褪黑素对细菌脂多糖致宫内感染胎鼠脑组织氧化损伤和细胞凋亡的影响

目的探讨褪黑素(MT)对细菌脂多糖(LPS)致宫内感染胎鼠脑组织氧化损伤和细胞凋亡的影响。方法妊娠第19天SD大鼠72只随机均分为空白对照(S)组、宫内感染(LPS)组和MT处理(MT)组。LPS组和MT腹腔注射LPS 500μg/kg建立大鼠宫内感染模型,MT组同时腹腔注射MT 10mg/kg。分别于注药后1、6、12、24、48和72h剖宫取胎鼠,测定胎鼠脑组织匀浆的超氧化物歧化酶(SOD)和丙二醛(MDA)含量,TUNEL法测定胎鼠脑细胞凋亡指数。结果 LPS组较S组胎鼠脑组织中SOD活力下降,MDA含量上升,大脑皮质神经细胞凋亡指数增加(P<0.05或P<0.01)。与LPS组比较,MT能提高胎鼠脑组织中SOD活力、降低MDA含量、减少脑细胞凋亡指数(P<0.05)。结论 MT能减轻LPS致宫内感染胎鼠脑细胞氧化损伤,抑制脑细胞凋亡,对胎鼠脑损伤有保护作用。     

D-R聚甘酯对局灶性脑缺血大鼠的保护作用

目的研究D-聚甘酯(多糖类化合物)对大鼠局灶性脑缺血再灌注损伤(RI)的保护作用及其可能机制。方法用改良Longa法,建立大鼠局灶性脑缺血2 h再灌注损伤模型,观察D-聚甘酯对脑缺血再灌注大鼠的脑组织中丙二醛(MDA)含量及对超氧化物歧化酶(SOD)、谷胱苷肽过氧化物酶(GSH-PX)活性的影响。结果模型组大鼠在RI 24 h、RI 72 h及RI 144h时,MDA含量明显高于假手术组;而SOD和GSH-PX活性降低。D-聚甘酯可降低MDA含量,升高SOD和GSH-PX活性,尤其是在RI 144 h。结论 D-聚甘酯对脑缺血再灌注损伤有保护作用,其机制可能与抗缺血性脑组织中的自由基有关。     

宫内急性缺血及再灌注对胎鼠肾SOD和MDA的影响

目的利用大鼠宫内急性缺血及再灌注模型检测胎龄21d鼠肾损伤后超氧化物歧化酶(SOD)、丙二醛(MDA)的变化,以探讨宫内缺血/再灌注时肾损伤的发病机制。方法选取孕21dWistar大鼠,腹腔麻醉后,暴露双角子宫及供应子宫和卵巢的动静脉血管,钳夹其双角子宫一侧动静脉血管,钳夹时间分别为10、30min,达要求时间后取下动脉夹行再灌注,再灌注时间分别为0.5、2、6、24h,对侧未钳夹宫角内的胎鼠为对照组,每个时间点留取7份标本。分别检测各个时间点胎鼠肾SOD、MDA的含量。结果①SOD活性:缺血10min时SOD活性开始降低(P>0.05),缺血30min时SOD活性下降明显(P<0.05),随再灌注时间的延长,SOD活性逐渐降低,于再灌注6h时达最低(P<0.01),而后SOD活性开始升高,再灌注24h时虽未恢复正常,但与假手术组无差异(P>0.05);缺血10min组与缺血30min组相比,后组明显低于前组,尤为再灌注0.5h和再灌注6h(P<0.01);②MDA含量:缺血10minMDA含量即开始升高(P>0.05),缺血30min时MDA含量升高明显(P<0.05);随再灌注时间的延长,MDA含量逐渐升高,尤为再灌注2、6、24h(P<0.01);缺血10min组与缺血30min组相比,后组明显高于前组,尤为再灌注6h(P<0.01)。结论宫内缺血无再灌注时即有自由基损伤的存在;自由基损伤可能是宫内缺血再灌注肾损伤的发病机制之一。     

褪黑素对脑缺血再灌注后脑内抗氧化酶及MDA的影响

目的　研究褪黑素 (melatonin ,MT)对脑缺血再灌注沙土鼠脑组织谷胱甘肽过氧化物酶 (GPx)、超氧化物歧化酶(SOD)活性及丙二醛 (MDA)含量的影响 ,探讨MT的脑保护作用机制。方法　采用沙土鼠双侧颈总动脉结扎法制作前脑缺血再灌注损伤的模型 ,缺血前 30min腹腔注射MT ,测定脑缺血再灌注 1h沙土鼠大脑皮层和纹状体GPx、SOD活性及MDA含量。结果　脑缺血再灌注后大脑皮层和纹状体GPx、SOD活性降低 ,MDA含量升高 ;MT预处理能部分反转这种变化。结论　MT对脑缺血再灌注损伤有保护作用 ,其机制可能与保护GPx、SOD活性 ,减少脂质过氧化有关     

甲磺酸桂哌齐特对大鼠脑缺血-再灌注损伤的神经保护作用

目的 探讨甲磺酸桂哌齐特对脑缺血-再灌注(I-R)损伤的保护作用及机制.方法 50只雄性SD大鼠用线栓法建立大脑中动脉I-R损伤模型后随机均分为五组:B组为模型对照,C、D和E组分别用甲磺酸桂哌齐特20、40和80 mg/kg处理,F组用马来酸桂哌齐特40 mg/kg处理;另外取10只雄性SD大鼠作为空白对照(A)组.观察I-R后4、8及22 h神经功能缺损、脑含水量、脑指数的变化;I-R损伤24 h后测定脑组织超氧化物歧化酶(SOD)、乳酸脱氢酶(LDH)、一氧化氮合酶(NOS)的活力和丙二醛(MDA)、乳酸(LD)的含量.结果 与B组比较,D组和E组I-R后8h和22 h神经功能缺损评分、脑含水量和脑指数降低(P＜0.05);与B组比较,C、D、E、F组I-R脑组织SOD和LDH活性升高、MDA、LD含量和NOS活性降低(P＜0.05).结论 甲磺酸桂哌齐特对脑I-R损伤有保护作用;其机制可能与抗自由基损伤、抑制NOS等的升高有关.     

依达拉奉对大鼠脑缺血再灌注后自由基含量的影响

目的通过观察雄性大鼠脑缺血再灌注后SOD活力、MDA、NO的表达,探讨依达拉奉的脑保护作用。方法选用雄性SD大鼠30只,随机分为3组:假手术(SO)组、缺血再灌注(I/R)组和依达拉奉(ED)组,每组10只。建立大鼠右侧大脑中动脉闭塞局灶性脑缺血再灌注模型,用生化法测定3组脑缺血再灌注后SOD活力、MDA、NO含量。结果 ED组及SO组脑组织SOD活力均高于I/R组(P<0.05),MDA及NO含量显著低于I/R组(P<0.05)。结论依达拉奉能增强SOD活力、减少MDA及NO含量,改善自由基代谢,有效减轻缺血再灌注损伤后的脑损伤。     

纳洛酮联合地塞米松对脑缺血再灌注损伤模型小鼠脑组织的保护作用

目的:研究纳洛酮联合地塞米松对脑缺血再灌注损伤模型小鼠脑组织的保护作用。方法:取小鼠随机分为假手术(0.9%氯化钠注射液)组、模型(0.9%氯化钠注射液)组、纳洛酮(1 mg/kg)组、地塞米松(1 mg/kg)组和联用(纳洛酮1 mg/kg+地塞米松1mg/kg)组,每组10只。后4组采用双侧颈总动脉同时阻断后再灌注法复制脑缺血再灌注损伤小鼠模型,再灌注5 min后各组小鼠ip给予相应药物。再灌注24 h后对各组小鼠卒中指数和神经病学症状进行评分,显微镜观察神经细胞形态学变化,检测小鼠脑组织匀浆中超氧化物歧化酶(SOD)活性、丙二醛(MDA)含量。结果:与假手术组比较,模型组小鼠卒中指数和神经病学症状评分升高,脑组织匀浆中MDA含量增加、SOD活性减弱,差异具有统计学意义(P<0.01);与模型组比较,纳洛酮组、地塞米松组和联用组小鼠卒中指数和神经病学症状评分降低,脑组织匀浆中MDA含量减少、SOD活性增强,差异具有统计学意义(P<0.01或P<0.05);与纳洛酮组或地塞米松组比较,联用组小鼠卒中指数和神经病学症状评分减小,脑组织匀浆中MDA含量减少、SOD活性增强,差异具有统计学意义(P<0.01或P<0.05)。镜下观察,模型组小鼠神经细胞排列松散,形态异常肿大,出现核固缩等病理变化;纳洛酮组小鼠神经元细胞基本正常,但仍有部分细胞出现核固缩;地塞米松组小鼠出现严重的神经细胞凋亡等病理变化;联用组小鼠神经细胞基本正常,只有极少数细胞异常。结论:纳洛酮、地塞米松对脑缺血再灌注损伤模型小鼠的脑组织具有一定的保护作用,且二者具有协同作用。     

不同时程治疗性浅低温对大鼠脑缺血再灌注损伤的影响

目的 评价不同时程治疗性浅低温对大鼠脑缺血再灌注损伤的影响.方法 健康成年雄性SD大鼠72只,体重250～300g,采用随机数字表法,将其随机分为6组(n=12):假手术组(S组)、脑缺血再灌注损伤组(IR组)、缺血后即刻治疗性浅低温组(MTH1组)、缺血再灌注即刻治疗性浅低温组(MTH2组)、缺血再灌注后1h治疗性浅低温组(MTH3组)和缺血再灌注后2h治疗性浅低温组(MTH4组).IR组、MTH1组、MTH2组、MTH3组和MTH4组采用线栓法进行脑缺血6h再灌注制备大鼠脑缺血再灌注损伤模型,S组不置入线栓.S组和IR组置于室温下,MTH1组、MTH2组、MTH3组和MTH4组分别于大鼠脑缺血后即刻、缺血再灌注即刻、再灌注后1h及再灌注后2h时进行治疗性浅低温处理并维持4h.于再灌注后24h进行改良神经系统损害严重程度评分(NSS评分),行为学测试结束后取大鼠脑组织,采用TTC染色检测脑梗死体积,TUNEL检测神经元凋亡情况,化学比色法检测脑组织超氧化物歧化酶(SOD)及丙二醛(MDA)活性,ELISA法测定脑组织肿瘤坏死因子-α(TNF-α)及白细胞介素-6(IL-6)水平,Western-blot法检测脑组织Caspase-3、Bax及Bcl-2蛋白表达.结果 与S组比较,其余5组大鼠NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Cas-pase-3及Bax表达均升高,脑组织SOD活性及Bcl-2表达降低(P<0.05);与IR组比较,MTH1组、MTH2组、MTH3组和MTH4组大鼠NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Caspase-3及Bax表达均降低,脑组织SOD活性及Bcl-2表达升高(P<0.05);与MTH1组比较,MTH2组、MTH3组和MTH4组大鼠NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Caspase-3及Bax表达均升高,脑组织SOD活性及Bcl-2表达降低(P<0.05);与MTH2组比较,MTH3组和MTH4组NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Caspase-3及Bax表达均升高,脑组织SOD活性及Bcl-2表达降低(P<0.05).结论 治疗性浅低温可减轻大鼠脑缺血再灌注损伤,且在脑缺血后即刻进行治疗性浅低温处理效果最佳.     

不同时程治疗性浅低温对大鼠脑缺血再灌注损伤的影响

目的 评价不同时程治疗性浅低温对大鼠脑缺血再灌注损伤的影响.方法 健康成年雄性SD大鼠72只,体重250～300g,采用随机数字表法,将其随机分为6组(n=12):假手术组(S组)、脑缺血再灌注损伤组(IR组)、缺血后即刻治疗性浅低温组(MTH1组)、缺血再灌注即刻治疗性浅低温组(MTH2组)、缺血再灌注后1h治疗性浅低温组(MTH3组)和缺血再灌注后2h治疗性浅低温组(MTH4组).IR组、MTH1组、MTH2组、MTH3组和MTH4组采用线栓法进行脑缺血6h再灌注制备大鼠脑缺血再灌注损伤模型,S组不置入线栓.S组和IR组置于室温下,MTH1组、MTH2组、MTH3组和MTH4组分别于大鼠脑缺血后即刻、缺血再灌注即刻、再灌注后1h及再灌注后2h时进行治疗性浅低温处理并维持4h.于再灌注后24h进行改良神经系统损害严重程度评分(NSS评分),行为学测试结束后取大鼠脑组织,采用TTC染色检测脑梗死体积,TUNEL检测神经元凋亡情况,化学比色法检测脑组织超氧化物歧化酶(SOD)及丙二醛(MDA)活性,ELISA法测定脑组织肿瘤坏死因子-α(TNF-α)及白细胞介素-6(IL-6)水平,Western-blot法检测脑组织Caspase-3、Bax及Bcl-2蛋白表达.结果 与S组比较,其余5组大鼠NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Cas-pase-3及Bax表达均升高,脑组织SOD活性及Bcl-2表达降低(P<0.05);与IR组比较,MTH1组、MTH2组、MTH3组和MTH4组大鼠NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Caspase-3及Bax表达均降低,脑组织SOD活性及Bcl-2表达升高(P<0.05);与MTH1组比较,MTH2组、MTH3组和MTH4组大鼠NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Caspase-3及Bax表达均升高,脑组织SOD活性及Bcl-2表达降低(P<0.05);与MTH2组比较,MTH3组和MTH4组NSS评分、脑梗死体积、梗死体积百分比、神经元凋亡指数、脑组织MDA活性、TNF-α、IL-6水平、Caspase-3及Bax表达均升高,脑组织SOD活性及Bcl-2表达降低(P<0.05).结论 治疗性浅低温可减轻大鼠脑缺血再灌注损伤,且在脑缺血后即刻进行治疗性浅低温处理效果最佳.     

依达拉奉对脑缺血再灌注损伤大鼠脑组织Fas及细胞凋亡的影响

目的观察依达拉奉对脑缺血再灌注损伤大鼠脑组织Fas及细胞凋亡的影响。方法24只雄性SD大鼠随机分为三组：假手术组（SH组）、缺血再灌注组（IR组）、依达拉奉治疗组（EDA组）,每组8只。IR组和EDA组线栓法制备脑缺血再灌注模型;SH组栓线只进入颈外动脉。EDA组于再灌注前30min和再灌注12h经腹腔注射依达拉奉3mg/kg,SH组和IR组在相同时间点注射等容量生理盐水。再灌注24h取血清测超氧化物歧化酶（SOD）活力、丙二醛（MDA）含量;取脑组织检测缺血半暗带Fas的表达及细胞凋亡情况;于再灌注3h和24h,参照Zealonga五级神经功能缺损评分标准评价神经功能损伤情况。结果与SH组比较,IR组和EDA组再灌注24h血清SOD活力降低（P〈0.01）,IR组SOD活力低于EDA组（P〈0.01）。与SH组比较,IR组和EDA组再灌注24h时血清MDA含量升高（P〈0.01）;IR组MDA含量高于EDA组（P〈0.05）。SH组脑组织无或仅有少量细胞Fas表达呈阳性,IR组与EDA组缺血半暗带均有大量Fas表达;EDA组平均灰度值较IR组大（P〈0.01）。SH组脑组织仅有少量凋亡细胞,IR组与EDA组缺血半暗带可见大量凋亡神经细胞;EDA组凋亡细胞数较IR组少（P〈0.01）。SH组各时点无神经损伤症状,再灌注3h,IR组与EDA组大鼠神经功能损伤差异无显著性（P〉0.05）;再灌注24h,与IR组比较EDA组大鼠神经功能损伤减轻（P〈0.05）。结论脑缺血再灌注后,大鼠血清SOD活力降低、MDA含量升高、大脑皮层半暗带Fas表达及凋亡细胞数明显增多。依达拉奉可保护SOD活力,降低MDA含量,减少缺血再灌注大脑皮层半暗带Fas的表达及细胞凋亡,从而减轻神经功能损伤,对脑缺血再灌注损伤具有一定的保护作用。     

人参茎叶皂苷预适应对自发性高血压大鼠心肌缺血再灌注损伤的保护作用

目的研究人参茎叶皂苷(GSLS)预适应对自发性高血压大鼠(SHR)心肌缺血再灌注损伤(I-R)的保护作用及可能机制。方法SHR于I-R造模前每日1次灌胃给予GSLS50和100mg.kg-1,连续3周,于缺血40min和再灌注30min内测定大鼠血压、心功能和心脏血流动力学指标,生化方法测定心肌ATPase酶、乳酸脱氢酶(LDH)和超氧化物歧化酶(SOD)活性及丙二醛(MDA)和NO含量,镉血红素饱和法测定心肌和肝脏金属硫蛋白(MT)含量,免疫组化方法测定细胞热休克蛋白70(HSP70)表达。结果GSLS50和100mg.kg-1预适应组显著改善I-R损伤SHR的心率、左室内压峰值和左室内压最大变化速率(±dp/dtmax),明显提高心肌ATPase活性,减少LDH漏出,提高心肌SOD活性,增加NO含量,降低MDA含量,增加心肌和肝脏MT含量,增加心肌HSP70阳性细胞百分数。结论GSLS预适应对心肌I-R损伤具有保护作用,其作用机制与改善SHR心肌舒缩功能,改善心肌代谢,增强抗氧化活性和诱导内源性心肌保护物质的释放有关。     

褪黑素对海洛因依赖大鼠催促戒断症状的治疗作用

目的··:研究褪黑素对海洛因依赖大鼠催促戒断症状的治疗效果。方法··:大鼠按剂量递增法连续皮下注射海洛因42d,用纳洛酮催促成瘾的大鼠,给予不同剂量的褪黑素治疗。结果··:褪黑素保护组、褪黑素单剂量治疗组在剂量为25mg·kg-1、250mg·kg-1时,能缓解大鼠的戒断症状(与海洛因对照组比较,P<0.05);褪黑素50mg·kg-1、75mg·kg-1、125mg·kg-1单剂量给药组能明显缓解大鼠的戒断症状(与海洛因对照组比较分别为P<0.01、P<0.01、P<0.001)。结论··:褪黑素能控制海洛因依赖大鼠的戒断症状;在剂量为25-125mg·kg-1范围内存在一定的剂量依赖关系。     

Melatonin-mediated regulation of human MT(1) melatonin receptors expressed in mammalian cells

In mammals, the pineal hormone melatonin activates G protein-coupled MT(1) and MT(2) melatonin receptors. Acute exposure of recombinant MT(1) and MT(2) melatonin receptors to supraphysiological concentrations of melatonin differentially regulates these two receptors with the MT(2), but not the MT(1), exhibiting rapid desensitization and internalization. In the present study, we sought to determine whether prolonged exposure to supraphysiological and physiological concentrations of melatonin desensitized and/or internalized the MT(1) melatonin receptor. Using a Chinese hamster ovary (CHO) cell line stably expressing MT(1)-FLAG or transiently expressing MT(1)-green fluorescent protein (GFP) melatonin receptors, we found that prolonged exposure (8h) to supraphysiological concentrations of melatonin (100 nM) significantly increased the number of MT(1) melatonin receptors and decreased the affinity (K(i)) of melatonin for competition for 2-[125]iodomelatonin. A similar treatment also desensitized the MT(1) melatonin receptor-mediated stimulation of [(35)S]GTPgammaS binding, but did not internalize the receptor. In contrast, prolonged exposure to a concentration of melatonin mimicking nocturnal levels (400 pM) did not affect the number of MT(1) melatonin receptors, the affinity for melatonin, or the functional sensitivity of the receptor. We conclude that in vivo endogenous melatonin does not significantly affect the functional sensitivity of MT(1) melatonin receptors, however, exogenous melatonin taken therapeutically at doses above physiological levels could desensitize the receptor thereby affecting physiological responses mediated following activation of MT(1) melatonin receptors.     

褪黑素和己酮可可碱减缓肝缺血再灌注损伤的实验研究

目的　探讨褪黑素 (MT)和己酮可可碱 (PTX)对肝脏缺血再灌注损伤的保护作用。方法　 12 8只SD大鼠随机分为4组 :对照组、MT组、PTX组及MT与PTX联合组。所有大鼠均在阻断第一肝门 35min后恢复入肝血流 ,其间行肝左外叶切除。测定缺血前、后及再灌注时的血清ALT、LDH、TNF α、肝组织MDA、SOD及ET 1的含量 ;并观察大鼠一周的生存率。结果　①肝功能 :各组ALT和LDH值均明显升高 ,但用药组的上升幅度明显低于对照组 ,且以联合用药组的降低更为明显 ;②ET 1:各组ET 1值均明显增加 ,但用药组的升高幅度明显低于对照组 ;③MT疗效 :各组MDA及SOD均明显增加 ,但MT使用组 (含MT组和联合组 )的升高幅度较其它组别明显降低 ;④PTX疗效 :各组TNF α值均明显升高 ,但PTX使用组 (含PTX组及联合组 )的升高幅度明显低于其它组别 ,且生存率较其它组别明显增加。结论　①MT可降低脂质过氧化程度 ,但对提高生存率无明显作用 ;②PTX可减轻炎性细胞因子释放、提高生存率 ;③联合应用MT和PTX可显著减轻肝功能损害 ,提高大鼠生存率。     

胰高血糖素样肽-2对幼鼠肠缺血-再灌注损伤的保护作用

目的 研究胰高血糖素样肽2(GLP-2)对肠缺血-再灌注(I-R)幼鼠肠屏障功能的保护作用.方法 采用肠I-R模型,将24只雄性Wistar幼鼠随机均分为假手术(C组)、肠I-R损伤(B组)和肠I-R损伤+GLP-2保护(A组)三组.光镜下观察小肠黏膜形态学改变,检测肠系膜淋巴结的细菌菌落情况、肠黏膜丙二醛(MDA)、血清D-乳酸、内毒素和肿瘤坏死因子α(TNF-α)水平的变化.结果 B组肠黏膜损伤最明显,Chiu's评分、肠系膜淋巴结细菌菌落计数、肠黏膜MDA、血清D-乳酸、内毒素和TNF-α水平均显著高于C组(P<0.01);与B组相比,A组肠黏膜损伤明显减轻,且Chiu's评分、肠系膜淋巴结细菌菌落计数、肠黏膜MDA、血清乳酸、内毒素和TNF-α水平显著降低(P<0.05).结论 GLP-2能够减轻幼鼠肠I-R损伤、保护肠黏膜屏障、减轻细菌/内毒素易位、减少氧自由基和炎性介质的产生和释放.     

Dual coupling of MT(1) and MT(2) melatonin receptors to cyclic AMP and phosphoinositide signal transduction cascades and their regulation following melatonin exposure

In this investigation, we wanted to determine whether MT(1) or MT(2) melatonin receptors are capable of coupling to the phosphoinositide (PI) signal transduction cascade. In addition, we wanted to assess the effects of chronic melatonin exposure on MT(1) and MT(2) melatonin receptor-mediated stimulation of PI hydrolysis. We also assessed the effects of chronic melatonin exposure on other parameters of the MT(2) melatonin receptor function including total specific 2-[125I]-iodomelatonin binding, the affinity of melatonin for the receptor, and melatonin (1nM)-mediated inhibition of cyclic 3',5'-adenosine monophosphate (cAMP) accumulation. Investigation of the PI signal transduction cascade activated by either the MT(1) or MT(2) melatonin receptor expressed in Chinese hamster ovary (CHO) cells showed that melatonin (1pM to 1mM) was able to stimulate the formation of PIs to approximately 40-60% over basal [EC(50): MT(1)=29nM (2-300nM) and MT(2)=1.1nM (0.32-3.5nM), N=5]. This response was mediated via receptors based upon the findings that melatonin did not stimulate the formation of PIs in CHO cells devoid of receptor and that antagonism of MT(2) melatonin receptors by 4P-PDOT (AH 024; 4-phenyl-2-propionamidotetralin) attenuated melatonin-mediated stimulation of PI hydrolysis in CHO cells expressing the MT(2) melatonin receptor. The consequence of chronic melatonin exposure on MT(1) and MT(2) receptor function was also examined. Pretreatment of either MT(1)- or MT(2)-CHO cells with melatonin (1 microM for 5hr) resulted in: (a) a complete loss of melatonin-mediated stimulation of PI hydrolysis, and (b) an attenuation of melatonin (1nM)-mediated inhibition of forskolin-induced cAMP accumulation by approximately 20-40%. The desensitization of the PI hydrolysis signal transduction cascades coupled to either MT(1) or MT(2) melatonin receptors following chronic melatonin exposure was not due to depleted phospholipid pools, to elevated basal levels, or to decreases in receptor affinity and density. This dual coupling of melatonin receptors to different signal transduction cascades may contribute to the diversity of melatonin receptor function in vivo.     

Mutagenesis studies of the human MT2 melatonin receptor

Melatonin mediates its physiological effects through activation of high affinity G protein-coupled receptors. The vertebrate MT(1), MT(2) and Mel(1c) melatonin receptors are molecularly and pharmacologically distinct. Three molecular models of melatonin recognition for the MT(1) and/or Mel(1c) melatonin receptors have been proposed. To determine if these models applied to the MT(2) melatonin receptor, we mutated seven conserved residues to alanine in the hMT(2) melatonin receptor and expressed the receptors in HEK-293 cells. Competition of melatonin for 2-[125I]-iodomelatonin binding revealed that mutation of Asn 16 in TM4 or His 7 in TM5 of the hMT(2) melatonin receptor significantly decreased the binding affinity for melatonin when compared with wild-type. In addition, competition of 4P-ADOT, N-acetyltryptamine, luzindole, and 5-methoxytryptophol for 2-[125I]-iodomelatonin binding suggested Asn 16 in TM4 may facilitate binding of the 5-methoxy group of the melatonin molecule to the hMT(2) melatonin receptor. Trp 13 or Phe 6 in TM6 while not critical for melatonin binding, may interact with aromatic regions of luzindole and 4P-ADOT. Mutation of Ser 8 or Ser 12 in TM3, or Ser 6 in TM7 did not affect the affinity of melatonin for competition with 2-[125I]-iodomelatonin to the hMT(2) melatonin receptor, although equivalent serines (Ser 8 and Ser 12 in TM3) were reported to be critical for melatonin binding to the hMT(1) melatonin receptor. Thus these results are the first to identify residues within the transmembrane regions of the hMT(2) melatonin receptor critical for melatonin binding, highlighting potential structural differences between the MT(1) and MT(2) melatonin receptor binding pockets.     

Molecular cloning and pharmacological characterization of rat melatonin MT1 and MT2 receptors

In order to interpret the effects of melatonin ligands in rats, we need to determine their activity at the receptor subtype level in the corresponding species. Thus, the rat melatonin rMT(1) receptor was cloned using DNA fragments for exon 1 and 2 amplified from rat genomic DNA followed by screening of a rat genomic library for the full length exon sequences. The rat rMT(2) receptor subtype was cloned in a similar manner with the exception of exon 1 which was identified by screening a rat genomic library with exon 1 of the human hMT(2) receptor. The coding region of these receptors translates proteins of 353 and 364 amino acids, respectively, for rMT(1) and rMT(2). A 55% homology was observed between both rat isoforms. The entire contiguous rat MT(1) and MT(2) receptor coding sequences were cloned, stably expressed in CHO cells and characterized in binding assay using 2-[(125)I]-Iodomelatonin. The dissociation constants (K(d)) for rMT(1) and rMT(2) were 42 and 130 pM, respectively. Chemically diverse compounds previously characterized at human MT(1) and MT(2) receptors were evaluated at rMT(1) and rMT(2) receptors, for their binding affinity and functionality in [(35)S]-GTPgammaS binding assay. Some, but not all, compounds shared a similar binding affinity and functionality at both rat and human corresponding subtypes. A different pharmacological profile of the MT(1) subtype has also been observed previously between human and ovine species. These in vitro results obtained with the rat melatonin receptors are thus of importance to understand the physiological roles of each subtype in animal models.     

银杏叶总黄酮对肾缺血-再灌注损伤大鼠p38 MAPK活性的影响

目的观察银杏叶总黄酮(TFG)对肾缺血-再灌注(I-R)损伤大鼠p38丝裂素活化蛋白激酶(MAPK)活性的影响。方法 120只SD大鼠随机均分为假手术组I、-R组和TFG预处理组(TFG 250 mg/kg,每天3次)。3 d后采用夹闭双侧肾蒂致肾缺血45 min后再灌注制作大鼠肾I-R损伤模型。Western blot检测p38 MAPK和磷酸化p38 MAPK蛋白表达;免疫组化方法检测肾组织磷酸化p38 MAPK的分布情况。结果磷酸化p38 MAPK表达活性在再灌注10 min开始增加,1 h达最高峰,持续至24 h仍高于正常水平,且主要在肾小管细胞表达。TFG预处理组磷酸化p38 MAPK的表达较I-R组明显减弱(P<0.01)。结论 TFG可能通过抑制肾I-R损伤大鼠p38 MAPK的活化而发挥防治作用。     

褪黑素对梗阻性黄疸肠组织ICM-1表达的影响

目的探讨褪黑素对大鼠梗阻性黄疸后肠组织细胞间粘附分子-1(ICAM-1)表达的影响。方法将36只大鼠随机分为3组(每组12只):假手术对照组(SO)、梗阻性黄疸组(OJ)、褪黑素治疗组(MT)。观察各组小肠组织中ICAM-1的表达及小肠组织形态学改变,并测量肠绒毛高度和黏膜厚度。结果梗阻性黄疸组小肠组织ICAM-1的表达明显增强,肠绒毛高度、黏膜厚度明显降低,与假手术对照组有显著性差异(P<0.01,P<0.01);褪黑素治疗组与梗阻性黄疸组比较小肠组织ICAM-1的表达明显减弱(P<0.01),肠绒毛高度、黏膜厚度增高,肠组织结构损害减轻(P<0.01)。结论褪黑素通过抑制梗阻性黄疸后肠组织ICAM-1的表达,减轻小肠黏膜的损伤。