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.

Release of Active and Inactive Kallikrein from the Isolated Perfused Rat Kidney

1984 ◽  
Vol 66 (2) ◽  
pp. 207-215 ◽  
Author(s):  
B. H. Van Leeuwen ◽  
S. M. Grinblat ◽  
C. I. Johnston
Keyword(s):  
Rat Kidney ◽  
Active Form ◽  
Similar Proportion ◽  
Rat Urine ◽  
Isolated Perfused Rat Kidney ◽  
Inactive Form ◽  
Perfused Rat Kidney ◽  
Kallikrein 2 ◽  
Normal Rat ◽  
Immunological Assays

1. The release of kallikrein into the perfusate and urine of the isolated perfused rat kidney was studied. 2. Comparison between enzymic and immunological assays for kallikrein demonstrated the presence of an enzymically inactive form of kallikrein. 3. Of kallikrein found in normal rat urine 77 ± 4% is active and 23% is in an inactive form. 4. In the isolated perfused rat kidney a similar proportion of active kallikrein (84%) was excreted into the urine but very little enzymically active kallikrein (2%) could be detected in the perfusate. 5. However, significant amounts of enzymically inactive but immunologically reactive kallikrein could be found in the kidney perfusate. The rate of release of kallikrein into the perfusate was approximately one-fifth of the rate of release into the urine. 6. Renin showed a similar pattern of release into the perfusate and urine but the lysosomal enzyme marker acid phosphatase was not detectable. 7. These results show that kallikrein is secreted from the kidney into the circulation as well as being excreted in the urine. However, in urine the enzyme is predominantly in an enzymically active form whereas it is secreted into the circulation in an inactive form.

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.

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.

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

EFFECTS OF CYCLOSPORINE ON THE ISOLATED PERFUSED RAT KIDNEY

1987 ◽  
Vol 43 (6) ◽  
pp. 795-799 ◽  
Author(s):  
David R. Luke ◽  
Bertram L. Kasiske ◽  
Gary R. Matzke ◽  
Walid M. Awni ◽  
William F. Keane
Keyword(s):  
Rat Kidney ◽  
Isolated Perfused Rat Kidney ◽  
Perfused Rat Kidney
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