L-arginine is the physiological precursor for the formation of nitric oxide in endothelium-dependent relaxation

The nitric oxide synthesis/pathway mediates the inhibitory serotoninergic responses of the pressor effect elicited by sympathetic stimulation in diabetic pithed rats

We investigated the involvement of the nitric oxide pathway in the inhibitory mechanisms of 5-hydroxytryptamine (5-HT) in the pressor responses induced by stimulation of sympathetic vasopressor outflow in diabetic pithed rats. Diabetes was induced in male Wistar rats by a single s.c. injection of alloxan. Four weeks later, the animals were anaesthetized, pretreated with atropine, and pithed. Electrical stimulation of the sympathetic outflow from the spinal cord (0.1, 0.5, 1 and 5 Hz) resulted in frequency-dependent increases in blood pressure. The inhibition of electrically induced pressor responses by 5-HT (10 microg/kg/min) in diabetic pithed rats could not be elicited after i.v. treatment with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 microg/kg), a guanylyl cyclase inhibitor, or N-omega-L-Arginine methyl ester hydrochloride (L-NAME) (10 mg/kg), a nitric oxide synthase (NOS) inhibitor. The inhibitory effect produced by infusion of the selective 5-HT(1A) receptor agonist 8-hydroxydipropylaminotretalin hydrobromide (8-OH-DPAT) (20 microg/kg/min) was abolished in the presence of ODQ (10 microg/kg), or L-NAME (10 mg/kg) in diabetic pithed rats. The administration of L-Arginine (100 mg/kg) 30 min after L-NAME reproduced the inhibitory effect caused by 5-HT (10 microg/kg/min) and 8-OH-DPAT (20 microg/kg/min) on the electrically induced pressor responses, whereas in the presence of D-Arginine (100 mg/kg)+L-NAME the 5-HT or 8-OH-DPAT inhibitory effect on the pressor responses was abolished. In conclusion, in diabetic pithed rats, the inhibition produced by prejunctional 5-HT(1A) activation on electrically induced sympathetic pressor responses is mediated by the NO synthesis/pathway.

Does central nitric oxide chronically modulate the acute hypoxic ventilatory response in conscious rats?

AIM

Hypoxia initiates an increase in ventilation (VE) through a cascade of events of which central nitric oxide (NO) has been implicated as an important neuromodulator. There have not been any reports describing the consequences of long-term imbalances in the central NO pathways on the modulation of the acute hypoxic ventilatory response (HVR). Chronic hypoxia (CH) can potentially modify the HVR, and so we hypothesized that central NO may be involved. In this study we describe the long-term role of central NO in the modulation of HVR before and after CH.

METHODS

Male Sprague-Dawley rats (BW c. 200-320 g; n = 21) were implanted with an osmotic pump for continuous intracerebroventricular administration of either artificial cerebrospinal fluid (control), Nomega-nitro-L-arginine methyl ester (L-NAME) (150 microg kg(-1) day(-1)) or the NO-donor, 3-[4-morpholinyl]-sydnonimine-hydrochloride (SIN-1) (100 microg kg(-1) day(-1)). The VE response to acute poikilocapnic hypoxia (8% O2 for 20 min) was measured by plethysmography seven days after surgery, in normoxia, and again after 14 days of exposure to CH (CH = 12% O2).

RESULTS

The magnitude of the HVR (c. 230% increase in VE) was unaltered by centrally infusing either L-NAME or SIN-1 for 1 week. CH did not modify the HVR, although baseline VE and HVR were shifted downward by L-NAME during CH - because of a reduction in the frequency component.

CONCLUSIONS

These results suggest that long-term alterations in central NO levels may not alter the HVR under moderate CH, presumably because of the onset/development of compensatory mechanisms. However, NO appears to be an important component of the HVR following CH.

Short-term dehydroepiandrosterone treatment increases platelet cGMP production in elderly male subjects

OBJECTIVE

Several clinical and population-based studies suggest that dehydroepiandrosterone (DHEA) and its sulphate (DHEA-S) play a protective role against atherosclerosis and coronary artery disease in human. However, the mechanisms underlying this action are still unknown. It has recently been suggested that DHEA-S could delay atheroma formation through an increase in nitric oxide (NO) production.

STUDY DESIGN AND METHODS

Twenty-four aged male subjects [age (mean +/- SEM): 65.4 +/- 0.7 year; range: 58.2-67.6 years] underwent a blinded placebo controlled study receiving DHEA (50 mg p.o. daily at bedtime) or placebo for 2 months. Platelet cyclic guanosine-monophosphate (cGMP) concentration (as marker of NO production) and serum levels of DHEA-S, DHEA, IGF-I, insulin, glucose, oestradiol (E(2)), testosterone, plasminogen activator inhibitor (PAI)-1 antigen (PAI-1 Ag), homocysteine and lipid profile were evaluated before and after the 2-month treatment with DHEA or placebo.

RESULTS

At the baseline, all variables in the two groups were overlapping. All parameters were unchanged after treatment with placebo. Conversely, treatment with DHEA (a) increased (P < 0.001 vs. baseline) platelet cGMP (111.9 +/- 7.1 vs. 50.1 +/- 4.1 fmol/10(6) plts), DHEA-S (13.6 +/- 0.8 vs. 3.0 +/- 0.3 micromol/l), DHEA (23.6 +/- 1.7 vs. 15.3 +/- 1.4 nmol/l), testosterone (23.6 +/- 1.0 vs. 17.7 +/- 1.0 nmol/l) and E(2) (72.0 +/- 5.0 vs. 60.0 +/- 4.0 pmol/l); and (b) decreased (P < 0.05 vs. baseline) PAI-1 Ag (27.4 +/- 3.8 vs. 21.5 +/- 2.5 ng/ml) and low-density lipoprotein (LDL) cholesterol (3.4 +/- 0.2 vs. 3.0 +/- 0.2 mmol/l). IGF-I, insulin, glucose, triglycerides, total cholesterol, HDL cholesterol, HDL2 cholesterol, HDL3 cholesterol, apolipoprotein A1 (ApoA1), apolipoprotein B (ApoB) and homocysteine levels were not modified by DHEA treatment.

CONCLUSIONS

This study shows that short-term treatment with DHEA increased platelet cGMP production, a marker of NO production, in healthy elderly subjects. This effect is coupled with a decrease in PAI-1 and LDL cholesterol levels as well as an increase in testosterone and E(2) levels. These findings, therefore, suggest that chronic DHEA supplementation would exert antiatherogenic effects, particularly in elderly subjects who display low circulating levels of this hormone.

Nitric oxide synthase inhibition results in immediate postoperative recovery of gastric, small intestinal and colonic motility in awake rats

BACKGROUND

Nitric oxide (NO) is known to inhibit gastrointestinal motility. However, no detailed analysis of gastric, small intestinal and colonic motor effects, including effects on contraction frequency, has, as yet, been reported after NO inhibition in awake rats. We therefore investigated the effects of NO synthase inhibition on gastric, small intestinal and colonic motility in awake rats under baseline conditions and in a postoperative ileus model.

METHODS

In Sprague-Dawley rats, strain gauge transducers were sutured either to the gastric corpus, the small intestine or the colon. After 3 days, L-NMMA (NO synthase inhibitor), D-NMMA or vehicle was given i.v., while the motility was recorded continuously. In addition, postoperative gastric, small intestinal or colonic motility was investigated after L-NMMA or vehicle treatment prior to abdominal surgery. The motility index, the contraction amplitude, the area under the contraction amplitude and the contraction frequency were analysed.

RESULTS

L-NMMA decreased gastric motility to 60+/-8% for about 15 min, but continuously increased small intestinal motility to 221+/-22% and colonic motility to 125+/-7% compared to baseline (baseline=100%; p<0.01 for all comparisons). L-NMMA increased the contraction frequency throughout the gastrointestinal tract (stomach, 13+/-2%; small intestine, 8+/-1%; colon, 16+/-5%; p<0.01 vs. baseline for all comparisons). L-NMMA injection prior to surgery did not prohibit intraoperative inhibition of gastrointestinal motility, but did result in immediate recovery of gastric, small intestinal and colonic motility postoperatively (L-NMMA vs. vehicle, 0-60 min postoperatively; stomach, 90+/-9% vs. 53+/-3%; small intestine, 101+/-5% vs. 57+/-3%; colon, 134+/-6% vs. 60+/-5%; p<0.01 for all comparisons; no significant difference between preoperative baseline motility and L-NMMA treated rats postoperatively).

CONCLUSIONS

Under baseline conditions, endogenous NO inhibits small intestinal and colonic motility and gastric, small intestinal and colonic contraction frequency in awake rats. In the early postoperative period, endogenous NO is a major inhibitory component that seems to constitute the common final pathway of mediators and the neural pathways inhibiting gastrointestinal motility in rats.

Protection of endothelial function: targets for nutritional and pharmacological interventions

The vascular endothelium synthesizes and releases a spectrum of vasoactive substances and therefore plays a fundamental role in the basal and dynamic regulation of the circulation. Nitric oxide (NO)-originally described as endothelium-derived relaxing factor-is released from endothelial cells in response to shear stress produced by blood flow, and in response to activation of a variety of receptors. After diffusion from endothelial to vascular smooth muscle cells, NO increases intracellular cyclic guanosine-monophosphate concentrations by activation of the enzyme guanylate cyclase leading to relaxation of the smooth muscle cells. NO has also antithrombogenic, antiproliferative, leukocyte-adhesion inhibiting effects, and influences myocardial contractility. Endothelium-derived NO-mediated vascular relaxation is impaired in spontaneously hypertensive animals. NO decomposition by free oxygen radicals is a major mechanism of impaired NO bioavailability. The resulting imbalance of endothelium-derived relaxing and contracting substances disturbs the normal function of the vascular endothelium. Endothelin acts as the natural counterpart to endothelium-derived NO. Besides its arterial blood pressure rising effect in humans, endothelin-1 induces vascular and myocardial hypertrophy, which are independent risk factors for cardiovascular morbidity and mortality. Current therapeutic strategies concentrate mainly on lowering low-density lipoprotein cholesterol and an impressive reduction in the risk for cardiovascular morbidity and mortality has been achieved. Inflammatory mechanisms play an important role in vascular disease and inflammatory plasma markers correlate with prognosis. The production of reactive oxygen species under pathological conditions may represent an important inflammatory trigger. Novel therapeutic strategies specifically targeting inflammation thus bear great potential for the prevention and treatment of atherosclerotic vascular disease. In this context, the vascular actions of flavanol-rich cocoa, particularly with regard to enhanced NO synthesis and endothelial function observed in humans following consumption, warrants further attention. This review discusses pharmacological and dietary intervention.

Phylogenesis of constitutively formed nitric oxide in non-mammals

It is widely recognized that nitric oxide (NO) in mammalian tissues is produced from L-arginine via catalysis by NO synthase (NOS) isoforms such as neuronal NOS (nNOS) and endothelial NOS (eNOS) that are constitutively expressed mainly in the central and peripheral nervous system and vascular endothelial cells, respectively. This review concentrates only on these constitutive NOS (cNOS) isoforms while excluding information about iNOS, which is induced mainly in macrophages upon stimulation by cytokines and polysaccharides. The NO signaling pathway plays a crucial role in the functional regulation of mammalian tissues and organs. Evidence has also been accumulated for the role of NO in invertebrates and non-mammalian vertebrates. Expression of nNOS in the brain and peripheral nervous system is widely determined by staining with NADPH (reduced nicotinamide adenine dinucleotide phosphate) diaphorase or NOS immunoreactivity, and functional roles of NO formed by nNOS are evidenced in the early phylogenetic stages (invertebrates and fishes). On the other hand, the endothelium mainly produces vasodilating prostanoids rather than NO or does not liberate endothelium-derived relaxing factor (EDRF) (fishes), and the ability of endothelial cells to liberate NO is observed later in phylogenetic stages (amphibians). This review article summarizes various types of interesting information obtained from lower organisms (invertebrates, fishes, amphibians, reptiles, and birds) about the properties and distribution of nNOS and eNOS and also the roles of NO produced by the cNOS as an important intercellular signaling molecule.

Asymmetric dimethylarginine (ADMA): a novel risk marker in cardiovascular medicine and beyond

There is abundant evidence that the endothelium plays a crucial role in the maintenance of vascular tone and structure. One of the major endothelium-derived vasoactive mediators is nitric oxide (NO), an endogenous messenger molecule formed in healthy vascular endothelium from the amino acid precursor L-arginine. Endothelial dysfunction is caused by various cardiovascular risk factors, metabolic diseases, and systemic or local inflammation. One mechanism that explains the occurrence of endothelial dysfunction is the presence of elevated blood levels of asymmetric dimethylarginine (ADMA)--an L-arginine analogue that inhibits NO formation and thereby can impair vascular function. Supplementation with L-arginine has been shown to restore vascular function and to improve the clinical symptoms of various diseases associated with vascular dysfunction.

Nitric oxide as a pro-apoptotic as well as anti-apoptotic modulator

Nitric oxide (NO), synthesized from L-arginine by NO synthases, is a small, lipophilic, diffusible, highly reactive molecule with dichotomous regulatory roles in many biological events under physiological and pathological conditions. NO can promote apoptosis (pro-apoptosis) in some cells, whereas it inhibits apoptosis (anti-apoptosis) in other cells. This complexity is a consequence of the rate of NO production and the interaction with biological molecules such as metal ion, thiol, protein tyrosine, and reactive oxygen species. Long-lasting overproduction of NO acts as a pro-apoptotic modulator, activating caspase family proteases through the release of mitochondrial cytochrome c into cytosol, up-regulation of the p53 expression, and alterations in the expression of apoptosis-associated proteins, including the Bcl-2 family. However, low or physiological concentrations of NO prevent cells from apoptosis that is induced by the trophic factor withdrawal, Fas, TNFalpha/ActD, and LPS. The anti-apoptotic mechanism is understood on the basis of gene transcription of protective proteins. These include: heat shock protein, hemeoxygenase, or cyclooxygenase-2 and direct inhibition of the apoptotic executive effectors caspase family protease by S-nitrosylation of the cysteine thiol group in their catalytic site in a cell specific way. Our current understanding of the mechanisms by which NO exerts both pro- and anti-apototic action is discussed in this review article.

Exogenous nitric oxide centrally enhances pulmonary reactivity in the normal and hypertensive rat

1. Chronic hypoxia causes sustained pulmonary hypertension and, although impairment of the pulmonary endothelial nitric oxide (NO) pathway has been implicated, no study has described the central role of NO in modulating pulmonary vascular tone and reactivity. Centrally, NO inhibits sympathetic outflow, so we hypothesised that central NO would modulate pulmonary vascular tone and its reactivity to acute hypoxia, especially in the hypertensive state. 2. Male adult Sprague-Dawley rats were exposed to normoxia (N) or chronic hypoxia (CH; 12% O2) for 14 days. Mean pulmonary arterial pressure (MPAP), systemic mean arterial blood pressure (MABP), cardiac output and heart rate were then measured in pentobarbitone-anaesthetized, artificially ventilated rats. The N and CH rats were exposed to acute hypoxia (10% O2 for 4 min) after the intracerebroventricular (i.c.v.) administration of artificial cerebrospinal fluid (control) and then again after either i.c.v. NG-nitro-L-arginine methyl ester (L-NAME; 150 microg in 10 microL) or 3-morpholino-sydnonimine hydrochloride (SIN-1; 100 microg in 10 microL). 3. Chronic hypoxia caused pulmonary hypertension (MPAP 20+/-1 vs 30+/-1 mmHg in N and CH rats, respectively) and attenuated acute hypoxic pulmonary vasoconstriction (HPV). Central inhibition of NO synthesis (by l-NAME) did not alter baseline MPAP or the acute HPV in either N or CH rats, but it did elevate MABP. The NO donor SIN-1 did not alter baseline MPAP, but it did enhance (N rats) or restore (CH rats) the HPV and decreased MABP. 4. The results of the present study indicate that central NO has a limited role in the tonic modulation of MPAP during normoxia and after chronic hypoxia. However, the acute HPV seems to be enhanced by exogenous NO.

L-Arginine-NO-cGMP signaling following acute liver injury in the rat

The incidence of liver diseases has increased over the past few years. For this reason, the consequences of induced nitric oxide (NO) synthesis in liver damages warrant further studies. To address this issue, we investigated the expression of key enzymes engaged in the control of NO signaling in the rat liver after carbon tetrachloride (CCl4) intoxication and subsequent regeneration. CCl4 intoxication resulted in up-regulation of the entire NO signal transduction machinery. Expression patterns of arginase, soluble guanylyl cyclase and cyclic nucleotide phosphodiesterase revealed striking parallels with that of NO synthase (NOS). Co-expression of the major components of the l-arginine-NO-cGMP signaling cascade both in hepatocytes and in nonparenchymal cells indicates an autocrine rather than a paracrine fashion of NO signaling in the liver. Up-regulation of NOS after CCl4 intoxication fell behind the oxidative stress and was found to be associated with the initiation of parenchymal regeneration implying a beneficial effect of NO.

Oxidative stress, lipid profile and liver functions in average Egyptian long term depo medroxy progesterone acetate (DMPA) users

Depo-medroxy progesterone acetate (DMPA, Depo-Provera) is used in more than 80 countries as a long-acting contraceptive administered as a single intramuscular(i.m) injection of 150 mg/3 months. The present study was set up to investigate the effects of DMPA on 80 average Egyptian women classified into four groups comprising those using the drug for one, two, three and four years, respectively, compared to a control group (N = 20) of married non-hormonally - treated women of similar ages. The drug showed a transient significant elevation of alanine aminotransferase activity (ALT)without an apparent effect on other liver indices, namely total bilirubin (T.Bil) level,aspartate aminotransferase (AST) and alkaline phosphatase (ALP) activities. Only the low density/high density lipoproteins cholesterol ratio (LDLC/HDLC) was gradually and non-significantly (ns) increased in comparison to control group, however, neither total cholesterol (TC) nor triglycerides (TG) were affected by the drug. The lipid peroxide product malondialdehyde (MDA) was significantly elevated in an gradual manner with a corresponding decrease in reduced glutathione (GSH), without any change in blood nitric oxide (NO) levels. It can be concluded that DMPA may be considered as a safe contraceptive medication for the studied group of women, but that special care should be exercised for cardiovascular, hepatic and other patients more sensitive to the harmful effects of free radicals. Alternatively, supportive medications are advisable for each exposed case to secure against the possible irreversible adverse effects of the drug by continuous use. In addition, annual re-evaluation is much more advisable despite the proven safety of the drug.

Gastrointestinal function regulation by nitrergic efferent nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Ventricular hypertrophy and arterial hemodynamics following deprivation of nitric oxide in rats

In the present study, we elucidated the possible role of hemodynamic parameters and chemical factors in the development of ventricular hypertrophy (VH) following chronic nitric oxide (NO) deprivation with Nomega-nitro-L-arginine methyl ester (L-NAME). Impedance spectral analysis was used to obtain the arterial hemodynamics including the steady and pulsatile components. Body weight (BW), left ventricular (LV) weight (LVW), LVW/BW ratio, LV collagen volume fraction (LVCVF), cyclic GMP, and nitrite/nitrate were measured. The extent of VH was evaluated by the LW/BW, total number, numerical density, and size of cardiomyocytes. Sprague-Dawley rats were given L-NAME 10, 20, and 40 mg/kg/day from the age of 10 to 18 weeks. Control and age-matched rats were given vehicle for the same period. Treatment of L-NAME for 8 weeks caused a dose-dependent increase in tail cuff pressure and a reduction in BW with increases in LVW, LVW/BW, number, numerical density, and size of myocytes. There was elevation of aortic pressure with decreases in cardiac output, and arterial compliance. The total peripheral resistance, characteristic impedance and pulse wave reflection were increased. Histological finding revealed severe myocardial hypertrophy and fibrosis with fibroblast infiltration. The LVCVF was increased, while LV cGMP and nitrite/nitrate were reduced in a dose-dependent manner. The results suggest that chronic NOS blockade causes hypertension, impairment of large vessel properties, and VH. The development of VH may result partly from the decreases in cGMP and nitrite/nitrate in the ventricle. Correlation analysis indicates that the extent of VH is equally related to the steady and pulsatile hemodynamics.

Asymmetric dimethylarginine and the risk of cardiovascular events and death in patients with coronary artery disease: results from the AtheroGene Study

As a competitive inhibitor of endothelial nitric oxide synthase, asymmetric dimethylarginine (ADMA) has been related to atherosclerotic disease. Little is known about the prognostic impact of baseline ADMA determination. In a prospective cohort of 1908 patients with coronary artery disease, we assessed baseline serum concentration of ADMA in 1874 consecutive patients with coronary artery disease. One hundred fourteen individuals developed the primary end point of death from cardiovascular causes or nonfatal myocardial infarction during a mean follow-up of 2.6+/-1.2 years. Median concentrations of ADMA levels were higher among individuals who subsequently developed the primary end point than among those who did not (0.70 versus 0.63 micromol/L; P<0.001). The risk of future cardiovascular event was associated with increasing thirds of baseline ADMA (P for trend, <0.001) such that individuals in the highest third at entry had a hazard ratio 2.48 times higher than those in the lowest third (95% confidence interval, 1.52 to 4.06; P<0.001). This relationship remained nearly unchanged after adjustment for most potential confounders. Prediction models that simultaneously incorporated ADMA, B-type natriuretic peptide, C-reactive protein, and creatinine in addition to traditional risk factors revealed B-type natriuretic peptide (hazard ratio, 1.96; 95% confidence interval, 1.3 to 3.0; P=0.002) and ADMA (hazard ratio, 1.90; 95% confidence interval, 1.3 to 2.8; P=0.001) as the strongest risk predictors. High levels of baseline ADMA independently predict future cardiovascular risk. ADMA has prognostic value beyond traditional risk factors and novel biomarkers and might guide therapeutic strategies.

mRNA expression and localization of bNOS, eNOS and iNOS in human cervix at preterm and term labour

BACKGROUND

Preterm birth is the primary cause of the neonatal mortality and morbidity. There will be no preterm birth without a cervical softening. Nitric oxide (NO) is shown to be a mediator of term cervical ripening. The aim of this study was to investigate mRNA expression of the three isomers of NO synthases (NOS) and to identify them by immunohistochemistry in the human cervix at preterm birth compared to term.

METHODS

The three isomers of NOS--inducible (iNOS), endothelial (eNOS) and neuronal (bNOS)--were investigated in the human cervix. The expression of mRNA was determined using Real-Time Multiplex RT-PCR. The localisation of synthases in the cervical tissue was analysed using immunohistochemistry. Cervical biopsies were obtained from 4 groups of women without clinical signs of infection: preterm (PTL), term labour (TL), preterm not in labour (PTnotL) and term not in labour (TnotL) patients. One-Way ANOVA, Kruskal-Wallis, Student t-test or Mann-Whitney test were applied as appropriate to determine statistically significant differences among the groups.

RESULTS

Patients in preterm labour had significantly (p < 0.01) higher mRNA levels of all the three NOS isomers compared to those in term labour. Women not in labour, irrespective of gestational age, thus with unripe cervices, had significantly lower eNOS mRNA levels compared to those in labour (p < 0.01). Immunoreactivity for all three NO synthases was observed in each examined sample in all groups. The bNOS staining was the most prominent.

CONCLUSION

The mRNA levels were higher in the preterm labour group compared to the women at term labour. The significant increase of the eNOS mRNA expression, from the unripe to the favourable cervical state during labour, may indicate a role of eNOS and supports the role of NO in the cervical ripening process. All the three synthases were identified by immunohistochemistry in all the groups of study.

Macrophages overexpressing tartrate-resistant acid phosphatase show altered profile of free radical production and enhanced capacity of bacterial killing

Activated macrophages and osteoclasts express high amounts of tartrate-resistant acid phosphatase (TRACP, acp5). TRACP has a binuclear iron center with a redox-active iron that has been shown to catalyze the formation of reactive oxygen species (ROS) by Fenton's reaction. Previous studies suggest that ROS generated by TRACP may participate in degradation of endocytosed bone matrix products in resorbing osteoclasts and degradation of foreign compounds during antigen presentation in activated macrophages. Here we have compared free radical production in macrophages of TRACP overexpressing (TRACP+) and wild-type (WT) mice. TRACP overexpression increased both ROS levels and superoxide production. Nitric oxide production was increased in activated macrophages of WT mice, but not in TRACP+ mice. Macrophages from TRACP+ mice showed increased capacity of bacterial killing. Recombinant TRACP enzyme was capable of bacterial killing in the presence of hydrogen peroxide. These results suggest that TRACP has an important biological function in immune defense system.

An in situ evidence for autocrine function of NO in the vasculature

The concept of endothelium derived relaxing factor (EDRF) implies that nitric oxide (NO) generated by NO synthase in the endothelium diffuses to the underlying vascular smooth muscle cells (VSMC) modulating thereby vascular tone. VSMC were regarded as passive recipients of NO from endothelial cells. However, this paradigm of a paracrine function of NO became currently subject to considerable debate. To address this issue, we examined the localization of enzymes engaged in l-arginine-NO-cGMP signaling in the rat blood vessels. Employing multiple immunocytochemical labeling complemented with signal amplification, electron microscopy, Western blotting, and RT-PCR, we found that NO synthase was differentially expressed in blood vessels depending on the blood vessel type. Moreover, the expression pattern of NO synthase in VSMC showed striking parallels with arginase and soluble guanylyl cyclase. Our findings challenge the commonly accepted view that the expression of NO synthase is restricted to vascular endothelial cells and lends further support to an alternative mechanism, by which constitutive local NOS expression in VSMC may modulate vascular functions in an endothelium-independent manner. Moreover, the co-expression of enzymes engaged in l-arginine-NO-cGMP signaling (NO synthase, arginase, and soluble guanylyl cyclase) in VSMC is indicative of an autocrine fashion of NO signaling in the vasculature in addition to the paracrine role of NO generated in the endothelium.

Local and systemic expression of inducible nitric oxide synthase in comparison with that of cyclooxygenase-2 in rat carrageenin-induced pleurisy

Expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) is up-regulated in response to inflammatory stimuli. To evaluate the extent to which local pleural inflammation involves additional site in the pleural cavity and elsewhere, we investigated the time course of the levels of iNOS and its product in the inflammatory and other sites, and compared those with a level of COX-2 in rat carrageenin-induced pleurisy. The exudate and plasma NOx levels rose, reaching peaks at 9 and 14 h, respectively. Both COX-2 and iNOS became detectable in exudate leukocytes, their levels reaching peaks at 3 and 9 h after irritation, respectively. COX-2 was detectable mainly in neutrophils, but iNOS was detectable in both neutrophils and mononuclear leukocytes. Furthermore, iNOS became detectable in neutrophils and mononuclear leukocytes in enlarged parathymic lymph nodes from 3h in addition to those in peripheral blood and Kupffer cells from 3 to 14 h, respectively. The gene product is also detectable in thymic large dendritic cells of pleurisy-induced rats as well as normal control rats. COX-2 became detectable in stellar dendritic cells of the enlarged draining lymph nodes from 14 h. Thus, these gene products were induced in the immediate proximity of regional lymph nodes, and even at a considerable distance of liver by the local inflammatory stimulus. Although their expression pattern was quite different from each other, these gene products were detectable in phagocytic cells.

Sensory nitrergic meningeal vasodilatation and non-nitrergic plasma extravasation in anaesthesized rats

The aim of the present study was to evaluate the role of nitric oxide (NO) of sensory neural origin in neurogenic inflammatory response in the trigeminovascular system. Antidromic vasodilatation and plasma extravasation in response to electrical stimulation (15 V, 5 Hz, 0.5 ms, 100 impulses) of the trigeminal ganglion were investigated in the dura mater and nasal mucosa/upper eyelid by laser Doppler flowmetry and [(125)I]-labelled bovine serum albumin, respectively. Electrical stimulation of the trigeminal ganglion of rats elicited a reproducible ipsilateral enhancement of both meningeal and nasal mucosal blood flow. N(omega)-nitro-L-arginine (L-NNA; 4, 8, and 16 mg/kg, i.v.), a nonselective inhibitor of nitric oxide synthase (NOS), inhibited antidromic vasodilatation both in the dura mater (15.86+/-2.05%, 22.82+/-2.51%, and 36.28+/-4.37%) and nasal mucosa (35.46+/-8.57%, 58.72+/-9.2%, and 89.99+/-8.94%) in a dose-dependent manner. Specific inhibitors of neuronal NOS, 7-nitroindazole (7-NI; 20 mg/kg, i.v.) and 3-bromo-7-nitroindazole (3Br-7NI; 10 mg/kg, i.v.) were administered to assess the possible role of NO released from the trigeminal sensory fibres. The meningeal vasodilatation was inhibited by both 3Br-7NI and 7-NI (63.36+/-7.7% and 49+/-6.5%, respectively). The nasal hyperaemic response was also reduced by 3Br-7NI (78.26+/-8.7%). Plasma extravasation in the dura mater and upper eyelid evoked by electrical stimulation of the trigeminal ganglion (25 V, 5 Hz, 0,5 ms, 5 min), expressed as extravasation ratios (ERs) of the stimulated vs. nonstimulated sides, was 1.80+/-0.8 and 4.63+/-1.24, respectively. This neurogenic oedema formation was not inhibited by neither L-NNA nor 3Br-7NI. It is concluded that neural nitrergic mechanisms are involved in the meningeal vasodilatation evoked by electrical stimulation of the trigeminal ganglion.

Protection of endothelial function

The vascular endothelium synthesizes and releases a spectrum of vasoactive substances and therefore plays a fundamental role in the basal and dynamic regulation of the circulation. Nitric oxide (NO)--originally described as endothelium-derived relaxing factor--is released from endothelial cells in response to shear stress produced by blood flow, and in response to activation of a variety of receptors. After diffusion from endothelial to vascular smooth muscle cells, NO increases intracellular cyclic guanosine-monophosphat concentrations by activation of the enzyme guanylate cyclase leading to relaxation of the smooth muscle cells. NO has also antithrombogenic, antiproliferative, leukocyte-adhesion inhibiting effects, and influences myocardial contractility. Endothelium-derived NO-mediated vascular relaxation is impaired in spontaneously hypertensive animals. NO decomposition by free oxygen radicals is a major mechanism of impaired NO bioavailability. The resulting imbalance of endothelium-derived relaxing and contracting substances disturbs the nor- mal function of the vascular endothelium. Endothelin acts as the natural counterpart to endothelium-derived NO. In man, besides its effect of increasing arterial blood pressure, ET-1 induces vascular and myocardial hypertrophy, which are independent risk factors for cardiovascular morbidity and mortality. Current therapeutic strategies concentrate mainly on lowering of low-density lipoprotein cholesterol and an impressive reduction in the risk for cardiovascular morbidity and mortality has been achieved. Inflammatory mechanisms play an important role in vascular disease and inflammatory plasma markers correlate with prognosis. Novel therapeutic strategies specifically targeting inflammation thus bear great potential for the prevention and treatment of atherosclerotic vascular disease.

Endothelium-dependent vasorelaxing activity of aqueous extracts of lyophilized seeds of Casimiroa edulis (AECe) on rat mesenteric arterial bed

The vasorelaxing activity of the aqueous extracts of Casimiroa edulis seeds F(AECe) on mesenteric arterial bed (MAB) of rats was studied. MAB precontracted with methoxamine was mounted on a tissue bath and exposed to plant extracts (bolus 50, 500, 2500 and 5000 microg). The bolus injections of AECe significantly inhibited, in a concentration-dependent manner, the maximal contractile response induced by methoxamine (30 microm) in MAB. After endothelium removal, the vascular ability of Casimiroa edulis aqueous extract was significantly changed. Treatment with an inhibitor of NO synthase (L-NOA, 10 microM) also modified the AECe effect. The guanilate cyclase inhibitor methylene blue (MB, 100 microM) inhibited the AECe-induced vasodilatation. These results suggest the involvement of NO of endothelial source (or related factors) in this vasodilator effect.

In vivo administration of d-arginine: effects on blood pressure and vascular function in angiotensin II-induced hypertensive rats

OBJECTIVE

We tested the hypothesis that D-arginine (D-Arg), which is not a substrate for nitric oxide synthase but scavenges reactive oxygen in vitro, is protective in vivo.

METHODS

Rats were made hypertensive by administering angiotensin II (Ang II) (0.7mg kg(-1) per day) for 7 days (Ang II group). Two other groups additionally received either 3 mmol D-Arg (Ang II + D-Arg group) or vitamin C (1g) (Ang II + Vit C group) per day. Sham-operated animals served as controls (n = 6-9). Systolic blood pressure was monitored daily and cardiovascular function determined ex vivo at 7 days.

RESULTS

Ang II raised systolic blood pressure to 184mmHg, the increase was slightly attenuated by D-Arg treatment (-17mmHg; P < 0.05 versus Ang II alone) and prevented by Vit C. Acetylcholine-induced coronary relaxation was impaired in the Ang II group (P < 0.05 versus sham), the impairment was no different in the Ang II + D-Arg group, but prevented by Vit C. Likewise, Vit C but not D-Arg ameliorated reperfusion endothelium-dependent relaxation. However, in aortic rings D-Arg slightly improved acetylcholine relaxation (P < 0.05). Oxidative stress load estimated in plasma with thiobarbituric acid reactive substance was higher in the Ang II than the sham group, Vit C abolished the increase, but D-Arg was without effect.

CONCLUSION

D-Arg is weakly antihypertensive in vivo and ameliorates aortic, but not coronary endothelium-dependent relaxation ex vivo. Because D-Arg had no effect on plasma oxidant status, this protection appears to be independent of reactive oxygen scavenging activity.

Effect of exercise training on endothelium-derived nitric oxide function in humans

Vascular endothelial function is essential for maintenance of health of the vessel wall and for vasomotor control in both conduit and resistance vessels. These functions are due to the production of numerous autacoids, of which nitric oxide (NO) has been the most widely studied. Exercise training has been shown, in many animal and human studies, to augment endothelial, NO-dependent vasodilatation in both large and small vessels. The extent of the improvement in humans depends upon the muscle mass subjected to training; with forearm exercise, changes are restricted to the forearm vessels while lower body training can induce generalized benefit. Increased NO bioactivity with exercise training has been readily and consistently demonstrated in subjects with cardiovascular disease and risk factors, in whom antecedent endothelial dysfunction exists. These conditions may all be associated with increased oxygen free radicals which impact on NO synthase activity and with which NO reacts; repeated exercise and shear stress stimulation of NO bioactivity redresses this radical imbalance, hence leading to greater potential for autacoid bioavailability. Recent human studies also indicate that exercise training may improve endothelial function by up-regulating eNOS protein expression and phosphorylation. While improvement in NO vasodilator function has been less frequently found in healthy subjects, a higher level of training may lead to improvement. Regarding time course, studies indicate that short-term training increases NO bioactivity, which acts to homeostatically regulate the shear stress associated with exercise. Whilst the increase in NO bioactivity dissipates within weeks of training cessation, studies also indicate that if exercise is maintained, the short-term functional adaptation is succeeded by NO-dependent structural changes, leading to arterial remodelling and structural normalization of shear. Given the strong prognostic links between vascular structure, function and cardiovascular events, the implications of these findings are obvious, yet many unanswered questions remain, not only concerning the mechanisms responsible for NO bioactivity, the nature of the cellular effect and relevance of other autacoids, but also such practical questions as the optimal intensity, modality and volume of exercise training required in different populations.

Adaptive cytoprotection through modulation of nitric oxide in ethanol-evoked gastritis

AIM: To assess the mechanisms of protective action by different mild irritants through maintenance of gastric mucosal integrity and modulation of mucosal nitric oxide (NO) in experimental gastritis rats.

METHODS: Either 200 mL/L ethanol, 50 g/L NaCl or 0.3 mol/L HCl was pretreated to normal or 800 mL/L ethanol-induced acute gastritis Sprague-Dawley rats before a subsequent challenge with 500 mL/L ethanol. Both macroscopic lesion areas and histological damage scores were determined in the gastric mucosa of each group of animals. Besides, gastric mucosal activities of NO synthase isoforms and of superoxide dismutase, along with mucosal level of leukotriene (LT)C₄ were measured.

RESULTS: Macroscopic mucosal damages were protected by 200 mL/L ethanol and 50 g/L NaCl in gastritis rats. However, although 200 mL/L ethanol could protect the surface layers of mucosal cells in normal animals (protection attenuated by N^G-nitro-L-arginine methyl ester), no cytoprotection against deeper histological damages was found in gastritis rats. Besides, inducible NO synthase activity was increased in the mucosa of gastritis animals and unaltered by mild irritants. Nevertheless, the elevation in mucosal LTC₄ level following 500 mL/L ethanol administration and under gastritis condition was significantly reduced by pretreatment of all three mild irritants in both normal and gastritis animals.

CONCLUSION: These findings suggest that the aggravated 500 mL/L ethanol-evoked mucosal damages under gastritis condition could be due to increased inducible NO and LTC₄ production in the gastric mucosa. Only 200 mL/L ethanol is truly “cytoprotective” at the surface glandular level of non-gastritis mucosa. Furthermore, the macroscopic protection of the three mild irritants involves reduction of LTC₄ level in both normal and gastritis mucosa, implicating preservation of the vasculature.

Hypercholesterolemia impairs basal nitric oxide synthase turnover rate: a study investigating the conversion of l-[guanidino-15N2]-arginine to 15N-labeled nitrate by gas chromatography–mass spectrometry

Endothelial function is impaired in hypercholesterolemia and atherosclerosis, which is probably due to reduced biological activity of endothelium-derived nitric oxide (NO). NO is synthesized in functionally intact endothelium by oxidation of the terminal guanidino nitrogen atom(s) of the amino acid precursor, L-arginine. We applied stable isotope dilution techniques and gas chromatographic-mass spectrometric approaches to investigate metabolism of L-[guanidino-(15)N(2)]-arginine to (15)N-labeled nitrate in hypercholesterolemic rabbits and controls. After 4 weeks on control or 1% cholesterol-enriched diet, rabbits received 267 +/- 6 micromol of L-[guanidino-(15)N(2)]-arginine/kg of body weight via gastric cannulation. (15)N-isotope content of L-arginine in plasma and in platelet lysates increased 2h later in both groups, and almost returned to baseline until 24h. (15)N-isotope content of plasma nitrite and nitrate also increased in both groups at 2h, and had almost returned to natural content 24h later. (15)N-isotope content of urinary nitrate was significantly increased in control animals in urines collected from 0 to 12, 12 to 24, and had returned to baseline in the urine sample collected from 24 to 48 h. In the cholesterol group only a slight, insignificant elevation of (15)N-isotope content was observed for urinary nitrate. The extent of conversion of L-[guanidino-(15)N(2)]-arginine to (15)N-labeled nitrate was strongly and inversely correlated to plasma concentration of the endogenous NO synthase inhibitor, asymmetric dimethylarginine (ADMA), which was elevated in cholesterol-fed rabbits (R=0.77; p < 0.05). Our data show that baseline NO synthase turnover rate is reduced in rabbits during early hypercholesterolemia. Our study gives evidence that the mechanism of the impaired conversion of L-[guanidino-(15)N(2)]-arginine to (15)N-labeled nitrate most likely involves inhibition of NO synthase by ADMA, which is present in elevated concentrations in hypercholesterolemia.

Modulation of eosinophil migration from bone marrow to lungs of allergic rats by nitric oxide

Chronic blockade of nitric oxide (NO) synthesis attenuates the eosinophil infiltration into airways of allergic rats. This study was designed to investigate whether the inhibition of eosinophil influx to the lung of allergic rats reflects modifications in the pattern of cell mobilization from the bone marrow to peripheral blood and/or to lung. Male Wistar rats were treated with N(omega)-nitro-l-arginine methyl ester (l-NAME; 20mg/rat per day) for 4 weeks and sensitized with ovalbumin (OVA). In control rats, the pulmonary OVA-challenge promoted an early (24h) increase in the bone marrow eosinophil population that normalized at 48 h after OVA-challenge, at which time the eosinophils disappeared from the blood and reached the lungs in mass. In l-NAME-treated rats, an accumulation of eosinophils in bone marrow was observed at 24 and 48 h post-OVA-challenge. No variation in this cell type number was observed in peripheral blood and bronchoalveolar lavage throughout the time-course studied. In control rats, the adhesion of bone marrow eosinophils to fibronectin-covered wells was significantly increased at 24h after OVA-challenge, whereas in l-NAME-treated rats the increased adhesion was detected at 48 h. A 32% decrease in the expression of inducible nitric oxide synthase (iNOS) (but not endothelial nitric oxide synthase; eNOS) in eosinophils from l-NAME-treated rats was observed. The levels of IgE, IgG(1) and IgG(2a) were not affected by the l-NAME treatment. Our findings suggest that inhibition of NO synthesis upregulates the binding of eosinophils to extracellular matrix proteins such as fibronectin, producing a delayed efflux of eosinophils from bone marrow to peripheral blood and lungs.

In vivo spin trapping of nitric oxide

The measurement of nitric oxide (NO) in biological samples has normally required destructive chemical techniques. The ability to detect NO non-invasively in living animals or excised organs has great potential using specialized electron paramagnetic resonance (EPR) methods. Although NO is paramagnetic, it cannot be observed directly unless it is complexed with ferrous iron-dithiocarbamate ligand spin trap complexes. Despite the minimally invasive nature of the technique, highly sensitive localized concentrations of NO may be observed ("trapped") in vivo by both L-band EPR and magnetic resonance imaging.

Basic Science and Dialysis: Nitric Oxide and Hemodialysis

Nitric oxide (NO), previously thought of as a noxious gas, is now recognized as an important mediator of vascular responsiveness. Soon after its discovery, it was realized that the actions of NO are similar to the previously described endothelium-derived relaxing factor (EDRF). It is synthesized in the vascular endothelium utilizing the enzyme nitric oxide synthase (NOS) and diffuses in the adjacent vascular media, where it has a vasodilatory action. Opposing actions of NO and vasoconstrictor agents (such as endothelin-1, angiotensin IotaIota, and others) maintain the vascular tone of the renal arteries. The same balance at the level of the macula densa maintains glomerular filtration rate (GFR) during varying levels of salt excretion. Lack of NO can result in disruption of this fine balance, with resultant vasoconstriction and disease progression, hypertension, and accelerated atherosclerosis. In addition, hypertension may result from positive salt balance that occurs when macula densa NOS is inhibited. While most investigators report low levels of NO in uremic subjects, the levels in hemodialysis (HD) patients have not been characterized adequately. This is primarily because HD patients are exposed to both stimulatory and inhibitory factors for NO synthesis. Retention of inhibitors of NOS tends to decrease NO levels, whereas production of NO will be increased by cytokines generated during blood-dialyzer interaction. There is less disagreement, however, over the finding of elevated levels in those with dialyzer reactions and dialysis-induced hypotension. Recent developments in the isolation of inducible and constitutive forms of NOS makes understanding of its pathophysiologic effects more complete. Newer treatment directed at inhibiting only the inducible forms of NOS (sparing the constitutive forms) may soon be found useful for the treatment and prevention of hypotension and dialyzer reactions in HD patients.

Exercise and the nitric oxide vasodilator system

In the past two decades, normal endothelial function has been identified as integral to vascular health. The endothelium produces numerous vasodilator and vasoconstrictor compounds that regulate vascular tone; the vasodilator, nitric oxide (NO), has additional antiatherogenic properties, is probably the most important and best characterised mediator, and its intrinsic vasodilator function is commonly used as a surrogate index of endothelial function. Many conditions, including atherosclerosis, diabetes mellitus and even vascular risk factors, are associated with endothelial dysfunction, which, in turn, correlates with cardiovascular mortality. Furthermore, clinical benefit and improved endothelial function tend to be associated in response to interventions. Shear stress on endothelial cells is a potent stimulus for NO production. Although the role of endothelium-derived NO in acute exercise has not been fully resolved, exercise training involving repetitive bouts of exercise over weeks or months up-regulates endothelial NO bioactivity. Animal studies have found improved endothelium-dependent vasodilation after as few as 7 days of exercise. Consequent changes in vasodilator function appear to persist for several weeks but may regress with long-term training, perhaps reflecting progression to structural adaptation which may, however, have been partly endothelium-dependent. The increase in blood flow, and change in haemodynamics that occur during acute exercise may, therefore, provide a stimulus for both acute and chronic changes in vascular function. Substantial differences within species and within the vasculature appear to exist. In humans, exercise training improves endothelium-dependent vasodilator function, not only as a localised phenomenon in the active muscle group, but also as a systemic response when a relatively large mass of muscle is activated regularly during an exercise training programme. Individuals with initially impaired endothelial function at baseline appear to be more responsive to exercise training than healthy individuals; that is, it is more difficult to improve already normal vascular function. While improvement is reflected in increased NO bioactivity, the detail of mechanisms, for example the relative importance of up-regulation of mediators and antioxidant effects, is unclear. Optimum training schedules, possible sequential changes and the duration of benefit under various conditions also remain largely unresolved. In summary, epidemiological evidence strongly suggests that regular exercise confers beneficial effects on cardiovascular health. Shear stress-mediated improvement in endothelial function provides one plausible explanation for the cardioprotective benefits of exercise training.

Oxidative stress and aging

Free radical-derived reactive oxygen species (ROS) are constantly generated in most living tissue and can potentially damage DNA, proteins and lipids. "Oxidative stress" occurs if ROS reach abnormally high concentrations. Harman was the first to propose that the damaging effects of ROS may play a key role in the mechanism of aging. Genetic studies of such distantly related species as C. elegans, Drosophila melanogaster, and mice support this hypothesis. However, ROS are not only a cause of structural damage, but also physiologically important mediators in biological signaling processes. Abnormally high levels of ROS may therefore lead to dysregulation of redox-sensitive signaling pathways. The redox-sensitive targets in these pathways are often signaling proteins with redox-sensitive cysteine residues which are oxidized to sulfenic acid moieties and mixed disulfides, thereby altering the signaling function of the protein. Because the formation of these mixed disulfides can also occur through a prooxidative shift in the intracellular thiol/disulfide redox status (REDST), the respective signaling pathways respond not only to ROS but also to changes in REDST. Information about the concentration of ROS in living tissue is scarce, but aging-related changes in REDST are well documented. Several studies with cell cultures or experimental animals have shown that the oxidative shift in the intracellular glutathione REDST is typically associated with cellular dysfunction. Complementary studies in humans have shown that oxidative changes in the plasma (i.e., extracellular) REDST are correlated with aging-related pathophysiological processes. The available evidence suggests that these changes play a key role in various conditions which limit the human life span. Several attempts have been made to ameliorate the consequences of aging by thiol-containing antioxidants, but this approach requires a detailed knowledge of the effects of thiol-containing antioxidants on cysteine homeostasis, REDST, and redox-sensitive signaling pathways of the host.

Platelet cGMP inversely correlates with age in healthy subjects

Biochemical modifications associated with the increase in platelet activity with age are not well defined. Furthermore it is well known that the nitric oxide/cyclic 3', 5'-guanosine monophosphate (cGMP) pathway regulates platelet aggregation. The aim of the present study was to examine the relationship between platelet content of cGMP and age. 120 normal subjects, evaluating the cGMP platelet concentration, 17betaE2, IGF-I, dehydroepiandrosterone sulphate (DHEAS), insulin, plasma glucose, lipid pattern, homocysteine and PAI-I antigen, were studied. The multivariate analysis in a model with cGMP as dependent variable and with age, LDL, apolipoprotein B (ApoB), DHEAS, E2 and insulin-like growth factor (IGF)-I as independent variables shows a negative correlation between cGMP and age (p<0.01, beta=-0.388). In conclusion our data suggest that the reduced efficiency of the system constitutive nitric oxide synthase (cNOS)/guanylate cyclase represents at least one of the reasons of the increased platelet aggregability with age.

Vascular endothelium is the organ chiefly responsible for the catabolism of plasma asymmetric dimethylarginine – an explanation for the elevation of plasma ADMA in disorders characterized by endothelial dysfunction

Plasma levels of asymmetric dimethylarginine (ADMA), an endogenously produced competitive inhibitor of nitric oxide synthase (NOS), have been found to be elevated in a large number of disorders characterized by endothelial dysfunction; this remarkable phenomenon has yet to receive a plausible explanation. ADMA arises by proteolysis of methylated proteins throughout the body; the majority of this ADMA is catabolized by the enzyme dimethylarginine dimethylaminohydrolase (DDAH), found in many tissues, including those that express NOS. Since the production of ADMA can be considered constitutive, and little intact ADMA emerges in the urine, impaired catabolism is most likely responsible for elevations of plasma ADMA. The association of elevated ADMA with endotheliopathy is readily explained if we assume that vascular endothelium is the organ chiefly responsible for the catabolism of plasma ADMA--a view that is credible owing to the privileged access of endothelium to plasma, the capacity of endothelium for active transport of arginine (and methylated arginines), and the ample DDAH activity of healthy endothelial cells--and further assume that endothelial dysfunction is often attended by a loss of DDAH activity and/or an impairment of arginine transport, reducing the efficiency of ADMA catabolism. Indeed, there is recent evidence that DDAH is inhibited by endothelial oxidative stress, a typical feature of endotheliopathy; there is also some reason to suspect that arginine transport may be less efficient in dysfunctional endothelium. From this perspective, increased plasma ADMA is not the primary cause of the endothelial dysfunction in various disorders, but rather its effect--though the rise in ADMA can then exacerbate this dysfunction by inhibiting endothelial NOS. Supplemental arginine should be of some clinical benefit in disorders characterized by elevated ADMA, since it can offset that adverse impact of ADMA on NOS activity, and possibly exert other beneficial effects on endothelium--but it cannot be expected to reverse the primary cause of the endothelial dysfunction. Whether or not ADMA plays an important pathogenic role, it seems likely to emerge as a potent risk factor for adverse vascular events, since it may be viewed as a barometer of endothelial health.

Gestational diabetes affects platelet behaviour through modified oxidative radical metabolism

AIMS

Patients with Type 1 and Type 2 diabetes mellitus show altered platelet function including decreased nitric oxide synthase (NOS) activity and increased peroxynitrite production. Gestational diabetes mellitus (GDM) is a clinical condition which is ideal for evaluating short-term effects of impaired glucose metabolism, ruling out the possibility that the platelet abnormalities are a consequence of diabetic complications. The aim of the present work was to study NO metabolism in platelets from pregnant women with GDM. The production of peroxides was also studied as it is strongly involved in peroxynitrite formation.

METHODS

Platelet NOS activity and peroxynitrite production, levels of hydroperoxides and thiobarbituric acid reactive substances (TBARS) in platelet membranes in the basal state and after in vitro peroxidative stress with phenylhydrazine were determined in 40 pregnant women with GDM, 40 healthy pregnant women (pregnant controls) of comparable age and gestational age, and 15 healthy non-pregnant women (controls).

RESULTS

NOS activity was significantly increased in both groups of pregnant women compared with non-pregnant ones, and in GDM women compared with pregnant controls. Production of peroxynitrite was higher in GDM women than in pregnant controls, who also had significantly reduced production compared with non-pregnant women. Basal levels of peroxidation of the platelet membranes evaluated either by hydroperoxide content and TBARS levels or the susceptibility to peroxidation were increased in GDM patients in comparison with both control groups.

CONCLUSIONS

We have shown a modification in platelet NO and peroxynitrite production and an increase in platelet indicators of oxidative stress in GDM women compared with healthy pregnant women which might be at the basis of a cellular dysfunction.

Expression of endothelial and inducible nitric oxide synthases is modulated in the endometrium of cyclic and early pregnant mares

The expression of the endothelial and inducible nitric oxide synthases (eNOS and iNOS, respectively) was examined in the endometrium of cyclic and pregnant mares by real-time polymerase chain reaction and immunohistology. The concentration of eNOS mRNA varied throughout the oestrous cycle, with significantly higher transcripts on Day 5 of the oestrous cycle (P < 0.05), whereas iNOS transcription did not change significantly over time (P > 0.05). In early pregnant mares both eNOS and iNOS mRNA increased between Days 12 and 15 (P < 0.05). In cyclic mares, eNOS protein was detected immunocytochemically in endometrial epithelia, the basement membrane, the endothelial layer and smooth muscle cells of the vasculature. Using immunocytochemical methods, iNOS protein was undetectable in the endometrium of cyclic mares but could be demonstrated in pregnant mares. Endometrial epithelia of pregnant mares were immunopositive for both proteins with a more intense labelling for iNOS. Thus, the present study describes for the first time the modulation and spatial distribution of eNOS and iNOS expression during the oestrous cycle and early pregnancy, suggesting that ovarian steroids are differently involved in the regulation of each NOS. Localisation of eNOS protein in endometrial epithelia and various vascular components indicates that this isoform may be involved in the regulation of endometrial cyclicity. The presence and increase of both forms of NOS during early gestation suggest a role for them in the control of endometrial vascular bed and glandular activity to provide a suitable microenvironment for successful pregnancy.

Nitric oxide formation contributes to beta-adrenergic dilation of epicardial coronary arteries in response to intravenous administration of dobutamine in dogs

To examine the role of nitric oxide in the beta-adrenergic vasodilation of epicardial coronary arteries in dogs, 12 dogs were instrumented for measurement of left anterior descending coronary artery diameter by transthoracic echocardiography before and after dobutamine (5 microg/kg/min IV) with and without intracoronary infusion of NG-monomethyl-L-arginine (L-NMMA) (1 mg/kg). In all 12 dogs, the diameter of left anterior descending coronary artery increased significantly from 2.35 +/- 0.25 mm to 2.59 +/- 0.24 mm (P<0.001) after dobutamine administration. In 6 of the 12 dogs, the percent change in left anterior descending coronary artery diameter induced by dobutamine decreased significantly from 12.5% +/- 8.6% to -1.5% +/- 5.4% (P<0.05) after the administration of intracoronary L-NMMA (1 mg/kg for 5 min) to block nitric oxide synthesis from L-arginine. The study demonstrated that nitric oxide formation contributes to the beta-adrenergic dilatory response of epicardial coronary arteries to dobutamine in dogs.

Nitric oxide synthase inhibition does not affect regulation of muscle sympathetic nerve activity during head-up tilt

To test the hypothesis that systemic inhibition of nitric oxide (NO) synthase does not alter the regulation of sympathetic outflow during head-up tilt in humans, in eight healthy subjects NO synthase was blocked by intravenous infusion of NG-monomethyl-L-arginine (L-NMMA). Blood pressure, heart rate, cardiac output, total peripheral resistance (TPR), and muscle sympathetic nerve activity (MSNA) were recorded in the supine position and during 60 degrees head-up tilt. In the supine position, infusion of L-NMMA increased blood pressure, via increased TPR, and inhibited MSNA. However, the increase in MSNA evoked by head-up tilt during L-NMMA infusion (change in burst rate: 24 +/- 4 bursts/min; change in total activity: 209 +/- 36 U/min) was similar to that during head-up tilt without L-NMMA (change in burst rate: 23 +/- 4 bursts/min; change in total activity: 251 +/- 52 U/min, n = 6, all P > 0.05). Moreover, changes in TPR and heart rate during head-up tilt were virtually identical between the two conditions. These results suggest that systemic inhibition of NO synthase with L-NMMA does not affect the regulation of sympathetic outflow and vascular resistance during head-up tilt in humans.

Inducible nitric oxide synthase is involved in corticotropin-releasing hormone-mediated central sympatho-adrenal outflow in rats

Brain nitric oxide (NO), recognized as a neurotransmitter or a neuromodulator, is mainly generated either by neuronal NO synthase (NOS) or by inducible NOS. NO has been shown to activate cyclooxygenase (a prostaglandin-forming enzyme) in addition to guanylate cyclase. Recently, we reported that the intracerebroventricularly (i.c.v.) administered corticotropin-releasing hormone (CRH) increases plasma catecholamines through brain cyclooxygenase-dependent mechanisms in rats. In the present experiments, therefore, we examined whether NO is involved in the CRH-induced increase of plasma catecholamines using urethane-anesthetized rats. I.c.v. administered CRH increased plasma noradrenaline and adrenaline in a dose-dependent manner (0.5, 1.5, and 3.0 nmol/animal). The CRH (1.5 nmol/animal, i.c.v.)-induced increase of plasma catecholamines was reduced by N(omega)-nitro-L-arginine methyl ester (a non-selective inhibitor of NOS) [111 nmol (30 microg)/animal, i.c.v.], but not by the same dose of N(omega)-nitro-D-arginine methyl ester (an inactive isomer of N(omega)-nitro-L-arginine methyl ester). The CRH-induced increase of plasma catecholamines was also reduced either by cycloheximide (an inhibitor of protein synthesis) [107 nmol (30 microg)/animal, i.c.v.] or by S-methylisothiourea (an inhibitor of inducible NOS) [71 nmol (20 microg) and 711 nmol (200 microg)/animal, i.c.v.]. These results suggest the involvement of brain inducible NOS in the CRH-induced activation of the central sympatho-adrenomedullary outflow in rats.

[Endothelium-derived factors in hypertensive blood vessels, especially nitric oxide and hypertension]

Endothelium-dependent relaxation (EDR) in the blood vessels of spontaneously hypertensive rats (SHR) and the role of nitric oxide (NO) in the initiation of hypertension are reviewed. EDR was impaired in blood vessels of SHR depending on age and degree of hypertension when compared with those of normotensive rats. The cause of the impairment varied among the type of blood vessels: a decrease in the production of NO and endothelium-derived relaxing factor (EDRF) and an increase in the production of endothelium-derived contracting factor (EDCF) are the main causes of the impairment in large arteries, while a decrease in endothelium-dependent hyperpolarization and increased release of EDCF are the main causes of the impairment in small arteries. Interactions among these endothelium-derived factors and changes in the interactions are also causes of impairment. Superoxide may be involved in the impairment of EDR by destroying NO. The endothelium depresses smooth muscle contraction, including spontaneous tone developed in vascular smooth muscle, and the depressing effect of the endothelium is impaired in the preparations from SHR. The endothelium of blood vessels of SHR are structurally injured as demonstrated by scanning electron microscopy. Antihypertensive treatment prevented these functional and structural changes. Chronic treatment with inhibitors of NO production in normotensive rats impaired EDR and elevated blood pressure. The impairment of EDR is a secondary change due to continued hypertension, and early initiation of antihypertensive therapy is recommended.

Comparative regional haemodynamic effects of the nitric oxide synthase inhibitors, S-methyl-L-thiocitrulline and L-NAME, in conscious rats

1. The regional haemodynamic effects of the putative nNOS inhibitor, S-methyl-L-thiocitrulline (SMTC), were compared with those of the nonselective NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), in conscious, male Sprague-Dawley rats. 2. SMTC (0.3 mg kg(-1) bolus) produced a significant, short-lived, pressor effect associated with renal, mesenteric and hindquarters vasoconstriction; the same dose of L-NAME did not affect mean blood pressure (BP), although it caused bradycardia and mesenteric vasoconstriction. 3. At the highest dose tested (10 mg kg(-1)), L-NAME produced a significantly greater bradycardia and fall in mesenteric vascular conductance than SMTC, although the initial pressor response to SMTC was greater, but less sustained, than that to L-NAME. 4. Infusion of SMTC or L-NAME (3 mg kg(-1) h(-1)) induced rises in BP and falls in renal, mesenteric and hindquarters vascular conductances, but the effects of L-NAME were greater than those of SMTC, and L-NAME also caused bradycardia. 5. The renal vasodilator response to acetylcholine was markedly attenuated by infusion of L-NAME, but unaffected by SMTC. The hindquarters vasodilatation induced by salbutamol was attenuated by L-NAME, but not by SMTC. The mesenteric vasodilator response to bradykinin was modestly enhanced by SMTC, but not by L-NAME. The depressor and renal, mesenteric and hindquarters vasodilator responses to sodium nitroprusside were enhanced by L-NAME, whereas SMTC modestly enhanced the hypotensive and renal vasodilator effects of sodium nitroprusside, but attenuated the accompanying tachycardia. 6. The results are consistent with the cardiovascular effects of low doses of SMTC being attributable to nNOS inhibition.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Exercise training improves ageing-induced decrease in eNOS expression of the aorta

AIMS

Ageing impairs endothelial function such as the regulation of vascular tone. The release of nitric oxide (NO), which has a potent vasodilator effect and antiatherosclerotic property, is decreased in the aorta of aged rats. Exercise training, however, has been reported to increase the expression of endothelial NO synthase (eNOS) in the aorta of young rats. In aged rats, it is not known whether the expression of eNOS is altered by exercise training. We hypothesized that exercise training would improve the ageing-induced decrease in eNOS expression in vessels, and examined the messenger RNA (mRNA) and protein expression of eNOS in the aorta of sedentary-young rats (sedentary-young group; 4 months old), sedentary-aged rats (sedentary-aged group; 23 months old), and swim-trained aged rats (training-aged group; 23 months old, swimming training for 8 weeks, 5 days week(-1), 90 min day(-1)).

RESULTS

Body weight was significantly lower, and citrate synthase activity in the epitrochlearis muscle was significantly higher in the training-aged group compared with the sedentary-aged group. The mRNA expression of eNOS in the aorta was significantly higher in the training-aged group than in the sedentary-aged group, while it was significantly lower in both the sedentary-aged and training-aged groups than in the sedentary-young group. The expression of eNOS protein in the aorta was also significantly higher in the training-aged group than in the sedentary-aged group, while it was also significantly lower in the sedentary-aged group, but not in the training-aged group, than in the sedentary-young group.

CONCLUSION

The present results revealed that the production of eNOS in the aorta decreases with ageing, and that the decreased production is increased by exercise training in aged rats, which may produce beneficial effects on the impaired cardiovascular system caused by ageing.

Transport of L-arginine and nitric oxide formation in human platelets

The results of the present study show that human platelets take up l-arginine by two transport systems which are compatible with the systems y+ and y+L. These Na+independent transporters have been distinguished by treating platelets with N-ethylmaleimide that blocks selectively system y+. System y+, that accounts for 30-40% of the total transport, is characterized by low affinity for l-arginine, is unaffected by l-leucine, is sensitive to changes of membrane potential and to trans-stimulation. The other component of l-arginine transport identified with the system y+L (approximately 60-70% of the total flux) shows high affinity for l-arginine, is insensitive to N-ethylmaleimide treatment, unaffected by changes in membrane potential, sensitive to trans-stimulation and inhibited by l-leucine in the presence of Na+. Moreover a strict correlation between l-arginine transport and nitric oxide (NO) production in whole cells was found. N-ethylmaleimide and l-leucine decreased NO production as well as cGMP elevation, and the effect on NO and cGMP were closely related. It is likely that the l-arginine transport systems y+ and y+L are both involved in supplying substrate for NO production and regulation in human platelets.

Stimulated murine macrophages as a bioassay for H. pylori-related inhibition of nitric oxide production

BACKGROUND

Interference with the L-arginine/nitric oxide pathway may be a virulence strategy for the gastric pathogen Helicobacter pylori. This study evaluates a bioassay for such inhibitory actions on nitric oxide synthase.

METHODS

Cultured murine macrophages were stimulated by lipopolysaccharide and interferon-gamma. Nitric oxide synthesis and the expression of inducible nitric oxide synthase (iNOS) at increasing concentrations of L-arginine were analysed using chemiluminescence and Western blotting, respectively.

RESULTS

The bioassay was evaluated against nitrite accumulation and two established NOS inhibitors. Bacterial extracts or whole cells of one H. pylori strain inhibited nitric oxide production at low L-arginine concentrations (2-20 microM). A higher concentration of L-arginine (200 microM) was not associated with such inhibition. The iNOS expression was not affected by any of the additives compared to stimulated controls.

CONCLUSIONS

This bioassay is a reliable and simple method for analysing iNOS inhibition, resolving effects on enzyme activity or enzyme expression. H. pylori water extract and whole cells exert an L-arginine-dependent NOS inhibition, not influencing iNOS expression.