Effect of Decrease in Bicarbonate Concentration on Metabolism of the Isolated Perfused Rat Kidney

1979 ◽  
Vol 57 (1) ◽  
pp. 103-111 ◽  
Author(s):  
B. D. Ross ◽  
R. L. Tannen
Keyword(s):  
Metabolic Acidosis ◽  
Metabolic Regulation ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Rat Kidney ◽  
Ammonia Production ◽  
Perfusion Medium ◽  
Isolated Perfused Rat Kidney ◽  
Acid Urine ◽  
Perfused Rat Kidney ◽  
Acute Metabolic Acidosis

1. An isolated perfused rat kidney preparation which responds to acidification of the perfusion medium with the production of an acid urine and increased ammonia production was used to study the metabolic regulation of ammonia production from glutamine. 2. An inhibitor of gluconeogenesis at phosphoenolpyruvate carboxykinase(GTP), mercaptopicolinate, completely prevented the increase in ammoniagenesis, without preventing acidification of the urine. 3. Acidification of the perfusion medium from pH 7·4 to 7·0 reduced the renal concentrations of malate and 2-oxoglutarate. 4. Malate concentration was restored by inhibition of phosphoenolpyruvate carboxykinase(GTP), but 2-oxoglutarate content remained low. This indicates that accelerated gluconeogenesis in acute acidosis cannot be the explanation for the fall in 2-oxoglutarate concentration. 5. The fall in 2-oxoglutarate content is taken to indicate an important fall in tissue pH or in the redox ratio (NAD+/NADH) or both during acute metabolic acidosis. 6. From these studies with lowered bicarbonate two separate stimuli to ammoniagenesis in acute metabolic acidosis are postulated: urinary trapping of ammonia and increased disposal of glutamine carbon atoms via the pathway of glucose synthesis.

Ammoniagenesis by the Isolated Perfused Rat Kidney: The Critical Role of Urinary Acidification

1979 ◽  
Vol 56 (4) ◽  
pp. 353-364 ◽  
Author(s):  
R. L. Tannen ◽  
B. D. Ross
Keyword(s):  
Metabolic Acidosis ◽  
Rat Kidney ◽  
Critical Role ◽  
Sodium Reabsorption ◽  
Ammonia Production ◽  
Bicarbonate Concentration ◽  
Urine Ph ◽  
Average Value ◽  
Acute Metabolic Acidosis

1. The effect of metabolic acidosis simulated in vitro on ammoniagenesis was investigated by using the isolated kidney of the rat perfused with an albumin Krebs—Henseleit medium containing glutamine and glucose. 2. Addition of HCl to a perfusate of normal bicarbonate concentration resulted in a prompt increase in urine flow rate, decrease in fractional sodium reabsorption and decrease in urine pH. 3. A minimum urine pH as low as 5·15 was achieved, with an average value of 5·92, indicating that this preparation has the capacity to acidify normally. 4. In contrast with studies in vitro with other preparations, with the functional perfused kidney a diminution in perfusate bicarbonate concentration resulted in a prompt increase in ammonia production, which was strikingly correlated with the decrease in urine pH. 5. The increase in ammonia production was diminished in studies carried out with a non-urinating kidney, in comparison with those that exhibited significant urine acidification. 6. These data suggest that a decrease in urine pH with trapping of ammonia in the urine may be a critical stimulus for increased ammonia production in acute metabolic acidosis.

Ammoniagenesis: D-Glutamyltransferase as a Source of Ammonia in the Rat Kidney

1975 ◽  
Vol 53 (8) ◽  
pp. 930-933 ◽  
Author(s):  
P. Wadoux ◽  
T. C. Welbourne
Keyword(s):  
Glutamate Dehydrogenase ◽  
Rat Kidney ◽  
Ammonia Production ◽  
Normal Kidney ◽  
Isolated Perfused Rat Kidney ◽  
Perfused Rat Kidney ◽  
Total Ammonia ◽  
Normal Rat

The contribution of D-glutamyltransferase (D-GT) (EC 2.3.2.1) to total renal ammonia production was determined by employing DL-methionine-DL-sulfoximine (MSO) as an inhibitor of D-GT. Rat kidney homogenates were assayed for NH3-liberating activity under optimal D-GT or γ-glutamyltranspeptidase (γ-GTP) (EC 2.3.2.2) conditions. MSO inhibits only D-GT activity. The contribution of D-GT to total renal ammonia production was then evaluated in the isolated perfused rat kidney employing identical substrate (5 mML-glutamine) and inhibitor (15 mM MSO) concentrations as employed in the homogenate study. Under these conditions, MSO inhibits 70% of the total ammonia production by the normal kidney; in addition, the ratio of ammonia produced per glutamine taken up rose from 1.0 to 1.8. In kidneys from chronically acidotic rats, MSO reduced total ammonia production only 35% while the NH3/glutamine ratio rose from 1.0 to 1.8. D-GT appears to be the predominant source of NH3 production in the normal rat kidney; γ-GTP does not contribute significantly. The rise in the NH3/glutamine ratio after D-GT inhibition is consistent with glutamine utilization via the activated mitochondrial glutaminase (EC 3.5.1.2) – glutamate dehydrogenase (EC 1.4.1.2) pathway.

Glutamine synthesis in the perfused rat kidney and in isolated rat cortical tubules: regulation by pH

1985 ◽  
Vol 69 (6) ◽  
pp. 701-707 ◽  
Author(s):  
Henri Lanctin ◽  
John T. Brosnan ◽  
Brian D. Ross
Keyword(s):  
Metabolic Acidosis ◽  
Isotope Dilution ◽  
Rat Kidney ◽  
Ammonia Excretion ◽  
Ammonia Production ◽  
Dilution Technique ◽  
Isotope Dilution Technique ◽  
Perfused Rat Kidney ◽  
Glutamine Synthesis ◽  
Isolated Rat

1. The possible involvement of renal glutamine synthesis in the regulation of ammoniagenesis during metabolic acidosis has been investigated. 2. Using an isotope dilution technique glutamine synthesis has been demonstrated in the intact perfused rat kidney, despite zero net balance for glutamine in this preparation. 3. Inhibition of glutamine synthesis resulted in increased ammonia production in isolated cortical tubules. The rates of these processes were comparable. 4. We conclude that recycling of nitrogen through glutamine synthesis and glutamine hydrolysis could play a quantitatively significant role in the control of ammonia excretion by the kidney, particularly in acute acidosis where the fall in pH seems to inhibit glutamine synthesis.

Stimulation of ammoniagenesis by acute acidosis: evidence for a urinary inhibitor

1980 ◽  
Vol 239 (5) ◽  
pp. F445-F451
Author(s):  
N. Terao ◽  
R. L. Tannen
Keyword(s):  
Metabolic Acidosis ◽  
Rat Kidney ◽  
Respiratory Acidosis ◽  
Urinary Ph ◽  
Isolated Perfused Kidney ◽  
Isolated Perfused Rat Kidney ◽  
Perfused Rat Kidney ◽  
Standard Collection ◽  
Acute Changes ◽  
Stimulation Of

To elucidate the factors mediating the response of renal ammoniagenesis to acute acidosis, the isolated perfused rat kidney was subjected to acute metabolic and respiratory acidosis with either standard collection or drainage of urine back into the perfusate. Midway during a 90-min perfusion with 0.4 mM glutamine and 5 mM glucose, perfusate pH was decreased to 6.8 by addition of HCl or alteration of the PCO2. Metabolic acidosis increased NH3 production, acidified the urine, and increased urinary NH4 excretion. Respiratory acidosis increased NH3 production to a comparable degree without urine acidification and with a minimal increase in NH4 excretion. When respiratory acidosis preceded perfusion at control PCO2 levels, NH3 production was increased but NH4 excretion was lower than control values. If urine drained back into the perfusate, NH3 production was not altered by either metabolic or respiratory acidosis. Accordingly, acute changes in perfusate pH stimulate renal ammoniagenesis by the isolated perfusate pH stimulate renal ammoniagenesis by the isolated perfused kidney independent of changes in urinary pH and NH4 excretion. This response is inhibited by an unidentified factor excreted in the urine.

Effect of acute metabolic acidosis on ammonia metabolism in kidney

1989 ◽  
Vol 256 (2) ◽  
pp. F321-F328
Author(s):  
R. T. Bogusky ◽  
R. L. Dietrich
Keyword(s):  
Metabolic Acidosis ◽  
Glutamate Dehydrogenase ◽  
Rat Kidney ◽  
Methionine Sulfoximine ◽  
Amide Nitrogen ◽  
Ammonia Metabolism ◽  
Perfused Rat Kidney ◽  
Purine Nucleotide Cycle ◽  
Acute Metabolic Acidosis ◽  
Ammonia Formation

To understand the mechanisms that initiate the increase in ammonia formation during acute acidosis in kidney [amino-15N]- and [amino-15N]glutamine were used as substrates in isolated perfused rat kidney experiments. Perfused kidneys from methionine sulfoximine-treated rats take up glutamine nitrogen at the rate of 1.50 +/- 0.08 mumol.g kidney-1.min-1 while forming ammonia at a rate of 0.65 +/- 0.09 mumol.g.kidney-1.min-1. Mass spectrometer analysis of the perfusate and urine reveals that ammonia is formed from the amide nitrogen of glutamine at the rate of 0.32 +/- 0.06 mumol.g kidney-1.min-1 and ammonia is formed from glutamate derived from glutamine at the rate of 0.21 +/- 0.04 mumol.g kidney-1.min-1. The balance of the ammonia formed is from unidentified endogenous sources. Addition of HCl to the perfusate to lower perfusate pH increases ammonia formation to 1.09 +/- 0.10 mumol.g kidney-1.min-1. The results exclude a role for the purine nucleotide cycle during acute acidosis and confirm that ammonia formation from glutamate derived from glutamine is via glutamate dehydrogenase. Lowering perfusate pH increases the rate of glutamine deamidation significantly by 0.33 +/- 0.06 mumol.g kidney-1.min-1 and increases the rate of ammonia formation via glutamate dehydrogenase insignificantly by only 0.08 +/- 0.04 mumol.g kidney-1.min-1, whereas ammonia formation from endogenous sources remains unchanged. The results demonstrate that regulation of glutamine deamidation is an important controlling step in ammonia formation during acute metabolic acidosis in kidney.

Ammonia production and glutamine incorporation into glutathione in the functioning rat kidney

1979 ◽  
Vol 57 (3) ◽  
pp. 233-237 ◽  
Author(s):  
T. C. Welbourne
Keyword(s):  
Resting State ◽  
Loading Condition ◽  
Rat Kidney ◽  
Incorporation Rate ◽  
Ammonia Production ◽  
Glutamine Concentration ◽  
Glutathione Synthesis ◽  
Isolated Perfused Rat Kidney ◽  
Perfused Rat Kidney ◽  
Glutamine Uptake

Incorporation of glutamine's γ-glutamyl moiety into glutathione was studied in the isolated perfused rat kidney under two conditions: (1) a resting state and (2) during reabsorption of a filtered glycylglycine load (designed to stimulate glutathione breakdown). Glutamine uptake and ammonia production were monitored simultaneously with [14C]glutamine (γ-glutamyl moiety) incorporation into glutathione.Renal glutathione content was highly dependent upon the presence of glutamine; in its absence, glutathione levels fell 40% in 30 min indicating synthesis does not keep pace with degradation. Presenting the kidney with a glycylglycine load doubled the rate of glutathione degradation. However, perfusing kidneys with physiological L-glutamine concentration (1 mM) maintained glutathione levels significantly above those in glutamine's absence in either condition 1 or 2. Evidence that glutamine functions as the γ-glutamyl donor in glutathione synthesis was established by the significant incorporation of [14C]glutamine into glutathione during condition 1 and the accelerated incorporation rate during glycylglycine loading (condition 2). Stimulating glutathione breakdown (condition 2) resulted in a significant increase in renal glutamine uptake and ammonia production apparently via the γ-glutamyltransferase pathway since inhibiting this activity blocked the incremental rise in glutamine uptake during glycylglycine loading. These results are consistent with the interpretation that stimulating γ-glutamyl cycle activity with a γ-glutamyl acceptor (glycylglycine) accelerates γ-glutamyl donor uptake (glutamine) and ammonia production via the γ-glutamyltransferase pathway.

Validation of a toxicity testing model by evaluating oxygen supply and energy state in the isolated perfused rat kidney

1991 ◽  
Vol 25 (3) ◽  
pp. 195-204 ◽  
Author(s):  
Takano Takehito ◽  
Nakata Kazuyo ◽  
Kawakami Tsuyoshi ◽  
Miyazaki Yoshifumi ◽  
Murakami Masataka ◽  
...  
Keyword(s):  
Oxygen Supply ◽  
Energy State ◽  
Rat Kidney ◽  
Toxicity Testing ◽  
Testing Model ◽  
Isolated Perfused Rat Kidney ◽  
Perfused Rat Kidney

Aldosterone Effects on Renal Function in the Isolated Perfused Rat Kidney

1979 ◽  
Vol 2 (1) ◽  
pp. 1-11
Author(s):  
Richard Solomon ◽  
Patricio Silva ◽  
Franklin H. Epstein
Keyword(s):  
Renal Function ◽  
Rat Kidney ◽  
Isolated Perfused Rat Kidney ◽  
Perfused Rat Kidney
Sign in / Sign up

Export Citation Format

Share Document