五味子乙素对氧化损伤的晶状体上皮细胞凋亡的影响

目的:探讨五味子乙素(Sch B)对实验性氧化损伤大鼠晶状体上皮细胞(LEC)凋亡的影响。方法:采用无菌操作摘取SD大鼠双眼,并在手术显微镜下分离晶状体,随机分为空白对照组、过氧化氢组(H₂O₂)、吡诺克辛(PS)组和Sch B组。使晶状体孵育在300μmol·L^-1H₂O₂培养液中复制LEC凋亡模型,同时加入终浓度为0.5mmol·L^-1的SchB,置二氧化碳培养箱共同孵育24h。取晶状体前囊膜,采用TUNEL法检测LEC凋亡及凋亡率,透射电子显微镜观察LEC超微结构改变和凋亡小体形成。结果:H₂O₂组LEC凋亡率(92.0±2.6)显著高于空白对照组(3.5±1.8)(P<0.01);SchB组LEC凋亡率(13.8±3.0)显著低于H₂O₂组,且与PS组(56.0±9.9)有显著的差异(P<0.05)。超微结构研究显示,H₂O₂组绝大多数LEC发生凋亡,并呈凋亡各期严重改变的全过程;Sch B组仅少数LEC发生凋亡,并多为早期或中期的轻微改变。结论:Sch B可明显抑制实验性氧化损伤大鼠LEC凋亡,且明显优于PS滴眼液。     

远志皂苷元对H2O2诱导的大鼠海马神经元损伤的影响及其机制

目的: 观察远志皂苷元(senegenin, Sen)对过氧化氢(H₂O₂)诱导的SD大鼠海马神经元损伤的影响并探讨其作用机制。方法: SD大鼠海马神经元培养至第6 d,随机分为正常组、H₂O₂组、Sen+ H₂O₂ 组和Sen组,药物干预后检测细胞存活率、丙二醛(MDA)含量和超氧化物歧化酶(SOD)活性,并用 Hoechst 33258染色观察细胞核形态变化,荧光定量PCR(real-time PCR)检测神经元凋亡相关基因 bcl-2和bax 的表达,进一步采用Western blotting观察Bcl-2和Bax蛋白表达,酶荧光活性检测试剂盒测定caspase-3的活性改变。结果: 与正常组相比,H₂O₂组细胞存活率降低。与H₂O₂组相比,20 μmol/L Sen+ H₂O₂ 组细胞存活率升高,SOD活性升高,MDA含量下降,并且远志皂苷元能够上调bcl-2 mRNA表达、下调bax mRNA表达,降低caspase-3活性,Western blotting结果进一步表明Bcl-2蛋白表达升高,Bax蛋白表达下降,各指标均有显著差异(P<0.05)。结论: 远志皂苷元对H₂O₂处理的海马神经元有一定保护作用,其机制可能与远志皂苷元增强海马神经元抗氧化能力、调节细胞凋亡相关蛋白从而抑制凋亡有关。     

金属硫蛋白对羟自由基损伤的大鼠肝细胞核核苷三磷酸酶的保护作用

目的:研究金属硫蛋白(MTs)是否对羟自由基(hydroxylradical,·OH^-)损伤的大鼠肝细胞核核苷三磷酸酶(NTPase)具有保护作用。方法:以羟自由基发生系统Fe³⁺/H₂O₂单独或与MTs共同孵育大鼠离体肝细胞核,检测分别用ATP和GTP作底物时大鼠肝细胞核NTPase活性。结果:不同浓度Fe³⁺/H₂O₂(μmol·L^-1/μmol·L^-1:0.1/0.5、0.5/2.5、1/5、5/25)孵育肝细胞核,浓度依赖地增强核NTPase活性,与对照组差异显著(P＜0.01)。用不同浓度的MT(10^-9-10^-4mol·L^-1)与Fe²⁺/H₂O₂(1μmol·L^-1/5μmol·L^-1)共孵育,浓度依赖地拮抗Fe³⁺/H₂O₂诱导的效应(P＜0.01)。用MT单独孵育肝细胞核对NTPase的活性没有影响(P＞0.05)。结论:Fe³⁺/H₂O₂系统产生的·OH对核NTPase活性具有强烈的抑制效应,MT浓度依赖地拮抗·OH导致的NTPase活性降低。     

复方SZ滴眼液对晶状体上皮细胞凋亡的抑制作用及其信号转导机制

目的： 探讨复方SZ滴眼液（Co-SZ）抑制H₂O₂诱导的晶状体上皮细胞（LEC）凋亡的作用及信号转导机制。为将Co-SZ作为防治白内障的有效药物提供实验依据。 方法： (1)将H₂O₂与Co-SZ和SD大鼠晶状体共同孵育后：TUNEL法检测LEC凋亡率。透射电镜观察LEC超微结构改变及凋亡形成。(2)H₂O₂与Co-SZ和体外培养的牛LEC共同孵育后,四甲基偶氮唑蓝法（MTT）检测不同浓度的Co-SZ抑制LEC凋亡率。流式细胞仪（FCM）检测LEC细胞核内DNA含量。荧光分光光度法检测LEC内游离Ca2+浓度。放射免疫分析法检测LEC内环化腺苷酸（cAMP）和环化鸟苷酸（cGMP）浓度。 结果： TUNEL法检测Co-SZ组LEC凋亡率显著低于H₂O₂组。Co-SZ组LEC超微结构变化也显著轻于H₂O₂组。MTT检测Co-SZ组细胞活性明显高于H₂O₂并具有剂量依赖关系。Co-SZ组LEC核内DNA含量增加。Co-SZ使LEC内游离Ca2+、cAMP降低、cGMP升高。结论：Co-SZ能有效抑制H₂O₂诱导的LEC发生的凋亡 。Co-SZ抑制LEC凋亡的机制可能是通过抑制LEC核内DNA降解，并通过抑制细胞内游离钙离子浓度升高、阻断Ca2+-钙调蛋白依赖性蛋白激酶途径和Ca2+-蛋白激酶C信号转导途径。     

热休克蛋白参与PI3K/Akt 介导H2O2 预处理的抗凋亡作用

目的: 探讨热休克蛋白(HSP)是否参与PI3K/Akt信号通路介导的H₂O₂预处理的抗细胞凋亡作用。方法: 利用PC12细胞建立H₂O₂预处理对抗高浓度H₂O₂诱导细胞凋亡的实验模型,分组如下:(1)空白对照组;(2) 损伤组;(3)预处理＋损伤组; (4)LY294002＋预处理＋损伤组;(5) LY294002组;(6) quercetin＋预处理＋损伤组;(7) 17-AAG＋预处理＋损伤组;(8) 溶剂对照组。应用Hoechst 33258染色观察细胞凋亡形态,碘化丙啶(PI)染色流式细胞术检测细胞凋亡率,比色法测定caspase-3的活性,免疫印迹法(Western blotting)测定HSP的表达水平。结果: 100 μmol/L H₂O₂预处理PC12细胞90 min可显著地抑制300 μmol/L H₂O₂引起的细胞凋亡,使caspase-3的活性降低,同时上调HSP70和HSP90的表达。HSP70和HSP90的抑制剂quercetin和17-AAG拮抗H₂O₂预处理的抗细胞凋亡作用。 PI3K抑制剂LY294002不仅拮抗了H₂O₂预处理抗细胞凋亡的作用,并且抑制H₂O₂预处理对HSP70和HSP90的表达上调。结论: PI3K/Akt通路、HSP70和HSP90均参与H₂O₂预处理诱导的细胞保护作用。并且HSP70和HSP90参与PI3K/Akt信号通路介导H₂O₂预处理的抗细胞凋亡作用。     

Bcl-2、Bax在NHE-1抑制导致的大鼠肺动脉平滑肌细胞凋亡中的作用

目的:探讨Bcl-2、Bax蛋白表达在Na⁺/H⁺交换器-1(NHE-1)抑制而诱导大鼠肺动脉平滑肌细胞(PASMC)凋亡中的作用。方法: 荧光指示剂(Fura-2/AM)测定法检测转染NHE-1特异性核酶基因的大鼠PASMC内Ca²⁺(i)变化;RT-PCR方法检测细胞内bcl-2和baxmRNA表达变化, 免疫组化法检测细胞内Bcl-2和Bax蛋白表达变化。 结果:转染NHE-1特异性核酶基因后, 大鼠PASMC内i显著升高, bcl-2mRNA及蛋白表达显著降低, baxmRNA和蛋白表达显著增加。结论: NHE-1抑制诱导的PASMC凋亡与i增加、bcl-2表达降低及bax表达增加有关。     

过氧化氢对乳鼠心肌细胞内游离钙浓度的影响及牛磺酸的拮抗作用

目的:研究过氧化氢(H₂O₂)对心肌细胞i的影响,以及牛磺酸对H₂O₂诱导钙超载的拮抗作用。方法:采用SD大鼠乳鼠进行心肌细胞培养,实验分4组:①正常对照组;②H₂O₂组:加入终浓度为100μmol/L的H₂O₂;③H₂O₂＋牛磺酸(同时)组:牛磺酸30mmol/L与H₂O₂100μmol/L同时加入;④H₂O₂＋牛磺酸(先后)组:先加入终浓度为100μmol/L的H₂O₂,2min后再加20mmol/L的牛磺酸。以Fluo-3/AM荧光指示剂负载,应用激光共聚焦显微镜技术,分别于加入H₂O₂后即刻与15min,检测i变化。结果:对照组心肌细胞内荧光强度和荧光光密度值较低。H₂O₂加入后即刻,细胞内荧光光密度值开始增加,15min后细胞内荧光强度和荧光光密度值显著高于对照组(P＜0.05)。而H₂O₂＋牛磺酸(同时)组细胞内荧光光密度值显著低于H₂O₂组(P＜0.05vsH₂O₂组);H₂O₂＋牛磺酸(先后)组细胞内荧光光密度值显著低于H₂O₂组(P＜0.05vsH₂O₂组)。结论:H₂O₂可引起心肌细胞内钙超载;牛磺酸能显著减轻H₂O2诱导的心肌细胞内Ca²⁺超载。     

4种归肝经明目中药对晶状体上皮细胞凋亡相关基因Bcl-2和Bax的调控

目的 :探讨 4种归肝经明目中药车前子、青葙子、菊花和熟地对实验性氧化损伤大鼠晶状体上皮细胞 (lensepithelialcell,LEC)凋亡相关基因Bcl- 2和Bax的调控。方法 :将SD大鼠双眼随机分成 7组 :空白对照组、过氧化氢 (H2 O2 )组、吡诺克辛(PS)组和 4种归肝经明目中药车前子、青葙子、菊花和熟地组。无菌操作摘除眼球并在手术显微镜下分离晶状体 ,使晶状体孵育在 30 0 μmol·L-1H2 O2 培养液中复制LEC凋亡模型 ,同时采用 4种归肝经明目中药干预 ,置二氧化碳培养箱共同孵育 2 4h。取晶状体前囊膜采用免疫组化法检测凋亡相关基因Bcl- 2…     

过氧化氢对血管平滑肌细胞增殖和明胶酶A及其抑制因子基因表达的影响

目的:探讨过氧化氢(H₂O₂)对体外培养大鼠血管平滑肌细胞(VSMC)增殖和明胶酶A(MMP-2)、及其抑制因子(TIMP-2)基因表达的影响。方法:先用四甲基偶氮唑(MTT)法筛选出H₂O₂对VSMC的毒性作用浓度和增殖作用浓度,在此基础上用逆转录聚合酶链反应(RT-PCR)法测定H₂O₂对MMP-2、TIMP-2mRNA表达的影响。结果:H₂O₂浓度大于300μmol/L后显示出对VSMC的致死毒性作用;H₂O₂浓度在0.01-5.0μmol/L内可以刺激VSMC的增殖,且呈时间依赖性;1μmol/LH₂O₂、10μmol/LH₂O₂对MMP-2基因转录有明显的促进作用;不同浓度的H₂O₂对TIMP-2基因转录无明显促进作用。结论:适当浓度的H₂O₂可以促进VSMC的增殖和MMP-2mRNA表达,但对TIMP-2mRNA表达无明显作用,提示H₂O₂参与了血管重塑的不同病理环节。     

钙网蛋白参与缺氧预处理对氧化应激损伤大鼠成心肌H9c2细胞的保护作用

目的： 观察缺氧预处理(HPC)对氧化应激诱导大鼠成心肌H9c2细胞损伤的保护作用，探讨钙网蛋白(CRT)是否参与其保护效应及p38 MAPK是否参与其信号转导过程。方法: H9c2细胞随机分为8组：氧化应激(H₂O₂)组、短暂缺氧(HPC)组、HPC+H₂O₂组、SB203580+HPC + H₂O₂组、反义干扰(AS)组、AS+H₂O₂组、AS+HPC+H₂O₂组和对照组。以细胞存活率、乳酸脱氢酶 (LDH)活性及流式细胞术检测细胞损伤情况；采用RT-PCR和Western blotting分别检测CRT表达和p38 MAPK磷酸化水平。结果: (1)HPC可减轻氧化应激损伤，与H₂O₂组比较，HPC+ H₂O₂组细胞凋亡率和LDH漏出分别降低13.4%和44.0%，存活率增高12.7%(均P<0.05)；HPC前以特异性p38 MAPK抑制剂 SB203580预孵育消除HPC的保护作用，与HPC+H₂O₂组相比，细胞凋亡率和LDH漏出分别增高5.4%和45.0%，存活率降低5.0%(均P<0.05)；(2)氧化应激明显上调CRT表达(较对照组高3.6倍)(P<0.05)；单纯短暂缺氧可诱导CRT表达(较对照组高1.4倍,P<0.05)，但上调程度较H₂O₂组低48%(P<0.05)；HPC可降低CRT过表达程度(降低26%) (P<0.05)；(3)反义寡核苷酸干扰CRT表达后HPC对氧化应激的保护作用降低，相关分析显示HPC诱导的CRT适度表达与细胞存活率正相关(r=0.8573,P<0.05)；(4) HPC前应用p38 MAPK抑制剂，抑制CRT表达上调(分别较HPC+H₂O₂组和HPC组低38%和23%) (均P<0.05)。结论: HPC可通过p38 MAPK信号途径诱导CRT表达上调，减轻大鼠成心肌H9c2细胞氧化应激损伤。     

阿魏酸钠对SNP诱导的凋亡海马神经元bcl-2、bax基因表达的影响

目的：探讨阿魏酸钠(SF)对一氧化氮（NO）供体硝普钠(SNP)引起的大鼠海马神经元凋亡及bcl-2、bax基因表达的影响。方法:采用SD大鼠海马神经元原代培养，经终浓度分别为10、20、40、80、120、160 μmol/L SF预处理后，用50 μmol/L SNP处理24 h，采用MTT法检测细胞存活率，Hoechst 33258荧光染色及DNA琼脂糖凝胶电泳分析等方法检测凋亡，Western blotting及RT-PCR检测bcl-2、bax基因表达。结果:不同剂量SF (10-160 μmol/L)预处理6 h可显著提高神经元的存活率，减少SNP引起的核固缩、凝聚和碎裂现象；DNA凝胶电泳图谱未见典型的“梯状”改变；增加bcl-2 mRNA及蛋白的表达, 降低bax mRNA及蛋白的表达。结论:SF 抑制NO供体SNP诱导的海马神经元凋亡，其机制可能与其增加Bcl-2蛋白表达，降低Bax蛋白表达，增高Bcl-2/Bax的比值有关。     

碱性成纤维细胞生长因子对β-淀粉样蛋白诱导PC12细胞凋亡的抑制作用

目的:利用体外培养的PC12表现出神经细胞的特性,用Aβ_25-35诱导PC12细胞凋亡,建立神经细胞毒性作用的模型,来探索bFGF对Aβ_25-35作用和治疗老年性痴呆(AD)的机制。方法:通过Giema's、PI染色法、DNA琼脂糖凝胶电泳、Westernblot及流式细胞仪研究了加入Aβ_25-35培养的以及Aβ_25-35和bFGF共培养的PC12细胞的形态和分子生物学改变及凋亡相关基因Bcl-2,Bax表达的变化。结果:Aβ_25-35可诱导PC12细胞核DNA发生降解,出现染色质浓缩成块状、胞浆浓缩、胞膜内陷、凋亡小体形成等;而Aβ_25-35和bFGF共培养的PC12细胞则能缓解这种形态学上的变化,细胞凋亡率减少,Bcl-2的表达量上调而Bax的表达量下调。结论:bFGF能抑制Aβ_25-35对神经细胞的毒性作用,其机制可能是通过调控Bcl-2、Bax的表达来实现的。     

Diazoxide Pretreatment Enhances L6 Skeletal Myoblast Survival and Inhibits Apoptosis Induced by Hydrogen Peroxide

Skeletal myoblast (SKM) transplantation is a promising approach to regenerate tissue and improve the function of the injured heart. However, the number of survival cells transplanted to host myocardium is quite poor due to high rate of apoptosis; diazoxide (DZ) is a highly selective mito‐KATP channel opener that may reduce cell apoptosis by relieving reactive oxygen species (ROS) damage. The aim of this study is to explore the protective effects of DZ on L6 SKM damage induced by hydrogen peroxide (H₂O₂) in vitro. Different dose and time of H₂O₂ and DZ treatment were performed and only 24 hr of 1.00 mmol/L H₂O₂ treatment and 200 μmol/L DZ pretreatment for 30 min were used for further experiment. L6 SKMs were cultured and divided into control group (no treatment), H₂O₂ group (24 hr of 1.00 mmol/L H₂O₂ treatment) and DZ + H₂O₂ group (pretreated with 200 μmol/L DZ for 30 min before 24 hr of 1.00 mmol/L H₂O₂ treatment). Compared with control group, H₂O₂ treatment caused cell damage, increased lactate dehydrogenase release, cell apoptosis, and bax gene expression, while reduced cell proliferation and decreased bcl‐2 expression. DZ pretreatment may protect cells from damage induced by H₂O₂ and reduce cell apoptosis by increasing bcl‐2 and decreasing bax expression. DZ pretreatment may also promote cell proliferation measured by both PCNA expression and flow cytometry method. These results suggest that DZ may protect L6 SKMs from damage induced by H₂O₂ by maintaining integrity of cell membrane, reducing apoptosis and increasing proliferation in vitro. Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.     

天然抗氧化剂对抗晶状体氧化损伤作用的实验研究

目的:探讨五味子乙素(SchB)、水飞蓟宾(SIB)、没食子酸丙酯(PG)、阿魏酸钠(SF)和沙棘总黄酮(TFH)5种天然抗氧化剂对抗实验性晶状体氧化损伤的作用。方法:将兔眼透明晶状体温育在Fenton氧化反应模型中造成晶状体氧化损伤,同时分别加入上述5种天然抗氧化剂共同温育24h后,测定晶状体总蛋白和可溶性蛋白、SOD、GSH-Px、GSH、VitC、总抗氧化能力和MDA的水平,观察5种抗氧化剂对上述指标的影响。结果:5种抗氧化剂均不同程度地升高氧化损伤晶状体的抗氧化指标,降低脂质过氧化终末产物MDA含量,且优于白内停滴眼液。其中SF和SchB的作用更为显著。结论:5种天然抗氧化剂对实验性晶状体氧化损伤有良好的对抗作用,从天然抗氧化剂中寻找高效的抗白内障药物具有广阔的前景。     

Differential effects of reactive oxygen species on native synovial fluid and purified human umbilical cord hyaluronate

The ability of reactive oxygen species produced by triggered neutrophilic leukocytes, hypoxanthine/xanthine oxidase (HX/XAO), hydrogen peroxide, and hypochlorous acid/mycloperoxidase (HOC1/MPO) systems to degrade hyaluronate (HA) in human synovial fluid (SF) and purified umbilical cord HA was compared by measuring the molecular weight distribution of HA using high-performance liquid chromatography with a size-exclusion column. The exposure of noninflammatory SF to phorbol myristic acetate (PMA) -activated neutrophils or to hydrogen peroxide (H₂O₂) caused depolymerization of SF HA to the degree corresponding to that found in rheumatoid SFs. When HX/XAO was used as radical generator, the molecular weight of SF HA decreased from 3.42×10⁶ to 1.40 × 10⁴ daltons with concomitant decrease of SF viscosity to 36% from the original value. The HOC1/MPO system caused no depolymerisation of SF HA, even at very high unphysiological HOC1 concentrations that induced the precipitation of SF HA together with SF proteins. This effect was found to be comparable to conventional mucin clot formation in SF. However, purified human umbilical cord HA was easily depolymerized with HOC1/ MPO or with H₂O₂, but these effects were sensitive to the hydroxyl radical scavenger mannitol and iron chelator desferrioxamine, indicating that the formation of reactive hydroxyl radical (OH) is likely to participate in these reactions. Thus we conclude that in inflammatory SF HA is mainly depolymerized by OH produced by decomposition of H₂O₂ catalyzed by iron, free or locally bound to HA itself. In contrast to what has been reported earlier, HOC1/MPO only depolymerizes purified umbilical cord HA (in a hydroxyl radical-dependent manner) but does not depolymerize HA in SF. As a matter of fact, HOC1/MPO has a scavenging action on SF HA by consuming H₂O₂ and thus preventing the formation of reactive hydroxyl radicals.     

阿魏酸钠对结肠炎大鼠结肠巨噬细胞功能的影响

目的:探讨阿魏酸钠在整体水平下对结肠炎大鼠结肠巨噬细胞功能的影响及其机制。方法:建立大鼠免疫性结肠炎模型。阿魏酸钠(SF)灌肠用药21d后检测结肠组织MDA、NO、PGE₂含量,SOD、IL-1、TNF-α、MPO活性及NF-κBp65表达水平。结果:阿魏酸钠(200、400、800mg/kg)灌肠用药剂量依赖性降低模型组大鼠显著升高的MDA、NO、PGE₂含量,IL-1、TNF-α、MPO活性及NF-κBp65表达水平,同时升高显著降低的SOD活性。结论:SF整体水平下减弱结肠炎大鼠结肠活化巨噬细胞的生物活性,缓解结肠炎症反应,机制可能与抑制NF-κB表达有关。     

Effect of corticosteroids on the production of superoxide and hydrogen peroxide and the appearance of chemiluminescence by phagocytosing polymorphonuclear leukocytes

Human polymorphonuclear leukocytes were incubated with either methylprednisolone sodium succinate, hydrocortisone sodium succinate, or distilled water, and then latex spherules were added as target particles for phagocytosis. At low concentrations of these corticosteroids (0.04–0.22 mM), no effect was observed on O₂ ^–· production, H₂O₂ production, or chemiluminescence. At high concentrations of these steroids (2.7 mM), a significant inhibition was observed in both O₂ ^–· production and H₂O₂ production. At 2.7 mM, methylprednisolone sodium succinate significantly decreased chemiluminescence, whereas hydrocortisone sodium succinate was without effect on chemiluminescence.     

Protection against hydrogen peroxide-induced injury by Z-ligustilide in PC12 cells

Z-ligustilide (Z-LIG) is the primary lipophilic compound of the Chinese medicine Danggui (Radix Angelica sinensis). Previous studies demonstrated that Z-LIG had significant neuroprotective potential in both transient and permanent cerebral ischemia, possibly through antioxidant and anti-apoptotic mechanisms. The present study examined the mechanisms of Z-LIG on hydrogen peroxide (H₂O₂)-induced injury in PC12 cells. Following exposure of the cells to H₂O₂ (500 μM), a significant reduction in cell survival and total antioxidant capacity (TAC), as well as increased intracellular reactive oxygen species (ROS), were observed. In addition, H₂O₂ treatment significantly upregulated Bax expression, cleaved-caspase 3, and cytosolic cytochrome-c, and decreased Bcl-2 protein levels. Pretreatment of the cells with Z-LIG (0.1, 1.0, 2.5, or 5.0 μg/ml) significantly attenuated H₂O₂-induced cell death, attenuated increased intracellular ROS levels, and decreased Bax expression, cleaved-caspase 3, and cytochrome-c. Further, Z-LIG improved cellular TAC and concentration-dependently upregulated Bcl-2 expression. These results demonstrate that Z-LIG has a pronounced protective effect against H₂O₂-induced cytotoxicity, at least partly through improving cellular antioxidant defense and inhibiting the mitochondrial apoptotic pathway. These findings suggest that Z-LIG may be useful in the treatment of neurodegenerative disorders in which oxidative stress and apoptosis are mainly implicated.     

Effect of Cold Exposure on Free Water Reabsorption in Hydropenic Man

With clearance technique, changes in tubular reabsorption of solute free water(T_H2_O^c), were studied in a group of 9 healthy hydropenic volunteers during a cold stress of 1 h at + 15°C. Increases were found in(T^c_H20)and in fractional excretion of sodium and osmoles during cold. Since(T^C_H2_O)was used as an index of sodium reabsorption in the ascending limb of Henle's loop, the findings indicated that under the conditions used in this study, the concentrating ability of the kidney was not negatively influenced by cold, despite a significant increase in arterial pressure. It is suggested that the reabsorption by the ascending limb of the loop was increased secondary to a reduced proximal tubular reabsorption of sodium.