低盐诱导的致密斑细胞环氧化酶2表达与p38丝裂素激活蛋白激酶信号通路

目的 探讨低盐(LS)培养对小鼠致密斑细胞 (MMDD1)环氧化酶2 (COX-2)表达、前列腺素E2(PGE2)释放的诱导作用及p38丝裂素激活蛋白激酶(MAPK)信号通路的调控作用。方法 采用RT-PCR和免疫印迹方法检测正常盐(NS)与LS培养对MMDD1细胞COX-2表达的影响。用ELISA法检测上清液PGE2的含量。用免疫印迹检测细胞内p-p38 MAPK表达的变化。 结果 与NS培养相比,LS培养均能诱导MMDD1细胞COX-2 mRNA和蛋白表达增加(16 h时高峰 mRNA 0.94±0.12比0.26±0.09,28 h时高峰蛋白0.59±0.02比0.25±0.07,P均< 0.01);PGE2分泌各时间点均显著升高,于24 h达高峰 [(644.33±26.54)ng/L比(224.0±18.33)ng/L, P < 0.01。LS培养后,MMDD1细胞内p38MAPK的磷酸化程度显著上调,180 min时较高(从0.17±0.01升至0.28±0.01,P < 0.01)。20 μmol/L p38抑制剂SB-203580下调 LS诱导的COX-2蛋白表达(从0.58±0.01降至0.19±0.02, P < 0.01)。 结论 低盐培养促进MMDD1细胞COX-2的表达和PGE2的分泌。p38 MAPK激活介导了低盐诱导的MMDD1细胞COX-2表达。     

阿利吉仑对2型糖尿病db/db小鼠肾脏损伤的保护作用

目的 观察肾素抑制剂阿利吉仑对2型糖尿病db/db小鼠肾脏损伤的保护作用。 方法 8周龄db/db和db/m小鼠行单侧肾切除,16周进入实验,分为4组：db/m小鼠对照组（db/m组）、db/db糖尿病小鼠对照组（db/db组）、db/db糖尿病小鼠阿利吉仑3 mg&#8226;kg-1&#8226;d-1治疗组（db/db+A3组）和db/db糖尿病小鼠阿利吉仑25 mg&#8226;kg-1&#8226;d-1治疗组(db/db+A25组)。阿利吉仑溶于磷酸盐缓冲液（PBS,350 mg/L）皮下泵入（0.25 μl/h）给药,疗程４周。治疗前后检测体质量、血糖、糖化血红蛋白、尿蛋白量、血压水平;PAS染色观察肾脏组织学变化;ELISA法检测肾皮质转化生长因子β1（TGF-β1）和纤溶酶原激活抑制因子1（PAI-1）含量;间接免疫荧光检测肾小球Ⅳ型胶原（ColⅣ）和纤连蛋白（FN）表达;实时定量PCR检测TGF-β1、PAI-1、ColⅣ、FN和肾素mRNA表达;放射免疫法检测肾皮质肾素活性和血管紧张素Ⅱ（AngⅡ）水平。 结果 与db/m组小鼠比较,db/db组小鼠有大量蛋白尿,肾小球细胞外基质沉积增加,TGF-β1、PAI-1、ColⅣ和FN蛋白及mRNA表达增加,同时肾皮质肾素mRNA、肾素活性和AngⅡ水平增高（均P < 0.05）。阿利吉仑25 mg&#8226;kg-1&#8226;d-1治疗在没有影响血压情况下,显著减少db/db小鼠24 h尿蛋白量,减少肾小球细胞外基质沉积,减少TGF-β1、PAI-1、ColⅣ、FN蛋白和mRNA表达,同时降低肾皮质肾素活性和AngⅡ水平（均P < 0.05）。 结论 阿利吉仑对2型糖尿病db/db小鼠肾脏损伤有保护作用。     

β1/β2肾上腺素能受体基因缺失对肾脏球旁器颗粒细胞肾素分泌的影响

目的观察β肾上腺素能受体对肾脏球旁器颗粒（JG）细胞肾素分泌的调节作用。方法密度梯度离心原代分离野生型和131／132肾上腺素受体基因敲除小鼠肾小球球旁器（JGA）颗粒细胞（JGC）。实时PCR明确JG细胞上存在β1/β2肾上腺素能受体基因表达。激光共聚焦显微镜下动态观察喹林和LysoTracker-Red染色条件下异丙肾上腺素促使JG活细胞分泌肾素的动态过程。尾静脉取血，用放射免疫方法测定清醒状态野生型和β1/β2肾上腺素能受体基因敲除小鼠基础肾素水平。不同浓度前列腺素E2（PGE2）、异丙肾上腺素和福斯高林刺激野生型和β1/β2肾上腺素能受体基因缺失小鼠JG细胞，放免法测定细胞内和上清中肾素活性。实时PCR测定肾皮质及JG细胞中肾素mRNA水平，以及不同浓度福斯高林对JG细胞内cAMP浓度的影响。结果成功分离的JG细胞上存在13肾上腺素能受体基因表达。激光共聚焦显微镜能观察到异丙肾上腺素明显刺激JG细胞分泌包含肾素的酸性颗粒。β1/β2肾上腺素能受体基因敲除小鼠血浆基础肾素降低，与肾脏皮质肾素mRNA降低平行。原代培养的β1/β2肾上腺素能受体基因敲除小鼠的JG细胞，肾素产生和分泌都明显降低，肾素mRNA也降低。PGE2、异丙肾上腺素和福斯高林呈剂量依赖性增加野生型小鼠JG细胞肾素转录、合成和分泌。β1/β2肾上腺素能受体基因敲除小鼠JG细胞对13肾上腺素能受体激动剂没有反应，而大剂量福斯高林能刺激其肾素分泌。福斯高林呈剂量依赖性上调JG细胞内cAMP水平。结论JG细胞上存在的肾上腺素能β受体，通过上调JG细胞内cAMP，促使JG细胞合成和分泌肾素。     

血管紧张素Ⅱ调节肾脏球旁器颗粒细胞合成肾素的机制研究

目的 观察血管紧张素Ⅱ（AngⅡ）对肾脏球旁器颗粒细胞肾素分泌的调节作用。 方法 密度梯度离心原代分离小鼠肾小球球旁器颗粒细胞（JGC）。实时定量PCR法检测JGC内血管紧张素转换酶（ACE）、AngⅡ受体（AT）1型和2型（AT1和AT2） mRNA表达。不同浓度的AngⅡ与球旁器细胞共孵育后,放射免疫法测定上清中肾素活性;实时定量PCR法测定细胞内肾素mRNA表达;化学发光法测定细胞内、外环磷酸腺苷（cAMP)水平的剂量和时间效应。改变细胞内钙离子浓度后,观察JGC内和上清中cAMP浓度改变。实时定量PCR法检测AngⅡ对JGC内腺苷酸环化酶（AC）5和AC6 mRNA表达的影响。 结果 成功分离的JGC存在ACE、AT基因表达。AngⅡ可抑制JGC肾素分泌[（370.6±36.9）比（299.6±25.7） ng AngI&#8226;ml-1&#8226;h-1,P = 0.014],并能抑制基础状态和前列腺素E2、去甲肾上腺素诱导的肾素mRNA表达。AngⅡ剂量依赖地降低JGC内和上清中cAMP水平。内质网上的Ca-ATP泵抑制剂毒胡萝卜内酯和环盐酸吗甲吡嗪酸均能剂量依赖地降低cAMP水平。细胞内钙离子螯合剂BAPTA-AM可降低细胞内钙离子浓度,进而使细胞内cAMP水平显著升高[（11.09±0.48）比（3.55±0.47） nmol/L,P < 0.01]。AngⅡ能通过减少42.12%的AC5 mRNA 表达,进而抑制肾素分泌。 结论 AngⅡ直接抑制肾素分泌可能是通过影响AC5,进而抑制cAMP表达来实现的。JGC内调节肾素分泌过程中,钙离子途径和GSα-cAMP两大信号传导途径中存在交联对话。     

急性马兜铃酸肾损伤大鼠血清分泌型磷脂酶A2的变化

目的 通过测定急性马兜铃酸肾损伤大鼠血清分泌型磷脂酶A2（sPLA2）活性的变化,探讨sPLA2在马兜铃酸肾病（AAN）发病机制中的作用。 方法 将Wistar大鼠按随机数字表法分为两组：模型组给予关木通水煎剂（相当于生药30 g&#8226;kg-1&#8226;d-1）灌胃7 d,停药后正常喂养至第14天;对照组以自来水灌胃。光镜观察肾脏病理变化并用半定量方法评价肾小管间质损伤程度;生化法测定肾小球及肾小管功能;巯基显色法分别检测血清sPLA2活性;Western印迹法测定肾皮质和肾髓质环氧化酶2（COX-2）蛋白表达;放射免疫法分别测定血清和尿液中前列腺素类（PGs）代谢产物6-keto-PGF1α与血栓烷B2（TXB2）水平并计算二者的比值。 结果 给药后模型组大鼠出现明显的肾小管间质损伤和肾功能下降,并在第8天达高峰,肾小管间质损伤指数（8.14±2.55）较对照组（1.50±0.71）显著升高（P < 0.05）,Scr水平显著增高[（0.24±0.10）比（0.19±0.02） μmol/g,P < 0.05]。给药第8天时模型组血清中sPLA2活性（μmol&#8226;min-1&#8226;mg-1）（133.15±17.05）较对照组（101.3±16.07）显著增强（P < 0.05）,同时肾皮质COX-2蛋白表达也显著增加（1.16±0.36 比0.69±0.28,P < 0.05）,但肾髓质的COX-2蛋白表达无变化。尽管模型组血清中6-keto-PGF1α、TXB2及其比值无变化,但其尿液中6-keto-PGF1α和TXB2水平显著升高,分别为对照组的2倍和3倍（P < 0.05）,二者的比值显著降低（207.53±17.52比296.64±51.31,P < 0.05）。上述变化除肾小管间质损伤指数外,均在第14天时恢复,与对照组差异无统计学意义。 结论 在急性马兜铃酸肾损伤大鼠模型中,血清sPLA2呈激活状态,伴随出现的肾皮质COX-2表达增加及尿液中缩血管类PGs代谢产物增加,提示肾脏缩血管反应增强,可能是马兜铃酸肾损害时组织缺血改变的机制之一。     

血管紧张素1a型受体基因敲除小鼠肾脏局部肾素-血管紧张素系统的变化及其对糖尿病肾小球硬化的影响

目的 探讨血管紧张素1a型受体（AT1aR）基因敲除小鼠肾脏局部肾素-血管紧张素系统（RAS）的组分改变对糖尿病肾病（DN）肾小球硬化的影响及其可能机制。 方法 AT1aR基因敲除小鼠和野生型小鼠腹腔注射链脲佐菌素（STZ，300 mg/kg）诱导糖尿病模型12周后，取肾脏组织作冰冻组织切片，用激光捕获微切割技术分离肾小球，提取RNA。用实时定量PCR的方法检测肾小球内AT1aR、血管紧张素1b型受体（AT1bR）、血管紧张素2型受体（AT2R）、血管紧张素原、血管紧张素转化酶（ACE）、肾素、醛固酮合成酶（CYP11B2）的mRNA表达。PAS染色观察肾脏病理变化。免疫组化检测转化生长因子β1（TGF-β1）、1型纤溶酶原激活物抑制物(PAI-1)、单核细胞趋化因子1(MCP-1)和肾素的表达。比较不同基因型小鼠肾小球细胞外基质和各细胞因子的表达变化。 结果 与野生型小鼠相比，AT1aR基因敲除小鼠肾小球内AT1bR、血管紧张素原、肾素、CYP11B2的表达明显上调（P < 0.05），AT2R表达下调，ACE无明显改变；AT1aR基因敲除小鼠肾小球细胞外基质明显增加（P < 0.05），TGF-β1、PAI-1、MCP-1和肾素的表达均明显增加（P < 0.05）。 结论 AT1aR基因敲除并不能使糖尿病小鼠肾脏病变改善。RAS组分的表达改变（AT1bR的上调和AT2 的下调，肾素的上调和CYP11B2的上调）参与糖尿病肾小球病变过程。     

塞来昔布延缓Han:SPRD大鼠肾衰竭进展的实验研究

目的 通过观察塞来昔布（CXB）对常染色体显性多囊肾病（ADPKD）动物模型Han:SPRD大鼠的作用,从而研究CXB延缓肾衰竭进展的机制。 方法 选取3周龄杂合（cy/+）Han:SPRD大鼠共57只,随机分成3组（每组19只）进行实验。按照CXB在饲料中的含量分为对照组（0 mg&#8226;kg－1&#8226;d－1）、小剂量组（3 mg&#8226;kg－1&#8226;d－1）和大剂量组（10 mg&#8226;kg－1&#8226;d－1）。在大鼠4、6、8、10、12和16周龄时测定血清BUN、Scr。ELISA法检测16周龄大鼠血浆6-酮前列腺素F1α（6-keto-PGF-1α）和血栓烷B2（TXB2）的含量。实时荧光定量PCR法检测大鼠肾组织肿瘤坏死因子α（TNF-α）的mRNA水平。免疫荧光共聚焦显微镜检测TNF-α和环氧化酶2（COX-2）的蛋白表达。Western印迹检测16周龄大鼠TNF-α的蛋白表达量。 结果 对照组BUN、Scr持续升高,分别于6、8周龄时即大于正常范围;至16周龄时,ＢＵＮ为（26.56±9.19） mmol/L,Ｓｃｒ为（95.08±67.54） μmol/L;CXB小剂量组和大剂量组均能减缓BUN、Scr上升速度,减小其上升幅度。16周龄大鼠CXB小剂量组血浆中6-keto-PGF-1α和TXB2[（1831.68±233.31） ng/L和（156.62±9.29） ng/L]和大剂量组两者的含量[（1148.57±105.80） ng/L和(157.87±10.16） ng/L]均显著低于对照组[（2792.26±830.48） ng/L和（248.88±93.72） ng/L]（均P < 0.05）。实时荧光定量PCR结果示,16周龄大鼠肾组织小剂量组和大剂量组TNF-α　mRNA水平均显著低于对照组（均P < 0.05）。免疫荧光共聚焦显微镜显示,对照组TNF-α和COX-2在小管间质区高表达,小剂量组和大剂量组荧光强度显著减弱。与对照组比较,CXB小剂量组和大剂量组大鼠肾组织蛋白表达量显著减少,差异有统计学意义（均P < 0.05）。 结论 CXB可能通过抑制COX-2的活性,阻止膜磷脂释放花生四烯酸代谢产物6-keto-PGF-1α和TXB2,减少炎性因子TNF-α的含量,正反馈避免诱导COX-2的高表达,发挥抗炎作用来延缓肾衰竭的进展。     

中晚期慢性肾脏病患者肾功能进展危险因素——单中心慢性肾脏病专业门诊队列研究

目的 探讨在慢性肾脏病（CKD）专业门诊管理下CKD 3~5期未透析患者肾功能进展相关危险因素。 方法 采取前瞻性队列研究设计,收集北京大学第一医院CKD专业门诊规律随访的CKD 3~5期未透析患者的血压、血红蛋白、钙磷代谢及蛋白尿等指标控制及肾功能的变化情况,进行肾功能进展的多因素分析。肾功能进展定义为每年估计的肾小球滤过率（eGFR）下降大于4 ml&#8226;min-1&#8226;(1.73 m2)-1、开始肾脏替代治疗和（或）肾脏病相关的死亡。 结果 共纳入138例患者,其中CKD 3期84例,4期36例,5期18例。进入队列时基线年龄为（56.5±16.7）岁,基线eGFR为（32.3±13.4） ml&#8226;min-1&#8226;(1.73 m2)-1,平均随访（27.1±12.1）个月。随访过程中患者平均血压（126.5±12.4）/（76.4±7.9） mm Hg;平均血红蛋白（123.4±17.6）g/L;平均钙磷乘积（45.2±7.7） mg2/dl2。分别有70例（50.7%）血压控制达标;102例（73.9%）血红蛋白控制达标;123例（89.1%）患者钙磷乘积控制达标;62例（44.9%）患者肾功能进展。多因素分析显示,随访过程中蛋白尿和血红蛋白水平与肾功能进展独立相关。 结论 通过CKD专业门诊的一体化治疗,能够有效控制中晚期CKD患者的各种并发症。控制蛋白尿和（或）改善贫血有利于延缓中晚期CKD患者肾功能进展。     

5/6肾切除大鼠肾组织肾素-血管紧张素-醛固酮系统的昼夜节律

目的：研究慢性肾衰竭大鼠循环及肾局部肾素-血管紧张素-醛固酮（RAAS）的近日节律。方法：60只Wistar大鼠建立5/6肾衰竭大鼠模型,随机分为两组：肾衰组（A组,30只）,假手术组（B组,30只）。大鼠在恒温（22±2）℃,12：12h明（L）：暗（D）交替的环境中饲养12周。早上7：00开灯,记为ZT0时,依次类推,晚上19：00时关灯,记为ZT12时。在11周时留尿测24h尿蛋白定量。12周时分别留取血及肾标本。放免法检测血及肾脏肾素活性、血管紧张素Ⅱ（AngⅡ）及醛固酮（Ald）浓度。结果：与假手术组比较,肾衰组血肌酐水平及24h尿蛋白定量明显升高（P〈0.001）。无论是A组还是B组,肾组织肾素活性（KRA）、AngⅡ及Ald的近日节律与血浆中肾素活性（PRA）、AngⅡ及Ald节律不一致。如A、B组KPA的谷、峰值时间与PRA相反;血浆AngⅡ峰值时间A组在ZT20,B组在ZT16时,A、B组肾脏中AngⅡ峰值时间则在ZT4时。B组的血浆及肾RAAS各组分的近日节律与A组差异也有统计学意义。结论：大鼠肾局部RAAS节律与血浆中RAAS节律不同,慢性肾衰竭组RAAS节律与假手术组比较也发生改变。     

血管紧张素Ⅱ灌注诱导大鼠肾脏血管紧张素转换酶2表达改变

目的 研究血管紧张素Ⅱ(AngⅡ)灌注后大鼠肾脏血管紧张素转换酶2(ACE2)表达的改变及其意义。 方法 雄性SD大鼠随机分为AngⅡ灌注组(400 ng&#8226;kg-1&#8226;min-1)、生理盐水灌注组和健康对照组，每组6只。测定28 天内大鼠血压及尿蛋白量变化。于第28天处死动物取肾，观察组织学改变，并用免疫组化、RT-PCR及Western印迹法检测ACE2表达及分布变化；凝胶电泳迁移率分析法(EMSA)检测核因子(NF)-κB的DNA结合活性变化。 结果 (1) AngⅡ灌注组大鼠血压升高，并出现明显蛋白尿。AngⅡ灌注后第28天，部分肾小球出现轻中度系膜增生，少数有节段性硬化；部分肾小管上皮细胞变性、坏死或萎缩，间质灶性炎性细胞浸润。(2) 健康大鼠肾脏ACE2主要分布于肾小管，以近端肾小管刷状缘分布最多。AngⅡ灌注后第28天，肾皮质ACE2 mRNA及蛋白表达均明显下降(P均< 0.05)，NF-κB结合活性显著增加(P < 0.05)。相关分析表明，ACE2表达与NF-κB结合活性之间呈负相关(r = -0.64，P < 0.01)。 结论 AngⅡ灌注可致大鼠肾脏ACE2表达明显下降，后者与肾损害的程度密切相关。肾脏ACE2表达下降可能是AngⅡ引起肾损害的重要机制     

Furosemide stimulates macula densa cyclooxygenase-2 expression in rats

BACKGROUND: During a low salt intake, maintenance of renal blood flow and renin secretion depends on intact formation of prostaglandins. In the juxtaglomerular apparatus, the inducible isoform of cyclooxygenase, cyclooxygenase-2 (COX-2), is restricted to the macula densa and the cortical thick ascending limb of Henle (cTALH) cells, and is inversely regulated by dietary salt intake. This study aimed to elucidate whether the effect of NaCl on macula densa COX-2 expression is mediated by transepithelial transport of NaCl. METHODS: To this end, male Sprague-Dawley rats received subcutaneous infusions of the loop diuretic furosemide (12 mg/day) or were fed with the diuretic hydrochlorothiazide (30 mg/kg day) for seven days each. To compensate for their salt and water loss, the animals had free access to normal water and to salt water (0.9% NaCl, 0.1% KCl). COX-2 expression in kidney cortex was assessed by immunohistochemical staining and by semiquantitative ribonuclease protection assay for COX-2 mRNA. RESULTS: After six days of furosemide infusion to salt-substituted rats, there was no change of extracellular volume. Furosemide led to a fivefold and threefold increase of plasma renin activity and renocortical renin mRNA level, respectively. In parallel, there was a threefold increase of renocortical COX-2 abundance, while the COX-1 mRNA level remained unchanged. Moreover, the percentage of juxtaglomerular apparatuses immunopositive for COX-2 increased threefold in response to furosemide compared with vehicle-infused animals. Hydrochlorothiazide treatment increased plasma renin activity twofold but did not change kidney cortical renin mRNA, COX-2 mRNA, or COX-2 immunoreactivity. CONCLUSION: Our findings suggest that inhibition of salt transport in the loop of Henle, but not in the distal tubule, causes a selective stimulation of COX-2 expression in the macula densa region. This up-regulation may be of relevance for macula densa signaling, which links tubular salt transport rate with glomerular filtration rate and renin secretion.     

Cyclooxygenase-2 expression is associated with the renal macula densa of patients with Bartter-like syndrome

BACKGROUND: Bartter-like syndrome (BLS) is a heterogeneous set of congenital tubular disorders that is associated with significant renal salt and water loss. The syndrome is also marked by increased urinary prostaglandin E2 (PGE2) excretion. In rodents, salt and volume depletion are associated with increased renal macula densa cyclooxygenase-2 (COX-2) expression. The expression of COX-2 in human macula densa has not been demonstrated. The present studies examined whether COX-2 can be detected in macula densa from children with salt-wasting BLS versus control tissues. METHODS: The intrarenal distribution of COX-2 protein and mRNA was analyzed by immunohistochemistry and in situ hybridization in 12 patients with clinically and/or genetically confirmed BLS. Renal tissue rejected for transplantation, from six adult patients not affected by BLS, was also examined. RESULTS: The expression of COX-2 immunoreactive protein was observed in cells of the macula densa in 8 out 11 patients with BLS. In situ hybridization confirmed the expression of COX-2 mRNA in the macula densa in 6 out of 10 cases. COX-2 protein was also detected in the macula densa in a patient with congestive heart failure. The expression of COX-2 immunoreactive protein was not observed in cells associated with the macula densa in kidneys from patients without disorders associated with hyper-reninemia. CONCLUSION: These studies demonstrate that COX-2 may be detected in the macula densa of humans. Since macula densa COX-2 was detected in cases of BLS, renal COX-2 expression may be linked to volume and renin status in humans, as well as in animals.     

Role of renocortical cyclooxygenase-2 for renal vascular resistance and macula densa control of renin secretion

This study aimed to assess the role of cyclooxygenase-2 (COX-2)-derived prostanoids for the macula densa control of renal afferent arteriolar resistance and for renin secretion. For this purpose, studied were the effects of blocking macula densa salt transport by the loop diuretic bumetanide (100 microM) on renal perfusate flow and on renin secretion in isolated perfused rats, in which renocortical COX-2 expression was prestimulated in vivo by treatment with the angiotensin-converting enzyme inhibitor ramipril, with low-salt diet, or with a combination of both. These maneuvers stimulated COX-2 expression in an order of ramipril + low salt> low salt > ramipril > controls. Flow rates through isolated kidneys at a constant pressure of 100 mmHg were dependent on the pretreatment regimen, in the way that they went in parallel with COX-2 expression. The COX-2 inhibitor NS-398 (10 microM) lowered flow rates depending on the COX-2 expression level and was most pronounced therefore after pretreatment with low salt + ramipril. NS-398 did not change the increase of flow in response to bumetanide but attenuated the stimulation of renin secretion in response to bumetanide in a manner depending on the expression level of COX-2. These findings suggest that in states of increased renocortical expression of COX-2, overall renal vascular resistance and the macula densa control of renin secretion become dependent on COX-2-derived prostanoids.     

Synthesis and secretion of renin in mice with induced genetic mutations

The juxtaglomerular (JG) cell product renin is rate limiting in the generation of the bioactive octapeptide angiotensin II. Rates of synthesis and secretion of the aspartyl protease renin by JG cells are controlled by multiple afferent and efferent pathways originating in the CNS, cardiovascular system, and kidneys, and making critical contributions to the maintenance of extracellular fluid volume and arterial blood pressure. Since both excesses and deficits of angiotensin II have deleterious effects, it is not surprising that control of renin is secured by a complex system of feedforward and feedback relationships. Mice with genetic alterations have contributed to a better understanding of the networks controlling renin synthesis and secretion. Essential input for the setting of basal renin generation rates is provided by β-adrenergic receptors acting through cyclic adenosine monophosphate, the primary intracellular activation mechanism for renin mRNA generation. Other major control mechanisms include COX-2 and nNOS affecting renin through PGE2, PGI2, and nitric oxide. Angiotensin II provides strong negative feedback inhibition of renin synthesis, largely an indirect effect mediated by baroreceptor and macula densa inputs. Adenosine appears to be a dominant factor in the inhibitory arms of the baroreceptor and macula densa mechanisms. Targeted gene mutations have also shed light on a number of novel aspects related to renin processing and the regulation of renin synthesis and secretion.     

Increase in heme oxygenase-1 levels ameliorates renovascular hypertension

BACKGROUND: The heme oxygenase system (HO-1 and HO-2) catalyzes the conversion of heme to free iron, carbon monoxide (CO), a vasodepressor, and biliverdin, which is further converted to bilirubin, an antioxidant. HO-1 induction has been shown to suppress arachidonic acid metabolism by cytochrome P450 (CYP450) monooxygenases and cyclooxygenases (COX), and to decrease blood pressure in spontaneously hypertensive rats (SHR). The Goldblatt 2K1C model is a model of renovascular hypertension in which there is increased expression of COX-2 in the macula densa and increased renin release from the juxtaglomerular apparatus of the clipped kidney. We examined whether HO-1 overexpression, as a prophylactic approach, would attenuate renovascular hypertension and evaluated potential mechanisms that may account for its effect. METHODS: 2K1C rats were treated with cobalt protoporphyrin (CoPP) or tin mesoporphyrin (SnMP) one day before surgery and weekly for three weeks thereafter. We measured systolic blood pressure, HO activity, HO-1, HO-2, COX-1 and COX-2 protein expression, heme content, and nitrotyrosine levels as indices of oxidative stress. Urinary prostaglandin excretion (PGE2), plasma renin activity (PRA), and plasma aldosterone levels were also measured. RESULTS: CoPP administration induced renal HO-1 expression by 20-fold and HO activity by 6-fold. This was associated with a reduction in heme content, nitrotyrosine levels, COX-2 expression and urinary PGE2 excretion, and attenuation of the development of hypertension in the 2K1C rats. There was no decrease in plasma renin activity; however, plasma aldosterone levels were significantly lower. In the 2K1C SnMP-treated rats, blood pressure was significantly higher than that of untreated 2K1C rats throughout the study, and the difference in the size of the smaller left clipped kidney compared to the nonclipped right kidney was significantly increased. CONCLUSION: These findings define an action of prolonged HO-1 induction to interrupt and counteract the influence of the renin-angiotensin-aldosterone system (RAAS) to increase in blood pressure in the 2K1C model of renovascular hypertension. Multiple mechanisms include a decrease in oxidative stress as indicated by the decrease in cellular heme and nitrotyrosine levels, an anti-inflammatory action as evidenced by a decrease in COX-2 and PGE2, interference with the action of angiontensin II (Ang II) as evidenced by an increase in PRA in the face of a decrease in PGE2 and aldosterone, as well as the inhibition of aldosterone synthesis.     

Temporal adaptation of tubuloglomerular feedback: effects of COX-2

BACKGROUND: Reductions in proximal reabsorption cause increases in delivery of sodium chloride to the macula densa (MD), which activates the tubuloglomerular feedback (TGF) mechanism and reduces glomerular filtration rate. TGF undergoes temporal adaptation, permitting filtration rate to rise in spite of elevated MD delivery of NaCl. Inhibitors of nitric oxide synthase I (NOS I) prevent TGF adaptation, but angiotensin-converting enzyme inhibitors have no effect. COX-2 activity moves in parallel with changes in NOS I and intrarenal renin. We examined the impact of COX-2 inhibition on TGF temporal adaptation and effects of inhibition of COX-2 and NOS I on plasma and kidney angiotensin II (Ang II). METHODS: Kidney blood flow (RBF) and glomerular filtration rate (GFR) were measured before and during benzolamide (BNZ) infusion in control Wistar rats and rats concurrently receiving COX-2 inhibitors. Plasma and kidney angiotensin II content was evaluated by radioimmunoassay in control rats, rats after 60 minutes of BNZ, and during COX-2 and NOS-1 inhibition after BNZ. RESULTS: BNZ reduced both RBF and GFR in all groups. During BNZ, RBF and GFR returned to normal control values within 60 minutes. COX-2 inhibitors totally prevented TGF adaptation. Plasma and kidney Ang II did not change after BNZ, and NOS I and COX-2 inhibitors had no effect on plasma or intrarenal Ang II. CONCLUSION: Within 1 hour after BNZ, rats undergo TGF temporal adaptation. Administration of COX-2 inhibitors prevented TGF temporal adaptation, identical to the effect of NOS I inhibition. Changes in intrarenal Ang II cannot explain this prevention of TGF temporal adaptation.     

Lack of connexin 40 causes displacement of renin-producing cells from afferent arterioles to the extraglomerular mesangium

In the adult kidney, renin-producing cells are typically located in the walls of afferent arterioles at the transition into the glomerular capillary network. The mechanisms that are responsible for restricting renin expression to the juxtaglomerular position are largely unknown. This study showed that in mice that lack connexin 40 (Cx40), the predominant connexin of renin-producing cells, renin-positive cells are absent in the vessel walls and instead are found in cells of the extraglomerular mesangium, glomerular tuft, and periglomerular interstitium. Blocking macula densa transport function by acute administration of loop diuretics strongly enhances renin secretion in vivo and in isolated perfused kidneys of wild-type mice. This effect of loop diuretics is markedly attenuated in vivo and even blunted in vitro in Cx40-deficient mice. Even after prolonged stimulation of renin secretion by severe sodium depletion, renin expression is not seen in juxtaglomerular cells or in cells of more proximal parts of the arterial vessel wall as occurs normally. Instead, renin remains restricted to the extra-/periglomerular interstitium in Cx40-deficient mice. In contrast to the striking displacement of renin-expressing cells in the adult kidney, renin expression in the vessels of the developing kidney was found to be normal. This is the first evidence to indicate that cell-to-cell communication via gap junctions is essential for the correct juxtaglomerular positioning and recruitment of renin-producing cells. Moreover, these findings support the notion that gap junctions are relevant for the macula densa signaling to renin-producing cells.     

Cycloxygenase-2 is expressed in vasculature of normal and ischemic adult human kidney and is colocalized with vascular prostaglandin E2 EP4 receptors

The study was performed to elucidate the distribution and cellular localization of cyclooxygenase (COX)-2 in human kidney and to address localization of downstream targets for COX-derived prostanoids. Cortex and outer and inner medulla tissue were obtained from control kidneys (cancer specimens), kidneys with arterial stenosis, and kidneys of patients who received angiotensin II inhibition or acetylsalicylic acid. Ribonuclease protection assay and Western blot test revealed that COX-1 and -2 mRNA and protein were expressed in all regions of human kidney (mRNA ratio, cortex:outer medulla:inner medulla COX-1 1:3:20 and COX-2 1:1:3). In adult kidney, immunohistochemical labeling for COX-2 was associated with smooth muscle cells in pre- and postglomerular vessels and with endothelium, particularly in vasa recta and medullary capillaries. Western blot test confirmed COX-2 expression in renal artery. COX-2 had a similar localization in fetal kidney and was additionally observed in Henle's loop and macula densa. Human tissue arrays displayed COX-2 labeling of vascular smooth muscle in multiple extrarenal tissues. Vascular COX-2 expression was significantly increased in kidneys with arterial stenosis. COX-1 was colocalized with microsomal prostaglandin E(2) synthase (PGES) in collecting ducts, and PGES was also detected in macula densa cells. Vascular COX-2 was colocalized with prostaglandin E(2) EP4 receptors but not with EP2 receptors. Thus, renovascular COX-2 expression was a constitutive feature encountered in human kidneys at all ages, whereas COX-2 was seen in macula densa only in fetal kidney. Vascular COX-2 activity in human kidney and extrarenal tissues may support blood flow and affect vascular wall-blood interaction.     

Cyclooxygenase-2-selective inhibitors impair glomerulogenesis and renal cortical development

BACKGROUND: Antenatal exposure to nonsteroidal anti-inflammatory drugs (NSAIDs) has been associated with renal dysgenesis in humans. METHODS: These studies characterized cyclooxygenase-2 (COX-2) versus COX-1-selective inhibition on nephrogenesis in the rodent using histomorphometry, immunohistology, and in situ hybridization. RESULTS: Administration of a COX-2-selective inhibitor (SC58236), started during pregnancy until weaning, significantly impaired development of the renal cortex and reduced glomerular diameter in both mice and rats. An identical phenotype was demonstrated in COX-2 -/- mice. In contrast to its effects on the developing kidney, a COX-2 inhibitor had no effect on glomerular volume in adult mice. This effect was specific for COX-2 because maternal administration of a COX-1-selective inhibitor (SC58560) did not affect renal development despite significantly inhibiting gastric mucosal prostaglandin E2 (PGE2) synthesis in pups. The expression of COX-2 immunoreactivity peaked in the first postnatal week and was localized to S-shaped bodies and the macula densa in the cortex. Treatment with a COX-2 inhibitor during this period (from postnatal day 0 to day 21) severely reduced glomerular diameter, whereas treatment limited to pregnancy did not affect glomerular size. CONCLUSION: These data demonstrate an important role for COX-2 activity in nephrogenesis in the rodent, and define a specific time period of susceptibility to these effects.