Mechanical strain stimulates nitric oxide production by rapid activation of endothelial nitric oxide synthase in osteocytes.

Previous studies have indicated that physiological levels of dynamic mechanical strain produce rapid increases in nitric oxide (NO) release from rat ulna explants and primary cultures of osteoblast-like cells and embryonic chick osteocytes derived from long bones. To establish the mechanism by which loading-induced NO production may be regulated, we have examined: nitric oxide synthase (NOS) isoform mRNA and protein expression, the effect of mechanical loading in vivo on NOS mRNA expression, and the effect of mechanical strain on NO production by bone cells in culture. Using Northern blot analyses, in situ hybridization, and immunocytochemistry we have established that the predominant NOS isoform expressed in rat long bone periosteal osteoblasts and in a distinct population of cortical bone osteocytes is the endothelial form of NOS (eNOS), with little or no expression of the inducible NOS or neuronal NOS isoforms. In contrast, in non-load-bearing calvariae there are no detectable levels of eNOS in osteocytes and little in osteoblasts. Consistent with these observations, ulnar explants release NO rapidly in response to loading in vitro, presumably through the activation of eNOS, whereas calvarial explants do not. The relative contribution of different bone cells to these rapid increases in strain-induced NO release was established by assessment of medium nitrite (stable NO metabolite) concentration, which showed that purified populations of osteocytes produce significantly greater quantities of NO per cell in response to mechanical strain than osteoblast-like cells derived from the same bones. Using Northern blot hybridization, we have also shown that neither a single nor five consecutive daily periods of in vivo mechanical loading produced any significant effect on different NOS isoform mRNA expression in rat ulnae. In conclusion, our results indicate that eNOS is the prevailing isoform expressed by cells of the osteoblast/osteocyte lineage and that strain produces increases in the activity of eNOS without apparently altering the levels of eNOS mRNA.     

Overexpression of endothelial nitric oxide synthase increases skeletal muscle blood flow and oxygenation in severe rat hind limb ischemia

OBJECTIVE: Although nitric oxide (NO) has a critical role in angiogenesis, the therapeutic potential of NO synthase overexpression in severe ischemia remains undefined. We tested the hypothesis that overexpression of endothelial NO synthase (eNOS) would improve tissue perfusion in severe hind limb ischemia. METHODS: Severe hind limb ischemia was induced in 122 adult male Sprague-Dawley rats. Ten days after the induction of hind limb ischemia, vascular isolation and intraarterial delivery of an adenoviral vector encoding eNOS (AdeNOS), a control adenoviral vector (AdE1), or phosphate-buffered saline solution (PBS) was performed. Skeletal muscle blood flow, muscle oxygen tension, angiography, and immunohistochemistry for capillary counts were measured. RESULTS: Gene transfer of AdeNOS increased eNOS protein expression and enzyme activity. Two weeks after gene transfer, skeletal muscle blood flow was fourfold higher in eNOS-transduced than in AdE1-transduced or PBS treated rats and was similar to exercise-induced maximal flow in nonischemic muscle. eNOS overexpression increased muscle oxygen tension in a titer-dependent fashion. This increase persisted 1 month after transduction, even though eNOS enzyme activity had declined to normal levels. Angiography and capillary counts showed that eNOS overexpression increased the size and number of collateral arteries, but did not significantly increase the capillary-muscle fiber ratio. CONCLUSIONS: eNOS overexpression in an ischemic rat hind limb significantly increased skeletal muscle blood flow, muscle oxygen tension, and collateral arteries (arteriogenesis). Furthermore, eNOS overexpression did not result in capillary angiogenesis above control levels. These studies demonstrate the potential for eNOS overexpression as treatment for severe limb ischemia in human beings.     

血管内皮生长因子对关节软骨细胞诱导型一氧化氮合酶的影响

目的 观察血管内皮生长因子(VEGF)对体外培养的关节软骨细胞诱导型一氧化氮合酶(iNOS)表达的影响。方法 体外培养SD乳鼠关节软骨细胞,用白细胞介素(IL)-1β诱导的方法建立骨关节炎(OA)体外模型,实验分为4组,每组加入不同处理因素进行干预,A组:(正常对照组)不加任何处理因素;B组:10 μg/L VEGF;C组:10 μg/L IL-1β;D组:10 μg/L VEGF+ 10 μg/LIL-1β。采用实时荧光定量PCR( Real Time PCR)检测iNOS mRNA的表达,采用蛋白免疫印迹法( Western blot)检测iNOS蛋白的表达。结果 iNOS mRNA的表达:A组iNOS mRNA无表达,B组(9.64±1.64)、C组(17.27±2.01)及D组(28.93±6.63),3组的iNOS mRNA表达量显著升高,进一步组间比较,D组软骨细胞iNOS的mRNA表达水平明显高于B组(P＜0.01)及C组(P＜0.05),C组软骨细胞iNOS的mRNA表达水平高于B组(P＜0.05)。iNOS蛋白的表达:A组iNOS蛋白无表达,B组(0.44±0.12)、C组(0.74±0.07)及D组(1.38±0.38),3组的iNOS蛋白表达量显著升高,进一步组间比较,D组软骨细胞iNOS的蛋白表达水平明显高于B组(P＜0.01)及C组(P＜0.05),C组软骨细胞iNOS的mRNA表达水平高于B组(P＜0.01)。结论 在OA的发病过程中,VEGF可能通过上调软骨细胞iNOS的表达发挥重要作用。     

严重烧伤大鼠胸腺诱导型一氧化氮合酶表达对细胞凋亡的影响

目的观察严重烧伤大鼠胸腺诱导型一氧化氮合酶(iNOS)表达对胸腺细胞凋亡的影响,探讨一氧化氮(NO)与胸腺病理损害的关系。方法将56只雄性Wistar大鼠随机分为对照组(8只)、烧伤组(24只)、烧伤 硫酸甲基异硫脲(SMT)组(24只)。后两组大鼠背部造成30％TBSAⅢ度烧伤,伤后分别立即静脉注射等渗盐水、等渗盐水 SMT(7．5 mg／kg);对照组不予烧伤及SMT处理。两烧伤组分别于伤后6、24、72 h检测胸腺重量、胸腺细胞凋亡情况(原位缺口末端标记法)、胸腺iNOS表达情况(免疫组织化学染色法),采用体视学方法测定阳性细胞密度,每时相点8只;同时测定对照组相应指标。结果烧伤组大鼠伤后24、72 h胸腺重量分别为(153±14)、(91±22)mg,明显轻于对照组[(243±12)mg,P<0．01];烧伤 SMT组此时明显高于烧伤组(P<0．01)。对照组大鼠胸腺皮、髓质可见散在少量凋亡阳性细胞、iNOS阳性细胞。烧伤组大鼠伤后6 h胸腺皮质有凋亡阳性细胞及少量iNOS阳性细胞;伤后24 h时凋亡阳性细胞分布于被膜下皮质、皮髓交界处及髓质,iNOS阳性细胞广泛出现在小叶间隔内血管旁;伤后72 h时凋亡阳性细胞使胸腺皮质广泛呈现棕褐色;伤后6～72 h烧伤组iNOS阳性细胞呈进行性增加(P<0．05)。烧伤 SMT组大鼠伤后各时相点阳性细胞较少且分布不均,凋亡灶少见,未见iNOS阳性细胞。烧伤组大鼠伤后24、72 h凋亡阳性细胞密度分别为(2．428±0．728)×10-5／μm3、(5．586±1．233)×10-5／μm3,高于对照组和烧伤 SMT组(P<0．01)。结论严重烧伤大鼠伤后早期胸腺细胞凋亡率增加,iNOS在胸腺表达增强并促进了胸腺细胞凋亡;SMT则能部分改善这一现象。     

Effect of aging on expression of nitric oxide synthase I and activity of nitric oxide synthase in rat penis

Aim: To investigate the effect of aging on the expression of nitric oxide synthase I (NOS I) and the activity of NOS in rat penis. Methods: Sixty male rats from 3 age groups (adult, old and senescent) were investigated. The expression of NOS I protein and mRNA in rat penis were detected by Western blot and RT-PCR respectively and the NOS activity, with ultraviolet spectrophotometry. Results: In the old and senescent group, NOS I protein expression was significantly decreased as compared with the adult. NOS I mRNA expression was well correlated with the protein expression. NOS activity was not statistically different between the adult and old groups, but it was significantly reduced in the senescent compared with the adult group (P<0.01). Conclusion: The aging-induced decreases in NOS I expression and NOS activity may be one of the main mechanisms leading to erectile dysfunction in the senescent rats.     

金属硫蛋白对离体心脏细胞凋亡和NO、NOS表达的影响

目的 探讨金属硫蛋白（Mr）与离体心脏细胞凋亡和一氧化氮（NO）、一氧化氮合酶（NOS）的关系。方法 Wistar大鼠16只，分为2组：对照组（c），腹腔注射蒸馏水0．5ml24h后取离体心脏灌注HTK心脏保护液，4℃保存3h后建立Langendorff灌注模型，灌注KH液2h；实验组（E）腹腔注射3．6％ZnSO4（1．5ml／ks）24h后取离体心脏，处理方法同C组。测定心肌MT含量、心肌细胞凋亡率、NO、NOS的含量。结果 MT含量E组明显较C组增高（P〈0．05），心肌细胞凋亡率E组明显低于C组（P〈0．01），琼脂糖凝胶电泳检测DNA片段梯E组与C组比较，光密度明显减弱（P〈0．01），E组与C组比较，NO、NOS的含量明显增多（P〈0．01）。MT含量与凋亡细胞率呈负相关（r=-0．96，P〈0．01），与心肌组织中NO含量呈正相关（r=0．97，P〈0．01）。结论 心肌MT可增加心肌中NO、NOS的表达，减少再灌后心肌细胞凋亡的发生。     

异丙酚对高血压大鼠胸主动脉内皮型一氧化氮合酶和诱导型一氧化氮合酶表达的影响

目的 评价异丙酚对高血压大鼠胸主动脉内皮型一氧化氮合酶(eNOS)和诱导型一氧化氮合酶(iNOS)表达的影响.方法 SD大鼠,雌雄各半,体重240～ 280 g,采用皮下注射去氧皮质酮的方法制备高血压模型,采用随机数字表法,将64只造模成功的大鼠随机分为4组(n＝16):高血压组(H组)、小剂量异丙酚组(P1组)、中剂量异丙酚组(P2组)和大剂量异丙酚组(P3组).P1组、P2组和P3组分别静脉输注异丙酚20、30、40 mg·kg-1·h-13 h,H组给予等容量生理盐水.分别于给药前、给药1h、3h时记录平均动脉压(MAP).给药3h时处死大鼠,摘眼球法采集血样,硝酸还原酶法测定血清一氧化氮(N0)浓度,取胸主动脉,采用RT-PCR和Western blot法测定eNOS mRNA、iNOS mRNA及其蛋白表达水平.结果 与H组比较,P1组、P2组和P3组给药3h时MAP降低,血清NO浓度升高,主动脉eNOS mRNA及其蛋白表达上调,主动脉iNOS mRNA及其蛋白表达下调,且呈剂量依赖性(P<0.05或0.01).结论 异丙酚降低高血压大鼠血压的机制与下调iNOS表达,上调血管内皮细胞eNOS表达,促进NO释放有关.     

Propofol reduces nitric oxide-induced apoptosis in testicular ischemia-reperfusion injury by downregulating the expression of inducible nitric oxide synthase

Background: The aim of the present study was to investigate the underlying mechanisms in the preventive effects of intravenous anesthetics on testicular ischemia–reperfusion injury.
Methods: Forty male Wistar Albino rats were randomly assigned to four groups of 10 rats each. Anesthesia was induced and maintained with thiopental in groups 1 and 2 and with propofol in groups 3 and 4. Groups 2 and 4 received left testicular ischemia (torsion) for 1 h and reperfusion (detorsion) for 24 h. Groups 1 and 3 (control groups) had no testicular torsion and detorsion. At 24 h of reperfusion, animals were killed and ipsilateral testes were removed for determination of tissue nitric oxide (NO) levels and immunohistochemical evaluation of endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), and apoptosis protease-activating factor 1 (APAF-1).
Results: Between groups 1 and 3, there were no differences in tissue NO levels and eNOS, iNOS, and APAF-1 expressions. iNOS and APAF-1 expressions were markedly increased in group 2, but these parameters were at the mild to moderate level in group 4 at 24 h of reperfusion. Also, elevated expression of iNOS was accompanied by a high NO production in group 2 compared with group 4. Although eNOS expressions were increased in both the groups (groups 2 and 4), there were no significant differences between these groups.
Conclusions: Propofol as an anesthetic agent may attenuate germ cell-specific apoptosis and decrease NO biosynthases through downregulation of iNOS expression in an animal model of testicular torsion and detorsion.     

Increased expression of nitric oxide synthase in human lung transplants after nitric oxide inhalation

BACKGROUND: The effects of the ischemia-reperfusion process of organ transplantation on nitric oxide (NO) synthase (NOS) in humans are unknown. The effects of NO inhalation on endogenous NOS expression and activity are controversial. The authors hypothesized that NO inhalation may affect ischemia-reperfusion-induced alterations of the endogenous NOS system. METHODS: The authors performed lung biopsy on patients in a randomized phase II clinical trial of NO inhalation during lung transplantation. After lung implantation, 20 ppm of NO or placebo gas was administered 10 min after the start of reperfusion. Lung tissues were collected from 20 patients (NO, n=9; placebo, n=11) after cold and warm ischemia, 1 hr and 2 hr after reperfusion. The protein levels of NOS isoforms were analyzed by Western blotting and the total NOS activity was measured. RESULTS: The protein levels of inducible NOS did not change significantly in either of the groups. In contrast, during the 2-hr reperfusion period, constitutive NOS (neuronal NOS [nNOS] and endothelial NOS) tended to decrease in the placebo group, but gradually increased in the NO group. After 2 hr of reperfusion, the nNOS protein in the NO group was significantly higher than that in the placebo group (P <0.05). However, the total NOS activity remained at low levels in both groups. CONCLUSIONS: NO inhalation-induced increase of constitutive NOS proteins indicates the interaction between inhaled NO molecules and lung tissues. However, the activity of these newly synthesized NOS proteins remains suppressed during the ischemia-reperfusion period of lung transplantation.     

Differential nitric oxide synthase expression during hepatic ischemia-reperfusion

BACKGROUND: In recent years the important role of nitric oxide in hepatic ischemia-reperfusion injury has been increasingly recognised. The prevailing consensus is that reperfusion injury may be partly the result of decreased production of nitric oxide from endothelial nitric oxide synthase and excessive production of nitric oxide from the inducible isoform. We therefore undertook this study to characterize the expression of different nitric oxide synthase isoforms during hepatic reperfusion. METHODS: Male Wistar rats (n = 6) were subjected to 45 minutes of partial hepatic ischemia (left lateral and median lobes) followed by 6 hours of reperfusion. Control animals (n = 6) were subjected to sham laparotomy. The expression of endothelial and inducible nitric oxide synthase was examined using immunohistochemistry and Western blotting. Liver sections were also stained with nitrotyrosine antibody, a specific marker of protein damage induced by peroxynitrite (a highly reactive free radical formed from nitric oxide). RESULTS: Liver sections from all the control animals showed normal expression of the endothelial isoform and no expression of inducible nitric oxide synthase. Livers from all the animals subjected to hepatic ischemia showed decreased expression of endothelial nitric oxide synthase, and all but one animal from this group showed expression of the inducible isoform both in inflammatory cells and in hepatocytes. Western blotting confirmed these findings. Staining with the antinitrotyrosine antibody was also confined to five liver sections from animals subjected to hepatic ischemia. CONCLUSIONS: During the reperfusion period after hepatic ischemia, endothelial nitric oxide synthase is downregulated while inducible nitric oxide synthase is expressed in both hepatocytes and inflammatory cells. The presence of nitrotyrosine in livers subjected to hepatic ischemia-reperfusion suggests that the expression of inducible nitric oxide synthase plays an important role in mediating reperfusion injury in this model.     

Effects of icariin on erectile function and expression of nitric oxide synthase isoforms in castrated rats

Aim： To investigate the effect of icariin on erectile function and the expression of nitric oxide synthase （NOS） isoforms in castrated rats. Methods： Thirty-two adult male Wistar rats were randomly divided into one shamoperated group （A） and three castrated groups （B, C and D）. One week after surgery, rats were treated with normal saline （groups A and B） or oral icariin （1 mg/[kg·day] for group C and 5 mg/[kg·day] for group D） for 4 weeks. One week after treatment, the erectile function of the rats was assessed by measuring intracavernosal pressure （ICP） during electrostimulation of the cavernosal nerve. The serum testosterone （ST） levels, the percent of smooth muscle （PSM） in trabecular tissue, and the expression of mRNA and proteins of neuronal nitric oxide synthase （nNOS）, inducible nitric oxide synthase （iNOS）, endothelial nitric oxide synthase （eNOS） and phosphodiesterase V （PDES） in corpus cavernosum （CC） were also evaluated. Results： ICP, PSM, ST and the expression of nNOS, iNOS, eNOS and PDE5 were significantly decreased in group B compared with those in group A （P 〈 0.01）. However, ICE PSM and the expression of nNOS and iNOS were increased in groups C and D compared with those in group B （P 〈 0.05）. Changes in ST and the expression of eNOS and PDE5 were not significant （P 〉 0.05） in groups C and D compared with those in group B. Conclusion： Oral treatment with icariin （〉 98.6 % purity） for 4 weeks potentially improves erectile function. This effect is correlated with an increase in PSM and the expression of certain NOS in the CC of castrated rats. These results suggest that icariin may have a therapeutic effect on erectile dysfunction.     

异丙酚对缺氧复氧后大鼠海马神经元诱生型一氧化氮合酶表达的影响

目的 观察异丙酚对原代培养海马神经元缺氧复氧后诱生型一氧化氮合酶(iNOS)表达及存活率的影响。方法 原代培养SD大鼠海马神经元随机分为四组:正常对照组、缺氧组、缺氧 异丙酚4μg/ml组、缺氧 异丙酚12μg/ml组。MTT法测定体外缺氧4h复氧24h后海马神经元的存活率,免疫细胞化学法测定iNOS表达的程度。结果 与缺氧组比较,两异丙酚组缺氧复氧后海马神经元的存活率提高(P<0.05),iNOS表达的灰度值降低(P<0.05或0.01),iNOS阳性表达率降低,并呈剂量依赖性(P<0.01)。结论 异丙酚可降低大鼠海马神经元缺氧复氧后iNOS的表达,提高存活率。     

衰老对大鼠阴茎海绵体NOS I的表达和NOS活性的影响

目的 :探讨衰老对大鼠阴茎海绵体一氧化氮合酶Ⅰ (NOSⅠ)mRNA、蛋白的表达和NOS活性的影响。　方法 :30只雄性SD大鼠按不同月龄分为成年组、老年组和衰老组 ,应用Western印迹、RT PCR方法分别检测不同年龄组阴茎海绵体NOSⅠ蛋白及mRNA的表达 ;用紫外分光光度计测定不同年龄组阴茎海绵体NOS的活性。　结果 :成年组NOSⅠ 蛋白的表达量最高 ,老年组和衰老组显著降低 ,分别为成年组的 75 .6 %和 6 1.2 % ;NOSⅠmRNA的表达与蛋白表达的变化一致 ;老年组NOS活性与成年组差异无显著性 (P >0 .0 5 ) ,衰老组NOS活性明显降低 ,是成年组的70 .4 % ,并且差异非常显著 (P <0 .0 1)。　结论 :衰老引起NOSⅠ 蛋白及mRNA的表达降低和NOS活性的显著降低 ,可能是老年性阴茎勃起功能障碍的主要机制之一。     

大鼠心肌组织中热休克蛋白70水平与NO、NO合酶表达以及心肌细胞凋亡的关系

目的 探讨离体大鼠心肌组织中热休克蛋白70(HSP70)水平与NO、NO合酶(NOS)表达以及心肌细胞凋亡的关系.方法 将Wistar大鼠分为2组,实验组腹腔注射重酒石酸去甲肾上腺素,24 h后取离体心脏,灌注Histidine-trytophan-ketoglurate(HTK)液,置于4℃HTK液中保存3 h,然后以Krebs-Henseleit(K-H)液行Langendorff灌流2 h;对照组腹腔注射蒸馏水0.5 ml,24 h后取离体心脏,冷保存和Langendorff灌流同实验组.灌流结束后,取心肌组织,测定其HSP70、NO和NOS的含量以及心肌细胞凋亡指数.结果 实验组心肌组织中HSP70、NO和NOS的含量分别为(17.8±1.8)%、(8.7±1.7)μmol/g组织和(0.91±0.18)IU/mg组织,均明显高于对照组(P<0.01),而心肌细胞凋亡指数为(5.6±1.0)%,明显低于对照组(P<0.01).HSP70含量与细胞凋亡指数呈负相关(r=-0.946,P<0.01),与NO含量(r=0.087,P<0.01)和NOS含量(r=0.953,P<0.01)呈正相关.结论 心肌组织中HSP70与NO和NOS的表达呈正相关,而与心肌细胞的凋亡呈负相关,促进HSP70的表达可能有利于抑制心肌细胞凋亡.     

Effects of estrogen on nitric oxide synthase expression in rat aorta allograft and smooth muscle cells.

BACKGROUND: We find that chronic estradiol treatment inhibits the development of transplant arteriosclerosis (TA). The mechanism of this inhibition remains unclear. The objective of this study is to investigate in a non-cyclosporin-requiring TA model whether estradiol-17beta treatment modulates the expression of both endothelial nitric oxide synthase (ecNOS) and inducible nitric oxide synthase (iNOS) in the early phase following transplantation. METHODS: Orthotopic abdominal aorta allograft transplantation was performed in male rats using Brown-Norway rats as donors and Lewis rats as recipients. The recipients (n = 50) were treated with estradiol 20 microg/kg/day or placebo by osmotic minipump from 2 days prior to surgery until sacrifice on post-operative days 1, 3, 7, 14, and 21. The allografts were harvested and cross-sections of the vascular tissues were used for immunohistochemical staining of ecNOS and iNOS. The effects of estradiol on cytokine-induced (tumor necrosis factor-alpha and interleukin-1 beta iNOS protein and messenger RNA (mRNA) expression were also evaluated on rat aorta smooth muscle cells by Western blotting and RT-PCR in vitro, respectively. RESULTS: The expression of ecNOS and iNOS was graded semiquantitatively from 0 to +3. Estrogen elevates ecNOS expression in the intima in the early phase following transplantation, 0.85 +/- 0.14 (day 7) and 1.08 +/- 0.11 (day 14) vs 1.53 +/- 0.25 (day 7) and 1.60 +/- 0.17 (day 14) for placebo and estradiol treated groups respectively, p < 0.01. Estrogen suppresses iNOS expression in neointima (0.67 +/- 0.17 vs 0.24 +/- 0.04, p < 0.01, day 14), media (1.03 +/- 0.15 vs 0.4 +/- 0.09, p < 0.01, day 7), and adventitia (1.55 +/- 0.12 vs 1.02 +/- 0.10, p < 0.05, day 14) in the same phase. Estradiol treatment inhibits cytokine-induced iNOS mRNA expression in cultured smooth muscle cells. CONCLUSIONS: Chronic estrogen treatment modulates both ecNOS and iNOS expression in the early phase following transplantation. This is associated with the estrogen-protective effects on TA.     

胆管癌中一氧化氮合酶的表达及其意义

目的 探讨nNOS,iNOS,eNOS的表达与胆管癌临床病理特征及预后的关系.方法 检测和比较胆管癌与正常肝外胆管组织的nNOS,iNOS,eNOS表达.结果 (1)与正常胆管比较,胆管癌中iNOS及eNOS表达增强(P＜0.05),nNOS无表达增强(P＞0.05).(2)iNOS在晚期和中期胆管癌组间阳性表达率差异有显著性(P＜0.01);eNOS在晚期、中期、有无远处转移胆管癌组间阳性表达率差异均有显著性(P＜0.05).(3)eNOS阴性表达组预后明显优于阳性表达组(P＜0.01),nNOS及iNOS表达与预后无关(P＞0.05).结论 (1)胆管癌eNOS的过度表达与胆管癌的临床病理分期、远处转移及预后有关,提示检测胆管癌中eNOS表达可能有助于对胆管癌病情及预后的判断.(2)iOS表达与胆管癌的临床病理分期关系密切,与有无远处及淋巴结转移、预后无关,推测iNOS可能有促进胆管癌的局部浸润生长,促进病情发展的作用.     

Acute and chronic regulation of thick ascending limb endothelial nitric oxide synthase by statins

Statins, 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, acutely increase endothelial nitric oxide synthase (eNOS) activity and chronically increase eNOS expression in endothelial cells. NO decreases transport in thick ascending limbs (TAL). We hypothesized that statins inhibit TAL transport by acutely activating eNOS, thereby increasing NO production and chronically enhancing eNOS expression. Oxygen consumption (QO(2)) by TAL suspensions from Sprague-Dawley rats was used as a measure of active NaCl reabsorption. Na/K ATPase activity was assessed by measuring ATP hydrolysis in the presence and absence of ouabain. eNOS expression was measured by Western blot. A total of 50 micro M pravastatin decreased QO(2) by 18.6 +/- 3.4% (P < 0.01). In the presence of 500 micro M furosemide and 200 micro M amiloride, transport blockers, QO(2) remained the same after pravastatin was added. Na/K ATPase activity was not different from controls and TAL treated with 50 micro M pravastatin (0.33 +/- 0.07 versus 0.29 +/- 0.04 nmol P(i)/ micro g protein/min, where P(i) is inorganic phosphate). Nystatin stimulated QO(2) to 178 +/- 13.7 in pravastatin-treated TAL and 195 +/- 11.5 in furosemide-treated TAL. The inhibitory effect of pravastatin on QO(2) was blocked by L-nitroarginine methyl ester, an NOS inhibitor. In addition, pravastatin increased NO production as measured by the fluorescent dye DAF-2A. Pravastatin at a dose of 10 mg/kg per d had no effect on eNOS protein at 1 d (24.1 +/- 2.7 versus 25.5 +/- 1.1 arbitrary units [AU]) or 7 d (24.1 +/- 2.7 versus 20.9 +/- 1.3 AU). Similarly, at 1 d, 50 mg/kg per d had no effect on expression (24.1 +/- 2.7 versus 21.2 +/- 3.6 AU). At 7 d, this dose decreased eNOS protein from 24.1 +/- 2.7 to 11.8 +/- 4.4 AU. It is concluded that pravastatin acutely decreases NaCl entry into the TAL by releasing NO. Pravastatin does not chronically increase eNOS expression in TAL.