Plasma Ornithine Concentrations Research Articles

Lysinuric protein intolerance: Pearls to detect this otherwise easily missed diagnosis.

BACKGROUND:Lysinuric protein intolerance (LPI) is a rare autosomal recessive disorder characterized by deficient membrane transport of cationic amino acids. It is caused by pathogenic variants in SLC7A7, resulting in impairment of intestinal import and renal proximal tubule loss of the affected amino acids. LPI typically presents with gastrointestinal symptoms, such as vomiting, diarrhea, and failure to thrive.CASE REPORT:A 4-year-old African-American boy presented with multiple respiratory tract infections, weight loss in the setting of chronic diarrhea and worsening abdominal distention, and multiple episodes of rectal prolapse. Development was unaffected. Laboratory examination demonstrated mild anemia, hypokalemia and hypoalbuminemia, transaminitis, and normal ammonia. Initial urine amino acid analysis did not show major elevations of lysine and ornithine, often lower than expected in the setting of malnutrition. Upon initiation of total parenteral nutrition (TPN), his urine amino acids showed a characteristic profile of dibasic aminoaciduria.CONCLUSIONS:Failure to thrive, chronic diarrhea, and hepatomegaly should raise suspicion for LPI. Urine amino acids can be normal in this condition in the setting of malnutrition, a common complication of the disease. Additionally, it has been previously shown that the plasma arginine and ornithine concentration is higher in LPI subjects.

A randomized-controlled trial of arginine infusion in severe sepsis on microcirculation and metabolism.

Sepsis is hypothesized as an arginine deficient state, with lack of nitric oxide (NO) for adequate microcirculation and local perfusion. This study aimed to investigate if prolonged (72-h) intravenous l-arginine administration in sepsis patients improves microcirculation. Secondly, effects on arginine and protein metabolism, and organ function were studied. Critically ill patients with a diagnosis of septic shock participated in a long-term (72h) randomized double-blind placebo-controlled parallel-group study. l-arginine-HCl (1.2μmolkg-1min-1; n=9) or l-alanine (isocaloric control: 2.4μmolkg-1min-1; n=9) was continuously infused. Primary study outcome was microcirculation, assessed as gastric mucosal perfusion by gastric tonometry (Pr-aCO2 gap) and skin perfusion by Laser Doppler flowmetry. Secondary endpoints were whole body (WB) arginine and protein metabolism, organ function and clinical outcomes. We measured global hemodynamics continuously for safety monitoring. Statistical analyses were performed by mixed model for repeated measures with treatment by time interaction as estimate for between-group difference. Pr-aCO2 increased only in the l-arginine group (p=0.006), without a significant between-group difference (p=0.17). We found no significant differences in skin perfusion parameters. l-arginine infusion resulted in a larger increase of plasma arginine and ornithine concentrations (p<0.01), WB (endogenous) arginine appearance (p<0.001), WB NO synthesis (p=0.027) and WB arginine to urea conversion (p<0.001) than infusion of l-alanine. We found no effect on global hemodynamics, and protein metabolism by l-arginine infusion. Organ function parameters were unaffected, except for a significant difference between groups in intra-abdominal pressure over time (p=0.029). Prolonged intravenous l-arginine administration does not improve local perfusion and organ function despite an increase in WB NO synthesis. Administration is safe with regard to global hemodynamics, but the observed increase in Pr-aCO2 and intra-abdominal pressure warrants careful application of l-arginine infusion and further research, especially in the early stage of septic shock.

Identification of arginine and its "Downstream" molecules as potential markers of breast cancer.

Breast cancer (BC) is the most commonly diagnosed cancer in women worldwide. Arginine is a semiessential amino acid in humans and is essential for several biological pathways in malignant and normal cells, such as ornithine and N1, N12-diacetylspermine (DiAcSpm). This study aimed to determine the role of arginine and these downstream molecules in BC. Plasma arginine, ornithine, and arginine-to-ornithine ratio (AOR) were analysed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Urine samples were measured by the colloid gold aggregation to test determination of urinary diAcSpm. A principal component analysis was performed to evaluate the results observed between breast tumor and control characteristics. Differences in individual metabolite concentrations between BC patients and controls were tested by receiver operating characteristics (ROC) analyses. Student's t tests were used to detect the differences between two groups of normally distributed variables, and Wilcoxon sign rank tests were performed for asymmetrically distributed variables. As we analyzed, BC patients had lower plasma arginine and arginine/ornithine level, and higher plasma ornithine and urinary DiAcSpm concentrations as compared with control patients (P = 0.028, 0.020, 0.002, and 0.011, respectively). And the ROC curve was drawn and the area under the curve of the metabolites was calculated to be 0.659 (P = 0.028), 0.645 (P = 0.045), 0.7233 (P = 0.002), 0.683 (P = 0.011), respectively. In addition, our analysis showed that arginine concentrations and AOR had a positive correlation with ER status, while ornithine had a negative correlation with T stage (P = 0.042, 0.023, respectively).In conclusion, arginine and these downstream molecules were biomarkers for BC. More studies are needed to highlight the theoretical strengths. © 2016 IUBMB Life, 68(10):817-822, 2016.

L-ornithine hydrochloride ingestion increased carbohydrate oxidation but not lipid oxidation during submaximal endurance exercise following resistance exercise

This study aimed to examine the effect of L-ornithine hydrochloride ingestion on lipid oxidation during submaximal endurance exercise following resistance exercise. Ten healthy young male adults with no history of regular resistance exercise (age: 26.0 +/- 4.4) conducted resistance exercise after L-ornithine hydrochloride or placebo ingestion (0.1 g/kg). Subjects exercised for 60 min on an ergometer at 50% VO2peak 120 min after resistance exercise. Plasma ornithine concentrations measured immediately, 120min and 180min after resistance exercise in the L-ornithine hydrochloride ingestion condition were significantly greater than those in the placebo condition. No significant difference was found in serum growth hor mone concentrations between both conditions (F = 4.4, p = 0.065). Serum free fatty acid concentrations were significantly greater immediately after submaximal ergometer bicycle exercise in both conditions than those before ingestion, immediately after resistance exercise and 120min after resistance exercise (F = 43.4, p .001, 300% - 508%), but no significant difference was found between both conditions (F = 3.6, p = 0.090). A similar trend was observed in serum ketone bodies as well. Although total energy production during submaximal ergometer exercise did not significantly differ (t = 0.74, p = 0.238), a significant difference was found in energy production via carbohydrate and lipid oxidation; the former was greater in the Lornithine hydrochloride ingestion condition (t = 1.89, p = 0.046, d = 0.44, 106%), and the latter was greater in the placebo condition (t = 1.89, p = 0.046, d = 0.78%, 145%). From the above, L-ornithine hydrochloride ingestion may not affect lipid metabolism during submaximal endurance exercise following resistance exercise. It may be involved in energy production via carbohydrate oxidation with glucogenic amino acid.

Impaired fracture healing associated with amino acid disturbances

Five percent to 10% of all fracture patients experience an inadequate healing process that results in a nonunion of fracture parts. Previous experimental studies have indicated the importance of sufficient nitric oxide production from arginine during normal fracture healing. However, during conditions of stress, such as inflammation, arginine availability can become limited, which may lead to a nonunion as a result of insufficient callus formation. The aim of this study was to measure callus and plasma amino acid concentrations in patients with and without a fracture nonunion. Amino acid concentrations in plasma and callus were measured with HPLC in atrophic nonunions (n = 12) and compared with those in hypertrophic nonunions (n = 12), acute fractures (n = 15), and healed fractures (n = 8). Arginine (61 compared with 180 μmol/mg; P < 0.0001), citrulline (13 compared with 44 μmol/mg; P < 0.0001), and ornithine (25 compared with 149 μmol/mg; P < 0.0001) in callus were significantly lower in atrophic-nonunion patients than in healed-fracture patients. In hypertrophic nonunions, arginine was significantly higher and ornithine was lower than in healed fractures. Plasma arginine concentrations were significantly lower in patients with hypertrophic nonunions (62 μmol/L; P < 0.001) and acute-fracture patients (41 μmol/L; P < 0.001) but not in atrophic-nonunion patients. Plasma ornithine concentrations were lower in all groups than in acute-fracture patients. Amino acid concentrations were significantly changed in nonunion patients. Atrophic nonunions had lower concentrations of all amino acids, whereas hypertrophic nonunions had higher arginine and lower ornithine concentrations at fracture sites than did healed-fracture and acute-fracture patients.

Oral citrulline does not affect whole body protein metabolism in healthy human volunteers: Results of a prospective, randomized, double-blind, cross-over study

Citrulline increases protein synthesis during refeeding in rodents with short bowel syndrome, aging and malnutrition, and improves nitrogen balance in fed healthy humans. The aim of the current study therefore was to determine whether citrulline had affected protein metabolism in healthy volunteers. In a randomized, double-blind, cross-over study, 12 healthy adults received a 5-h intravenous infusion of L-[1-(13)C]-leucine in the post-absorptive state, after a 7-day oral supplementation with 0.18 g/kg/day citrulline, or an iso-nitrogenous placebo. Treatment order was randomized, treatment periods were separated by 13-day wash out. Leucine appearance rate (Ra) was determined from plasma [1-(13)C]-keto-iso-caproate enrichment and leucine oxidation from expired (13)CO(2), and nitrogen balance was estimated from 6-h urinary urea excretion. Compared with placebo, oral citrulline supplementation increased plasma citrulline, arginine and ornithine concentrations, but failed to affect albumin, transthyretin, free insulin and insulin-like growth factor (IGF)-1 plasma concentrations, urinary nitrate excretion, or nitrogen balance. Citrulline supplementation did not alter leucine Ra, leucine oxidation, nor whole-body protein synthesis. In healthy, well nourished volunteers, oral citrulline increases plasma citrulline and arginine availability but does not affect whole-body protein kinetics in the post-absorptive state.

OP054 REGULATION OF NEURONAL SURVIVAL FACTORS BY ß-HYDROXY-ß-METHYLBUTYRATE (HMB): FUTURE THERAPEUTIC IMPLICATIONS

plasma [13C]-ketoisocaproate and leucine oxidation from breath CO2. Results: Compared with placebo, oral citrulline supplementation increased plasma citrulline (mean±SD, 303±98 vs. 27±5mmol/L, P< 0.001), arginine (163±25 vs.72±154mmol/L, P< 0.001) and ornithine (96±37 vs. 52±14mmol/L, P< 0.001) concentrations, but failed to affect albumin, transthyretin, insulin and insulin-like growth factor (IGF)-1 plasma concentrations, urinary nitrate excretion, or nitrogen balance ( 4.8±2.4 vs. 4.1±2.5 g/6 h). Protein breakdown (125±8 vs. 124±9 mmol/kg/h), leucine oxidation (23±3 vs. 22±4mmol/ kg/h), and whole-body protein synthesis (102±9 vs. 102±6mmol/kg/h) were not affected by citrulline supplementation. Conclusion: In healthy volunteers, oral citrulline does not affect whole-body protein kinetics in the postabsorptive state, but strongly increases plasma citrulline and arginine availabilities.

OP053 TRANSCRIPTION OF THE MEVALONATE PATHWAY IS UP-REGULATED BY AMINO ACIDS IN L6 SKELETAL MUSCLE CELLS SUGGESTING LOCAL STEROIDOGENESIS FOR ANABOLIC REACTIONS

plasma [13C]-ketoisocaproate and leucine oxidation from breath CO2. Results: Compared with placebo, oral citrulline supplementation increased plasma citrulline (mean±SD, 303±98 vs. 27±5mmol/L, P< 0.001), arginine (163±25 vs.72±154mmol/L, P< 0.001) and ornithine (96±37 vs. 52±14mmol/L, P< 0.001) concentrations, but failed to affect albumin, transthyretin, insulin and insulin-like growth factor (IGF)-1 plasma concentrations, urinary nitrate excretion, or nitrogen balance ( 4.8±2.4 vs. 4.1±2.5 g/6 h). Protein breakdown (125±8 vs. 124±9 mmol/kg/h), leucine oxidation (23±3 vs. 22±4mmol/ kg/h), and whole-body protein synthesis (102±9 vs. 102±6mmol/kg/h) were not affected by citrulline supplementation. Conclusion: In healthy volunteers, oral citrulline does not affect whole-body protein kinetics in the postabsorptive state, but strongly increases plasma citrulline and arginine availabilities.

Effects ofdl-2-hydroxy-4-methylthiobutyrate on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability

The present study was conducted in a one-factorial arrangement to determine the effects of dl-2-hydroxy-4-methylthiobutyrate (dl-HMTB) on the first-pass intestinal metabolism of dietary methionine and its extra-intestinal availability. Barrows (n 6; aged 35 d; weight 8.6 kg), implanted with arterial, portal, mesenteric and gastric catheters, were fed a diet containing dl-methionine (dl-MET) or dl-HMTB once hourly and infused intramesenterically with 1 % p-aminohippurate and intragastrically with [1-13C]methionine at 7.0 mumol/kg body weight per h. Arterial and portal blood samples were taken at hourly intervals until 6 h of tracer infusion and pigs was then killed for collection of muscle, intestine, liver and kidney samples. The net portal appearance of methionine, expressed as the fraction of ingested directly available l-methionine, was higher (P < 0.05) in the dl-HMTB than in the dl-MET diet, and there was no difference (P = 0.26) in the fractional portal balance of [1-13C]methionine between the diets. [1-13C]methionine enrichment (tracer:tracee ratio; mol/100 mol amino acid) in the jejunum, arterial and portal plasma, liver, kidney and muscle was also not different (P>0.05) between the groups. Over the 6 h period after the start of feeding, the average concentration of citrulline both in the arterial and portal plasma was higher (P < 0.05) in the dl-HMTB than in the dl-MET group, and arterial plasma ornithine and taurine concentration was also higher (P < 0.05) in the dl-HMTB than in the dl-MET group. However, plasma urea concentration both in the arterial and portal vein was lower (P < 0.05) in the dl-HMTB than in the dl-MET group. These results suggested that the potential difference in the first-pass use of methionine by the intestine between the dl-HMTB and dl-MET diets might affect intestinal and systemic metabolism of other amino acids, which may provide new important insights into nutritional efficiency of different methionine sources.

Secondary creatine deficiency in ornithine delta-aminotransferase deficiency

Aims Ornithine delta-aminotransferase (OAT) deficiency causes gyrate atrophy (GA) of the retina, as a consequence of high plasma ornithine concentrations. Because creatine synthesis requires the conversion of arginine and glycine into ornithine and guanidinoacetate, high ornithine concentration inhibits this reaction thus causing secondary creatine deficiency. The aim of this study was to evaluate the neuropsychological features and creatine metabolism in patients with GA. Methods The study involved 7 GA patients, aged from 11 to 27 years who underwent neuropsychological evaluation and cerebral proton magnetic resonance spectroscopy (MRS). Results Neurocognitive impairment was found in 5/7 patients, including mental retardation (3/7), school failure (1/7), major visuospatial dyspraxia (1/7), aggressive behavior (3/7) and epilepsy (2/7). Two patients had normal neuropsychological evaluation. Cerebral proton magnetic resonance spectroscopy revealed a profound creatine deficiency in all patients. MRS data were confirmed by decreased levels of creatine and/or guanidinoacetate in plasma and urine in all patients. Conclusions In our group of patients with GA, we found a high prevalence of neurological impairment, not reported so far, and possibly related to secondary creatine deficiency and hyperornithinemia. We propose to treat mentally retarded GA patients with high doses of creatine, as it may normalize brain creatine levels and help to reduce ornithine levels.

Overexpression of ornithine aminotransferase: consequences on amino acid homeostasis

Ornithine aminotransferase (OAT) is a reversible enzyme expressed mainly in the liver, kidney and intestine. OAT controls the interconversion of ornithine into glutamate semi-aldehyde, and is therefore involved in the metabolism of arginine and glutamine which play a major role in N homeostasis. We hypothesised that OAT could be a limiting step in glutamine-arginine interconversion. To study the contribution of the OAT enzyme in amino acid metabolism, transgenic mice that specifically overexpress human OAT in the liver, kidneys and intestine were generated. The transgene expression was analysed by in situ hybridisation and real-time PCR. Tissue (liver, jejunum and kidney) OAT activity, and plasma and tissue (liver and jejunum) amino acid concentrations were measured. Transgenic male mice exhibited higher OAT activity in the liver (25 (sem 4) v. 11 (sem 1) nmol/min per microg protein for wild-type (WT) mice; P < 0.05) but there were no differences in kinetic parameters (i.e. Km and maximum rate of reaction (Vmax)) between WT and transgenic animals. OAT overexpression decreased plasma and liver ornithine concentrations but did not affect glutamine or arginine homeostasis. There was an inverse relationship between ornithine levels and OAT activity. We conclude that OAT overexpression has only limited metabolic effects, probably due to the reversible nature of the enzyme. Moreover, these metabolic modifications had no effect on phenotype.

Metabolic effects of glutamine and glutamate ingestion in healthy subjects and in persons with chronic obstructive pulmonary disease

Because low plasma glutamate and glutamine concentrations are often seen in chronic obstructive pulmonary disease (COPD), glutamine or glutamate supplementation may be a good option for preventing further metabolic disturbances in COPD patients. However, the metabolic effects of glutamate supplementation have never been compared with those of glutamine supplementation. We compared the metabolic effects of repeated ingestion of glutamine and glutamate in COPD patients and in age-matched healthy control subjects. On 3 d separated by intervals of > or = 2 d, a protocol of primed constant and continuous infusion of [2H5]phenylalanine and [2H2]tyrosine was performed for 3 h in 8 stable male COPD patients and 8 healthy control subjects. After a 90-min tracer infusion, all subjects ingested a glutamine or glutamate drink or the same amount of water every 20 min for 80 min. Blood samples were taken at the end of the postabsorptive and ingestion periods to test for effects on plasma amino acid and substrate concentrations and whole-body protein turnover. Glutamate but not glutamine ingestion resulted in higher plasma ornithine concentrations than did water ingestion (P < 0.01). The change in plasma arginine, citrulline, and urea concentrations was significantly (P < 0.01) higher after glutamine ingestion than after water or glutamate ingestion. Whole-body protein turnover decreased overall, independent of the drink consumed. Repeated ingestion of glutamine and glutamate resulted in different effects on the plasma amino acid concentration. In both groups, ingestion of glutamine but not of glutamate increased the plasma concentrations of citrulline and arginine, substrates produced in the intestine and the liver.

Blood cell NO synthesis in response to exercise

Nitric oxide (NO) is important for the maintenance of cardiovascular homeostasis and is also involved in immunity and inflammation. The aim of our work was to determine the effects of intense exercise on plasma and blood cell NO handling. Nine voluntary male professional cyclists participated in the study. Blood samples were taken in basal conditions and 3h after finishing a mountain cycling stage. Exercise-induced neutrophilia, lymphopenia, and hemolysis. Plasma and erythrocytes maintained basal nitrite levels, whereas neutrophils and lymphocytes decreased nitrite concentration after intense exercise. Basal iNOS levels and SOD activity were similar in neutrophils and lymphocytes. iNOS levels and SOD activity dropped in neutrophils and rose in lymphocytes after exercise. Arginase activity rose only in lymphocytes. Neutrophil nitrite was correlated with SOD activity and iNOS levels, but not in lymphocytes. iNOS levels were correlated with SOD in both neutrophils and lymphocytes. Intense exercise maintained plasma basal arginine and ornithine concentration, and decreased citrulline concentration. Intense exercise induced important changes in NO handling in neutrophils and lymphocytes, yet the basal picture was maintained in erythrocytes.

Supplemental enteral arginine is metabolized to ornithine in injured patients 1

Arginine has been added to immune enhancing diets that may improve patient outcomes, but little is known about the metabolic fate of supplemental arginine. We hypothesize that supplemental enteral arginine in injured patients is metabolized to ornithine by increased activity of the enzyme arginase. Twenty-five adult patients with injury severity scores > or =20 received up to 14 days of enteral nutrition supplemented with arginine (30 g/day) or placebo in a prospective, randomized, blinded study. Plasma arginine, citrulline, and ornithine concentrations and peripheral blood mononuclear cell (PBMC) arginase activity were measured at baseline and on days 1, 3, 5, 7, 10, and 14. Clinical data collected included demographics, injury patterns, lengths of stay, and infectious complications. Data were analyzed using ANOVA and t test. PBMC arginase activity was elevated in all patients. In the supplemented group, plasma arginine concentrations increased at days 7, 10, and 14 when compared to baseline (P < 0.05) and were higher at day 14 when compared to those of controls (P < 0.05). Citrulline concentrations in both groups were unchanged over time. Ornithine concentration increased within 24 h of arginine supplementation and remained elevated when compared to baseline (P < 0.01). Ornithine concentration in the supplemented group was higher at days 1, 3, 5, and 7 when compared to that of controls (P < 0.05). There were no differences in clinical outcomes. Supplemental enteral arginine is absorbed in injured patients and increases arginine levels. Supplemental arginine appears to be metabolized to ornithine. Increased arginase enzyme activity in peripheral blood mononuclear cells may be a contributor.

A decrease in glucose production is associated with an increase in plasma citrulline response to oral arginine in normal volunteers

Acute arginine administration (30 g) increases insulin secretion and reduces glucose production (GP). A slower administration of l-arginine may have direct effect on the liver without increasing C-peptide or insulin secretion. We tested the direct effect of oral l-arginine on fasting GP in 15 normal-weight volunteers and compared these to a group of l-alanine-treated controls (placebo). Volunteers were admitted to the General Clinical Research Center for a 3-day stay. Three grams of freebase arginine or alanine was ingested hourly between 4 am and 2 pm. Neither arginine nor alanine had an effect on C-peptide or insulin concentration. Oral arginine, but not alanine, increased plasma arginine, citrulline, and ornithine concentrations. Arginine-treated volunteers had a greater fall in GP as compared to the alanine-treated group (16.2% ± 1.9% v 9.7% ± 3.6%, respectively; P < .05). Five volunteers treated with arginine had less than a 30% increase in citrulline concentration (26 ± 2 to 32 ± 2 μmol/L, mean ± SEM) and 10 volunteers had equal to or greater than a 30% increase in plasma citrulline concentration (29 ± 2 to 49 ± 4 μmol/L, P <.05). Since citrulline is generated in the conversion of arginine to nitric oxide (NO), the failure of oral arginine to increase citrulline concentration suggests that NO generation may be varied in different individuals. The increased plasma citrulline group reduced GP by 18.2% ± 1.9% over the final 4 hours of arginine administration (2.00 ± 0.08 to 1.64 ± 0.07 mg/kg/min; P < .01). In contrast, GP only decreased by 12.4% ± 3.9% (1.97 ± 0.13 to 1.73 ± 0.13 mg/kg/min; not significant [NS]) in those who had little to no increase in plasma citrulline concentration. The 12% decrease in GP in the hyporesponders was similar to the 10% decrease seen in the alanine-treated normal volunteers (9.7% ± 3.6%). Individuals may have a variable NO response from an oral arginine administration. GP is suppressed in those who have a greater increase in plasma citrulline concentration.

Effects of dietary salt intake on plasma arginine

Because L-arginine is degraded by hepatic arginase to ornithine and urea and is transported by the regulated 2A cationic amino acid y(+) transporter (CAT2A), hepatic transport may regulate plasma arginine concentration. Groups of rats (n = 6) were fed a diet of either low salt (LS) or high salt (HS) for 7 days to test the hypothesis that dietary salt intake regulates plasma arginine concentration and renal nitric oxide (NO) generation by measuring plasma arginine and ornithine concentrations, renal NO excretion, and expression of hepatic CAT2A, and arginase. LS rats had lower excretion of NO metabolites and cGMP, lower plasma arginine concentration (LS: 83 +/- 7 vs. HS: 165 +/- 10 micromol/l, P < 0.001), but higher plasma ornithine concentration (LS: 82 +/- 6 vs. HS: 66 +/- 4 micromol/l, P < 0.05) and urea excretion. However, neither the in vitro hepatic arginase activity nor the mRNA for hepatic arginase I was different between groups. In contrast, LS rats had twice the abundance of mRNA for hepatic CAT2A (LS: 3.4 +/- 0.4 vs. HS: 1.6 +/- 0.5, P < 0.05). The reduced plasma arginine concentration with increased plasma ornithine concentration and urea excretion during LS indicates increased arginine metabolism by arginase. This cannot be ascribed to changes in hepatic arginase expression but may be a consequence of increased hepatic arginine uptake via CAT2A.

L-arginine attenuates trauma-hemorrhage-induced liver injury.

Liver injury is common after trauma-hemorrhage for which the underlying mechanism is not clear. Although administration of the essential amino acid L-arginine has been reported to restore the depressed cardiovascular functions and cell-mediated immune responses after trauma-hemorrhage, it remains unknown whether L-arginine protects against liver injury under those conditions. A prospective, controlled animal study. A university research laboratory. Male Sprague-Dawley rats. Rats underwent sham operation or laparotomy and were bled to and maintained at a mean arterial blood pressure of 40 mm Hg until 40% of the maximum shed blood volume was returned in the form of lactated Ringer's solution. Hemorrhaged rats were then resuscitated with lactated Ringer's solution, four times the maximum shed blood volume over 1 hr. During resuscitation, animals received either 300 mg/kg of L-arginine or saline (vehicle) intravenously. At 3 and 5 hrs after resuscitation, rats were killed, blood was obtained, and the liver was fixed for histology (hematoxylin & eosin staining). Plasma glutathione S-transferase (a marker of liver damage), L-arginine, citrulline, and ornithine concentrations were assessed. The increased concentrations of plasma glutathione S-transferase observed in vehicle-treated hemorrhage animals were normalized with L-arginine treatment at 5 hrs after resuscitation. Moreover, the histology indicated that L-arginine prevented liver edema and neutrophil infiltration after trauma-hemorrhage. Plasma L-arginine and citrulline were increased in L-arginine-treated rats. Because citrulline is a by-product of nitric oxide generation by nitric oxide synthase from L-arginine, this amino acid may be a useful adjunct for preventing hepatic injury after trauma-hemorrhage via endothelial derived nitric oxide production.

Influence of dietary arginine concentration on lymphoid organ growth in chickens

In vivo effects of graded dietary levels of arginine on the body and lymphoid organs were investigated using Cornell K strain chickens of the B15/B15 haplotype. Two-week-old birds were fed an arginine-deficient basal diet (0.53% arginine) supplemented with additional arginine (up to 1.0% L-arginine to the diet). At four weeks of age, body weight, lymphoid organ weight, and concentrations of amino acids in plasma were measured. Arginine supplementation produced significant increases in plasma arginine (from 200 nM in chicks fed the basal diet to 2,000 nM in chicks receiving the 1.5% arginine diet) and ornithine concentrations (from 17 nM in chicks fed the basal diet to 500 nM in chicks receiving the 1.5% arginine diet). The arginine-deficient diet reduced body weight gain (P < 0.0001) and thymus, spleen, and bursa of Fabricius weights (P < 0.05). In contrast to the bursa weight, the thymus and spleen weights, as percentages of body weight, were also decreased (P < 0.05). This study suggests that arginine markedly influences lymphoid organ development, with a more pronounced effect on the thymus and spleen than on the bursa of Fabricius.

Reduced brain creatine in gyrate atrophy of the choroid and retina with hyperornithinemia.

To analyze in vivo brain creatine (Cr) content in gyrate atrophy of the choroid and retina with hyperornithinemia (GA). GA is caused by inherited deficiency of ornithine-delta-aminotransferase activity. Patients lose their vision by middle age and develop selective atrophy of type II skeletal muscle fibers. As demonstrated by MRS, the patients' skeletal muscles have diminished stores of high-energy Cr phosphate. Minor structural and electrophysiologic abnormalities in the brain of these patients also imply that the CNS may be affected. The authors acquired proton MR spectra of the basal ganglia of 22 healthy control subjects and 20 GA patients. Nine patients received supplementary Cr or its precursors, and one child was on an arginine-restricted diet to normalize plasma ornithine concentration. The ratios of N-acetylaspartate (NAA) to Cr, NAA to choline (Cho), and Cho to Cr, and the ratios of NAA, Cho, and Cr to tissue water were calculated. NAA/Cr (Cho/Cr) in the untreated and treated patients and control subjects were (mean +/- SD) 3.3+/-0.4, 2.0+/-0.4, and 1.5+/-0.7 (1.9+/-0.3, 1.3+/-0.4, and 0.9+/-0.2), indicating that Cr content in untreated GA patients was proportionally and markedly diminished, and partially corrected by therapy (p < 0.0001). NAA/Cho was similar in all three groups. Cr/water in the untreated patients was only 46%, and increased to 75% of the control ratios in the treated patients (p < 0.0001). Hyperornithinemia-associated Cr deficiency in GA also affects the CNS, further supporting the possibility that Cr deficiency also has a pathogenetic role in the retina. The deficiency was partially corrected by Cr supplementation and an arginine-restricted diet.

Studies of Arginine Metabolism and Salt Sensitivity in the Dahl/Rapp Rat Models of Hypertension

Previous studies by our group demonstrated a striking relationship among arginine, nitric oxide production, and salt-sensitive hypertension in the Dahl/Rapp rat. We hypothesized that enzymes of the urea cycle may be involved in this process. We specifically examined the activities of liver and kidney argininosuccinate synthetase (AS), because this enzyme is an essential step of arginine synthesis and a likely control point. We found that salt-sensitive (S) rats on a high-salt diet developed hypertension without change in plasma concentrations of arginine, citrulline, and ornithine. Baseline plasma concentrations of these amino acids were the same in rats of all three genotypes: Sprague-Dawley (SD), S, and salt-resistant (R) Dahl/Rapp rats. In contrast, R rats on the high-salt diet remained normotensive coincidentally with elevated levels of arginine and ornithine, as compared to normotensive R rats on low-salt diet with no changes in amino acid concentrations. S rats on high-salt diet became hypertensive coincidentally with no changes in amino acid concentrations. None of the rat groups had significantly different activity of liver or kidney AS coincidental with the salt in the diet and the changes in amino acid concentrations found in the R rats. Thus, given the lack of alteration in plasma concentrations of the urea cycle amino acids of arginine, citrulline, and ornithine in S rats, genes of the urea cycle/arginine synthesis are unlikely to be involved in salt-sensitive hypertension in this strain. The mechanism of increased plasma arginine and ornithine concentrations in R rats was not determined, but was not related to AS activity.