Inducible but not constitutive production of nitric oxide by vascular smooth muscle cells

Nitric oxide donors (nitrates), L-arginine, or nitric oxide synthase inhibitors for acute stroke

BACKGROUND

Nitric oxide (NO) has multiple effects that may be beneficial in acute stroke, including lowering blood pressure, and promoting reperfusion and cytoprotection. Some forms of nitric oxide synthase inhibition (NOS-I) may also be beneficial. However, high concentrations of NO are likely to be toxic to brain tissue. This is an update of a Cochrane review first published in 1998, and last updated in 2002.

OBJECTIVES

To assess the safety and efficacy of NO donors, L-arginine, and NOS-I in people with acute stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (last searched 6 February 2017), MEDLINE (1966 to June 2016), Embase (1980 to June 2016), ISI Science Citation Indexes (1981 to June 2016), Stroke Trials Registry (searched June 2016), International Standard Randomised Controlled Trial Number (ISRCTN) (searched June 2016), Clinical Trials registry (searched June 2016), and International Clinical Trials Registry Platform (ICTRP) (searched June 2016). Previously, we had contacted drug companies and researchers in the field.

SELECTION CRITERIA

Randomised controlled trials comparing nitric oxide donors, L-arginine, or NOS-I versus placebo or open control in people within one week of onset of confirmed stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria, assessed trial quality and risk of bias, and extracted data. The review authors cross-checked data and resolved issues through discussion. We obtained published and unpublished data, as available. Data were reported as mean difference (MD) or odds ratio (OR) with 95% confidence intervals (CI).

MAIN RESULTS

We included five completed trials, involving 4197 participants; all tested transdermal glyceryl trinitrate (GTN), an NO donor. The assessed risk of bias was low across the included studies; one study was double-blind, one open-label and three were single-blind. All included studies had blinded outcome assessment. Overall, GTN did not improve the primary outcome of death or dependency at the end of trial (modified Rankin Scale (mRS) > 2, OR 0.97, 95% CI 0.86 to 1.10, 4195 participants, high-quality evidence). GTN did not improve secondary outcomes, including death (OR 0.78, 95% CI 0.40 to 1.50) and quality of life (MD -0.01, 95% CI -0.17 to 0.15) at the end of trial overall (high-quality evidence). Systolic/diastolic blood pressure (BP) was lower in people treated with GTN (MD -7.2 mmHg (95% CI -8.6 to -5.9) and MD -3.3 (95% CI -4.2 to -2.5) respectively) and heart rate was higher (MD 2.0 beats per minute (95% CI 1.1 to 2.9)). Headache was more common in those randomised to GTN (OR 2.37, 95% CI 1.55 to 3.62). We did not find any trials assessing other nitrates, L-arginine, or NOS-I.

AUTHORS' CONCLUSIONS

There is currently insufficient evidence to recommend the use of NO donors, L-arginine or NOS-I in acute stroke, and only one drug (GTN) has been assessed. In people with acute stroke, GTN reduces blood pressure, increases heart rate and headache, but does not alter clinical outcome (all based on high-quality evidence).

Bacterial lipopolysaccharide-induced hyporeactivity in perfused rat resistance vessels: modulating effects of dexamethasone

The present study was carried out on mesenteric vascular bed from LPS-injected rats in order to investigate possible mechanisms underlying hyporesponsiveness in resistance blood vessels in the course of septic shock syndrome. The involvement of L-arginine (L-Arg)/nitric oxide (NO) pathway was evaluated by administration of L-Arg, which produced a decrease in perfusion pressure in LPS-treated rats, whereas it was ineffective in control rats. Of note, dexamethasone (DEX) pretreatment in endotoxaemic rats significantly reduced the vasorelaxation by L-Arg; however, this non selective inhibitor of inducible-NOS expression was not able to prevent noradrenaline (NA) hyporeactivity. Furthermore, in order to evaluate whether hyporesponsiveness could be due to an altered contraction mechanism, the effect of endothelin (ET)-1 was tested. This peptide was able to markedly enhance the contractile response to noradrenaline in LPS-treated rats. Collectively, our findings suggest that vascular hyporesponsiveness during septic shock can only be partially explained by activation of the L-Arg/NO pathway. Other mechanisms, probably related to smooth muscle cell contractility, may be involved.

RhoA/Rho-kinase and nitric oxide in vascular reactivity in rats with endotoxaemia

RhoA/Rho-kinase (RhoA/ROK) pathway promotes vasoconstriction by calcium sensitivity mechanism. LPS causes nitric oxide (NO) overproduction to induce vascular hyporeactivity. Thus, we tried to examine the role of RhoA/ROK and NO in the regulation of vascular reactivity in different time-point of endotoxaemia. Male Wistar rats were intravenously infused for 10 min with saline or E. coli endotoxin (lipopolysaccharide, LPS, 10 mg/kg) and divided to five groups (n = 8 in each group): (i) Control, sacrificed at 6 h after saline infusion; (ii) LPS1h, sacrificed at 1 h after LPS infusion; (iii) LPS2h, sacrificed at 2 h after LPS infusion; (iv) LPS4h, sacrificed at 4 h after LPS infusion; and (v) LPS6h, sacrificed at 6 h after LPS infusion. LPS1h and LPS2h were regarded as early endotoxaemia, whereas LPS4h and LPS6h were regarded as late endotoxaemia. Indeed, our results showed that LPS reproduced a biphasic hypotension and sustained vascular hyporeactivity to noradrenaline (NA) in vivo. Interestingly, this hyporeactivity did not occur in ex vivo during early endotoxaemia. This could be due to increases of aortic RhoA activity (n = 5, P<0.05) and myosin phosphatase targeting subunit 1 phosphorylation (n = 3, P<0.05). In addition, pressor response to NA and vascular reactivity in early endotoxaemia were inhibited by ROK inhibitor, Y27632. Furthermore, plasma bradykinin was increased at 10 min (24.6±13.7 ng/mL, n = 5, P<0.05) and aortic endothelial NO synthase expression was increased at 1 h (+200%. n = 3, P<0.05) after LPS. In late endotoxaemia, the vascular hyporeactivity was associated with aortic inducible NO synthase expression (n = 3, P<0.05) and an increased serum NO level (n = 8, P<0.05). Thus, an increased RhoA activity could compensate vascular hyporeactivity in early endotoxaemia, and the large NO production inhibiting RhoA activity would lead to vascular hyporeactivity eventually.

Nitric oxide function in atherosclerosis

Atherosclerosis is a chronic inflammatory process in the intima of conduit arteries, which disturbs the endothelium-dependent regulation of the vascular tone by the labile liposoluble radical nitric oxide (NO) formed by the constitutive endothelial nitric oxide synthase (eNOS). This defect predisposes to coronary vasospasm and cardiac ischaemia, with anginal pain as the typical clinical manifestation. It is now appreciated that endothelial dysfunction is an early event in atherogenesis and that it may also involve the microcirculation, in which atherosclerotic lesions do not develop. On the other hand, the inflammatory environment in atherosclerotic plaques may result in the expression of the inducible NO synthase (iNOS) isozyme. Whether the dysfunction in endothelial NO production is causal to, or the result of, atherosclerotic lesion formation is still highly debated. Most evidence supports the hypothesis that constitutive endothelial NO release protects against atherogenesis e.g. by preventing smooth muscle cell proliferation and leukocyte adhesion. Nitric oxide generated by the inducible isozyme may be beneficial by replacing the failing endothelial production but excessive release may damage the vascular wall cells, especially in combination with reactive oxygen intermediates.

Nitric oxide: considerations for the treatment of ischemic stroke

Some 40 years ago it was recognized by Furchgott and colleagues that the endothelium releases a vasodilator, endothelium-derived relaxing factor (EDRF). Later on, several groups identified EDRF to be a gas, nitric oxide (NO). Since then, NO was identified as one of the most versatile and unique molecules in animal and human biology. Nitric oxide mediates a plethora of physiological functions, for example, maintenance of vascular tone and inflammation. Apart from these physiological functions, NO is also involved in the pathophysiology of various disorders, specifically those in which regulation of blood flow and inflammation has a key role. The aim of the current review is to summarize the role of NO in cerebral ischemia, the most common cause of stroke.

Protamine sulfate causes endothelium-indepen-dent vasorelaxation via inducible nitric oxide syn-thase pathway

PURPOSE

The precise mechanism of systemic hypotension frequently observed with the use of protamine is unclear. Although it has been reported that protamine stimulates the release of nitric oxide (NO) from endothelium NO synthase (eNOS), the association with inducible NOS (iNOS) remains unknown, despite the induction of iNOS by lipopolysaccharides (LPS) and/or inflammatory cytokines during cardiopulmonary bypass (CPB). The purpose of this study was to determine whether protamine stimulates the release of NO from iNOS induced by LPS.

METHODS

We performed prospective and controlled functional examinations with isolated endothelium-denuded thoracic aortas from 21 male Wister rats. Aortic strips were mounted in Krebs solution and treated with LPS (1 microg x mL(-1)) for six hours to induce iNOS. Changes in tension caused by L-arginine (a substrate of NOS), protamine or a heparin-protamine complex (heparin: protamine = 1 unit: 10 microg) were measured in strips pre-contracted by phenylephrine.

RESULTS

No drug relaxed the strips before LPS-treatment, but each drug relaxed the strips in a dose-dependent manner after LPS-treatment (P < 0.05). Aminoguanidine (an iNOS inhibitor) and methylene blue (a guanylyl cyclase inhibitor) inhibited the relaxations.

CONCLUSION

These results indicate that protamine and the heparin-protamine complex stimulated the release of NO from iNOS. As iNOS is induced during CPB, protamine or a heparin-protamine complex might cause systemic hypotension, at least in part, by stimulating iNOS.

Effect of dexamethazone on hepatic vascular response in experimental sepsis

BACKGROUND

The aim of the present study was to evaluate the effect of dexamethasone-pretreatment on the hepatic artery and portal vein of septic rats, which were generated by lipopolisaccarides (LPS) intraperitoneal injection.

METHOD

Thirty-six albino Wistar rats were used and constructed as LPS (n = 12), control (n = 12), dexamethazone-pretreatment (n = 6) and dexamethazone-control (n = 6) groups. Hepatic artery and portal vein rings were excised and placed in Krebs-Henseleit solution. Vessel rings were contracted with phenylephrine adding to the organ chamber in cumulative doses. Then the contraction-response curves were drawn.

RESULTS

In the LPS group, phenylephrine evoked contractions were reduced in both hepatic artery and portal vein rings in comparison to the control group. In the dexamethasone-control group, phenylephrine-evoked contractions were increased but not significantly. Dexamethasone-pretreatment increased the phenylephrine-evoked contractions close to the values of control group for both types of rings.

CONCLUSIONS

Dexamethasone pretreatment corrected the vascular hyporeactivity to phenyleprine in isolated portal vein and hepatic artery rings prepared from the LPS treated rats in experimental sepsis. This might have occurred as a result of inhibition of inducible nitric oxide synthase expression.

Ageing alters the production of nitric oxide and prostanoids after IL-1beta exposure in mesenteric resistance arteries

We aimed to analyse age influence on the production of inflammatory mediators from inducible isoforms of nitric oxide synthase (iNOS) and cyclooxygenase (COX-2) in rat mesenteric resistance arteries (MRA). The second and/or third branches of MRA from young (3-month-old) and old (22-month-old) male Sprague-Dawley rats were incubated in culture medium with or without interleukin-1ss (IL-1ss; 10 ng/ml, 14 h). IL-1ss did not modify endothelial NOS (eNOS) expression or endothelial cell distribution. However, IL-1ss increased nitrite production and iNOS expression in endothelial and smooth muscle cells more in arteries from young than from old rats. IL-1ss also increased PGI(2) levels and COX-2 expression in the three layers of the vascular wall. Ageing did not affect COX-2 expression but did increase TXA(2) and PGF(2alpha) levels. The maximum contraction to phenylephrine was increased in arteries from old rats after IL-1ss treatment. Inhibition of iNOS and COX-2 with 1400 W and NS398, respectively, abolished the differences in phenylephrine contraction. In conclusion, IL-1ss induced an inflammatory response in MRA with associated increases in iNOS and COX-2 expression. The lower increase in nitrite production from iNOS together with a greater contractile prostanoid production in the old rats would be responsible for the increase observed in their contraction to phenylephrine after IL-1 ss treatment.

NOS 3 subcellular localization in the regulation of nitric oxide production

Endothelium-derived nitric oxide (NO) is a key signalling molecule in the maintenance of cardiovascular health. Endothelial NO synthase (NOS 3), which catalyses the formation of NO, is targeted to the plasma membrane by dual acylation. In vitro studies suggest that membrane localization of NOS 3 is an important regulatory element of NO production. Dysfunction of the vascular endothelium and a decrease in NO bioavailability is associated with the development and progression of a number of cardiovascular diseases, including hypertension. Our laboratory has previously published that in salt-dependent hypertension there is an altered localization of NOS 3, with an increase in cytosolic expression. These data have led us to question whether the increased cytosolic NOS 3 expression is a form of compensation for endothelial dysfunction in hypertension, or an indicator and contributing factor to endothelial dysfunction. This review will outline the importance of subcellular localization in the regulation of NOS 3 in vitro, the role of NOS 3 in endothelial dysfunction associated with salt-dependent hypertension, and the potential physiological consequences of altered NOS 3 localization in vivo.

Endothelial dysfunction in acute and chronic coronary syndromes: evidence for a pathogenetic role of oxidative stress

The past two decades have highlighted the pivotal role of the endothelium in preserving vascular homeostasis. Among others, nitric oxide (NO) is currently believed to be the main component responsible for endothelium dependent vasorelaxation and therefore for endothelial function integrity. Reduced NO bioavailability causes the so-called "endothelial dysfunction," which seems to be the common molecular disorder comprising stable atherosclerotic narrowing lesions or acute plaque rupture causing unstable angina or myocardial infarction. Compelling evidence is accumulating, stressing the role of oxidative stress in causing reduced NO bioavailability and subsequently endothelial dysfunction (ED). More recently, the role of endothelial cell (EC) apoptosis as a possible final stage of ED and plaque activation has been suggested. In vitro and in vivo evidence suggests a role of oxidative stress also as a putative mechanism finally leading to plaque denudation and activation through increased EC apoptosis. Thus, oxidative stress, irrespective of atherosclerotic disease stages, seems to represent a key phenomenon in vascular disease progression and possible prevention.

Peroxynitrite Decreases Dopamine???s Vasoconstrictive Activity

Peroxynitrite (ONOO(-1)) reacts with dopamine to form an oxidized derivative. To investigate the vasoconstrictive activity of this derivative, we performed functional examinations with dopamine treated with ONOO(-1) or 3-morpholinosydonimine-N-ethyl-carbamine (SIN-1; an ONOO(-1) producer) on isolated strips of rat thoracic aorta. To exclude the direct effect of ONOO(-1), the strips were pretreated with methylene blue, a guanylyl cyclase inhibitor. Dopamine induced concentration-dependent contraction, but dopamine pretreated with ONOO(-1) decreased the contraction in an ONOO(-1)-concentration-dependent manner. Both maximum contractions and 50% effective concentration values for dopamine-induced vasocontraction were significantly decreased by pretreatment with ONOO(-1). Dopamine incubated with SIN-1 also decreased the contraction, the decrease being dependent on the incubation time. ONOO(-1) formation is a favored reaction and occurs easily when cellular production of both nitric oxide and superoxide increases, as in septic shock. These results may, at least in part, account for dopamine's limitation as a vasoconstrictor in septic shock.

IMPLICATIONS

Peroxynitrite (ONOO(-1)) reacts with dopamine to form an oxidized derivative. We investigated the vasoconstrictive activity of this derivative with functional examinations using rat thoracic aorta and found the activity decreased. As ONOO(-1) formation increases in septic shock, our results may account for dopamine's limitation as a vasoconstrictor in septic shock.

A novel antioxidant, octyl caffeate, suppression of LPS/IFN-gamma-induced inducible nitric oxide synthase gene expression in rat aortic smooth muscle cells

In the present study, we investigated the effects and mechanisms of a novel potent antioxidant, octyl caffeate, on the induction of iNOS expression by lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) in cultured primary rat aortic smooth muscle cells (RASMCs) in vitro and LPS-induced hypotension in vivo. Octyl caffeate (0.1-1.0 microM) exerted a concentration-dependent inhibition of iron-catalyzed lipid peroxidation in rat brain homogenates. Furthermore, octyl caffeate (20, 50, and 100 microM) concentration-dependently diminished the initial rate of superoxide-induced NBT reduction and the enzymatic activity of xanthine oxidase. It also concentration-dependently (1-50 microM) inhibited the NO production, iNOS protein and messenger RNA expressions upon stimulation by LPS (100 microg/mL)/IFN-gamma (100U/mL) in RASMCs. In addition, we found that octyl caffeate did not significantly affect IkappaBalpha degradation stimulated by LPS/IFN-gamma in RASMCs. On the other hand, octyl caffeate (10 and 50 microM) significantly suppressed activation of c-Jun-N-terminal kinase and extracellular signal-regulated kinase. Moreover, octyl caffeate (10mg/kg, i.v.) significantly inhibited the fall in mean arterial pressure stimulated by LPS (7.5mg/kg) in rats. In conclusion, we demonstrate that a novel potent antioxidant, octyl caffeate, significantly ameliorates circulatory failure of endotoxemia in vivo by a mechanism involving suppression of iNOS expression through inactivation of mitogen-activated protein kinases in RASMCs.

The nitric oxide pathway in the cardiovascular system

The present review analyzes the role nitric oxide (NO) plays in the homeostasis of the cardiovascular system. By regulating vascular smooth muscle cell and myocyte contractility, myocardial oxygen consumption and renal tubular transport, this simple molecule plays a central role in the control of vascular tone, cardiac contractility and short and long term regulation of arterial pressure. Fifteen years ago, all we knew about NO is that it had very similar properties as those of endothelium-derived relaxing factor and that its action was probably mediated by cGMP. An enormous amount of knowledge has since been amassed on the biochemical pathways that NO follows from the moment it is synthesized from L-arginine until the physiological or pathological actions take place in the effector cells. This review intends to organize this knowledge in a fashion that is easy to understand. We will dissect the NO pathway in different steps, focusing on the physiological and pathophysiological actions of the isoenzymes which synthesize NO, the molecules involved in this synthesis such as caveolins, protein kinases and cofactors, the situations in which endogenous inhibitors of NO synthase are formed from L-arginine instead of NO, the way in which NO exerts its physiological actions through cGMP-dependent protein kinases and finally, the pathological routes NO may follow when the oxidative status of the cell is high.

Functional NOS 1 in the rat mesenteric arterial bed

Previously we have demonstrated functional nitric oxide synthase (NOS) 1 in large arteries. Because resistance arteries largely determine blood pressure, this study examined whether functional NOS 1 also exists in resistance arteries. Phenylephrine (PE) contraction was measured in the absence and presence of the NOS 1 inhibitor N(5)-(1-imino-3-butenyl)-L-ornithine (VNIO) in isolated mesenteric resistance arteries (endothelium intact and denuded) from Sprague-Dawley rats. For NOS 1 activity and expression, the mesenteric arterial bed was separated into cytosolic and particulate fractions. NOS activity was assayed by measuring the conversion of [(3)H]arginine to [(3)H]citrulline inhibited by a nonselective NOS inhibitor or VNIO. VNIO increased PE sensitivity in endothelium-intact and -denuded arteries. In cytosolic and particulate fractions of the arterial bed, approximately 40% of NOS activity was inhibited by VNIO. Immunoprecipitation and Western blot analysis revealed two NOS 1 immunoreactive bands. One band corresponded to the rat brain isoform, whereas the second was of a slightly lower molecular mass. The cytosolic fraction contained both isoforms; however, the particulate fraction had only the lower molecular mass form. These studies demonstrate the existence of functional NOS 1 in resistance arteries.

Temporal and segmental distribution of constitutive and inducible nitric oxide synthases after traumatic spinal cord injury: effect of aminoguanidine treatment

Nitric oxide (NO) has been shown to play an important role in the pathophysiology of traumatic brain injury (TBI) and cerebral ischemia. However, its contribution to the pathogenesis of traumatic spinal cord injury (SCI) remains to be clarified. This study determined the time course of constitutive and inducible nitric oxide synthases (cNOS and iNOS, respectively) after SCI. Rats underwent moderate SCI at T10 using the NYU impactor device and were allowed to survive for 3, 6, or 24 h and 3 days after SCI (n = 5 in each group). For the determination of enzymatic activities, spinal cords were dissected into five segments, including levels rostral and caudal (remote) to the injury site. Other rats were perfusion fixed for the immunohistochemical localization of iNOS protein levels. cNOS activity was significantly decreased at 3 and 6 h within the traumatized T10 segment and at 3, 6, and 24 h at the rostral (T9) level (p < 0.05). Rostral (T8) and caudal (T11, T12) to the injury site cNOS activity was also decreased at 3 h after injury (p < 0.05). However, cNOS activity returned to control levels within 6 h at T8, T11 and T12 and at one day at T10 and T9 segments. iNOS enzymatic activity was elevated at all time points tested (p < 0.05), with the most robust increase observed at 24 h. Immunostaining for iNOS at 24 h revealed that a significant cellular source of iNOS protein appeared to be invading polymorphonuclear leukocytes (PMNLs). To assess the functional consequences of iNOS inhibition, aminoguanidine treatment was initiated 5 min after SCI and rats tested using the BBB open field locomotor score. Treated rats demonstrated significantly improved hindlimb function up to 7 weeks after SCI. Histopathological analysis of contusion volume showed that aminoguanidine treatment decreased lesion volume by 37% (p < 0.05). In conclusion, these results indicate that (1) cNOS and iNOS activities are regionally and temporally affected after moderate SCI, (2) the early accumulation of PMNLs are a potentially significant source of NO-induced cytotoxic products, and (3) acute aminoguanidine treatment significantly improves functional and histopathological outcome after SCI.

L-arginine-induced relaxation of the rat isolated penile bulb

The effects of L-arginine, the precursor in the synthesis of nitric oxide (NO), were investigated in the penile bulb isolated from saline (control) or lipopolysaccharide (20 mg/kg, i.p.)-treated rats. Four consecutive concentration-response curves for L-arginine were made at hourly intervals with the penile bulb. L-arginine (10(7)-10(-3) M) elicited a concentration- and time-dependent relaxation response in the control group. The NO synthase (NOS) inhibitors, N(G)-methyl-L-arginine (L-NMMA) and aminoguanidine, guanylate cyclase inhibitor, 1-H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) and protein synthesis inhibitor, cycloheximide, inhibited L-arginine-induced relaxation. In the lipopolysaccharide-group, L-arginine produced a pronounced non-time-dependent relaxation at the first concentration-response curve, which was not different from the fourth response of the control group. This response was also inhibited by aminoguanidine. These results show that L-arginine induced NO-mediated relaxation and suggest the presence of a biochemical pathway converting L-arginine to NO, which is probably an inducible type in the penile bulb.

Effects of chronic and acute aminoguanidine treatment on tail artery vasomotion in ageing rats

1. This study was designed to evaluate the effects of aminoguanidine, a selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS), on the reactivity and intracellular calcium ([Ca(2+)](i)) mobilization induced by noradrenaline in the perfused tail artery from aged WAG/Rij rats. Global mean internal diameter was 350+/-15 microns and wall thickness 161+/-3 microns. The influence of the endothelium on these responses was also analysed. The intracellular dye fura-2 for [Ca(2+)](i) measurements was used. 2. Noradrenaline-induced vasoconstriction decreased progressively from 3 to 20 and 30 months. Removal of the endothelium attenuated vasoconstriction in 20 and 30 month-old rats (P<0.05) but not in young rats. 3. Chronic administration of aminoguanidine (50 mg kg(-1) day(-1), p.o.) to WAG/Rij rats from 20 to 30 months enhanced (P<0. 01) the [Ca(2+)](i)-sensitivity of noradrenaline-induced vasoconstriction. 4. Aminoguanidine (300 microM) in vitro significantly shifted the concentration-vasoconstriction curve to noradrenaline to the left (P<0.01) in denuded vessels from both 20 and 30 month-old rats. The acute inhibitory effect of aminoguanidine was also observed after chronic aminoguanidine treatment. Aminoguanidine failed to modify vasoconstriction in the presence of the endothelium. 5. Acute aminoguanidine (300 microM) treatment did not modify vasoconstriction induced by noradrenaline in young rats. 6. Quantification of iNOS mRNA expression in tail arteries from 3 and 20 month-old WAG/Rij rats showed that expression was enhanced (x2.1, P<0.01) with age. 7. These results suggest that an inflammatory process develops in the media of the rat tail artery with age and that the subsequent increase in non-endothelial iNOS activity attenuates noradrenaline-induced vasoconstriction.

Functional expression of NOS 1 in vascular smooth muscle

Substances that increase intracellular calcium concentration ([Ca(2+)](i)), such as serotonin, are known to induce vascular smooth muscle (VSM) contraction. However, increases in [Ca(2+)](i) also activate Ca(2+)/calmodulin-dependent nitric oxide synthases (NOS), which leads to increases in cGMP and activation of cGMP-dependent protein kinase (PKG). One recently identified substrate protein of PKG is the small heat shock protein, HSP20. The purpose of this study was to determine if serotonin activates a Ca(2+)-dependent NOS in VSM. Strips of bovine carotid arterial smooth muscle denuded of endothelium were stimulated with serotonin in the presence and absence of the nonspecific NOS inhibitor N-monomethyl-L-arginine (L-NMMA). Activation of NOS was determined by increases in cGMP and in the phosphorylation of HSP20. Immunohistochemical and Western blotting techniques were performed to identify specific NOS isoforms in bovine carotid arterial smooth muscle preparations. Serotonin stimulation led to significant increases in cGMP and in the phosphorylation of HSP20, which were inhibited by pretreatment with L-NMMA. Antibodies against NOS 1 stained the media of bovine carotid and human renal arteries, whereas antibodies against NOS 3 stained only the endothelium. Additionally, the conversion of radiolabeled L-arginine to L-citrulline NOS activity demonstrated a consistent amount of activity present in the endothelium-denuded smooth muscle preparations that was reduced by 99% with an NOS 1 specific inhibitor. Finally, an NOS 1 specific inhibitor, 7-nitroindazole, augmented contractions induced by high extracellular KCl. This study demonstrates that NOS 1 is present in VSM and may effect physiological contractile responses.

Effect of pre-exposure to vasoconstrictors on isoprenaline-induced relaxation in rat aorta: involvement of inducible nitric oxide synthase

1. The aim of this study was to determine whether a brief (30 min) episode of contractile receptor stimulation could affect the degree of a subsequent vasorelaxation. Therefore, concentration - relaxation curves of the rat aorta to isoprenaline were compared before and after exposure of the tissue to noradrenaline (100 microM) or prostaglandin F2alpha (PGF2alpha, 100 microM). 2. Exposure to noradrenaline enhanced the second maximal relaxant effect of isoprenaline (from 20 - 95% relaxation). This effect was not due to significant differences in precontraction levels and was not modified by the presence of the endothelium. Treatment with PGF2alpha mimicked the actions of noradrenaline on subsequent vasorelaxation to isoprenaline. 3. Before exposure to noradrenaline (100 microM), forskolin (10 microM) did not produce any significant relaxation of the rat aorta. After exposure to noradrenaline, forskolin caused a concentration-dependent relaxation with a maximal effect of more than 90% in rings with and without endothelium suggesting that the change in vasorelaxation to isoprenaline occurred downstream from the beta-adrenoceptor. 4. The increase in relaxation due to exposure to noradrenaline was markedly attenuated by treatment with a protein synthase inhibitor (cycloheximide), a nitric oxide (NO) synthase inhibitor (L-NG-nitroarginine methyl ester, L-NAME) and an inhibitor of the activation of soluble guanylyl cyclase (methylene blue). 5. Western blot analysis showed an increase of inducible NO synthase (iNOS) in aortic rings exposed to noradrenaline or PGF2alpha. 6. Together, these findings suggest that pretreatment of rat aorta with noradrenaline or PGF2alpha could induce vascular NOS which would in turn result in an increase in isoprenaline-induced vasorelaxation, this increase occurring downstream from receptor activation. Such a mechanism might participate in cardioprotection during preconditioning induced by noradrenaline.

The inducible nitric oxide synthase in vascular and cardiac tissue

Expression of the inducible form of nitric oxide synthase (iNOS) has been reported in a variety of cardiovascular diseases. The resulting high output nitric oxide (NO) formation, besides the level of iNOS expression, depends also on the expression of the metabolic pathways providing the enzyme with substrate and cofactor. NO may trigger short and long term effects which are either beneficial or deleterious, depending on the molecular targets with which it interacts. These interactions are governed by local factors (like the redox state). In the cardiovascular system, the major targets involve not only guanylyl cyclase, but also other haem proteins, protein thiols, iron-non-haem complexes, and superoxide anion (forming peroxynitrite). The latter has several intracellular targets and may be cytotoxic, despite the existence of endogenous defence mechanisms. These interactions may either trigger NO effects or represent releasable NO stores, able to buffer NO and prolong its effects in blood vessels and in the heart. Besides selectively inhibiting iNOS, a number of other therapeutic strategies are conceivable to alleviate deleterious effects of excessive NO formation, including peroxynitrite (ONOO-) scavenging and inhibition of metabolic pathways triggered by ONOO-. When available, these approaches might have the advantage to preserve beneficial effects of iNOS induction. Counteracting vascular hyper-responsiveness to endogenous vasoconstrictor agonists in septic shock, or inducing cardiac protection against ischaemia-reperfusion injury are examples of such beneficial effects of iNOS induction.

Nonadrenergic noncholinergic vasodilation of guinea pig pulmonary arteries is mediated by nitric oxide

Nonadrenergic noncholinergic (NANC) mediated vasodilation may contribute to the maintenance of low pulmonary vascular tone. The NANC neurotransmitters, nitric oxide (NO) and the sensory neuropeptides, substance P and calcitonin gene related peptide (CGRP), were investigated as possible mediators of NANC vasodilation in guinea pig pulmonary arteries. Fresh guinea pig pulmonary artery rings, with and without an intact endothelium, were mounted in organ baths containing Krebs solution and precontracted with the prostaglandin F2α analogue U44069. In both endothelium-intact and denuded vessels, electrical field stimulation (1-12 Hz) in the presence of guanethidine and atropine resulted in a frequency-dependent vasodilation. The peptide fragment hCGRP8-37, a competitive antagonist of the CGRP receptors, the peptide fragment NK1 antagonist SP4-11, and the nonpeptide NK1 antagonist RP67580 had no effect on NANC vasodilation. In both endothelium-intact and denuded vessels, NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthesis, inhibited NANC vasodilation, an effect that was reversible with L-arginine. We conclude that NANC vasodilation in guinea pig pulmonary arteries is mediated predominantly through NO activity.Key words: nonadrenergic noncholinergic, pulmonary artery, nitric oxide, vasodilation.

Dietary beta-adrenoceptor agonists have a persistent effect on nitric oxide synthesis in rat cultured smooth muscle cells

Several compounds including lipopolysaccharide and sympathomimetics stimulate the expression of the inducible nitric oxide synthase in vascular smooth muscle cells. We evaluated the effect of clenbuterol on nitric oxide (NO) production by vascular smooth muscle cells of the rat aorta in culture. Wistar rats were divided into three diet groups (control, clenbuterol and washout). Aortic vascular smooth muscle cells from rats from these 3 diet groups were cultured in the presence and absence of lipopolysaccharide and/or beta-adrenoceptor agonists. NO release was measured by Griess reagent. Clenbuterol or salbutamol added to cells from control rats potentiated lipopolysaccharide-induced NO release. Cells from rats fed on clenbuterol, in a medium without beta-adrenoceptor agonists, showed a similar potentiation, even after a 10-day washout period. The addition of beta-adrenoceptor agonists to the latter cells did not increase NO production. NG-Nitro-L-arginine decreased nitrite production in lipopolysaccharide-stimulated cells. Our results demonstrate that dietary clenbuterol has a persistent 'ex vivo' effect on lipopolysaccharide-induced NO production by cultured vascular smooth muscle cells.

Inducible nitric oxide synthase expression after traumatic brain injury and neuroprotection with aminoguanidine treatment in rats

OBJECTIVE

We investigated the time course of inducible nitric oxide synthase (iNOS) enzymatic activity and immunocytochemical localization of iNOS expression after traumatic brain injury (TBI), as well as the possible role of iNOS in the pathogenesis of TBI.

METHODS

Male Sprague-Dawley rats were anesthetized and underwent moderate parasagittal fluid-percussion brain injury. Rats were decapitated 5 minutes, 6 hours, 1 day, 3 days, 7 days, or 14 days later, and iNOS enzymatic activities were measured (n = 6-8). To determine whether nitric oxide produced by iNOS contributed to the histopathological consequences of TBI, inhibition of iNOS activity using aminoguanidine (intraperitoneal injections of 100 mg/kg aminoguanidine [n = 9] or vehicle [n = 8], twice each day) was conducted for 3 days.

RESULTS

Significantly elevated iNOS activity was detected at 3 days (276.8+/-72.3% of contralateral value, means +/- standard errors; P < 0.05), and the most robust increase occurred 7 days after TBI (608.0+/-127.0%, P < 0.01) in the injured parietal cerebral cortex. Immunostaining for iNOS and glial fibrillary acidic protein, at 3 and 7 days after TBI, revealed that the major cellular sources of iNOS expression were cortical Layer 1 astrocytes and macrophages within the subarachnoid space. Administration of aminoguanidine did not reduce contusion volume significantly; however, treatment reduced total cortical necrotic neuron counts (1367.6+/-210.3; P < 0.01, compared with vehicle, 2808.5+/-325.1).

CONCLUSION

These data indicate that iNOS is expressed after moderate parasagittal fluid-percussion brain injury, in a time-dependent manner, and that inhibition of iNOS synthesis improves histopathological outcomes. Thus, inhibition of iNOS activation may represent a potential therapeutic strategy for the treatment of TBI.

Role of nitric oxide in traumatic brain injury in the rat

OBJECT

Although nitric oxide (NO) has been shown to play an important role in the pathophysiological process of cerebral ischemia, its contribution to the pathogenesis of traumatic brain injury (TBI) remains to be clarified. The authors investigated alterations in constitutive nitric oxide synthase (NOS) activity after TBI and the histopathological response to pharmacological manipulations of NO.

METHODS

Male Sprague-Dawley rats underwent moderate (1.7-2.2 atm) parasagittal fluid-percussion brain injury. Constitutive NOS activity significantly increased within the ipsilateral parietal cerebral cortex, which is the site of histopathological vulnerability, 5 minutes after TBI occurred (234.5+/-60.2% of contralateral value [mean+/-standard error of the mean ¿SEM¿], p < 0.05), returned to control values by 30 minutes (114.1+/-17.4%), and was reduced at 1 day after TBI (50.5+/-13.1%, p < 0.01). The reduction in constitutive NOS activity remained for up to 7 days after TBI (31.8+/-6.0% at 3 days, p < 0.05; 20.1+/-12.7% at 7 days, p < 0.01). Pretreatment with 3-bromo-7-nitroindazole (7-NI) (25 mg/kg), a relatively specific inhibitor of neuronal NOS, significantly decreased contusion volume (1.27+/-0.17 mm3 [mean+/-SEM], p < 0.05) compared with that of control (2.52+/-0.35 mm3). However, posttreatment with 7-NI or pre- or posttreatment with nitro-L-arginine-methyl ester (L-NAME) (15 mg/kg), a nonspecific inhibitor of NOS, did not affect the contusion volume compared with that of control animals (1.87+/-0.46 mm3, 2.13+/-0.43 mm3, and 2.18+/-0.53 mm3, respectively). Posttreatment with L-arginine (1.1+/-0.3 mm3, p < 0.05), but not 3-morpholino-sydnonimine (SIN-1) (2.48+/-0.37 mm3), significantly reduced the contusion volume compared with that of control animals.

CONCLUSIONS

These data indicate that constitutive NOS activity is affected after moderate parasagittal fluid percussion brain injury in a time-dependent manner. Inhibition of activated neuronal NOS and/or enhanced endothelial NOS activation may represent a potential therapeutic strategy for the treatment of TBI.

Endothelium-dependent vasodilation in response to Pseudomonas aeruginosa lipopolysaccharide: an in vitro study on canine arteries

Early systemic arterial hypotension is a common clinical feature of Pseudomonas septicemia. To determine if Pseudomonas aeruginosa endotoxin induces the release of endothelium-derived nitric oxide (EDNO), an endogenous nitrovasodilator, segments of canine femoral, renal, hepatic, superior mesenteric, and left circumflex coronary arteries were suspended in organ chambers (physiological salt solution, 95% O2/5% CO2, pH 7.4, 37 degrees C) to measure isometric force. In arterial segments contracted with 2 microM prostaglandin F2 alpha, Pseudomonas endotoxin (lipopolysaccharide (LPS) serotype 10(Habs) from Pseudomonas aeruginosa (0.05 to 0.50 mg/ml) induced concentration-dependent relaxation of segments with endothelium (P < 0.05) but no significant change in tension of arteries without endothelium. Endothelium-dependent relaxation in response to Pseudomonas LPS occurred in the presence of 1 microM indomethacin, but could be blocked in the coronary artery with 10 microM NG-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of nitric oxide synthesis from L-arginine. The inhibitory effect of L-NMMA on LPS-mediated vasorelaxation of the coronary artery could be reversed by exogenous 100 microM L-arginine but not by 100 microM D-arginine. These experiments indicate that Pseudomonas endotoxin induces synthesis of nitric oxide from L-arginine by the vascular endothelium. LPS-mediated production of EDNO by the endothelium, possibly through the action of constitutive nitric oxide synthase (NOSc), may decrease systemic vascular resistance and may be the mechanism of early hypotension characteristic of Pseudomonas septicemia.

Nitrite production does not always reflect nitric oxide synthesis by isolated glomeruli

The goal of this paper was the measurement of nitric oxide (NO) production in isolated rat glomeruli using two different techniques. NO production was detected directly by a NO-specific electrode and the results were compared with data measured by the Griess reaction, an indirect index to evaluate NO production. The NO production, determined by both techniques, was dependent on the number of glomeruli. Pretreatment with Nw-nitro-L-arginine methyl ester, an inhibitor of the NO synthesis, reduced the NO concentration detected by the NO-sensor, but increased the NO2-concentration (when both results where compared with glomeruli without treatment). Preincubation with 1 mg/ml of Escherichia coli lipopolysaccharide significantly enhanced both NO and NO2-concentrations. Therefore, the present study provides direct evidence of NO generated in isolated glomeruli under physiological conditions and demonstrates that the measurement of NO2- by the Griess reaction, is not always an adequate technique to evaluate the actual NO production.

Role of adventitial nitric oxide in vascular hyporeactivity induced by lipopolysaccharide in rat aorta

This study was designed to elucidate the role of the adventitia in NO-mediated vascular effects of lipopolysaccharide (LPS). After incubation of rat aorta with LPS, the adventitia generated 3.5 times more nitrite plus nitrate than a corresponding segment of media. Control media covered by adventitia from LPS-treated aortic rings exhibited a 4 fold elevated level of cyclic GMP. Medial layers from LPS-treated aortic rings (like LPS-treated adventitia-intact rings) exhibited a decrease in sensitivity to noradrenaline (NA) that was reversed by 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (1 microM) or N omega-nitro-L-arginine methylester (0.3 mM). However, in contrast to LPS-treated adventitia-intact rings, medial layers showed no reduction in maximal contraction to NA and virtually no relaxation to L-arginine. These data indicate that in blood vessels exposed to LPS, the adventitia is a more powerful source of NO than the media. The adventitia-derived NO can reach soluble guanylyl cyclase in the medial layer and contribute greatly to vascular hyporeactivity and L-arginine-induced relaxation observed in blood vessels exposed to LPS.

Coexpression of GTP cyclohydrolase I and inducible nitric oxide synthase mRNAs in mouse osteoblastic cells activated by proinflammatory cytokines

Proinflammatory cytokines, a combination of IL-1beta, TNF-alpha, and IFN-gamma, caused mRNA expression of GTP cyclohydrolase I (GTP-CH), the rate-limiting enzyme in tetrahydrobiopterin (BH4) biosynthesis, and of inducible nitric oxide synthase (iNOS) in a well-characterized osteoblastic clone MC3T3-E1 cell line. We found the expression of the GTP-CH gene in osteoblasts for the first time. The expression of GTP-CH and iNOS mRNAs was found to be maximal at 3 and 9 h, respectively. The expression of both genes elicited increases in BH4 and NO levels. Pharmacological studies using 2,4-diamino-6-hydroxypyrimidine, an inhibitor of GTP-CH activity, showed that BH4 is involved in the activity of iNOS, but not in the induction of iNOS mRNA. The results using an inhibitor of nuclear factor (NF)-kappaB and activating protein-1 (AP-1) activation suggested that coinduction of the two genes in response to cytokines occurred via activation of NF-kappaB and AP-1. In MC3T3-E1 cells BH4 and sepiapterin, producing BH4, could protect against apoptosis, i.e. the degradation of nuclear DNA in the cells, induced by NO derived from S-nitroso-N-acetyl-D-L-penicillamine. These results suggest that the induction of BH4 together with NO by proinflammatory cytokines could protect against NO-induced apoptosis in MC3T3-E1 cells.

Induction of nitric oxide synthase by protein synthesis inhibition in aortic smooth muscle cells

1. The role of de novo protein synthesis in inducible NO synthase (iNOS) activation was investigated in vitro by evaluating the effects of protein synthesis inhibitors cycloheximide (CH) and anisomycin (ANI) on iNOS activity, protein and mRNA levels in rat aortic smooth muscle cells (RASMC). 2. As determined by cyclic GMP accumulation, substrate (L-arginine)- and inhibitor (N(G)-monomethyl-L-arginine, NMMA)-sensitive iNOS activity was significantly elevated in CH- or ANI-treated RASMC after 24 h. 3. Lipopolysaccharide (LPS) produced a time-dependent increase in cyclic GMP levels with maximal stimulation at 6 h and a decline to near baseline at 24 h. CH attenuated LPS-induced cyclic GMP accumulation at 3 and 6 h. However, cyclic GMP levels were superinduced at later times by CH. The concentration-dependence of cyclic GMP stimulation by cycloheximide was biphasic both in the absence and presence of LPS, with maximal stimulation at 10 microM and inhibition at higher concentrations. 4. Increased iNOS activity by CH was associated with elevated levels of immunoreactive iNOS protein as judged by Western blotting in LPS- and CH-treated cells. 5. CH-induced iNOS activity and superinduction of iNOS by CH in cells treated with LPS were both significantly inhibited by actinomycin D, a transcription inhibitor. 6. RT-PCR revealed elevated iNOS mRNA levels after 12 h of exposure to CH. The combination of LPS and CH caused a significant increase in iNOS gene expression relative to LPS- or CH stimulation alone. 7. These results show that partial protein synthesis inhibition by CH alone upregulates iNOS mRNA and superinduces iNOS mRNA in cytokine-treated RASMC, which is translated to the functional enzyme generating biologically active NO. Thus iNOS activation in these cells not only requires new protein synthesis but it also appears to be negatively regulated by newly synthesized proteins.

Internally applied endotoxin and the activation of BK channels in cerebral artery smooth muscle via a nitric oxide-like pathway

1. In this study the role of nitric oxide synthase (NOS) in the acute activation of large conductance, Ca2+-activated K+ channels (BK channels) by internally applied E. coli lipopolysaccharide (LPS, endotoxin) was examined in vascular smooth muscle cells. 2. Cerebrovascular smooth muscle cells (CVSMCs) were enzymatically dispersed from the middle, posterior communicating and posterior cerebral arteries of adult Wistar rats and maintained at 4 degrees C for 2-4 days before recording with standard patch-clamp techniques. 3. Acute application of LPS (100 microg ml(-1)) to inside-out patches of CVSMC membrane isolated in a cell-free environment rapidly and reversibly increased the open probability, Po of BK channels in these patches by 3.3+/-0.30 fold. 4. Acute application of the nitric oxide (NO) donor sodium nitroprusside (SNP, 100 microM) to inside-out patches of CVSMC membrane, studied in the presence of intact cells, also reversibly increased Po, by some 1.8+/-0.2 fold over control. 5. Kinetic analysis showed that both LPS and SNP increased Po by accelerating the rate of BK channel reopening, rather than by retarding the closure of open channels. 6. Neither LPS nor SNP altered the reversal potential or conductance of BK channels. 7. The NOS substrate L-arginine (1 microM) potentiated the acute activation of BK channels by LPS, while the synthetic enantiomer D-arginine (1 microM) inhibited the action of LPS on BK channels. 8. The acute activation of BK channels by LPS was suppressed by pre-incubation of cells with N(omega)-nitro-L-arginine (50 microM) or N(omega)-nitro-L-arginine methyl ester (1 mM), two competitive antagonists of nitric oxide synthases. N(omega)-nitro-D-arginine (50 microM), a poor inhibitor of NOS in in vitro assays, had no effect on BK channel activation by LPS. 9. These results indicate that excised, inside-out patches of CVSMC membrane exhibit a NOS-like activity which is acutely activated when LPS is present at the cytoplasmic membrane surface. Possible relationships between this novel mechanism and the properties of known isoforms of nitric oxide synthase are discussed.

Neuronal NOS gene expression in gastrointestinal myenteric neurons and smooth muscle cells

Nitric oxide synthase (NOS) has been characterized in different tissues, and its localization has been suggested in different neuronal tissues, including the myenteric neurons and other nonneuronal cells. The present study examined the distribution of the neuronal NOS (nNOS) mRNA in different tissues of the opossum gastrointestinal tract, internal anal sphincter (IAS) smooth muscle cells, and myenteric neurons using slot-blot and Northern blot hybridization techniques with a specific rat brain nNOS cDNA probe. Significant levels of nNOS gene expression were found in both smooth muscle cells and myenteric neurons of the opossum IAS. This finding was confirmed by reverse transcriptase-polymerase chain reaction analysis of the RNA obtained from cultured opossum IAS smooth muscle cells and myenteric neurons and also from human intestinal smooth muscle and neuroblastoma cell lines. Pyloric sphincter had the highest level of nNOS gene expression compared with other gastrointestinal tissues. There was no significant difference in the nNOS gene expression between other sphincteric and nonsphincteric tissues examined. The present study shows the presence of nNOS gene expression in both neurons and smooth muscle cells. The higher levels of nNOS gene expression in the pyloric sphincter compared with other tissues may have pathophysiological significance in some disease conditions.

Capsaicin-induced nitric-oxide-dependent relaxation in isolated dog urethra

Capsaicin (5 x 10[-8] to 5 x 10[-5] M) produced a non-adrenergic and non-cholinergic phasic relaxation in a concentration-dependent manner in isolated dog urethral preparations precontracted by noradrenaline. The mode of action of capsaicin was investigated with special reference to the possible involvement of endogenous nitric oxide (NO). A marked tachyphylaxis was observed in the responses to capsaicin. Pretreatment with NG-nitro-L-arginine-methyl-ester (L-NAME) prevented or markedly reduced the inhibitory effect of L-NAME. Methylene blue inhibited the capsaicin-induced relaxation. In preparations stored at 4 degrees C for 72 h, the reduction in the capsaicin-induced relaxation was significantly greater than that in the relaxation induced by either electrical field stimulation or by sodium nitroprusside. We conclude that capsaicin produces an endogenous-NO-dependent relaxation in the isolated dog urethra via mechanisms that deteriorate during cold storage of the preparations.

Immunohistochemical description of nitric oxide synthase isoforms in human clitoris

PURPOSE

Our aim was to identify and localize nitric oxide synthase isoforms in the human clitoris in support of the hypothesis that nitric oxide mediates erectile function in this organ.

MATERIALS AND METHODS

Nitric oxide synthase immunohistochemistry studies specific for neuronal, inducible and endothelial isoforms of the enzyme were performed on human clitoral tissue obtained from 4 patients (3 with female pseudohermaphroditism and 1 with true hermaphroditism) at feminizing genitoplasty and from 1 phenotypically normal woman at autopsy.

RESULTS

Neuronal nitric oxide synthase immunoreactivity was detected in nerve bundles and fibers coursing within the glans clitoris and corpora cavernosa of the clitoris, predominating in the latter tissue. Specific inducible nitric oxide synthase immunoreactivity was not identified. Endothelial nitric oxide synthase immunoreactivity was detected in vascular and sinusoidal endothelium of these tissues with a predominance in the glans clitoris.

CONCLUSIONS

The presence and anatomical localizations of nitric oxide synthase isoforms in the human clitoris indicate that nitric oxide is generated in this organ. These data suggest that nitric oxide may be involved in the erectile physiology of the clitoris as a modulator of clitoral smooth muscle activity. Functional studies are required to support this hypothesis.

Endotoxin alters the systemic disposition of nitric oxide synthase inhibitors in the awake sheep

1. We evaluated the haemodynamic effects and systemic disposition of the nitric oxide synthase (NOS) inhibitor NL-nitro-L-arginine (NOLA) after intravenous (i.v.) administration of two different doses (5 and 20 mg/kg) in awake healthy sheep and awake sheep given a continuous i.v. infusion of endotoxin (lipopolysaccharide, 12 ng/kg per h, i.v., for 18 h). In addition, we determined the systemic disposition of another NOS inhibitor, NL-nitro-L-arginine methylester (L-NAME; 20 mg/kg, i.v.) in awake healthy sheep only. 2. NL-Nitro-L-arginine produced a dose-dependent decrease in heart rate (HR) and cardiac output (CO) together with a dose-dependent increase in mean arterial pressure (MAP) and peripheral vascular resistance (PVR) when compared to baseline. In endotoxic sheep NOLA produced a greater increase in MAP and mean pulmonary arterial pressure (MPAP). 3. In healthy sheep there was a dose-related increase in total body clearance (Cl) of NOLA. The Cl increased from 0.028 L/min after the lower dose to 0.032 L/min after the higher dose. The infusion of endotoxin caused an increase in Cl of NOLA to 0.040 and 0.047 L/min, respectively, and a decrease in plasma slow half-life (t1/2) from 825 to 546 min and from 780 to 453 min, respectively. 4. NL-Nitro-L-arginine methylester was rapidly cleared from the plasma with a slow half-life of approximately 7.5 min and there was a simultaneous appearance of NOLA in the plasma. 5. These results support the view that nitric oxide has a significant role in regulating vascular tone in healthy and endotoxic sheep and indicate that the increases in Cl of NOLA with an increase in its dose and the presence of endotoxin will be important in influencing appropriate dosage regimens in clinical studies.

Endothelial nitric oxide synthase is downregulated during hyperdynamic sepsis

Although studies have shown that endothelium-derived nitric oxide (NO) release is depressed during endotoxic shock or polymicrobial sepsis, it remains unknown whether the decreased release of endothelium-derived NO during the hyperdynamic stage of sepsis is due to downregulation of endothelial NO synthase. To study this, adult rats were subjected to sepsis by cecal ligation and puncture (CLP). At 10 h after CLP (i.e., hyperdynamic sepsis) or sham operation, the aorta was removed and a monoclonal antibody against endothelial (constitutive) NO synthase (E-NOS) was used to determine the immunohistochemical presence and electron microscopic localization of E-NOS in rat aortic endothelial cells. Image analysis was used to quantify aortic E-NOS. In additional groups of animals, the aorta was isolated at 10 h after CLP and the vascular responses to an endothelium-dependent vasodilator, acetylcholine, and an endothelium-independent vasodilator, nitroglycerine, were determined. The results indicate that the number of E-NOS negative endothelial cells increased from 7% in shams to 22% in septic animals. E-NOS densely labeled endothelial cells were significantly reduced from 20% to 8% at 10 h after CLP. The E-NOS positive area in aortic endothelial cells was reduced from 26.1 +/- 1.0 microm2/standard frame in sham to 22.3 +/- 0.9 microm2/standard frame in septic animals. Moreover, acetylcholine-induced but not nitroglycerine-induced vascular relaxation was significantly depressed at 10 h after the onset of sepsis. These results, taken together, indicate that the decreased E-NOS in the vascular endothelial cell is at least in part responsible for endothelial cell dysfunction (i.e., the reduced endothelium-derived NO release) observed during the early, hyperdynamic stage of polymicrobial sepsis.

Evidence against a role of cytochrome P450-derived arachidonic acid metabolites in endothelium-dependent hyperpolarization by acetylcholine in rat isolated mesenteric artery

1. In rat mesenteric artery, acetylcholine (ACh) causes endothelium-dependent hyperpolarization by releasing endothelium-derived hyperpolarizing factor (EDHF). Recent evidence suggests that EDHF may be a cytochrome P450-derived arachidonic acid metabolite. The aim of the present study was to investigate whether such a metabolite is indeed contributing to ACh-induced hyperpolarization observed in rat mesenteric artery. 2. The phospholipase A2 inhibitor quinacrine (30 microM) nearly completely eliminated ACh-induced hyperpolarization. However, the hyperpolarizing effect of pinacidil was also abolished in the presence of quinacrine. 3. The imidazole antimycotic agents ketoconazole (50 microM), clotrimazole (30 microM) and miconazole (10 microM), which bind to the heme moiety of cytochrome P450, eliminated not only ACh-induced hyperpolarizations but also those induced by pinacidil. SKF525A (30 microM), a prototype inhibitor of the enzyme, also abolished the hyperpolarizing responses to both agents. In contrast, neither 17-octadecynoic acid (10 microM), a mechanism-based inhibitor of cytochrome P450 metabolism of fatty acids, nor eicosatetraynoic acid (20 microM), an inhibitor of all arachidonic acid metabolic pathways, altered ACh-induced hyperpolarization. Furthermore, the hyperpolarization was unaffected by the preferential inhibitors of specific cytochrome P450 isozymes, alpha-naphtoflavone (1 microM), diedthyldithiocarbamate (50 microM), metyrapone (20 microM) and troleandomycin (10 microM). 4. Pretreatment of rats with lipopolysaccharide (2 mg kg-1) and exposure to nitroprusside (10 microM), both of which are expected to inhibit cytochrome P450 activity due to nitric oxide overproduction, were without effect on ACh-induced hyperpolarization. Pretreatment of rats for 3 days with pentobarbitone (80 mg kg-1 day-1), a cytochrome P450 inducer, also did not affect the hyperpolarizing response to ACh. 5. Arachidonic acid in concentrations up to 100 microM had no detectable effect on smooth muscle membrane potential. 11, 12-Epoxyeicosatrienoic acid (EET, 10 microM), one of cytochrome P450-derived epoxygenase metabolites of arachidonic acid, elicited a small endothelium-independent membrane hyperpolarization. The hyperpolarizing response to EET was blocked by glibenclamide (30 microM), in contrast to the response to ACh. 6. These results suggest that the contribution of a cytochrome P450-derived metabolite of arachidonic acid to ACh-induced hyperpolarization via EDHF release is minimal or absent in rat mesenteric artery.

Decreased L-arginine-nitric oxide pathway in cultured myoblasts from spontaneously hypertensive versus normotensive Wistar-Kyoto rats

The hypertrophy of the arterial media exhibited by spontaneously hypertensive rats is related to the hyperproliferation of their smooth muscle cells in culture. Using two methods to assay nitric oxide synthase activity, we showed that this abnormal proliferation results from a decreased activity of the inducible NOS II and less modulation of this enzymatic activity by these cells compared to control Wistar Kyoto cells.

Hyporeactivity of mesenteric vascular bed in endotoxin-treated rats

Vascular reactivity and activation of the nitric oxide (NO) pathway were investigated in perfused mesenteric vascular bed removed from rats 5 h after i.p. injection of bacterial lipopolysaccharide (E. coli lipopolysaccharide, 30 mg kg -1). Lipopolysaccharide treatment induced hyporesponsiveness to noradrenaline. Maximal noradrenaline-induced vasoconstriction was significantly reduced in lipopolysaccharide-treated vs. untreated preparations. Continuous infusion of L-arginine (L-Arg) (0.2 mM) enhanced noradrenaline hyporeactivity of lipopolysaccharide-treated rats. N omega-Nitro-L-arginine methyl ester (L-NAME) (0.2 mM), a non-selective inhibitor of NO synthase, failed to completely restore the noradrenaline hyporeactivity of lipopolysaccharide-treated + L-Arg-infused mesenteric vascular bed. After L-NAME treatment. Methylene blue (10 microM), a guanylate cyclase inhibitor, produced no additional increase of noradrenaline vasoconstriction in lipopolysaccharide-treated + L-Arg-infused mesenteric vascular bed, suggesting that an NO-independent activation of guanylate cyclase may be excluded. In lipopolysaccharide-treated preparations, L-Arg (0.2 mM) elicited a significant increase in nitrite production, which was antagonized by L-NAME. In conclusion, lipopolysaccharide-induced noradrenaline hyporesponsiveness of rat resistance vessels can only be partially explained by NO overproduction. Other mechanisms, probably related to vasoconstriction, may be involved.

Inhibition of nitric oxide formation with L-canavanine attenuates endotoxin-induced vascular hyporeactivity in the rat

L-Canavanine, a selective inhibitor of inducible nitric oxide (NO) synthase, has beneficial effects on the circulatory failure of rats with endotoxin shock. To investigate the direct relationship between these beneficial effects and the inhibition of the formation of NO in response to L-canavanine in endotoxin shock in the rat, we detected changes in venous nitrosyl-hemoglobin (NO-hemoglobin) levels using an electron spin resonance (ESR) assay. Anaesthetized rats were injected with lipopolysaccharide (10 mg/kg i.v.). 1 h after the lipopolysaccharide injection, the rats were divided into four groups: a lipopolysaccharide group receiving 0.3 ml of saline hourly, an L-canavanine 10 or an L-canavanine 20 group receiving L-canavanine 10 or 20 mg/kg i.v. hourly, respectively, and an L-NAME group receiving NG-nitro-L-arginine methyl ester (L-NAME) 15 mg/kg followed by 10 mg/kg i.v. hourly. A sham group received saline instead of lipopolysaccharide, and an L-canavanine group received L-canavanine 20 mg/kg i.v. hourly, 1 h after the saline injection. At 5 h after the lipopolysaccharide or saline injection, pressor responses to noradrenaline (1 microgram/kg i.v.) were obtained. In the lipopolysaccharide group, lipopolysaccharide caused a progressive decrease in mean arterial pressure and an impairment of pressor responsiveness to noradrenaline. Administration of L-canavanine or L-NAME attenuated the endotoxin-induced hypotension and vascular hyporeactivity to noradrenaline. L-Canavanine did not alter mean arterial pressure and the pressor response to noradrenaline in the L-canavanine group. The endotoxin-induced increases in venous levels of NO-hemoglobin were significantly inhibited by L-canavanine or L-NAME. These data indicate that the beneficial hemodynamic effects of L-canavanine are associated with inhibition of the enhanced formation of NO by inducible NO synthase in a rat model of endotoxin shock. L-Canavanine is a potential agent in the treatment of endotoxin shock.

Nitric oxide is an autocrine feedback inhibitor of vascular smooth muscle contraction

BACKGROUND

Substances that increase intracellular calcium ([Ca2+]i), such as potassium chloride and serotonin, are known to induce vascular smooth muscle (VSM) contraction. One form of nitric oxide synthase, which converts L-arginine to nitric oxide, exists as a Ca(2+)-calmodulin dependent enzyme. The objective of this study was to determine whether agonists that induce VSM contraction by increasing [Ca2+]i might also activate Ca(2+)-calmodulin dependent nitric oxide synthase in VSM.

METHODS

Strips of bovine carotid arterial smooth muscle denuded of endothelium were equilibrated in a physiologic muscle bath. A maximal contractile response to high extracellular potassium chloride and serotonin was established. The strips were then preincubated with NG-monomethyl-L-arginine (L-NMMA), a structural analog of L-arginine and specific inhibitor of nitric oxide synthase, and again treated with either KCl or 5-hydroxytryptamine.

RESULTS

The contractile responses of muscle strips to KCl or 5-hydroxytryptamine were significantly greater in muscle strips pretreated with L-NMMA than responses in the absence of L-NMMA (p < 0.02, Student's t test). To determine whether this response was Ca2+ dependent, phorbolester-induced contractions in Ca(2+)-free conditions were examined. No difference was noted in the magnitude of Ca(2+)-free, phorbol ester-induced contractions in the presence and absence of L-NMMA.

CONCLUSIONS

These data thus suggest that Ca(2+)-calmodulin dependent nitric oxide synthase is functionally present in VSM and may function as an autocrine regulatory mechanism of VSM contraction.

Regulation of nitric oxide-like activity by prostanoids in smooth muscle of the canine saphenous vein

1. Organ bath experiments and measurements of prostanoids were performed to investigate the presence of nitric oxide synthase in venous smooth muscle and its interaction with cyclo-oxygenase. 2. In rings of canine saphenous vein without endothelium, the inhibitor of cyclo-oxygenase, indomethacin (10 microM), induced contraction. NG-nitro-L-arginine (100 microM) (L-NOARG), an inhibitor of nitric oxide synthase did not affect the tone of rings of canine saphenous vein when administered alone. However, in the presence of indomethacin L-NOARG (100 microM) induced further contraction. 3. Similar results were obtained in response to NG-monomethyl-L-arginine (L-NMMA)(300 microM or NG-nitro-L-arginine methylester (L-NAME)(100 microM). 4. When rings of canine saphenous vein without endothelium were contracted with phenylephrine (1 microM) instead of indomethacin, neither L-NOARG or L-NMMA induced further contraction. 5. When rings of canine saphenous vein without endothelium were contracted with noradrenaline (0.3 microM) in the presence of indomethacin (10 microM) plus L-NOARG (100 microM), a relaxation to L-arginine was observed. Transient relaxations to superoxide dismutase (150 u ml-1) were observed in all rings. 6. When rings of saphenous vein without endothelium were incubated with lipopolysaccharide (LPS) (100 micrograms ml-1) or interleukin-1 beta (10 u ml-1) the concentration-contraction curve to noradrenaline was not affected. 7. Rings without endothelium released prostaglandin E2 and prostaglandin I2, as measured by radioimmunoassay. The basal production was abolished by indomethacin and not affected by L-NOARG. 8. These results suggest that when cyclo-oxygenase is inhibited, a nitric oxide synthase activity is revealed in rings of canine saphenous vein without endothelium.

Induction of L-arginine transport and nitric oxide synthase in vascular smooth muscle cells: synergistic actions of pro-inflammatory cytokines and bacterial lipopolysaccharide

1. The interactions between pro-inflammatory cytokines and bacterial lipopolysaccharide (LPS) on L-arginine transporter and inducible nitric oxide synthase (iNOS) activities were examined in rat cultured aortic smooth muscle cells. 2. LPS induced a concentration (0.01-100 micrograms ml-1) and time (8-24 h)-dependent stimulation of nitrite production which was accompanied by a parallel increase in L-arginine transport. 3. Unlike LPS, activation of smooth muscle cells with either interferon-gamma (IFN-gamma, 100 u ml-1), tumour necrosis factor-alpha (TNF-alpha, 300 u ml-1) or interleukin-1 alpha (IL-1 alpha, 100 u ml-1) failed to stimulate L-arginine transport or increase nitrite accumulation. 4. When applied in combination with LPS (100 micrograms ml-1) both IFN-gamma and TNF-alpha, but not IL-1 alpha, enhanced the effects observed with LPS alone. Furthermore, activation of cells with LPS and IFN-gamma had no effect on uptake of the neutral amino acid L-citrulline but selectively increased the Vmax for L-arginine transport 2.8 fold and nitrite levels from 24 +/- 7 to 188 +/- 14 pmol micrograms-1 protein 24 h-1. 5. The substrate specificity, Na- and pH-independence of saturable L-arginine transport in both unactivated (K(m) = 44 microM, Vmax = 3 pmol micrograms-1 protein min-1) and activated (K(m) = 75 microM, Vmax = 8.3 pmol micrograms-1 protein min-1) smooth muscle cells were characteristic of the cationic amino acid transport system y+. 6. Cycloheximide (1 microM) abolished induction of L-arginine transport and nitrite accumulation in response to LPS and IFN-gamma. In contrast, the glucocorticoid dexamethasone (10 microM, 24 h) selectively inhibited nitrite production. 7. Our results demonstrate that pro-inflammatory mediators selectively enhance transport of L-arginine under conditions of sustained NO synthesis by vascular smooth muscle cells. In addition, the differential inhibition of iNOS and L-arginine transporter activity by dexamethasone suggests that distinct signalling pathways mediate induction of the cationic transport protein and iNOS. The close coupling between substrate supply and NO production may have important implications in the pathogenesis of several disease states including endotoxin shock.

Nitric oxide synthase induction and relaxation in lipopolysaccharide-treated gastric fundus muscle of rats

To investigate whether L-arginine/nitric oxide (NO) pathway activated after treatment with lipopolysaccharide (LPS) could relax the gastric fundus smooth muscle, we made functional examinations and measured NO synthase activity by the conversion of radiolabelled L-arginine to L-citrulline in rat gastric fundus strips treated with LPS in vitro. L-arginine caused a relaxation of the mucosa-free gastric fundus strips which had been treated with LPS for 6 h in vitro and then contracted by PGF2alpha beforehand. This relaxation was partially reversed by N(G)-nitro-L-arginine (a nitric oxide synthase inhibitor) or methylene blue (a soluble guanylate cyclase inhibitor). Ca(2+)-independent NO synthase activity was induced after LPS-treatment. Co-incubation with LPS and cycloheximide for 6 h inhibited the relaxation to L-arginine and the induction of NO synthase. On the other hand, Ca(2+)-dependent NO synthase activity was decreased after LPS-treatment. These results strongly suggest that Ca(2+)-independent NO synthase is induced by endotoxin in the gastric fundus muscle, resulting in inhibition of the contractile response.

Induction of nitric oxide synthase activity in rodent brain following middle cerebral artery occlusion

The conversion of L-[3H]arginine to L-[3H]citrulline in the absence of calcium can be used to assay selectively the activity of inducible nitric oxide synthase (NOS) in rat spleen homogenates 6 h after lipopolysaccharide administration. Using similar assay conditions, changes in inducible NOS activity were measured within ischemic brain tissue between 2 h and 7 days following permanent middle cerebral artery (MCA) occlusion in Sprague-Dawley rats and SV-129 mice. Total (constitutive and inducible) NOS activity was measured in the presence of 0.5 mM CaCl2. Whereas total NOS activity in rat decreased dramatically to 16% and 6% of baseline 6 and 12 h after MCA occlusion, inducible NOS activity remained undetectable before 2 days after occlusion, became maximal at 3 days, and decreased to less than 10% of maximal iNOS activity at 7 days. In the mouse, total NOS activity decreased after MCA occlusion but inducible NOS activity was undetectable from 2 h to 4 days after occlusion. Sustained NO production by inducible NOS activity does not contribute to ischemic injury within 24 h after MCA occlusion, but may contribute to infarct maturation 2-4 days after ischemia in some but not all species.