightly decreased. By comparison with preincubation with inhibitors, simultaneous addition of substrates (alanine; lactate plus lysine) and inhibitors (cycloserine; aminomethoxybutenoic acid) resulted in smaller decreases in aminotransferase activities and in metabolic rates. Other compounds were less satisfactory as selective inhibitors. Ethylhydrazinoacetate inactivated the two aminotransferases to similar extents. Vinylglycine was almost equally effective in blocking the two enzymes in vitro, but was a very weak inhibitor when used with intact cells. Concentrations of DL-propargylglycine (4 mM) required to cause at least 90% inhibition of alanine aminotransferase in hepatocytes also caused a 16% decrease in aspartate aminotransferase. When tested in vitro, alanine aminotransferase was, as previously reported by others, more sensitive to inhibition by amino-oxyacetate than was aspartate aminotransferase, but in liver cell incubations the latter enzyme was more rapidly inactivated by amino-oxyacetate.

Subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis in the batrachoidid fishes Opsanus beta, Opsanus tau and Porichthys notatus

1995 ◽  
Vol 198 (3) ◽  
pp. 755-766 ◽  
Author(s):  
P Walsh
Keyword(s):  
Glutamine Synthetase ◽  
Subcellular Localization ◽  
Biochemical Properties ◽  
Nitrogen Excretion ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate ◽  
Opsanus Beta ◽  
Opsanus Tau ◽  
Porichthys Notatus ◽  
The Family

The subcellular localization and biochemical properties of the enzymes of carbamoyl phosphate and urea synthesis were examined in three representatives of fishes of the family Batrachoididae, the gulf toadfish (Opsanus beta), the oyster toadfish (Opsanus tau) and the plainfin midshipman (Porichthys notatus). The primary objective of the study was to compare the biochemical characteristics of these fishes, which represent a range between ammoniotelism and ureotelism (O. beta being facultatively ureotelic), with previous patterns observed for an ammoniotelic teleost (Micropterus salmoides, the largemouth bass) and an obligate ureogenic elasmobranch (Squalus acanthias, the dogfish shark). The present study documents the expression of mitochondrial carbamoyl phosphate synthetase (CPSase) III and cytosolic CPSase II (and its associated enzymes of pyrimidine synthesis, dihydro-orotase and aspartate carbamoyltransferase) in the livers of all three batrachoidid species. Both mitochondrial and cytosolic activities of arginase were present in the livers of all three species, as were cytosolic glutamine synthetase and argininosuccinate synthetase and lyase. However, O. beta also showed mitochondrial glutamine synthetase activity and higher total hepatic levels of glutamine synthetase than either O. tau or P. notatus. Taken together, these observations confirm that the arrangement of these enzymes in the batrachoidid fishes has greater similarity to that of M. salmoides than to that of S. acanthias. However, differences within the family appear to coincide with the different nitrogen excretion strategies. O. tau and P. notatus are primarily ammoniotelic and most closely resemble the ammoniotelic M. salmoides, whereas ureotelism in O. beta is correlated with the presence of a mitochondrial glutamine synthetase and the ability to induce higher total glutamine synthetase activities than O. tau or P. notatus. Additionally, isolated mitochondria from O. beta were able to generate citrulline from glutamine, whereas those from O. tau were not. Also in contrast to S. acanthias, glutamine synthetase activities in the mitochondria of O. beta are consistently lower than those of CPSase III. This and other kinetic observations lend support to the hypothesis that glutamine synthetase may be an important regulatory control point in determining rates of ureogenesis in O. beta.

Delayed onset of acute renal failure after significant paracetamol overdose: A case series

2009 ◽  
Vol 29 (1) ◽  
pp. 63-68 ◽  
Author(s):  
WS Waring ◽  
H. Jamie ◽  
GE Leggett
Keyword(s):  
Renal Failure ◽  
Acute Renal Failure ◽  
Serum Creatinine ◽  
Alanine Aminotransferase ◽  
Paracetamol Overdose ◽  
Peak Serum ◽  
Wilcoxon Test ◽  
Aminotransferase Activity ◽  
Baseline Serum ◽  
Alanine Aminotransferase Activity

Acute renal failure is a recognized manifestation of paracetamol toxicity, but comparatively little data is available concerning its onset and duration. The present study sought to characterize the time course of rising serum creatinine concentrations in paracetamol nephrotoxicity. Renal failure was defined by serum creatinine concentration ≥150 μmol/L (1.69 mg/dL) or ≥50% increase from baseline. Serum creatinine concentrations and alanine aminotransferase activity were considered with respect to the interval after paracetamol ingestion. There were 2068 patients with paracetamol overdose between March 2005 and October 2007, and paracetamol nephrotoxicity occurred in 8 (0.4%). All had significant hepatotoxicity, and peak serum alanine aminotransferase activity occurred at 2.5 days (2.2 to 2.9 days) after ingestion. Peak serum creatinine concentrations did not occur until 5.5 days (4.4 to 5.9 days) after ingestion (p = .031 by Wilcoxon test). Serum creatinine concentrations slowly restored to normal, and renal replacement was not required. In this patient series, rising serum creatinine concentrations only became detectable after more than 48 hours after paracetamol ingestion. Therefore, renal failure might easily be missed if patients are discharged home before this. Further work is required to establish the prevalence of paracetamol-induced nephrotoxicity, and its clinical significance.

Effect of Lactate Dehydrogenase Isoenzymes on the Coupled Enzymatic Assay for Alanine Aminotransferase Activity

1975 ◽  
Vol 21 (3) ◽  
pp. 330-333 ◽  
Author(s):  
Michael M Chang ◽  
Tai Wha Chung
Keyword(s):  
Lactate Dehydrogenase ◽  
Dehydrogenase Activity ◽  
Alanine Aminotransferase ◽  
Rabbit Muscle ◽  
Aminotransferase Activity ◽  
Lactate Dehydrogenase Activity ◽  
Enzymatic Assays ◽  
Substrate Specificities ◽  
Lactate Dehydrogenase Isoenzymes ◽  
Alanine Aminotransferase Activity

Abstract We show an example of the importance of specifying the form of isoenzyme and source of indicator enzymes to be used in coupled enzymatic assays. When we compared H4 (pig heart) and M4 (rabbit muscle) isoenzymes of lactate dehydrogenase for their suitability as indicator enzymes in the assay for alanine aminotransferase activity, we found that about fourfold as much M4 as H4 was required in terms of lactate dehydrogenase activity to reflect accurately equivalent amounts of alanine aminotransferase activity. Moreover, the substrate specificities of the two isoenzymes differed quantitatively.

Regulation of urea synthesis by acid-base balance in vivo: role of NH3 concentration

1987 ◽  
Vol 252 (2) ◽  
pp. F221-F225 ◽  
Author(s):  
S. Cheema-Dhadli ◽  
R. L. Jungas ◽  
M. L. Halperin
Keyword(s):  
Ammonium Concentration ◽  
Urea Synthesis ◽  
Carbamoyl Phosphate ◽  
Acid Base Balance ◽  
Acid Base ◽  
Fixed Rate ◽  
Rate Limiting Step ◽  
Base Balance

The purpose of this study was to clarify how changes in acid-base balance influence the rate of urea synthesis in vivo. Since ureagenesis was increased by an ammonium infusion into rats, regulation seemed to be a function of the blood ammonium concentration. The rate of urea synthesis was constant at a fixed rate of ammonium infusion and independent of the conjugate base infused, chloride or bicarbonate. The steady-state blood ammonium concentration was higher in the rats that developed metabolic acidosis. Thus it appeared that regulation was not directly mediated by this ammonium concentration per se. The rate of urea synthesis was also independent of the blood pH. Accordingly, the rate of urea synthesis was examined as a function of the plasma NH3 concentration. The rate of ureagenesis was found to be directly proportional to the plasma NH3 concentration. Assuming that plasma NH3 levels reflect those in mitochondria, the NH3 concentration yielding half-maximal rates of urea synthesis (close to 2 microM) was in the same range as Km for the rate-limiting step in ureagenesis, carbamoyl phosphate synthetase (EC 6.3.4.16). These results suggest that, at a constant ammonium concentration, the decreased rate of ureagenesis caused by a pH fall in vitro could reflect an acidosis-induced decline in the concentration of true substrate (NH3) for this pathway.

Sign in / Sign up

Export Citation Format

Share Document