没食子酸乙酯对人乳腺癌MDA-MB-231细胞侵袭能力的影响及其机制

研究狼毒大戟中没食子酸乙酯(ethyl gallate,EG)对人乳腺癌MDA-MB-231细胞侵袭能力的影响,并对其作用机制进行探讨。采用细胞与Matrigel黏附实验,Transwell小室检测EG对人乳腺癌MDA-MB-231细胞黏附、侵袭和运动能力的影响。RT-PCR检测EG对MMP-2、MMP-9的m RNA表达的影响;Western blot法检测EG对Akt-NF-κB信号转导通路蛋白表达的变化。结果显示,EG在体外可显著抑制人乳腺癌MDA-MB-231细胞的侵袭、运动以及黏附能力(P<0.05)。EG可抑制MMP-2、MMP-9的m RNA水平,抑制Akt-NF-κB信号转导通路中的Akt磷酸化和NF-κB蛋白表达。因此认为EG在体外具有一定的抑制乳腺癌细胞侵袭迁移的作用,其机制与抑制MMP-2、MMP-9的m RNA水平、抑制Akt磷酸化过程和NF-κB蛋白表达有关。     

延龄草总皂苷抑制乳腺癌细胞MDA-MB-231转移的作用及机制研究

目的观察延龄草总皂苷对乳腺癌细胞MDA-MB-231侵袭与迁移的影响及相关机制。方法培养乳腺癌细胞MDA-MB-231,加入延龄草总皂苷(1.5、3 mg·L~(-1))24 h后,采用细胞侵袭实验、划痕实验观察延龄草总皂苷对MDA-MB-231细胞侵袭与迁移的影响,以Western blot方法检测细胞中MMP-2、MMP-9蛋白的表达。结果延龄草总皂苷能够有效地抑制MDA-MB-231细胞的侵袭与迁移,降低MMP-2与MMP-9的蛋白表达并呈现浓度依赖性。结论延龄草总皂苷能够有效地抑制乳腺癌细胞MDA-MB-231侵袭与迁移,其可能机制与降低MMP-2、MMP-9的表达水平有关。     

金雀异黄酮对三阴乳腺癌MDA-MB-231细胞凋亡及EGFR/PI3K/Akt通路的影响

目的研究金雀异黄酮(genistein)诱导三阴性乳腺癌MDA-MB-231细胞凋亡及其机制。方法 MTT法观察金雀异黄酮对乳腺癌MDA-MB-231细胞增殖的抑制作用;Hoechst 33258染色观察金雀异黄酮对MDA-MB-231细胞核凋亡形态学的影响;qRT-PCR法观察金雀异黄酮干预MDAMB-231细胞36 h后,EGFR mRNA表达水平的变化;金雀异黄酮干预MDA-MB-231细胞36 h后,Western blot检测凋亡相关蛋白Bcl-2、Bax、caspase-3,EGFR、Akt、p-Akt蛋白的变化;Akt激活剂胰岛素(insulin)、金雀异黄酮单独及联合胰岛素干预乳腺癌MDA-MB-231细胞后,Western blot检测Akt和p-Akt蛋白表达量的变化。结果 MTT结果显示,金雀异黄酮呈时间浓度依赖性抑制乳腺癌MDA-MB-231细胞增殖;Hoechst 33258染色结果显示,金雀异黄酮干预乳腺癌MDAMB-231细胞36 h后细胞核呈现典型凋亡形态学改变;qRTPCR结果显示,经金雀异黄酮干预MDA-MB-231细胞36 h后,EGFR的mRNA表达水平明显下降(P<0.01);Western blot结果显示金雀异黄酮干预乳腺癌MDA-MB-231细胞36 h后,与对照组对比,Bcl-2、EGFR、Akt、p-Akt蛋白表达水平明显下调(P<0.01),Bax、caspase-3蛋白表达水平明显上调(P<0.01),Akt激活剂胰岛素可以明显激活p-Akt(P<0.01),金雀异黄酮可以明显下调被激活的p-Akt(P<0.01)。结论金雀异黄酮能抑制三阴乳腺癌MDA-MB-231细胞生长并诱导其凋亡,其机制可能与抑制EGFR/PI3K/Akt信号通路有关。     

芦荟大黄素对高转移乳腺癌细胞MDA-MB-231体外转移潜能的影响

目的研究芦荟大黄素(Aloe emodin,AE)对人高转移乳腺癌细胞MDA-MB-231体外转移潜能的影响及其作用机制。方法 MTT法检测AE对MDA-MB-231细胞增殖的抑制作用;Transwell chamber法检测AE对MDA-MB-231细胞侵袭重组基底膜能力和趋化性运动能力的影响;RT-PCR、Western blot法检测AE对MDA-MB-231细胞黏着斑激酶(FAK)mRNA和蛋白表达的影响。明胶酶谱法检测MDA-MB-231细胞分泌的基质金属蛋白酶-9(MMP-9)活性。结果 80μmol·L-1 AE抑制MDA-MB-231细胞体外侵袭重组基底膜能力、趋化性运动能力,其抑制率分别为(52.98±5.46)%,(45.88±8.51)%。作用于MDA-MB-231细胞24 h后,AE下调FAK mRNA和蛋白表达,下调MDA-MB-231细胞分泌MMP-9。结论 AE抑制MDA-MB-231细胞体外侵袭能力、趋化性运动能力,其作用机制与其下调FAK表达和MMP-9的分泌有关。     

下调 HOX转录反义 RNA对三阴性乳腺癌细胞 MDA-MB-231增殖、周期及侵袭能力的影响

目的 研究下调HOX转录反义RNA(HOTAIR)水平对三阴性乳腺癌(TNBC)细胞MDA-MB-231增殖、周期及侵袭能力的影响.方法 si-HOTAIR对MDA-MB-231细胞转染,实验分为对照组、si-阴性对照组、si-HOTAIR组,实时荧光定量法测定转染后MDA-MB-231细胞中HOTAIR表达水平;分别用MTT法、流式细胞仪、Transwell小室实验测定转染后MDA-MB-231细胞活性、周期、侵袭能力;蛋白印迹法(WB)测定转染后MDA-MB-231细胞中c-myc、Ki-67、PCNA、基质金属蛋白酶9(MMP-9)、基质金属蛋白酶2(MMP-2)表达水平.结果 与MCF-10A细胞组相比,对照组MDA-MB-231细胞中HOTAIR表达水平升高[(1.85±0.21)比(1.06±0.13),P<0.05].与对照组、si-阴性对照组相比,si-HOTAIR组MDA-MB-231细胞中HOTAIR表达水平(1.34±0.15)、细胞活性(98.04±6.28)％、侵袭能力(35.66±8.04)降低(P<0.05),细胞G0/G1期下调,阻滞在G2/M期;与对照组、si-阴性对照组相比,si-HOTAIR组MDA-MB-231细胞中c-myc、Ki-67、PCNA、MMP-9、MMP-2表达水平降低(P<0.05).结论 HOTAIR在MDA-MB-231细胞中高表达,下调HOTAIR表达水平可抑制MDA-MB-231细胞增殖、阻滞细胞周期、降低肿瘤细胞侵袭能力.     

Grb2-相关蛋白2参与RANKL诱导的乳腺癌细胞MDA-MB-231迁移的机制研究

目的探讨Grb2-相关蛋白2(Gab2)在核因子-κB受体活化因子配体(RANKL)诱导的乳腺癌细胞MDA-MB-213迁移中的作用。方法流式细胞术检测MDA-MB-231细胞表面RANK的表达。Transwell法测定RANKL刺激后细胞迁移能力的改变。免疫沉降及Western-blot检测RANKL刺激后p-Tyr-Gab2和Gab2的表达。结果 MDA-MB-231细胞表达RANK蛋白,RANKL诱导MDA-MB-231细胞迁移能力增强。RANKL刺激后MDA-MB-231细胞p-Tyr-Gab2表达一过性升高。结论 Gab2参与RANKL诱导的乳腺癌细胞MDA-MB-231迁移。     

川芎嗪对人乳腺癌细胞株MDA-MB-231侵袭黏附能力的影响

目的观察不同浓度川芎嗪干预后乳腺癌细胞侵袭、黏附能力的改变及MMP-2/MMP-9的表达。方法用细胞黏附实验,检测川芎嗪对MDA-MB-231细胞黏附力的抑制作用;用Transwell小室检测不同浓度川芎嗪干预后MDA-MB-231细胞体外侵袭能力的改变;用半定量逆转录-聚合酶联反应(RT-PCR)检测川芎嗪对MDA-MB-231细胞MMP-2/MMP-9 mRNA表达的抑制作用。结果川芎嗪对MDA-MB-231细胞黏附力有明显抑制作用,对MDA-MB-231细胞的MMP-2 mRNA的表达有明显抑制作用;但对MMP-9mRNA的表达无明显影响。结论川芎嗪能显著抑制MDA-MB-231细胞的黏附和侵袭能力,其抑制效应与药物的浓度呈正相关。川芎嗪可能通过下调MDA-MB-231细胞MMP-2mRNA的表达而抑制细胞的黏附、侵袭能力。     

Raptor通过上皮-间质转化促进乳腺癌的侵袭与转移

目的探讨Raptor在乳腺癌侵袭与转移过程中的作用。方法采用Western blot检测乳腺癌细胞MCF-7和MDA-MB-231(MDA231)中Raptor蛋白的表达情况。应用小干扰RNA技术下调乳腺癌细胞MDA231中Raptor的表达量,同时将过表达质粒转入乳腺癌细胞MCF-7中,应用Western blot法检测转染后各组细胞中上皮性钙黏着蛋白(E-cadherin)和波形蛋白(Vimentin)的表达;应用Transwell体外侵袭实验检测转染后各组细胞的侵袭能力;应用细胞核质分离实验检测转染后各组细胞中Snail蛋白的转核情况。结果MCF-7细胞中Raptor蛋白的表达量明显低于MDA231细胞中的表达量;转染后,与对照组Scr/MDA231相比,siRaptor/MDA231组中Raptor蛋白的表达量明显降低,Vimentin蛋白表达量降低,而E-cadherin蛋白表达量升高;与对照组MCF-7/Con相比,MCF-7/Raptor组中Raptor蛋白的表达量明显升高,并伴有Vimentin蛋白表达量升高,而Ecadherin蛋白表达量降低。siRaptor/MDA231细胞组中穿过Matrigel小室的细胞数量明显减少(P<0.05);MCF-7/Raptor细胞组中穿过Matrigel小室的细胞数量明显升高(P<0.05)。细胞核质分离实验结果显示,siRaptor/MDA231组中Snail蛋白表达量较Scr/MDA231组中明显降低;MCF-7/Raptor组中Snail蛋白表达量较MCF-7/Con组中明显升高。结论 Raptor能够促进乳腺癌EMT的发生,对乳腺癌的侵袭与转移有重要作用。     

吞噬细胞运动蛋白1在IL-8诱导的乳腺癌细胞的侵袭和转移中发挥重要作用

目的探讨吞噬细胞运动蛋白1(engulfment and cell motility 1,ELMO1)在IL-8诱导的乳腺癌细胞侵袭和转移过程中的作用。方法采用趋化运动实验检测不同浓度IL-8刺激下乳腺癌细胞的趋化运动能力;采用Western blot检测乳腺癌细胞中ELMO1的表达情况;利用小RNA干扰技术,瞬时转染乳腺癌细胞MDA-MB-231,用过表达质粒上调乳腺癌细胞MCF-7中ELMO1的表达;应用趋化运动实验和Transwell侵袭实验检测各组转染细胞的趋化和侵袭能力。结果趋化运动实验结果显示,在IL-8刺激下,乳腺癌细胞MDA-MB-231和MCF-7的运动能力明显增强,具有剂量依赖性;Western blot结果显示ELMO1在si ELMO1/MDA-MB-231细胞中的表达明显降低,而在MCF-7/ELMO1细胞中的表达明显增高;趋化运动实验结果显示在IL-8刺激下,Si ELMO1/MDA-MB-231细胞组的趋化运动能力明显降低,MCF-7/ELMO1细胞组的趋化运动能力明显增强;Transwell侵袭实验结果显示在IL-8刺激下,敲除ELMO1明显降低MDA-MB-231细胞的侵袭能力,过表达ELMO1明显增强MCF-7细胞的侵袭能力。结论 IL-8能促进MDA-MB-231和MCF-7细胞的趋化运动和侵袭能力,而ELMO1在IL-8诱导的乳腺癌细胞趋化和侵袭作用中发挥重要作用。     

癌基因iASPP在乳腺癌细胞株和浸润性导管癌中表达及意义

目的研究iASPP在乳腺癌细胞株和乳腺浸润性导管癌中的表达情况,为乳腺癌的诊断治疗和预后提供新的指标。方法设计引物采用RT-PCR技术分别扩增5种人乳腺癌细胞株(MDA-MB-231,MCF-7,Bcap-37,HBL-100和ZR-75-30)和乳腺浸润性导管癌组织中iASPP的mRNA,应用Quality One软件分析iASPP扩增产物的相对含量。免疫组化染色判断iASPP在乳腺癌细胞株和乳腺浸润性导管癌中的表达情况。结果iASPP基因只在乳腺癌细胞株Bcap-37、MCF-7和HBL-100中表达,在其它2株细胞中不表达;iASPP mRNA在58例乳腺浸润性导管癌组织中有51例表达iASPP(87.9%),癌旁组织不表达iASPP。免疫组化染色显示iASPP蛋白在58例乳腺浸润性导管癌中有53例表达(91.4%),而在对应的癌旁组织中不表达iASPP。结论iASPP mRNA在乳腺癌细胞株中的表达具有差异性;iASPP蛋白在乳腺浸润性导管癌中表达,有助于浸润性导管癌的诊断,有望成为乳腺浸润性导管癌患者治疗的新靶点。     

Cerebral metabolism of [3H]-p-chloroamphetamine

The time-dependent metabolism of intraventricularly administered $\text{[}{}^3\text{H}\text{]-p-}\text{chloroamphetamine}$ was followed. The parent compound and its metabolites were recovered by high pressure liquid chromatography and characterized by high pressure liquid chromatography, thin-layer chromatography, and gas chromatography-mass spectrometry. By 4 hr after injection, two major toluene-soluble metabolites were present in brain. Their biological half-lives were different from the parent compound. On the basis of their analyses, one of the metabolites is p-chloronorephedrine, the other (P₃) is as yet unidentified. Pretreatment with Lilly 110140 prevented or markedly reduced the synthesis of both p-chloronorephedrine and P₃. Iprindole prevented the synthesis of p-chloronorephedrine. The P₃ appeared first in the brain then in the liver, suggesting that both of these organs can metabolize p-chloroamphetamine to this compound. The metabolites were recovered primarily from the nuclear and microsomal fractions following subcellular fractionation of the brain, with small quantities present in the synaptosomal fraction. The level of metabolites was higher in the brainstem than in the neocortex. Glutathione, administered simultaneously with p-chloroamphetamine either intraventricularly or intraperitoneally failed to alter the toxicity of p-chloroamphetamine.     

Clevudine University of Georgia/Abbott/Bukwang/Triangle/Yale University

The pyrimidine analog, clevudine (L-FMAU: 2'-fluoro-5-methyl-beta-L-arabinofuranosyluridine) is a potent antihepatitis B virus (HBV) and anti-Epstein-Barr virus (EBV) agent, discovered by researchers at the University of Georgia, in collaboration with Yale University and Bukwang. Bukwang transferred its technology to Triangle Pharmaceuticals in 1998 together with a license to develop clevudine worldwide except Korea [279649], [281942]. In June 1999, Triangle and Abbott Laboratories entered into a strategic alliance to copromote antiviral products including L-FMAU [326798]. In September 2000, Triangle Pharmaceuticals Inc initiated a 30-day phase I/II evaluation of clevudine in HBV-infected patients [381755]. Clevudine is a much less toxic derivative of the toxic agent P-D-FMAU. The mechanism of action of clevudine is not yet clear, but the agent induces a rapid decrease in HBV nucleic acid as doses increase from 0.3 to 10 mg/kg [319145]. It is believed that the target for clevudine lies in the viral replication mechanism. Clevudine is phosphorylated to the triphosphate form intracellularly. This is removed slowly from the cells, thus exerting a sustained inhibitory antiviral activity [178173], [320720], [320721].     

Spotlight from the American Society for Preventive Cardiology on Key Features of the 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guidelines on the Management of Blood Cholesterol

The 2018 AHA/ACC/AACVPR/AAPA/ABC/ACPM/ADA/AGS/APhA/ASPC/NLA/PCNA Guideline on the Management of Blood Cholesterol retains focus on recommendations for statin treatment in the original four statin-eligible groups [those with atherosclerotic cardiovascular disease (ASCVD), diabetes, low-density lipoprotein cholesterol (LDL-C) ≥ 190 mg/dL, and higher risk primary prevention] without the use of treatment initiation or target LDL-C levels from the earlier 2013 American College of Cardiology/American Heart Association (ACC/AHA) guideline, but has several new features. First, patients with primary prevention are divided into those who are at low (< 5%), borderline (5% to < 7.5%), intermediate (7.5% to < 20%), and high (≥ 20%) risk based on the ASCVD risk estimator. Moreover, the new guideline goes further to consider a wider range of factors [now called “risk enhancers”—premature family history of ASCVD, persistently high LDL-C, chronic kidney disease (CKD), metabolic syndrome, conditions specific to women, inflammatory diseases, and high-risk ethnicities] that can be used to better inform the treatment decision. Moreover, more detailed recommendations on how the results of coronary calcium scanning can be used to inform the treatment decision are provided, including how it may be used to “de-risk” certain patients for delaying or avoiding the use of statin therapy. There are also specific sections for cholesterol management in other patient subgroups including women, children, certain ethnic groups, those with CKD, chronic inflammatory disorders and HIV, as well as discussion on the management of hypertriglyceridemia. Importantly, for persons with known ASCVD, a distinction is made for those who are at “very high risk” based on having had two major ASCVD events or one major event and two or more other high risk conditions, such as diabetes or other major risk factors, or bypass surgery or percutaneous intervention. Finally, the concept of a threshold LDL-C for initiating a non-statin therapy (after considering highest tolerated statin dosage) is provided, with ezetimibe recommended as the key non-statin to be added if the LDL-C still remains ≥ 70 mg/dL for all ASCVD patients, and in those who are at “very high risk”, further consideration for using a proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitor. While the new guideline does have greater detail (and arguably, complexity), the refinements provide a strategy for guiding the clinician to target both statin and non-statin therapy to those most likely to derive benefit.     

Pitavastatin Nissan/Kowa Yakuhin/Novartis/Sankyo

Pitavastatin (nisvastatin) is an HMG CoA reductase inhibitor being developed jointly by Nissan, Kowa Kogyo, Novartis and Sankyo for the potential treatment of atherosclerosis and hyperlipidemia.     

Amlodipine/Valsartan/Hydrochlorothiazide

Amlodipine/valsartan/hydrochlorothiazide (HCTZ) is a fixed-dose combination of the well established antihypertensive agents amlodipine (a calcium channel antagonist), valsartan (an angiotensin II receptor antagonist), and HCTZ (a thiazide diuretic). In patients with moderate or severe hypertension, triple combination therapy with amlodipine + valsartan + HCTZ produced significantly greater reductions from baseline in mean sitting systolic and diastolic BP (msSBP and msDBP) than either valsartan + HCTZ, amlodipine + HCTZ, or amlodipine + valsartan in a large, 8-week, randomized, double-blind, multinational, phase III trial. Furthermore, the proportion of patients achieving overall BP control at endpoint was significantly greater with the triple combination regimen than with any of the dual regimens, with significantly more triple combination recipients achieving msSBP and msDBP control at each assessment throughout the trial. Subgroup analyses of this study suggested that amlodipine + valsartan + HCTZ was generally more effective in reducing BP and providing overall BP control than the dual combination therapies, irrespective of age, race, gender, ethnicity, or hypertension severity. Several smaller studies provide data that support the efficacy of amlodipine + valsartan + HCTZ in patients whose BP is inadequately controlled with amlodipine + valsartan, amlodipine + HCTZ, or valsartan + HCTZ dual combination therapy. Treatment with amlodipine + valsartan + HCTZ for up to 8 weeks was generally well tolerated in the large, phase III trial, with most adverse events being transient and of mild to moderate severity.     

N-Nitroso-N-Methyldodecylamine and N-Nitroso-N-Methyltetradecylamine in household dishwashing liquids

Eleven household dishwashing liquids and four household surface cleaners were analysed for N-nitroso-N-methyldodecylamine and N-nitroso-N-methyltetradecylamine by gas chromatography with detection using a Thermal Energy Analyzer. Both nitrosamines were found in three of the dishwashing detergents and one of the surface cleaners. [1-¹⁴C]-N-Nitroso-N-methyldodecylamine was used to determine recoveries, which were between 65 and 88%. Levels of N-nitroso-N-methyldodecylamine ranged from 112 to 661 ppb and those of N-nitroso-N-methyltetradecylamine from 46 to 151 ppb. A simple method was developed to screen the products for N,N-dimethyldodecylamine-N-oxide, a surfactant ingredient suspected of being the source of these nitrosamines. By application of this method it was established that all of the products formulated with this amine oxide contained these two nitrosamines, whereas in products that did not contain this ingredient, these nitrosamines were not detected.     

PROTON AND POTASSIUM TRANSPORT BY H+/K+-ATPases

1. H⁺/K⁺-ATPases are members of the P-type ATPase multigene family. The prototypical H⁺/K⁺-ATPase is the protein that acidifies gastric luminal contents. The physiological and pharmacological significance of this pump has led to a detailed investigation of its biochemistry and molecular and cell biology. 2. Recently, a number of closely related H⁺/K⁺-ATPase isoforms have been discovered. These isoforms are present in organs other than the stomach, including the colon and kidney, where they contribute to acid—base and potassium homeostasis. The structure, expression and physiological roles of the gastric H⁺/K⁺-ATPase and other isoforms are reviewed.     

INTERACTIONS OF Na+, H2O2 AND THE Na+-Ca2+ EXCHANGER STIMULATE Ca2+ RELEASE IN CK1.4 CELLS

1. The present study aimed to demonstrate that interactions of cations, hydrogen peroxide (H₂O₂) and the Na⁺-Ca²⁺exchanger stimulate Ca²⁺ release and oscillations of cytosolic Ca²⁺ [Ca²⁺]i in non-transfected Chinese Hamster Ovary (CHO) C1 cells and in transfected CHO (CK1.4) cells that contained an expression vector coding the Na⁺-Ca²⁺ exchanger sequence. 2. The [⁴⁵Ca²⁺] uptake assay, fura-2 fluorescence imaging and 2² and 2³ factorial orthogonal statistics provide comparative, direct, efficient, quantitative and transient methods to delineate the effects of such interactions on Ca²⁺ influx, Ca²⁺release and [Ca²⁺]i in C1 and CK1.4 cells. 3. In contrast to the control of either Na⁺-, Ca²⁺- or H₂O₂-free or CI cells, an elevated [⁴⁵Ca²⁺] uptake was induced by Ca²⁺, Na⁺ and H₂O₂ individually and in combination, intracellular Ca²⁺ release was activated by H₂O₂ and by combinations of either H₂O₂ and Na⁺, H₂O₂ and the Na⁺-Ca²⁺ exchanger, Na⁺ and the Na⁺-Ca²⁺ exchanger or by H₂O₂, Na⁺ and the Na⁺-Ca²⁺ exchanger and a rise in [Ca²⁺]i was triggered by H₂O₂, Na⁺ and a combination of Na⁺ and the Na⁺-Ca²⁺exchanger. 4. These results indicate that interactions between H₂O₂, Na⁺ and the Na⁺-Ca²⁺ exchanger stimulate intracellular Ca²⁺mobilization via Ca²⁺-induced Ca²⁺ release mechanisms, ATP-activated G-protein coupled P_2y-purinoceptor-sensitive pathways, Na⁺-Ca²⁺ exchanger-mediated Ca²⁺ influx and cation-π interaction (a strong non-covalent force between the cation and the π face of an aromatic structure in the transmembrane protein). 5. The present findings provide important clues for understanding Ca²⁺ signal transduction mechanisms from the plasma membrane to the endoplasmic reticulum.     

EFFECTS OF THE OPIOID PEPTIDES [MET5]ENKEPHALIN-ARG6-PHE7 AND [MET5]ENKEPHALIN-ARG6-GLY7-LEU8 ON CHOLINERGIC NEUROTRANSMISSION IN THE RABBIT ISOLATED ATRIA

1. The effect of the opioid peptides [Met5]enkephalin-Arg6-Phe7 (MEAP) and [Met5]enkephalin-Arg6-Gly7-Leu8 (MEAGL) were compared with those of [Leu5]enkephalin and [D-Ala2,Met5]enkephalinamide (DAME) on cholinergic neurotransmission in the rabbit isolated atria. 2. Rabbit isolated atria had a resting rate of 190 beats/min. In the presence of the beta-adrenoceptor antagonist propranolol (0.3 mumol/l), atria responded to electrical field stimulation with a cholinergically mediated negative chronotropic response. The opioid peptides had no effect on the resting rate, but inhibited the negative chronotropic response to field stimulation. The IC50 values for inhibiting the cholinergic responses were 1.4 mumol/l for [Leu5]enkephalin (LE), 1.4 mumol/l for MEAP, 1.3 mumol/l for MEAGL and 0.2 mumol/l for DAME. Responses of a similar magnitude to exogenous acetylcholine were unaffected. 3. Thus, MEAP, MEAGL and LE had similar potencies but DAME was about seven times more potent in inhibiting cholinergic neurotransmission in the rabbit isolated atria. The site of inhibition appears to be prejunctional.