ENDOGENOUS NITRIC OXIDE PRODUCTION IS AUGMENTED AS THE SEVERITY ADVANCES IN PATIENTS WITH LIVER CIRRHOSIS

Acute-on-chronic liver disease enhances phenylephrine-induced endothelial nitric oxide release in rat mesenteric resistance arteries through enhanced PKA, PI3K/AKT and cGMP signalling pathways

Acute-on-chronic liver disease is a clinical syndrome characterized by decompensated liver fibrosis, portal hypertension and splanchnic hyperdynamic circulation. We aimed to determine whether the alpha-1 agonist phenylephrine (Phe) facilitates endothelial nitric oxide (NO) release by mesenteric resistance arteries (MRA) in rats subjected to an experimental microsurgical obstructive liver cholestasis model (LC). Sham-operated (SO) and LC rats were maintained for eight postoperative weeks. Phe-induced vasoconstriction (in the presence/absence of the NO synthase –NOS- inhibitor L-NAME) and vasodilator response to NO donor DEA-NO were analysed. Phe-induced NO release was determined in the presence/absence of either H89 (protein kinase –PK- A inhibitor) or LY 294002 (PI3K inhibitor). PKA and PKG activities, alpha-1 adrenoceptor, endothelial NOS (eNOS), PI3K, AKT and soluble guanylate cyclase (sGC) subunit expressions, as well as eNOS and AKT phosphorylation, were determined. The results show that LC blunted Phe-induced vasoconstriction, and enhanced DEA-NO-induced vasodilation. L-NAME increased the Phe-induced contraction largely in LC animals. The Phe-induced NO release was greater in MRA from LC animals. Both H89 and LY 294002 reduced NO release in LC. Alpha-1 adrenoceptor, eNOS, PI3K and AKT expressions were unchanged, but sGC subunit expression, eNOS and AKT phosphorylation and the activities of PKA and PKG were higher in MRA from LC animals. In summary, these mechanisms may help maintaining splanchnic vasodilation and hypotension observed in decompensated LC.

Postreperfusion syndrome during liver transplantation

As surgical and graft preservation techniques have improved and immunosuppressive drugs have advanced, liver transplantation (LT) is now considered the gold standard for treating patients with end-stage liver disease worldwide. However, despite the improved survival following LT, severe hemodynamic disturbances during LT remain a serious issue for the anesthesiologist. The greatest hemodynamic disturbance is postreperfusion syndrome (PRS), which occurs at reperfusion of the donated liver after unclamping of the portal vein. PRS is characterized by marked decreases in mean arterial pressure and systemic vascular resistance, and moderate increases in pulmonary arterial pressure and central venous pressure. The underlying pathophysiological mechanisms of PRS are complex. Moreover, risk factors associated with PRS are not fully understood. Rapid and appropriate treatment with vasopressors, volume replacement, or venesection must be provided depending on the cause of the hemodynamic disturbance when hemodynamic instability becomes profound after reperfusion. The negative effects of PRS on postoperative early morbidity and mortality are clear, but the effect of PRS on postoperative long-term mortality remains a matter of debate.

Influence of Nitric Oxide and cGMP on Agonist-Induced Platelet Adhesion – An In Vitro Study in Platelets Isolated from Patients with Liver Cirrhosis / Uticaj Azot-Oksida I cGMP Na Adheziju Trombocita Izazvanu Agonistima – In Vitro Studija Na Izolovanim Trombocitima Pacijenata Sa Cirozom Jetre

Variceal bleeding, one of the major complications of liver cirrhosis, is primarily due to platelet activation defect and secondarily due to coagulation defects. Platelet adhesion is the key event in hemostasis. Since nitric oxide (NO) related stress is known to influence platelet functions in liver cirrhosis, we undertook the present study to evaluate the possible mechanism involved in the inhibition of platelet adhesion by NO.

Methods:Agonist-induced platelet adhesion in vitro was measured in platelets isolated from normal subjects and cirrhosis patients. The time-dependent changes in nitric oxide synthase (NOS), NO, 3',5'-cyclic guanosine monophosphate (cGMP) and cytosolic calcium (Ca2+) levels were monitored during adhesion. The percentage of platelet adhesion was also monitored in the presence of an eNOS inhibitor and a cGMP inhibitor.

Results:The percentage of adhesion was significantly lower in cirrhosis platelets. Time-dependent changes in the cGMP NO and NOS level in platelets stimulated with collagen were significantly high, with a significantly low level of elevation of cytosolic Ca2+in cirrhosis as adhesion proceeded. The results showed improved platelet adhesion with inhibitors of NOS and cGMP with concomitant elevation in Ca2+level.

Conclusions:It is inferred that elevation in the formation of cGMP due to stimulation of NOS activity inhibits Ca2+mobilization from the internal store, an essential process to trigger platelet activation. The abnormal alterations were significantly lower in cirrhosis patients without bleeding complications. So, it could be stated that the bleeding abnormality in liver cirrhosis might be due to defective platelet adhesion influenced by the NO-cGMP pathway.

Increased plasma nitric oxide, L-arginine, and arginase-1 in cirrhotic patients with progressive renal dysfunction

BACKGROUND AND AIMS

Increased levels of nitric oxide (NO) are hypothesized to contribute to renal dysfunction in patients with decompensated cirrhosis. In this study, we examined whether splanchnic and/or peripheral NO levels and L-arginine (L-Arg) correlate with progressive renal dysfunction in cirrhotics.

METHODS

Serum NO metabolites (NOx) and L-Arg were measured in: controls (n = 10); organ donors (n = 12); compensated cirrhotics (n = 17), cirrhotics with ascites (n = 25), refractory ascites (n = 11) or hepatorenal syndrome type II (HRS) (n = 11) and chronic renal failure patients (n = 18).

RESULTS

Plasma NOx and L-Arg levels rose progressively with worsening renal function in decompensated cirrhotics. Both NOx and L-Arg levels were highest in patients with HRS (P < 0.001 and P < 0.025, respectively). While there were no differences in NOx levels related to the site of sampling, L-Arg levels were lowest in hepatic venous blood. There were significant relationships of NOx and L-Arg with Model for End-Stage Liver Disease score and Child-Pugh scores (P < 0.04 and P < 0.01, respectively). Multivariate analysis showed a significant relationship between NOx, L-Arg and HRS.

CONCLUSION

Worsening renal function in decompensated cirrhosis is accompanied by progressive elevation in plasma NOx and L-Arg. These findings support the hypothesis that NO-mediated vasodilation is probably linked with the mechanism of progressive renal failure in decompensated cirrhotics.

Is there a link between hyperbilirubinemia and elevated urine nitrite

OBJECTIVE

The aim of this study was to determine whether hyperbilirubinemia affects the association between a positive urine nitrite test and a positive urine culture.

METHODS

We conducted an institutional review board-approved, retrospective review of 12 months of patient data, compiling information for patients having urinalysis, urine culture, and total serum bilirubin. Patients were divided into 3 groups according to total serum bilirubin: less than 1.5 mg/dL, 1.5 to 3.0 mg/dL, and greater than 3.0 mg/dL. The point estimates and 95% confidence intervals of the sensitivity, specificity, false-positive proportion (proportion of false positive to all positive tests), and other test characteristics of urine nitrite as an indicator of urinary tract infection were calculated and tested for trend as a function of the 3 total serum bilirubin ranges.

RESULTS

Three thousand one hundred seventy-four patients met our study criteria. Specificity of the nitrite test decreased as a function of increasing total serum bilirubin (0.974, 0.966, and 0.855 for the 3 total bilirubin levels, respectively) with a significant trend (P < .0001). There was no significant trend in comparable sensitivity values (0.380, 0.417, and 0.241, respectively) with P = .55. The false-positive proportion also increased as a function of total serum bilirubin (17.5%, 17.3%, and 72.0%) with P < .0001. Thus, if a patient's total serum bilirubin was elevated to the point of jaundice (>3.0 mg/dL), it was approximately 4 times more likely that a positive urine nitrite test would be a "false positive" (ie, nitrite-positive/culture-negative) compared with those with normal serum bilirubin levels.

CONCLUSIONS

Specificity of the urine nitrite test for urinary tract infection decreases as a function of increasing serum bilirubin. Most patients with hyperbilirubinemia and a positive nitrite test in our sample did not have an associated urinary tract infection.

Overexpression of inducible nitric oxide synthase in gastric mucosa of rats with portal hypertension: correlation with gastric mucosal damage

BACKGROUND

An increased biosynthesis of nitric oxide (NO) has been implicated in the hyperdynamic circulation and development of collaterals of portal hypertension (PHT) because of its potent vasodilatory effects. NO is synthesized from L-arginine by three different isozymes of nitric oxide synthase (nNOS, iNOS and eNOS). Thus, the expression of inducible NOS (iNOS) might account for NO overproduction in PHT. However, in previous investigations, the role of iNOS in the pathogenesis of PHT gastropathy remained controversial. Our current study was in both molecular and protein levels to determine whether the expression of iNOS is responsible for PHT gastropathy.

MATERIALS AND METHODS

PHT was induced experimentally by partial ligation of the portal vein. Fourteen days after partial ligation of the portal vein, the rats were randomly assigned to receive either vehicle or L-NAME (NOS inhibitor) at doses of 5 mg/kg/day, 10 mg/kg/day, or 25 mg/kg/day by gastric lavage twice a day for 1 week. Sham operated rats served as controls. Northern hybridization and in situ hybridization are used to compare the expression of gastric mucosa iNOS mRNA in the PHT rats and the controls. NO was measured by the Griess method after reduction of nitrate to nitrite with nitrate reductase. Immunohistochemical staining was carried out to detect the iNOS protein. In addition, the severity of gross gastric mucosal lesions was evaluated macroscopically by a gross ulcer index.

RESULTS

The iNOS expression at both mRNA and protein was prominently increased in PHT rats, accompanied with the enhanced NO production. The gastric mucosa iNOS mRNA and serum NO levels were significantly decreased after L-NAME administration (P < 0.05). However, the markedly reduced gastric mucosal damage in PHT rats was observed only at high does of L-NAME (25 mg/kg/day) administration.

CONCLUSION

PHT triggers overexpression of iNOS mRNA and proteins in rat gastric mucosa, but that this alone does not account for PHT gastropathy.

Change in lipid profile and impairment of endothelium-dependent relaxation of blood vessels in rats after bile duct ligation

Hyperlipidemia, a condition normally observed in cholestatic liver disease, is also a risk factor for the development of atherosclerosis. The relationship between the elevation of lipoproteins in cholestatic liver diseases and atherosclerosis formation has not been elucidated. In this study, we propose that the impairment of endothelium-dependent relaxation (EDR) of blood vessels in cholestatic liver diseases may lead to the development of atherosclerosis. Using bile duct ligation (BDL) in rats as a model, we examined the liver function, serum lipid profile, EDR and morphologic change of the aorta from both sham operated and BDL rats. Significant increases in liver and spleen weights, serum alanine transaminase (ALT) and aspartate transaminase (AST) activities and the bilirubin level were observed in BDL rats. Upon bile duct ligation, the total and low-density lipoprotein cholesterol levels were increased but the high-density lipoprotein cholesterol and triglyceride levels were reduced. Less contractility and lowered response to acetylcholine-induced relaxation were found in aorta segments. In addition, the acetylcholine-induced relaxation was blocked by both L-NAME and 15 mM KCl. Our results suggest that both nitric oxide and endothelium-derived hyperpolarizing factor are important elements for the impairment of the EDR in BDL rats. In addition, a mild atrophy of the media of the aorta was detected in BDL rats. We conclude that the alterations of lipid profile and the mild atrophy of the media may lead to the impairment of EDR in the aorta in BDL rats, and these factors may potentiate the development of atherosclerosis.

Nitric oxide in liver diseases: friend, foe, or just passerby?

Research on the free radical gas, nitric oxide (NO), during the past twenty years is one of the most rapid growing areas in biology. NO seems to play a part in almost every organ and tissue. However, there is considerable controversy and confusion in understanding its role. The liver is one organ that is clearly influenced by NO. Acute versus chronic exposure to NO has been associated with distinct patterns of liver disease. In this paper we review and discuss the involvement of NO in various liver diseases collated from observations by various researchers. Overall, the important factors in determining the beneficial versus harmful effects of NO are the amount, duration, and site of NO production. A low dose of NO serves to maximize blood perfusion, prevent platelet aggregation and thrombosis, and neutralize toxic oxygen radicals in the liver during acute sepsis and reperfusion events. NO also demonstrates antimicrobial and antiapoptosis properties during acute hepatitis infection and other inflammatory processes. However, in the setting of chronic liver inflammation, when a large sustained amount of NO is present, NO might become genotoxic and lead to the development of liver cancer. Additionally, during prolonged ischemia, high levels of NO may have cytotoxic effects leading to severe liver injury. In view of the various possible roles that NO plays, the pharmacologic modulation of NO synthesis is promising in the future treatment of liver diseases, especially with the emergence of selective NO synthase inhibitors and cell-specific NO donors.

The effect of methylene blue on the hemodynamic changes during ischemia reperfusion injury in orthotopic liver transplantation

After graft reperfusion in orthotopic liver transplantation (OLT), ischemia reperfusion syndrome (IRS) is characterized by persistent hypotension with a low systemic vascular resistance. Methylene blue (MB) has been used as a vasopressor in sepsis and acute liver failure. We investigated the effect of MB on IRS during OLT. Thirty-six patients undergoing elective OLT were randomized to receive either a bolus of MB 1.5 mg/kg before graft reperfusion, or normal saline (placebo). We recorded hemodynamic variables, postoperative liver function tests, and time to hospital discharge. Blood samples were analyzed for arterial lactate concentration, cyclic 3',5'-monophosphate, and plasma nitrite/nitrate concentrations. The MB group had higher mean arterial pressure (P = 0.035), higher cardiac index (P = 0.04), and less epinephrine requirement (P = 0.02). There was no difference in systemic vascular resistance or central venous pressure. Serum lactate levels were lower at 1 h after reperfusion in MB patients, suggesting better tissue perfusion (P = 0.03). In the presence of MB, there was a reduction in cyclic 3',5'-monophosphate (P < 0.001), but not plasma nitrites. Postoperative liver function tests and time to hospital discharge were the same in both groups. MB attenuated the hemodynamic changes of IRS in OLT acting via guanylate cyclase inhibition.

IMPLICATIONS

Methylene blue attenuates the hemodynamic changes of the ischemia reperfusion syndrome in liver transplantation, and this effect involves guanylate cyclase inhibition.

Variation at the Angiotensin-converting enzyme and endothelial nitric oxide synthase genes is associated with the risk of esophageal varices among patients with alcoholic cirrhosis

Esophageal varices are a frequent complication among patients with liver cirrhosis. Nitric oxide and other vasoactive molecules regulate the vascular tone in both the liver microcirculation and the systemic and splanchnic circulation. Several genes that encode proteins involved in the maintenance of vascular tone, such as the endothelial-constitutive nitric oxide synthase (ecNOS), the angiotensinogen (AGT), the angiotensin-converting enzyme (ACE), and the angiotensin II receptor type 1 (AT1R) are polymorphic, and these polymorphisms have been associated with several cardiovascular diseases. Our aim was to define a possible role for DNA polymorphisms at these genes in the risk of developing esophageal varices among patients with alcoholic cirrhosis. We analyzed 145 male patients with liver cirrhosis. Patients and 200 healthy controls were genotyped by polymerase chain reaction for the ACE-I/D, the AGT-M235T, the AT1R-A1166C, and the ecNOS-4/5 (intron 4) polymorphisms. Ninety-five patients had varices and 50 did not show this complication. Carriers of the ACE-I allele (ID + II genotypes) were at a significantly higher frequency among patients with varices (p = 0.013). Patients without varices had a higher frequency of the ecNOS-4 allele compared with patients with varices (p = 0.026). ACE-I carriers + ecNOS-55 were at a significantly higher frequency (p = 0.0012; odds ratio = 3.19; 95% CI = 1.55-6.55) among patients with varices (51 of 95, 54%) compared with patients without (18 of 50, 36%). Allele and genotype frequencies for the AGT and AT1R polymorphisms did not differ between the two groups. The genotypes associated with an increased risk for varices have been linked to higher plasma levels of nitric oxide and reduced levels of ACE. These genotypes could have a vasodilatory effect in the systemic and splanchnic circulation, thus favoring the development of portocollaterals.

Levels of circulating endothelin-1 and nitrates/nitrites in patients with virus-related hepatocellular carcinoma

A balance between endothelins (ET) and nitric oxide (NO) might interfere with liver haemodynamics and disease progression in various liver diseases. Increased levels of endothelin 1 (ET-1) and nitrites and nitrates (NOx, the end products of NO metabolism) have been reported in hepatocellular carcinoma (HCC), but the balance has not been studied. The purpose of this study was to assess the ratio of NOx to ET-1 in patients with virus-related hepatocellular carcinoma and to investigate its correlation with the extent of the disease. Eighteen patients with virus-related HCC (six Okuda stage I, six Okuda stage II and six Okuda stage III) were included in the study and were compared with 22 patients with viral cirrhosis (14 decompensated, eight compensated) and seven normal controls. ET-1 was measured with an ELISA assay and NOx with a modification of the Griess reaction. Patients with virus-related HCC had the highest levels of circulating ET-1 and NOx (13.24 +/- 0.82 pg/ml and 112.28 +/- 18.56 micromol/l) compared to compensated cirrhosis (9.47 +/- 0.50 pg/ml, P < 0.004 and 54.47 +/- 2.36 micromol/l, P < 0.01), decompensated cirrhosis (9.57 +/- 0.32 pg/ml, P < 0.001 and 90.20 +/- 11.23 micromol/l, NS) and normal controls (8.84 +/- 0.61 pg/ml, P < 0.001 and 51.17 +/- 6.18 micromol/l, P < 0.01). There was a significant increase of ET-1 and NOx at HCC stage III compared to HCC stages I and II, cirhotics and controls. HCC stage III patients also had a NOx/ET-1 ratio that was higher than HCC stages I and II patients, normal controls and patients with compensated cirrhosis. Virus-related HCC patients have high levels of circulating ET-1, compared to compensated or decompensated cirrhosis. Highest levels of ET-1 are produced in Okuda III tumours. NOx are also increased but only in Okuda stage III tumours. The NOx/ET-1 ratio is increased in virus-related HCC and DC. This increase may account for the known increase in tumour blood flow.

Hepatorenal failure

Since the description of HRS more than 100 years ago, significant advances have been made in understanding the pathophysiology of HRS and in the management of these patients. There is now a therapeutic armamentarium: medical (ornipressin plus plasma volume expansion), radiographic (TIPS shunt), and surgical (liver transplantation). The diagnosis of HRS is no longer synonymous with a death sentence; instead, it is a therapeutic challenge, and a coordinated approach by intensivists, hepatologists, nephrologists, interventional radiologists, and transplant surgeons is needed to continue to improve the prognosis of cirrhotic patients presenting with HRS. Increased understanding of HRS will allow preventative rather than therapeutic measures to be used. As in all fields of medicine, these advances will come only with innovative clinical investigation.

Role of nitric oxide in haemodialysis hypotension

To investigate the possible involvement of nitric oxide (NO) in haemodialysis hypotension, we measured plasma concentrations of nitrate anion (NO3-), a metabolite of NO, in 114 patients undergoing maintenance haemodialysis. Mean plasma NO3- concentrations before dialysis were greater in subjects with lower blood pressure (155 +/- 16 micromol L-1) than in those with middle (117 +/- 8 micromol L-1) or higher blood pressure (105 +/- 12 micromol L-1) before dialysis. Further, mean plasma NO3- concentrations before dialysis were greater in subjects with lower blood pressure (186 +/- 13 micromol L-1) than in those with middle (112 +/- 7 micromol L-1) or higher blood pressure (64 +/- 11 micromol L-1) after dialysis. Plasma NO3- concentrations before dialysis were inversely correlated with mean blood pressure before dialysis (r=0.318, P=0.0006), and showed a strong inverse correlation with mean blood pressure after dialysis (r=0.608, P=0.0001). In the selected participants who had equal range of mean blood pressure before dialysis, mean plasma NO3- concentrations were greater in subjects with severe hypotension during dialysis (180 +/- 14 micromol L-1) than in those with mild hypotension (99 +/- 11 micromol L-1) or without hypotension (53 +/- 12 micromol L-1); plasma NO3- concentrations before dialysis were inversely correlated with changes in mean blood pressure during dialysis and mean blood pressure after dialysis. Results indicate that enhanced NO production may be involved in acute hypotension during dialysis, and suggest the possible involvement of NO in the pathogenesis of chronic hypotension associated with maintenance haemodialysis.

Gallbladder hyporesponsiveness to an exogenous nitric oxide donor, glyceryl trinitrate, in patients with advanced liver cirrhosis

OBJECTIVE

An increased production of nitric oxide (NO) in liver cirrhosis has been documented. NO could intervene in regulating gallbladder contraction, as suggested by clinical and experimental studies. Our aim was to investigate the influence of an NO donor on gallbladder motility in cirrhotic patients in relation to the severity of liver cirrhosis.

METHODS

The subjects were six controls and 18 patients with liver cirrhosis (six in each Child class). Gallbladder emptying was monitored by ultrasound for 90 min after a mixed meal (14 g fat, 425 kcal). Fasting gallbladder volume, minimal residual volume, ejection fraction, area under emptying curve, and half contraction time of the gallbladder were assessed at 15-min intervals. The patients were evaluated on two consecutive days, with or without perlingual administration of 0.5 mg glyceryl trinitrate (GTN). Statistical analysis was performed by the two-tailed Student's t test and Pearson's correlation coefficient.

RESULTS

GTN significantly reduced gallbladder motility in controls and compensated cirrhotics (p < 0.02), but had no effect upon gallbladder emptying in Child class B and C cirrhotics.

CONCLUSIONS

Gallbladder hypocontractility in liver cirrhosis is related to the severity of the disease. This study is the first to show that GTN has no effect upon gallbladder motility in advanced liver cirrhosis when administered in doses that induce relaxation in controls and compensated cirrhosis.

Enhanced release of nitric oxide in response to changes in flow and shear stress in the superior mesenteric arteries of portal hypertensive rats

Increased nitric oxide (NO) release has been implicated in the pathogenesis of the hyperdynamic circulation in portal hypertension. NOS 3 (eNOS) causes NO release from the endothelium in response to physical stimuli, such as increased blood flow and shear stress. We evaluated the functional activity of the endothelium in the superior mesenteric arterial bed of portal hypertensive rats through direct measurement of NO metabolites (NOx) during changes in flow and shear stress. The in vitro perfusion system (McGregor) was used in sham and portal vein-ligated (PVL) rats. Shear stress was applied gradually to superior mesenteric arterial beds by increasing the perfusion rate. Flow studies were performed serially before and after incubation with either Krebs solution alone or with the NO-inhibitor, NG-monomethyl-L-arginine (L-NMMA). NOx concentrations in the perfusate were measured using chemiluminescence. The slope of NOx release versus flow-induced shear stress was calculated. Before L-NMMA administration, NOx concentrations and release of NO in PVL rats were significantly elevated in comparison with sham rats at flow rates of 32, 40, and 48 mL/min. The slope of NOx production versus shear stress index was significantly higher in PVL than in sham rats. After L-NMMA incubation, the decrease in slope was significantly larger in PVL rats. This study provides direct evidences of an increased NO synthesis by the superior mesenteric arterial vascular endothelium of PVL animals in response to shear stress. The increased NO output in response to shear stress suggests an adaptative mechanism developed by the vascular endothelial cells in response to a chronic increase in flow-mediated shear stress.

Nitric oxide inactivates rat hepatic methionine adenosyltransferase In vivo by S-nitrosylation

We investigated the mechanism of nitric oxide (NO) action on hepatic methionine adenosyltransferase (MAT) activity using S-nitrosoglutathione (GSNO) as NO donor. Hepatic MAT plays an essential role in the metabolism of methionine, converting this amino acid into S-adenosylmethionine. Hepatic MAT exists in two oligomeric states: as a tetramer (MAT I) and as a dimer (MAT III) of the same subunit. This subunit contains 10 cysteine residues. In MAT I, S-nitrosylation of 1 thiol residue per subunit was associated with a marked inactivation of the enzyme (about 70%) that was reversed by glutathione (GSH). In MAT III, S-nitrosylation of 3 thiol residues per subunit led to a similar inactivation of the enzyme, which was also reversed by GSH. Incubation of isolated rat hepatocytes with S-nitrosoglutathione monoethyl ester (EGSNO), a NO donor permeable through the cellular membrane, induced a dose-dependent inactivation of MAT that was reversed by removing the NO donor from the cell suspension. MAT, purified from isolated rat hepatocytes, contained S-nitrosothiol groups and the addition of increasing concentrations of EGSNO to the hepatocyte suspension led to a progressive S-nitrosylation of the enzyme. Removal of the NO donor from the incubation media resulted in loss of most NO groups associated to the enzyme. Finally, induction in rats of the production of NO, by the administration of bacterial lipopolysaccharide (LPS), induced a fivefold increase in the S-nitrosylation of hepatic MAT, which led to a marked inactivation of the enzyme. Thus, the activity of liver MAT appears to be regulated in vivo by S-nitrosylation.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

Prolonged decreases in plasma nitrate levels at early postoperative phase after hepato-pancreato-biliary surgery

Nitric oxide (.NO) is known to influence circulatory, neural, immunologic, and metabolic alterations. To evaluate the clinical significance of .NO production under surgical stress, serial measurements of plasma nitrite plus nitrate levels were performed in 45 surgical patients. Group A included 19 patients who underwent major surgery with uneventful postoperative courses. Group B included 18 patients who underwent laparoscopic cholecystectomy. Group C included 8 patients whose surgery was complicated by intra-abdominal abscesses. Eight healthy volunteers served as controls. Plasma nitrate levels were determined with a redox chemiluminescence .NO analyzer and coincided with measurements made by high-performance liquid chromatography (r = 0.868, p < 0.0001, 58 samples). During laparotomy, arterial nitrate levels correlated well with peripheral, portal, and hepatic venous nitrate levels (r = 0.966, 0.938, and 0.949, respectively; p < 0.0001). A significant decrease in nitrate from preoperative levels in groups A (postoperative day (POD) 1 and 3; p < 0.0005) and B (POD 1, p < 0.0001) was observed; nitrate levels in group C did not decrease for 14 days after surgery. Plasma nitrate levels in groups A and B were significantly different (POD 1 through 6, p < 0.05) and at POD 3 were significantly lower in group A (p < 0.005). Plasma nitrate levels measured before and after fasting or food intake were not significantly different. These results suggest that surgical stress leads to a decrease in the end product of .NO in the whole body, and that the greater the surgical stress the longer the duration of decreased .NO production.