细脚拟青霉多糖诱导小鼠巨噬细胞一氧化氮生成和iNOS mRNA的表达

目的研究单一组分细脚拟青霉多糖(Paecilomyces tenuipespolysaccharide,PTPS)诱导小鼠腹腔巨噬细胞的免疫调节活性及其作用机制。方法应用水提、乙醇沉淀、DEAE-纤维素色谱,对PTPS进行提取并分级;用CCK-8试剂检测PTPS对小鼠脾细胞的增殖作用,硝酸盐还原酶法检测小鼠腹腔巨噬细胞一氧化氮(NO)的生成量和RT-PCR半定量法检测iNOS mRNA的表达。结果从细脚拟青霉菌丝体中分离出含糖量为92%的中性多糖PTPS,可促进脾细胞的增殖,并在一定浓度下显示剂量依赖效应;能明显诱导小鼠腹腔巨噬细胞NO的生成和iNOS mRNA的表达。结论PTPS通过诱导小鼠巨噬细胞NO合成和iNOS的转录,表明其具有免疫调节和潜在的抗肿瘤活性。     

香菇多糖对巨噬细胞一氧化氮和一氧化氮合酶活性的影响

目的研究香菇多糖(LTN)诱导巨噬细胞的一氧化氮(NO)生成和一氧化氮合酶(iNOS)的活性,探讨LTN的免疫调节作用机理.方法采用Griess反应和荧光法测定不同剂量的LTN作用小鼠腹腔巨噬细胞后NO的生成量和iNOS活性.观察mRNA转录抑制剂、蛋白质合成抑制剂和iNOS抑制剂对巨噬细胞NO的生成和iNOS活性的影响.结果LTN能使小鼠腹腔巨噬细胞NO生成增加,iNOS活性增高,并呈作用剂量依赖关系.3种抑制剂均能抑制LTN诱导的小鼠腹腔巨噬细胞N0的生成和iNOS活性.结论LTN能刺激小鼠腹腔巨噬细胞提高iNOS活性和NO的生成.提示LTN的免疫调节作用机制可能与LTN刺激巨噬细胞NO生成有关.     

香菇多糖对巨噬细胞一氧化氦和一氧化氦合酶活性的影响

目的 研究香菇多糖(LTN)诱导巨噬细胞的一氧化氮(NO)生成和一氧化氮合酶(iNOS)的活性，探讨LTN的免疫调节作用机理。方法 采用Griess反应和荧光法测定不同剂量的LTN作用小鼠腹腔巨噬细胞后NO的生成量和iNOS活性。观察mRNA转录抑制剂、蛋白质合成抑制剂和iNOS抑制剂对巨噬细胞NO的生成和iNOS活性的影响。结果 LTN能使小鼠腹腔巨噬细胞NO生成增加，iNOS活性增高，并呈作用剂量依赖关系。3种抑制剂均能抑制LTN诱导的小鼠腹腔巨噬细胞NO的生成和iNOS活性。结论 LTN能刺激小鼠腹腔巨噬细胞提高iNOS活性和NO的生成。提示LTN的免疫调节作用机制可能与LTN刺激巨噬细胞NO生成有关。     

香菇多糖对巨噬细胞一氧化氮和一氧化氮合酶活性的影响

目的研究香菇多糖(LTN)诱导巨噬细胞的一氧化氮(NO)生成和一氧化氮合酶(iNOS)的活性,探讨LTN的免疫调节作用机理.方法采用Griess反应和荧光法测定不同剂量的LTN作用小鼠腹腔巨噬细胞后NO的生成量和iNOS活性.观察mRNA转录抑制剂、蛋白质合成抑制剂和iNOS抑制剂对巨噬细胞NO的生成和iNOS活性的影响.结果LTN能使小鼠腹腔巨噬细胞NO生成增加,iNOS活性增高,并呈作用剂量依赖关系.3种抑制剂均能抑制LTN诱导的小鼠腹腔巨噬细胞N0的生成和iNOS活性.结论LTN能刺激小鼠腹腔巨噬细胞提高iNOS活性和NO的生成.提示LTN的免疫调节作用机制可能与LTN刺激巨噬细胞NO生成有关.     

灵芝多糖肽对小鼠腹腔巨噬细胞一氧化氮产生的影响

目的　研究灵芝多糖肽 (GLPP)对小鼠腹腔巨噬细胞一氧化氮产生的影响并探讨其作用机制。方法　以Griess法 ,观察GLPP对LPS诱导小鼠腹腔巨噬细胞一氧化氮(NO)产生的影响 ;以免疫组化法检测诱导型一氧化氮合成酶 (iNOS)的表达 ,观察GLPP对iNOS的影响。结果　GLPP(2 5～ 2 0 0mg·kg-1)灌胃给药 5d或体外给药 (3 12 5～ 2 0 0mg·L-1)均可促进巨噬细胞NO释放 ,但对LPS刺激NO的释放影响不大 ;GLPP(10 0mg·kg-1)灌胃给药 5d或体外给药 (10mg·L-1)均可使巨噬细胞iNOS含量增加。结论　GLPP可增加小鼠腹腔巨噬细胞NO产生 ,其机制可能与其促进巨噬细胞iNOS合成有关。     

胰岛素抵抗状态下血红素氧合酶-1/一氧化碳与一氧化氮合酶/一氧化氮相互调节的研究

目的探讨胰岛素抵抗状态下血红素氧合酶-1（HO-1）／一氧化碳（CO）与一氧化氮合酶（NOS）／一氧化氮（NO）的相互调节关系。方法通过6周高脂饮食成功复制胰岛素抵抗SD大鼠模型44只，分为胰岛素抵抗组26只，正铁血红素组10只，锌原卟啉组8只；分别腹腔注射生理盐水、正铁血红素、锌原卟啉。12只经6周普通饲料喂养的SD大鼠为对照组，给予腹腔注射生理盐水。检测血CO含量以及胸主动脉组织的NO、诱导型NOS（iNOS）、内皮型NOS（eNOS）的水平，RT-PCR检测主动脉iNOS、eNOS mRNA的表达。结果正铁血红素提高胰岛素抵抗大鼠主动脉组织eNOS活性及其mRNA表达，降低iNOS活性及其mRNA表达。降低血清及动脉组织的NO水平。增加动脉血CO水平。结论HO-1通过对NOS／NO信息通道的调节。抑制iNOS的活性，从而使应激状态下NO水平下降。发挥HO-1的血管保护作用。     

二苯乙烯苷预防性干预大鼠动脉硬化对其一氧化氮合酶表达的影响

目的探讨二苯乙烯苷(TSG)对动脉粥样硬化(AS)大鼠一氧化氮(NO)含量及主动脉一氧化氮合酶(NOS)表达的影响。方法SD大鼠60只,♂,随机分为6组:①正常对照组;②模型组;③TSG低剂量组;④TSG中剂量组;⑤TSG高剂量组;⑥辛伐他汀阳性对照组。造模12wk后,颈动脉取血,检测血清NO含量。取血后分离主动脉,保存于-70℃,检测主动脉组织中NOS含量,RT-PCR检测大鼠主动脉eNOS和iNOS mRNA表达。实验数据采用STATA8.0软件进行统计分析。结果与模型组相比,辛伐他汀组和TSG各剂量组均能增加血清及主动脉组织NO的含量、主动脉组织NOS的水平、主动脉组织eNOS mRNA的表达及降低主动脉组织iNOS mRNA的表达,并呈剂量依赖性。结论TSG能上调AS大鼠动脉壁eNOS mRNA的表达,抑制AS大鼠动脉壁iNOS mRNA的表达,这可能是TSG抗AS的机制之一。     

氯沙坦对糖尿病大鼠肾皮质血管紧张素Ⅱ2型受体及诱生型一氧化氮合酶基因表达的影响

目的研究氯沙坦对糖尿病大鼠肾组织血管紧张素系统与一氧化氮系统的影响及其二者之间的关系。方法SD大鼠随机分成3组:对照组、糖尿病组和氯沙坦(30 m.gkg-1.d-1×8周,ig)治疗组。应用RT-PCR技术检测大鼠肾皮质血管紧张素Ⅱ2型受体(AT2)、Ⅳ型胶原及诱生型一氧化氮合酶(iNOS)mRNA表达。并同时检测大鼠肾皮质血管紧张素Ⅱ(AngⅡ)、NO含量及一氧化氮合酶(NOS)活性。结果糖尿病组大鼠尿蛋白排泄率、肾皮质AngII含量、Ⅳ型胶原mRNA及iNOS mRNA表达较对照组明显升高;糖尿病大鼠肾皮质NOS活性也较对照组明显增强;然而糖尿病大鼠肾皮质NO含量及AT2mRNA水平却较对照组大鼠明显降低;氯沙坦治疗能显著降低糖尿病大鼠尿蛋白排泄率及肾皮质Ⅳ型胶原mRNA表达;并能明显增加肾皮质AT2及iNOS mRNA表达及总NOS活性及NO含量。结论AT2的激活与氯沙坦的肾脏保护作用有关,并可能参与了对肾脏iNOS mRNA表达的上调。     

大黄酚对铅中毒小鼠学习记忆的改善作用及其机制研究

目的研究大黄酚对铅中毒小鼠学习记忆障碍的改善作用,探讨其可能的作用机制。方法采用连续8 d腹腔注射7 mg.kg-1醋酸铅造成铅中毒小鼠模型,应用避暗实验、水迷宫实验,观察腹腔注射大黄酚(10.0、1.0、0.1 mg.kg-1)14 d对铅中毒模型小鼠记忆障碍的改善作用,大黄酚治疗14 d后测定小鼠血铅、脑铅及脑组织中MDA含量SOD,GSH-Px活力,一氧化氮(NO)含量及一氧化氮合酶(NOS)、诱导型一氧化氮合酶(iNOS)的活性。结果连续8 d腹腔注射7 mg.kg-1醋酸铅造成铅中毒小鼠学习记忆障碍,使小鼠脑铅、血铅升高,导致小鼠脑组织内SOD和GSH-Px活性降低,使小鼠脑组织内MDA含量增加,小鼠脑组织内NO含量增加,NOS和iNOS活性升高;连续ip大黄酚14d治疗后,可不同程度改善小鼠铅中毒造成的学习记忆障碍,降低血铅及脑铅水平,大黄酚(0.1 mg.kg-1)可升高铅中毒小鼠脑内SOD和GSH-Px的活性(P<0.01),对MDA含量无影响;大黄酚(10.0、1.0 mg.kg-1)可升高铅中毒小鼠脑内SOD和GSH-Px的活性,降低小鼠脑内MDA含量(P<0.01);大黄酚(0.1 mg.kg-1)可降低小鼠脑内NOS、iNOS的活性(P<0.05),对NO含量无影响;大黄酚10.0,1.0 mg.kg-1治疗组可降低小鼠脑内NO含量和NOS、iNOS的活性(P<0.01)。结论大黄酚通过提高铅中毒小鼠脑组织抗氧化酶活性同时降低NOS、iNOS的活性,抑制脂质过氧化,明显拮抗铅诱导的小鼠学习记忆障碍。     

糖皮质激素对双氯氛酸钠肝损伤大鼠一氧化氮合酶及一氧化氮的影响

目的探讨糖皮质激素地塞米松(Dex)对双氯氛酸钠(Dcf)肝损伤大鼠一氧化氮合酶(NOS)表达及一氧化氮(NO)的影响。方法大鼠随机分为正常组、Dcf组及Dex组。Dcf组给予Dcf 100 mg/kg腹腔注射,Dex组在Dcf注射前1 h予10 mg/kg腹腔注射,24 h后测血清ALT、AST、TBil水平观察肝组织病理学变化,化学法检测血清及肝组织NO含量,免疫组化法检测肝组织内皮型NOS(eNOS)和诱导型NOS(iNOS)的表达。结果 Dcf组血清ALT、AST、TBil水平明显升高(P<0.05),病理积分大幅度增高,血清和肝组织NO含量明显高于正常组(P<0.01),肝组织iNOS表达显著增强(P<0.01),eNOS表达减弱。Dex可明显改善升高的转氨酶及病理积分(P<0.05),并降低肝组织iNOS表达及NO含量(P<0.05)。结论 iNOS和NO在Dcf肝损伤中起促进作用,糖皮质激素可能通过抑制体内iNOS表达,减少NO合成起到肝保护作用。     

芦荟大黄素对LPS诱导的RAW264.7细胞NO生成及iNOS表达的影响

目的观察芦荟大黄素(aloe-emodin)对脂多糖(LPS)诱导的RAW264.7细胞一氧化氮(NO)生成及诱生型一氧化氮合酶(iNOS)mRNA表达的作用。方法采用LPS诱导的RAW264.7细胞株建立细胞炎症反应模型。采用Griess试剂法测定NO释放量;采用硝普钠释放NO法测定NO自由基含量的变化;采用反转录聚合酶链反应(RT-PCR)分析iNOS mRNA表达改变。结果芦荟大黄素在0.69～2.50mg·L-1剂量范围内可抑制LPS诱导的RAW264.7细胞NO的释放,并呈剂量和时间依赖关系;芦荟大黄素在0.63～5.00mg·L-1剂量范围内可下调LPS诱导的RAW264.7细胞iNOS mRNA含量;而此范围内芦荟大黄素无直接清除NO自由基作用,不影响iNOS活性。结论芦荟大黄素可明显降低LPS诱导的RAW264.7细胞NO释放,呈时间和剂量依赖关系,此作用并非通过捕捉NO或抑制iNOS活性来实现,而是通过抑制iNOS mRNA表达发挥作用的。     

细胞因子对膀胱平滑肌细胞内诱导性一氧化氮合酶的激活作用(英文)

探讨肿瘤坏死因子α (TNFα)和γ干扰素(INFγ)对大鼠膀胱平滑肌细胞诱导性一氧化氮合酶(iNOS )的影响 .将TNFα (1nmol·L- 1)或INFγ(5 0kU·L- 1)分别或同时加入膀胱平滑肌细胞培养液 ,2 4h后测定细胞培养液中一氧化氮 (NO)水平 ,并用Western印迹方法检测iNOS的表达 .结果显示 ,TNFα或INFγ单独不能诱导iNOS表达 ,也不能引起NO水平显著提高 .但当TNFα和INFγ联合诱导细胞 2 4h ,则细胞培养液中NO水平明显升高 ,用Western印迹分析可见iNOS表达 ,说明TNFα和INFγ具有协同诱导作用 .在TNFα和INFγ加入膀胱平滑肌细胞前 30min ,加入NOS抑制剂L 氮 精氨酸甲酯 (L NAME) ,可显著抑制TNFα和INFγ对NO的生成诱导 .结果提示 ,TNFα和INFγ联合应用可激活膀胱平滑肌细胞iNOS .     

NO和iNOS在大鼠糖尿病早期肾脏中的变化

目的:观察糖尿病大鼠早期肾脏中一氧化氮(Nitric oxide,NO)含量和诱导型一氧化氮合酶(Inducible nitric oxide syn-thase,iNOS)活性变化,探讨NO/iNOS在糖尿病早期肾脏损害中的作用机制。方法:取成年健康SD大鼠60只,随机分成糖尿病组(DM组)和正常对照组(NC组),每组30只。DM组大鼠采用一次性腹腔内注射STZ制造糖尿病大鼠模型,成模后和NC组分别于第1、2、4周麻醉取左肾,用硝酸还原酶法和吸光光度法测定肾组织中NO含量、一氧化氮合酶(nitric oxide synthase,NOS)和iNOS活性。所有数据用SPSS11.5统计软件进行统计学处理。结果:①DM组大鼠肾组织中NO含量、NOS和iNOS活性分别较同批NC组有显著性差异(P<0.05);②各组大鼠中NO含量与NOS活性、iNOS活性呈正相关。结论:糖尿病大鼠早期肾脏中iNOS活性增强,催化生成的NO在糖尿病早期肾脏损害中发挥重要作用。     

Trichloroethylene induce nitric oxide production and nitric oxide synthase mRNA expression in cultured normal human epidermal keratinocytes

Trichloroethylene (TCE), a major chemical hazard during occupational exposure, can cause obvious skin lesions, including irritant reactions and dermatitis. Nitric oxide (NO) synthesized by nitric oxide synthase (NOS) is involved in a broad array of pathogenesis of skin inflammatory and immune responses. To understand the mechanisms of TCE-induced dermatoxicity, we investigated the effects of TCE on NO production and NOS mRNA expression in cultured normal human epidermal keratinocytes (NHEK). Cells were treated with TCE (0 mM, 0.125 mM, 0.25 mM, 0.5 mM, 1.0 mM, 2.0 mM) for 4 h, and then incubated for 12 h, 24 h, 48 h and 72 h. At each given time point, NO production were evaluated indirectly by measuring nitrite plus nitrate concentration in the culture medium using Griess reaction, as well as cell viability determined by MTT test, iNOS and cNOS activities assayed with a NOS activity detecting kit. The expression of iNOS and cNOS mRNA was detected using RT-PCR. TCE decreases cell viability and enhance NO production from NHEK in concentration- and time-dependent manner. Aminoguanidine (AG), an inhibitor of NOS, can prevent NO production and cell viability decrease in NHEK by TCE induced. Change to NO production was accompanied by increased activities of both types of NOS, but the iNOS activity accounted mainly for the TCE-induced NO production. RT-PCR detection showed that NHEK expressed both iNOS and cNOS mRNA by TCE exposure. Whereas a concentration- and time-dependent up-regulation of the mRNA expression was observed for iNOS and cNOS following TCE exposure, changes to iNOS were more marked. These results suggest that TCE caused increase in NO production, attributed to activation of iNOS as well as cNOS, and expression of iNOS and cNOS mRNA. These cellular changes may contribute to the pathological and physiological features of TCE-induced erythema and skin inflammation.     

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.     

Extract from <Emphasis Type="Italic">Calotropis procera</Emphasis> latex activates murine macrophages

Calotropis procera latex has long been used in traditional medicines. Extracts from C. procera latex have been reported to have various pharmacological actions, including protection from myocardial infarction, hepatoprotective action, antitumor activity, antinociceptive, and pro- and anti-inflammatory actions. To evaluate the immunomodulatory functions of the water-soluble C. procera extract (CPE), we investigated its ability to activate macrophages—effector cells in inflammatory and immune responses. Intraperitoneal injection of CPE in mice (2 mg/mouse) induced migration of macrophages to the intraperitoneal cavity, confirming the proinflammatory effects of water-soluble CPE. The direct effects of CPE on macrophages were then assessed by measuring the production of nitric oxide (NO) as an indicator for macrophage activation. Addition of CPE (1–10 μg/ml) to the culture medium of the murine monocyte/macrophage cell line RAW264.7 caused an increase in NO production in a time- and dose-dependent manner. CPE-elicited NO production was blocked by application of an inhibitor of inducible nitric oxide synthase (iNOS). Expression of iNOS mRNA was induced by treatment of cultured macrophages with CPE. Injection of CPE in mice also resulted in an increase in plasma NO level. The results suggest that CPE activates macrophages and facilitates NO production via up-regulation of iNOS gene expression. A. l. S. Seddek and M. Elsayed Mahmoud contributed equally to this work.     

Role of inducible nitric oxide synthase-derived nitric oxide in lipopolysaccharide plus interferon-gamma-induced pulmonary inflammation

Exposure of mice to lipopolysaccharide (LPS) plus interferon-gamma (IFN-gamma) increases nitric oxide (NO) production, which is proposed to play a role in the resulting pulmonary damage and inflammation. To determine the role of inducible nitric oxide synthase (iNOS)-induced NO in this lung reaction, the responses of inducible nitric oxide synthase knockout (iNOS KO) versus C57BL/6J wild-type (WT) mice to aspirated LPS + IFN-gamma were compared. Male mice (8-10 weeks) were exposed to LPS (1.2 mg/kg) + IFN-gamma (5000 U/mouse) or saline. At 24 or 72 h postexposure, lungs were lavaged with saline and the acellular fluid from the first bronchoalveolar lavage (BAL) was analyzed for total antioxidant capacity (TAC), lactate dehydrogenase (LDH) activity, albumin, tumor necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-2 (MIP-2). The cellular fraction of the total BAL was used to determine alveolar macrophage (AM) and polymorphonuclear leukocyte (PMN) counts, and AM zymosan-stimulated chemiluminescence (AM-CL). Pulmonary responses 24 h postexposure to LPS + IFN-gamma were characterized by significantly decreased TAC, increased BAL AMs and PMNs, LDH, albumin, TNF-alpha, and MIP-2, and enhanced AM-CL to the same extent in both WT and iNOS KO mice. Responses 72 h postexposure were similar; however, significant differences were found between WT and iNOS KO mice. iNOS KO mice demonstrated a greater decline in total antioxidant capacity, greater BAL PMNs, LDH, albumin, TNF-alpha, and MIP-2, and an enhanced AM-CL compared to the WT. These data suggest that the role of iNOS-derived NO in the pulmonary response to LPS + IFN-gamma is anti-inflammatory, and this becomes evident over time.     

In situ generation of nitric oxide by myenteric neurons but not by mononuclear cells of the human colon

1. Production of nitric oxide (NO) is implicated in the pathogenesis of inflammatory bowel disease. However, the cells responsible for the production of NO in situ in the human colon remain unknown. 2. Surgical samples from 12 patients with ulcerative colitis, eight patients with Crohn's disease and 10 controls were studied. Possible generation of NO was visualized by reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity in human colon. Immunohistological staining for various NO synthase (NOS) isoforms (endothelial, neuronal and inducible), nitrotyrosine and interleukin-2 was also performed. 3. Reduced NADPH diaphorase activity was not found in lamina propria mononuclear cells, but was found in colonic epithelium, endothelium and myenteric neurons and their processes. 4. The NADPH-diaphorase activity positive processes were significantly less common in colon from patients with Crohn's disease compared with control colon. 5. Endothelial NOS was constitutively expressed on colonic endothelium. 6. Neuronal NOS was constitutively expressed on myenteric neurons. 7. Expression of inducible NOS (iNOS) was increased in the epithelium and endothelium of the colon of patients with ulcerative colitis. 8. No correlation was found between expression of iNOS and NADPH diaphorase activity. 9. Nitrotyrosine was expressed by lamina propria leucocytes, but not by epithelium. 10. Interleukin-2 was expressed on both leucocytes and myenteric neurons. 11. Colonic epithelium, endothelium and myenteric neurons synthesize NO. Myenteric neurons were principally responsible for NO production and NO may act as a neurotransmitter in the enteric nervous system.