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PubMed2000

Influence of the novel urease inhibitor N-(n-butyl) thiophosphoric triamide on ruminant nitrogen metabolism: II. Ruminal nitrogen metabolism, diet digestibility, and nitrogen balance in lambs.

Three lamb metabolism experiments were conducted to investigate the effects of chronic administration of the novel urease inhibitor N (n-butyl) thiophosphoric triamide (NBPT) on ruminal N metabolism, fermentation, and N balance. In Exp. 1, ruminally cannulated wethers (n = 28; 45.0 +/- .9 kg) were administered one of seven doses of NBPT (0 [control], .125, .25, .5, 1, 2, or 4 g of NBPT daily) and fed a common cracked corn/cottonseed hull-based diet twice daily containing 2% urea at 2.5% of initial BW for the duration of the 15-d experiment. Overall, NBPT decreased (linear P < .0001; quadratic P < .001) ruminal urease activity, resulting in linear increases (P < .0001) in ruminal urea and decreases in ruminal NH3 N concentrations. However, the detection of an NBPT x day interaction (d 2 vs 15; P < .01) indicated that this depression in urea degradation diminished as the experiment progressed. Increasing NBPT linearly decreased (P < .01) total VFA concentrations on d 2 of the experiment, but it had no effect (P > .10) on d 15. Increasing NBPT had no effect (P > .10) on DM or ADF digestibilities, but it linearly decreased (P < .01) N digestibility. Supplementing NBPT produced a linear increase (P < .05) in urinary N excretion and a linear decrease (P < .01) in N retention. In Exp. 2, ruminally cannulated wethers (n = 30; 46.8 +/- .6 kg) were fed one of two basal diets (2.0 vs 1.1% dietary urea) at 2.5% of initial BW and dosed with either 0 (control), .25, or 2 g of NBPT daily for the duration of the 15-d experiment. There were no NBPT x dietary urea interactions (P > .10) for Exp. 2. Increasing NBPT depressed (linear and quadratic P < .0001) ruminal urease activity, producing linear (P < .0001) increases in urea N and linear decreases in NH3 N in the rumen. As in Exp. 1, an NBPT x day interaction (P < .05) was noted for urea, NH3 N, and total VFA concentrations; the maximum response to NBPT occurred on d 2 but diminished by d 15 of the experiment. Administration of NBPT did not influence (P > .10) DM, ADF, or N digestibilities in Exp. 2. In Exp. 3, wether lambs (n = 30; 26.4 +/- .7 kg) were subjected to the same treatment regimen as in Exp. 2 for a 14-d N balance experiment. Although several NBPT x dietary urea interactions (P < .05) were noted, increasing NBPT did not affect (P > .10) N digestibility. Administration of NBPT quadratically increased (P < .10) urinary N excretion, producing a linear decrease (P < .05) in N retention. These results suggest that although NBPT is capable of inhibiting ruminal urease short-term, the ruminal microflora may be capable of adapting to chronic NBPT administration, thereby limiting its practical use in improving the utilization of dietary urea.

Ammonia↗
PubMed1985

Nitrogen sparing effect of Ornicetil in the immediate postoperative state clinical biochemistry and nitrogen balance.

The salt complex of alpha-ketoglutarate and ornithine, L(+)ornithine alpha-ketoglutarate - ORNICETIL (OR) - is able to bind six amino groups per molecule without enzymatic intervention. The present study was undertaken to determine whether intravenous administration of OR together with total parenteral nutrition (TPN) has a beneficial effect on nitrogen utilization in the immediate postoperative phase. Thirteen patients were investigated after major abdominal operations (resection of colon or rectum). All patients received TPN for 5 days postoperatively. Energy (165 kJ/kg BW) was given as fat (Intralipid 20%) and carbohydrate (Glucose 20%). Seven patients (controls) received 0.15 g amino acid (AA)-N/kg BW (Vamin). Six patients had an isonitrogenous regimen but with 2.5 g AA-N being replaced by Ornicetil (OR group). The excretion of urea, creatinine, ammonia, 3-methyl-histidine (3-MeHis) and total-N was determined throughout the study and the daily nitrogen balance was calculated. Blood samples were drawn serially before and after surgery for routine clinical biochemistry. The day-to-day nitrogen balance was significantly better when OR was given. Urea excretion was significantly reduced, and the urinary ammonia losses in the OR group were one third of those in the control group. In the control group 3-MeHis correlated negatively with the nitrogen balance. The regression line obtained, y = 265 - 21.6 x (p < 001), and the calculated correlation coefficient, r = 0.87 (p < 0.001), were highly significant. In contrast, no correlation could be demonstrated between 3-MeHis output and nitrogen balance in the OR group (r = 0.18, N.S.). The results indicate better postoperative nitrogen economy in the OR group than in the control group. Stimulation of insulin and growth hormone secretion may be contributing factors in the better nitrogen utilization. The increased ammonia excretion postoperatively in the control group was completely abolished when OR was given simultaneously with decreased urea formation, suggesting a product inhibition of arginase in the liver cytosol and also indicating that amino groups generated by the enhanced gluconeogenesis were trapped by OR owing to stimulated transamination in peripheral muscle tissues. The significant negative correlation between 3-MeHis excretion and nitrogen balance in the control group strongly indicates a correlation between net protein catabolism and increased postoperative muscle protein breakdown. In contrast, the total absence of correlation between nitrogen balance and 3-MeHis excretion in the OR group suggests a diminished (or zero) net muscle protein breakdown.

Journal Article↗
PubMed2000

Growth and nitrogen metabolism of Catasetum fimbriatum (orchidaceae) grown with different nitrogen sources.

Catasetum fimbriatum is an epiphytic orchid from South America that has been used for 15 years as a model plant for metabolic and developmental studies in our laboratory. In this work, C. fimbriatum plants were aseptically grown with 6 mol m(-3) of either glutamine or inorganic nitrogen forms (NO(3)(-):NH(4)(+) ratios). The highest biomass accumulation was found in plants supplied with glutamine; no significant difference was observed in plants incubated in the presence of inorganic nitrogen sources. Nitrogen assimilation was limited in the presence NO(3)(-) as a sole nitrogen source. C. fimbriatum did not accumulate NO(3)(-) and very low rates of in vivo nitrate reductase activity were observed. Most nitrate reductase activity (70%) was detected in the 2 cm apical roots. Nitrate-treated plants exhibited relatively lower amounts of free amino-N, chlorophyll and free NH(4)(+) contents and higher soluble sugar contents than the NH(4)(+)-treated plants. While shoot glutamine synthetase activity was only slightly affected by nitrogen sources, root glutamine synthetase activity was not modified by any nitrogen form. Glutamate dehydrogenase-NADH activity in shoot tissues was not influenced by any nitrogen source. However, the glutamate dehydrogenase-NADH activity in roots was enhanced when NH(4)(+) tissue contents was augmented by increasing NH(4)(+) in the medium and by the presence of glutamine. Our results strongly suggest that organic nitrogen and NH(4)(+) are probably the most important nitrogen sources to C. fimbriatum plants.

Journal Article↗
PubMed2001

Pattern of cyanophycin accumulation in nitrogen-fixing and non-nitrogen-fixing cyanobacteria.

The temporal and spatial accumulation of cyanophycin was studied in two unicellular strains of cyanobacteria, the diazotrophic Cyanothece sp. strain ATCC 51142 and the non-diazotrophic Synechocystis sp. strain PCC 6803. Biochemistry and electron microscopy were used to monitor the dynamics of cyanophycin accumulation under nitrogen-sufficient and nitrogen-deficient conditions. In Cyanothece sp. ATCC 51142 grown under 12 h light/12 h dark nitrogen-fixing conditions, cyanophycin was temporally regulated relative to nitrogenase activity and accumulated in granules after nitrogenase activity commenced. Cyanophycin granules reached a maximum after the peak of nitrogenase activity and eventually were utilized completely. Knock-out mutants were constructed in Synechocystis sp. PCC 6803 cphA and cphB genes to analyze the function of these genes and cyanophycin accumulation under nitrogen-deficient growth conditions. The mutants grew under such conditions, but needed to degrade phycobilisomes as a nitrogen reserve. Granules could be seen in some wild-type cells after treatment with chloramphenicol, but were never found in Delta cphA and Delta cphB mutants. These results led to the conclusion that cyanophycin is temporally and spatially regulated in nitrogen-fixing strains such as Cyanothece sp. ATCC 51142 and represents a key nitrogen reserve in these organisms. However, cyanophycin appeared to play a less important role in the non-diazotrophic unicellular strains and phycobilisomes appeared to be the main nitrogen reserve.

Bacterial Proteins↗