Possible role for nitric oxide releasing nerves in the regulation of ocular blood flow in the rat

AIM—To investigate the role of nitrergic nerves in the regulation of ocular blood flow.
METHODS—Conscious, lightly restrained rats were treated with either the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI), or the non-selective inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and ocular blood flow was measured ex vivo from tissue samples, using the fully quantitative [14C]-iodoantipyrine technique.
RESULTS—In the peripheral circulation, L-NAME produced an increase in arterial blood pressure (+22%) while 7-NI had no effect. In contrast, both 7-NI and L-NAME produced significant decreases in ocular blood flow (−31% and −59% respectively). The ocular vascular resistance calculated from ocular blood flow and mean arterial blood pressure increased by 29% following 7-NI, but by 130% following L-NAME.
CONCLUSIONS—Nitric oxide releasing neurons may play an important contributory role in regulating ocular blood flow.

Keywords: nitric oxide; neuronal nitric oxide synthase; 7-nitroindazole; NG-nitro-L-arginine methyl ester; ocular blood flow     

遗传性视网膜谱性视细胞凋亡与视网膜诱生型一氧化氮合酶活性的时程变化

目的 研究遗传性视网膜变性视细胞凋亡与诱生型一氧化氮合酶活性之间的关系。方法 对生后不同鼠龄RCS大鼠和Wistar大鼠的视网膜进行凋亡细胞的TUNEL检测、计算机自动图像分析及诱生型一氧化氮合酶活性的测定。结果 RCS大鼠视网膜视细胞自生后第25天出现凋亡,第30-35天达高峰;视细胞凋亡初期,即生后第25天,视网膜诱生型一氧化氮合酶活性达高峰。结论 在遗传性视网膜变性的视网膜。诱生型一氧化合酶激活可能在视细胞凋亡中起诱导作用。     

糖尿病早期NOS亚型的蛋白表达及其在血流变化中作用的实验研究

目的探讨在糖尿病早期,3种亚型一氧化氮合酶(NOS)在大鼠视网膜不同组织细胞中蛋白表达的变化,及其与视网膜血流变化的关系。方法将Wistar大鼠随机分成正常对照组与链脲佐菌素(STZ)腹腔注射诱导的糖尿病组各10只,采用彩色多谱勒对大鼠视网膜中央动脉(CRA)进行血流参数的测量,运用免疫组织化学技术观察视网膜eNOS、iNOS、nNOS蛋白表达的变化。结果8wk糖尿病大鼠视网膜尚未出现病变,但血流参数已显著异常,表现为糖尿病组大鼠CRA的血流速度较对照组显著降低(P<0.05),而阻力指数则显著增高(P<0.05),搏动指数高于对照组,但尚未有显著意义。3种亚型NOS在糖尿病与正常对照组视网膜中表达部位一致;但与正常对照组比较,iNOS免疫反应的强度在糖尿病大鼠视网膜中的内核层显著增强,而eNOS与nNOS的免疫反应强度则未见显著变化。结论在糖尿病早期,大鼠视网膜已开始出现血流灌注不良,此时NOS亚型中iNOS在视网膜中的表达上调可能与之相关。     

诱导型一氧化氮合成酶与视网膜新生血管形成的关系

新生血管生成是缺氧诱导的各种视网膜病变的主要病理变化之一.诱导型一氧化氮合成酶(inducible nitric oxide synthase,iNOS)在此过程中起重要作用,其作用机制错综复杂,且与多种促血管生成因子密切相关.为了阐明iNOS的作用机制,iNOS抑制剂的研究也逐渐受到重视,而使用选择性iNOS抑制剂来抑制视网膜新生血管(Retinal neovascularization,RNV)已成为该领域一大研究热点.本文就iNOS及其抑制剂在RNV形成过程中的作用机制及研究进展进行简要综述.     

过度光照后诱导型一氧化氮合酶在大鼠视网膜色素上皮的表达

目的探讨过度光照诱导大鼠视网膜色素上皮（retinal pigment epithelium．RPE）细胞表达诱导型一氧化氮合酶（inducible nitric oxide synthase，iNOS）的作用及其病理学意义。方法应用免疫组织化学的方法分别检测处于自然光照环境中的正常大鼠及接受强光过度照射后大鼠的视网膜RPE细胞中iNOS的表达情况。结果正常大鼠RPE细胞中未见iNOS的表达，而过度光照后大鼠RPE细胞的胞浆中表达高水平的iNOS，同时视网膜外核层感光细胞发生结构损伤。结论过度光照可诱导RPE细胞表达iNOS．这一异常改变可能是视网膜感光细胞结构损伤的重要原因。     

神经生长因子对单眼剥夺大鼠视觉中枢nNOS表达的影响

目的 观察单眼剥夺(monocular deprivation,MD)大鼠神经生长因子(nerve growth factor,NGF)治疗前后视中枢神经型一氧化氮合酶(neuronal nitric oxide synthase,nNOS)阳性神经元表达的改变.方法 健康雄性SD大鼠,随机分为正常组(N组)、MD组、MD脑室内注射NGF组(MD+NGF组)和MD脑室内注射生理盐水组(MD+NS组).剥夺自14 d龄开始,每组随机分为2个亚组,分别于28 d、42 d龄处死,MD+NGF组和MD+Ns组中的2个亚组分别于14 d、28 d龄开始行脑室内注射β-NGF或NS.采用免疫组织化学染色法观察视中枢nNOS阳性神经元的表达.结果 nNOS阳性神经元在视皮层V1区Ⅱ～Ⅵ层和外侧膝状体背核散在分布.28 d龄时,MD组V1区nNOS阳性神经元数密度(除Ⅳ层外)、胞体截面积和树突总长度分别为(1.47±1.14)mm-2、(201.84±37.00)μm2、(423.86±105.86)μm,较N组明显减少,差异有统计学意义(P<0.05);MD+NGF组上述表达较MD组及MD+NS组明显增强,差异有统计学意义(P<0.05),与N组比较差异无统计学意义(P>0.05).42 d龄时,MD组V1区胞体截面积减小、外侧膝状体背核nNOS阳性神经元数密度降低,与N组比较差异有统计学意义(P<0.05);MD+NGF组上述表达与MD组及MD+NS组比较,差异无统计学意义(P>0.05).结论 视觉发育具有可塑性,NO是影响视觉发育的一个环节.在视觉发育敏感期内,外源性提供NGF,可以促进视觉中枢nNOS增多,从而拮抗剥夺效应.     

Effect of NO synthase inhibition on retinal vessel reaction to isometric exercise in healthy humans

Purpose: It has been shown that retinal blood flow is autoregulated, meaning that flow is independent of perfusion pressure within a certain range. We tested the hypothesis that nitric oxide (NO) synthase inhibition alters the response of retinal arterial and venous vessels during isometric exercise. Methods: In this study, nine healthy subjects were included. Each subject received the NO synthase inhibitor Ng ‐monomethyl‐l‐Arginine (l ‐NMMA, the α‐receptor agonist phenylephrine or placebo intravenously on three study days. Retinal vessel diameter was assessed with the retinal vessel analyser (RVA), at baseline and during a squatting period of 6–7 min in absence or presence of l ‐NMMA, phenylephrine or placebo. Results: Mean arterial pressure (MAP) and pulse rate (PR) increased significantly during all pretreatment squatting periods (p < 0.001) Retinal venous and arterial diameters showed a continuous decrease during squatting (p < 0.001). Phenylephrine increased MAP and PR but did not alter the retinal vessel diameter response to squatting. Administration of l ‐NMMA lead to a significant decrease in venous diameter before isometric exercise (p = 0.004). In addition, the retinal venous diameter response during administration of the NO synthase inhibitor was less pronounced than during phenylephrine or placebo (p < 0.001). Conclusion: Our study confirms that NO plays an important role in the control of retinal vascular tone at rest. In addition, the present data indicate a role of NO in retinal autoregulation, because the response of retinal venous diameters was altered after NO synthase inhibition. The nature of involvement, however, appears to be complex and requires further studies.     

氧化应力对晶状体一氧化氮和一氧化氮合酶活性的影响

探讨氧化应力、５种抗白内障药物对晶状体一氧化氮合酶（ＮＯＳ）活性及一氧化氮（ＮＯ）水平的影响,方法建立晶状体温育模型：培养液分７组：（１）对照组含ＤＭＥＭ １０ｍｌ;（２）－（７）ｘｅｇ ｗｙｎｋＤＭＥＭ１０ｍｌ外尚有３０％Ｈ２Ｏ２０．２ｍｌ,ＦｅＣＬ３２ｍｇ并于（３）－（７）组中分别加入海珠视、麝珠明目、益视安、晶福及视明露滴眼液各１．０ｍｌ,晶状体制备均浆上清,测ＮＯＳ,ＮＯ,ＭＤＡ。结果１．     

Advanced glycation end products induce death of retinal neurons via activation of nitric oxide synthase

The purpose of this study was to determine whether advanced glycation end products (AGEs) are neurotoxic for cultured retinal neurons consisting mainly of amacrine cells, and to determine whether endogenous nitric oxide (NO) is involved in the toxicity. Cultured retinal neurons obtained from fetal Wistar rats (gestational age 19 days) were maintained in culture for 10 days, and then exposed to different concentrations of AGEs (0.02, 0.1, and 0.5 mg ml(-1)) in cultured media for different lengths of time. Both trypan blue exclusion and TUNEL assay were used to determine whether AGEs were neurotoxic, and NG-nitro-L-arginine methyl ester (L-NAME, 500 microM), a nitric oxide synthase (NOS) inhibitor, was used to determine whether NO was involved. Immunohistochemical analyses were performed to determine whether specific receptors of AGEs (RAGE) are present on cultured retinal neurons; caspase-3 was activated, and 3-nitrotyrosine was expressed on neurons treated with AGEs. Nitrite levels were measured in the supernatants of the media where neurons were incubated with AGEs. AGEs induced cell death in a time- and dose-dependent manner. TUNEL-positive cells and immunoreactivity to cleaved caspase-3 were enhanced on neurons following exposure to AGEs. L-NAME significantly suppressed the AGEs-induced neurotoxicity as assessed by both trypan blue exclusion and TUNEL assays. Activation of NOS was suggested by enhanced immunoreactivity to 3-nitrotyrosine on neurons and increased nitrite levels in the media incubated with AGEs. These results indicate that AGEs are neurotoxic to retinal neurons in culture through the activation of NOS. Apoptotic pathways may be in part involved in the death of the neurons.     

褪黑素对高糖刺激人视网膜色素上皮细胞诱导型一氧化氮合酶表达的影响

目的研究褪黑素对高糖刺激体外培养的人视网膜色素上皮（retinal pigment epithelial,RPE）细胞诱导型一氧化氮合酶（inducible nitric oxide synthase,iNOS）表达的影响。方法培养人RPE细胞,分为对照组、甘露醇组、高糖组和高糖＋褪黑素组,作用48h后,光镜观察细胞形态;MTT法检测细胞活性;免疫荧光染色法和Western blot检测RPE细胞中iNOS的蛋白表达。结果MTT检测结果表明高糖可以抑制RPE细胞增生,加入褪黑素后,抑制作用减弱;免疫荧光染色法和Western blot检测结果表明,与对照组相比,高糖组iNOS蛋白表达明显增高,加入褪黑素后,iNOS表达被显著抑制。结论高糖可以抑制RPE细胞增生,诱导RPE细胞iNOS的表达上调,而褪黑素可减轻细胞损伤。     

一氧化氮合成酶在正常幼猫视觉系统的分布

目的 观察一氧化氮合成酶在正常幼猫视觉系统的分布,探讨一氧化氮在视觉系统中的作用。方法 用ＮＡＤＰＨ黄递酶（ＮＤＰ）组织化学染色法观察了一氧化氮合成酶在正常幼猫视觉系统视网膜、外侧膝状体、视皮 分布、结果 正常幼猫视网膜和视皮层１７区均可见ＮＯＳ阳性细胞和纤维;外太体（ＬＧＮ）各层无ＮＯＳ阳性细胞,但可见ＮＯＳＢ是性纤维,结论一氧化氮可能作为一种重要的神经递质参与视觉信息的形成、整合传递     

Endothelin-1 (ET-1) causes death of retinal neurons through activation of nitric oxide synthase (NOS) and production of superoxide anion

Endothelin-1 (ET-1) is the most potent and long-acting vasoconstricting peptide presently known. In addition to its vascular effects, endothelin signaling pathway exists in the central nervous system (CNS), which is deeply related to neuronal degeneration. In the present study, we evaluated the effect of ET-1 on death of retinal neurons consisting mainly of amacrine cells, and its interaction with nitric oxide synthase (NOS) and superoxide production. Cultured retinal neurons from fetal rats were exposed to various doses of ET-1 (0.1, 1.0, 10 and 100nM). Neuronal toxicity of ET-1 was assessed by trypan blue exclusion, Hoechst 33,258 staining and TUNEL assay at different times. Intracellular levels of nitric oxide (NO), superoxide and peroxynitrite were determined semiquantitatively by DAF2-DA, hydroethidine and dihydrorhodamine-123, respectively. The effects of adding SOD (100U/ml) and L-NAME with ET-1 on these changes were evaluated. In addition, the receptor mechanisms involved in these reactions were determined by BQ-123 and BQ-788, receptor antagonists for ET A and ET B receptors, respectively. Exposure of cultured retinal neurons to ET-1 reduced the percentage of living cells in a dose- and time-dependent way, and the percentage of living cells was significantly increased by addition of SOD and L-NAME. Fluorometric analyses revealed that ET-1 increased the intracellular NO level in a dose- and time-dependent manner. The intracellular superoxide and peroxynitrite levels were also significantly increased 24h after incubation with 100nM of ET-1, and this elevation was suppressed by SOD and L-NAME. These ET-1-induced alterations were significantly suppressed when both BQ-123 and BQ-788 were added simultaneously with ET-1 to the medium. These results indicate that the neuronal death caused by ET-1 is most likely mediated by the activation of NOS in association with the formation of superoxides and peroxynitrite.     

急性高眼压状态大鼠虹膜睫状体一氧化氮及其合酶的变化

目的：通过对急性高眼压大鼠虹膜睫状体一氧化氮及其合酶变化的分析,探讨一氧化氮在青光眼发病机理中可能的作用。方法：Ｗｉｓｔｅｒ大鼠２４只,随机分为高眼压３０分钟组;高眼压６０分钟组;高眼压９０分钟组;前房加压灌主制成高眼压模型。得用镀铜镉还原法测定虹膜中ＮＯ２＾－／ＮＯ３＾－的含量从而间接反映虹膜组织中ＮＯ的含量。利用免疫组织化学法研究睫状体内内皮结构型一氧化氮梧酶（ｅｃＮＯＳ）的分布及其变化。结果     

Troglitazone reverses the inhibition of nitric oxide production by high glucose in cultured bovine retinal pericytes

In the retinal microcirculation, there is a basal release of nitric oxide (NO) which maintains the retinal blood flow. The proportions of endothelial cells and pericytes in the retinal capillaries are almost equal, so pericytes appear to play a important role in the regulation of microcirculatory hemodynamics in the retina. It has been suggested that the pathogenesis of early diabetic retinopathy may involve a reduced bioavailability or diminished production of NO. In this study, we investigated the role of troglitazone, a potent agonist of peroxisome proliferator activated receptor-gamma (PPARgamma) used for the treatment of diabetes, on the NO release and the effect of exposure to high glucose on the production of NO in cultured bovine retinal pericytes. Troglitazone significantly increased NO production and iNOS expression after 24hr in a dose-and PPARgamma-dependent manner. Elevation of D-glucose, but not L-glucose, from 5.5 to 30 mm for 24 hr decreased NO production, but co-treatment with troglitazone reversed high glucose-induced inhibition of NO production as well as iNOS expression. In conclusion, high glucose inhibits iNOS expression and subsequently NO synthesis in cultured bovine retinal pericytes, and troglitazone restores the NO production.     

Inducible nitric oxide synthase mediates retinal DNA damage in Goto-Kakizaki rat retina

PURPOSE: To examine the nitrosative and oxidative DNA damage induced by 8-nitroguanine and 8-hydroxy-2-deoxy guanosine (8-OHdG), and to determine the role played by inducible nitric oxide synthase (iNOS) in damage to DNA in the retina of the Goto-Kakizaki (GK) rat. METHODS: Experiments were performed on GK rats, an animal model of spontaneous type 2 diabetes without obesity or visible diabetic vascular lesions. Immunohistochemistry was used to determine the retinal distribution of 8-nitroguanine, 8-OHdG, and iNOS in GK rats and control rats. The change in the expression of 8-nitroguanine and 8-OHdG in GK rats was also determined following an intravitreal injection of 1400W, an inhibitor of iNOS activity. RESULTS: Immunohistochemical analysis showed that 8-nitroguanine and 8-OHdG were expressed strongly in the inner nuclear layer of GK retinas but only weakly in control retinas. This expression was correlated with an increase in the expression of iNOS in GK retinas, which was confirmed by the inhibition of iNOS activity by 1400W. CONCLUSION: These findings demonstrate that iNOS plays a crucial role in nitrosative and oxidative DNA damage in GK rats, suggesting a retinal neurotoxic role of nitric oxide and superoxide in diabetic retinas.     

0．2％阿法根滴眼液对视网膜血流影响的研究

目的 研究0．2％阿法根（Brimonidine）滴眼液对视网膜血流的影响。方法 选取开角型青光眼或高眼压症患者15例,采用自身对照方法,于0．2％阿法根滴眼液治疗前和治疗后2h分别行海德堡视网膜血流计（HRF）检查,观察视网膜中央动脉颞上、颞下、鼻上、鼻下4条分支血管血容量、血流及血流速度的变化。结果 0．2％阿法根滴眼液治疗前后视网膜中央动脉颞止、颞下、鼻上、鼻下4条分支血管的血容量、血流及血流速度无明显改变。结论 0．2％阿法根滴眼液局部使用对视网膜血流无影响。     

氨基胍对兔缺血-再灌注损伤后视网膜形态学及一氧化氮和一氧化氮合酶表达的影响

背景临床研究表明,多种眼科疾病如青光眼、视网膜中央动脉阻塞、缺血性视神经病变等均可导致视网膜缺血-再灌注损伤（RIRI）,严重影响视功能,因而对治疗RIRI药物的研究是非常必要的。目的观察并探讨氨基胍对兔RIRI后形态学的变化,并研究其对一氧化氮（NO）及一氧化氮合酶（iNOS）在视网膜中表达的影响及其机制。方法清洁级日本大耳白兔66只,以随机数字表法分为正常组、RIRI模型组和氨基胍治疗组。用前房灌注生理盐水法升高眼压60min后恢复灌注建立兔RIRI模型,氨基胍治疗组每日在模型兔腹腔内注射氨基胍注射液80mg／kg,而RIRI模型组以同样的方法注射等量生理盐水。RIRI模型组和氨基胍治疗组分别于缺血即时、再灌注后6、24、72h各取2只兔活体行眼底彩色照相及荧光素眼底血管造影（FFA）。各组兔分别于再灌注后1、6、24、72h用空气栓塞法处死并摘除眼球以制备视网膜切片,用TUNEL法检测视网膜组织神经细胞的凋亡变化,通过硝酸还原酶法检测NO浓度,比色法检测iNOS活力。结果各时间点眼底彩色照相及FFA检查结果表明,与RIRI模型组比较,氨基胍治疗组视网膜水肿程度减轻,血管闭塞程度及比例降低,荧光素渗漏量及面积减轻并减少。TUNEL染色凋亡细胞计数检测表明,正常组兔视网膜未见TUNEL阳性细胞,而缺血-再灌注1、6、24、72h后RIRI模型组兔视网膜凋亡细胞计数均明显高于氨基胍治疗组（F分组=2762．37,P=0．00;F时间=894．24,P=0．00）。RIRI模型组和氨基胍治疗组各组内相邻时间点之间TUNEL阳性细胞的差异均有统计学意义（RIRI模型组：q=24．47、36．59、-20．37,P〈0．05;氨基胍治疗组：q=20．94、16．79、-6．92,P〈0．05）,再灌注后24h各组TUNEL阳性细胞数量达到高峰。各时间点RIRI模型组兔视网膜NO浓度明显高于氨基胍治疗组（q=3．84、4．01、8．91、3．75,P〈0．05）,各组内相邻时间点之间NO浓度的差异均有统计学意义（RIRI模型组：q=4．77、13．40、-10．29,P〈0．05;氨基胍治疗组：q=4．55、9．05、-5．08,P〈0．05）,各组24h视网膜中NO浓度达峰值。各时间点RIRI组视网膜iNOS活力均明显高于氨基胍治疗组（q=-3．74、-4．94、-6．53、-3．98,P〈0．05）;各组内相邻时间点间iNOS活力的差异均有统计学意义（RIRI模型组：q=8．43、6．71、-6．39,P〈0．05;氨基胍治疗组：q=4．16、5．08、-3．93,P〈0．05）,各组24h iNOS活力达峰值。结论氨基胍对维持RIRI后的视网膜形态和功能起保护作用,其作用机制可能为抑制iNOS的活性,减少NO的生成。     

一氧化氮与眼病的关系

一氧化氮（nitric oxide,NO）是近年来眼科疾病的研究热点.其在体内一氧化氮合酶（nitric oxide synthase,NOS）的催化下生成,作为一种小分子介质调节眼部血流.诸多脉络膜视网膜疾病如葡萄膜炎、青光眼、缺血-再灌注损伤、前部缺血性视神经病变、糖尿病视网膜病变以及视网膜色素变性等发病机制中均发现NO的异常,与NO相拮抗的内皮素-1（Endothelin-1,ET-1）也日益受到关注.对NO合成途径的干预有望成为一种新的眼科治疗手段.