3-Hydroxy-2-methylbutyryl-CoA dehydrogenase deficiency.

A boy now 8 years old presented at 21 months of age with developmental arrest, followed by regression, cortical blindness and myoclonic seizures. Urine organic acid analysis revealed 3-hydroxy-2-methylbutyric acid and tiglyglycine; 3-ketothiolase enzyme activity was normal and he was subsequently found to have 3-hydroxy-2-methylbutyryl-CoA dehydrogenase deficiency.

Analysis of guanidinoacetate and creatine by isotope dilution electrospray tandem mass spectrometry.

Guanidinoacetate methyltransferase (GAMT) deficiency is a disorder of creatine metabolism characterized by low plasma creatine concentrations in combination with elevated guanidinoacetate (GAA) concentrations. Although rare, GAMT deficiency has been identified in children with seizures, extrapyramidal movements, developmental delay, myopathies and behavioral abnormalities. Treatment with creatine monohydrate has been proven to be effective. We describe an isotope dilution electrospray tandem mass spectrometry (ES-MS/MS) assay for the simultaneous determination of plasma GAA and creatine using multiple reaction monitoring (MRM), d(3)-creatine as the internal standard and derivatization of GAA and creatine as butyl-esters. We analysed plasma of 16 healthy adults and 20 healthy children as well as three affected children. Plasma GAA concentrations were 5.02+/-1.84 micromol/l (mean+/-S.D.) in adults, 3.91+/-0.76 micromol/l in children age 5-10 years and 11.57, 15.16, 14.36 micromol/l in children with GAMT deficiency. Plasma creatine concentrations were 34.7+/-15.25 micromol/l in adults, 58.96+/-22.30 micromol/l in children and 5.37, 8.15, 403.5 micromol/l in two untreated children and one treated child with GAMT deficiency, respectively. GAA can also be reliably measured from filter cards, which is sufficient to make the correct diagnosis while creatine is consistently falsely elevated probably secondary to liberation of red cell creatine. In nine healthy newborn infants, GAA concentrations from filter cards were 4.83+/-1.43 and 5.04+/-1.84 micromol/l in 16 healthy adults. We conclude that isotope dilution ES-MS/MS is ideal for rapid high-throughput diagnosis of GAMT deficiency both from plasma and filter paper cards. Using this technique neonatal screening is feasible for this treatable inborn error of creatine metabolism.

Alterations in arginine metabolic enzymes in trauma.

Arginine is the sole substrate for nitric oxide (NO) synthesis by NO synthases (NOS) and promotes the proliferation and maturation of human T-cells. Arginine is also metabolized by the enzyme arginase, producing urea and ornithine, the precursor for polyamine production. We sought to determine the molecular mechanisms regulating arginase and NOS in splenic immune cells after trauma. C3H/HeN mice underwent laparotomy as simulated moderate trauma or anesthesia alone (n = 24 per group). Six, 12, 24, or 48 h later, 6 animals from each group were sacrificed, and splenectomy was performed and plasma collected. Six separate animals had neither surgery nor anesthesia and were sacrificed to provide resting values (t = 0 h). Spleen arginase I and II and iNOS mRNA abundance, arginase I protein expression, and arginase activity were determined. Plasma NO metabolites (nitrite + nitrate) were also measured. Trauma increased spleen arginase I protein expression and activity (P = 0.01) within 12 and for at least 48 h after injury and coincided with up-regulated arginase I mRNA abundance at 24 h. Neither arginase II nor iNOS mRNA abundance in the spleen was significantly increased by trauma at 24 h. Plasma nitrite + nitrate was decreased in animals 48 h post-injury compared to anesthesia controls (P < 0.05). Trauma induces up-regulation of arginase I gene expression in splenic immune cells within 24 h of injury. Arginase II is not significantly up-regulated at that time point. Arginase I, rather than iNOS appears to be the dominant route for arginine metabolism in splenic immune cells 24 h after trauma.

Arginase I expression and activity in human mononuclear cells after injury.

OBJECTIVE: To determine the effect of trauma on arginase, an arginine-metabolizing enzyme, in cells of the immune system in humans. SUMMARY BACKGROUND DATA: Arginase, classically considered an enzyme exclusive to the liver, is now known to exist in cells of the immune system. Arginase expression is induced in these cells by cytokines interleukin (IL) 4, IL-10, and transforming growth factor beta, corresponding to a T-helper 2 cytokine profile. In contrast, nitric oxide synthase expression is induced by IL-1, tumor necrosis factor, and gamma interferon, a T-helper 1 cytokine profile. Trauma is associated with a decrease in the production of nitric oxide metabolites and a state of immunosuppression characterized by an increase in the production of IL-4, IL-10, and transforming growth factor beta. This study tests the hypothesis that trauma increases arginase activity and expression in cells of the immune system. METHODS: Seventeen severely traumatized patients were prospectively followed up in the intensive care unit for 7 days. Twenty volunteers served as controls. Peripheral mononuclear cells were isolated and assayed for arginase activity and expression, and plasma was collected for evaluation of levels of arginine, citrulline, ornithine, nitrogen oxides, and IL-10. RESULTS: Markedly increased mononuclear cell arginase activity was observed early after trauma and persisted throughout the intensive care unit stay. Increased arginase activity corresponded with increased arginase I expression. Increased arginase activity coincided with decreased plasma arginine concentration. Plasma arginine and citrulline levels were decreased throughout the study period. Ornithine levels decreased early after injury but recovered by postinjury day 3. Increased arginase activity correlated with the severity of trauma, early alterations in lactate level, and increased levels of circulating IL-10. Increased arginase activity was associated with an increase in length of stay. Plasma nitric oxide metabolites were decreased during this same period. CONCLUSIONS: Markedly altered arginase expression and activity in cells of the human immune system after trauma have not been reported previously. Increased mononuclear cell arginase may partially explain the benefit of arginine supplementation for trauma patients. Arginase, rather than nitric oxide synthase, appears to be the dominant route for arginine metabolism in immune cells after trauma.

Perinatal development of endothelial nitric oxide synthase-deficient mice.

The purpose of this study was to evaluate the influence of endothelial nitric oxide synthase (eNOS) deficiency on fetal growth, perinatal survival, and limb development in a mouse model with a targeted mutagenesis of the Nos3 gene. Wild-type (Nos3+/+) and eNOS-deficient fetuses (Nos3-/-) were evaluated on Gestational Day (E)15 and E17, and newborn pups were observed on Day 1 of life (D1). The average term duration of pregnancy was 19 days. For the evaluation of postnatal development, a breeding scheme consisting of Nos3+/- x Nos3+/- and Nos3-/- x Nos3-/- mice was established, and offspring were observed for 3 wk. Southern blotting was used for genotyping. No significant differences in fetal weight, crown-rump lengths (CRL), and placental weight were seen between Nos3+/+ and Nos3-/- fetuses on E15. By E17, Nos3-/- fetuses showed significantly reduced fetal weights, CRL, and placental weights. This difference in body weight was also seen throughout the whole postnatal period. In pregnancies of Nos3-/- females, the average number of pups alive on D1 was significantly decreased compared to either E15 or E17. Placental histology revealed no abnormalities. On E15, E17, and D1, Nos3(-/-) fetuses demonstrated focal acute hemorrhages in the distal limbs in 0%, 2.6%, and 5.7%, respectively, of all mutant mice studied on the respective days. Bone measurements showed significantly shorter bones in the peripheral digits of hindpaws of Nos3-/- newborns. We conclude mice deficient for eNOS show characteristically abnormal prenatal and postnatal development including fetal growth restriction, reduced survival, and an increased rate of limb abnormalities. The development of this characteristic phenotype of eNOS-deficient mice dates back to the prenatal development during the late third trimester of pregnancy.

Generation of a mouse model for arginase II deficiency by targeted disruption of the arginase II gene.

Mammals express two isoforms of arginase, designated types I and II. Arginase I is a component of the urea cycle, and inherited defects in arginase I have deleterious consequences in humans. In contrast, the physiologic role of arginase II has not been defined, and no deficiencies in arginase II have been identified in humans. Mice with a disruption in the arginase II gene were created to investigate the role of this enzyme. Homozygous arginase II-deficient mice were viable and apparently indistinguishable from wild-type mice, except for an elevated plasma arginine level which indicates that arginase II plays an important role in arginine homeostasis.

Endothelial-derived nitric oxide and angiotensinogen: blood pressure and metabolism during mouse pregnancy.

The regulation of blood pressure during pregnancy involves several biological pathways. Candidate genes implicated in hypertensive diseases during pregnancy include those of the renin-angiotensin system and nitric oxide synthase (NOS). We evaluated blood pressure and metabolic characteristics during pregnancy in mutant mice. These included mice with a null mutation in the endothelial NOS (eNOS) gene (Nos3(-/-)), four copies of the angiotensinogen gene (Agt(2/2)), and mutations in both genes [four copies of Agt and heterozygous deficient for eNOS (Agt(2/2)Nos3(+/-)), four copies of Agt and homozygous deficient for eNOS (Agt(2/2)Nos3(-/-))]. Blood pressure measurements of nulliparous females from mutant strains were compared with two common laboratory strains C57Bl6/J and SV129 throughout their first pregnancy. Serum and urine analysis for the evaluation of renal and liver physiology were measured in the prepregnant state and during the third trimester of pregnancy. Throughout pregnancy blood pressures in all mutant strains were higher compared with controls. Agt(2/2)Nos3(-/-) showed the highest blood pressures and C57Bl6/J the lowest. Control mice, but not mutant mice, showed a second trimester decline in blood pressure. No immediate differences were noted regarding behavioral characteristics, renal or liver function parameters. Mice deficient for eNOS, mice with overexpression of Agt, and mice with mutations in both genes demonstrated higher blood pressure throughout pregnancy. There was no evidence of renal dysfunction, liver dysfunction, or hemolysis among any of the strains studied. We conclude that Nos3 and Agt are important genes in the regulation of blood pressure during pregnancy.

An endothelial nitric oxide synthase gene polymorphism is associated with preeclampsia.

OBJECTIVE: We sought to test the hypothesis that a polymorphism of the endothelial nitric oxide synthase gene (NOS3) is associated with preeclampsia. METHODS: We collected and performed polymerase chain reaction (PCR) on genomic DNA from pregnant patients with and without preeclampsia. Patient history and clinical course were evaluated. MAIN OUTCOME MEASURE(S): Frequency of the intron 4 polymorphism of NOS3 (designated allele A) among patients with preeclampsia compared with controls. Clinical features of patients with preeclampsia and the A allele compared with those patients with preeclampsia who did not have the A allele. RESULTS: The frequency of the A allele was 0.10 among controls versus 0.39 among patients with preeclampsia (p < 0.01). The odds ratio of developing preeclampsia when at least one A allele was present was 6.5 [95% confidence interval (CI): 2.1-19.7]. After adjusting for ethnic variation, the odds ratio increased to 7.2 (95% CI: 2.0-25.5). Among patients with preeclampsia, systolic blood pressure at the time of admission was higher for patients with at least one A allele compared with patients homozygous for the B allele (168 versus 156 mm Hg; p = 0.03), independent of gestational age (p = 0.01). CONCLUSION: These data provide evidence for an association between NOS3 and preeclampsia. In defined ethnic groups, this NOS3 may offer predictive information regarding the subsequent development of preeclampsia and its clinical course.

Genetic contributions of the endothelial nitric oxide synthase gene to ovulation and menopause in a mouse model.

OBJECTIVE: To investigate the influence of the endothelial nitric oxide synthase gene (Nos3) on ovulatory capacity and reproductive senescence. DESIGN: Prospective, controlled study. SETTING: Academic research institution. SUBJECT(S): Laboratory mice with targeted mutagenesis of Nos3. INTERVENTION(S): Hyperstimulation protocol, oocyte culture, and ovarian histology using wild-type (Nos3(+/+); n = 20), heterozygous (Nos3(+/m); n = 39), and homozygous deficient (Nos3(m/m); n = 11) female mice; observation of reproductive outcomes. MAIN OUTCOME MEASURE(S): Number and survival of oocytes; onset of menarche and menopause. RESULT(S): The mean number of superovulated oocytes (18 +/- 36 vs. 41 +/- 4) and the 48-hour overall survival rate of embryos (65% vs. 81%) were significantly reduced for Nos3(m/m) female mice compared with Nos3(+/+) female mice. Nos3(m/m) females showed a significantly reduced number and size of antral follicles and corpora lutea compared with wild-type controls. Compared with Nos3(+/m) x Nos3(+/m) breedings, Nos3(m/m) x Nos3(m/m) breedings showed a higher female age at first litter (76.2 +/- 10.3 vs. 107.8 +/- 26.6 days), fewer litters (10.5 +/- 3.6 vs. 7. 8 +/- 4.2), and a lower female age at reproductive senescence (400.2 +/- 64.5 vs. 332.1 +/- 27.4 days), respectively. CONCLUSION(S): Our data suggest that Nos3 deficiency is associated with reduced ovulatory capacity and impaired early embryonic viability and that it influences the onset of menarche and menopause.

Nitric oxide release and contractile properties of skeletal muscles from mice deficient in type III NOS.

Skeletal muscle constitutively expresses both the type I (neuronal) and type III (endothelial) isoforms of nitric oxide synthase (NOS). We tested the functional importance of type III NOS using skeletal muscles with similar levels of type III NOS expression (diaphragm and soleus) from wild-type, heterozygous, and type III NOS-deficient littermate mice. Muscles were incubated at 37 degrees C in Krebs-Ringer solution. NO accumulation in the medium was measured by chemiluminescence; force-frequency and fatigue characteristics were measured using direct electrical stimulation. Diaphragm and soleus released NO at similar rates during passive incubation; these rates increased during active contraction. NO release by type III NOS-deficient muscle was not different from that of wild-type muscle under any condition tested. Force-frequency and fatigue characteristics also were unaffected by genotype. Because type III NOS deficiency did not alter function, we conclude that NO effects previously observed in wild-type muscle are likely to be mediated by type I NOS.

First report of prenatal biochemical diagnosis of Lowe syndrome.

The oculocerebrorenal syndrome of Lowe (OCRL) is a rare X-linked disorder with a severe phenotype characterized by congenital cataracts, renal tubular dysfunction and neurological deficits. The gene has been characterized and mutations have been identified in patients. Owing to the allelic heterogeneity exhibited by this gene, prenatal diagnosis by molecular analysis is limited to families in which the mutation is already known or in which linkage is informative. A more generally applicable diagnostic test would be valuable for families at risk for Lowe syndrome. Since ocrl1 is now known to encode a phosphatidylinositol 4,5-bisphosphate 5-phosphatase (Ptdlns(4,5)P2 phosphatase), we assessed whether biochemical testing could be used for prenatal diagnosis. We report here the first case of prenatal diagnosis for Lowe syndrome by measuring phosphatidylinositol 4,5-bisphosphate 5-phosphatase activity in cultured amniocytes.

Targeted disruption of mouse long-chain acyl-CoA dehydrogenase gene reveals crucial roles for fatty acid oxidation.

Abnormalities of fatty acid metabolism are recognized to play a significant role in human disease, but the mechanisms remain poorly understood. Long-chain acyl-CoA dehydrogenase (LCAD) catalyzes the initial step in mitochondrial fatty acid oxidation (FAO). We produced a mouse model of LCAD deficiency with severely impaired FAO. Matings between LCAD +/- mice yielded an abnormally low number of LCAD +/- and -/- offspring, indicating frequent gestational loss. LCAD -/- mice that reached birth appeared normal, but had severely reduced fasting tolerance with hepatic and cardiac lipidosis, hypoglycemia, elevated serum free fatty acids, and nonketotic dicarboxylic aciduria. Approximately 10% of adult LCAD -/- males developed cardiomyopathy, and sudden death was observed in 4 of 75 LCAD -/- mice. These results demonstrate the crucial roles of mitochondrial FAO and LCAD in vivo.

Limb reduction defects in endothelial nitric oxide synthase-deficient mice.

Nitric oxide synthases are a family of enzymes capable of converting L-arginine to L-citrulline with the subsequent release of nitric oxide (NO). NO has been shown to have multiple biologic effects depending on the isoform responsible for its production and its tissue of origin. Murine endothelial nitric oxide synthase (eNOS) is encoded by Nos3, located on mouse chromosome 5. NO produced from this isoform causes vascular smooth muscle relaxation. Other investigators have shown that the administration of nonspecific inhibitors of nitric oxide synthases to pregnant rats induces limb reduction defects. However, mice deficient in Nos3 have not previously been noted to show such abnormalities. To explore the importance of eNOS during development, we produced mice deficient in eNOS using embryonic stem cell technology. Limb reduction defects were seen in approximately 10% of the null animals. We also observed increased neonatal loss of homozygous deficient pups. One functional copy of Nos3 eliminates the risk of limb defects observed in our mouse strain. These findings have implications for understanding genetic predisposition to sporadic limb reduction defects in humans.

Cost analysis of hospital material management systems.

Integrated healthcare material management begins with manufactures of medical/surgical supplies, uses distributors and ends at the point of use at hospitals. Recent material management philosophies in the healthcare industry, such as just-in-time and stockless systems, are yet to be fully evaluated. In order to evaluate the cost effectiveness of each type of material management technique, a cost model for hospital materials management has been designed. Several case scenarios are analyzed and results are reported.

Structure of the murine arginase II gene.

Mammals contain two genes encoding distinct isoforms of arginase (arginases I and II), both of which catalyze the conversion of arginine to ornithine and urea. However, their subcellular localization and tissue-specific patterns of expression are very different, indicating that they perform distinct physiologic roles. As an initial step in elucidating the regulation and physiologic roles of arginase II, this report describes the characterization of a mammalian arginase II gene. The murine arginase II gene contains eight exons like the arginase I gene. The six internal exons have intron/exon boundaries that are identical to the arginase I gene; however, exon three of the arginase II gene has obtained a three-base-pair insertion. The identity of the exon/intron boundaries is consistent with a gene duplication as the origin of the arginase isozymes with the small insertion occurring after the duplicative event. The promoter region of the arginase II gene, which bears no resemblance to that of the arginase I genes, contains numerous potential binding sites for enhancer and promoter elements but does not contain a TATA box.

Combined malonic and methylmalonic aciduria with normal malonyl-coenzyme A decarboxylase activity: a case supporting multiple aetiologies.

We identified a patient who excreted large amounts of methylmalonic acid and malonic acid. In contrast to other patients who have been described with combined methylmalonic and malonic aciduria, our patient excreted much larger amounts of methylmalonic acid than malonic acid. Since most previous patients with this biochemical phenotype have been reported to have deficiency of malonyl-CoA decarboxylase, we assayed malonyl-CoA decarboxylase activity in skin fibroblasts derived from our patient and found the enzyme activity to be normal. We examined four isocaloric (2000 kcal/day) dietary regimes administered serially over a period of 12 days with 3 days devoted to each dietary regimen. These diets were high in carbohydrate, fat or protein, or enriched with medium-chain triglycerides. Diet-induced changes in malonic and methylmalonic acid excretion became evident 24-36 h after initiating a new diet. Total excretion of malonic and methylmalonic acid was greater (p < 0.01) during a high-protein diet than during a high-carbohydrate or high-fat diet. A high-carbohydrate, low-protein diet was associated with the lowest levels of malonic and methylmalonic acid excretion. Perturbations in these metabolites were most marked at night. On all dietary regimes, our patient excreted 3-10 times more methylmalonic acid than malonic acid, a reversal of the ratios reported in patients with malonyl-CoA decarboxylase deficiency. Our data support a previous observation that combined malonic and methylmalonic aciduria has aetiologies other than malonyl-CoA decarboxylase deficiency. The malonic acid to methylmalonic acid ratio in response to dietary intervention may be useful in identifying a subgroup of patients with normal enzyme activity.

Evaluation of gene therapy for citrullinaemia using murine and bovine models.

Citrullinaemia is an autosomal recessive disorder caused by the deficiency of argininosuccinate synthase. The deficiency of this enzyme results in an interruption in the urea cycle and the inability to dispose of excess ammonia derived from the metabolism of protein. The only treatment for this disorder has been dietary restriction of protein and supplementation with medications allowing for alternative excretion of excess nitrogen. Gene therapy offers the possibility of a long-term cure for disorders like citrullinaemia by expressing the deficient gene in the target organ. We have explored the use of adenoviral vectors as a treatment modality for citrullinaemia in two animal models, a naturally occurring bovine model and a murine model created by molecular mutagenesis. Mice treated with adenoviral vectors expressing argininosuccinate synthase lived significantly longer than untreated animals (11 days vs 1 day; however, the animals did not exhibit normal weight gain during the experiment, indicating that the therapeutic effectiveness of the transducing virus was suboptimal. It is speculated that part of the failure to observe better clinical outcome might be due to the deficiency of arginine. In the bovine model, the use of adenoviral vectors did not result in any change in the clinical condition of the animals or in the level of plasma ammonia. However, the use of 15N isotopic ammonia allowed us to assess the flux of nitrogen through the urea cycle during the experiment. These studies revealed a significant increase in the flux through the urea cycle following administration of adenoviral vectors expressing argininosuccinate synthase. We conclude that the use of adenoviral vectors in the treatment of citrullinaemia is a viable approach to therapy but that it will be necessary to increase the level of transduction and to increase the level of enzyme produced from the recombinant viral vector. Future experiments will be designed to address these issues.

L-citrulline conversion to L-arginine in sphenopalatine ganglia and cerebral perivascular nerves in the pig.

The presence of nitric oxide synthase (NOS), argininosuccinate synthetase (ASS), and argininosuccinate lyase (ASL) and their coexistence with NADPH-diaphorase (NADPHd), a marker for NOS, in the porcine sphenopalatine ganglia (SPG), pial veins, and the anterior cerebral arteries was examined using immunohistochemical and histochemical staining techniques. NOS-immunoreactive (I), ASS-I, and ASL-I fibers were found in pial veins and the anterior cerebral arteries. NOS, ASS, and ASL immunoreactivities were also found in neuronal cell bodies in the SPG. Almost all neuronal cell bodies in the SPG and nerve fibers in pial veins and the anterior cerebral arteries that were reactive to ASS, ASL, and NOS were also stained positively with NADPHd, suggesting that ASS, ASL, and NOS were colocalized in the same neurons in the SPG and perivascular nerves. With the use of in vitro tissue bath techniques, L-citrulline but not D-citrulline reversed inhibition of neurogenic vasodilation in isolated porcine pial veins produced by NOS inhibitors such as NG-nitro-L-arginine methyl ester. In the presence of L-aspartate, L-arginine was synthesized from L-citrulline in homogenates of SPG and endothelium-denuded cerebral arteries and pial veins. These results provide evidence indicating that perivascular nerves in pial veins like cerebral arteries can convert L-citrulline to L-arginine for synthesizing nitric oxide. The conversion is most likely via an argininosuccinate pathway.

Morphologic evidence for L-citrulline conversion to L-arginine via the argininosuccinate pathway in porcine cerebral perivascular nerves.

Results from biochemical and pharmacologic studies suggest that Lcitrulline is taken up by cerebral perivascular nerves and is converted to Larginine for synthesizing nitric oxide (NO). The current study was designed using morphologic techniques to determine whether Lcitrulline is taken up into axoplasm of perivascular nerves and to explore the possibility that conversion of Lcitrulline to Larginine in these nerves is through the argininosuccinate pathway in porcine cerebral arteries. Results from light and electron microscopic autoradiographic studies indicated that dense silver grains representing L-[3H] citrulline uptake were found in cytoplasm of perivascular nerves, smooth muscle cells, and endothelial cells. The neuronal silver grains were significantly decreased in arteries pretreated with glutamine, which has been shown biochemically to block neuronal uptake of Lcitrulline. Results from light and electron microscopic immunohistochemical and histochemical studies indicate that dense nitric oxide synthase-immunoreactive (NOS-I), argininosuccinate synthetase-immunoreactive (ASS-I), and argininosuccinate lyase-immunoreactive (ASL-I) fibers were found in the adventitia of cerebral arteries. NOS-, ASS-, and ASL-immunoreactivities fibers were found in the axoplasm and in the endothelium. In whole-mount preparations, the NOS-I, ASS-I, and ASL-I fibers were completely coincident with NADPH diaphorase fibers, suggesting that axoplasmic ASS, ASL, and NOS were co-localized in the same neurons. These studies provide the first morphologic evidence indicating that Lcitrulline is taken up into cytoplasm of cerebral perivascular nerves and that the axoplasmic enzymes catalyzing the conversion of Lcitrulline to Larginine (for synthesizing NO) by argininosuccinate pathway always are co-localized in same neurons. These results support the hypothesis that Lcitrulline, the by-product of NO synthesis, is recycled to form Larginine for synthesizing NO in perivascular nerves to mediate cerebral neurogenic vasodilation. Results of the current morphologic studies also support the presence of Lcitrulline-Larginine cycle in cerebral vascular endothelium.

Differential regulation of L-arginine transport and nitric oxide production by vascular smooth muscle and endothelium.

Since NO production is dependent on the availability of L-arginie, we examined whether L-arginine transport and NO synthesis are coregulated by vascular smooth muscle cells and endothelial cells cultured from the same vessel wall source. L-Arginine transport by both bovine aortic smooth muscle cells (BASMCs) and endothelial cells (BAECs) was primarily Na+ independent (approximately 70%) and was mediated by both a high- and low-affinity transport system. Treatment of BASMCs with tumor necrosis factor-alpha (TNF-alpha) or interleukin-1 beta (IL-1 beta) resulted in a significant increase in L-arginine transport (approximately 20%) and in the induction of NO release. Exposure of BASMCs to interferon gamma (IFN-gamma) or lipopolysaccharide (LPS) also stimulated NO release but did not affect L-arginine transport. In contrast, incubation of BAECs with TNF-alpha or LPS strikingly enhanced L-arginine uptake (2.5-fold), whereas IL-1 beta and IFN-gamma had no effect. Treatment of BAECs with any of the inflammatory mediators did not stimulate NO production. These results demonstrate that L-arginine uptake and NO synthesis by these cells are differentially regulated. In BASMCs, the coinduction of L-arginine transport and NO formation may function to provide increased levels of substrate to the cell during activation of the NO synthase enzyme. In contrast, the selective stimulation of L-arginine uptake in BAECs indicates that L-arginine transport is dissociated from NO generation in these cells.