异丙酚对大鼠肠缺血再灌注时肠粘膜细胞凋亡的影响

目的评价异丙酚对大鼠肠缺血再灌注（I／R）时肠粘膜细胞凋亡的影响。方法24只SD大鼠随机分为3组（n=8），假手术组（S组）仅分离肠系膜上动脉（SMA）；肠缺血再灌注组（I／R组）阻断SMA1h；异丙酚组（P组）阻断SMA前30min腹腔注射异丙酚100mg／kg。于再灌注3h处死大鼠，取回肠末端组织，电镜及TUNEL法观察肠粘膜上皮细胞凋亡情况，并计算肠粘膜上皮细胞凋亡指数；测定肠粘膜超氧化物歧化酶（SOD）活性、丙二醛（MDA）及神经酰胺（CER）含量，RT-PCR法测定肠粘膜鞘磷脂酶（SMase）mRNA表达。结果与S组比较，I／R组肠粘膜SOD活性降低，MDA含量、CER含量、肠粘膜上皮细胞凋亡指数及SMasemRNA表达升高（P〈0．05或0．01）；与I／R组比较，P组MDA含量、CER含量、肠粘膜上皮细胞凋亡指数及SMasemRNA表达降低，S01）活性升高（P〈0．05或O．01）。I／R组肠粘膜SOD活性与CER含量呈负相关（r＝-0．775，P〈0．01），肠粘膜上皮细胞凋亡指数与CER含量呈正相关（r=0．852，P〈0．01）；P组肠粘膜上皮细胞凋亡指数与CER含量呈正相关（r=0．782，P〈0．01）。结论异丙酚可抑制大鼠肠缺血再灌注时肠粘膜上皮细胞凋亡，可能与清除氧自由基、下调SMasemRNA表达、减少CER生成有关。     

脂联素对高糖环境下大鼠肾小管上皮细胞血管内皮生长因子表达的影响

目的探讨脂联素（adiponectin,ADPN）对高糖环境下大鼠肾小管上皮细胞（NRK-52E）血管内皮生长因子（vascular endothelialgrowthfactor,VEGF）表达的影响。方法用含不同浓度葡萄糖的DMEM培养基体外培养NRK-52E细胞,随机分6组（每组5个样本,重复5次）：A组,含5．5mmol／L葡萄糖培养基对照组;B组,含5．5mmol／L葡萄糖＋甘露醇19．5mmol／L培养基组;C组,含25mmol／L葡萄糖培养基组;D组,含25mmol／L葡萄糖培养基＋脂联素1mg／L组：E组,含25mmol／L葡萄糖培养基＋脂联素2．5mg／L组;F组,含25mmol／L葡萄糖培养基＋脂联素5mc／L组,培养24h。以逆转录一聚合酶链反应（RT-PCR）检测VEGF的表达,免疫荧光检测不同浓度干预组VEGF蛋白的表达影响。结果A组细胞VEGFmRNA表达量为（0．367±0．028）;B组为（0．346±0．045）,与A组比较无统计学差异（P〉0．05）;C组为（0．692±0．053）,显著高于A组（P〈0．01）;D组为（0．562±0．049）,低于C组（P〈0．05）。E组为（0．381±0．035）,与A组相近,但无统计学差异（P〉0．05）;F组为（0．295±0．031）,低于A组（P〈0．01）。不同浓度脂联素各组间比较,有统计学差异（P〈0．05）。免疫荧光检测VEGF表达情况;B组与A组无差异;C组显著高于A组（P〈0．01）;D组低于C组（P〈0．05）。E组与A组相近,但无统计学差异（P〉0．05）;F组低于A组（P〈0．05）。不同浓度脂联素各组间比较有统计学差异（P〈0．05）。结论ADPN能通过减少肾小管上皮细胞VEGF的表达对肾小管间质起保护作用。     

参附注射液对大鼠肠缺血再灌注损伤后肠黏膜细胞凋亡的影响

目的：研究参附注射液对大鼠肠缺血再灌注期间黏膜上皮细胞凋亡的影响，并探讨其可能机制。方法：采用大鼠肠缺血再灌注模型。24只大鼠随机分为假手术对照组（C组）、缺血再灌注组（I／R组）和参附治疗组（SF组），在规定时间检测小肠黏膜上皮细胞caspase-3、Bcl-2蛋白的表达，凋亡细胞数目，同时观察小肠黏膜病理形态学改变。结果：IR组肠黏膜上皮细胞凋亡指数（apoptosisindex,AI）、caspase-3、Bcl-2蛋白显著高于C组（P〈0．01）。SF组AI、caspase-3蛋白低于IR组（P〈0.01或P〈0．05），而Bcl-2蛋白较IR组上调（P〈0．01）。caspase-3表达与AI呈正相关（r=0，914，P〈0，01）；Bel-2的表达与AI、caspase-3呈直线负相关（r分别=-0．375，-0．367，P〈001）。SF组小肠黏膜病理损伤程度较I／R组明显减轻（P〈0.01）。结论：参附注射液通过抑制caspase-3表达和促进Bcl-2基因表达减少缺血再灌注期间肠黏膜上皮细胞的凋亡。从而一定程度上减轻肠黏膜缺血再灌注损伤。     

肠缺血再灌流时肠内给予葡萄糖能增加肠黏膜血流量

目的 探讨肠制备再灌流损伤时肠内营养与肠黏膜血流改变的关系。方法 SD大鼠随机分为丙氨酸组（12只）、葡萄糖组（14只）和甘露醇对照组（10只）。先制作空肠袋,将激光多谱勒探头和肠黏膜张力计放置在空肠代两端,分别向袋内注入丙氨酸、葡萄糖和甘露醇。用动脉夹阻断肠系膜上动脉血流60min后,再恢复灌流60min。每30min分别测定肠黏膜血流量和局部PCO2张力（PrCO2）。结果 缺血再灌流过程中,与甘露醇组比较,葡萄糖组肠黏膜血流量显著增加,PrCO2降低,P＜0.01。结论 缺血再灌流过程中,肠内给予葡萄糖能增加肠黏膜血流量,对缺血再灌流损伤的肠道提供保护作用。     

谷氨酰胺和ω—3多不饱和脂肪酸对大鼠肠道缺血再灌注损伤时肠道通透性和肺细胞凋亡的影响

目的研究大鼠肠道缺血再灌注损伤时,肠淋巴管结扎和不同肠内营养对肠道通透性、系统炎性反应和肺损伤的影响。方法SPF级雄性大鼠胃造瘘术后随机分为正常饮食组、普通肠内营养组、谷氨酰胺（Gin）肠内营养组、ω-3多不饱和脂肪酸（ω-3PUFA）肠内营养组和假手术组．前4组根据淋巴管是否结扎又各分为结扎和不结扎组．共9组．每组8只。所有肠内营养组均经胃造瘘给予等氮（1．8gN·kg-1·d-1）等热卡（1046kJ·kg-1·d-1）的营养支持,7d后除假手术组外其他8组实施肠道缺血60min,结扎组在缺血前同时进行淋巴管结扎：然后继续原营养再灌注3d。在胃造瘘术后第5、7和9天测定肠道通透性（尿中乳果糖／甘露醇浓度值．L／M）：术后第11天取血检测血清二胺氧化酶、内毒素、细胞因子及ALT、AST的水平：取小肠黏膜检测黏膜厚度和绒毛高度;取肺组织检测髓过氧化物酶（MPO）、NO和NO合酶（NOS）浓度及细胞凋亡指数。结果肠道缺血60min可引起肠道损伤;缺血后第1天,各组L／M均显著增加（P〈0．05）;缺血后第3天L／M明显下降（P〈0．05）,其中Gin肠内营养组和（ω-3PUFA肠内营养组已恢复至接近缺血前水平（P〉0．05）．且淋巴管结扎组L／M明显低于不结扎组（P〈0．05）。在肠道缺血再灌注损伤时．与普通肠内营养和正常饮食组比较,Gln肠内营养组和ω-3PUFA肠内营养组血清内毒素和细胞因子水平显著降低．小肠黏膜厚度和绒毛高度明显增高（P〈0．05）;且淋巴管结扎后效果更为明显（P〈0．05）。予以Gln或（ω-3PUFA肠内营养以及淋巴管结扎后,肺组织MPO、NO、NOS及细胞凋亡指数都有不同程度的下降（P〈0．05）。结论肠道缺血再灌注损伤引起的肺等远隔组织损伤及系统性炎性反应可能与肠淋巴液中的某些因子有关．阻断“肠-淋巴途径”和（或）补充Gln和ω-3PUFA的肠内营养可以降低缺血引起的肠道通透性增加．降低循环内毒素水平．增加肠黏膜的厚度．减轻系统炎性反应和肺组织损伤。     

U50 488H预处理及低温保存对离体兔心的保护作用

目的观察U50 488H预处理及低温保存对离体兔心的保护作用。方法将40只大白兔均分为5组，每组8只。通过Langendorff装置建立离体心脏灌注模型，对照组：不用药物进行预处理，用UW液保存心脏6h；组Ⅰ：用含U50 488H（1．6mmol／L）的St．ThomasⅡ心脏停搏液预处理，离体心脏低温保存4h；组Ⅱ：预处理同组Ⅰ，低温保存6h；组Ⅲ：预处理同组Ⅰ，低温保存8h；组Ⅳ：预处理同组Ⅰ，低温保存10h。离体心脏在再灌注30min后检测心功能、心肌肌浆网钙离子三磷酸腺苷酶（SRCa^2＋-ATPase）活性和心肌线粒体Ca^2＋浓度。结果随着离体心脏低温保存时间的延长，心功能各项指标的恢复率、冠状动脉流量（Cf）的恢复率和SRCa^2＋-ATPase的活性呈下降趋势，而线粒体Ca^2＋浓度随着心脏低温保存时间的延长而逐渐升高。组Ⅰ和组Ⅱ上述心功能指标恢复率分别高于组Ⅲ和组Ⅳ（P〈0．05，0．01），组Ⅲ恢复率高于组Ⅳ（P〈0．05）。组ⅡCf的恢复率（84．56％±10．38％）高于组Ⅲ（79．45％±9．67％）、组Ⅳ（68．31％±6．84％，P〈0．01），组Ⅲ高于组Ⅳ（P〈0．05）。组ⅡSRCa^2＋-ATPase的活性（4．43±0．41μmol／mg·h）分别高于对照组（3．04±0．22μmol／mg·h）、组Ⅲ（3．26±0．29μmol／mg·h）和组Ⅳ（2．57±0．63μmol／mg·h，P〈0．05），组Ⅲ高于组Ⅳ（P〈0．01）。组Ⅱ线粒体Ca^2＋浓度（38．76±4．30μmol／g·dw）和对照组（40．23±3．75μmol／g·dw）分别低于组Ⅲ（43．25±5．16μmol／g·dw）和组Ⅳ（45．78±3．26μmol／g·dw，P〈0．05，0．01）。结论U50 488H预处理及U50 488H保存液对离体供心的低温保存时间应控制在8h以内；UW液对离体心脏的保存作用与U50 488H预处理及低温保存6h效果相当。     

肝糖原贮备对热缺血再灌注大鼠肝细胞凋亡的影响

目的探讨肝糖原贮备对热缺血再灌注肝细胞凋亡及肝损伤的影响。方法建立大鼠肝热缺血模型。实验分组：术前24h静脉注射25％葡萄糖组，2ml／只，每6h1次，高糖饮食（H组）；术前禁食24h，饮水不限（L组）；正常饮食对照组（N组）和假手术组（S组）。缺血45min，再灌注2、24h取材。流式细胞术检测细胞凋亡及Bcl-2、Bax蛋白。同时进行肝酶学检测、肝组织形态学观察。结果1．细胞凋亡及蛋白表达：（1）24h细胞凋亡百分率。s组〈H组〈N组〈L组（P〈0．01），各组24h凋亡率均高于2h（P〈0．01，S组除外）。（2）Bcl-2、Bax蛋白表达量。①再灌注24hBcl-2表达量：H组明显高于其余3组（P〈0．01），L组〈N组（P〈0．05），与2h比较H组表达升高（P〈0．01）；②再灌注24hBax表达量：S组明显低于其余3组（P〈0．01），L组〉N组（P〈0．01）。2．肝酶学指标：各时相点4组间比较差异有统计学意义（P〈0．05），S组〈H组〈N组〈L组。3．肝脏病理组织学改变：再灌注24hH组明显轻于N组及L组，并接近S组，L组最严重。结论预防性增加肝糖原贮备可抑制热缺血再灌注过程中肝细胞凋亡，减轻肝损伤，并可能通过影响Bcl-2、Bax的表达发挥作用。     

参附注射液对大鼠胰腺移植受体小肠肠粘膜屏障的保护作用

目的探讨参附注射液（SF）对大鼠胰腺移植受体肠粘膜屏障的保护作用及机制。方法24只糖尿病大鼠随机分为缺血再灌注组（IR组。n=12），参附注射液预处理组（SF组．n=12），12只正常大鼠为对照组，IR组和SF组大鼠均接受胰腺移植，再灌注后5d检测小肠通透性和吸收功能，检测血清TNF-α、NO、SOD和淀粉酶活性，取受体空肠粘膜组织检测小肠粘膜粘膜湿重、微绒毛高度及宽度、MDA含量及MPO活性，同时取肠系膜静脉血、肠系膜淋巴结、肝及脾组织进行细菌培养，观察细菌易位情况。结果再灌注后SF组血清TNF—α含量（P〈0．01）、淀粉酶活性（P〈0．01）、MDA含量（P〈0．01）、MPO活性（P〈0．01）、小肠通透性（P〈0．01）、细菌易位率（P〈0．01）和小肠粘膜损伤程度均低于IR组；血清NO和SOD含量、小肠吸收功能均高于IR组（P〈0．01）。结论SF预处理可保护大鼠胰腺移植受体小肠肠粘膜屏障，降低细菌易位率，机制可能与降低胰酶活性、减少TNF—α生成、减轻PMNs粘附与聚集、增加NO和SOD含量有关。     

白三烯受体拮抗剂改善哮喘患儿肺功能的临床研究

目的探讨白三烯受体拮抗剂改善哮喘患儿肺功能的效果。方法应用脉冲振荡（IOS）肺功能仪分别测定20例哮喘患儿单纯糖皮质激素吸入（常规治疗组）治疗前后和30例哮喘患儿加用孟鲁司特（孟鲁司特组）治疗前后肺功能。另选取20例健康儿童作为对照组,并对其疗效进行比较。结果常规治疗组治疗前、孟鲁司特组治疗前脉冲频率为5、20Hz时的气道黏性阻力（R4、R30）、热振频率（Fres）高于对照组[（1．10±0.26）、（1．10±0．21）kPa/（L·g）比（0．54±0．15）kPa／（L·g）;（0．75±010）、（0．70±0.11）kPa／（L·g）比（0．53±0．10）kPa／（L·g）;（20．11±194）、（19．99±2．64）Hz比（16．90±1.77）Hz],脉冲频率为5Hz时的气道弹性阻力（X5）低于对照组[（-0．44±0．08）、（-0．42±0.13）kPa／（L·g）比（=0．19±0．10）kPa/（L·g）]．差异有统计学意义（P〈0．01）,而常规治疗组治疗前与孟鲁司特组治疗前各项指标比较差异无统计学意义（P〉0．05）。常规治疗组治疗前后R5、R20比较差异有统计学意义（P〈0．01）．X4、Fres比较差异无统计学意义（P〉0．05）。孟鲁司特组治疗前后比较差异有统计学意义（P〈0．01）。常规治疗组治疗后与孟鲁司特组治疗后备项指标比较差异有统计学意义（P〈0．01或〈0．05）。常规治疗组治疗后各项指标与对照组比较差异仍有统计学意义（P〈0．01）．孟鲁司特组治疗后R20、Fres与对照组比较差异无统计学意义（P〉0．05）.结论加用孟鲁司特治疗时改善哮喘儿重肺功能的效果较好．对提高患儿生活质量有一定的作用。     

大鼠创伤后胰岛素抵抗与葡萄糖转运关系的研究

目的探讨创伤后骨骼肌对葡萄糖转运能力的改变及其与创伤后胰岛素抵抗（m）之间的关系。方法通过对大鼠实施小肠部分切除手术建立创伤模型，观察大鼠血糖和血清胰岛素浓度的变化规律。运用高胰岛素-正常血糖钳夹技术评估外周组织葡萄糖廓清率。[^3H]标记葡萄糖示踪法检测创伤后骨骼肌葡萄糖转运能力的变化。最后分别测定大鼠骨骼肌组织中葡萄糖转运蛋白-4（GLUT-4）的mRNA和蛋白表达。结果大鼠小肠部分切除术后血糖浓度明显升高，血清胰岛素浓度则先短暂降低然后升高。创伤组大鼠外周组织对葡萄糖的廓清率下降了47％（P〈0．01）。创伤组大鼠骨骼肌对葡萄糖的转运能力明显低于对照组（P〈0．01）。两组大鼠骨骼肌中GLUT4mRNA和GLUT-4蛋白总量的表达差异无统计学意义（P〉0．05），但是创伤组大鼠骨骼肌细胞膜上的GLUT-4蛋白含量明显少于对照组（P〈0．05）。结论大鼠手术后早期即存在胰岛素抵抗现象，但胰岛素分泌量并未减少。创伤后早期骨骼肌细胞膜上GLUT-4分布减少以及对葡萄糖转运能力降低可能是导致创伤后胰岛素抵抗的机制之一。     

Cytokine modulation of Na(+)-dependent glutamine transport across the brush border membrane of monolayers of human intestinal Caco-2 cells.

Previous studies have demonstrated that Na(+)-dependent brush border glutamine transport is diminished in septic patients. To examine the potential regulation of this decreased transport by endotoxin, cytokines, or glucocorticoids, the human intestinal Caco-2 cell line was studied in vitro. Na(+)-dependent glutamine transport across the apical brush border membrane was assayed in confluent monolayers of differentiated cells that were 10 days old. Uptake of 50 microM glutamine was determined after a 12-hour incubation with varying doses (10 to 1000 U/mL) of tumor necrosis factor-alpha, interleukin-1, interleukin-6, interferon-gamma, and various combinations of these cytokines. Studies were also done in cells incubated with E. coli endotoxin (1 micrograms/mL) or dexamethasone (1 and 10 microM). Endotoxin, tumor necrosis factor, interleukin-1, and interleukin-6 alone and in combination did not significantly reduce Na(+)-dependent glutamine transport across the brush border of Caco-2 cells. Dexamethasone decreased glutamine transport by 20%, but this decrease was not apparent for 48 hours. Interferon consistently decreased glutamine transport by 30%; this was due to a reduction in carrier maximal transport velocity (3427 +/- 783 pmol/mg protein/minute in controls versus 2279 +/- 411 in interferon, p less than 0.05) rather than a change in Km (276 +/- 29 microM in controls versus 333 +/- 74 in interferon, p = not interferon + dexamethasone + tumor necrosis factor + interleukin-1 resulted in a 38% decrease in transport activity. Cytokines and glucocorticoids may work independently and synergistically in regulating Na(+)-dependent brush border glutamine transport in human intestinal cells. Whether these signal molecules play a central role in the cause of the diminished brush border glutamine transport that occurs in septic patients requires further study.     

Brush border transport of glutamine and other substrates during sepsis and endotoxemia

The effects of severe infection on luminal transport of amino acids and glucose by the small intestine were investigated. Studies were done in endotoxin-treated rats and in septic patients who underwent resection of otherwise normal small bowel. In rats the kinetics of the brush border glutamine transporter and the glutaminase enzyme were examined. In patients the effects of severe infection on the transport of glutamine, alanine, leucine, and glucose were studied. Transport was measured using small intestinal brush border membrane vesicles that were prepared by Mg++ aggregation/differential centrifugation. Uptake of radiolabeled substrate was measured using a rapid mixing/filtration technique. Vesicles demonstrated 15-fold enrichments of enzyme markers, classic overshoots, transport into an osmotically active space, and similar 2-hour equilibrium values. The sodium-dependent pathway accounted for nearly 90% of total carrier-mediated transport. Kinetic studies on rat jejunal glutaminase indicated a decrease in activity as early as 2 hours after endotoxin secondary to a decrease in enzyme affinity for glutamine (Km = 2.23 +/- 0.20 mmol/L [millimolar] in controls versus 4.55 +/- 0.67 in endotoxin, p less than 0.03), rather than a change in Vmax. By 12 hours the decrease in glutaminase activity was due to a decrease in Vmax (222 +/- 36 nmol/mg protein/min in controls versus 96 +/- 16 in endotoxin, p less than 0.03) rather than a significant change in Km. Transport data indicated a decrease in sodium-dependent jejunal glutamine uptake 12 hours after endotoxin secondary to a 35% reduction in maximal transport velocity (Vmax = 325 +/- 12 pmol/mg protein/10 sec in controls versus 214 +/- 8 in endotoxin, p less than 0.0001) with no change in Km (carrier affinity). Sodium-dependent glutamine transport was also decreased in septic patients, both in the jejunum (Vmax for control jejunum = 786 +/- 96 pmol/mg protein/10 sec versus 417 +/- 43 for septic jejunum, p less than 0.01) and in the ileum (Vmax of control ileum = 1126 +/- 66 pmol/mg protein/10 sec versus 415 +/- 24 in septic ileum, p less than 0.001) The rate of jejunal transport of alanine, leucine, and glucose was also decreased in septic patients by 30% to 50% (p less than 0.01). These data suggest that there is a generalized down-regulation of sodium-dependent carrier-mediated substrate transport across the brush border during severe infection, which probably occurs secondary to a decrease in transporter synthesis or an increase in the rate of carrier degradation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of fibroblast growth factor-23 on phosphate transport in proximal tubules

BACKGROUND: Fibroblast growth factor-23 (FGF-23) has been implicated in the renal phosphate wasting in tumor-induced osteomalacia, X-linked hypophosphatemia, and autosomal-dominant hypophosphatemic rickets. METHODS: In this in vitro microperfusion study we examined if FGF23R176Q, a stable mutant of FGF-23, impairs phosphate transport in rabbit proximal convoluted and proximal straight tubules perfused in vitro. We also examined if heparin, a molecule that is known to facilitate binding of FGFs to their receptor was necessary for the action of FGF23R176Q on transport. RESULTS: In the presence of heparin, FGF23R176Q reduced phosphate transport from 10.8 +/- 2.0 to 9.9 +/- 1.9 pmol/mm/min in proximal convoluted tubules and 1.0 +/- 0.2 to 0.8 +/- 0.2 pmol/mm/min in proximal straight tubules (both P < 0.05). There was no effect of FGF23R176Q in the absence of heparin. Incubation of finely minced mouse renal cortical tissue in tissue culture media for 3 hours resulted in a reduction in brush border membrane vesicles (BBMV) sodium-dependent phosphate transport (NaPi-2A) protein abundance in the presence but not in the absence of heparin. CONCLUSION: These data demonstrate that the inhibition of phosphate transport by FGF23R176Q in vitro requires heparin. The action of FGF23R176Q is associated with a reduction in BBMV NaPi-2A protein abundance.     

Dietary modulation of small intestinal glutamine transport in intestinal brush border membrane vesicles of rats

The effects of a glutamine-enriched diet on the transport of glutamine across brush border membrane vesicles (BBMV) from the rat jejunum were studied to gain further insight into the effects of diet on regulating gut glutamine utilization. Following fasting, rats were randomized to one of three nutritionally complete elemental diets supplemented with glutamine, glutamate, or glycine (control). Brush border membrane vesicles were prepared by a Mg2+ aggregation/differential centrifugation technique and uptake of radioactive [3H]glutamine by the BBMV was studied using a rapid mixing/filtration technique. BBMVs from all test diet groups were enriched in alkaline phosphatase 14-fold. [3H]Glutamine uptake courses for all groups demonstrated sodium dependency, overshoots, and similar 2-hr equilibrium values. Vesicles from animals fed the glutamine-enriched diet had a 75% increase in glutamine uptake compared to those of the control diet and a 250% increase compared to those of the glutamate-enriched diet (P less than 0.05). alpha-Methylamino isobutyric acid and glycine did not significantly inhibit total [3H]glutamine uptake, whereas asparagine and glutamine inhibited total [3H]glutamine uptake compared to the mannitol control. The brush border appears to possess the glutamine selective System N transporter, the activity of which can be stimulated by providing dietary glutamine.     

The early response of the jejunal brush border glutamine transporter to endotoxemia.

The early effects of endotoxin (4 hr after a single dose of Escherichia coli LPS, 7.5 mg/kg) on L-glutamine (GLN) transport across the jejunal brush border of rats were studied. Jejunal brush border membrane vesicles (BBMVs) were prepared by a Mg2+ aggregation/differential centrifugation technique. Vesicle purity and integrity were confirmed by a 15-fold enrichment of brush border marker enzymes, osmotic activity, transport overshoots in the presence of sodium, and similar 1- and 2-hr equilibrium values. L-[3H]GLN transport in jejunal BBMVs was measured by a millipore filtration technique. Na(+)-dependent glutamine transport, which accounted for greater than 80% of total transport, was increased twofold in BBMVs from endotoxin-treated rats (67 +/- 5 pmole/mg protein/15 sec vs 38 +/- 3, P less than 0.01). Endotoxin treatment did not alter the activity of the Na(+)-independent carrier. Simultaneously, intestinal extraction of glutamine from the bloodstream fell by 56% (15.1 +/- 2.3% in controls vs 6.6 +/- 1.3% in endotoxin-treated rats, P less than 0.01). This reduction in the uptake of circulating glutamine could not be accounted for by a fall in the arterial concentration. Thus, soon after endotoxemia brush border glutamine uptake is increased while consumption of glutamine across the basolateral membrane is decreased. This increased uptake may support protein synthesis and may provide a biochemical rationale for the use of early enteral nutrition after the onset of critical illness.     

Effect of chronic cisplatin administration on phosphate and glucose transport by the renal brush border membrane

Cisplatin (CIS-diamine dichloroplatinum) is a highly nephrotoxic antineoplastic agent which may cause acute renal failure and renal tubular dysfunction. In the present study we have examined the effect of chronic cisplatin administration on sodium-dependent 32P-phosphate and 3H glucose transport by the renal brush border membrane vesicles (BBMV). Our results indicate that both transport mechanisms were significantly reduced at the BBMV following cisplatin therapy due to an increased Km (0.13 +/- 0.09 vs. 0.34 +/- 0.09 mM; p = less than 0.01) without significant change in Vmax (56 +/- 18 vs. 44 +/- 17 pM/mg/s). The results of these studies indicate that cisplatin causes a diffuse renal injury in the proximal segment of the nephron altering both transport mechanisms. Possible mechanisms of cisplatin nephrotoxicity are discussed.     

Na+‐Dependent Transport of d‐Xylose by Bovine Intestinal Brush Border Membrane Vesicles (BBMV) is Inhibited by Various Pentoses and Hexoses

To detect whether pentoses and hexoses occurring in rumen bacteria or in hemicellulose ingested with feed and partly released in the small intestine have an affinity for the Na⁺‐dependent glucose transporter of the bovine intestinal brush border membrane (BBM), we investigated whether these monosaccharides inhibit Na⁺‐dependent transport of ¹⁴C‐labelled d ‐xylose across the BBM using brush border membrane vesicles (BBMV) isolated from the mid‐jejunum of cows. We used d ‐xylose as the transport substrate, because it has a low affinity for the Na⁺‐dependent glucose transporter and thus its uptake into BBMV is more efficiently competitively inhibited by other sugars than that of d ‐glucose. d‐ Ribose, d ‐mannose and l ‐rhamnose occurring in rumen bacteria significantly inhibited Na⁺‐dependent uptake of d ‐xylose into BBMV, but their inhibitory effect was less than that of d ‐glucose, d ‐xylose and phlorizin. This also applied to l ‐arabinose (and d ‐arabinose), which is, like d ‐xylose and d ‐galactose, a constituent of hemicellulose, and to 2‐deoxy‐d ‐glucose. Of all monosaccharides tested, only d ‐fructose did not affect Na⁺‐dependent d ‐xylose transport. It is concluded that some pentoses and hexoses occurring in rumen bacteria (d ‐ribose, d ‐mannose and l ‐rhamnose) or hemicellulose (l ‐arabinose and d ‐xylose) have a low affinity for the Na⁺‐dependent glucose transporter of the bovine BBM and may therefore be absorbed from the jejunum when released in the small intestine.     

Selective stimulation of brush border glutamine transport in the tumor-bearing rat

Intestinal extraction of circulating glutamine across the basolateral membrane is diminished in the tumor-bearing rat (TBR). This study was designed to investigate the effects of progressive malignant growth on brush border glutamine transport in order to gain further insight into the adaptive/regulatory changes in intestinal glutamine metabolism that occur in the tumor-bearing rat. Fischer 344 rats (225 +/- 5 g) were implanted with fibrosarcoma cells and were studied at various time points after implantation when the tumors comprised 7%, 20%, and 29% of total body weight. Control and tumor-bearing rats were pair-fed throughout the study. Jejunal brush border membrane vesicles (BBMVs) were prepared by magnesium aggregation/differential centrifugation and transport of radioactively labeled L-glutamine, L-leucine, L-alanine, and D-glucose by BBMVs was measured using a Millipore filtration technique. BBMVs were enriched 15-fold in alkaline phosphatase, indicating brush border vesicle purity. Uptake of all substrates occurred into an osmotically active space, exhibited overshoots, and had similar 1-hr equilibrium values. The rate of glutamine uptake by BBMVs from all tumor-bearing rats was significantly greater than controls, regardless of tumor size. The increase in transport activity was not due to a change in carrier affinity but rather to an increase in maximal transport velocity. In rats with small tumors (7% of body weight), the Vmax was 431 +/- 40 pmole/mg protein/10 sec compared to 259 +/- 30 in control animals (P less than 0.01). In marked contrast, the mean transport of alanine was diminished in BBMVs from TBR (31 +/- 3 pmole/mg protein/10 sec in TBR vs 23 +/- 2 in controls, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Vitamin D status and brush border membrane vesicles: 1,25-dihydroxyvitamin D3 induced destabilization

Purified chick duodenal brush border membrane vesicles (BBMV) were used to assess the effect of vitamin D on intestinal Ca2+ transport and membrane stability. BBMV preparations are right-side-out as judged by a nine-fold increase in accessibility of lactoperoxidase to core material actin in the presence of Triton X-100. Freshly prepared BBMV from vitamin D-deficient chicks support both sodium-dependent glucose transport and Ca2+ uptake. In vivo treatment with 1,25(OH)2D3 results in an 85% increase in the Vmax of Ca2+-uptake from 2.2 to 3.9 nmol/min/mg protein. The Km of Ca2+-uptake (0.9 mM) is independent of the vitamin D status of the chick. The majority of BBMV derived from vitamin D-replete chicks were destabilized and rendered incapable of supporting either sodium-dependent glucose uptake or Ca2+ uptake if they were held at 0-4 degrees C for 2 to 24 h. In 40 separate experiments, 80% of membranes derived from vitamin D-replete chicks showed characteristics of destabilization, whereas only 24% of all control membranes exhibited a lack of viability.     

Effect of total parenteral nutrition on amino acid and glucose transport by the human small intestine.

OBJECTIVE: The effect of total parenteral nutrition (TPN) on small intestinal amino acid transport activity was studied in humans. SUMMARY BACKGROUND DATA: Studies in humans receiving TPN indicate that a decrease in the activities of the dissacharidase enzymes occurs, but morphologic changes are minimal with only a slight decrease in villous height. METHODS: Surgical patients were randomized to receive TPN (n = 6) or a regular oral diet (controls, n = 7) for 1 week before abdominal surgery. Ileum (5 controls, 5 TPN) or jejunum (2 controls, 1 TPN) were obtained intraoperatively and brush-border membrane vesicles (BBMV) were prepared by magnesium aggregation/differential centrifugation. Transport of L-MeAlB (a selective system A substrate), L-glutamine, L-alanine, L-arginine, L-leucine, and D-glucose was assayed by a rapid mixing/filtration technique in the presence and absence of sodium. RESULTS: Vesicles demonstrated approximately 18-fold enrichments of enzyme markers, classic overshoots, transport into an osmotically active space, and similar 1-hour equilibrium values. TPN resulted in a 26-44% decrease in the carrier-mediated transport velocity of all substrates except glutamine across ileal BBMVs. In the one patient receiving TPN from whom jejunum was obtained, there was also a generalized decrease in nutrient transport, although glutamine was least affected. Kinetic studies of the system A transporter demonstrated that the decrease in uptake was secondary to a reduction in carrier Vmax, consistent with a decrease in the number of functional carriers in the brush-border membrane. CONCLUSIONS: TPN results in a decrease in brush-border amino acid and glucose transport activity. The observation that glutamine transport is not downregulated by 1 week of bowel rest may further emphasize the important metabolic role that glutamine plays as a gut fuel and in the body''s response to catabolic stresses.