Up-regulation of inducible nitric oxide synthase expression in cancer-prone p53 knockout mice

High concentrations of nitric oxide (NO) cause DNA damage and apoptosis in many cell types. Thus, regulation of NO synthase (NOS) activity is essential for minimizing effects of cytotoxic and genotoxic nitrogen oxide species. We have shown previously that NO-induced p53 protein accumulation down-regulates basal and cytokine-modulated inducible NOS (NOS2) expression in human cells in vitro. To further characterize the feedback loop between NOS2 and p53, we have investigated NO production, i.e., urinary nitrate plus nitrite excretion, and NOS2 expression in homozygous p53 knockout (KO) mice. We report here that untreated p53 KO mice excreted 70% more nitrite plus nitrate than mice with wild-type (wt) p53. NOS2 protein expression was constitutively detected in the spleen of untreated p53 KO mice, whereas it was undetectable in the spleen of wt p53 controls. Upon treatment with heat-inactivated Corynebacterium parvum, urinary nitrite plus nitrate excretion of p53 KO mice exceeded that of wt controls by approximately 200%. C. parvum treatment also induced p53 accumulation in the liver. Splenectomy reduced the NO output of C. parvum-treated p53 KO mice but not of wt p53 controls. Although NO production and NOS2 protein expression were increased similarly in KO and wt p53 mice 10 days after injection of C. parvum, NOS2 expression returned to baseline levels only in wt p53 controls while remaining up-regulated in p53 KO mice. These genetic and functional data indicate that p53 is an important transrepressor of NOS2 expression in vivo and attenuates excessive NO production in a regulatory negative feedback loop.     

Decreased neointimal thickening after arterial wall injury in inducible nitric oxide synthase knockout mice

Mechanical injury in vivo results in the expression of the inducible form of nitric oxide synthase (iNOS) in vascular smooth muscle cells. However, the role of iNOS in modulating neointima formation after arterial wall injury is not clear. To determine whether the induction of iNOS gene expression promotes or attenuates the neointimal response to injury, we used a murine model of perivascular injury induced by placing a periadventitial collar around the carotid arteries in both wild-type and iNOS knockout mice (iNOS-KO mice). Periadventitial injury induced iNOS expression in the wild-type but not the iNOS-KO mice. Neointimal area and the intima/media ratio were significantly less in the iNOS-KO mice compared with the wild-type mice at 21 days. Injury-induced proliferation of medial cells and vascular cell adhesion molecule-1 expression were also attenuated in iNOS-KO mice compared with wild-type mice. The induction of iNOS and the activation of the nuclear factor-kappaB-mediated pathway were also demonstrated in an in vitro injury model. We conclude that mechanical injury in vivo and in vitro induces iNOS expression and that lack of iNOS expression attenuates neointima formation after perivascular arterial injury. Taken together, these findings suggest that iNOS expression after vascular injury may promote neointima formation.     

Overexpression of hepatic inducible nitric oxide synthase in biliary atresia

Aims: Biliary atresia (BA) is a rare and serious liver disease in infants characterized by progressive inflammatory cholangiopathy. The aims of this study were to investigate hepatic expression of inducible nitric oxide synthase (iNOS) in BA and to associate the iNOS expression with their early therapeutic outcome. Methods: Hepatic iNOS expression was determined using immunohistochemistry from liver biopsies of 24 BA patients, and 16 non‐BA patients whose liver tissues were needed in the treatment process. Six months after surgery, the BA patients were categorized into two groups;good and poor outcome. The iNOS expression of hepatocyte areas was evaluated based on its intensity using ImageJ software. Unpaired t‐tests were used for the comparisons of iNOS expression between groups. Results: Hepatic iNOS expression of BA patients was significantly stronger than that of non‐BA patients (P < 0.0001). The largest area of hepatic iNOS expression was the area of hepatocytes. Subgroup analysis of BA patients at 6 months post‐op revealed that there was no difference in iNOS expression between the patients with good outcome and those with poor outcome (P = 0.732). Conclusions: Overexpression of hepatic iNOS in BA patients was demonstrated. Within liver tissues, hepatocytes were the major source of hepatic iNOS production. However, the expression was not associated with the early therapeutic outcome. These results suggest that iNOS plays a role in the liver pathology of BA but its expression cannot be used as a predictor for therapeutic outcome.     

Temporal expression of hepatic inducible nitric oxide synthase in liver cirrhosis

AIM: Nitric oxide (NO) has been implicated in the pathogenesis of liver cirrhosis. We have found inducible nitric oxide synthase (iNOS) can be induced in hepatocytes of cirrhotic liver. This study further investigated the temporal expression and activity of hepatic iNOS in cirrhosis development. METHODS: Cirrhosis was induced in rats by chronic bile duet ligatjon (BDL). At different time points after the operation, samples were collected to examine NO concentration, liver function, and morphological changes. Hepatocytes were isolated for determination of iNOS mRNA, protein and enzymatic activity. RESULTS: Histological examination showed early cirrhosis 1-2 wk after BDL, with advanced cirrhosis at 3-4 wk. Bilirubin increased dramatically 3 d after BDL, but decreased by 47% on d 14. Three weeks after BDL, it elevated again. Systemic NO concentration did not increase significantly until 4 wk after BDL, when ascites developed. Hepatocyte iNOS mRNA expression was identified 3 d after BDL, and enhanced with time to 3 wk, but reduced thereafter. iNOS protein showed a similar pattern to mRNA expression. iNOS activity decreased from d 3 to d 7, but increased again thereafter till d 21. CONCLUSION: Hepatic iNOS can be induced in the early stage, which increases with time as cirrhosis develops. lts enzymatic activity is significantly correlated with protein expression and histological alterations of the liver, but not with systemic NO levels, nor with absolute values of liver function markers.     

Development of lyme arthritis in mice deficient in inducible nitric oxide synthase

Nitric oxide (NO) is a powerful antimicrobial agent and an important regulatory molecule of the innate immune response. To determine if NO has a role in experimental Lyme disease, arthritis-resistant DBA/2J and arthritis-susceptible C3H/HeJ mice were bred to be genetically deficient for inducible NO synthase (iNOS). Following footpad injection of Borrelia burgdorferi, arthritis was similar between iNOS-deficient and control animals regardless of their genetic background. Histologic examination and arthritis severity scores of ankles revealed no differences in arthritis development between iNOS-deficient and control animals. Despite being deficient in a key antimicrobial agent, iNOS-deficient mice had tissue levels of B. burgdorferi similar to those in control mice. Thus, NO does not have a critical role in susceptibility to Lyme arthritis through tissue damage via an overexuberant inflammatory response, nor is it required in resistance through the clearance of spirochetes from tissues.     

BXSB小鼠肾组织诱生型一氧化氮合酶的异常表达及甲泼尼龙干预效应

目的探讨诱生型一氧化氮合酶(iNOS)是否参与介导BXSB小鼠狼疮肾炎(LN)及甲泼尼龙(MPS)是否可通过影响iNOS表达而缓解LN。方法用MPS对BXSB自发狼疮小鼠进行体内实验,利用反转录-聚合酶链反应(RT-PCR)和免疫组织化学技术研究了MPS对狼疮小鼠肾脏iNOS表达的影响,并观察了狼疮小鼠MPS治疗前后24h尿蛋白和NO3-/NO2-排泄量。结果BXSB狼疮小鼠肾组织检测到了iNOSmRNA的表达,而BALB/C小鼠未见表达;免疫组织化学示iNOS表达于BXSB小鼠肾小管上皮细胞、血管内皮细胞、肾间质及肾小球浸润的炎症细胞胞质内。MPS治疗组BXSB狼疮小鼠肾组织iNOSmRNA表达量显著低于未治疗组(P<0.01);治疗组24h尿蛋白及NO3-/NO2-排泄量显著低于未治疗组(P<0.01,P<0.05)。结论iNOS及其合成的一氧化氮(NO)可能参与介导了LN。MPS可能通过抑制肾组织iNOS的表达缓解LN。     

Involvement of inducible nitric oxide synthase in the inflammatory process of myocardial infarction

Inducible nitric oxide synthase (iNOS), which catalyzes the reaction of -arginine to -citrulline and nitric oxide (NO), plays an important role in immune-mediated cardiac disorders. The present report summarizes and discusses findings on the induction of NOS in myocardial infarction of rabbits. iNOS was significantly increased in infarcted myocardium 48 h after coronary artery ligation. The effect persisted for 14 days and declined thereafter. Immunohistochemical localization revealed macrophages as a major source of iNOS expression; iNOS expression was also present in infarcted human myocardium. Increased iNOS activity appeared to be related to the induction of apoptosis in infiltrating macrophages and cardiomyocytes. Moreover, preferential inhibition of iNOS by S-methylisothiourea sulfate (SMT) resulted in significant improvement of left ventricular performance and increased regional myocardial blood flow. These findings suggest that selective inhibition of iNOS activity may provide a therapeutic strategy in cardiac disorders such as myocardial infarction.     

Expression of cardiac cytokines and inducible form of nitric oxide synthase (NOS2) in Trypanosoma cruzi-infected mice

Expression of Cardiac Cytokines and Inducible Form of Nitric Oxide Synthase (NOS2) in Trypanosoma cruzi-infected Mice. Journal of Molecular and Cellular Cardiology (1999) 31, 75-88. Both cardiac cytokine and inducible nitric oxide synthase (NOS2) expression have been implicated in the cardiac dysfunction associated with myocarditis and cardiomyopathy. Chagas' disease, caused by Trypanosoma cruzi, is an important cause of cardiomyopathy. We examined the effect of T. cruzi (Brazil strain) infection with or without verapamil treatment on the expression of cytokines and NOS2 in the heart. Messenger RNA for NOS2, IL-1beta, and TNF-alpha was induced in the myocardium of infected mice, and Western blot analysis as well as immunohistochemistry demonstrated a significant increase in NOS2 protein. Verapamil treatment reduced the expression of cardiac NOS2 protein and the mRNAs for NOS2, TNF-alpha, and IL-1beta. Infection-associated increases in cardiac L-citrulline were also reduced by verapamil treatment. Verapamil-treated infected mice that survived for 80 days exhibited less inflammation and fibrosis compared to untreated mice. Gated MRI and echocardiography revealed an increased right ventricular inner diameter (RVID) in untreated but not in verapamil-treated infected CD1 mice. This suggests that the infection-associated expression of cytokines and NOS2 in the heart correlate with the severity of myocarditis and the effect of verapamil. The RVID was significantly increased in infected wild-type (WT) compared to infected syngeneic NOS2 knockout (NOS2-/-) mice. Fractional shortening was decreased and myocardial L-citrulline was increased in infected WT mice. These data suggest that NO generated from cardiac NOS2 may participate in the pathogenesis of murine chagasic heart disease.     

Monomeric inducible nitric oxide synthase localizes to peroxisomes in hepatocytes

Hepatocytes are capable of repeated inducible NO synthase (iNOS) expression, which occurs under inflammatory and stress conditions. This iNOS expression regulates a number of cellular functions as well as cell viability. To better understand the posttranslational mechanisms that regulate the fate of iNOS in these cells, we characterized the iNOS distributed within peroxisomes. The selective permeabilization of membranes (plasma vs. peroxisomal) confirmed that there are cytosolic and peroxisomal pools of iNOS in cytokine-stimulated hepatocytes and that the iNOS protein associates with peroxisome. Detergent solubilization of the membrane fraction released iNOS to the soluble fraction. iNOS localized to membrane fraction is predominantly monomeric, but dimerization is partially reconstituted rapidly upon incubation with tetrahydrobiopterin. The reconstituted iNOS exhibits a lower specific activity than iNOS isolated from the soluble pool. Depletion of intracellular tetrahydrobiopterin with an inhibitor of de novo pterin synthesis resulted in a predominance of monomeric iNOS without a greater relative distribution of iNOS to the peroxisomal pool. Thus, iNOS exists in a least two pools in hepatocytes: a soluble pool composed of both active dimer and monomer and a peroxisomal pool of monomeric iNOS. iNOS might localize to peroxisomes in long-lived cells such as hepatocytes as a protective mechanism to remove incompetent enzyme.     

Decreased arteriolar density in endothelial nitric oxide synthase knockout mice is due to hypertension, not to the constitutive defect in endothelial nitric oxide synthase enzyme

BACKGROUND : Hypertension in endothelial nitric oxide synthase knockout (eNOS-/-) mice is believed to be partly due to altered vasodilatation. However, nitric oxide (NO) is also known to play an important part in angiogenesis. OBJECTIVE : To investigate whether capillary and arteriolar density were impaired in eNOS-/- mice, as this could account for increased vascular resistance and hypertension. METHODS : Using immunohistochemistry with mouse monoclonal smooth muscle alpha-actin antibody to detect arterioles and rabbit polyclonal fibronectin antibody to detect capillaries, we quantified arteriolar and capillary density in the left ventricle and in the gracilis muscle from eNOS-/- mice compared with those in C57BL6J littermates (n = 6-8) in 8- and in 12-week-old mice. In a second set of experiments, we treated 8-week-old normotensive eNOS-/- mice with the antihypertensive vasodilator, hydralazine, for 1 month. RESULTS : Eight-week-old eNOS-/- mice were normotensive and presented similar arteriolar and capillary densities in cardiac and skeletal muscles compared with those in eNOS+/+ mice. Twelve-week-old eNOS/- mice were hypertensive (mean arterial pressure 118 +/- 21 mmHg compared with 64 +/- 2 mmHg; P < 0.05). Capillary densities were similar in eNOS-/- mice and eNOS+/+ mice in the heart (4154 +/- 123 and 4051 +/- 247/mm2, respectively) and in skeletal muscle (961 +/- 40 and 1025 +/- 41/mm2, respectively). Arteriolar densities were 15% lower in skeletal muscle and in the heart in eNOS-/- mice than in the eNOS+/+ control group (P < 0.05). Hydralazine prevented hypertension and arteriolar rarefaction in eNOS-/- mice, whereas capillary density was unaffected by treatment with the vasodilator. CONCLUSION : In young non-hypertensive eNOS-/- mice, the lack of eNOS did not affect microvascular densities in either of the muscles studied. In adult hypertensive eNOS-/- mice, we observed a lower arteriolar density, but a similar capillary density compared with controls. Hydralazine prevented hypertension and arteriolar rarefaction in adult mice, suggesting a non-NO-dependent pathway. Capillary density was not affected by hydralazine.     

Beneficial effects of low-dose benidipine in acute autoimmune myocarditis: suppressive effects on inflammatory cytokines and inducible nitric oxide synthase.

Excessive production of nitric oxide (NO) by inducible NO synthase (iNOS) contributes to the progression of myocardial damage in myocarditis. Some dihydropyridine calcium channel blockers reportedly inhibit NO production and proinflammatory cytokines and the present study sought to clarify if a low dose of benidipine, a novel dihydropyridine calcium channel blocker, would ameliorate experimental autoimmune myocarditis (EAM). Rats with or without myocarditis were administered oral benidipine at a dose of 3 mg. kg(-1). day(-1) for 3 weeks. Low-dose benidipine did not decrease blood pressure significantly compared with the untreated group, but markedly reduced the severity of myocarditis. Myocardial interleukin-1beta (IL-1beta) expression and IL-1beta-positive cells were significantly less in rats with EAM that were treated with low-dose benidipine compared with untreated rats. Also, myocardial iNOS expression and iNOS-positive cells were markedly reduced in in the treated rats compared with the untreated group. Furthermore, myocardial NO production and nitrotyrosine expression were suppressed by the treatment in rats with EAM. The cardioprotection of low-dose benidipine may be caused by suppression of inflammatory cytokines and inhibition of NO production.     

Cardiac fibrogenesis following infarction in mice with deletion of inducible nitric oxide synthase

BACKGROUND: Studies have shown that the absence of inducible nitric oxide synthase (iNOS) improves cardiac function and survival after myocardial infarction (MI). The responsible mechanisms, however, remain uncertain. Cardiac iNOS is significantly increased after MI, which is colocalized with fibrous tissue formation. Herein, we tested our hypothesis that iNOS is involved in the development of cardiac fibrosis. METHODS: Wild-type and iNOS-knockout mice were subjected to MI by left coronary artery ligation. At week 1, 2, 3, and 4 post-MI, we addressed cardiac expression of profibrogenic mediator, growth of collagen-producing cells, collagen synthesis, and degradation. RESULTS: In the infarcted myocardium of wild-type and iNOS-knockout mice, transforming growth factor (TGF)-beta1 expression was significantly increased, particularly in the early stage; myofibroblasts appeared and became abundant for over 4 weeks; matrix metalloproteinase-1 expression was low, whereas tissue inhibitor of matrix metalloproteinase-1 was significantly elevated; type-I collagen mRNA was significantly increased and collagen was continuously accumulated. In the noninfarcted myocardium, TGF-beta1 and type-I collagen mRNA levels as well as collagen volume were also elevated, but less evident than infarcted myocardium. However, there was no significant difference in cardiac TGF-beta1 expression, myofibroblast population, collagen synthesis/degradation, and collagen volume between wild-type and iNOS-knockout mice with MI. CONCLUSION: The current study suggests that iNOS-induced nitric oxide production may not mediate cardiac fibrosis after MI. Thus, other mechanisms are involved in nitrosative stress-induced cardiac dysfunction after MI.     

Decreased Helicobacter pylori associated gastric carcinogenesis in mice lacking inducible nitric oxide synthase

BACKGROUND AND AIMS: Overproduction of nitric oxide via inducible nitric oxide synthase (iNOS) is suggested to be a significant pathogenic factor in Helicobacter pylori induced gastritis. The purpose of this study was to examine the role of iNOS in H pylori associated gastric carcinogenesis. METHODS: Two types of mice were used in this study: iNOS deficient mice (iNOS-/-) and wild-type littermates. Gastric cancer was generated in mice using a combination treatment comprising N-methyl-N-nitrosourea administration and H pylori infection. Fifty weeks after treatment, tumours in gastric tissues from both types of mice were examined using histopathology, immunohistochemistry, and immunoblotting for iNOS and 3-nitrotyrosine. RESULTS: The overall incidence of gastric cancer at week 50 was significantly lower in iNOS-/- compared with iNOS wild-type mice (p<0.05). When analysed according to tumour pathology, the incidence of gastric adenocarcinoma was significantly lower in iNOS-/- compared with iNOS wild-type mice (p<0.05). Immunostaining for iNOS was clearly observed in adenocarcinoma cells of iNOS wild-type mice, and was characterised by a strong cytoplasmic expression pattern. 3-Nitrotyrosine was expressed mostly in the area of the lamina propria of gastritis and adenoma lesions in iNOS wild-type mice. Immunoblotting analyses showed that iNOS and 3-nitrotyrosine were also expressed in both adenoma and adenocarcinoma tissues from iNOS wild-type mice. iNOS and 3-nitrotyrosine expression was greater in tumour tissues than in non-tumour tissues. CONCLUSIONS: These findings suggest that iNOS contributes to H pylori associated gastric carcinogenesis in mice.     

Lipopolysaccharide-induced diaphragmatic contractile dysfunction in mice lacking the inducible nitric oxide synthase.

The goal of this study was to evaluate the importance of the inducible nitric oxide synthase (iNOS) in lipopolysaccharide (LPS)-induced diaphragmatic contractile dysfunction. Many investigators have proposed that iNOS induction in the ventilatory and limb muscles of animals injected with Escherichia coli LPS leads to impaired muscle contractility and increased fatigability. We tested this proposal by examining wild-type mice and iNOS-deficient (iNOS knockout) mice. Both types of mice were injected with either saline (control) or E. coli LPS and killed after 12 h. Diaphragm nitric oxide synthase (NOS) activity, NOS expression, and muscle contractility were assessed with L-citrulline assay, immunoblotting, and in vitro bath preparation, respectively. LPS injection in wild-type mice induced iNOS protein expression and augmented total diaphragmatic NOS activity, which coincided with impaired muscle force generated at frequencies higher than 30 Hz. In iNOS knockout mice, injection of LPS augmented constitutive muscle NOS activity, upregulated the expression of the neuronal NOS (nNOS), but elicited a significantly greater decline in force generated in response to high frequency of stimulation compared with wild-type animals. We conclude that iNOS may play a protective role in attenuating the inhibitory influence of LPS on muscle contractility.     

Lack of inducible nitric oxide synthase leads to increased hepatic apoptosis and decreased fibrosis in mice after chronic carbon tetrachloride administration

The role of nitric oxide (NO) in liver injury and fibrosis is unclear. The purpose of this study was to determine whether inducible NO synthase deficiency (iNOS(-/-)) affects liver injury and fibrosis produced in mice by chronic carbon tetrachloride (CCl(4)) administration. Wild-type (WT) or iNOS(-/-) mice were subjected to biweekly CCl(4) injections over 8 weeks, whereas controls were given isovolumetric injections of olive oil. Serum aminotransferases were lower after CCl(4) in the iNOS(-/-) than in the WT mice, which correlated with decreased necrosis on liver histology. There was increased apoptosis, a lower number of stellate cells, and a lesser degree of fibrosis after CCl(4) in the iNOS(-/-) as compared with the WT mice. alpha(1)(I) collagen messenger RNA (mRNA) was markedly increased after CCl(4) in the WT and to a significantly lesser extent in the iNOS(-/-) mice. Liver matrix metalloproteinase-9 (MMP-9) mRNA and MMP-2 mRNA were increased more in the WT than in the iNOS(-/-) mice after CCl(4). Also tissue inhibitor metalloproteinase 1 (TIMP-1) mRNA was increased to a much greater extent in the WT than in the iNOS(-/-) mice after CCl(4) (P < 0.05). However, MMP-9 and TIMP-1 protein, determined by western blot, were similarly increased after CCl(4) in both groups of mice. CONCLUSION: NO protects against CCl(4)-induced apoptosis. In the absence of iNOS, there is decreased necrosis, increased apoptosis, and reduced liver fibrosis.     

Experimental abdominal aortic aneurysms in mice lacking expression of inducible nitric oxide synthase

To determine if nitric oxide synthase (NOS) contributes to the pathophysiology of abdominal aortic aneurysms (AAAs), C57BL/6J mice underwent transient aortic injury to induce a chronic inflammatory response. Wild-type mice developed a significant increase in aortic diameter within 14 days of elastase perfusion (115+/-16%, 40% incidence of AAAs), along with intense and widespread staining for nitrotyrosine, mononuclear inflammation, and delayed destruction of the elastic lamellae. Expression of both endothelial and neuronal forms of NOS was substantially decreased within AAAs, whereas inducible NOS (iNOS) mRNA was increased 360%, and the enzyme was localized to infiltrating inflammatory cells. By using mice with targeted deletion of iNOS to evaluate the functional importance of this enzyme, male iNOS(-/-) mice developed the same extent of aneurysmal dilatation as congenic controls (121+/-22%, 40% incidence of AAAs) and exhibited similar structural features except for diminished nitrotyrosine staining. Aneurysmal dilatation was actually enhanced in female iNOS(-/-) mice (141+/-16%, 80% incidence of AAAs; P<0.05), but this effect was reversed by previous oophorectomy. Although extensive protein nitration and increased expression of iNOS accompany the development of elastase-induced experimental AAAs, iNOS is not required in this process and its absence may be deleterious.     

Responses to Leishmania donovani in mice deficient in both phagocyte oxidase and inducible nitric oxide synthase

Mice deficient in phagocyte oxidase (phox) and inducible nitric oxide synthase (iNOS), which are primary macrophage killing mechanisms, generated tissue granulomas but showed unrestrained Leishmania donovani visceral replication and suboptimal initial responsiveness to antimony treatment. Nevertheless, visceral infection was controlled post-treatment and did not recur. A phox/iNOS-independent macrophage mechanism, which was not triggered by L. donovani, emerges after chemotherapy.     

Role of neuronal nitric oxide synthase and inducible nitric oxide synthase in intestinal injury in neonatal rats

AIM: To investigate the dynamic change and role of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) in neonatal rat with intestinal injury and to define whether necrotizing enterocolitis (NEC) is associated with the levels of nitric oxide synthase (NOS) in the mucosa of the affected intestine tissue. METHODS: Wistar rats less than 24 h in age received an intraperitoneal injection with 5 mg/kg lipopolysaccharide (IPS). Ileum tissues were collected at 1, 3, 6, 12 and 24 h following LPS challenge for histological evaluation of NEC and for measurements of nNOS and iNOS. The correlation between the degree of intestinal injury and levels of NOS was determined. RESULTS: The LPS-injected pups showed a significant increase in injury scores versus the control. The expression of nNOS protein and mRNA was diminished after LPS injection. There was a negative significant correlation between the nNOS protein and the grade of median intestinal injury within 24 h. The expression of iNOS protein and mRNA was significantly increased in the peak of intestinal injury. CONCLUSION: nNOS and iNOS play different roles in LPS-induced intestinal injury. Caution should be exerted concerning potential therapeutic uses of NOS inhibitors in NEC.