RhoA经基质金属蛋白酶-3、-9通路介导心力衰竭大鼠心肌重塑及心功能恶化

目的:探讨RhoA、Rho激酶、基质金属蛋白酶家族(MMPs)MMP-3、MMP-9表达与心肌重塑及心功能损害的关系。方法:建立假手术组及心力衰竭大鼠(造模12周及20周)模型。应用Nikon 4多导生理记录仪检测血液动力学指标以评价心功能情况,心肌肥厚指数及H-E染色评价心肌重塑情况,并采用RT-PCR方法检测各组大鼠心肌组织RhoA、Rho激酶及MMP-3、MMP-9基因表达。结果:造模20周、造模12周心力衰竭组大鼠与假手术组大鼠对比,随心肌重塑加重、心功能恶化,RhoA、Rho激酶及MMP-3、MMP-9基因表达显著增加,且直线相关分析结果显示RhoA基因表达与Rho激酶、MMP-3、MMP-9基因表达呈正相关趋势。结论:RhoA可能通过刺激MMP-3、MMP-9的表达引起细胞外基质结构发生改变,引起心肌重塑和心功能恶化。     

RhoA和肌球蛋白轻链在肝纤维化大鼠肝组织中的表达

目的观察Rho/Rho激酶信号转导通路关键信号分子RhoA和磷酸化肌球蛋白轻链[p-MLC(Thr18/Ser19)]在大鼠肝纤维化组织中的表达规律。方法HE及Masson三色染色观察肝病理组织学变化;用Western blot检测RhoA、p-MLC(Thr18/Ser19)蛋白的表达;RT-PCR方法检测RhoAmRNA的表达。结果随着肝纤维化的进展,RhoA、p-MLC(Thr18/Ser19)蛋白表达明显增加,RhoAmRNA基因表达也逐渐加强。RhoA和p-MLC(Thr18/Ser19)分别与α-平滑肌肌动蛋白(α-SMA)呈显著正相关。结论Rho/Rho激酶信号转导通路在肝纤维化形成过程中发生变化。     

卡维地洛与压力负荷心衰大鼠心室重塑和Rho激酶表达的关系

目的研究卡维地洛(α1肾上腺素受体阻断剂、β肾上腺素受体非选择性阻断剂)对升主动脉缩窄压力超负荷心力衰竭大鼠心室重塑、RhoA、Rho激酶表达的影响,探讨卡维地洛改善心力衰竭的新机制。方法将升主动脉缩窄术后心力衰竭Wistar雌性大鼠随机分为2组,一组为心力衰竭组,给予生理盐水灌胃,每日2次(n=10);一组为卡维地洛组,12.5mg/Kg卡维地洛灌胃,每日2次(n=10),治疗12周。同时制备模型设置假手术组作为对照(n=10),不予处置。观察各组大鼠各项指标变化。结果与假手术组相比,心力衰竭大鼠心肌肥厚指数增加,HE染色心肌排列紊乱,血液动力学指标明显异常,心肌细胞RhoA、Rho激酶表达显著升高(P<0.05);药物治疗12w后,与心力衰竭组对比,卡维地洛治疗组心肌肥厚指数降低,HE染色示心肌重塑不明显,血液动力学参数改善,RhoA、Rho激酶表达显著降低。结论卡维地洛可通过对心肌细胞α-Gq-RhoA/Rho激酶通路表达干预,明显缓解心力衰竭症状、改善心室重塑,卡维地洛这种α1肾上腺素受体阻断剂可能对心力衰竭更有利。     

羟丁酸钠通过Rho / Rho 激酶信号通路减轻脑缺血再灌注大鼠脑损伤

目的:探讨羟丁酸钠通过Rho/Rho激酶信号通路对脑缺血再灌注大鼠脑损伤的作用。方法:通过右侧血管内大脑中动脉闭塞(MCAO)构建局灶性脑缺血再灌注模型。造模前40 min腹腔给予50、100、200 mg/kg羟丁酸钠,1次/d,连续灌胃1周。尼莫地平组腹腔每天给予0.7 mg/kg尼莫地平,水仙环素组和给药高剂量+水仙环素组以相同方式每天给予10 mg/kg水仙环素。对照组和模型组大鼠注射等体积生理盐水。开场行为检测自发活动情况,T迷宫实验检测学习记忆能力,检测脑组织含水量,HE染色观察脑损伤,TUNEL染色检测脑细胞凋亡情况,qRT-PCR检查RhoA、Rho-kinaseα和Rho-kinaseβmRNA表达水平,Western blot检测cleaved caspase-3、 Bax、Bcl-2、RhoA、Rho-kinaseα和Rho-kinaseβ蛋白表达水平。结果:与模型组相比,给药高剂量组大鼠10 min内爬行经过的格子数目明显减少(P0.01),选择正确次数明显增多(P0.01),脑组织含水量明显减少(P0.01),脑组织细胞凋亡率明显减少(P0.01),脑组织cleaved caspase-3和Bax表达明显下调、Bcl-2表达明显上调(P0.01),脑组织RhoA、Rho-kinaseα和Rho-kinaseβmRNA表达水平明显下调(P0.01),给予Rho/Rho激酶信号通路激活剂水仙环素后,可逆转上述改变。结论:羟丁酸钠通过抑制Rho/Rho激酶信号通路减轻脑缺血再灌注大鼠脑损伤。     

脊髓损伤模型大鼠神经修复与法舒地尔和RhoA基因沉默的干预

背景：研究认为Rho激酶可致使神经生长锥塌陷,对神经修复具有抑制作用。 目的：观察Rho激酶抑制剂法舒地尔及RNA干预介导的RhoA基因沉默对脊髓损伤大鼠在体神经损伤修复的作用。 方法：雄性SD大鼠60只半切法制成脊髓半横断模型,随机等分成对照组、法舒地尔组和RhoA siRNA组。法舒地尔组于腹腔注射10 mg/kg法舒地尔,2次/d,连续用药1周;RhoA siRNA干扰组将RhoA siRNA表达质粒注射于大鼠脊髓损伤区。 结果与结论：伤后4周,法舒地尔和RhoA siRNA组大鼠后肢运动功能均有明显恢复,可见少量神经轴索样结构,辣根过氧化物酶阳性神经纤维数增多(P < 0.05),体感诱发电位的潜伏期明显缩短、波幅显著增强(P < 0.05)。提示大鼠脊髓损伤后给予Rho激酶抑制剂法舒地尔及RNA介导的RhoA基因沉默能够促进受损伤的脊髓神经功能恢复。     

雌激素对大鼠血管平滑肌细胞囊泡素-1基因表达的影响

目的:探讨雌激素对血管平滑肌细胞囊泡素-1基因表达的影响。方法:取Wistar雌性大鼠,分为3组:假手术组,卵巢切除后皮下埋植雌激素组 (OVX+E组)及卵巢切除后皮下埋植安慰剂组(OVX+V组)。用药2周后处死大鼠,剥离主动脉平滑肌组织,提取总RNA进行半定量RT-PCR分析,检测雌激素对囊泡素-1(caveolin-1)基因表达的影响。为进一步明确雌激素是否直接调节血管平滑肌细胞caveolin-1基因表达,又采用100 nmol/L 17β-雌二醇(17β-E₂)处理培养的大鼠血管平滑肌细胞24 h,通过Northern blot分析检测雌激素对细胞caveolin-1 mRNA表达的影响。结果:OVX+E组大鼠主动脉平滑肌组织caveolin-1基因表达量明显高于OVX+V组,17β-E₂处理的培养细胞中caveolin-1基因mRNA表达量高于未用药的培养细胞。 结论:雌激素可促进血管平滑肌细胞caveolin-1基因表达,反映了雌激素心血管作用机理的一个方面。     

三羟异黄酮对去势雌性大鼠主动脉壁NF-κB的表达影响

目的：观察三羟异黄酮(GST)对去势雌性大鼠主动脉壁核因子-Kappa B表达的影响。 方法： 将40只成年雌性大鼠随机分成4组：(1)假手术组，(2)去势组，(3)雌激素组，(4)GST组。给药6周后处死大鼠。免疫组化法检测主动脉壁中NF-κB p65的表达。 结果： 去势大鼠主动脉壁NF-κB p65的表达明显多于假手术组，细胞核呈阳性表达；雌激素组和GST组NF-κB p65的表达明显少。去势组大鼠伴有主动脉血管动脉粥样硬化的病理改变。 结论： GST可抑制NF-κB p65在大鼠主动脉的表达，减轻动脉粥样硬化的病理改变。     

RhoA调节失血性休克大鼠血管反应性的机制

目的： 探讨RhoA调节失血性休克大鼠血管反应性的机制。方法: 采用SD大鼠复制休克模型,取离体血管环,观察Rho激酶、肌球蛋白轻链磷酸酶（MLCP）、肌球蛋白轻链磷酸激酶（MLCK）对RhoA增加血管反应性的作用;同时取原代血管平滑肌细胞（VSMCs）,观察RhoA对缺氧后VSMC Rho激酶、MLCP和MLCK活性的调节作用以及对肌球蛋白轻链（MLC20）磷酸化水平的影响。结果: 失血性休克后大鼠肠系膜上动脉（SMA）对NE收缩反应性明显降低,RhoA的激动剂U-46619可明显升高休克后血管反应性,RhoA特异性抑制剂C3酶可拮抗U-46619所引起的血管收缩反应性的升高。Rho激酶抑制剂Y-27632可降低由U-46619所引起的血管反应性的升高,MLCP的抑制剂Calyculin可进一步增加由U-46619所引起的血管反应性的升高,而MLCK抑制剂对U-46619的作用影响不明显。缺氧后MLCK、Rho激酶活性以及MLC20磷酸化水平明显降低,MLCP活性明显升高,RhoA激动剂U-46619可明显升高缺氧后VSMC的MLC20磷酸化水平、Rho激酶活性和降低MLCP的活性,且U-46619的这一作用可被RhoA抑制剂C3酶所拮抗,调节RhoA的活性对MLCK活性无明显调节作用。结论: RhoA可通过Rho激酶调节MLCP活性和 MLC20磷酸化水平调节休克后血管反应性。     

雌激素对去势大鼠髁突软骨雌激素受体基因表达的影响

目的探讨不同浓度的雌二醇(E2)对去势大鼠髁突软骨雌激素受体(ER)基因ERα和ERβ表达的影响。方法将SD大鼠分为对照组(control)、假手术组(sham)、去势组(OVX)、及时和延迟替代治疗组(OVX/17β-E2),每天静脉注射不同浓度雌二醇(5×10、5×10~2和5×10~3μg/kg),阴道上皮脱落细胞涂片监测雌激素水平,用Western blot和real-time PCR法检测大鼠颞下颌关节髁突软骨ERα和ERβ的蛋白及mRNA表达。结果去势大鼠阴道上皮细胞MI指数180/12/8,表明雌激素水平低下(P0.05)。及时补给生理浓度雌二醇(5×10~2μg/kg)能维持髁突软骨ER于正常范围,延迟补给生理浓度雌二醇不能恢复或改善ER表达;及时和延迟补给高浓度(5×10~3μg/kg)及低浓度(50μg/kg)E2均抑制ER蛋白和mRNA合成(P0.05),且高浓度效应显著。结论及时补充合理浓度的雌激素对去势大鼠颞下颌关节的正常生理功能具有重要意义。     

糖尿病结肠动力障碍结肠平滑肌细胞相关凋亡基因和蛋白表达及其意义

目的 探讨糖尿病(DM)结肠动力障碍结肠平滑肌细胞的相关凋亡基因和蛋白表达情况.方法 36只雄性SD大鼠随机分为对照6和10周组、DM 6和10周组,每组9只.检测空腹血糖(FBG)、胃肠推进率及血清胰岛素(FINS),HE染色观察结肠平滑肌变化,荧光实时定量PCR(RT-qPCR)检测结肠平滑肌细胞的BAX、BCL-2及caspase-3的mRNA表达,免疫组化法检测caspase-3蛋白表达.结果 (1)DM组大鼠较同时间点对照组大鼠空腹血糖显著增高,胃肠推进率及血清胰岛素显著降低,结肠平滑肌变薄,BAX及caspase-3的mRNA表达增强,CCL-2的mRNA表达降低,caspase-3蛋白表达增强(对照6和10周组分别为4694±807、4711±812;DM 6和10周组分别为6 974±952、12474±967)(P<0.01);(2)DM 10周组较DM 6周组上述变化进一步增加(P<0.05).结论 糖尿病结肠动力障碍可能与结肠平滑肌细胞的凋亡基因和蛋白表达改变密切相关,且细胞凋亡可能随病程发展而加重.     

Developmental changes in contraction of gastric smooth muscle cells in rats correlate with their differences in RhoA/ROCK pathway

Previous research has shown that smooth muscle of the stomach undergoes developmental changes in the intracellular regulatory mechanism responsible for the contractile process. Whether these developmental changes relate to differences in the expression and/or activity of the key enzymes regulating smooth muscle contraction has not been previously evaluated. Therefore, we aimed to examine the expression and activation of the small monomeric G protein "RhoA" and Rho kinase (ROCK) as well as their correlation with the contraction of gastric smooth muscle cells (GSMCs) in newborn vs. adult rats. Freshly isolated single GSMCs from Sprague-Dawley rats at 1 week (newborn) and 3 months (adult) of age were used in the study. Protein and mRNA expression levels of both ROCK2 and total RhoA were higher in adult compared to newborn rats. Moreover, acetylcholine (ACh)-induced contractions of GSMCs in adult rats were significantly higher than that in newborn animals. Meanwhile, ROCK and Rho activation was higher in adult stomach cells compared to newborn ones. Pretreatment of GSMCs with Y-27632, the ROCK inhibitor, significantly reduced ACh-induced contraction in both groups of cells and greatly abolished contractile differences. In conclusion, our results indicate that RhoA/ROCK pathway and contraction of stomach muscle cells are under developmental regulation.     

Rho-kinase and contractile apparatus proteins in murine airway hyperresponsiveness

Airway hyperresponsiveness (AHR) is a hallmark of bronchial asthma. Increased expression of smooth muscle contractile proteins or increased responsiveness of the contractile apparatus due to RhoA/Rho-kinase activation may contribute to AHR. BALB/c mice developed AHR following systemic sensitization by intraperitoneal injections of 20 microg ovalbumin (OVA) in presence of 2mg Al(OH)(3) on days 1 and 14, and airway challenge by 1% OVA-inhalation for 20 min each on days 28, 29 and 30. As assessed by Western blot, protein expression of RhoA, MLC (myosin light chain) and smMLCK (smooth muscle myosin light chain kinase) was increased in lungs of OVA/OVA-animals with AHR, as well as in lungs of OVA-sensitized and sham-challenged animals (OVA/PBS) without AHR, compared with lungs of PBS/PBS-animals. Pretreatment with the specific Rho-kinase inhibitor Y-27632 reduced MLC-phosphorylation and AHR. Contribution of Rho-kinase to bronchoconstriction was increased in lungs of OVA/OVA-animals compared with OVA/PBS- and PBS/PBS-animals, respectively. Furthermore, bronchoconstriction following MCh stimulation was significantly reduced after Y-27632 application. In conclusion, systemic allergen-sensitization increased pulmonary expression of proteins involved in smooth muscle contraction, which may contribute to development of AHR. However, this observation was independent from local allergen challenge, suggesting that additional cofactors may be required for the activation of Rho-kinase and thereby the induction of AHR. Rho-kinase may play an important role in murine AHR, and the bronchodilating action of Rho-kinase inhibition may offer a new therapeutic perspective in obstructive airway disease.     

17Beta-estradiol rapid stimulation of rat aorta NOS activity is prevented by oestrogen deficiency

OBJECTIVES: The purpose of this study was to determine the effects of chronic oestrogen deficiency on rat aorta rapid response to 17beta-estradiol treatment. METHODS: Rat aortic strips (RAS) were isolated from Wistar female rats of three different groups: rats 6-7-month old with normal oestrogen levels (NER); aged rats, 24-month old, with low oestrogen levels (LER); and young rats after 2 months of bilateral ovariectomy (OVX). Platelet aggregation was measured after incubation of RAS in a platelet rich plasma by addition of 10 microM ADP. NO production by RAS was measured by 3H-citrulline technique. RESULTS: RAS obtained from NER treated with 17beta-estradiol produced an inhibition of platelet aggregation specific for ovarian hormones, since testosterone was devoid of any effect. In aortic tissue isolated from male rats no increment in nitric oxide (NO) production was found. RAS from LER and OVX treated with 1-10 nM failed to induce a significant inhibition of platelet aggregation compared with NER (5 and 17%; 6 and 20% vs. 45 and 77% inhibition of platelet aggregation respect to control, respectively). In contrast to NER, 5 min treatment of LER and OVX aortic tissue with 1 nM 17beta-estradiol did not incremented NO production (NER 1.14 vs. 2.3 (P < 0.05); LER 1.14 vs. 1.42; OVX 1.24 vs. 1.52 pmol NO per mg protein). CONCLUSIONS: These results suggest that chronic oestrogen deprivation impairs the inhibition of platelet aggregation and suppresses the rapid stimulation of aortic NOS induced by acute 'in vitro' treatment with 17beta-estradiol.     

重组ACE2抑制人脐动脉平滑肌细胞Profilin-1表达及增殖

 摘要 目的：探讨重组血管紧张素转换酶2（ACE2）基因对血管平滑肌细胞前纤维蛋白-1（Profilin-1）表达及细胞增殖的影响。方法：培养人脐动脉平滑肌细胞（HUASMC），用重组ACE2基因（rACE2）干预，进行血管紧张素II（Ang II）刺激实验，分别用MTT法、实时定量PCR及Western blot检测HUASMC增殖与Profilin-1表达。 结果：与对照组相比，经Ang II（100 nmol /L）刺激6 h后，HUASMC中Profilin-1 表达明显增高（3.50±0.30 vs. 1.00±0.10, P<0.05）。而重组ACE2基因干预显著抑制上述增加（1.73±0.12 vs. 3.50±0.30, P<0.05）。结论：ACE2基因过表达可明显逆转HUASMC中Ang II诱导的Profilin-1表达上调。     

Effect of oestrogen on myofibre size and myosin expression in growing rats

This study examined the effect of oestrogen deprivation and replacement on plantaris muscle size and myosin heavy chain (MHC) isoform composition in rats during a period of physiological growth. Seven-week-old female Sprague-Dawley rats were assigned to one of the three treatment groups: (1) control animals (Sham); (2) ovariectomized animals without oestrogen replacement (OVX/CO); and (3) ovariectomized animals with 17beta-oestradiol replacement (OVX/E2). OVX/CO and OVX/E2 animals were pair-fed with Sham animals to rule out the potentially confounding effects of differences in food intake and weight gain. Rats were killed 4 weeks after surgery and the plantaris muscle was removed for analysis. Ovariectomy had no effect on muscle fibre size, but reduced the relative amount of type IIx MHC. This was reversed with oestrogen replacement, suggesting that the reduction in type IIx MHC expression was an oestrogen-mediated effect. Oestrogen replacement reduced type IIb MHC expression and fast muscle fibre size. Changes in fast fibre size and type IIb MHC expression were not seen with ovariectomy, indicating that these changes were not simply due to the presence of oestrogen in the ovariectomized, oestrogen-replaced animals. These results suggest that another ovarian hormone may counteract the effect of oestrogen on fast fibre size and type IIb MHC expression in intact animals.     

Signal transduction by G-proteins, Rho-kinase and protein phosphatase to smooth muscle and non-muscle myosin II

We here review mechanisms that can regulate the activity of myosin II, in smooth muscle and non-muscle cells, by modulating the Ca²⁺ sensitivity of myosin regulatory light chain (RLC) phosphorylation. The major mechanism of Ca²⁺ sensitization of smooth muscle contraction and non-muscle cell motility is through inhibition of the smooth muscle myosin phosphatase (MLCP) that dephosphorylates the RLC in smooth muscle and non-muscle. The active, GTP-bound form of the small GTPase RhoA activates a serine/threonine kinase, Rho-kinase, that phosphorylates the regulatory subunit of MLCP and inhibits phosphatase activity. G-protein-coupled release of arachidonic acid may also contribute to inhibition of MLCP acting, at least in part, through the Rho/Rho-kinase pathway. Protein kinase C(s) activated by phorbol esters and diacylglycerol can also inhibit MLCP by phosphorylating and thereby activating CPI-17, an inhibitor of its catalytic subunit; this mechanism is independent of the Rho/Rho-kinase pathway and plays only a minor, transient role in the G-protein-coupled mechanism of Ca²⁺ sensitization. Ca²⁺ sensitization by the Rho/Rho-kinase pathway contributes to the tonic phase of agonist-induced contraction in smooth muscle, and abnormally increased activation of myosin II by this mechanism is thought to play a role in diseases such as high blood pressure and cancer cell metastasis.     

Site difference in RhoA expression between rat bronchial and tracheal smooth muscles after antigen challenge - relation to development of hyperresponsiveness

OBJECTIVE: The present study compared the effects of repeated antigen exposure on the development of hyperresponsiveness and the expression of RhoA in the main bronchial and lower tracheal smooth muscles of sensitized METHODS: Actively sensitized rats were repeatedly challenged by antigen inhalation. Twenty-four hours after the final antigen challenge the isometrical contractions of the bronchial and tracheal smooth muscles were measured. Immunoblottings were also performed using bronchial and tracheal homogenates and the density ratios of RhoA/beta-actin were calculated to quantify the levels of RhoA. RESULTS: Acetylcholine-induced contraction of bronchial, but not tracheal, smooth muscle of antigen-treated rats was significantly augmented as compared with that of control rats, indicating that airway hyperresponsiveness appeared by antigen challenge in bronchial smooth muscle. RhoA expression in bronchial, but not tracheal, smooth muscle was significantly increased in the antigen-treated animals. CONCLUSION: The increased expression of RhoA is suggested to have an important role in developing hyperresponsiveness of bronchial smooth muscle.     

脾切除对门脉高压症大鼠CD4、CD8和脾功能的影响

目的:研究肝硬化门脉高压症（PHT）大鼠脾次全切除术后CD4、CD8与脾功能的变化。 方法: 皮下注射60％四氯化碳复制大鼠肝硬化模型。共分5组：正常大鼠组、肝硬化（PHT）组、正常大鼠脾切除组、PHT全脾切除组、PHT脾次全切除组，每组10只。手术后第4周检测各组血常规、肝功能、tuftsin、CD4、CD8等指标。 结果:PHT高压症大鼠脾切除术后tuftsin水平［（171±21）ng/L vs （433±44） ng/L,P<0.01］、CD4/CD8（2.01±0.22 vs 1.12±0.12, P<0.01)均显著低于PHT组;PHT大鼠脾次全切除组tuftsin［（434±42）ng/L vs （171±21）ng/L, P<0.01］、CD4/CD8 （1.97±0.18 vs 1.12±0.12, P<0.01)显著高于PHT大鼠脾切除组。肝功能两者无显著差异（P>0.05）。 结论: PHT脾次全切组大鼠术后免疫和脾功能比PHT脾全切组大鼠明显改善，肝功能两者无显著变化。     

一氧化氮及其信号转导通路在糖尿病性勃起功能障碍的作用

勃起功能障碍（erectile dysfunction,ED）是糖尿病的常见并发症,影响人们的生活质量,其病变机理还不甚清楚.一氧化氮（NO）由一氧化氮合酶（NOS）合成,是调节海绵体肌肉松弛和阴茎勃起的重要的神经递质.PI3-kinase/Akt （PKB）通路使eNOS磷酸化,NO的产量增加;NO/cGMPPKG通路参与平滑肌的舒张;RhoA和Rho-kinase参与平滑肌的收缩,抑制eNOS基因表达和酶的活性.周围血管病变和自主神经变性是引起糖尿病性ED的主要原因之一.基因和干细胞（eNOS、 RhoA/Rho-kinase与Mesenchymal stem cell-based cell）治疗糖尿病性ED取得一些进展.     

Rho-kinase activation is involved in hypoxia-induced pulmonary vasoconstriction.

Rho-associated serine/threonine kinase (Rho-kinase) is a downstream effector of small GTPase RhoA that has recently been shown to play an important role in regulating smooth muscle contraction. The present study investigated the role of Rho/ Rho-kinase in hypoxia-induced pulmonary vasoconstriction (HPV). Small pulmonary resistance vessels and cultured pulmonary arterial smooth muscle cells (PASMCs) from the rat were used. PASMCs exposed to hypoxia (PO(2) = 26 +/- 2 mm Hg) showed a significant increase in Rho-kinase activity. Exposure to hypoxia for 20, 40, 60, 90, and 120 min also resulted in a significant increase in myosin light chain (MLC) phosphorylation at all time points in PASMCs. Hypoxia-induced MLC phosphorylation was inhibited by Y-27632 (a Rho-kinase inhibitor), exoenzyme C3 (a specific Rho inhibitor), or toxin B (an inhibitor for Rho proteins). In addition, hypoxia-induced Rho-kinase activation was blocked by C3 and toxin B. Small rat intrapulmonary arterial rings, which were made hypoxic (PO(2) = 30 +/- 3 mm Hg), showed a slow sustained contraction, and Y-27632 caused a significant relaxation during the sustained phase of HPV in a concentration-dependent manner. In summary, the data show that Rho-kinase is activated by hypoxia in PASMCs, and Rho/Rho-kinase is functionally linked to hypoxia-induced MLC phosphorylation and plays a role in the sustained phase of HPV.