L-arginine treatment alters the kinetics of nitric oxide and superoxide release and reduces ischemia/reperfusion injury in skeletal muscle

Nitric oxide synthase inhibitors affect nitric oxide synthesis in normoxic but not in ischemic organs during intestinal ischemia and early reperfusion

Inhibition of endogenous nitric oxide (NO) synthesis during early intestinal ischemia/reperfusion (I/R(i)) enhances remote organ damage related to I/R(i). However, the effects of NO synthase (NOS) inhibitors on NO formation in various organs have not yet been specified. We therefore investigated the effects of N-G-monomethyl-L-arginine (L-NMMA), a nonspecific NOS inhibitor, and L-arginine, the NOS substrate, on NO formed in ischemic intestine versus normoxic remote organs (lung and liver). We used electron paramagnetic resonance spectroscopy and a specific NO trap to assay NO in blood, intestine, lung, and liver of rats subjected to local I/R(i), with and without L-NMMA and L-arginine supplementation. We found that I/R(i) increased NO levels in the intestine and blood, but not in the remote organs lung and liver. Administration of L-NMMA before I/R(i) decreased I/R(i)-independent basal NO levels in normoxic lung and liver without influencing I/R(i)-induced increase in NO levels in intestinal tissue or in blood. L-arginine supplementation increased circulating levels of NO, with sensitivity to L-NMMA, without affecting NO levels in normoxic or ischemic tissue. Our data suggest that NOS activity controls the NO generated in normally perfused remote organs during early I/R(i). Hence NOS inhibitors, when administered during I/R(i), decrease physiological NO levels in normoxic remote organs without affecting increased NO levels originating from ischemic intestine. This may explain the harmful effect of nonspecific NOS inhibitors during early I/R(i). In addition, the generation of NO in remote organs is not limited by tissue L-arginine concentrations and, therefore, not influenced by exogenous L-arginine. The protective effect of L-arginine supplementation during I/R(i) is probably related to increasing intravascular NO formation.

Endothelial injury: cause and effect of alloimmune inflammation

This review discusses the concept that endothelial cells may facilitate inflammation, but are also targets of the inflammatory response. Endothelial cells express several molecules that promote leukocyte recruitment, and other molecules, such as MHC class I that enable endothelial injury. Circulating alloantibodies produced following transplantation may also target the endothelium for injury. It has been shown that the expression of select protective genes within endothelial cells, including anti-apoptotic genes, may provide resistance to immune-mediated injury. Thus, an understanding of the mechanisms by which endothelial cells are injured and by which endothelial cells are protected is important for our understanding of allograft rejection.

The flux of arginine after ischemia-reperfusion in the rat kidney

BACKGROUND

Renal arginine synthesis is regulated by arginine plasma levels. The amino acid arginine is synthesized in the proximal tubule of the kidney. Renal ischemia reperfusion (I-R) injury as seen after shock, trauma and major vascular surgery, leading to acute tubular necrosis, might reduce arginine production.

METHODS

Wistar rats received either bovine liver arginase (ASE), to lower arginine plasma levels, or saline (SAL). Following the ASE or SAL infusion, rats were randomized to receive a renal artery clamp for 70 minutes, followed by 150 minutes of reperfusion. Renal arteriovenous blood samples were measured and plasma flow was calculated in the I-R kidney (SAL/I-R and ASE/I-R) and the contralateral kidney (SAL/C-L and ASE/C-L) in order to determine renal arginine metabolism.

RESULTS

Arginase infusion resulted in lower arginine plasma levels compared to SAL treatment (SAL/I-R vs. ASE/I-R, P < 0.005, and SAL/C-L vs. ASE/C-L, P < 0.005). Renal plasma flow was similar for all groups. The kidney switched from arginine production into arginine uptake after ischemia reperfusion (SAL/I-R vs. SAL/C-L, P < 0.01, and ASE/I-R vs. ASE/C-L, P < 0.01). Renal uptake of glutamine and citrulline increased after ischemia reperfusion (SAL/I-R vs. SAL/C-L and ASE/I-R vs. ASE/C-L, both P < 0.01). Histopathological slices of the kidney showed significantly higher counts of hyperchromasia, pyknosis, nuclear fragmentation and mitoses in individual kidney cells after ischemia reperfusion.

CONCLUSION

Decreased renal arginine production is observed with unilateral ischemia-reperfusion, and this change in arginine flux could contribute to or slow the recovery from the low plasma levels of arginine seen in conditions like trauma, shock, or after vascular procedures.

Nitric oxide in the penumbra of a focal cortical necrosis in rats

After a focal cortical freezing lesion in rats, nitric oxide (NO) end products were studied with microdialysis in the extracellular space of the penumbra throughout the whole period of secondary expansion of the cortical necrosis (i.e. 24 h). Under baseline conditions, the dialysate concentration of nitrate (nitrite) was 1.8 +/- 0.78 microM (5.00 +/- 1.50 microM) in the sham-operated group and 2.28 +/- 0.62 microM (3.25 +/- 1.32 microM) in the trauma group. In animals of both groups, these parameters neither showed significant alterations within the observation period compared with baseline values nor between the groups at each individual study time point. After focal cortical trauma, NO does not mediate secondary necrosis expansion via the extracellular space.

Neuroprotection and aging of the cholinergic system: a role for the ergoline derivative nicergoline (Sermion)

The aging brain is characterized by selective neurochemical changes involving several neural populations. A deficit in the cholinergic system of the basal forebrain is thought to contribute to the development of cognitive symptoms of dementia. Attempts to prevent age-associated cholinergic vulnerability and deterioration therefore represent a crucial point for pharmacotherapy in the elderly. In this paper we provide evidence for the protective effect of nicergoline (Sermion) on the degeneration of cholinergic neurons induced by nerve growth factor deprivation. Nerve growth factor deprivation was induced by colchicine administration in rats 13 and 18 months old. Colchicine induces a rapid and substantial down-regulation of choline acetyltransferase messenger RNA level in the basal forebrain in untreated adult, middle-aged and old rats. Colchicine failed to cause these effects in old rats treated for 120 days with nicergoline 10 mg/kg/day, orally. Moreover, a concomitant increase of both nerve growth factor and brain-derived neurotrophic factor content was measured in the basal forebrain of old, nicergoline-treated rats. Additionally, the level of messenger RNA for the brain isoform of nitric oxide synthase in neurons of the basal forebrain was also increased in these animals. Based on the present findings, nicergoline proved to be an effective drug for preventing neuronal vulnerability due to experimentally induced nerve growth factor deprivation.

Overexpression of endothelial nitric oxide synthase in endothelial cells is protective against ischemia-reperfusion injury in mouse skeletal muscle

Microvascular injury has been proposed to be a main cause of ischemia-reperfusion (I/R) injury. The roles of endothelial nitric oxide synthase (eNOS)-derived NO, a key regulator of vascular function, in I/R injury are incompletely understood. We used transgenic mice overexpressing eNOS in endothelial cells (eNOS-Tg) and their littermates wild-type mice (WT) to investigate the roles of eNOS in I/R injury in skeletal muscle. Superoxide levels in the affected muscles were reduced by approximately 50% in eNOS-Tg compared with WT during reperfusion. In WT, the disassembly of endothelial junctional proteins seen in the early period of reperfusion was recovered in the later phase. These findings were correlated with the increased vascular permeability in vivo. In contrast, eNOS-Tg maintained the endothelial junction assembly as well as vascular permeability during reperfusion. Leukocyte extravasation into tissue and up-regulated expression of adhesion molecules in the reperfused vessels were significantly inhibited in eNOS-Tg. Tissue viability of the affected muscle was decreased in WT time-dependently after reperfusion, whereas eNOS-Tg showed no significant reduction. NOS inhibition completely reversed these protective effects of eNOS overexpression in I/R injury. Thus, eNOS overexpression appears to prevent the I/R injury in skeletal muscle by maintaining vascular integrity.

Mechanisms of dysfunction of the nitric oxide pathway in vascular diseases

Vascular nitric oxide (NO) is involved in many physiologic and pathophysiologic processes throughout the body. Many vascular diseases have a reduction in the activity of endothelium-derived NO as an important component involved in the initiation and/or progression of the disease. It is now known that there are multiple mechanisms for this reduction in NO activity with one or more mechanisms operating depending on the specific condition or stage of a disease. In other instances, the therapy for certain diseases is responsible for the reduction in NO activity and contributes to the acceleration of vascular disease. This review details the known mechanisms of dysfunction of the NO pathway leading to vascular diseases, which provides the rationale for why certain therapies can improve while other therapies adversely affect vascular health.

[The arginine paradox]

L-Arginine has attracted major interest because it has been identified as the natural substrate of nitric oxide synthase and is now recognized as a major player in the regulation of biological function. The arginine paradox refers to the phenomenon that exogenous L-arginine causes NO-mediated biological effects despite the fact that nitric oxide synthases (NOS) are theoretically saturated with the substrate L-arginine. There have been several explanations for this phenomenon, although none of them can explain the arginine paradox fully: (1) L-arginine-induced insulin, which has vasodilatory actions. (2) Neither extracellular nor intracellular concentration determines the NOS activity but rather the L-arginine amount transported across the plasma membrane may do so. (3) Endogenous NOS inhibitors reduce the enzyme sensitivity to L-arginine. These inhibitors include, NG, NG-dimethyl-L-arginine, L-citrulline, argininosuccinic acid and agmatine. (4) Intracellular L-citrulline, an NOS product, is a potent inhibitor of NOS so that the cells may need extra L-arginine to compete with L-citrulline inhibition.

Óxido nítrico: revisão

O óxido nítrico é um mediador gasoso responsável por uma variedade de fenômenos fisiológicos. A l-arginina é a precursora da síntese do óxido nítrico, na presença de óxido nítrico-sintase. Este artigo revê as funções das óxido nítrico-sintases e como o óxido nítrico atua na permeabilidade vascular e na síndrome de isquemia e reperfusão, assim como possíveis métodos para sua mensuração.

Detection of reactive oxygen and reactive nitrogen species in skeletal muscle

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are usually identified with pathological states and mediators of cellular injury. However, over the last decade ROS and RNS have been identified in skeletal muscle under physiological conditions. Detection of ROS and RNS production by skeletal muscle cells is fundamental to the problem of differentiating between physiological and pathological levels. The goal of this paper is to review the techniques that have been used to detect ROS and RNS in skeletal muscle. Electron spin resonance, fluorescent assays, cyotchrome c reduction, chemiluminescence, hydroxylation of salicylate, and nitration of phenylalanine are some of the assay systems that have been used thus far. A large body of evidence now indicates that ROS and RNS are continually produced by many different skeletal muscle types studied in vivo, in situ, and in vitro. Under resting conditions, ROS and RNS are detectable in both intracellular and extracellular compartments. Production increases during both non-fatiguing and fatiguing muscle contractions. In the absence of disease, the individual molecular species detected in skeletal muscle include parent radicals for the ROS and RNS cascades: superoxide anions and nitric oxide. Both are generated at rates estimated to range from pmol-to-nmol/mg muscle/minute. Evidence indicates that hydrogen peroxide, hydroxyl radicals, and peroxynitrite are also present under physiological conditions. However, the molecular species that mediate specific biological effects remains largely undetermined, as do the sources of ROS and RNS within muscle fibers. Eventual delineation of the mechanisms whereby ROS and RNS regulate cellular function will hinge on our understanding of the production and distribution of ROS and RNS within skeletal muscle.

Hyperglycemia reduces coronary collateral blood flow through a nitric oxide-mediated mechanism

We tested the hypothesis that hyperglycemia alters retrograde coronary collateral blood flow by a nitric oxide-mediated mechanism in a canine Ameriod constrictor model of enhanced collateral development. Administration of 15% dextrose to increase blood glucose concentration to 400 or 600 mg/dl decreased retrograde blood flow through the left anterior descending coronary artery to 78 +/- 9 and 82 +/- 8% of baseline values, respectively. In contrast, saline or L-arginine (400 mg x kg(-1) x h(-1)) had no effect on retrograde flow. Coronary hypoperfusion and 1 h of reperfusion decreased retrograde blood flow similarly in saline- or L-arginine-treated dogs (76 +/- 11 and 89 +/- 4% of baseline, respectively), but these decreases were more pronounced in hyperglycemic dogs (47 +/- 10%). L-arginine prevented decreases in retrograde coronary collateral blood flow during hyperglycemia (100 +/- 5 and 95 +/- 6% of baseline at blood glucose concentrations of 400 and 600 mg/dl, respectively) and after coronary hypoperfusion and reperfusion (84 +/- 14%). The results suggest that hyperglycemia decreases retrograde coronary collateral blood flow by adversely affecting nitric oxide availability.

Effects of nitric oxide donor and inhibitor on prostaglandin E2-like activity, malondialdehyde and reduced glutathione levels after skeletal muscle ischemia-reperfusion

Oxygen free radicals are implicated in the pathophysiology of ischemia-reperfusion (I/R) injury in skeletal muscle. Nitric oxide (NO) and prostaglandin E2 (PGE2) are important regulators of the microcirculation in skeletal muscle. The effects of L-arginine, substrate for NO, and N(G)-nitro L-arginine methyl ester (L-NAME) on PGE2 synthesis, lipid peroxidation and reduced glutathione (GSH) levels was investigated in the rat gastrocnemius muscle after 3 h of reperfusion following 2 h of ischemia. Lipid peroxidation and GSH levels showed a non-significant changes in the I/R groups compared to the control group. According to these results, it can be assumed that skeletal muscle can resist 2 h of ischemia followed by 3 h of reperfusion-induced oxidative stress. PGE2-like activity in the gastrocnemius muscle increased in the L-NAME treated and I/R groups. L-arginine administration reversed the increase in PGE2-like activity of reperfused skeletal muscle. These findings support the conclusion that endothelium-derived PGE2 synthesis increases during reperfusion and suggest that PGE2 may have a protective role in the maintenance of endothelial function.

Better preserved pulmonary endothelium-dependent vasodilation with off-pump coronary surgery

OBJECTIVE

To investigate if endothelium-dependent vasodilation in the pulmonary circulation was better maintained after off-pump coronary artery bypass grafting (CABG). An impaired pulmonary vascular response to acetylcholine has been observed after cardiopulmonary bypass (CPB) in children, adults and experimentally.

DESIGN

Fourteen patients operated off-pump were compared with 21 patients undergoing conventional CABG with CPB. The indexed pulmonary vascular resistance was measured before and during an infusion of acetylcholine, aiming at a concentration of 10(-6) mol/l in the pulmonary artery. Twelve patients operated on-pump received saline instead of acetylcholine.

RESULTS

Before surgery pulmonary vascular resistance decreased during infusion of acetylcholine by 28% and 25% in the off-pump and on-pump groups. After surgery the decrease was 16% and 6%, respectively (p = 0.028 and p < 0.001, compared to preoperative response). The response did not differ between the two groups before, but did so after surgery (p = 0.01). Saline had no effect.

CONCLUSION

The better maintained endothelium-dependent vasodilation in the off-pump group indicated less endothelial dysfunction.

The clinical pharmacology of L-arginine

L-Arginine (2-amino-5-guanidinovaleric acid) is the precursor of nitric oxide, an endogenous messenger molecule involved in a variety of endothelium-mediated physiological effects in the vascular system. Acute and chronic administration of L-arginine has been shown to improve endothelial function in animal models of hypercholesterolemia and atherosclerosis. L-Arginine also improves endothelium-dependent vasodilation in humans with hypercholesterolemia and atherosclerosis. The responsiveness to L-arginine depends on the specific cardiovascular disease studied, the vessel segment, and morphology of the artery. The pharmacokinetics of L-arginine have recently been investigated. Side effects are rare and mostly mild and dose dependent. The mechanism of action of L-arginine may involve nitric oxide synthase substrate provision, especially in patients with elevated levels of the endogenous NO synthase inhibitor asymmetric dimethylarginine. Endocrine effects and unspecific reactions may contribute to L-arginine-induced vasodilation after higher doses. Several long-term studies have been performed that show that chronic oral administration of L-arginine or intermittent infusion therapy with L-arginine can improve clinical symptoms of cardiovascular disease in man.

Cicletanine stimulates nitric oxide release and scavenges superoxide in endothelial cells

Cicletanine ((+/-)3-(4-chlorophenyl)-1,3-dihydro-7-hydroxy-6-methylfuro-[3,4-c] pyridine) 3-(4-chlorophenyl)-1,3-dihydro-7-hydroxy-6-methylfuro-[3,4-c] pyridine) is a novel antihypertensive vasodilator with an incompletely understood mechanism of action. In the studies described here, the release of nitric oxide and superoxide (O2-) stimulated by cicletanine was measured simultaneously in the endothelium of isolated rat aortic rings. Highly sensitive electrochemical nitric oxide and O2- microsensors were placed near the surface of endothelial cells and the kinetics of nitric oxide and O2- release were monitored in situ. The response times for nitric oxide and O2- microsensors were 100 micros and 50 micros, respectively, and detection limit was 10(-9) M. Cicletanine stimulated nitric oxide release in aorta endothelium at (micromolar) therapeutic concentrations that were consistent with the concentrations of the compound to induce endothelium-dependent vasorelaxation in isolated rat aorta. The peak concentration of nitric oxide was 160+/-8 nM. This concentration was about 70% and was 60% lower as compared with the nitric oxide peak concentration observed after stimulation with receptor-independent agonist (calcium ionophore A23187) and receptor-dependent agonist (acetylcholine), respectively. However, after administration of cicletanine, only a small concentration of O2- was recorded (peak 3.1+/-0.2 nM) contrary to a large concentration (27+/-1.35 nM) observed after stimulation with A23187). Cicletanine not only stimulated nitric oxide release but also was a potent scavenger of O2- at nanomolar level. Both of these effects may contribute to potent vasorelaxation properties of cicletanine and its long-term therapeutic actions, resulting in cardiovascular tissue protection.

Nitric Oxide Measurements during Endotoxemia

Background: Excessive continuous NO release from inducible NO synthase over prolonged periods under pathological conditions, such as endotoxemia, contributes significantly to circulatory failure, hypotension, and septic shock. This NO production during endotoxemia is accompanied by superoxide release, which contributes to the fast decay of NO. Therefore, the amount of NO that diffuses to target sites may be much lower than the total amount released under pathological conditions.

Methods: We performed in vivo and ex vivo measurements of NO (electrochemical) and ex vivo in situ measurements of superoxide, peroxynitrite (chemiluminescence), and nitrite and nitrate (ultraviolet-visible spectroscopy). We determined the effect of lipopolysaccharide administration (20 mg/kg) on diffusible NO, total NO (diffusible plus consumed in chemical reactions), and superoxide and peroxynitrite release in the pulmonary arteries of rats.

Results: An increase in diffusible NO generated by constitutive NO synthase was observed immediately after administration of lipopolysaccharide, reaching a plateau (145 ± 18 nmol/L) after 540 ± 25 s. The plateau was followed by a decrease in NO concentration and its subsequent gradual increase after 45 min because of NO production by inducible NO synthase. The concentration of superoxide increased from 16 ± 2 nmol/L to 30 ± 3 nmol/L after 1 h and reached a plateau of 41 ± 4 nmol/L after 6 h. In contrast to the periodic changes in the concentration of diffusible NO, the total concentration of NO measured as a sum of nitrite and nitrate increased steadily during the entire period of endotoxemia, from 2.8 ± 0.2 μmol/L to 10 ± 1.8 μmol/L.

Conclusions: The direct measurement of NO concentrations in the rat pulmonary artery demonstrates dynamic changes throughout endotoxemia, which are related to the production of superoxide and the subsequent increase in peroxynitrite. Monitoring endotoxemia with total nitrate plus nitrite is not sensitive to these fluctuations in NO concentration.

The influence of l-arginine on heart rate and tissue oxygen extraction in haemorrhaged rabbits

Several studies have already indicated some beneficial effects of L-arginine in haemorrhaged rats. The aim of our study was to assess whether intravenous bolus injection of L-arginine could improve some cardiovascular and metabolic parameters in anaesthetized haemorrhaged rabbits (intermittent bleeding; 40% of the estimated blood volume for 15 min). I.v. bolus injection of L-arginine ( 300 mg kg(-1)--L-Arg(300)) increased heart rate (app. 10%) and decreased venous haemoglobin saturation with oxygen (sO(2)) (app. 23%) 60 min after the cessation of bleeding, without changes in arterial pressure. D-arginine (300 mg kg(-1)i.v. bolus-D-Arg(300)) produced similar, but insignificant haemodynamic and metabolic changes. In addition, no difference was found between the effects of the L- and D-isomers. Accordingly, L-arginine produces beneficial effects on the heart rate and tissue oxygen extraction in haemorrhaged rabbits. However, such changes do not appear to be stereospecific.

No effect of L-arginine supplementation on pulmonary endothelial dysfunction after cardiopulmonary bypass

BACKGROUND

Acetylcholine is an endothelium-dependent vasodilator through the L-arginine-nitric oxide pathway. After ischemia-reperfusion this effect is attenuated, also demonstrated in the pulmonary circulation after cardiopulmonary bypass. Administration of L-arginine has been shown to have a protective effect on endothelial function in reperfusion injury. The aim of the current study was to test the possible effect of L-arginine on the acetylcholine reactivity in the pulmonary circulation after cardiopulmonary bypass.

METHODS

Thirty-five patients with ischemic and/or valvular heart disease were investigated in a randomized, double-blinded, placebo-controlled study. The patients were divided into three groups. Group 1: high dose L-arginine (n=10), group 2: low dose L-arginine (n=10), group 3: placebo, no L-arginine, (n=15). The acetylcholine reactivity was tested with measurements of pulmonary vascular resistance before surgery and 1, 2 and 3-4 h after cardiopulmonary bypass.

RESULTS

After cardiopulmonary bypass an attenuation of the acetylcholine reactivity over time was observed in all groups, with no differences between groups.

CONCLUSION

In the current study L-arginine had no protective effect on the pulmonary endothelium after cardiopulmonary bypass, measured as reactivity to an infusion of acetylcholine.

L-arginine supplementation improves function and reduces inflammation in renal allografts

Recovery from ischemia/reperfusion and immune-mediated injury in the renal transplant is associated with reduced renal hemodynamics and increased leukocyte infiltration. In diverse models of renal failure, L-arginine supplementation improved hemodynamics and reduced inflammation. However in a proinflammatory environment, L-arginine can worsen renal injury. This study investigated the therapeutic potential of L-arginine supplementation in allogeneic renal transplantation: Brown Norway rat kidneys were transplanted into Lewis rat recipients, with one native kidney remaining. Recipients received low-dose cyclosporin A (2.5 mg/kg per d subcutaneously) to obtain moderate vascular and interstitial rejection, with or without 1% L-arginine in drinking water for 7 d posttransplantation. Transplantation increased renal vasoconstriction (from 16.9 +/- 1.33 to 35.1 +/- 8.6 units; P: < 0.01), thereby reducing GFR (from 0.96 +/- 0.09 to 0.48 +/- 0.10 ml/min; P: < 0.05). Treatment with L-arginine restored renal graft function to levels found in normal donors (renal vascular resistance, 15.7 +/- 1.69 units; GFR, 0.80 +/- 0.06 ml/min). L-arginine significantly reduced vascular occlusion because of less inflammation, endothelial disruption, and thrombosis. L-arginine also decreased tubulitis, interstitial injury, and macrophage infiltration. These protective effects suggest that L-arginine might be useful as additive therapy to conventional immune suppression.

Cellular regulation of endothelial nitric oxide synthase

Renal function is highly dependent on endothelium-derived nitric oxide (NO). Several renal disorders have been linked to impaired NO bioavailability. The enzyme that is responsible for the synthesis of NO within the renal endothelium is endothelial NO synthase (eNOS). eNOS-mediated NO generation is a highly regulated cellular event, which is induced by calcium-mobilizing agonists and fluid shear stress. eNOS activity is regulated at the transcriptional level but also by a variety of modifications, such as acylation and phosphorylation, by its cellular localization, and by protein-protein interactions. The present review focuses on the complex regulation of eNOS within the endothelial cell.

Physiology of nitric oxide in skeletal muscle

In the past five years, skeletal muscle has emerged as a paradigm of "nitric oxide" (NO) function and redox-related signaling in biology. All major nitric oxide synthase (NOS) isoforms, including a muscle-specific splice variant of neuronal-type (n) NOS, are expressed in skeletal muscles of all mammals. Expression and localization of NOS isoforms are dependent on age and developmental stage, innervation and activity, history of exposure to cytokines and growth factors, and muscle fiber type and species. nNOS in particular may show a fast-twitch muscle predominance. Muscle NOS localization and activity are regulated by a number of protein-protein interactions and co- and/or posttranslational modifications. Subcellular compartmentalization of the NOSs enables distinct functions that are mediated by increases in cGMP and by S-nitrosylation of proteins such as the ryanodine receptor-calcium release channel. Skeletal muscle functions regulated by NO or related molecules include force production (excitation-contraction coupling), autoregulation of blood flow, myocyte differentiation, respiration, and glucose homeostasis. These studies provide new insights into fundamental aspects of muscle physiology, cell biology, ion channel physiology, calcium homeostasis, signal transduction, and the biochemistry of redox-related systems.

Modulation of myocardial SOD and iNOS during ischemia-reperfusion by antisense directed at ACE mRNA

Renin-angiotensin system (RAS) is involved in the regulation of superoxide dismutase (SOD) and nitric oxide (NO) equilibrium, and its modulation protects hearts from ischemic dysfunction. We examined the effect of a new antisense-oligodeoxynucleotides (AS-ODNs) directed at ACE mRNA on SOD and iNOS expression during myocardial ischemia. Sprague-Dawley rats were treated with saline, AS-ODNs, or inverted-ODNs (IN-ODNs), given with liposome DOTAP/DOPE. Hearts were excised and subjected to 25 min of ischemia followed by 30 min of reperfusion. Ischemia-reperfusion in saline-treated hearts resulted in a decrease in the expression of SOD and an increase in the expression of inducible NOS (iNOS) genes concurrently with myocardial dysfunction. AS-ODNs, but not IN-ODNs, protected hearts against functional deterioration, and upregulated SOD expression and inhibited the expression of iNOS. ACE protein expression was decreased in the rat hearts of the AS-ODNs-treated group, but not in the IN-ODNs group. Thus manipulation of RAS with AS-ODNs directed at ACE mRNA can ameliorate cardiac dysfunction and modulate expression of SOD and iNOS at genomic level.

Endothelial nitric oxide synthase is a site of superoxide synthesis in endothelial cells treated with glyceryl trinitrate

Tolerance to glyceryl trinitrate (GTN) involves superoxide (O(2)(*-)) production by endothelial cells. Nitric oxide synthase (NOS) produces O(2)(*-) when L-arginine (L-arg) is limited. The purpose of this study was to test the hypothesis that GTN stimulates NOS to increase O(2)(*-) synthesis in endothelial cells when L-arg is limited. Production of O(2)(*-) by bovine aortic endothelial cells (BAEC, passages 3 - 5) was determined by spectrophotometrically measuring superoxide dismutase-inhibited reduction of ferricytochrome C to ferrocytochrome C. Cells were incubated in buffer without L-arg. O(2)(*-) production was measured using BAEC either untreated or treated with L-NAME or L-arg alone or following treatment with GTN (10(-9) to 10(-6) M) for 30 min or DPTA NONOate (10(-7) and 10(-6) M) alone or with GTN or DPTA NONOate after pretreatment with nitro-L-arginine methyl ester (L-NAME), L-arg or their inactive enantiomers, D-NAME or D-arg (all 5 x 10(-4) M) (n=6 - 7/group). L-NAME alone produced a 69% reduction in O(2)(*-) levels. Treatment with L-arg alone had no effect. Cells treated with GTN alone exhibited an increase in O(2)(*-). This effect was prevented by pretreatment with either L-NAME or L-arg, and was unaffected by D-NAME or D-arg. We observed a dose-response relationship in O(2)(*-) production to GTN over a range of 10(-9) to 10(-7) M. The NO donor, DPTA-NONOate, unlike GTN, did not have a significant effect on O(2)(*-) production. In conclusion, endothelial NOS is a site of O(2)(*-) synthesis in endothelial cells activated by GTN.

Ameliorated effect of L-arginine supplementation on gingival morphology in cyclosporin-treated rats

BACKGROUND

The role of nitric oxide (NO) in the pathogenesis of cyclosporin (CsA)-induced gingival overgrowth is unknown. The purpose of the present study was to evaluate the effect of NO substrate (L-arginine) and blockade (N-nitro-L-arginine methylester-hydrochloride, L-NAME) on the gingival morphology in CsA-fed rats.

METHODS

Sixty CsA-fed (10 mg/kg/day) male Sprague-Dawley rats were assigned to 3 groups. Animals in 2 experimental groups received L-arginine (1% weight/weight) in rat chowder or L-NAME (50 mg/l) in drinking water, respectively, for 4 weeks. Rats in the control group were fed a normal diet and water. At week 0, 2, and 4, dental stone models were made from the mandibular anterior region and the gingival dimensions (width, depth, and height) were measured. The tail cuff blood pressure and the plasma nitrate level were also measured at week 4 to monitor the effects of L-arginine and L-NAME treatment.

RESULTS

No significant difference in the gingival dimensions was noticed at week 0; however, significant differences were observed at weeks 2 and 4, except the buccolingual depth at week 2. While the magnitude of gingival dimensions was large, moderate, and small in control, L-NAME, and L-arginine groups, respectively, we found significantly reduced gingival dimensions in both L-arginine supplement and L-NAME groups. Nevertheless, the reduced gingival overgrowth in the L-NAME treatment group was far less than that in the exogenous NO treatment group. Plasma NO2-/NO3- concentrations were also significantly different; i.e., from the highest to the lowest levels were the L-arginine, CsA control, and L-NAME group, respectively. A significantly increased mean and diastolic blood pressure was found in the L-NAME group compared to the L-arginine group.

CONCLUSIONS

Gingival morphology in CsA-fed rats was evaluated after NO substrate (L-arginine) and blockade (L-NAME) treatment for 4 weeks. Significantly decreased dimensions were noted in the L-arginine group compared to the CsA group at weeks 2 and 4. Although an inhibitory effect on the gingival morphology was also observed in the L-NAME group, another unknown mechanism might be involved. Within the limitations of the study, we suggest that NO may have an important role in the mechanism of CsA-induced gingival overgrowth.

Modeling the interaction of peroxynitrite with low-density lipoproteins. III: the role of antioxidants

Peroxynitrite is a candidate for the substance responsible for the initiation of peroxidation of low-density lipoproteins (LDL) in blood. This is believed to be the initial step in the formation of atherosclerotic plaque. Using kinetic arguments, this paper examines possible routes in both LDL particles and in the surrounding plasma for antioxidants to block peroxidation. The antioxidants considered include ascorbate ion, glutathione and human serum albumin in plasma as well as alpha -tocopherol, ubiquinone-10 and carotenoids in the LDL particles. The results suggest that in the plasma compartment the most efficacious blocking mechanism is the reaction of ascorbate ion with the peroxynitrite precursor, superoxide ion. The situation in LDL particles is much less clear cut because of the paucity of kinetic data in this medium. However, some constraints are suggested on the requirements for an effective antioxidant.

Modeling the interaction of peroxynitrite with low-density lipoproteins. I. Plasma levels of peroxynitrite

Peroxynitrite is a strong candidate for the material responsible for the initiation of peroxidation of low-density lipoproteins (LDLs) which is considered the first step in the formation of atherosclerotic plaque. Recent advances in the understanding of peroxynitrite chemistry allow the construction of a kinetic model that can be used to understand the factors controlling levels in plasma. These results indicate that the carbon dioxide catalysed decomposition of peroxynitrite produces large quantities of reactive species, but the rapid decomposition of this intermediate, ONOOCO(-)(2), may limit its availability to attack LDLs at points distant from the site of production. In this case, peroxynitrite itself may be of greater quantitative importance in LDL peroxidation.

Influence of enteral diets supplemented with key nutrients on lymphocyte subpopulations in Peyer's patches of endotoxin-boostered mice

BACKGROUND AND AIMS

This study was undertaken to compare the effect of different key nutrients on lymphocyte subsets of Peyer's patches (PP) and spleen in endotoxemic mice.

METHODS

Female Balb/c mice were fed over a period of 10 days either with an isocaloric and isonitrogenous control diet (Control), a glutamine enriched diet (Diet I) or a diet containing glutamine, arginine, glycine, and n-3 fatty acids (Diet II). On day 7 the mice were challenged intraperitoneally with 25 microg LPS. The lymphocyte subpopulations (B cells, T cells, CD4+ and CD8+) of PP and spleen were analysed by flow cytometry. Glutathione content of small intestinal mucosa and spleen was determined by HPLC and luminal small intestinal IgA by ELISA.

RESULTS

Both experimental diets increased the number of B and T cells in the PP and that of T cells in the spleen (P<0.01). Glutathione content in PP and spleen was higher under administration of key nutrients (P<0.05). Diet II reduced luminal small intestinal IgA content in comparison to the two other groups.

CONCLUSION

The addition of arginine, glycine and n-3 fatty acids to a glutamine supplemented diet does not enhance lymphocyte numbers in PP and spleen, but reduces intestinal IgA content.

Nitric oxide dysfunction in the pathophysiology of preeclampsia

Researchers disagree as to the importance of nitric oxide (NO) in preeclampsia. Many researchers have alluded to NO's possible primary or secondary role in the development of preeclampsia, but few have correlated the dysfunction of nitric oxide production with the other metabolic derangements seen in this condition. This paper will review the evidence that the primary dysfunction in preeclampsia is a relative deficiency of available NO (secondary to oxidative degradation) and an excess of peroxynitrite (ONOO(-)). The combination of a deficiency of NO and an increase in ONOO(-) can directly or indirectly initiate the vast majority of physiological and serological changes associated with preeclampsia, such as blood pressure, increased glomerular filtration rate, proteinuria, platelet dysfunction, increased thromboxane and endothelin, and a decrease in prostacyclin. Understanding the complex role of nitric oxide in this condition may explain why previous interventions have been unsuccessful and suggest possible strategies for prevention and treatment in the future.

Brain nitric oxide changes after controlled cortical impact injury in rats

Nitric oxide (NO) and the NO end products, nitrate and nitrite, were measured at the impact site after a 5-m/s, 3-mm deformation controlled cortical impact injury in rats. Immediately after the impact injury and the NO and microdialysis probes could be replaced, there was an increase from baseline in NO concentration of 83 +/- 16 (SE) nM, compared with 0.5 +/- 4 nM in the sham injured animals (P < 0.001). This marked increase in NO occurred at the time of the initial rise in blood pressure (BP) and intracranial pressure (ICP) in response to the injury. After the initial increase in BP and ICP, the BP decreased and stabilized at a value which was approximately 20 mmHg below the preinjury values, and ICP plateaued at an average value of 20 mmHg, compared with 8 mmHg in the sham-injured animals. This provided an average cerebral perfusion pressure of 40-50 mmHg, compared with 65-75 mmHg for the sham-injured animals. These values were relatively constant for the remainder of the 3-h monitoring period. The NO values also stabilized during this time period. By 1 h after the impact injury the NO concentration measured directly using the NO electrode had decreased from baseline values by an average value of 25 +/- 6 nM. NO concentration remained significantly lower than baseline values throughout the remainder of the 3-h monitoring period. The concentration of nitrate/nitrite in the dialysate fluid also decreased by an average value of 341 +/- 283 nM 20-40 min after the injury. Dialysate nitrite/nitrate concentrations remained less than the preinjury baseline values throughout the remainder of the 3-h monitoring period. Preinjury treatment with L-nitro-arginine methyl ester (L-NAME) blunted the injury-induced increase in NO and resulted in more severe immediate intracranial hypertension and more severe systemic hypotension at one hour after injury. Mortality was also 67% with L-NAME pretreatment, compared with 1% in untreated animals.

Sustained nitric oxide production via l-arginine administration ameliorates effects of intestinal ischemia-reperfusion

BACKGROUND

The role of nitric oxide in intestinal ischemia-reperfusion is unclear-some studies link it to the harmful effects of ischemia-reperfusion, while others report it to be protective. We propose that nitric oxide levels diminish in the reperfusion period in conjunction with the onset of increased capillary permeability. The aim of this study is to determine the effect of supplementing nitric oxide synthase with its substrate, l-arginine, on development of local mucosal injury and systemic capillary leak.

MATERIALS AND METHODS

Rats underwent 30 min of superior mesenteric artery occlusion followed by 4 h of reperfusion. The vehicle groups received l-arginine either intravenously (4 mg/kg/min) or into the intestinal lumen. The intravenous groups received l-arginine either before the ischemic event or after 30 min of reperfusion. Capillary leak in the gut and lung were measured, as were degree of mucosal injury and number of infiltrating neutrophils. Appropriate controls were performed.

RESULTS

Thirty minutes of mesenteric ischemia followed by 4 h of reperfusion significantly increased gut and lung leak, neutrophil infiltration, and the severity of mucosal injury. l-Arginine given iv prior to ischemia inhibited lung leak, mucosal injury, and neutrophil infiltration. When arginine was given during the reperfusion period, lung leak and neutrophil infiltration but not mucosal injury were reduced. Intraluminal l-arginine reduced mucosa injury, but had no effect on capillary leak.

CONCLUSIONS

Supplementation with l-arginine enhances NO production, resulting in reduced systemic endothelial dysfunction. This may act as a useful clinical adjunct in the management of trauma patients in preventing the development of ARDS and multiple organ failure.

Localization of inducible nitric oxide synthase to mast cells during ischemia/reperfusion injury of skeletal muscle

Nitric oxide contributes to tissue necrosis after ischemia-reperfusion (IR). A biochemical and immunohistochemical study was made of the amounts and localization of both Ca++-independent nitric oxide synthase (NOS) II and Ca++-dependent (NOS I and NOS III) in rat skeletal muscle after ischemia and 0.5, 2, 8, 16, and 24 hours reperfusion. NOS II was not detectable in control muscle or during ischemia, was first detected after 2 hours reperfusion, increased further by 8 hours, and remained elevated at 24 hours. Both NOS II and nitrotyrosine, a marker of peroxynitrite formation, were localized exclusively to mast cells except after 24 hours reperfusion when some macrophages and neutrophils also showed positive immunoreactivity. Mast cells underwent extensive degranulation during reperfusion. NOS I was not detected in injured or control muscle. The level of NOS III, which was localized to the endothelium of blood vessels of all sizes in control muscle, decreased progressively during ischemia and reperfusion to reach undetectable levels after 16 hours reperfusion. These findings indicate that most of the nitric oxide formed during IR injury is generated by NOS II located almost exclusively in mast cells.

Correction of endothelial dysfunction in chronic heart failure: additional effects of exercise training and oral L-arginine supplementation

OBJECTIVES

The aim of this study was to analyze whether L-arginine (L-arg.) has comparable or additive effects to physical exercise regarding endothelium-dependent vasodilation in patients with chronic heart failure (CHF).

BACKGROUND

Endothelial dysfunction in patients with CHF can be corrected by both dietary supplementation with L-arg. and regular physical exercise.

METHODS

Forty patients with severe CHF (left ventricular ejection fraction 19 +/- 9%) were randomized to an L-arg. group (8 g/day), a training group (T) with daily handgrip training, L-arg. and T (L-arg. + T) or an inactive control group (C). The mean internal radial artery diameter was determined at the beginning and after four weeks in response to brachial arterial administration of acetylcholine (ACh) (7.5, 15, 30 microg/min) and nitroglycerin (0.2 mg/min) with a transcutaneous high-resolution 10 MHz A-mode echo tracking system coupled with a Doppler device. The power of the study to detect clinically significant differences in endothelium-dependent vasodilation was 96.6%.

RESULTS

At the beginning, the mean endothelium-dependent vasodilation in response to ACh, 30 microg/min was 2.54 +/- 0.09% (p = NS between groups). After four weeks, internal radial artery diameter increased by 8.8 +/- 0.9% after ACh 30 microg/min in L-arg. (p < 0.001 vs. C), by 8.6 +/- 0.9% in T (p < 0.001 vs. C) and by 12.0 +/- 0.3% in L-arg. +/- T (p < 0.005 vs. C, L-arg. and T). Endothelium-independent vasodilation as assessed by infusion of nitroglycerin was similar in all groups at the beginning and at the end of the study.

CONCLUSIONS

Dietary supplementation of L-arg. as well as regular physical exercise improved agonist-mediated, endothelium-dependent vasodilation to a similar extent. Both interventions together seem to produce additive effects with respect to endothelium-dependent vasodilation.

Histomorphology of rabbit thigh muscles: establishment of standard control values

The thigh muscles of New Zealand White (NZW) rabbits are frequently used in experimental surgery, particularly for evaluation after reinnervation or ischaemia. Although histomorphometric analyses are regularly performed, morphological data for untreated thigh muscles in previously unoperated animals are not available. Specimens from the rectus femoris (RF), vastus medialis (VM) and adductor magnus (AM) muscles from both thighs were harvested in 7 untreated rabbits and were processed for histomorphometric evaluation. The right RF and VM were harvested in a further 5 rabbit hindlimbs after experimental denervation and reinnervation of the contralateral RF and subsequently processed for histomorphometric analysis. Muscle fibre type distribution, diameter and connective tissue content were evaluated on serial transverse cryosections reacted for ATPase and NADH tetrazolium reductase activity and statistical analysis was performed. In all untreated animals RF revealed the highest proportion of type I muscle fibres (right: 8.4+/-4%, left: 11.4+/-4.9%), whereas VM showed the highest percentage of IIa fibres (right: 31.9+/-5.5%, left: 28.3+/-7.8%) and AM the highest proportion of IIb/d fibres (right: 80.5+/-8.6%, left: 84.4+/-6.3%). Fibre type distribution and diameter in rabbits after contralateral experimental operations revealed a statistically significant difference from the data obtained in bilaterally untreated animals. Knowledge of the morphology of untreated muscles is fundamental to the understanding of changes induced by intervention to the ipsi and/or contralateral thigh muscles.

Effects of NO donors and synthase agonists on endothelial cell uptake of L-Arg and superoxide production

It is commonly believed that the activity of NO synthase (NOS) solely controls NO production from its substrates, L-Arg and O(2). The Michaelis-Menten constant (K(m)) of NOS for L-Arg is in the micromolar range; cellular levels of L-Arg are much higher. However, evidence strongly suggests that cellular supply of L-Arg may become limiting and lead to reduced NO and increased superoxide anion (O(-)(2)*) formation, promoting cardiovascular dysfunction. Uptake of L-Arg into cells occurs primarily (approximately 85%) through the actions of a Na(+)-independent, carrier-mediated transporter (system y(+)). We have examined the effects of NOS agonists (substance P, bradykinin, and ACh) and NO donors (S-nitroso-N-acetyl-penicillamine and dipropylenetriamine NONOate) on transport of L-Arg into bovine aortic endothelial cells (BAEC). Our results demonstrate that NOS agonists increase y(+) transporter activity. A rapidly acting NO donor initially increases L-Arg uptake; however, after longer exposure, L-Arg uptake is suppressed. Exposure of BAEC without L-Arg to substance P and a Ca(2+) ionophore (A-23187) increased O(-)(2)* formation, which was blocked with concurrent presence of L-Arg or the NOS antagonist N(omega)-nitro-L-arginine methyl ester. We conclude that factors including NO itself control y(+) transport function and the production of NO and O(-)(2)*.

Inhibition of nitric oxide synthesis improves left ventricular contractility in neonatal pigs late after cardiopulmonary bypass

BACKGROUND

Following neonatal open heart surgery a nadir occurs in left ventricular function six to 12 hours after cardiopulmonary bypass. Although initiated by intraoperative events, little is known about the mechanisms involved.

OBJECTIVE

To evaluate the involvement of nitric oxide in this late phase dysfunction in piglets.

DESIGN

Piglets aged 2 to 3 weeks (4-5 kg) underwent cardiopulmonary bypass (1 h) and cardioplegic arrest (0.5 h) and then remained ventilated with inotropic support. Twelve hours after bypass, while receiving dobutamine (5 microg/kg/min), the left ventricular response to non-selective nitric oxide synthase inhibition (l-N(G)-monomethylarginine (l-NMMA)) was evaluated using load dependent and load independent indices (E(es), the slope of the end systolic pressure-volume relation; M(w), the slope of the stroke work-end diastolic volume relation; [dP/dt(max)](edv), the slope of the dP/dt(max)-end diastolic volume relation), derived from left ventricular pressure-volume loops generated by conductance and microtip pressure catheters.

RESULTS

10 pigs received 7.5 mg l-NMMA intravenously and six of these received two additional doses (37.5 mg and 75 mg). E(es) (mean (SD)) increased with all three doses, from 54.9 (40.1) mm Hg/ml (control) to 86.3 (69.5) at 7.5 mg, 117.9 (65.1) at 37.5 mg, and 119 (80.4) at 75 mg (p < 0.05). At the two highest doses, [dP/dt(max)](edv) increased from 260.8 (209.3) (control) to 470.5 (22.8) at 37.5 mg and 474.1 (296.6) at 75 mg (p < 0.05); and end diastolic pressure decreased from 16.5 (5.6) mm Hg (control) to 11.3 (5.0) at 37.5 mg and 11.4 (4.9) at 75 mg (p < 0. 05).

CONCLUSIONS

In neonatal pigs 12 hours after cardiopulmonary bypass with ischaemic arrest, low dose l-NMMA improved left ventricular function, implying that there is a net deleterious cardiac action of nitric oxide at this time.

New insights into nitric oxide and coronary circulation

Since its discovery over 20 years ago as an intercellular messenger, nitric oxide (NO), has been extensively studied with regard to its involvement in the control of the circulation and, more recently, in the prevention of atherosclerosis. The importance of NO in coronary blood flow control has also been recognized. NO-independent vasodilation causes increased shear stress within the blood vessel which, in turn, stimulates endothelial NO synthase activation, NO release and prolongation of vasodilation. Reactive hyperemia, myogenic vasodilation and vasodilator effects of acetylcholine and bradykinin are all mediated by NO. Ischemic preconditioning, which protects the myocardium from cellular damage and arrhythmias, is itself linked with NO and both the first and second windows of protection may be due to NO release. Exercise increases NO synthesis via increases in shear stress and pulse pressure and so it is likely that NO is an important blood flow regulatory mechanism in exercise. This phenomenon may account for the beneficial effects of exercise seen in atherosclerotic individuals. Whilst NO plays a protective role in preventing atherosclerosis via superoxide anion scavenging, risk factors such as hypercholesterolemia reduce NO release leading the way for endothelial dysfunction and atherosclerotic lesions. Exercise reverses this process by stimulating NO synthesis and release. Other factors impacting on the activity of NO include estrogens, endothelins, adrenomedullin and adenosine, the last appearing to be a compensatory pathway for coronary control in the presence of NO inhibition. These studies reinforce the pivotal role played by the substance in the control of coronary circulation.

The altered homeostatic theory: a holistic approach to multiple diseases, including atherosclerosis, ischemic diseases, and hypertension

The altered homeostatic theory proposes that multiple acquired and genetic factors (risk factors) move the basic homeostatic balance in an 'action' direction which 'inappropriately' activates defense mechanisms and thus favors multiple diseases; factors which improve these disorders move the homeostatic balance in the opposite 'rest' direction. Diseases include hypertension, atherosclerosis, and ischemic disorders as ischemic heart disease (IHD), stroke, migraine, and Raynaud's disease. The theory has its origins in the premises of the spasm-of-resistance-vessel (S-RV) concept of ischemic diseases (which attributes symptoms in ischemic diseases to S-RV), and in a study designed to provide more evidence for this concept. The study showed that multiple risk factors for IHD express the combination of S-RV and a tendency toward thrombosis, and are risk factors for hypertension, migraine, Raynaud's disease, and stroke; factors which ameliorate IHD express vasodilation of resistance vessels and are anti-thrombotic, and ameliorate the other disorders.

Nitric oxide synthase inhibitors reduce sarcomere addition in rat skeletal muscle

1. Mechanical stimuli are thought to modulate the number of sarcomeres in series (sarcomere number) in skeletal muscle fibres. However, the mechanisms by which muscle cells transduce mechanical signals into serial sarcomere addition have not been explored. In this study, we test the hypothesis that nitric oxide positively modulates sarcomere addition. 2. The soleus muscle was cast-immobilized in a shortened position in 3-week-old female Wistar rats. After 4 weeks, the casts were removed, creating a period of rapid sarcomere addition. During the remobilization period, nitric oxide synthase (NOS) inhibitors or substrate were administered. 3. Rats treated with the non-isoform-specific NOS inhibitor L-nitro-arginine methyl ester during 3 weeks of remobilization had smaller soleus sarcomere numbers than control rats. Rats treated with 1-(2-trifluoromethyl-phenyl)-imidazole, which has greater specificity for the neuronal isoform than for the endothelial isoform of NOS, also had smaller soleus sarcomere numbers than control rats. These results suggest that inhibition of the neuronal isoform of NOS reduces sarcomere addition during remobilization. 4. Rats treated with L-arginine, the substrate for NOS, during 1 week of remobilization had soleus sarcomere numbers for the immobilized-remobilized muscle which were closer to that for the contralateral, non-immobilized muscle than did rats that were not treated with L-arginine. 5. These results support the hypothesis that nitric oxide derived from the neuronal isoform of NOS positively modulates sarcomere addition.

Multivitamin administration before ischemia reduces ischemia-reperfusion injury in rabbit skeletal muscle

This study investigated the effect of a multivitamin preparation administered before ischemia or before reperfusion, on ischemia-reperfusion (I/R) injury of skeletal muscle. An in vivo hindlimb skeletal muscle I/R model (2.5 h/2 h) was carried out on adult New Zealand white rabbits. Animals used as I/R models were treated with a multivitamin preparation (0.4 ml/kg bw i.v. bolus), containing alpha-tocopherol, ascorbic acid, retinol, vitamin B complex, 30 min before starting ischemia (group MV(isc)) or 5 min before reperfusion (group MV(rep)) and compared to animals with I/R without treatment (group IR) and sham operated animals (group SHAM). Interstitial edema (muscle interfiber area, %MIFA) and changes in microvessel size (microvessel cross sectional area, MVCSA, microm(2)) were measured. Plasma malondialdehyde concentrations (MDA-TBA, nmol/ml) served as a measure of lipid peroxidation. After 2h of reperfusion, ischemia-reperfusion developed a significant microvascular constriction and an interstitial edema (IR, vs SHAM;P<< 0.01), but administration of antioxidative vitamins before the onset of ischemia reduced microvascular constriction and edema formation (P<< 0.05 vs IR group). In a similar manner, administration of vitamins before ischemia lowered plasma MDA-TBA levels as compared to the untreated group during reperfusion (p<< 0. 05). In animals treated with vitamins before reperfusion, the biochemical and morphological results showed no differences as compared to the untreated group. Antioxidative treatment with a multivitamin preparation exerted a beneficial effect on I/R injury of skeletal muscle when the aforementioned vitamins were administered before ischemia but not before the onset of reperfusion.

Superoxide production by primary rat cerebral endothelial cells in response to pneumococci

Animal studies of experimental bacterial meningitis have provided evidence for an involvement of reactive oxygen species (ROS) in the pathophysiology of this disease. Using a lucigenin-enhanced chemiluminescence (CL) method, we tested whether primary rat cerebral endothelial cells can be induced to release ROS upon stimulation with pneumococci. In addition, we determined CSF levels of two markers of lipid peroxidation in patients with bacterial meningitis, compared to patients with viral meningitis and noninflammatory neurological disorders. Malondialdehyde/4-hydroxynonenal concentrations were significantly elevated in CSF samples obtained from patients with bacterial meningitis (23.12+/-5.47 microM), as compared to both control groups (5.43+/-0.18 microM and 7.80+/-0.33 microM, respectively). Cerebromicrovascular endothelial cells, granulocytes, and the macrophage cell line RAW 264.7 (but not astrocytes and neuron-like cells) produced an increase in CL intensity after stimulation with pneumococci. The peak value produced by endothelial cells (500+/-83 cpm) was significantly lower than the maximum CL response in macrophages (1386+/-142 cpm; p<0.05). After addition of superoxide dismutase (SOD), the CL signal returned to baseline values. Equal to the CL technique, nitroblue tetrazolium (NBT) staining of RAW 264.7 showed SOD-inhibitable formazan precipitation when stimulated with pneumococci. In conclusion, this study suggests an important role of endothelial cells in the pathophysiology of bacterial meningitis-namely as a source for ROS production.

L-arginine limits myocardial cell death secondary to hypoxia-reoxygenation by a cGMP-dependent mechanism

The objective of this study was to investigate the effect of L-arginine supplementation on myocardial cell death secondary to hypoxia-reoxygenation. Isolated rat hearts (n = 51) subjected to 40 min of hypoxia and 90 min of reoxygenation received 3 mM L-arginine and/or 1 microM 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; a selective inhibitor of soluble guanylyl cyclase) throughout the experiment or during the equilibration, hypoxia, or reoxygenation periods. The incorporation of L-[3H]arginine into myocytes during energy deprivation was investigated in isolated adult rat myocytes. The addition of L-arginine to the perfusate throughout the experiment resulted in higher cGMP release (P < 0.05), reduced lactate dehydrogenase release (P < 0.05), and increased pressure-rate product (P < 0.05) during reoxygenation. These effects were reproduced when L-arginine was added only during equilibration, but addition of L-arginine during hypoxia or reoxygenation had no effect. Addition of ODQ either throughout the experiment or only during reoxygenation reversed the beneficial effects of L-arginine. L-[3H]arginine was not significantly incorporated into isolated myocytes subjected to energy deprivation. We conclude that L-arginine supplementation protects the myocardium against reoxygenation injury by cGMP-mediated actions. To be effective during reoxygenation, L-arginine must be added before anoxia.

Simple and rapid method for the measurement of nitrite and nitrate in human plasma and cerebrospinal fluid by capillary electrophoresis

Nitrite and nitrate levels in physiological fluids are commonly used as an index of nitric oxide production. We developed simple and rapid method for the determination of these anions by capillary zone electrophoresis employing borate buffer (pH 10, 100 mmol/l) as running electrolyte. The anions were analyzed in plasma and cerebrospinal fluid (CSF) without deproteinization of the samples. Electrophoresis was carried out in a capillary (36.5 cm x 75 microm) at a potential of 15 kV, with on-column UV detection at 214 nm. Mean retention times for nitrite and nitrates were 4.631 and 5.152 min, respectively. The method was linear (r=0.999) within a 1-500 micromol/l concentration range. Physiological levels of nitrate in plasma (40.2 micromol/l) and CSF (15.3 micromol/l) could be determined with good precision (coefficients of variation <6%) and accuracy (recoveries of added nitrate to plasma and CSF were 97.4 and 104.5%, respectively). Measurements of the physiological levels of nitrite in plasma (6.1 micromol/l) and CSF (0.9 micromol/l) were less precise and accurate.

Direct electrochemical measurement of nitric oxide in vascular endothelium

The endothelium plays a critical role in maintaining vascular tone by releasing vasoconstrictor and vasodilator substances. Endothelium-derived nitric oxide (NO) is a vasodilator rapidly inactivated by superoxide and by Fe(II) and Fe(III), all found in significant quantities in biological systems. Thus due to the short life of NO in tissue (t1/2 = 3-6 s), in situ quantification of NO is a challenging problem. We designed the present study to perform direct measurements of nitric oxide using the electrochemical porphyrinic sensor. The most significant advantages of this sensor is small size (0.5-8 microm), rapid response time (0.1-1 ms), and low detection limit (10(-9) mol l(-1)). The porphyrinic sensor was used for in vitro and in vivo measurements of NO in an isolated single cell or tissue. Effects of hypertension, endotoxemia, and ischemia/reperfusion on the release of NO and/or its interaction with superoxide (O2-) were delineated. In the single endothelial cell (rabbit endocardium), NO concentration was highest at the cell membrane (950 +/- 50 nmol l(-1)), decreasing exponentially with distance from cell, and becoming undetectable at distances beyond 50 microm. The endothelium of spontaneously hypertensive rats (SHR) released 35% less NO (580 +/- 30 nmol l(-1)) than that of normotensive rats (920 +/- 50 nmol l(-1)), due to the higher production of O2- in SHR rats. Endothelial NO synthase (eNOS) generated NO (140 +/- 20 nmol l(-1)) in lung during the acute phase (first 10-15 min) of endotoxemia, followed by production of NO by inducible NOS. High production of O2- was observed during the entire period of endotoxemia. Ischemia (lower limb of rabbit) caused a significant increase of NO peaking at 15 min and decreasing thereafter, also due to O2- production.

Vascular endothelium viability and function after total cardiopulmonary bypass in neonatal piglets

Endothelium dysfunction with severe pulmonary hypertension may occur after total cardiopulmonary bypass (CPB) in infants as a result of a widespread inflammatory response. The aim of this study was to separate out the effects of lung ischemia-reperfusion from membrane oxygenator-induced activation of leukocytes on the function and viability of the pulmonary and systemic endothelia in neonatal piglets submitted to 90-min total CPB followed by 60-min reperfusion or in sham animals. Hemodynamics, gas exchange, endothelial-dependent relaxation in pulmonary and femoral arteries, and lung and skeletal muscle myeloperoxidase activity were assessed before, during, and after CPB, i.e., after reperfusion. Pulmonary and aortic endothelial cells and circulating leukocytes were harvested to assess reperfusion-induced changes in endothelial cells' viability and proliferation, and leukocyte-endothelial cell adhesion and cytotoxicity. Gas exchange worsened after reperfusion with pulmonary hypertension, increase in lung but not skeletal myeloperoxidase, and reduction of endothelial-dependent relaxation in pulmonary but not femoral arteries. After reperfusion, viabilities of pulmonary and aortic endothelial cells were reduced to 50%, endothelial cell growths were faster in pulmonary arteries than aorta, and leukocyte-pulmonary endothelial cell adhesion and cytotoxicity increased. These results suggest that in total CPB lung ischemia-reperfusion aggravates the inflammatory response and predisposes the lung endothelium to leukocyte-mediated injury.

Protective role of nitric oxide in ischemia and reperfusion injury of the liver

BACKGROUND

The suppressed production of nitric oxide (NO), associated with endothelial dysfunction, is thought to be a cause of ischemia and reperfusion injury of the liver. But findings of the salutary effects of NO enhancement on such injury have been conflicting. In this study, we tested our hypothesis that NO enhancement would attenuate ischemic liver injury. For this purpose, an NO precursor, L-arginine, and a novel NO donor, FK409, were applied to a 2-hour total hepatic vascular exclusion model in dogs.

STUDY DESIGN

L-arginine was administered IV at a dose of 100 mg/kg twice (n = 5), while 300 mg/kg twice of FK409 was infused continuously into the portal vein (n = 5). The drugs were given to the animals for 30 and 60 minutes before and after ischemia, respectively. Non-treated animals were used as the control (n = 10). Two-week survival, systemic and hepatic hemodynamics indices, liver function tests, energy metabolism, and histopathology were analyzed.

RESULTS

Both treatments comparably augmented hepatic tissue blood flow, decreased liver enzyme release, and increased high-energy phosphate restoration during the reperfusion period, all of which contributed to rescuing all of the treated animals from the 2-hour total hepatic ischemia. In contrast, ischemia caused 70% mortality in the control group. Histologically, structural abnormality and neutrophil infiltration were markedly attenuated by the treatments. Systemic hypotension was observed in the animals treated with FK409, however.

CONCLUSIONS

Our data demonstrate that NO enhancement alleviates the liver injury caused by ischemia and reperfusion. The supplementation of L-arginine, rather than FK409, is considered more applicable to clinical use because of the absence of systemic adverse effects.