Inducible nitric oxide synthase and inflammation

Nitric oxide (NO), derived from L-arginine (L-Arg) by the enzyme nitric oxide synthase (NOS), is involved in acute and chronic inflammatory events. In view of the complexity associated with the inflammatory response, the dissection of possible mechanisms by which NO modulates this response will be profitable in designing novel and more efficacious NOS inhibitors. In this review we describe the consequences associated with the induction of inducible nitric oxide synthase (iNOS) and its therapeutic implications.     

Adaptation of glycocalyx,nitric oxide synthase expression and vascular cell apoptosis in conduit arteries of tail‐suspended rats

The importance of vascular cell glycocalyx in mechanotransduction has been demonstrated by many studies. The simulated microgravity induced a region‐dependent adaptation of arterial glycocalyx including its thickness, coverage, and gene expression in conduit arteries of tail‐suspended rats has been reported in our previous studies. Herein, we extended this line of research by quantifying the mRNA levels of three nitric oxide synthase (NOSI, NOSII, and NOSIII) and evaluating the apoptotic rates of endothelial cells (ECs) and smooth muscle cells (SMCs) in the common carotid artery, abdominal aorta, and femoral artery of 3 week tail‐suspended rats. Results indicated that the tail suspension of rats induced about 0.36, 0.22, and 0.33 fold down‐regulation of NOSI, NOSII, and NOSIII in the abdominal aorta, while 3.21, and 3.48 fold up‐regulation of NOSII and NOSIII in the carotid artery and no significant effects on three NOS isoforms in the femoral artery. Moreover, the apoptosis of ECs and SMCs were significantly inhibited in both carotid artery and abdominal aorta, while enhanced in the femoral artery of the tail‐suspended rats. A linear positive correlation exists between the normalized coverage of the glycocalyx and the normalized NOSI and NOSIII mRNA levels. These results indicated that the redistribution of haemodynamics in the conduit arteries of 3 week tail‐suspended rats regulated the glycocalyx, NOS expression, and vascular cell apoptosis in a region‐dependent manner, contributing to the final vascular remodelling under simulated microgravity condition.     

Altered L-arginine/nitric oxide synthase/nitric oxide pathway in the vascular adventitia of rats with sepsis

1. In recent studies, the vascular adventitia has been established as an important source of inducible nitric oxide synthase (iNOS) and subsequent nitric oxide (NO) production, even more powerful than the media in response to certain inflammatory factors, such as lipopolysaccharide (LPS). The adventitia has an independent L-arginine (L-Arg)/NOS/NO pathway and is involved in the regulation of vascular function. In the present study, we explored the changes in and the pathophysiological significance of the L-Arg/NOS/NO pathway in the adventitia of rats with sepsis. 2. Sepsis was induced by caecal ligation and puncture in order to observe changes in L-Arg transport, NOS gene expression and activity and NO generation in the vascular adventitia to determine the mechanism of activation of the L-Arg/NOS/NO pathway. 3. Severe sepsis resulted in severe disturbance of haemodynamic features, with decreased mean arterial blood pressure, brachycardia and inhibited cardiac function (decreased left ventricular +/-dP/dt(max)). Left ventricular end-diastolic pressure was elevated threefold (P < 0.01) under anaesthesia. Rats with sepsis showed severe glucopenia and lacticaemia. Plasma levels of the inflammatory factors macrophage chemoattractant protein-1 and interleukin-8 were increased five- and 29-fold, respectively (P < 0.01). 4. In the adventitia of the thoracic and abdominal aortas, the L-Arg/NO pathway was similarly characterized: the uptake of [(3)H]-L-Arg was Na(+) independent, with the peak occurring at approximately 40 min incubation. Total NOS activity was largely calcium independent (> 90%). The V(max) of L-Arg transport in the sepsis group was increased by 83.5% (P < 0.01), but the K(m) value was not significantly different compared with controls. 5. The mRNA levels of cationic amino acid transporter (CAT)-1 and CAT-2B in the sepsis group were increased by 86 and 62%, respectively (both P < 0.01). Inducible NOS activity was increased 2.8-fold compared with controls (P < 0.01) and iNOS mRNA levels were elevated approximately sixfold (P < 0.01). The NO levels in the plasma and incubation media (incubation for 40 min) in the sepsis group were increased by 144 and 273%, respectively (both P < 0.01). 6. The Arg/NOS/NO pathway was activated in the vascular adventitia of rats with sepsis shock. The L-Arg/NOS/NO pathway in the aortic adventitia may play an important role in the pathogenesis of sepsis and septic shock.     

Exercise training upregulates nitric oxide synthases in the kidney of rats with chronic heart failure

相似文献   

年龄及人参皂甙 Rg1 对大鼠大脑皮层 NO 释放的影响

探讨了NO与衰老的关系及与Rg1抗衰老机制的关系。用Griess法,³H-L-精氨酸转化法分别研究大鼠大脑皮层细胞NO含量及NOS活性,观察其随龄变化及人参皂甙Rg1(Rg1)对老年鼠NO及NOS的影响。实验表明,成年鼠(9月龄)与青年鼠(3月龄)NO含量及NOS活性无显著性差异。老年鼠(27月龄)脑皮层NO含量明显高于青年鼠和成年鼠,NOS活性也明显增高。老年鼠给予Rg1后可显著减少大脑皮层NO含量和降低NOS活性。结果提示,NO与衰老关系密切,Rg1的抗衰老作用与其对NOS活性的抑制有关。     

Endogenous nitric oxide decreases hippocampal levels of serotonin and dopamine in vivo

Nitric oxide (NO) modulates the levels of various neurotransmitters in the CNS. Here we determined whether the specific nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI), the non-selective inhibitor of guanylate cyclase (GC) and NOS, methylene blue (MB), the NO-precursor L-arginine (L-Arg), and the selective soluble GC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) affect extracellular levels of serotonin (5-HT), dopamine (DA), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA) in the rat ventral hippocampus by using microdialysis in freely moving animals. Local perfusion of 7-NI (1 mM) and MB (1 mM) significantly increased extracellular level of 5-HT, whereas DA was increased by 7-NI only. Systemic administration of 7-NI (50 mg kg(-1)) and MB (30 mg kg(-1)) increased the extracellular levels of 5-HT and DA. Extracellular levels of 5-HIAA was not influenced by local or systemic MB or 7-NI. In contrast, extracellular level of HVA was decreased by systemic MB and retrodialyzed MB, but was not influenced by 7-NI. Retrodialysis of L-Arg (2 mM) decreased the levels of 5-HT, DA, 5-HIAA and HVA in the hippocampus. Systemic administration of L-Arg (250 mg kg(-1)) decreased the level of 5-HT, but failed to influence DA, 5-HIAA and HVA. Local perfusion of ODQ (400 microM) did not affect 5-HT overflow in the hippocampus. We conclude that NOS inhibitors increased extracellular levels of 5-HT and DA in the rat ventral hippocampus after local or systemic administration, whereas the NO precursor L-Arg had the opposite effect. Thus, endogenous NO may exert a negative control over the levels of 5-HT and DA in the hippocampus. However, this effect is probably not mediated by cyclic GMP.     

Cognitive dysfunction induced by phenytoin and valproate in rats: effect of nitric oxide

Phenytoin (PHT) and Valproate (VPA) are known to induce cognitive dysfunction, in terms of long term memory loss. Nitric oxide (NO) on the other hand is said to help in long term potentiation and hence enhance memory. The effects of nitric oxide donor L-arginine (L-Arg) and nitric oxide synthase inhibitor N-W-L-Nitroarginine (L-NOARG) were studied on the cognitive dysfunction, induced by PHT and VPA in normal healthy rats, using the step-through passive avoidance test (PAT). It was observed that combining L-Arg with PHT significantly enhanced long term memory while, combining PHT with L-NOARG decreased it, as compared to PHT alone. When combined with VPA, L-Arg and L-NOARG increased the retention latency as compared to PVA alone but this was not statistically significant. We conclude that the No donor L-Arg is able to increase the difference in LTE in acquisition and retention trials with both PHT and VPA, but with VPA the increase is not statistically significant.     

Pharmacologic manipulation of nitric oxide signaling: targeting NOS dimerization and protein-protein interactions

Nitric oxide (NO) is an endogenously-produced small molecule that has critical roles in cellular signaling and a variety of physiological processes in many tissues, including the brain, the vasculature, and the immune system. In several medical disorders, NO has been implicated in disease pathology, in most cases due to persistent activation or overproduction of one of three NO synthase (NOS) isoforms. Although NOS inhibitors that are both potent and cell-permeable have been developed, none is currently used in the treatment of any disorder. One reason that NOS inhibitors fail to have therapeutic efficacy may be linked to their very low isoform-selectivity. An additional possibility is that NOS inhibitors, even if they exhibit isoform selectivity, might indiscriminately affect beneficial and pathological NO signaling pathways. In this review, we discuss emerging approaches in the development of isoform-specific NOS-directed therapeutics including dimerization inhibitors, novel L-arginine (L-Arg) binding site inhibitors, and dimer stabilization. Additionally, we suggest novel strategies for the future including targeting subcellular localization of NOS and protein-protein interactions with NOS effectors.     

Nitric oxide modulates cardiovascular function in the rat by activating adenosine A2A receptors and inhibiting acetylcholine release in the rostral ventrolateral medulla

1. Nitric oxide (NO), a gas transmitter, modulates many physiological processes, including the central regulation of cardiovascular activity. However, the mechanisms underlying the regulation of cardiovascular activity remain relatively unexplored. In the present study, we hypothesized that central NO-dependent sympathetic inhibition is mediated by activation of adenosine A(2A) receptors (A(2A)R) and inhibition of acetylcholine (ACh) release in the rostral ventrolateral medulla (RVLM). 2. L-Arginine (L-Arg; an NO donor; 100 nmol/100 nL) was microinjected into the RVLM of male Sprague-Dawley rats and heart rate variability (HRV) was assessed as an index of cardiac sympathovagal balance. Following microinjection of L-Arg, decreases were seen in mean arterial pressure (MAP), heart rate (HR) and the ratio of the low- to high-frequency components (LF/HF) of HRV. Pretreatment of rats with SCH58261 (40 pmol/60 nL into the RVLM), a competitive antagonist of the A(2A) R, attenuated these effects. 3. Western blot analysis and ELISA revealed that adenosine and A(2A)R levels increased in the RVLM following L-Arg microinjection, whereas ACh and muscarinic M(1) receptor levels decreased significantly, in parallel with the cardiovascular responses to L-Arg microinjection. The decrease in ACh levels was abolished by SCH58261 pretreatment. 4. Microinjection of N(G)-nitro-L-arginine methyl ester (a non-selective inhibitor of NO synthase; 15 nmol/100 nL) into the RVLM significantly increased MAP, HR and sympathetic activity, as evidenced by HRV (LF, HF and the LF/HF ratio were all increased). 5. The results indicate that the central NO/NO synthase system in the RVLM may modulate cardiovascular activity by activating the A(2A)R, which subsequently inhibits activation of the muscarinic M(1) receptor.     

Effect of pregnancy on the roles of nitric oxide and prostaglandins in 5-hydroxytryptamine-induced contractions in rat isolated thoracic and abdominal aorta

1. Vascular resistance and sensitivity to circulating pressor and vasoconstrictor substances are blunted during pregnancy. This has been attributed mainly to an increased production of endothelium-derived mediators. The aim of the present study was to determine whether pregnancy changes the relative participation of nitric oxide (NO) and prostaglandins (PG) in the modulation of the contractile response to 5-hydroxytryptamine (5-HT) in two anatomically distint segments of the rat aorta. 2. Full concentration-response curves to 5-HT were obtained in isolated rings from the thoracic and abdominal portion of the aorta from pregnant and non-pregnant rats in the presence and absence of the NO synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME; 10 micromol/L) or the PG synthesis inhibitor indomethacin (10 micromol/L). Cyclo-oxygenase (COX)-1, COX-2 and endothelial (e) NOS protein expression were determined in the same tissues by immunoblot. 3. The effects of pregnancy were accentuated in the abdominal compared with the thoracic aorta. In addition, the relative participation of the NO and PG pathways seems to be changed during pregnancy. Although NO seems to be the mediator mainly responsible for the effect of pregnancy in the thoracic aorta, our results suggest a complex interaction between NO and PG in the abdominal aorta. Indomethacin significantly reduced the contractile response of both segments of the aorta, whereas expression of COX-1, COX-2 and eNOS were increased only in the abdominal segment of pregnant animals. 4. These results show that the effect of pregnancy is not homogeneous along the aorta. There seems to be a mutual interaction between PG and NO in the abdominal, but not in the thoracic, aorta from pregnant rats: the role of NO becomes evident in the absence of vasodilatory PG, whereas the participation of the latter increases in the absence of NO working as a compensatory mechanism.     

葛根素对糖尿病大鼠胰腺线粒体NO及自由基的影响

目的：探讨葛根素对实验性糖尿病大鼠胰腺线粒体保护作用的机制。方法：30只Wistar大鼠随机分为正常对照组、糖尿病组和治疗组。采用四氧嘧啶腹腔注射复制糖尿病动物模型。葛根素注射液治疗8周后,观测胰腺线粒体中超氧化物歧化酶（SOD）、谷胱甘肽过氧化物酶（GSH—Px）及一氧化氮合酶（NOS）活力;测定胰腺线粒体丙二醛（MDA）及一氧化氮（NO）含量。结果：葛根素治疗组胰腺线粒体SOD、GSH-Px活力较糖尿病组均有显著升高（P〈0．01或P〈0．05）,而NOS活力、MDA及NO含量明显降低（P〈0．01或P〈0．05）。结论：葛根素对糖尿病大鼠胰腺有保护作用。其机制可能是：清除自由基,减少脂质过氧化物的生成;降低线粒体NOS活力,从而减轻NO所致的损伤。     

Erythropoietin administration in vivo increases vascular nitric oxide synthase expression

This study was designed to determine whether recombinant human erythropoietin (rHuEpo) administration increases vascular nitric oxide (NO) production in healthy rats. We hypothesized that rHuEpo hypertension is associated with increased endothelial expression of nitric oxide synthase and augmented NO-dependent vasodilation. Male rats were instrumented with pulsed Doppler flow probes around their ascending aorta and with arterial and femoral catheters. Rats were treated for 14 days with rHuEpo (2 U/d) or vehicle. rHuEpo elevated hematocrit and increased mean arterial pressure (142 +/- 3 versus 116 +/- 4 mm Hg). Thoracic aorta segments from rHuEpo rats had a modest increase in NO-dependent relaxation assessed by acetylcholine (10(-10) to 10(-5) mol/L) relaxation of phenylephrine (PE) (10(-6) mol/L) contracted arteries. Relaxation to NO-donor, s-nitrosyl acetylpenicillamine, and PE contraction were not different from control arteries. The NO synthase inhibitor, N-omega-nitro-L-arginine, increased blood pressure and total peripheral resistance more in rHuEpo rats at both 10 and 30 mg/kg. NOS expression in rHuEpo aorta and plasma NOx concentrations were increased compared with control. Thus, it appears that vascular eNOS expression is increased and causes basal vasodilation in rHuEpo hypertensive rats.     

The role of nitric oxide (NO) in control of LHRH release that mediates gonadotropin release and sexual behavior

Nitric oxide (NO) plays a crucial role in reproduction at every level in the organism. In the brain, it activates the release of luteinizing hormone-releasing hormone (LHRH). The axons of the LHRH neurons project to the mating centers in the brain stem and by efferent pathways, evoke the lordosis reflex in female rats. In males, there is activation of NOergic terminals that release NO in the corpora cavernosa penis to induce erection by generation of cyclic guanosine monophosphate (cGMP). NO also activates the release of LHRH which reaches the pituitary and activates the release of gonadotropins by activating neural NO synthase (NOS) in the pituitary gland. Follicle stimulating hormone (FSH)RH selectively releases FSH also by activating NOS. Leptin releases LHRH by activating NOS to release FSH and LH with the same potency as LHRH. These actions are mediated by specific receptors on the gonadotropes for LHRH, FSHRH and leptin. The responsiveness of the pituitary is controlled by gonadal steroids. In the gonad, NO plays an important role inducing ovulation and in causing luteolysis; whereas in the reproductive tract, it relaxes uterine muscle via cGMP and constricts it by prostaglandins.     

木贼水煎剂对高血脂大鼠主动脉内皮细胞的保护作用

目的 探讨木贼对食饵性高脂血症大鼠主动脉内皮细胞的保护作用.方法 48只SD大鼠随机分为4组,成功复制高脂血症和早期动脉粥样硬化模型,测定血清NO含量及NOS活性;流式细胞仪检测内皮细胞凋亡率及Bcl-2和Bax基因蛋白的表达; 光镜和电镜观察内皮细胞的形态学改变.结果 木贼能纠正由高脂血症所致的NO代谢紊乱;调控Bcl-2和Bax的比值,降低内皮细胞的凋亡率;减轻动脉内皮细胞的损伤程度.结论 木贼可明显改善高脂血症所致的动脉内皮细胞的功能障碍和形态损伤.     

Correlation between brain nitric oxide synthase activity and opiate withdrawal

The opiate withdrawal induced by administration of naloxone to morphine-dependent mice correlates with an increment of calcium- dependent nitric oxide synthase (NOS) activity in the cerebellum. L-NAME, an irreversible competitive inhibitor of NOS (0.5, 5, 25, 50 mg/kg) injected sc. 45 min. prior to naloxone significantly reduced the number of escape jumps and other motor symptoms of abstinence. In addition, L-NAME also decreased NOS activity in cerebellum. L-arginine, but not D-arginine, when coadministered with L-NAME, prevented both the inhibition of NOS activity and the reduction of withdrawal symptoms induced by L-NAME in morphine-withdrawn animals. These results demonstrate a hyperactivity of the L-arginine: NO pathway in opiate withdrawal and suggests the possibility of a therapeutic use of NOS inhibitors in this state.Abbreviations EAA Excitatory amino acid - LC Locus coeruleus - L-NAME N-nitro L-arginine methyl ester - NMDA N-methyl-D-aspartate - NO Nitric oxide - NOS Nitric oxide synthase     

Sodium hydrosulfide alleviated pulmonary vascular structural remodeling induced by high pulmonary blood flow in rats

AIM: To explore the possible role of endogenous hydrogen sulfide (H(2)S), a novel gasotransmitter, in the pathogenesis of pulmonary vascular structural remodeling (PVSR) induced by high pulmonary blood flow. METHODS: Thirty-two Sprague-Dawley male rats were randomly divided into sham, shunt, sham+NaHS (a H(2)S donor) and shunt+NaHS groups. Rats in shunt and shunt+NaHS groups underwent an abdominal aorta-inferior vena cava shunt, and rats in shunt+NaHS and sham+NaHS groups were intraperitoneally injected with NaHS. PVSR was investigated using optical microscope and transmission electron microscope. Lung tissue H(2)S was evaluated by sulfide-sensitive electrodes. Nitric oxide synthase (NOS), heme oxygenase (HO-1), proliferative cell nuclear antigen (PCNA) and extracellular signal-regulated kinase (ERK) activation were analyzed by Western blotting. RESULTS: After 11 weeks of shunting, PVSR developed with a decrease in lung tissue H(2)S production and an increase in nitric oxide (NO). However, lung tissue carbon monoxide (CO) did not change. After the treatment with NaHS for 11 weeks, H(2)S donor ameliorated PVSR and downregulated PCNA expression and ERK activation with an increase in lung tissue CO production and HO-1 protein expression but a decrease in NO production, NOS activity and eNOS protein expression in shunted rats. CONCLUSIONS: H(2)S exerted a regulatory effect on PVSR induced by high pulmonary blood flow. Meanwhile, H(2)S down-regulated the ERK/MAPK signal pathway, inhibited the NO/NOS pathway and enhanced the CO/HO pathway in rats with high pulmonary blood flow.     

2型糖尿病大鼠主动脉内皮细胞氧化损伤及缬沙坦的保护作用

目的探讨2型糖尿病大鼠氧化应激与主动脉内皮细胞损伤的关系,观察缬沙坦对两者的影响。方法SD大鼠,用长期高能量饮食加小剂量注射链脲佐菌素(STZ)的方法复制模型。注射STZ12wk末,将大鼠分为3组:正常组、糖尿病组、缬沙坦治疗组(24mg·kg-1·d-1,灌胃给药8wk)。在注射STZ12和20wk末,检测大鼠的内皮依赖性血管舒张反应及主动脉内皮形态,血清超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)活性,丙二醛(MDA)和一氧化氮(NO)含量,以及主动脉一氧化氮合酶(NOS)基因表达情况。结果①12wk末,糖尿病大鼠主动脉对低浓度乙酰胆碱(ACh)舒张反应减弱,局部内皮隆起,血清SOD、GSH-Px活性增强,MDA和NO含量增加,主动脉iNOS mRNA表达明显上调,eNOS mRNA表达无明显改变。②20wk末,糖尿病大鼠主动脉对各浓度ACh的反应性均减弱,主动脉内皮变性、坏死,血清SOD、GSH-Px活性减弱,MDA含量进一步增加,NO含量下降,主动脉iNOS mRNA表达仍升高,eNOS mRNA表达降低,缬沙坦治疗后能减轻主动脉病变,改善血清SOD、GSH-Px、MDA、NO及主动脉NOS mRNA表达的异常。结论糖尿病大鼠的氧化应激和NO系统的紊乱参与了主动脉病变过程,增强机体抗氧化能力及调节NO生成可能是缬沙坦发挥主动脉保护作用的机制之一。     

有关高同型半胱氨酸血症与血管内皮功能的实验性研究

目的 :研究饮食所致高同型半胱氨酸血症时一氧化氮、内皮素、血管紧张素 等含量的改变 ,进而分析同型半胱氨酸对血管内皮功能的影响。方法 :采用新西兰大白兔 18只 ,随机等分为 3组 :分别给予正常饮食、高脂饮食、高蛋氨酸饮食。动态分析一氧化氮、一氧化氮合酶、内皮素、血管紧张素 等的变化以及它们与同型半胱氨酸的相关性。结果 :实验第 4周各指标均有不同程度的变化 :一氧化氮、一氧化氮合酶降低 ;内皮素、血管紧张素 增高。同型半胱氨酸与一氧化氮、一氧化氮合酶成显著负相关 ,与内皮素、血管紧张素 成显著正相关。结论 :高同型半胱氨酸血症早期可以明显抑制血管内皮功能 ,这可能是同型半胱氨酸导致动脉粥样硬化的机制之一。     

Vitamin E supplementation in streptozotocin-treated rats alters cerebellar and plasma nitric oxide metabolism

Nitric oxide (NO) free radicals appear to contribute to the pathogenesis of a number of disorders including diabetes mellitus. The aim of this study was to determine the effects of streptozotocin (STZ)-induced diabetes on nitric oxide (NO) metabolites in plasma and cerebellar nitric oxide synthase (NOS) activity. Further, it was of interest to determine whether an antioxidant, vitamin E, could reverse the STZ-induced effects. STZ significantly decreased cerebellar NOS but increased the level of plasma total nitrite + nitrate and the level of plasma nitrate. Supplementation with vitamin E effectively reduced the STZ-induced effects. Data demonstrate that vitamin E may serve as a protective antioxidant in STZ-induced diabetes.     

Role of nitric oxide system in hydroxyl radical generation in rat striatum due to carbon monoxide poisoning, as determined by microdialysis

We explored the possible role of the nitric oxide (NO) system in hydroxyl radical (*OH) generation induced by carbon monoxide (CO) poisoning in rat striatum by means of microdialysis with the use of NO synthase (NOS) inhibitors, N(G)-nitro-L-arginine methyl ester (L-NAME) and N(G)-monomethyl-L-arginine (L-NMMA), as well as L-arginine (L-Arg; the NOS substrate) and D-arginine (D-Arg). The CO-induced *OH generation was suppressed by both L-Arg and D-Arg. It was also suppressed by L-NAME, which inhibits generation of reactive oxygen species (ROS) via neuronal NOS (nNOS) and inducible NOS, but not via endothelial NOS. In contrast, L-NMMA, which inhibits only ROS generation via inducible NOS, potentiated the *OH generation. L-Arg completely reversed the L-NAME effect and partly reversed the L-NMMA effect. D-Arg reversed the L-NAME effect more potently than did L-Arg, resulting in much more *OH generation than was observed with CO alone, and also potentiated the L-NMMA effect. On the other hand, W-7, an antagonist of calmodulin, which is critical for nNOS activity, had no effect on the CO-induced *OH generation. These findings suggest that complex mechanisms operate in *OH generation in rat striatum upon CO poisoning and that the NO system might not be included among those mechanisms.