The L-arginine-nitric oxide pathway

Vanadate as factor of cardiovascular regulation by interactions with the catecholamine and nitric oxide systems

The effects of 1 microgram/mL of vanadium, given for 12 mo as sodium metavanadate in drinking water, on cardiovascular and biochemical indices of male rabbits were investigated. At the end of the exposure period, vanadium was more accumulated in bones and kidneys than in spleen and liver; the cardiac ventricles and the aorta contained similar amounts of this element. Blood pressure and heart rate were unchanged in the vanadate-exposed animals since the observed decrease of both cardiac inotropism and stroke volume was counteracted by an increase of peripheral vascular resistance, with reduction of arterial blood flow. The arterial levels of sodium, potassium and aldosterone were unmodified by vanadate which, however, strongly raised those of noradrenaline, adrenaline, L-DOPA, and dopamine. Vanadate caused a marked increase of the activity of monoamine oxidase in renal tubules and liver (probably in relation to the increased plasma catecholamine levels) and a reduction of that of glucose-6-phosphate dehydrogenase in the kidney. There was also evidence that vanadium reduces synthesis and/or release of nitric oxide, the endothelium-derived vasodilating factor, likely through a reduced formation from bradykinin. It was concluded that vanadium may represent an environmental factor of altered cardiovascular homeostasis.

L-arginine infusion reduces preterm uterine contractions

In order to investigate the role of nitric oxide in preterm labor, 10 women presenting with preterm onset of uterine contractions were infused with L-Arginine. In comparison to saline infusion, L-Arginine significantly reduced the number of contractions, together with an increase of both serum growth hormone and nitrates levels. These findings demonstrate that the enhancement of endogenous nitric oxide production through its physiological donor, L-Arginine, is able to transiently reduce preterm uterine spontaneous contractility.

The effects of arginine administration on the levels of arginine, other amino acids and related amino compounds in the plasma, heart, aorta, vena cava, bronchi and pancreas of the rat

Arginine (0.8g/kg, ip) or a vehicle was administered to rats and the levels of arginine and a large number of related amino compounds++ were measured in plasma, heart, aorta, vena cava, pancreas and bronchi at specified time intervals. Arginine levels (nmol/ml) increased in the plasma from 237 to 3172 at 15 min, 1236 at 30 min and 509 at 120 min. Peak concentrations (nmol/g) of arginine are reached in the tissues at 15 or 30 minutes with control and postinjection values of 500 and 1769 in the heart, 314 and 1563 in the aorta, 575 and 2976 in the vena cava, 760 and 1943 in the bronchi, and 234 and 3638 in the pancreas. Arginine injection also affects a number of amino acids and related compounds in the plasma and tissues most notably ornithine, isoleucine, phosphoserine, leucine and ethanolamine. However, plasma level changes do not predict tissue level changes which are highly specific for an individual compound and tissue. There was no general indication that arginine injection stimulates nitric oxide (NO) formation in any tissue. Thus, arginine is rapidly absorbed from the abdominal cavity into the blood stream, is quickly taken up by the tissues studied and disappears after about 2 to 3 hours. The effects seen after arginine administration could be caused by arginine per se and/or changes in one or more of the related amino compounds but not by NO.

Neural regulation of coronary vascular resistance: role of nitric oxide in reflex cholinergic coronary vasodilation in normal and pathophysiologic states

A number of reflexes participate in the control of coronary vascular resistance through activation of the sympathetic or parasympathetic nervous system. Classically, activation of vagal efferent fibers to the heart results in vasodilation due to the release of acetylcholine and activation of muscarinic receptors. Recently, we have found that activation of a number of reflexes in conscious dogs, the Bezold-Jarisch reflex and the carotid chemoreflex in particular, results in cholinergic coronary vasodilation which is blocked by an inhibitor of nitric oxide synthesis, nitro-L-arginine. After the development of pacing-induced heart failure, the cholinergic dilation subsequent to activation of the Bezold-Jarisch or carotid chemoreflex is essentially abolished, since coronary blood vessels no longer produce nitric oxide. In contrast, after brief exercise training, there is a potentiation of Bezold-Jarisch reflex-induced coronary vasodilation since exercise upregulates nitric oxide production by coronary blood vessels. Since the Bezold-Jarisch reflex may be important as a compensatory mechanism during acute myocardial infarction, and the carotid chemoreflex is the acute mechanisms responsible for ameliorating systemic hypoxemia, the role of nitric oxide in reflex cholinergic coronary vasodilation may be essential in the compensatory vascular adjustments evoked by these and other reflexes.

Chronic L-arginine administration attenuates cardiac hypertrophy in spontaneously hypertensive rats

Nitric oxide inhibits proliferation and migration of vascular smooth muscle cells and contractility of cardiomyocytes in vitro. In spontaneously hypertensive rats (SHR), evidence suggests intrinsic abnormalities of the L-arginine-nitric oxide axis, such as low cGMP-dependent protein kinase in the heart and abnormal L-arginine metabolism. To investigate the in vivo effect of L-arginine on cardiac hypertrophy, 30 SHR and 30 Wistar-Kyoto rats (WKY) were randomly grouped to receive L-arginine (7.5 g/L in drinking water) or vehicle for 12 weeks. L-Arginine treatment did not affect body weight or arterial pressure in either strain. In vehicle-treated animals, the heart/body weight ratio was significantly higher in SHR than in WKY (P < .01). L-Arginine treatment decreased the heart/body weight ratio in SHR (P < .05) but did not affect it in WKY. Expression of skeletal alpha-actin mRNA, known to be expressed in the hypertrophied myocardium, was attenuated in L-arginine-treated SHR compared with vehicle-treated SHR. Cardiac cGMP content and nitrate/nitrite content were less in SHR than WKY. L-Arginine treatment increased these levels only in SHR, suggesting enhanced nitric oxide production. Thus, chronic L-arginine administration attenuated cardiac hypertrophy independently of blood pressure and increased myocardial content of cGMP and nitrate/nitrite. Our results suggest that abnormality of the cardiac L-arginine-nitric oxide axis may play an important role in the pathogenesis of cardiac hypertrophy in SHR.

A smoking-dependent risk of coronary artery disease associated with a polymorphism of the endothelial nitric oxide synthase gene

Endothelium-dependent vasodilatation is mediated by release of nitric oxide formed by constitutively expressed endothelial nitric oxide synthase (ecNOS). We explored the distribution of polymorphism ecNOS4a/b in 549 subjects with, and 153 without, coronary artery disease in relation to smoking. In current and ex-cigarette smokers, but not nonsmokers, there was a significant excess of homozygotes for the rare ecNOS4a allele in patients with severely stenosed arteries, compared with those with no or mild stenosis. This genotype was also associated with a history of myocardial infarction. This smoking-dependent excess coronary risk in ecNOS4a homozygotes is consistent with predisposition to endothelial dysfunction.

Neuroimmunologic implications in coronary artery disease

In this review, the role of the macrophage in the pathophysiology of coronary artery disease (CAD) is examined. The central interaction of macrophage, endothelial cell and smooth muscle cell in the context of hyperlipidemia is considered. The macrophage appears to be at the beginning of a chain of events that starts with elevated low density lipoprotein (LDL). Stress, particularly in those with a core hostility, may be associated not only with higher catecholamine levels but also with higher serum lipid levels. These lipids will in turn be processed to oxidized LDL by macrophage and endothelial cells. Oxidized LDL molecules will contribute to atherosclerotic plaquing. A side effect of such plaque formation may be a diminished vasodilatory response to the nitric oxide (NO) produced by macrophages and endothelium. Indeed, paradoxical vasoconstriction occurs in atherosclerosis in response to neurotransmitters such as serotonin and acetylcholine, which under normal circumstances cause vasodilation. There also is evidence that both macrophages and endothelial cells can regulate NO production through a specific mu 3 morphine receptor, an effect that can be blocked by naloxone. The clinical effectiveness of morphine and nitroglycerin in CAD patients may relate to these mechanisms. More research will be needed to elucidate the neuroimmunologic basis for atherosclerosis with prospects for better treatment and management in future.

Do monoclonal antibodies and anticytokines still have a future in infectious diseases?

The continuing high mortality of septic shock has prompted a major effort by the research community to identify novel therapeutic targets. These targets can be conveniently grouped into (1) those derived from microbial components or products; (2) inflammatory mediators; and (3) effector molecules. Many of the experimental, so-called adjunctive agents developed have been monoclonal antibodies or anticytokine molecules of various kinds, and some have progressed into clinical trial. Unfortunately, these trials have failed to show unequivocal survival benefit for patients in shock, prompting a reappraisal of our approach to these agents. In this article, we discuss the possible reasons for these failures: (1) the targets are wrong; (2) the agents are inappropriate; or (3) the trial design is flawed. It would be premature to conclude that adjunctive agents have no future in the therapy of sepsis, but identifying the correct agent, and perhaps more importantly, the correct target population, is going to be more difficult than was at first believed.

The metabolites of nitric oxide in sickle-cell disease

Plasma NOx concentrations were raised in 22 acute painful crises in SCD. We have measured blood concentrations of nitric oxide metabolites (NOx) in sickle-cell disease (SCD), and shown that they are increased compared with healthy controls (P = 0.002), and haemoglobin E/beta-thalassaemic controls (P = 0.05). Concentrations in steady-state SCD were also higher than in healthy controls (P = 0.04) but not significantly different from the concentrations at the beginning of painful crises (P = 0.34). Importantly, in 12 regularly exchanged sicklers, the mean pre-transfusion NOx concentration did not differ significantly from the control population (P = 0.52), suggesting that the changes in NO metabolism can be reversed. It is unlikely that the increased concentrations of NOx in SCD result from anaemia or haemolysis as the untransfused haemoglobin E/beta-thalassaemics did not show increased levels.

Nitric oxide tonically depresses a voltage- and Ca-dependent outward current in hippocampal slices

In whole-cell recordings from CA1 neurons, net outward currents (at ca. -20 mV, from VH ca. -50 mV) were 40-50% depressed by sodium nitroprusside (100-500 microM) or L-arginine (L-ARG; 50-200 microM), but not by D-arginine (100 microM). The NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME; 200 microM) restored the L-ARG-depressed current to ca. 80% of control. In naive cells, L-NAME increased outward currents by 45 +/- 12.6%; the enhanced currents were then reduced by adding L-ARG (200-400 microM). The NO-sensitive current is Ca-dependent, because L-NAME and L-ARG were ineffective in Mn/low Ca medium or when electrodes contained 2.2 mM EGTA. Since high voltage-activated Ca-currents were unaltered by L-NAME, we conclude that NO tonically enhances excitability in slices by depressing a voltage- and calcium-dependent (IK(Ca)-type) outward current.

Chronic inhibition of nitric oxide synthesis causes coronary microvascular remodeling in rats

The aim of the present study was to investigate the effects of long-term blockade of nitric oxide synthesis with the L-arginine analogue N omega-nitro-L-arginine methyl ester (L-NAME) for 8 weeks on coronary vascular and myocardial structural changes. Four groups of Wistar-Kyoto rats were studied: those with no treatment, those treated with L-NAME 1 g/L (3.7 mmol/L in drinking water), those treated with L-NAME 0.1 g/L (0.37 mmol/L in drinking water), and those treated with L-NAME 1.0 g/L and hydralazine 120 mg/L (0.6 mmol/L in drinking water). After 8 weeks, the heart was excised, and the degrees of structural changes in coronary arteries (wall-to-lumen ratio and perivascular fibrosis), myocardial fibrosis, and myocyte size were quantified by an image analyzer. Chronic inhibition of nitric oxide synthesis increased arterial pressure compared with control animals. Chronic inhibition of nitric oxide synthesis caused significant microvascular remodeling (increased wall-to-lumen ratio and perivascular fibrosis). Cardiac hypertrophy was also observed after chronic inhibition of nitric oxide synthesis. Coadministration of hydralazine prevented arterial hypertension but did not affect microvascular remodeling and cardiac hypertrophy induced by the chronic inhibition of nitric oxide synthesis. In addition, chronic inhibition of nitric oxide synthesis caused scattered lesions of myocardial fibrosis, which was significantly attenuated by cotreatment with hydralazine. These results suggest that long-term blockade of nitric oxide synthesis caused coronary microvascular remodeling and cardiac hypertrophy in rats in vivo by a mechanism other than arterial hypertension. In contrast, arterial hypertension contributed to the development of myocardial fibrosis induced by long-term blockade of nitric oxide synthesis.

A hypoxia-responsive element mediates a novel pathway of activation of the inducible nitric oxide synthase promoter

Picolinic acid, a catabolite of L-tryptophan, activates the transcription of the inducible nitric oxide synthase gene (iNOS) in IFN-gamma-treated murine macrophages. We performed functional studies on the 5' flanking region of the iNOS gene linked to a CAT reporter gene to identify the cis-acting element(s) responsible for the activation of iNOS transcription by picolinic acid. Transient transfection assays showed that the full-length iNOS promoter in the murine macrophage cell line ANA-1 was activated by the synergistic interaction between IFN-gamma and picolinic acid. Deletion or mutation of the iNOS promoter region from -227 to -209, containing a sequence homology to a hypoxia-responsive enhancer (iNOS-HRE), decreased picolinic acid- but not LPS-induced CAT activity by more than 70%. Functional studies using a tk promoter-CAT reporter gene plasmid demonstrated that the iNOS-HRE was sufficient to confer inducibility by picolinic acid but not by IFN-gamma or LPS. Electrophoretic mobility shift assays confirmed that picolinic acid alone induced a specific binding activity to the iNOS-HRE. Furthermore, we found that the iNOS-HRE activity was inducible by hypoxia and that hypoxia in combination with IFN-gamma activated the iNOS promoter in transient transfection assays and induced iNOS transcription and mRNA expression. These data establish that the iNOS-HRE is a novel regulatory element of the iNOS promoter activity in murine macrophages and provide the first evidence that iNOS is a hypoxia-inducible gene.

Short-term effects of methylene blue on hemodynamics and gas exchange in humans with septic shock

OBJECTIVE

The aim of this study was to investigate the acute effects of methylene blue (MB), an inhibitor of the L-arginine nitric oxide pathway, in patients with septic shock.

DESIGN

A prospective, open, single-dose study.

SETTING

The medical ICU of a university hospital.

PATIENTS

Six patients with severe septic shock.

INTERVENTIONS

Complete hemodynamic values were recorded before and 20 min after the infusion of intravenous MB (3 mg kg(-1)). Arterial pressure was then monitored during the next 24 h or until death.

MEASUREMENTS AND RESULTS

Methylene blue increased the mean arterial pressure from 69.7 +/- 4.5 to 83.7 +/- 5.1 mmHg (p = 0.028) and the mean pulmonary artery pressure, from 34.3 +/- 7.2 to 38.7 +/- 8.0 mmHg (p = 0.023). Systemic vascular resistance index was increased from 703.1 +/- 120.6 to 903.7 +/- 152.2 dyne.s.cm(-5).m(-2) (p = 0.028) and pulmonary vascular resistance index, from 254.6 +/- 96.9 to 342.2 +/- 118.9 dyne.s.cm(-5) .m(-2) (p = 0.027). The PaO2/FIO2 decreased from 229.2 +/- 54.4 to 162.2 +/- 44.1 mmHg (p = 0.028), without significant modification of intrapulmonary shunting. Heart rate, cardiac index, right atrial pressure, DO2, VO2, oxygen extraction and arterial lactate were essentially unchanged. Sequential measurements of arterial pressure demonstrated a return to baseline level in 2-3 h. All but one patients died, three in shock and two in multiple organ failure.

CONCLUSIONS

MB induces systemic and pulmonary vasoconstriction in patients with septic shock, without significant decrease in cardiac index. The worsening of arterial oxygenation following MB injection may limit its use in patients with the adult respiratory distress syndrome. Larger studies are required to determine whether MB improves the outcome of patients with septic shock.

Clinical biology of nitric oxide

Nitric oxide is a pluripotential molecule that acts as both an autocrine and paracrine mediator of homoeostasis, and derangement of its metabolism can be linked with many pathophysiological events. This review provides a broad overview of the basic and clinical scientific aspects of nitric oxide.

Dietary supplementation with L-arginine limits cell proliferation in the remnant glomerulus

One effect of L-arginine is to increase nitric oxide (NO) production by endothelial cells. NO directly reduces endothelin-1 production by endothelial cells and also inhibits platelet-derived growth factor (PDGF) induced cell proliferation. Since subtotal renal ablation is associated with an early phase of cell proliferation in the glomerulus that precedes injury, we examined the effect of dietary supplementation with L-arginine on glomerular cell proliferation and expression of the cytokine endothelin-1 (ET-1). A first group of renal-ablated rats was untreated. A second group of renal-ablated rats received L-arginine (1%) in the drinking water. Two weeks after subtotal ablation renal cortical tissue was snap frozen for immunohistochemical analysis for proliferating cell nuclear antigen (PCNA) expression and ET-1. Protein and total RNA was extracted from sieved glomeruli. mRNA levels were quantitated by co-amplification RT-PCR utilizing specific 5' and 3' primers for rat ET-1 and beta-actin. L-arginine reduced the number of PCNA positive nuclei in remnant glomeruli, and Western blot Analysis of glomerular proteins also showed that L-arginine reduced PCNA expression. Glomerular ET-1 mRNA levels and protein immunostaining declined in the rats receiving L-arginine. We conclude that dietary supplementation with L-arginine reduces early cell proliferation in the remnant glomerulus, an effect that may be mediated, in part, by a decrease in ET-1 production.

Impact of the L-arginine/nitric oxide system in pregnancy

Nitric Oxide (NO) recently becomes of clinical interest because of its relaxant effects on smooth muscle. In addition to endothelial cells, also myometrial cells contain the enzyme implicated in the NO production. This review is aimed toward those studies concerned with the production, metabolism, and effects of NO that could be relevant for the obstetricians. The potential clinical interest of such information covers the main areas of pregnancy complications, namely preterm delivery, preeclampsia, and intrauterine growth retardation. Moreover, original data are included in order to support the therapeutical implications of the manipulation of L-arginine-NO system in case of pregnancy disorders.

The multiple organ dysfunction syndrome caused by endotoxin in the rat: attenuation of liver dysfunction by inhibitors of nitric oxide synthase

1. We have investigated whether (i) endotoxaemia caused by E. coli lipopolysaccharide in the anaesthetized rat causes a multiple organ dysfunction syndrome (MODS; e.g. circulatory failure, renal failure, liver failure), and (ii) an enhanced formation of nitric oxide (NO) due to induction of inducible NO synthase (iNOS) contributes to the MODS. In addition, this study elucidates the beneficial and adverse effects of aminoethyl-isothiourea (AE-ITU), a relatively selective inhibitor of iNOS activity, and NG-methyl-L-arginine (L-NMMA), a non-selective inhibitor of NOS activity on the MODS caused by endotoxaemia. 2. In the anaesthetized rat, LPS caused a fall in mean arterial blood pressure (MAP) from 117 +/- 3 mmHg (time 0) to 97 +/- 4 mmHg at 2 h (P < 0.05, n = 15) and 84 +/- 4 mmHg at 6 h (P < 0.05, n = 15). The pressor effect of noradrenaline (NA, 1 micrograms kg-1, i.v.) was also significantly reduced at 1 to 6 h after LPS (vascular hyporeactivity). Treatment of LPS-rats with AE-ITU (1 mg kg-1, i.v. plus 1 mg kg-1 h-1 starting at 2 h after LPS) caused only a transient rise in MAP, but significantly attenuated the delayed vascular hyporeactivity seen in LPS-rats. Infusion of L-NMMA (3 mg kg-1, i.v. plus 3 mg kg-1 h-1) caused a rapid and sustained rise in MAP and attenuated the delayed vascular hyporeactivity to NA. Neither AE-ITU nor L-NMMA had any effect on either MAP or the pressor effect elicited by NA in rats infused with saline rather than LPS. 3. Endotoxaemia for 6 h was associated with a significant rise in the serum levels of aspartate or alanine aminotransferase (i.e. GOT or GPT), gamma-glutamyl-transferase (gamma GT), and bilirubin, and hence, liver dysfunction. Treatment of LPS-rats with AE-ITU significantly attenuated this liver dysfunction (rise in GOT, GPT, gamma GT and bilirubin) (P < 0.05, n = 10). In contrast, L-NMMA reduced the increase in the serum levels of gamma GT and bilirubin, but not in GOT and GPT (n = 5). Injection of LPS also caused a time-dependent, but rapid (almost maximal at 2 h), increase in the serum levels of urea and creatinine, and hence, renal dysfunction. This renal dysfunction was not affected by either AE-ITU (n = 10) or L-NMMA (n = 5). In rats infused with saline rather than LPS, neither AE-ITU (n = 4) nor L-NMMA (n = 4) had any significant effect on the serum levels of GOT, GPT, gamma GT, bilirubin, creatinine or urea. 4. Endotoxaemia for 6 h resulted in a 4.5 fold rise in the serum levels of nitrite (9.13 +/- 0.77 microM, P < 0.01, n = 15), which was significantly reduced by treatment with AE-ITU (6.32 +/- 0.48 microM, P < 0.05, n = 10) or L-NMMA (5.10 +/- 0.40 microM, P < 0.05, n = 5). In addition, endotoxaemia for 6 h was also associated with a significant increase in iNOS activity in lung and liver homogenates, which was significantly reduced in lung or liver homogenates obtained from LPS-rats treated with either AE-ITU or L-NMMA. 5. Thus, AE-ITU or L-NMMA (i) inhibits iNOS activity in LPS-rats without causing a significant increase in MAP in rats infused with saline and, hence inhibition of endothelial NOS activity, and (ii) attenuates the delayed circulatory failure as well as the liver dysfunction caused by endotoxaemia in the rat. Thus, an enhanced formation of NO may contribute to the development of liver failure in endotoxic shock.

Sodium and water homeostasis

Disorders of sodium and water homeostasis are common occurrences in pediatric practice. They reflect distinct problems in the regulation of total body sodium balance and water distribution, respectively. Each of these groups of disorders has separate afferent and efferent mechanisms that are activated during disease states. Optimal therapy of children with fluid and electrolyte problems requires accurate delineation of the ECF volume and water distribution disturbance and the design of therapeutic regimens that account for each component of the clinical condition.

Peritoneal dialysis solutions reverse the hemodynamic effects of nitric oxide synthesis inhibitors

Nitric oxide (NO) synthesis is inhibited by a variety of L-arginine analogs including NG-nitro-L-arginine methyl ester (L-NAME) and NG NG-dimethylarginine (ADMA). ADMA is present in elevated concentrations in renal failure and potentially could alter microcirculatory hemodynamics during peritoneal dialysis (PD). This investigation utilized the techniques of intravital microscopy to quantitate the mesenteric arteriolar hemodynamic effects of PD solutions during NO synthesis inhibition. L-NAME (100 microns) produced maximum arteriolar vasoconstriction to 74% of baseline diameter (19.9 +/- 2.2 vs. 26.9 +/- 1.4 microns, P < 0.001, N = 10) and ADMA (100 microns) to 68% (20.5 +/- 2.5 vs. 30.1 +/- 2.0 microns, P < 0.01, N = 6). L-NAME decreased red blood cell velocity to 44% of baseline velocity (3.8 +/- 0.8 vs. 8.5 +/- 1.1 mm/second, P < 0.001) and ADMA to 52% (5.1 +/- 1.1 vs. 9.8 +/- 0.9 mm/second, P < 0.01, N = 6). Despite NO synthesis inhibition, standard PD solutions reversed these hemodynamic effects with both 1.5% and 4.25% Dianeal (Baxter) rapidly reversing the vasoconstriction and restoring blood flow back to baseline values. When Dianeal and L-NAME were simultaneously superfused, no L-NAME induced vasoconstriction occurred and Dianeal maintained vasodilatory properties despite L-NAME (P < 0.01, N = 5). This investigation reaffirms that basal levels of NO are important in maintaining normal hemodynamics in the mesenteric microcirculation. Reversal of the L-NAME induced arteriolar hemodynamic effects by Dianeal suggests that the endogenous NO synthesis inhibitor ADMA has no significant effects in the regulation of the mesenteric microvascular arteriolar hemodynamics during PD. Since these PD solutions remain vasoactive despite NO synthesis inhibition, this suggests that these PD solutions possess vasoactive properties primarily through a NO independent mechanism.

Inducible nitric oxide synthase activity and expression in a human colonic epithelial cell line, HT-29

1 We have determined which cytokines regulate the expression of human inducible nitric oxide synthase (iNOS) mRNA and nitrite generation in the human colonic-epithelial cell line HT-29. 2 Growth arrested cell cultures were stimulated with the human recombinant cytokines interleukin-1 alpha (IL-1 alpha), tumour necrosisfactor-alpha (TNF-alpha), interferon gamma (IFN-gamma) or vehicle added alone or in combination. Human iNOS mRNA was determined by Northern blot analysis and nitrite generation by the use of a fluorometric assay. 3 Unstimulated cells produced a small time-dependent increase in nitrite generation of 50 +/- 4, 75 +/- 8, and 103 +/- 8 nM per 10(6) cells at 24 h, 48 h, and 72 h respectively. This nitrite generation was unaffected by cycloheximide (5 micrograms ml-1) pretreatment and iNOS mRNA was not detected. 4 None of cytokines alone induced either iNOS mRNA expression or an increase in nitrite generation. The combination of IL-1 alpha/IFN-gamma produced a highly significant (P < 0.001) 4 fold increase in nitrite production at 48 h, compared to basal values, while no other pair of cytokines was effective. 5 Time course studies with IL-1 alpha/IFN-gamma combination revealed significant (P < 0.001) increases in nitrite at 24 h (153 +/- 7), 48 h (306 +/- 24), and 72 h (384 +/- 15) compared to basal values of 50 +/- 4, 75 +/- 8, and 103 +/- 8 nM per 10(6) cells respectively. 6 Studies with IL-1 alpha/IFN-gamma combination demonstrated a time dependent expression of iNOS mRNA, first observed at 6 h, peaked at 24 h and was undetectable by 72 h. IL-1 alpha (0.3-10 ng ml-1) and IFN-gamma (10-300 u ml-1) in combination induced a concentration-dependent expression of iNOS mRNA at 24 h. 7 Pretreatment with cycloheximide before IL-1 alpha/IFN-gamma stimulation reduced nitrite levels to basal values. These data suggest that the IL-1 alpha/IFN-gamma-induced nitrite production by HT-29 cells is dependent on de novo protein synthesis, probably the iNOS enzyme. 8 The addition of TNF-alpha produced a significant (P < 0.001) 3 fold increase of IL-1 alpha/IFN-gamma-induced nitrite generation. In marked contrast the presence of TNF-alpha had no effect on IL-1 alpha/IFN-gamma-induced iNOS mRNA expression by HT-29 cells. These findings suggest that the up-regulation by TNF-alpha of IL-1 alpha/IFN-gamma-induced nitrite generation is at the post-transcriptional level. 9 These data suggest that pro-inflammatory cytokines induce NO production in colonic epithelial cells probably due to the induction of iNOS and these cells may be a major source of NO generation in inflammatory bowel disease.

Identification of a prostanoid FP receptor population producing endothelium-dependent vasorelaxation in the rabbit jugular vein

1. Prostaglandin F2 alpha (PGF2 alpha) and its synthetic analogue, fluprostenol, potently relaxed the precontracted isolated jugular vein of the rabbit (RJuV). The vasorelaxant activity of PGF2 alpha and fluprostenol was dependent upon an intact vascular endothelium. Although removal of the vascular endothelium abolished activity associated with PGF2 alpha-like agonists, it did not significantly alter the relaxant effects of prostaglandin E2 (PGE2). 2. The nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), at 100 microM significantly inhibited the endothelium-dependent relaxations induced by PGF2 alpha. Lower doses (1 microM, 10 microM) of L-NAME had little or no effect. The relaxant effects of PGE2 were not affected by L-NAME (1-100 microM). D-NAME at 100 microM was without effect on the vasorelaxant responses to either PGF2 alpha or PGE2. 3. The potassium (K)-channel blockers tetraethylammonium (TEA, 1 mM), barium (1 mM) and quinine (100 microM), each tested in the presence of the inactive enantiomer D-NAME (100 microM) did not significantly affect the response to PGF2 alpha. Unexpectedly, both TEA and barium significantly and partially reversed the inhibitory effects of 100 microM L-NAME, whereas quinine had no effect. In similar studies, none of the three potassium channel blockers had any effect on relaxations elicited by PGE2 when given with D-NAME or L-NAME. 4. These results indicate that the PGF2 alpha-sensitive prostanoid receptors found in the vascular endothelium of the rabbit jugular vein are of the FP-receptor subtype. Nitric oxide (NO) appears to be the predominant messenger involved in PGF2 alpha-induced relaxation of the rabbit jugular vein. Potassium channels may have a minor role in mediating the vasorelaxation response to PGF2 alpha. When both NO synthesis and K-channels are simultaneously blocked, inhibition of PGF2 alpha-induced vasorelaxation by L-NAME is opposed by K-channel blockers. This diminution of the inhibitory effect of L-NAME by TEA and barium suggests that K-channels may possibly serve a compensatory role via the NO pathway.

Dietary antioxidants and cigarette smoke-induced biomolecular damage: a complex interaction

Epidemiologic evidence suggests that cigarette smoking is a major risk factor for chronic obstructive pulmonary diseases such as chronic bronchitis and emphysema, for carcinogenesis, and for cardiovascular disease. However, the precise mechanisms of these effects are incompletely understood. The gas phase of cigarette smoke contains abundant free radicals including nitric oxide. Hence, cigarette smoke may induce some of its damaging effects by free radical mechanisms. We report that exposure of plasma, a model for respiratory tract lining fluids, to gas-phase cigarette smoke causes depletion of antioxidants, including ascorbate, urate, ubiquinol-10, and alpha-tocopherol, and a variety of carotenoids, including beta-carotene. Gas-phase cigarette smoke induced some lipid peroxidation, as measured by cholesteryl linoleate hydroperoxide (18:2OOH) formation. Ascorbate was effective in preventing 18:2OOH formation. In contrast to the low concentrations of lipid hydroperoxides measured (< 1 mumol/L), protein carbonyl formation, a measure of protein modification, increased by approximately 400 mumol/L after nine puffs of cigarette smoke. Reduced glutathione inhibited protein carbonyl formation, whereas other plasma antioxidants, including ascorbate, were ineffective. alpha, beta-Unsaturated aldehydes (acrolein and crotonaldehyde) in cigarette smoke may react with protein -SH and -NH2 groups by a Michael addition reaction that results in a protein-bound aldehyde functional group. Gas-phase cigarette smoke is capable of converting tyrosine to 3-nitrotyrosine and dityrosine, indicating free radical mechanisms of protein damage by nitrogen oxides. Aldehydes and nitrogen oxides in cigarette smoke may be significant contributors to biomolecular damage, and endogenous antioxidants can attenuate some of these adverse effects.

Behavioural abnormalities in male mice lacking neuronal nitric oxide synthase

In addition to its role in blood vessel and macrophage function, nitric oxide (NO) is a neurotransmitter found in high densities in emotion-regulating brain regions. Mice with targeted disruption of neuronal NO synthase (nNOS) display grossly normal appearance, locomotor activity, breeding, long-term potentiation and long-term depression. The nNOS- mice are resistant to neural stroke damage following middle cerebral artery ligation. Although CO2-induced cerebral vasodilatation in wild-type mice is NO-dependent, in nNOS- mice this vasodilation is unaffected by NOS inhibitors. Establishing a behavioural role for NO has, until now, not been feasible, as NOS inhibitor drugs can only be administered acutely and because their pronounced effects on blood pressure and other body functions obfuscate behavioural interpretations. We now report a large increase in aggressive behaviour and excess, inappropriate sexual behaviour in nNOS- mice.

Inhibition of cytochrome c oxidase in turnover by nitric oxide: mechanism and implications for control of respiration

Binding of nitric oxide (NO) to isolated cytochrome c oxidase in turnover was investigated by static and kinetic spectroscopic methods. These studies indicate that cytochrome c oxidase rapidly binds NO when the enzyme enters turnover. Our results show that NO binds to ferrocytochrome a3, competing with oxygen for this binding site. However, the main features of the binding process, in particular the rapid onset of inhibition, cannot be fully explained on this basis. We suggest, therefore, that there is a second binding site for NO, which has lower affinity but nevertheless plays an important role in the inhibitory process. A likely possibility is that CuB+ constitutes this second binding site. The fast onset of inhibition observed in the presence of NO, along with the dependence on the oxygen concentration, suggests that under physiological conditions, where the oxygen concentration is low, nanomolar concentrations of NO can effectively act as a regulator of the mitochondrial respiratory chain.

Chronic inhibition of endothelium-derived nitric oxide synthesis causes coronary microvascular structural changes and hyperreactivity to serotonin in pigs

BACKGROUND

Endothelium-derived nitric oxide (NO) is believed to regulate myocardial perfusion and structural changes in the vascular wall. Our objective was to determine whether chronic inhibition of NO synthesis causes structural and functional changes in coronary arteries.

METHODS AND RESULTS

Coronary vasomotor response was studied in pigs before and after chronic oral administration of the NO synthesis antagonist N omega-nitro-L-arginine methyl ester (L-NAME) 30 mg.kg-1.d-1 for 2 weeks. Chronic L-NAME treatment increased (P < .01) arterial pressure but did not alter baseline coronary blood flow (CBF), epicardial coronary diameter, or heart rate. Chronic L-NAME treatment augmented (P < .01) the decrease in CBF in response to intracoronary serotonin (30 micrograms/kg) from 5 +/- 14% to 40 +/- 5% but did not alter the CBF response to prostaglandin F2 alpha. The serotonin-induced decrease in CBF after acute L-NAME administration was still less before (1.3 +/- 0.4%) than after chronic L-NAME treatment (51 +/- 6%). Chronic L-NAME treatment attenuated the increase in CBF with bradykinin (100 ng/kg) but did not alter the CBF response to nitroglycerin (10 micrograms/kg). Compared with intact pigs without L-NAME treatment, L-NAME-treated pigs had significant thickening of the media in the microvessels (diameter, < 300 microns) but not in the large epicardial vessels. Chronic intracoronary infusion of L-NAME at 3 mg.kg-1.d-1 for 2 weeks, which did not produce arterial hypertension, caused similar microvascular medial thickening.

CONCLUSIONS

These results indicate that chronic administration of L-NAME caused coronary microvascular structural changes and hyperreactivity to serotonin in pigs in vivo, suggesting an important role of defective NO synthesis in coronary microvascular disorders.

Estrogen increases nitric oxide synthase activity in the uterus of nonpregnant sheep

OBJECTIVE

The aim of this study was to characterize nitric oxide synthase activity in endometrium and myometrium of nonpregnant sheep and to determine whether estrogen administration affects uterine nitric oxide synthase activity.

STUDY DESIGN

Nonpregnant sheep were castrated during synchronized estrus and 4 days after surgery were treated with 100 micrograms/day of 17 beta-estradiol for 3 days. Nitric oxide synthase activity was measured by the citrulline conversion assay.

RESULTS

Citrulline generation found in soluble and particulate fractions had all the characteristics of nitric oxide synthase, namely, it was strictly dependent on reduced nicotinamide adenine dinucleotide phosphate and enhanced by flavin nucleotides and tetrahydrobiopterin. Estrogen administration significantly increased Ca(++)-dependent nitric oxide synthase activity in myometrium but not in endometrium. The effect of estrogen was more pronounced in the membrane-associated enzyme activity (approximately fivefold). Estrogen treatment increased myometrial nitric oxide synthase activity from 9.0 +/- 2.4 to 20.0 +/- 3.7 pmol/mg of protein per 30 minutes in the soluble fraction and from 12.0 +/- 5.1 to 62.0 +/- 13.1 pmol/mg of protein per 30 minutes in the particulate fraction (mean +/- SEM, p < 0.05 by t test). The increase in nitric oxide synthase activity was not mediated by an increase in tetrahydrobiopterin availability, as shown to be the case in macrophages.

CONCLUSION

These data show that in the nonpregnant sheep uterus > 90% of the nitric oxide synthase activity found in myometrium is Ca++ dependent and is up-regulated by estrogen in a tissue-specific manner.

Inhibition of inducible nitric oxide synthase ameliorates rat lung allograft rejection

Recently, the inducible isoform of nitric oxide synthase has been shown to be an important immunomodulation molecule in allograft rejection. We have observed the production of nitric oxide during rejection and the effect of nitric oxide synthase inhibition on allograft rejection in a rat lung transplant model. Rat left lung allotransplants were performed in two strain combinations: brown Norway-to-F344 (major histocompatibility complex incompatible); and Lewis-to-F344 (minor loci incompatible) as severe and mild rejection models respectively. Syngeneic F344-to-F344 transplants were performed as a negative control. Nitric oxide production during rejection was determined by measuring the recipient's serum nitrite/nitrate levels as a stable end product of nitric oxide. The progression of rejection was evaluated radiographically and the grade of rejection was determined histologically. After operation, recipients of allotransplantation were randomly divided into two groups and received either aminoguanidine (200 mg/kg, intraperitoneal every 6 hours), a potent inducible nitric oxide synthase inhibitor, or normal saline treatment. The levels of serum nitrite and nitrate in recipients increased in the early phase of rejection in both allotransplant combinations. However, in the terminal phase of rejection, the serum nitrite/nitrate level decreased significantly compared with the peak level in the brown Norway-to-F344 recipients. The serum nitrite/nitrate levels in the syngeneic transplant recipients were normal during the entire observation period. In aminoguanidine-treated animals, serum nitrite/nitrate levels remained normal in both allograft combinations. Significant suppression of rejection in aminoguanidine-treated recipients was observed histologically and radiographically in comparison with untreated recipients in the brown Norway-to-F344 combinations. In the Lewis-to-F344 combination, aminoguanidine treatment significantly ameliorated histologic rejection but did not affect radiologic appearance. We therefore conclude nitric oxide is produced during early allograft rejection and may prove to be a marker and mediator of early rejection. The inhibition of inducible nitric oxide synthase results in significant reduction in rat lung allograft rejection.

Close relation of endothelial function in the human coronary and peripheral circulations

OBJECTIVES

The relation between endothelium-dependent vasodilator function in the brachial and coronary arteries was determined in the same subjects.

BACKGROUND

Coronary artery endothelial dysfunction precedes the development of overt atherosclerosis and is important in its pathogenesis. A noninvasive assessment of endothelial function in a peripheral conduit vessel, the brachial artery, was recently described, but the relation between brachial artery function and coronary artery vasodilator function has not been explored.

METHODS

In 50 patients referred to the catheterization laboratory for the evaluation of coronary artery disease (mean age +/- SD 56 +/- 10 years), the coronary vasomotor response to serial intracoronary infusions of the endothelium-dependent agonist acetylcholine (10(-8) to 10(-6) mol/liter), was studied. Endothelium-dependent vasodilation was also assessed in the brachial artery by measuring the change in brachial artery diameter in response to reactive hyperemia.

RESULTS

Patients with coronary artery endothelial dysfunction manifested as vasoconstriction in response to acetylcholine had significantly impaired flow-mediated vasodilation in the brachial artery compared with that of patients with normal coronary endothelial function (4.8 +/- 5.5% vs. 10.8 +/- 7.6%, p < 0.01). Patients with coronary artery disease also had an attenuated brachial artery vasodilator response compared with that of patients with angiographically smooth coronary arteries (4.5 +/- 4.6% vs. 9.7 +/- 8.1%, p < 0.02). By multivariate analysis, the strongest predictors of reduced brachial dilator responses to flow were baseline brachial artery diameter (p < 0.001), coronary endothelial dysfunction (p = 0.003), the presence of coronary artery disease (p = 0.007) and cigarette smoking (p = 0.016). The brachial artery vasodilator response to sublingual nitroglycerin was independent of coronary endothelial responses or the presence of coronary artery disease. The positive predictive value of abnormal brachial dilation ( < 3%) in predicting coronary endothelial dysfunction is 95%.

CONCLUSIONS

This study demonstrated a close relation between coronary artery endothelium-dependent vasomotor responses to acetylcholine and flow-mediated vasodilation in the brachial artery. This noninvasive method may become a useful surrogate in assessing the predisposition to atherosclerosis in patients with cardiac risk factors.

Role of nitric oxide in anaphylactic shock

Nitric oxide, synthesized from the guanidino group of L-arginine by nitric oxide synthase, has an important role in pathophysiological changes associated with anaphylaxis. Nitric oxide production due to activation of constitutive nitric oxide synthase is detected using a nitric oxide-selective electrode in anaphylactic rabbits in vivo. A nitric oxide synthase inhibitor attenuates hypotension and hemoconcentration and decreases venous return but does not improve cardiac depression. Nitric oxide functionally antagonizes the effects of vasoconstrictors released by anaphylaxis in vitro. In animals pretreated with a nitric oxide synthase inhibitor, the cardiac output falls significantly, although venous return is increased. Pulmonary resistance is significantly increased with a nitric oxide synthase inhibitor, and L-arginine attenuates the bronchospasm. These findings suggest that production of nitric oxide may reduce the pathophysiologic changes, except for vasodilatation, associated with anaphylaxis.

The role of nitric oxide in hemodynamic and metabolic alterations induced by prostaglandin F2 alpha in the perfused rat liver

In the liver prostaglandins have been shown to be potent regulators of portal blood flow, carbohydrate metabolism and bile secretion. It is not known whether these effects represent a direct action of prostaglandins, and it has been suggested that nitric oxide (NO) might be a critical mediator for prostaglandin induced hepatic events. We have studied whether nitric oxide formation or inhibition alters the action of prostaglandin F2 alpha (PG F2 alpha) in a single-pass liver perfusion model. The liver of untreated rats (constitutive NO-synthase) or after pretreatment with endotoxin (inducible form of NO-synthase) was perfused at a constant pressure via the portal vein. Effluate were collected in 1-min intervals and bile in 5-min intervals. In both groups the addition of PG F2 alpha (10 microM) to the perfusate for 5 min resulted in a significant increase of glucose and lactate production, and in a significant decrease in portal blood flow (-0.56 +/- 0.04 ml/g per min), in bile flow (-60.7%) and in bile acid release (-60.6%). Inhibition of NO synthase by adding NG-monomethyl-L-arginine (L-NMMA, 100 microM) to the perfusate did not affect any of the alterations induced by PG F2 alpha. Substitution of the endogenous substrate for the NO synthase L-arginine (500 microM) in the perfusate completely prevented the hemodynamic alterations induced by PG F2 alpha in endotoxin pretreated livers and limited the flow reduction (0.15 +/- 0.04 ml/g per min) in the untreated group. The substitution of L-arginine in the perfusate of endotoxin pretreated livers raised nitrite (from 1.5 +/- 0.3 to 3.6 +/- 0.7 nmol/g per min) and urea release (from 65 +/- 25 to 294 +/- 68 nmol/g per min), but had no effect on any of the other metabolic parameters and bile secretion. We conclude that PG F2 alpha increases glucose and lactate production in the perfused rat liver and decreases portal flow bile secretion. The metabolic effects induced by PG F2 alpha appear to be independent of NO mediation and hemodynamic alterations. Portal flow alone can be influenced by endogenous NO formation.

Nitric oxide synthase in the hypothalamic suprachiasmatic nucleus of rat: evidence from histochemistry, immunohistochemistry and western blot; and colocalization with VIP

Nitric oxide (NO) is a neuroactive substance of high potency. Physiological results revealed the involvement of NO in circadian regulation of rats. Since neuronal structures containing NO-synthase (NOS) were previously not found in the circadian oscillator, the hypothalamic suprachiasmatic nucleus (SCN), in this species but are present in the hamster, we investigated the distribution of NO-producing structures in the rat SCN by Western blot analysis, immunohistochemistry of NOS, and by histochemistry (NADPH-diaphorase (NADPH-d) activity of NOS). Western blot analysis of SCN homogenates from rat (and, for comparison, hamster) showed a NOS-like immunoreactive (-LI) protein band of apparent molecular mass of 150 kDa, consistent with the neuronal NOS molecule. In the rat SCN, perikarya exhibiting NADPH-d staining of NOS-LI with a complete overlapping of both were found. Double-immunofluorescence experiments revealed that NOS cells are a subgroup of the neuronal SCN population that is characterized by immunoreactivity to vasoactive intestinal polypeptide. These data provide evidence for the existence of neuronal nitric oxide synthase in the rat SCN and may explain the involvement of NO in the mediation of photic information.

Quantitative assessment of coronary vasoreactivity in humans in vivo. Importance of baseline vasomotor tone in atherosclerosis

BACKGROUND

Disturbances in vasomotor tone are closely linked to the development of atherosclerosis and play an integral part in the pathophysiology of myocardial ischemia in patients with coronary artery disease. Currently, evaluation of coronary vasomotor tone relies on assessment of luminal changes in response to vasoactive stimuli by quantitative angiography. Assessment of luminal changes, however, may be misleading because of the effects of geometric magnification induced by atherosclerotic wall thickening and differences in basal tone, which may obscure potential effects of vasoactive stimuli.

METHODS AND RESULTS

Combining angiographic measurements of luminal changes with measurements of coronary wall architecture determined by intracoronary ultrasound, we calculated absolute coronary arterial vasomotor tone in 34 patients with angiographically normal or "minimally diseased" coronary arteries. Epicardial artery vasodilator capacity in response to intracoronary nitroglycerin decreased significantly with increasing atherosclerotic wall thickening. An inverse relation existed between local atherosclerotic plaque load and nitroglycerin-induced changes in vasomotor tone (r = -.65, P < .0001) regardless of potential systematically operative factors. At the same time, basal vasomotor tone significantly decreased with increasing local atherosclerotic wall thickening (r = -.38, P = .004). The vasomotor effects of acetylcholine, an endothelium-dependent vasodilator, were inversely related to wall thickening only in segments with very minor degrees of atherosclerosis, whereas no such relation was observed for epicardial artery segments with more advanced atherosclerotic wall thickening. In these segments, however, vasoreactivity to acetylcholine was closely correlated with basal vasomotor tone (r = -.62, P = .0002).

CONCLUSIONS

Atherosclerosis is associated with impairment of the vasodilator response to both nitroglycerin and acetylcholine in epicardial arteries in vivo. Basal vasomotor tone appears to be the primary determinant of the altered coronary vasoreactivity in response to vasoactive stimuli.

Nitric oxide inhibits the positive inotropic response to beta-adrenergic stimulation in humans with left ventricular dysfunction

BACKGROUND

Nitric oxide (NO) attenuates the contractile response to beta-adrenergic stimulation in cultured cardiac myocytes in vitro and in myocardium in vivo. We tested the hypothesis that NO synthesized in the heart inhibits the positive inotropic response to beta-adrenergic stimulation in humans with left ventricular (LV) dysfunction.

METHODS AND RESULTS

Patients with various degrees of LV dysfunction and free from epicardial coronary artery disease were instrumented with an infusion catheter in the left main coronary artery and a high-fidelity micromanometer-tipped catheter in the LV. Measurements included LV pressure, aortic pressure, heart rate, and LV peak +dP/dt. In eight subjects, dobutamine was infused via the left main coronary artery (25 or 50 micrograms/min) before and concurrent with intracoronary infusion of the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA, 20 mumol/min for 10 minutes). In six other subjects, dobutamine was infused (6, 10, or 15 micrograms.kg-1.min-1) via a peripheral vein. Intracoronary (n = 8) dobutamine infusions increased LV peak +dP/dt by an average of 33 +/- 3%. The intracoronary infusion of L-NMMA had no effect on baseline LV peak +dP/dt, LV systolic or end-diastolic pressures, aortic pressure, or heart rate. The intracoronary infusion of L-NMMA, concurrent with a second infusion of dobutamine, potentiated the +dP/dt response to dobutamine by 30 +/- 10% (P < .04 versus dobutamine alone). The intracoronary infusion of L-NMMA likewise potentiated the +dP/dt response to the peripheral infusion of dobutamine by 37 +/- 18%.

CONCLUSIONS

Nitric oxide produced in the heart attenuates the positive inotropic response to beta-adrenergic stimulation in humans with LV dysfunction. NO may contribute to beta-adrenergic hyporesponsiveness in patients with LV dysfunction.

Linkage of cell-mediated immunity to iron metabolism

Iron is essential for growing microorganisms and tumour cells, and is also crucial for the proliferation of immune cells. In this review, Günter Weiss, Helmut Wachter and Dietmar Fuchs focus on the complex network of interactions that link iron metabolism with cellular immune effector functions involving cytokines and nitric oxide, and draw a suitable model for the pathogenesis of anaemia of chronic disease.

Chronic treatment with nitric oxide synthase (NOS) inhibitor profoundly reduces cerebellar NOS activity and cyclic guanosine monophosphate but does not modify minimum alveolar anesthetic concentration

We previously found that acute administration of a nitric oxide synthase (NOS) inhibitor (N omega-nitro-L-arginine methyl ester [L-NAME]) does not reduce the minimum alveolar anesthetic concentration (MAC) of halothane in rats. However, a recent study has suggested that brain NOS activity could not be inhibited by more than approximately 50% by acute administration of L-NAME. To investigate the effect of marked inhibition of NOS activity on the MAC of halothane, we measured cerebellar NOS activity, cerebellar cyclic guanosine monophosphate (cGMP) levels, and halothane MAC in rats chronically treated with L-NAME and compared the results to those of the saline-treated control group. Although the cerebellar NOS activity and cGMP levels were significantly decreased (14% and 2.7% of control, respectively) by L-NAME, the value of the halothane MAC was not significantly affected. These results suggest that the anesthetic action of halothane, as measured by its MAC in rats, is not related to NOS activity or cGMP levels in the brain.

Molecular actions of ebselen--an antiinflammatory antioxidant

1. Ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one) is a non-toxic seleno-organic drug with antiinflammatory, antiatherosclerotic and cytoprotective properties. 2. Ebselen and some of its metabolites are effective reductants of hydroperoxides including those arising in biomembranes and lipoproteins. 3. By reactions with hydroperoxides and thiols several interconversion cycles are formed which include ebselen metabolites with varying oxidation number of the selenium. 4. In the presence of thiols ebselen mimics the catalytic activities of phospholipid hydroperoxide glutathione peroxidase. 5. Ebselen inhibits at low concentrations a number of enzymes involved in inflammation such as lipoxygenases, NO synthases, NADPH, oxidase, protein kinase C and H+/K(+)-ATPase. The inhibitions are manifested on the cellular level and may contribute to the antiinflammatory potential of ebselen.