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T C Welbourne

Publications and source records attributed to T C Welbourne.

At least 73 records · Page 4Linked to original sources
PubMed1982

Renal gamma-glutamyltranspeptidase: In situ antiluminal localization.

Renal localization of gamma-glutamyltranspeptidase was studied in functioning kidneys perfused with the gamma-glutamyl substrates, gamma-glutamyl-p-nitroanilide and N(gamma-L-glutamyl) 2-naphthylamide. In kidneys perfused with gamma-glutamyl-p-nitroanilide, 90% of the breakdown products appear in the blood (perfusate) rather than urine. The addition of the acceptor substrate glycylglycine to the perfusate stimulated gamma-glutamyl-p-nitroanilide breakdown 3-fold, both on the blood and urine sides, while the appearance of gamma-glutamylglycylglycine confirmed that the activity responsible stems indeed from gamma-glutamyltranspeptidase. Ureter ligation reduced the glomerular filtration rate to less than 10% of the control, while the breakdown of gamma-glutamyl-p-nitroanilide decreased only 5%. Kidneys perfused with N(gamma-L-glutamyl) 2-naphthylamide and the diazonium salt demonstrated staining of the glomeruli; isolated glomeruli and microvessels gave heavy staining when incubated with the histochemical substrates. These results demonstrate the association of a significant portion of the total renal gamma-glutamyltranspeptidase activity with the microvascular compartment.

Animals↗
PubMed1981

Ammonia partitioning between glutamine and urea: interorgan participation in metabolic acidosis.

The distribution of precursor nitrogen between urea and glutamine was studied in control and acidotic rats. Acidosis, either acutely induced with hydrochloric acid or chronically induced with ammonium chloride, resulted in a rise in ammonia and a fall in urinary urea excretion; the percent of urinary nitrogen excreted as ammonia rose from 3.5 +/- 0.4 and 4.9 +/- 0.5 in fed and pair-fed controls to 25.9 +/- 3.9 and 37 +/- 5 in acidosis induced by hydrochloric acid and ammonium chloride. Hepatoportal vein urea concentration differences were significantly reduced, whereas glutamine concentration differences were significantly elevated, consistent with a shift of nitrogen from ureagenesis to glutamine; alanine and ammonia concentration differences were significantly decreased and increased respectively in the acidotic animals, suggesting that former supported urea synthesis whereas ammonia may preferentially support glutamine synthesis. Evidence of a feed-forward involvement of the gut in influencing hepatic nitrogen distribution was suggested by an increased ammonia and decreased alanine release in acidotic rats. Bilateral ureteral ligation was performed on control and acidotic rats to determine the fate of the redirected urinary ammonia. Ammonia did not accumulate in the blood, rather it was initially incorporated into glutamine, elevating the plasma level, and then it was subsequently deposited into urea. The shift of nitrogen back into urea in acidotic animals was confirmed by the greater postligation urea production rates supported by hepatic uptake of both alanine and glutamine. These results are discussed in terms of interorgan participation involving the liver, gut, and muscle in the partitioning of nitrogen between glutamine and urea.

Acidosis, Renal Tubular↗
PubMed1981

Presence of gamma-glutamyltransferase in the renal microvascular compartment.

The association between the brush border enzyme alkaline phosphatase and gamma-glutamyltransferase was determined by sucrose density gradient analysis of crude kidney homogenates, isolated glomeruli, and isolated microvessels. As previously established there is an overlap of these enzyme activities in the crude homogenate corresponding to a density of 1.17 g.cm-3. In contrast, isolated glomeruli sedimented with a peak of 1.25 g. cm-3 and exhibited gamma-glutamyltransferase activity but little alkaline phosphatase activity; homogenizing isolated glomeruli shifted the fragments to a density coincident with that observed for the crude homogenate gamma-glutamyltransferase peak. A second population of capillaries, isolated microvessels, were homogenized and analysed on the sucrose density gradient. These fragments sedimented over the same range as crude homogenate gamma-glutamyltransferase peak but were devoid of alkaline phosphatase activity and yet exhibited remarkable gamma-glutamyltransferase activity. The results indicate homogenization of renal cortex results in a heterogeneous collection of particles from both tubular and microvascular locations exhibiting gamma-glutamyltransferase activity which overlap with the brush border alkaline phosphatase containing membranes. However, isolation of microvessels and glomeruli prior to homogenization allows separation of gamma-glutamyltransferase from alkaline phosphatase activity; between 10 and 20% of the total homogenate gamma-glutamyltransferase activity is estimated to be associated with the microvascular compartment.

Alkaline Phosphatase↗
PubMed1980

Acid-base balance and plasma glutamine concentration in man.

Plasma glutamine concentrations were measured in chronic metabolic acidosis and alkalosis in healthy male volunteers. Metabolic acidosis resulted in a significant drop in glutamine concentration while metabolic alkalosis significantly elevated glutamine levels. These changes in glutamine concentration correlated with both the bicarbonate and PCO2 levels. To determine whether bicarbonate or PCO2 levels influence the glutamine concentrations, respectively acidosis was induced by respiring 5% CO2. This resulted in a significant elevation in both PCO2 and glutamine while bicarbonate levels remained unchanged. The results demonstrate an effect of acid-base alterations upon plasma glutamine concentration mediated by PCO2.

Acidosis↗
PubMed1980

Renal glutamine utilization: glycylglycine stimulation of gamma-glutamyltransferase.

Glycylglycine stimulation of renal glutamine utilization was studied on the homogenate, subcellular and purified enzyme level. The results clearly establish the existence of two glutamine utilizing pathways, the mitochondrial dependent L-glutamine amidohydrolase (PDG) and a second, extramitochondrial pathway. In contrast to the mitochondrial pathway which produces stoichiometric amounts of ammonia and glutamate, this second pathway hydrolyzes glutamine to produce ammonia and transfers the gamma-glutamyl moiety, producing gamma-glutamyl peptides. In the crude systems, containing cyclotransferase, the gamma-glutamyl moiety appears mainly as 5-oxoproline; however, in the enzyme preparation, purified 112-fold, gamma-glutamyl peptides (transpeptidation) and a small amount of glutamate (hydrolysis) appear. D-Glutamine was also hydrolyzed, in contrast to the stereospecific PDG, but at less than one-half the rate of the L-isomer. The molecular weight of this extramitochondrial D- and L-glutamine utilizing enzyme was estimated by gel filtration on a Sephadex G-200 column and found to be approximately 70 000. Based on product formation, molecular weight estimation and copurification with the activity responsible for p-nitroanilide release from gamma-glutamyl-p-nitroanilide, we conclude that this reaction is catalyzed by gamma-glutamyltranspeptidase. Glycylglycine stimulated this enzyme to produce more ammonia while decreasing the appearance of glutamate; in contrast, the mitochondrial glutaminase was unaffected by glycylglycine. This extramitochondrial glutamine utilizing pathway can make a significant contribution to in vivo renal ammoniagenesis.

Animals↗
PubMed1980

Mithcondrial glutamine permeability and renal ammonia production in metabolic acidosis.

These experiments were undertaken to determine the correspondence between acidosis-induced in situ motochondrial glutamine uptake and the process by which glutamine moves across the mitochondrial membrane. Feeding rats 1.5% NH4Cl for 2 wk accelerated the in situ uptake rate from 0.12 +/- 0.08 to 1.89 +/- 0.28 mu mol/min or some 16-fold. To determine glutamine uptake independent of its metabolic conversion, D-glutamine was employed. In isolated mitochondria from non-acidotic rat kidneys, D-glutamine diffused into 71 +/- 10% of the mitochondria water volume; in acidotic mitochondria the diffusion volume increased to 127 +/- 16%. The reflection coefficients (sigma) for a series of amides, including glutamine, were determined by gravimetrically following volume decrements in increasing concentrations of solute; D-glutamine's sigma fell from 1.05 +/- 0.08 to 0.50 +/- 0.06 in acidotic rat kidney mitchondria, The permeability coefficients corresponding to the measured sigma were 10(-7) cm/s and 10(-5) cm/s in nonacidosis and acidosis, respectively. When viewed in situ proximal tubule mitochondria undergo dramatic alterations during chronic acidosis. These involved an enlargement in the mitochondria particularly in the basal region of the cell and a reduction in number. Furthermore, numerous autophagic vacuoles, containing mitochondria, appear in the basal region. The findings are consistent availability that becomes activated during acidosis as a consequence of mitochondrial glutamine permeability resulting in increased ammoniagenesis and accelerated organelle turnover.

Acidosis↗
PubMed1979

Organic mercurial diuresis: inhibition of glutamine utilization in the acidotic rat.

Organic mercurials inhibit mitochondrial glutamine metabolism in vitro while metabolic acidosis, a condition in which the predominant renal fuel is glutamine, potentiates mercurial diuresis. The following studies were undertaken to determine whether potentiation of diuresis reflects mercurial inhibition of glutamine utilization. (1) All three mercurials employed (mersalyl, chlormerodrin, and p-chloromercuribenzoate) are diuretics in the rat and this effect was potentiated by NH4Cl. (2) Despite reabsorbing less sodium, mercurial-treated rats had lower kidney ATP content (4.35 +/- 0.26 and 3.84 +/- 0.43 mumol/g dry weight (mercurial plus NH4Cl) than did controls (4.95 +/- 0.31 and 4.87 +/- 0.39 mumol/g dry weight (NH4Cl). (3) Isolated kidneys from NH4Cl and NH4Cl plus mercurial treated rats were perfused with 1 mM L-[U-14C]glutamine to determine rates of extraction and oxidation. Mercurial-treated acidotic rat kidneys had a reduced rate of glutamine uptake (40.8 +/- 7.4 vs. 64.8 +/- 5.8 mumol/h per kidney), a diminished rate of glutamine conversion to CO2 (14.8 +/- 3.6 vs. 26.4 +/- 5.2 mumol/h per kidney), and a reduction in glucose production (16 +/- 5 vs. 27 +/- 4 mumol/h per kidney). These results are consistent with an effect of organic mercurials upon glutamine utilization, limiting ATP availability, and thereby reducing tubular active sodium reabsorption.

Acidosis↗
PubMed1977

Influence of aldosterone on renal ammonia production.

Administering D-aldosterone, 7 microgram 100 g-1, to rats results in a marked rise in ammonium excretion and metabolic alkalosis. Increased ammonium excretion is not related to either a significant elevation in potassium excretion nor to hypokalemia. Consequently, potassium depletion does not appear to be the causative factor in the aldosterone-stimulated ammonium excretion. Isolated kidneys from aldosterone-treated rats, perfused with 1 mM L-glutamine, produced twice as much ammonia from glutamine as did controls. Ammonia production per glutamine extracted increased from 1.33 +/- 0.07 in control to 1.79 +/- 0.08 in kidneys from hormone-treated rats, suggesting stimulation of the mitochondrial glutaminase I-glutamate dehydrogenase pathway; this was supported by a proportional rise in production of glucose and CO2, end products of glutamine's carbon skeleton. Consequently, aldosterone-stimulated renal ammonia production, by specifically activating the mitochondrial pathway, leads to the elimination of hydrogen ions in the form of urinary ammonium excretion and an ensuing metabolic alkalosis.

Acid-Base Equilibrium↗
PubMed1976

Ammonia production and pathways of glutamine utilization in rat kidney slices.

Ammonia production from glutamine was studied in slices from non-acidotic and acidotic rat kidneys. Slices from non-acidotic kidneys made 53% as much ammonia from D-glutamine as from L-glutamine during the initial 15 min of incubation. Thereafter the production rate from the L-isomer accelerated while that from the D-isomer remained constant. The accelerated rate of ammonia production from L-glutamine was dependent upon tissue swelling since prevention of swelling reduced the production rate. Swelling activates the mitochondrial glutaminase I pathway as evidenced by the rise in ammonia produced per glutamine utilized ratio as well as by the accelerated rate of CO2 production derived from the oxidative disposal of glutamin's carbon skeleton. Cortical slice swelling activates the mitochondrial pathway in a manner not unlike that seen in vivo during chronic acidosis and may reflect increased permeability to glutamine. Acidotic rat kidneys are not swollen in vivo while cortical slices initially produce 4-fold more ammonia than do non-acidotic slices. After 15 min, this 4-fold difference in total ammonia production drops to only a 2-fold difference due to the swelling-induced activation of the mitochondrial pathway. Consequently, slice swelling obliterates the important fact that ammonia production by the mitochondrial pathway is 15-fold greater in acidotic than in non-acidotic kidneys.

Acidosis↗
PubMed1976

Acidosis activation of the pituitary-adrenal-renal glutaminase I axis.

Previous studies have demonstrated that the adrenal glands were necessary for acidosis activation of the mitochondrial glutaminase I pathway. The present studies were undertaken to determine if corticosterone levels are elevated in acidotic rats and if so, whether acidosis stimulates the adrenal glands directly or via the pituitary-adrenal axis. Metabolic acidosis induced by NH4Cl, either acute or chronic, increased corticosterone levels 100 to 130% in intact rats. Acute metabolic acidosis did not activate the mitochondrial pathway in adrenalectomized rats; corticosterone levels were not elevated in hypophysectomized rats nor did activation of the mitochondrial pathway occur in response to acidosis. Therefore, acidosis does not stimulate the adrenal gland directly; rather, it requires the intact pituitary. Administering exogenous corticotropin to hypophysectomized rats resulted in elevation of plasma corticosterone levels and activation of the mitochondrial pathway. The pituitary-adrenal cortex-renal glutaminase I axis apparently operates as a functional unit in the homeostatic response to metabolic acidosis.

Acidosis↗