The inducible nitric oxide synthase in vascular and cardiac tissue

Early administration of L-arginine in mdx neonatal mice delays the onset of muscular dystrophy in tibialis anterior (TA) muscle

Duchenne muscular dystrophy (DMD) is a genetic disorder that results in the absence of dystrophin, a cytoskeletal protein. Individuals with this disease experience progressive muscle destruction, which leads to muscle weakness. Studies have been conducted to find solutions for the relief of individuals with this disease, several of which have shown that utrophin, a protein closely related to dystrophin, when overexpressed in mdx neonatal mice (the murine model of DMD), is able to prevent the progressive muscle destruction observed in the absence of dystrophin. Furthermore, recent studies have shown that L‐arginine induces utrophin upregulation in adult mdx mice. We hypothesized that L‐arginine treatment also induces utrophin upregulation to prevent the development of muscle weakness in neonatal mdx mice. Hence, L‐arginine should also prevent progressive muscle destruction via utrophin upregulation in mdx neonatal mice. Mdx neonatal mice were injected intraperitoneally daily with 800 mg/kg of L‐arginine for 6 weeks, whereas control mice were injected with a physiological saline. The following experiments were performed on the tibialis anterior (TA) muscle: muscle contractility and resistance to mechanical stress; central nucleation and peripheral nucleation, utrophin, and creatine kinase quantification as well as a nitric oxide (NO) assay. Our findings show that early administration of L‐arginine in mdx neonatal mice prevents the destruction of the tibialis anterior (TA) muscle. However, this improvement was related to nitric oxide (NO) production rather than the expected utrophin upregulation.

HDAC6 Mediates Macrophage iNOS Expression and Excessive Nitric Oxide Production in the Blood During Endotoxemia

Excessive nitric oxide (NO) production and NO-mediated nitrative stress contribute to vascular dysfunction, inflammation, and tissue injury in septic shock. New therapeutic targets are urgently needed to provide better control of NO level during septic shock. In the present study, we investigated the role of HDAC6 in the regulation of NO production and nitrative stress in a mouse model of endotoxin-induced septic shock. HDAC6 deficient mice and a specific HDAC6 inhibitor were utilized in our studies. Our data clearly indicate that HDAC6 is an important mediator of NO production in macrophages. HDAC6 mediates NO production through the regulation of iNOS expression in macrophages. HDAC6 up-regulates iNOS expression in macrophages by modulating STAT1 activation and IRF-1 expression. HDAC6 inhibition potently blocked endotoxin-induced STAT1 activation and iNOS expression in macrophages. Furthermore, HDAC6 contributes to excessive NO production and nitrotyrosine level in the blood and promotes iNOS expression in the lung tissues during septic shock. Our data reveal a novel HDAC6/STAT1/iNOS pathway that mediates excessive NO production and nitrative stress in septic shock.

Relationship between inducible NOS single-nucleotide polymorphisms and hypertension in Han Chinese

BACKGROUND

Inducible nitric oxide synthase (iNOS) single-nucleotide polymorphisms have been reported to confer susceptibility to hypertension, but no consensus has been reached. The aim of this study was to investigate the association between iNOS and hypertension in a Chinese population.

METHODS

This was a case-control study including 1172 hypertensive and 1172 control subjects to investigate the association between iNOS and hypertension.

RESULTS

There were significant differences in the distribution of genotype and allele frequencies of rs2779249 and rs2297518 between hypertensive and normotensive subjects. Logistic regression analyses were performed with different genetic models (additive, dominant, recessive) adjusting for confounding risk covariates, including age, sex, body mass index, total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, smoking, drinking, and family history of hypertension. The odds ratio (OR) was 1.27 (1.12, 1.44) in the additive model, 1.31 (1.09, 1.59) in the dominant, and 1.68 (1.28, 2.19) in the recessive model of rs2779249; the OR was 1.26 (1.06, 1.50) in the additive model and 1.46 (1.13, 1.89) in the dominant model of rs2297518.

CONCLUSION

The current study provides evidence that iNOS is strongly associated with hypertension.

Involvement of inducible nitric oxide synthase in radiation-induced vascular endothelial damage

The use of radiation therapy has been linked to an increased risk of cardiovascular disease. To understand the mechanisms underlying radiation-induced vascular dysfunction, we employed two models. First, we examined the effect of X-ray irradiation on vasodilation in rabbit carotid arteries. Carotid arterial rings were irradiated with 8 or 16 Gy using in vivo and ex vivo methods. We measured the effect of acetylcholine-induced relaxation after phenylephrine-induced contraction on the rings. In irradiated carotid arteries, vasodilation was significantly attenuated by both irradiation methods. The relaxation response was completely blocked by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a potent inhibitor of soluble guanylate cyclase. Residual relaxation persisted after treatment with L-N(ω)-nitroarginine (L-NA), a non-specific inhibitor of nitric oxide synthase (NOS), but disappeared following the addition of aminoguanidine (AG), a selective inhibitor of inducible NOS (iNOS). The relaxation response was also affected by tetraethylammonium, an inhibitor of endothelium-derived hyperpolarizing factor activity. In the second model, we investigated the biochemical events of nitrosative stress in human umbilical-vein endothelial cells (HUVECs). We measured iNOS and nitrotyrosine expression in HUVECs exposed to a dose of 4 Gy. The expression of iNOS and nitrotyrosine was greater in irradiated HUVECs than in untreated controls. Pretreatment with AG, L-N(6)-(1-iminoethyl) lysine hydrochloride (a selective inhibitor of iNOS), and L-NA attenuated nitrosative stress. While a selective target of radiation-induced vascular endothelial damage was not definitely determined, these results suggest that NO generated from iNOS could contribute to vasorelaxation. These studies highlight a potential role of iNOS inhibitors in ameliorating radiation-induced vascular endothelial damage.

Excess no predisposes mitochondrial succinate-cytochrome c reductase to produce hydroxyl radical

Mitochondria-derived oxygen-free radical(s) are important mediators of oxidative cellular injury. It is widely hypothesized that excess NO enhances O(2)(•-) generated by mitochondria under certain pathological conditions. In the mitochondrial electron transport chain, succinate-cytochrome c reductase (SCR) catalyzes the electron transfer reaction from succinate to cytochrome c. To gain the insights into the molecular mechanism of how NO overproduction may mediate the oxygen-free radical generation by SCR, we employed isolated SCR, cardiac myoblast H9c2, and endothelial cells to study the interaction of NO with SCR in vitro and ex vivo. Under the conditions of enzyme turnover in the presence of NO donor (DEANO), SCR gained pro-oxidant function for generating hydroxyl radical as detected by EPR spin trapping using DEPMPO. The EPR signal associated with DEPMPO/(•)OH adduct was nearly completely abolished in the presence of catalase or an iron chelator and partially inhibited by SOD, suggesting the involvement of the iron-H(2)O(2)-dependent Fenton reaction or O(2)(•-)-dependent Haber-Weiss mechanism. Direct EPR measurement of SCR at 77K indicated the formation of a nonheme iron-NO complex, implying that electron leakage to molecular oxygen was enhanced at the FAD cofactor, and that excess NO predisposed SCR to produce (•)OH. In H9c2 cells, SCR-dependent oxygen-free radical generation was stimulated by NO released from DEANO or produced by the cells following exposure to hypoxia/reoxygenation. With shear exposure that led to overproduction of NO by the endothelium, SCR-mediated oxygen-free radical production was also detected in cultured vascular endothelial cells.

Effects of a selective iNOS inhibitor versus norepinephrine in the treatment of septic shock

Inhibition of NOS is not beneficial in septic shock; selective inhibition of the inducible form (iNOS) may represent a better option. We compared the effects of the selective iNOS inhibitor BYK191023 with those of norepinephrine (NE) in a sheep model of septic shock. Twenty-four anesthetized, mechanically ventilated ewes received 1.5 g/kg body weight of feces into the abdominal cavity to induce sepsis. Animals were randomized into three groups (each n = 8): NE-only, BYK-only, and NE + BYK. The sublingual microcirculation was evaluated with sidestream dark-field videomicroscopy. MAP was higher in the NE + BYK group than in the other groups, but there were no significant differences in cardiac index or systemic vascular resistance. Mean pulmonary arterial pressure was lower in BYK-treated animals than in the NE-only group. PaO2/FiO2 was higher and lactate concentration lower in the BYK groups than in the NE-only group. Mesenteric blood flow was higher in BYK groups than in the NE-only group. Renal blood flow was higher in the NE + BYK group than in the other groups. Functional capillary density and proportion of perfused vessels were higher in the BYK groups than in the NE-only group 18 h after induction of peritonitis. Survival times were similar in the three groups. In this model of peritonitis, selective iNOS inhibition had more beneficial effects than NE on pulmonary artery pressures, gas exchange, mesenteric blood flow, microcirculation, and lactate concentration. Combination of this selective iNOS inhibitor with NE allowed a higher arterial pressure and renal blood flow to be maintained.

Beneficial effects of melatonin on cardiological alterations in a murine model of accelerated aging

This study investigated the effect of aging-related parameters such as inflammation, oxidative stress and cell death in the heart in an animal model of accelerated senescence and analyzed the effects of chronic administration of melatonin on these markers. Thirty male mice of senescence-accelerated prone (SAMP8) and 30 senescence-accelerated-resistant mice (SAMR1) at 2 and 10 months of age were used. Animals were divided into eight experimental groups, four from each strain: two young control groups, two old untreated control groups, and four melatonin-treated groups. Melatonin was provided at two different dosages (1 and 10 mg/kg/day) in the drinking water. After 30 days of treatment, the expression of inflammatory mediators (tumor necrosis factor-alpha, interleukin 1 and 10, NFkBp50 and NFkBp52), apoptosis markers (BAD, BAX and Bcl2) and parameters related to oxidative stress (heme oxygenases 1 and 2, endothelial and inducible nitric oxide synthases) were determined in the heart by real-time reverse transcription polymerase chain reaction (RT-PCR). Inflammation, as well as, oxidative stress and apoptosis markers was increased in old SAMP8 males, when compared to its young controls. SAMR1 mice showed significantly lower basal levels of the measured parameters and smaller increases with age or no increases at all. After treatment with melatonin, these age-altered parameters were partially reversed, especially in SAMP8 mice. The results suggest that oxidative stress and inflammation increase with aging and that chronic treatment with melatonin, a potent antioxidant, reduces these parameters. The effects were more marked in the SAMP8 animals.

Increased expression of endothelial iNOS accounts for hyporesponsiveness of pulmonary artery to vasoconstrictors after paraquat poisoning

Paraquat is a toxic herbicide that induces severe acute lung injury (ALI) and pulmonary hypertension in humans. Although vascular disorders are present and contribute to increased mortality in ALI patients, there is little data available on vascular responsiveness after toxic exposure to paraquat. We aimed to evaluate the vascular response of isolated pulmonary arteries from rats treated with a dose of paraquat that induces ALI. Paraquat treatment did not modify the relaxant response of pulmonary artery to acetylcholine, but greatly reduced phenylephrine-induced contraction. Removal of the endothelium, inhibition of nitric oxide synthase (NOS) with L-NAME or selective inhibition of inducible NOS (iNOS) with L-NIL, restored contraction of vessels from paraquat poisoned rats to the same level as those not exposed to paraquat. The basal production of NO and expression of iNOS were increased in endothelium-intact but not in endothelium-denuded vessels from paraquat-poisoned rats. Expression of endothelial NOS was not modified. Our findings suggest that paraquat poisoning increases endothelial iNOS expression and basal NO production decreasing responsiveness of pulmonary artery to vasoconstrictors. Thus, our results do not support the hypothesis that pulmonary hypertension in paraquat-induced ALI is mediated by a reduction in endothelial NO production or increased contractility of pulmonary artery.

Additional lack of iNOS attenuates diastolic dysfunction in aged ET-1 transgenic miceThis article is one of a selection of papers published in the special issue (part 1 of 2) on Forefronts in Endothelin

Endothelin-1 (ET-1) exhibits potent proinflammatory and profibrotic properties. Moreover, inflammation is a potent stimulus for inducible NO synthase (iNOS), which has been shown to contribute to cardiac injury. We thus hypothesized that ET-1-induced cardiac injury is attenuated by concomitant lack of iNOS. We established crossbred animals of ET-1 transgenic mice (ET+/+) and iNOS knockout mice (iNOS−/−). At 13 months of age, mice were allocated according to their genotype to one of 4 study groups: wild type (WT) controls (n = 8); ET-1 transgenic (ET+/+) mice (n = 10); iNOS knockout (iNOS−/−) mice (n = 7); and crossbred (ET+/+ iNOS−/−) mice (n = 15). Left ventricular function was determined in vivo by using a tip catheter. Animals were subsequently euthanized and hearts were harvested for weight assessment and histologic evaluation. No cardiac hypertrophy was present, as evidenced by similar mean cardiac weight and myocyte diameter in all groups. Cardiac perivascular fibrosis was significantly increased in ET+/+ and iNOS−/− groups versus WT, whereas ET+/+ iNOS−/− mice did not differ from WT. Regarding left ventricular function, plasma B-type natriuretic peptide was elevated in ET+/+ and iNOS−/− mice, but again in crossbred animals this effect was blunted. Heart catheterization revealed a significantly increased stiffness constant in both ET-overexpressing groups versus WT, but this increase was significantly attenuated in the ET+/+iNOS−/− group versus the ET+/+ group. Parameters indicating systolic heart failure (EF, cardiac output), however, were not different between all study groups. Our study demonstrates that ET transgenic mice develop left ventricular stiffening with subsequent diastolic dysfunction in a slow, age-dependent manner. Additional knock out of iNOS significantly attenuates cardiac injury. We thus conclude that ET-1-induced cardiac injury is at least partially mediated by iNOS.

Novel aspects of endothelium-dependent regulation of vascular tone

The vascular endothelium plays a crucial role in the regulation of vascular homeostasis and in preventing the initiation and progress of cardiovascular disease by controlling mechanical functions of the underlying vascular smooth muscle. Three vasodilators: nitric oxide (NO), prostacyclin, and endothelium-derived hyperpolarizing factor, produced by the endothelium, underlie this activity. These substances act in a co-ordinated interactive manner to maintain normal endothelial function and operate as support mechanisms when one pathway malfunctions. In this review, we discuss recent advances in our understanding of how gender influences the interaction of these factors resulting in the vascular protective effects seen in pre-menopausal women. We also discuss how endothelial NO synthase (NOS) can act in both a pro- and anti-inflammatory action and therefore is likely to be pivotal in the initiation and time course of an inflammatory response, particularly with respect to inflammatory cardiovascular disorders. Finally, we review recent evidence demonstrating that it is not solely NOS-derived NO that mediates many of the beneficial effects of the endothelium, in particular, nitrite acts as a store of NO released during pathological episodes associated with NOS inactivity (ischemia/hypoxia). Each of these more recent findings has emphasized new pathways involved in endothelial biology, and following further research and understanding of the significance and mechanisms of these systems, it is likely that new and improved treatments for cardiovascular disease will result.

Nitric oxide/redox-based signalling as a therapeutic target for penile disorders

Oxidative and/or nitrosative stress is implicated in the pathogeneses of assorted penile disorders of clinical significance, notably erectile dysfunction, priapism and penile fibrosis. It is becoming increasingly recognised that the generation and activity of reactive oxygen and nitrogen species in the penis influence vascular homeostasis of this organ, with adverse effects exerted at cellular and molecular levels. Furthermore, these elements may interact with molecular signalling pathways operating in the penis, modulating their functional roles. This interaction in particular suggests that by accessing molecular targets associated with oxidative/nitrosative stress in the penis, new pharmacotherapeutic approaches may be developed to promote normal erectile ability and preserve erectile tissue health. This notion pertains to, but also extends beyond, interventions which predictably target components of the nitric oxide-based signal transduction pathway for the on-demand treatment of erectile dysfunction. The next line of pharmaceuticals for disorders of the penis, in general, may well spawn from an integrative understanding of the complex regulatory interactions influenced by, as well as influencing nitric oxide signalling in this organ.

Role of inducible nitric oxide synthase in cardiac function and remodeling in mice with heart failure due to myocardial infarction

Using inducible nitric oxide (NO) synthase (iNOS) knockout mice (iNOS−/−), we tested the hypotheses that 1) lack of iNOS attenuates cardiac remodeling and dysfunction and improves cardiac reserve postmyocardial infarction (MI), an effect that is partially mediated by reduction of oxidative stress due to reduced interaction between NO and reactive oxygen species (ROS); and 2) the cardioprotection afforded by iNOS deletion is eliminated by Nω-nitro-l-arginine methyl ester (l-NAME) due to inhibition of endothelial NOS (eNOS) and neuronal NOS (nNOS). MI was induced by ligating the left anterior descending coronary artery. Male iNOS−/− mice and wild-type controls (WT, C57BL/6J) were divided into sham MI, MI+vehicle, and MI+l-NAME (100 mg·kg−1·day−1 in drinking water for 8 wk). Cardiac function was evaluated by echocardiography. Left ventricular (LV) maximum rate of rise of ventricular pressure divided by pressure at the moment such maximum occurs (dP/d t/instant pressure) in response to isoproterenol (100 ng·kg−1·min−1 iv) was measured with a Millar catheter. Collagen deposition, myocyte cross-sectional area, and expression of nitrotyrosine and 4-hydroxy-2-nonenal (4-HNE), markers for ROS, were determined by histopathological and immunohistochemical staining. We found that the MI-induced increase in LV chamber dimension and the decrease in ejection fraction, an index of systolic function, were less severe in iNOS−/− compared with WT mice. l-NAME worsened LV remodeling and dysfunction further, and these detrimental effects were also attenuated in iNOS−/− mice, associated with better preservation of cardiac function. Lack of iNOS also reduced nitrotyrosine and 4-HNE expression after MI, indicating reduced oxidative stress. We conclude that iNOS does not seem to be a pathological mediator of heart failure; however, the lack of iNOS improves cardiac reserve post-MI, particularly when constitutive NOS isoforms are blocked. Decreased oxidative stress and other adaptive mechanisms independent of NOS may be partially responsible for such an effect, which needs to be studied further.

Effects of Inducible Nitric Oxide Synthase Inhibition on the Rat Tail Vascular Bed Reactivity Three Days After Myocardium Infarction

The acute phase of myocardial infarction promotes an inflammatory response that stimulates inducible nitric oxide synthase (iNOS). We investigated the iNOS role on the rat tail vascular bed reactivity 3 days after myocardial infarction. Vasodilator and vasoconstrictor responses were determined in isolated caudal vascular beds from Wistar rats 3 days after coronary artery ligation (CAL) and sham-operated animals (SHAM). Rats were treated with the iNOS inhibitor S-methylisothiourea sulfate (SMT), 5 mg Kg day, i.p. or placebo. Concentration of plasma nitrite/nitrate (NOx) and the expression of iNOS mRNA in tail arteries were evaluated. The CAL group showed increased maximal vasoconstrictor response to phenylephrine (SHAM= 241 +/- 8; CAL= 288 +/- 13 mm Hg, P < 0.05) and SMT treatment normalized this effect (CAL-SMT = 253 +/- 7 mm Hg, P < 0.05). The sensitivity to acetylcholine was reduced in the CAL group, but SMT treatment did not alter this response. The plasma NOx and iNOS mRNA expression in tail arteries were increased in CAL rats. SMT treatment reduced the plasma NOx in the CAL group and the arterial expression of iNOS mRNA in SHAM and CAL group. In conclusion, iNOS inhibition prevented the increased phenylephrine reactivity in rat caudal vascular beds 3 days after myocardial infarction.

The chemistry of nitrosative stress induced by nitric oxide and reactive nitrogen oxide species. Putting perspective on stressful biological situations

This review addresses many of the chemical aspects of nitrosative stress mediated by N2O3. From a cellular perspective, N2O3 and the resulting reactive nitrogen oxide species target specific motifs such as thiols, lysine active sites, and zinc fingers and is dependant upon both the rates of production as well as consumption of NO and must be taken into account in order to access the nitrosative environment. Since production and consumption are integral parts of N2O3 generation, we predict that nitrosative stress occurs under specific conditions, such as chronic inflammation. In contrast to conditions of stress, nitrosative chemistry may also provide cellular protection through the regulation of critical signaling pathways. Therefore, a careful evaluation of the chemistry of nitrosation based upon specific experimental conditions may provide a better understanding of how the subtle balance between oxidative and nitrosative stress may be involved in the etiology and control of various disease processes.

Hyperbaric oxygen therapy prevents vascular derangement during zymosan-induced multiple-organ-failure syndrome

OBJECTIVE

This study investigated the effects of hyperbaric oxygen (HBO) therapy on the cardiovascular alteration (e.g. mean arterial pressure, vascular reactivity of thoracic aorta rings changes) caused by zymosan in rats.

DESIGN

Rats.

SETTING

University research laboratory.

INTERVENTION AND MEASUREMENTS

We investigated the effects of HBO therapy (2 ATA at the fourth and eleventh hours after study onset) on the cardiovascular alteration caused by zymosan (500 mg/kg, administered i.p. as a suspension in saline) in rats. Cardiovascular alterations were assessed 18 h after administration of zymosan and/or HBO therapy.

RESULTS

Treatment of rats with HBO therapy attenuated the vasoplegic response to zymosan. In fact, the analysis of arterial pressure curves revealed no signs of vasoplegic shock. The aorta rings of animals treated with zymosan and HBO had a significantly increased contraction to norepinephrine (NE) and endothelin-1 (ET-1) and dilation to acetylcholine (ACh) compared with the zymosan group. The HBO therapy also attenuated the increase of malondialdehyde (MDA) levels caused by zymosan in the aorta. Immunohistochemical analysis for nitrotyrosine and for iNOS revealed positive staining in the aorta from zymosan-treated rats. The degree of staining for nitrotyrosine and iNOS was markedly reduced in tissue sections obtained from zymosan-rats treated with HBO therapy.

CONCLUSION

This study provides the first evidence that HBO therapy attenuates the degree of zymosan-induced cardiovascular derangement in the rat.

Constitutive nitric oxide production in bovine aortic and brain microvascular endothelial cells: a comparative study

Vascular endothelium constitutively generates nitric oxide (NO) in large vessels and induces a relaxation of smooth muscle cells. However, little is known about the production of NO in microvessels, where smooth muscle layers are thin or absent. In this study, we have compared the constitutive production of NO in bovine brain microvascular endothelial cells (BBECs) with that in bovine aortic endothelial cells (BAECs). ATP, acetylcholine (ACh) and A23187 induced Ca(2+) transients both in BBECs and BAECs. In contrast, although ATP and A23187 evoked a similar degree of [Ca(2+)](i) increase in both types of cell, they failed to induce NO production in BBECs, as measured with an NO-sensitive fluorescent dye DAF-2, whereas in BAECs there was an increase in DAF-2 fluorescence. Hypotonic stress induced ATP release and subsequent NO production in BAECs, but not in BBECs. We have developed an in vitro model vessel system that consists of aortic smooth muscle cells embedded in a collagen gel lattice and overlaid with endothelial cells. Precontracted gels showed relaxation in response to ACh, when BAECs were overlaid. However, ACh-induced relaxation was not observed in BBEC-overlaid gels. Expression of eNOS protein as well as cellular uptake of l-[(3)H]arginine were significantly lower in BBECs than in BAECs. These results indicate that Ca(2+)-dependent NO production is at an undetectable level in BBEC, for which at least two factors, i.e. low levels of eNOS expression and l-arginine uptake, are responsible.

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.

Age-related endothelial dysfunction : potential implications for pharmacotherapy

Aging per se is associated with abnormalities of the vascular wall linked to both structural and functional changes that can take place at the level of the extracellular matrix, the vascular smooth muscle and the endothelium of blood vessels. Endothelial dysfunction is generally defined as a decrease in the capacity of the endothelium to dilate blood vessels in response to physical and chemical stimuli. It is one of the characteristic changes that occur with age, independently of other known cardiovascular risk factors. This may account in part for the increased incidence of cardiovascular events in elderly people that can be reversed by restoring endothelial function. A better understanding of the mechanisms involved and the aetiopathogenesis of this process will help in the search for new therapeutic agents.Age-dependent alteration of endothelium-dependent relaxation seems to be a widespread phenomenon both in conductance and resistance arteries from several species. In the course of aging, there is an alteration in the equilibrium between relaxing and contracting factors released by the endothelium. Hence, there is a progressive reduction in the participation of nitric oxide and endothelium-derived hyperpolarising factor associated with increased participation of oxygen-derived free radicals and cyclo-oxygenase-derived prostanoids. Also, the endothelin-1 and angiotensin II pathways may play a role in age-related endothelial dysfunction. The use of drugs acting at different levels of these signalling cascades, including antioxidant therapy, lipid-lowering drugs and estrogens, seems to be promising.

Protective effect of 3-deazaadenosine in a rat model of lipopolysaccharide-induced myocardial dysfunction

Severe sepsis is accompanied by a profound depression of myocardial contractility. Leukocyte adhesion with subsequent local excess nitric oxide and reactive oxygen species production play major roles for this deleterious effect. We hypothesized that 3-deazaadenosine (c3Ado), an adenosine analogue with anti-inflammatory properties, prevents endotoxin-induced myocardial dysfunction. Wistar rats (8 per group) were treated with Escherichia coli lipopoly-saccharide (LPS, 1 mg/kg, i.p., strain 0111:B4) +/- c3Ado (10 mg/kg, i.p.) 8 h before their hearts were harvested for isolated perfusion, histochemical analysis, or electrophoretic mobility shift assay. LPS induced a marked depression of left ventricular contractility. Immunohistochemistry revealed an upregulation of the adhesion molecules VCAM-1, ICAM-1, and P-selectin within the postcapillary venules. c3Ado inhibited VCAM-1 and ICAM-1 upregulation, but not P-selectin, and prevented cardiodepression. Electrophoretic mobility shift assay revealed inactivation of the transcription factor nuclear factor-kappaB and immunohistochemical staining for gp91phox, ED1, and CD11b demonstrated that c3Ado prevented local recruitment of monocytes and polymorph nuclear neutrophils to the myocardium. Accordingly, significantly fewer leukocytes producing nitric oxide or reactive oxygen species accumulated within the myocardium. Intravital microscopy of intestinal venules confirmed that LPS-induced adhesion of leukocytes was prevented by c3Ado. Additionally, c3Ado prevented LPS-induced elevation of serum tumor necrosis factor-alpha levels. Our results imply that c3Ado may prove to have clinical relevance for inflammatory disease processes.

Cardiovascular and renal control in NOS-deficient mouse models

Nitric oxide (NO) plays an essential role in the maintenance of cardiovascular and renal homeostasis. Endogenous NO is produced by three different NO synthase (NOS) isoforms: endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS). To investigate which NOS is responsible for NO production in different tissues, NOS knockout (-/-) mice have been generated for the three isoforms. This review focuses on the regulation of cardiovascular and renal function in relation to blood pressure homeostasis in the different NOS-/- mice. Although regulation of vascular tone and cardiac function in eNOS-/- has been extensively studied, far less is known about renal function in these mice. eNOS-/- mice are hypertensive, but the mechanism responsible for their high blood pressure is still not clear. Less is known about cardiovascular and renal control in nNOS-/- mice, probably because their blood pressure is normal. Recent data suggest that nNOS plays important roles in cardiac function, renal homeostasis, and regulation of vascular tone under certain conditions, but these are only now beginning to be studied. Inasmuch as iNOS is absent from the cardiovascular system under physiological conditions, it may become important to blood pressure regulation only during pathological conditions related to inflammatory processes. However, iNOS is constitutively expressed in the kidney, where its function is largely unknown. Overall, the study of NOS knockout mice has been very useful and produced many answers, but it has also raised new questions. The appearance of compensatory mechanisms suggests the importance of the different isoforms to specific processes, but it also complicates interpretation of the data. In addition, deletion of a single gene may have physiologically significant effects in addition to those being studied. Thus the presence or absence of a specific phenotype may not reflect the most important physiological function of the absent gene.

Evidence that intrinsic iron but not intrinsic copper determines S-nitrosocysteine decomposition in buffer solution

The present experiments were designed to analyze the influence of copper and iron ions on the process of decomposition of S-nitrosocysteine (cysNO), the most labile species among S-nitrosothiols (RSNO). CysNO fate in buffer solution was evaluated by optical and electron paramagnetic resonance (EPR) spectroscopy, and the consequences on its vasorelaxant effect were studied on noradrenaline-precontracted rat aortic rings. The main results are the following: (i) copper or iron ions, especially in the presence of the reducing agent ascorbate, accelerated the decomposition of cysNO and markedly attenuated the amplitude and duration of the relaxant effect of cysNO; (ii) by contrast, the iron and copper chelators bathophenantroline disulfonic acid (BPDS) and bathocuproine disulfonic acid (BCS) exerted a stabilizing effect on cysNO, prolonged its vasorelaxant effect, and abolished the influence of ascorbate; (iii) in the presence of ascorbate, BPDS displayed a selective inhibitory effect toward the influence of iron ions (but not toward copper ions) on cysNO decomposition and vasorelaxant effect, while BCS prevented the effects of both copper and iron ions; (iv) L-cysteine enhanced stability and prolonged the relaxant effect of cysNO; (v) the process of iron-induced decomposition of cysNO was associated with the formation of EPR-detectable dinitrosyl-iron complexes (DNIC) either with non-thiol- or thiol-containing ligands (depending on the presence of L-cysteine), both of which exhibiting vasorelaxant properties. From these data, it is concluded that the amount of intrinsic copper was probably too low to produce a destabilizing effect even on the most labile RSNO, cysNO, and that only intrinsic iron, through the formation of DNIC, was responsible for the process of cysNO decomposition and thus influenced its vasorelaxant properties.

Gene transfer of inducible nitric oxide synthase impairs relaxation in human and rabbit cerebral arteries

BACKGROUND AND PURPOSE

These studies evaluated whether gene transfer of inducible nitric oxide synthase (iNOS) is a sufficient stimulus to produce vascular dysfunction in cerebral arteries.

METHODS

Intracranial (pial) arteries were dissected from human brain tissue obtained during elective surgery. Isolated human arteries were incubated in vitro with adenovirus containing iNOS (AdiNOS) or a nonexpressive transgene (control, AdBglII) (500 micro L, 3x10(9) plaque-forming units per milliliter), and vascular function was examined 24 hours later. In anesthetized rabbits, AdiNOS or AdBglII (300 microL 1x10(10)) was injected into the cisterna magna. Three days later, the basilar artery was removed, and reactivity was examined ex vivo.

RESULTS

In submaximally precontracted vessels, we observed impairment of NO-dependent relaxation in human cerebral arteries after gene transfer of iNOS. Maximum relaxation to bradykinin (1 micromol/L, an endothelium-dependent agonist) was 77+/-11% (mean+/-SE) after AdBglII and 31+/-22% (P<0.05) after AdiNOS. After AdiNOS, responses to nitroprusside (an endothelium-independent NO donor) also were impaired. Responses to both nitroprusside and bradykinin were improved by aminoguanidine (300 micromol/L), an inhibitor of iNOS. AdiNOS produced no change in vasoconstrictor responses to U46619. In basilar arteries from rabbits examined in vitro after gene transfer in vivo, responses to histamine, serotonin, and nitroprusside all were similar after AdiNOS or AdBglII. In contrast, relaxation to acetylcholine was significantly depressed after AdiNOS. Maximum relaxation to acetylcholine (10 micromol/L) was 90+/-3% after AdBglII and 68+/-5% (P<0.05) after AdiNOS. Relaxation of arteries after AdiNOS was improved by aminoguanidine.

CONCLUSIONS

These studies suggest that expression of iNOS may impair NO-dependent relaxation in both human and rabbit cerebral arteries.

Inhibition of leukocyte rolling by nitric oxide during sepsis leads to reduced migration of active microbicidal neutrophils

We developed two models of sepsis with different degrees of severity, sublethal and lethal sepsis, induced by cecal ligation and puncture. Lethal sepsis induced by cecal ligation and puncture (L-CLP) resulted in failure of neutrophil migration to the infection site and high mortality. Treatment of septic animals with aminoguanidine (AG), a nitric oxide (NO) synthase inhibitor, precluded the failure of neutrophil migration and protected the animals from death. However, cytokine-induced NO synthase (iNOS)-deficient (iNOS(-/-)) mice subjected to L-CLP did not present neutrophil migration failure, but 100% lethality occurred. iNOS(-/-) mice subjected to sublethal sepsis induced by cecal ligation and puncture (SL-CLP) also suffered high mortality despite the occurrence of neutrophil migration. This apparent paradox could be explained by the lack of microbicidal activity in neutrophils of iNOS(-/-) mice present at the infection site due to their inability to produce NO. Notably, SL- and L-CLP iNOS(-/-) mice showed high bacterial numbers in exudates. The inhibition of neutrophil migration by NO is due to inhibition of a neutrophil/endothelium adhesion mechanism, since a reduction in leukocyte rolling, adhesion, and emigration was observed in L-CLP wild-type mice. These responses were prevented by AG treatment and were not observed in the iNOS(-/-) L-CLP group. There was no significant change in L-selectin expression in neutrophils from L-CLP mice. Thus, it seems that the decrease in leukocyte rolling is due to a defect in the expression of adhesion molecules on endothelial surfaces mediated by iNOS-derived NO. In conclusion, the results indicate that despite the importance of NO in neutrophil microbicidal activity, its generation in severe sepsis reduces neutrophil migration by inhibiting leukocyte rolling and their firm adhesion to the endothelium, in effect impairing the migration of leukocytes and consequently their fundamental role in host cell defense mechanisms.

Failure of neutrophil chemotactic function in septic patients

OBJECTIVE

To investigate the in vitro chemotactic function of neutrophils obtained from patients with sepsis.

DESIGN

Prospective study in which purified neutrophils obtained from septic patients and nonseptic control volunteers were assayed for chemotactic function induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) and leukotriene B4. The sera nitrate concentrations also were quantified.

SETTING

University hospital.

PATIENTS

Twenty patients with sepsis caused by different infectious foci.

INTERVENTIONS

Routine blood tests, blood or other site cultures, blood collection for neutrophil purification sera collection for nitrate assay.

MEASUREMENTS AND MAIN RESULTS

Neutrophils from septic patients exhibited significantly less chemotactic activity than neutrophils obtained from healthy volunteers, in response to FMLP (93.4 +/- 6.6 vs. 51 +/- 8.3 migrated neutrophils) and leukotriene B4 (90.2 +/- 10 vs. 42.4 +/- 11.6 migrated neutrophils) stimuli, in a microchemotaxis chamber assay. The impaired chemotaxis occurred mainly in neutrophils from nonsurvivor patients. The extent of neutrophil chemotaxis inhibition (survivor/nonsurvivor) was 33.43%/61.67% and 43.4%/86.98%, in response to FMLP and leukotriene B4, respectively. Increased serum nitrate (micromoles of NO2 + NO3) concentrations were detected in septic patients, compared with controls, but no differences were found between survivor (91.84 +/- 14.12) and nonsurvivor (102.6 +/- 17.36) groups.

CONCLUSIONS

Septic patients present suppressed neutrophil chemotactic responses to FMLP and leukotriene B4 stimuli compared with healthy controls. This is accompanied by increased serum concentrations of nitrate. The impairment of neutrophil chemotaxis was observed mainly in the cells obtained from nonsurvivor patients and may thus be an additional factor contributing to disease outcome.

Nitric oxide transport and storage in the cardiovascular system

Despite short halflife in biological fluids, nitric oxide (NO) can produce remote or long lasting effect in the cardiovascular system. Long distance transport or local storage of NO might explain these effects. In blood, recent findings suggest that in addition to being a major consumption pathway, interaction of NO with hemoglobin may permit O(2)-governed transport of NO (as S-nitrosohemoglobin) to tissues in which NO may be released together with O(2), via transnitrosation of a transport protein. In blood vessels, two different putative NO stores have been characterized. The first is the photosensitive store, formed from endothelium-derived NO. The mechanism of NO release from this store in the body (in absence of light) and its physiological relevance are unknown. The second store is generated in conditions of high tissue NO levels, as a consequence of the inducible NO synthase activity or in various stress conditions. This NO store involves formation of protein-bound dinitrosyl iron complexes or S-nitrosated proteins, or both. Low molecular weight thiols can displace NO from these stores and probably transfer it to target membrane protein(s) such as K(+) channels, via transnitrosation reactions. These stores may be involved in defence mechanisms against inflammation or stress. Thus, NO transport and storage mechanisms may be implicated in a variety of NO effects. The mechanisms of their formation and of NO release and their physiologic and pathophysiologic relevance deserve further investigations.

Modification of alpha1 -adrenoceptors by peroxynitrite as a possible mechanism of systemic hypotension in sepsis

OBJECTIVE

It is well known that nitric oxide synthase is induced by endotoxin or inflammatory cytokines, and consequently large amounts of nitric oxide cause vascular hyporeactivity to vasoconstrictor agents and myocardial dysfunction, hence hypotension. However, there is considerable controversy as to whether these pathologic cardiovascular features are mediated directly by nitric oxide or also through the formation of secondary reaction products such as peroxynitrite (ONOO-1). Our objective was to investigate inhibitory effects of ONOO-1 on alpha1-adrenoceptors.

DESIGN

Prospective, controlled, in vitro, laboratory study.

SETTING

Laboratory of a health sciences university.

SUBJECTS

Chinese hamster ovary cells that expressed the human recombinant alpha1a-, alpha1b-, or alpha1d-adrenoceptors, rat aorta strips.

INTERVENTIONS

Binding experiments of [3H]prazosin were done in the Chinese hamster ovary cell membranes pretreated with 100 microM to 3 mM ONOO-1. Displacement experiments with noradrenaline or 3-nitro-l-tyrosine also were conducted. Mobilization of intracellular Ca2+ evoked by 1 nM to 10 microM noradrenaline was monitored in a fluorescence spectrophotometer with dual excitation at 340 nm/380 nm and emission at 500 nm in fura-2/AM-loaded Chinese hamster ovary cells. Contractile force produced by noradrenaline was monitored in rat aorta strips that have alpha1a- and alpha1d-adrenoceptors, pretreated with 1 mM ONOO-1. Either 0.3 N NaOH or the decomposed ONOO-1 was used as the control.

MEASUREMENTS AND MAIN RESULTS

The specific binding of [3H]prazosin to alpha1a- and alpha1d-adrenoceptor was inhibited by ONOO-1 in a concentration-dependent manner. We found that 3 mM ONOO-1 decreased maximum binding sites by 40% to 50% in alpha1a- and alpha1d-adrenoceptors. Binding affinities for prazosin and noradrenaline were not affected by 1 mM ONOO-1 in all subtypes. We found that 3-nitro-l-tyrosine did not affect the prazosin binding to three adrenoceptor subtypes. Noradrenaline increased intracellular Ca2+ concentration ([Ca2+]i) concentration-dependently, which was inhibited by ONOO-1 in alpha1a- and alpha1d-adrenoceptors. ONOO-1 had no effect on alpha1b-adrenoceptor. Contractile force produced by noradrenaline decreased significantly in aorta strips pretreated with ONOO-1.

CONCLUSION

ONOO-1 reduces the binding capacity of alpha1a- and alpha1d- but not alpha1b-adrenoceptors without changing the affinities. Treatment with ONOO-1 attenuates noradrenaline-stimulated increase in [Ca2+]i in alpha1a- and alpha1d-adrenoceptors but not in alpha1b-adrenoceptor. ONOO-1 also weakens noradrenaline-induced contractions in rat aorta that has alpha1a- and alpha1d-adrenoceptors. Cardiovascular hyporeactivity to catecholamines in septic shock may be caused in part by the inactivation of alpha-adrenoceptors by ONOO-1.

Protective effects of dihydropyridine Ca-blockers against endothelial cell oxidative injury due to combined nitric oxide and superoxide

Nitric oxide (NO) and superoxide anions (*O(2)(-) ), which are known to be generated by inflammatory cells under certain pathological conditions, may be cytotoxic to the endothelial cells (ECs) due to peroxynitrite formation. We reported previously that certain lipophilic dihydropyridine (DHP) Ca-blockers exhibit antioxidant activities. In the present study, the extent of antioxidant protection by nisoldipine against combined NO/*O(2)(-) or peroxynitrite-mediated EC injury was assessed and compared with nicardipine, nifedipine and Trolox (water-soluble vitamin E). When confluent bovine aortic ECs were exposed to combined NO/*O(2)(-) (generated from 0.25 mM SIN-1), dramatic loss of cell GSH (53 +/- 8%) occurred in 60 min; cell survival/viability, determined 24 h later by the tetrazolium MTT assay, decreased by 45 +/- 6%. NO alone or O(2)(-) alone were ineffective. Nisoldipine pretreatment (30 min) of the cells concentration dependently (0.3-10 micro M) attenuated the SIN-1-induced GSH loss: the EC(50)value was 4.7 micro M and the corresponding values for nicardipine and nifedipine were 7.8 micro M and >20 micro M, respectively, and that for Trolox was 5.2 micro M. These agents (10 micro M) also protected against the loss of cell viability: nisoldipine, 86 plus minus 8%; nicardipine, 60 +/- 7 %; nifedipine, 35 +/- 5 %, and Trolox, 78 +/- 9%. In addition, significant losses of GSH and viability could be induced by incubation of the EC monolayers with purified peroxynitrite (25 micro M). Attenuation of these peroxynitrite-mediated GSH and viability losses was observed with the following order of efficacy: nisoldipine > or = Trolox > nicardipine >> nifedipine. In a cell-free system containing 0.05 mM GSH, none of the agents (10 micro M) were able to inhibit SIN-1- (0.25 mM) or peroxynitrite- (25 micro M) induced depletion (approximately 50%) of GSH. However, with a purified microsomal membrane system, all four agents inhibited the SIN-1- (or peroxynitrite-) induced lipid peroxidation (TBARS) with the following IC(50)values: nisoldipine, 6.3 micro M; nicardipine, 10.6 micro M; nifedipine, >20 micro M, and Trolox, 6.5 micro M. In conclusion, nisoldipine, a vascular selective DHP calcium channel-blocker, demonstrated the greatest protection against the EC injury induced either by SIN-1 or peroxynitrite. The protective mechanism against the cytotoxicity is most likely through a lipophilic 'chain-breaking' antiperoxidative action against the 'OH-like species' released from peroxynitrite or SIN-1.

N-acetylcysteine inhibits in vivo nitric oxide production by inducible nitric oxide synthase

This in vivo study evaluates the effect of N-acetylcysteine (NAC) administration on nitric oxide (NO) production by the inducible form of nitric oxide synthase (iNOS). NO production was induced in the rat by the ip administration of 2 mg/100 g lipopolysaccharide (LPS). This treatment caused: (1) a decrease in body temperature within 90 min, followed by a slow return to normal levels; (2) an increase in plasma levels of urea, nitrite/nitrate, and citrulline; (3) the appearance in blood of nitrosyl-hemoglobin (NO-Hb) and in liver of dinitrosyl-iron-dithiolate complexes (DNIC); and (4) increased expression of iNOS mRNA in peripheral blood mononuclear cells (PBMC). Rat treatment with 15 mg/100 g NAC ip, 30 min before LPS, resulted in a significant decrease in blood NO-Hb levels, plasma nitrite/nitrate and citrulline concentrations, and liver DNIC complexes. PBMC also showed a decreased expression of iNOS mRNA. NAC pretreatment did not modify the increased levels of plasma urea or the hypothermic effect induced by the endotoxin. The administration of NAC following LPS intoxication (15 min prior to sacrifice) did not affect NO-Hb levels. These results demonstrate that NAC administration can modulate the massive NO production induced by LPS. This can be attributed mostly to the inhibitory effect of NAC on one of the events leading to iNOS protein expression. This hypothesis is also supported by the lack of effect of late NAC administration.

Inhibition of endotoxin-induced vascular hyporeactivity by 4-amino-tetrahydrobiopterin

The 4-amino analogue of tetrahydrobiopterin (4-ABH(4)) is a potent pterin-site inhibitor of nitric oxide synthases (NOS). Although 4-ABH(4) does not exhibit selectivity between purified NOS isoforms, a pronounced selectivity of the drug towards inducible NOS (iNOS) is apparent in intact cells. This work was carried out to investigate the potential iNOS selectivity of 4-ABH(4) in isolated pig pulmonary and coronary arteries. Endothelium-dependent relaxations of pig pulmonary and coronary artery strips to bradykinin or calcium ionophore A23187 were inhibited by 4-ABH(4) in a concentration-dependent manner. Half-maximal inhibition was observed at 60 - 65 microM (pulmonary artery) and 200 - 250 microM 4-ABH(4) (coronary artery). Pig coronary artery strips precontracted with 0.1 microM 9, 11-dideoxy-9, 11-methanoepoxy-prosta-glandin F(2alpha) (U46619) showed a time-dependent relaxation (monitored for up to 18 h) upon incubation with 1 microg ml(-1) lipopolysaccharide (LPS). Addition of 10 microM 4-ABH(4) 1 h after LPS led to a pronounced inhibition of the LPS-triggered relaxation, whereas the pterin antagonist had no effect when given> or =4 h after LPS. Incubation of pulmonary and coronary artery strips with 1 microg ml(-1) LPS attenuated contractile responses to norepinephrine (1 microM) and U46619 (0.1 microM). This hyporeactivity of the blood vessels to vasoconstrictor agents was inhibited by 4-ABH(4) in a concentration-dependent manner [IC(50)=17.5+/-5.9 microM (pulmonary artery) and 20.7+/-3 microM (coronary artery)]. The effect of 0.1 mM 4-ABH(4) was antagonized by coincubation with 0.1 mM sepiapterin, which is known to supply intracellular BH(4) via a salvage pathway. These results demonstrate that 4-ABH(4) is a fairly selective inhibitor of iNOS in an in vitro model of endotoxaemia, suggesting that this drug and/or related pterin-site NOS inhibitors may be useful to increase blood pressure in severe infections associated with a loss of vascular responsiveness to constrictor agents caused by endotoxin-triggered iNOS induction in the vasculature.

Effect of the selective adenosine A1-receptor antagonist KW-3902 on lipopolysaccharide-induced reductions in urine volume and renal blood flow in anesthetized dogs

We investigated the effects of KW-3902 (8-noradamantan-3-yl-1,3-dipropylxanthine), a potent and selective adenosine A1-receptor antagonist, on lipopolysaccharide (LPS)-induced reduction of urine volume (UV) in anesthetized dogs, in comparison with those of furosemide. LPS was intravenously administered at a dose of 0.5 mg/kg; and the heart rate (HR), systemic blood pressure (BP), renal blood flow (RBF) and UV were measured every 15 min for 4 h. Administration of LPS continuously decreased HR, BP, RBF and UV. KW-3902, furosemide or their corresponding vehicle was given as a bolus injection 5 min after the LPS injection. Treatment with KW-3902 (1 mg/kg, i.v.) ameliorated the LPS-induced decline of UV and RBF. Furosemide (3.2 mg/kg, i.v.) tended to ameliorate the LPS-induced decline of UV but not RBF, the duration of the effect being shorter than that of KW-3902. These results suggest that KW-3902 can ameliorate the oliguria and the decrease in RBF during the early phase of LPS-induced shock. Endogenous adenosine may be involved in the endotoxin-induced oliguria via the adenosine A1-receptor.

Basic FGF reduces stunning via a NOS2-dependent pathway in coronary-perfused mouse hearts

Basic fibroblast growth factor (FGF-2) may protect the heart from ischemia-reperfusion injury (stunning) by stimulating nitric oxide (NO) production. To test this hypothesis, we pretreated coronary-perfused mouse hearts with 1 microg/ml FGF-2 or vehicle control before the onset of ischemia. Intracellular calcium (Ca(i)(2+)) was estimated by aequorin, and NO release was measured with an NO-selective electrode. Hearts perfused with FGF-2 maintained significantly better left ventricular (LV) function during ischemia than hearts perfused with vehicle. FGF-2 significantly delayed the onset of ischemic contracture and improved LV recovery during reperfusion. Ca(i)(2+) was similar in both groups at baseline during ischemia and reperfusion. L-N(6)-(1-iminoethyl)lysine, a selective inhibitor of inducible NO synthase (NOS2), obliterated the protective effects of FGF-2. In transgenic hearts deficient in the expression of NOS2 (NOS2-/-), FGF-2 did not attenuate ischemia-induced LV dysfunction. Measurements of NO release demonstrated that FGF-2 perfusion significantly increased NO in wild-type but not in NOS2-/- hearts. We conclude that basic FGF attenuates myocardial stunning independent of alterations in Ca(i)(2+) by stimulating NO production via an NOS2-dependent pathway.