Thapsigargin-Insensitive Calcium Pools in Vascular Smooth Muscle Cells

Since sarcoplasmic Ca²⁺-ATPase may play an important role for the regulation of cytosolic free calcium concentration ([Ca²⁺]_i) and may be altered in primary hypertension, the effects of thapsigargin and bradykinin on intracellular calcium pools in cultured vascular smooth muscle cells (VSMC)     

Lead-Induced Hypertension Is Not Associated With Altered Vascular Reactivity In Vitro

In confirmation of a previous study (Am J Hypertens 1993;6:723), mean arterial blood pressure (MBP), as determined by tail cuff plethysmography, was found to be significantly elevated in Sprague-Dawley rats after 3 months of feeding 0.48 mmol/L (100 ppm) lead acetate/day (144 ± 3.3 [SEM], in lead-treated [L] v 107 ± 3.3 mm Hg in controls [C], P < .001). Thoracic aorta was excised from L and C animals (n = 6). Segments were suspended in tissue baths with Krebs’ bicarbonate solution, then tested sequentially for vasoreactivity to 68 mmol/L K⁺, followed by graded concentrations of phenylephrine (PE), 0.01 to 0.3 μmol/L, acetylcholine (Ach), 0.001 to 3 μmol/L, nitroprusside (SNP), 0.0001 to 0.1 μmol/L, norepinephrine (NE), 0.001 to 300 μmol/L. There were no differences between L and C animals with respect to either vasoconstrictors (PE and NE) or vasodilators (Ach and SNP). The tissue levels of cGMP measured with and without phosphodiesterase inhibition, and in the absence and presence of either Ach or SNP, were comparable in the two groups. We conclude that the intrinsic vascular responsiveness is unchanged in lead-treated animals. The elevation of MBP is due to the presence of circulating factor(s) and hemodynamic changes.     

Autocrine Effects of Endothelin on In Vitro Proliferation of Vascular Smooth Muscle Cells from Spontaneously Hypertensive and Normotensive Rats

According to previous studies, endothelin-1 (ET-1) is the most potent growth factor in the regulation of vascular smooth muscle cell (VSMC) proliferation in spontaneously hypertensive rats (SHR). To evaluate if the dominant effect of ET-1-induced VSMC proliferation is achieved by autocrine regulation, aortic smooth muscle cells from four-week-old SHR and WKY (Wistar-Kyoto) rats were cultured in 24-well dishes, and the effects of ET-1 on VSMC proliferation were determined by (a) ³H-thymidine incorporation assays with different ET-1 blocking treatments, including a specific anti-ET-1 antibody; BQ-123, an ETA receptor blocker; and BQ-788, an ETB receptor blocker; and (b) examining the ET-1 blockade on the effects of treatment with other growth factors, including thrombin and angiotension II (AT-II). These results demonstrated that the anti-ET-1 antibody, BQ-123, BQ-788, and BQ-123 plus BQ-788 all caused dose-dependent inhibition of proliferation. A 90% inhibitory effect was observed at the maximum doses used except for BQ-123. The ET-1 receptor blockers inhibited thrombin-induced VSMC growth; however, they did not efficiently inhibit AT-II-induced VSMC growth. These results indicate that the autocrine effects of ET-1 play a predominant role in the proliferation of VSMCs from SHR and WKY rats. They also suggest that thrombin-induced VSMC growth is mediated by the autocrine effects of ET-1, and angiotensin II-induced VSMC growth is mediated by other signal pathways.     

大鼠胸主动脉平滑肌细胞的培养与鉴定

目的 改进大鼠血管平滑肌细胞(VSMC)的培养方法.方法 采用机械刮除、差异贴壁等手段进行组织贴块法原代培养,胰蛋白酶消化传代,并应用相差显微镜和即用型SABC免疫组化染色试剂盒对细胞进行形态学和免疫组化鉴定.结果 镜下培养细胞呈典型的"谷峰状"生长,免疫组化染色显示胞浆内αactin阳性表达.结论 本法可获纯度高、结构和功能良好的VSMCs.     

细胞内钙信号的变化调节血管平滑肌细胞增殖

目的探讨细胞内钙信号的变化对大鼠血管平滑肌细胞(VSMC)增殖作用的影响及其对细胞内信号转导机制的变化。方法以培养的大鼠VSMC为模型,用雷尼丁(RY)剌激VSMC内贮Ca2 释放入胞浆,用3H亮氨酸及3H胸腺嘧啶掺入量作为反应VSMC增殖的指标,加入不同的细胞内信号转导阻断剂,观察对RY效应的影响。结果与对照组相比,RY浓度依赖性地促进细胞内游离钙浓度的增高,差异显著(P<0.05或0.01)。RY剌激组蛋白核酸合成速率明显增高,与对照组相比差异显著(P<0.01);尼卡地平(Nicardipine),蛋白激酶C抑制剂(H7),钙调素激酶(CaMPK)抑制剂(W7)和丝裂素活化蛋白激酶(MAPK)抑制剂(PD98059)能明显抑制RY介导的VSMC蛋白核酸合成速率增高,与RY剌激组相比差异显著(P<0.01)。结论细胞内钙信号的变化明显促进VSMC增殖,但其效应可能通过Ca2 、PKC、MAPK来介导。钙离子拮抗剂可抑制血管平滑肌细胞增殖。     

细胞内钙信号的变化调节血管平滑肌细胞增殖

目的探讨细胞内钙信号的变化对大鼠血管平滑肌细胞(VSMC)增殖作用的影响及其对细胞内信号转导机制的变化.方法以培养的大鼠VSMC为模型,用雷尼丁(RY)刺激VSMC内贮Ca2+释放入胞浆,用3H-亮氨酸及3H-胸腺嘧啶掺入量作为反应VSMC增殖的指标,加入不同的细胞内信号转导阻断剂,观察对RY效应的影响.结果与对照组相比,RY浓度依赖性地促进细胞内游离钙浓度的增高,差异显著(P＜0.05或0.01).RY刺激组蛋白核酸合成速率明显增高,与对照组相比差异显著(P＜0.01);尼卡地平(Nicardipine),蛋白激酶C抑制剂(H7),钙调素激酶(CaM-PK)抑制剂(W7)和丝裂素活化蛋白激酶(MAPK)抑制剂(PD98059)能明显抑制RY介导的VSMC蛋白核酸合成速率增高,与RY刺激组相比差异显著(P＜0.01).结论细胞内钙信号的变化明显促进VSMC增殖,但其效应可能通过Ca2+、PKC、MAPK来介导.钙离子拮抗剂可抑制血管平滑肌细胞增殖.     

Metformin Attenuates Agonist-Stimulated Calcium Transients in Vascular Smooth Muscle Cells

Metformin, an antidiabetic agent that increases insulin sensitivity, has been shown to lower blood pressure. However, the mechanism of action of metformin in vascular smooth muscle (VSM) cell is not fully understood. We have tested the hypothesis that metformin produces vascular changes by direct interaction with VSM cells by investigating its effect on platelet-derived growth factor (PDGF)- and angiotensin II (ANG II)-stimulated intracellular calcium concentration ([Ca²⁺]_i) and VSM cell proliferation in response to PDGF in cultured cells. VSM cells were cultured from rat thoracic aorta and [Ca²⁺]_i was estimated in single cells by image analysis. Treatment of VSM cells with 1 or 2 μg/ml metformin significantly decreased (p < 0.05) PDGF- or ANG II-stimulated [Ca²⁺]_i. Treatment of VSM cells with 1, 2, 5, or 10 μg/ml metformin had no significant effect on PDGF-stimulated [³H]-thymidine incorporation. However, metformin at pharmacological doses of 20 and 50 μg/ml significantly reduced (p< 0.05) PDGF-stimulated thymidine incorporation. We conclude that metformin mediates its vascular effects by attenuating agonist-stimulated [Ca²⁺]i.     

神经肽Y对大鼠血管平滑肌细胞内钙离子浓度的影响

目的 应用激光共聚焦显微镜动态观察神经肽Y(NPY)受体激动剂[Leu31, Pro34]-NPY干预大鼠血管平滑肌细胞(VSMC)产生的细胞内钙离子([Ca2 ]i)浓度变化,以确定NPY对大鼠VSMC[Ca2 ]i浓度的影响.方法 用分散细胞培养法培养VSMC.用10 μmol/L的Fluo-3孵育细胞.使其与细胞内的游离[Ca2 ]i相结合,从而能够在525 nm的激发光激发下产生荧光.分别用正常细胞外液、无钙细胞外液稀释的10-6 mol/L[Leu31, Pro34 ]-NPY、1 μmol/L硝苯地平、10-6 mol/L[Leu31, Pro34 ]-NPY 1 μmol/L硝苯地平灌流细胞,同时用激光共聚焦显微镜扫描、记录图像.用Leica图像分析系统分析图像,定量分析不同情况下的[Ca2 ]i荧光强度.结果 正常细胞外液灌流时[Ca2 ]i变化不明显,最高值为57.3±3.1,最低值为53.7±2.9,无明显差异(P＞0.05). [Leu31, Pro34]-NPY干预细胞时,[Ca2 ]i明显地升高,随后又开始下降.最高值为86.4±2.7,最低值为58.1±3.0,有非常显著差异(P＜0.01).无钙细胞外液 [Leu31, Pro34 ]-NPY灌流VSMC时[Ca2 ]i浓度变化不明显,最高值为52.5±3.5,最低值为48.0±1.2(P＞0.05);[Leu31, Pro34 ]-NPY 硝苯地平组[Ca2 ]i变化不明显,最高值为52.6±2.1,最低值为51.7±2.7,差异无统计学意义(P＞0.05).硝苯地平组[Ca2 ]i呈下降趋势,最高值为52.8±2.2,最低值为37.5±2.1,有非常显著差异(P＜0.01).结论 NPY能够通过NPY-Y1受体使细胞内的[Ca2 ]i浓度升高,这种升高是依赖于细胞外的[Ca2 ]i由L型[Ca2 ]i通道进入细胞的.     

神经肽Y对大鼠血管平滑肌细胞内钙离子浓度的影响

目的应用激光共聚焦显微镜动态观察神经肽Y(NPY)受体激动剂[Leu31,Pro34]-NPY干预大鼠血管平滑肌细胞(VSMC)产生的细胞内钙离子([Ca2 ]i)浓度变化,以确定NPY对大鼠VSMC[Ca2 ]i浓度的影响。方法用分散细胞培养法培养VSMC。用10μmol/L的Fluo-3孵育细胞。使其与细胞内的游离[Ca2 ]i相结合,从而能够在525nm的激发光激发下产生荧光。分别用正常细胞外液、无钙细胞外液稀释的10-6mol/L[Leu31,Pro34]-NPY、1μmol/L硝苯地平、10-6mol/L[Leu31,Pro34]-NPY 1μmol/L硝苯地平灌流细胞,同时用激光共聚焦显微镜扫描、记录图像。用Leica图像分析系统分析图像,定量分析不同情况下的[Ca2 ]i荧光强度。结果正常细胞外液灌流时[Ca2 ]i变化不明显,最高值为57.3±3.1,最低值为53.7±2.9,无明显差异(P>0.05)。[Leu31,Pro34]-NPY干预细胞时,[Ca2 ]i明显地升高,随后又开始下降。最高值为86.4±2.7,最低值为58.1±3.0,有非常显著差异(P<0.01)。无钙细胞外液 [Leu31,Pro34]-NPY灌流VSMC时[Ca2 ]i浓度变化不明显,最高值为52.5±3.5,最低值为48.0±1.2(P>0.05);[Leu31,Pro34]-NPY 硝苯地平组[Ca2 ]i变化不明显,最高值为52.6±2.1,最低值为51.7±2.7,差异无统计学意义(P>0.05)。硝苯地平组[Ca2 ]i呈下降趋势,最高值为52.8±2.2,最低值为37.5±2.1,有非常显著差异(P<0.01)。结论NPY能够通过NPY-Y1受体使细胞内的[Ca2 ]i浓度升高,这种升高是依赖于细胞外的[Ca2 ]i由L型[Ca2 ]i通道进入细胞的。     

血管损伤影响离体平滑肌细胞增殖与钙稳态有关

本实验采用球囊剥脱术在体损伤血管，于术后３天和１０天取出血管做平滑肌细胞培养。结果发现，血管损伤后血管平滑肌细胞增殖活性显著增加，ＤＮＡ和蛋白质合成加速，细胞数目增多。在血管平滑肌细胞增殖过程中，钙内流增加，胞内钙含量升高。应用１０μｍｏｌ·Ｌ￣（－１）异搏定不但对钙稳态变化有一定的抑制作用，而且还对血管损伤诱导的平滑肌细胞增殖有抑制作用。这些结果提示血管损伤可致血管平滑肌细胞增殖；钙稳态失衡可能是血管损伤诱导血管平滑肌细胞增殖的细胞学机制之一。     

钙磷诱导大鼠血管平滑肌细胞钙化的机制研究

目的：探讨氧化应激损伤在钙磷诱导的血管平滑肌细胞（VSMCs）钙化过程中的作用机制。
　　方法：采用氯化钙（CaCl2）联合β-甘油磷酸钠（β-GP）建立大鼠VSMCs钙化模型。实验分为4组,对照组、钙化组、钙化+过氧化氢（H2O2）组和钙化+过氧化氢酶组。8天后分别通过茜素红S染色法和邻甲酚肽络合酮比色法检测各组细胞钙结节形成及钙含量;活性氧检测试剂盒（DCFH-DA探针）检测各组细胞活性氧阳性细胞数;蛋白免疫印迹法检测各组细胞中成骨转录因子Runx2的蛋白表达量。
　　结果：钙化组活性氧的产生、钙结节、钙含量及Runx2蛋白表达量均显著高于对照组,钙化+过氧化氢组与钙化组相比,各项指标进一步升高,差异有统计学意义（P<0.05）。钙化+过氧化氢酶组活性氧产生量、钙结节、钙含量及Runx2蛋白表达量均低于钙化组和钙化+过氧化氢组,仍高于对照组,差异有统计学意义（P<0.05）,但其中Runx2蛋白表达量与对照组相比则差异无统计学意义（P>0.05）。
　　结论：氯化钙联合β-GP通过激活ROS-Runx2信号通路诱导大鼠VSMCs钙化形成。     

红细胞抗高血压因子对自发性高血压大鼠血管平滑肌细胞游离钙浓度的影响

观察从人红细胞中提取的抗高血压因子（ＡＨＦ）对自发性高血压大鼠（ＳＨＲ）和正常血压ＷＫＹ大鼠培养的主动脉平滑肌细胞胞内游离Ｃａ２＋浓度（［Ｃａ２＋］ｉ）的影响。结果ＳＨＲ和ＷＫＹ大鼠静息［Ｃａ２＋］ｉ无显著差别。ＫＣｌ（６０ｍｍｏｌ／Ｌ）对ＳＨＲ的激活显著大于ＷＫＹ大鼠，ＡＨＦ（１０－４ｇ／ｍｌ）可明显抑制由高钾诱导的［Ｃａ２＋］ｉ升高，对ＳＨＲ的抑制程度明显高于ＷＫＹ大鼠；去甲肾上腺素（ＮＥ，０．１ｍｍｏｌ／Ｌ）对两种大鼠的激活程度无显著差异。ＡＨＦ（１０－４ｇ／ｍＬ）也可明显抑制由ＮＥ（０．１ｍｍｏｌ／Ｌ）所诱导的ＶＳＭＣ［Ｃａ２＋］ｉ升高，对两种大鼠的抑制程度无显著差异。结论ＡＨＦ的降压作用可能与抑制细胞内［Ｃａ２＋］ｉ升高有关。     

雌激素对血管平滑肌细胞内游离钙的调节作用

目的：动态观察雌二醇（Ｅ２）对单个血管平滑肌细胞内游离钙离子浓度及血管紧张素Ⅱ引致的细胞内钙离子浓度变化的影响，以探讨雌激素对平滑肌细胞内储存钙释放的调节作用。方法：体外培养健康雌性兔胸主动脉中层平滑肌，细胞接种在５７０型粘附式细胞仪专用的培养皿中，加入１０－５、１０－７、１０－９ｍｏｌ／Ｌ３种不同浓度的Ｅ２处理。另用３种不同浓度的Ｅ２预处理细胞１小时后，加入血管紧张素Ⅱ。实验分单纯血管紧张素Ⅱ处理组和血管紧张素Ⅱ＋不同浓度Ｅ２预处理组，用ｆｕｒａ－３法测定细胞内钙离子浓度。结果：３种浓度Ｅ２对平滑肌细胞内游离钙离子浓度的基础水平无影响，但１０－５、１０－７ｍｏｌ／Ｌ的Ｅ２预处理细胞后血管紧张素Ⅱ未能激发细胞内游离钙离子浓度升高。结论：雌激素可能参与血管紧张素Ⅱ诱导的血管平滑肌细胞内钙离子浓度变化的调节     

高血压大鼠动脉平滑肌细胞钙超载与腺苷三磷酸酶

目的探讨自发性高血压大鼠(SHR)动脉血管平滑肌细胞钙超载与腺苷三磷酸酶(AT-Pase)的关系。方法组织块种植法培养SHR和Wistar-Kyoto(WKY)大鼠胸主动脉平滑肌细胞,应用流式细胞术、生化酶学方法和逆转录聚合酶链反应(RT-PCR)技术等检测SHR和WKY大鼠动脉平滑肌细胞内游离钙浓度([Ca2 ]i)、细胞膜Ca2 -ATPase和Na -K -ATPase活性及其mRNA表达水平。结果SHR动脉平滑肌细胞[Ca2 ]i浓度高于WKY大鼠[(307.7±32.1vs118.9±21.4)nmol/L,P<0.01)],Ca2 -ATPase和Na -K -ATPase活性低于WKY大鼠(1.3±0.2vs2.6±0.3;3.1±0.5vs4.9±0.5,P均<0.01),细胞质膜Ca2 -ATPase(plasmamembraneCa2 -ATPase,PMCA)亚型1和Na -K -ATPaseα1亚单位mRNA表达低于WKY大鼠(0.231±0.007vs0.403±0.021;0.253±0.028vs0.634±0.033,P均<0.01)。结论SHR动脉平滑肌细胞出现钙超载,其机制可能部分与细胞膜PMCA和Na -K -ATPase活性降低有关,两种ATPase功能降低可能是其基因转录水平下调的结果。     

高血压大鼠动脉平滑肌细胞钙超载与腺苷三磷酸酶

目的探讨自发性高血压大鼠(SHR)动脉血管平滑肌细胞钙超载与腺苷三磷酸酶(ATPase)的关系.方法组织块种植法培养SHR和Wistar-Kyoto( WKY )大鼠胸主动脉平滑肌细胞,应用流式细胞术、生化酶学方法和逆转录聚合酶链反应(RT-PCR)技术等检测SHR和WKY大鼠动脉平滑肌细胞内游离钙浓度([Ca2 ]i)、细胞膜Ca2 -ATPase和Na -K -ATPase活性及其mRNA表达水平.结果SHR动脉平滑肌细胞[Ca2 ]i浓度高于WKY大鼠[(307.7±32.1 vs 118.9±21.4)nmol/L,P<0.01)],Ca2 -ATPase和Na -K -ATPase活性低于WKY大鼠(1.3±0.2 vs 2.6±0.3; 3.1±0.5 vs 4.9±0.5,P均<0.01),细胞质膜Ca2 -ATPase(plasma membrane Ca2 -ATPase, PMCA)亚型1和Na -K -ATPase α1亚单位 mRNA表达低于WKY大鼠(0.231±0.007 vs 0.403±0.021;0.253±0.028 vs 0.634±0.033,P均<0.01).结论SHR动脉平滑肌细胞出现钙超载,其机制可能部分与细胞膜PMCA和Na -K -ATPase活性降低有关,两种ATPase功能降低可能是其基因转录水平下调的结果.     

Endothelin-Induced Renal Vasoconstriction and Increase in Cytosolic Calcium in Renal Vascular Smooth Muscle Cells

This study was designed to investigate the effects of the potent vasoconstrictor, endothelin, on renal hemodynamics in rats in vivo, and in addition, to measure intracellular calcium ion ([Ca²⁺].) in monolayers of renal vascular smooth muscle cells in culture using the fura-2 method. Endothelin (1 nmol) dramatically decreased renal blood flow from 7.0±0.5 ml/min to 2±6±1±0 ml/min, whereas it increased mean arterial pressure from 100±2 mmHg to 113±7 mmHg. These alterations persisted over 20 minutes in conscious and almost unrestrained rats. Endothelin (10^?8 -10^?7 mol/l) immediately increased [Ca²⁺]_i, although the increase by endothelin (10^?9 mol/l) was relatively slow. The increase persisted in the presence of 1 mmol/l extracellular calcium. In the absence of extracellular calcium, only a small, transient increase of [Ca²⁺]_i was observed. These results indicate that endothelin produces renal vasoconstriction and increases the [Ca²⁺]_i in cultured renal vascular smooth muscle cells. The latter effect is dependent mainly on extracellular calcium.     

Growth Properties and Receptor Expression in Vascular Smooth Muscle Cells from Hypertensive Rats

The objective of this study was to evaluate the growth properties and receptor expression in aorta-ring derived smooth muscle cells (SMCs) cultured from control (WKY) and spontaneously hypertensive rats (SHR). SHR-SMCs exhibited a 3–4 day lag period before migrating. In addition, SHR-SMCs had a significantly higher growth rate, shorter population doubling time and higher saturation density level characteristics that were retained at higher passage levels. O-adrenergic and angiotensin (AII) receptors were measured using iodocyanopindolol (ICYP) and [3H]-All, respectively. All receptor expression was similar in both WKY and SHR-SMC cultures. WKY-SMCs exhibited little ICYP binding (Bmax 8.27± 2.0 fmol/mg) while SHR-SMC binding capacity was 8 fold higher (Bmax 65± 9.2 fmol/mg). In addition, the responsiveness of the P-receptor, as assessed by adenylyl cyclase stimulation, was similar for WKY and SHR-SMCs. These data suggest that factors regulating SMC receptor expression in vitro are selective since All and adrenergic receptor densities exhibit different responses to hypertension.     

In Vitro Vascular Reactivity to Endothelin: A Comparison Between Young and Old Normotensive and Hypertensive Rats

In this study we have investigated whether the vascular smooth muscle of a large capacitance artery of spontaneously hypertensive rats (SHR) is hyperresponsive to endothelin-1 and whether the arterial responsiveness to endothelin-1 is affected by aging. Isometric contractions of spirally cut aortic strips from SHR of 11, 22, 33 and 44 weeks of age and from age-matched WKY were measured in parallel. The vessels from SHR did not exhibit a greater responsiveness to endothelin-1 than those from WKY. No difference of responsiveness to the peptide was found among the arteries isolated from WKY of different ages. In contrast, a progressive decrease of responsiveness to endothelin-1 with aging was observed in SHR. This finding seems to be specific for endothelin-1, since the responsiveness to norepinephrine was unchanged. The significant decrease of aortic responsiveness in SHR with aging might be due to chronic hypertension and indicate desensitization to endothelin-1. The latter might be related to chronic in vivo hyperproduction of endothelin, either genetically determined or related to the hypertension-induced endothelial damage.     

Coculture of Vascular Endothelial Cells and Smooth Muscle Cells from Spontaneously Hypertensive Rats

The effect of endothelium‐released vasoactive factors on vascular smooth muscle cell (VSMC) proliferation was studied in a coculture system. Isolated aortic endothelial cells and smooth muscle cells from 4‐week‐old spontaneously hypertensive rats (SHR) and age‐matched Wistar–Kyoto (WKY) rats were cocultured. After coculture, the VSMC proliferation rate was examined by ³H‐thymidine incorporation assay and the levels of the vasoactive factors in medium were determined by enzyme immunoassay (EIA). The results indicate that the proliferation rate of VSMCs in SHR was significantly higher than in WKY rats when VSMCs were cultured alone. When SHR vascular endothelial cells (VECs) were cocultured with VSMCs, the proliferation rate of SHR VSMCs was enhanced; however, there was no growth promoting effect in WKY VSMCs. When WKY VECs were cocultured with VSMCs, no VSMC proliferation effect was observed. When VSMCs were cultured alone, the endothelin‐1 (ET‐1) secretion in SHR was significantly higher than in WKY rats. When VECs and VSMCs were cocultured, the ET‐1 concentration increased in both SHR VEC and WKY VEC coculture groups in a similar manner; but the SHR VECs tended to release more thromboxaneA₂ (TXA₂) and less PGI₂ than WKY VECs. These results suggest that some kind of interaction between SHR VSMCs and SHR VECs is responsible for the high proliferation of SHR VSMCs but not the effects of SHR VECs per se.     

Acute and Chronic Effects of Losartan (Dup 753) on Blood Pressure and Vascular Reactivity in Normotensive Rats

The effects of in vivo treatment with the nonpeptide subtype 1 angiotensin II receptor antagonist, losartan, on blood pressure and vascular reactivity in normotensi male Sprague-Dawley rats were studied. Initial acute experiments demonstrated that blood pressure was significantly decreased six hours following a single injection of losartan (10 mg/kg, sc), but returned to control levels by 24 hours post-injection. Pressor responses to angiotensin II (0.1 ug/kg, iv) in these rats were significantly attenuated 2 and 24 hours following losartan injection. For chronic studies, rats were injected once daily for 21 days with either the same dose of losartan or saline vehicle. Blood pressure and pressor responses to angiotensin II were assessed at the end of the 21 day treatment period. A significant decrease in blood pressure was observed in chronic losartan treated rats 6 hours after the last injection on day 21; however, as in the acute studies, blood pressure had returned to control values by 24 hours post-injection. Although blood pressure had returned to normal, pressor responses to angiotensin II were significantly attenuated in chronic losartan treated rats 24 hours after the last injection. Following the in vivo studies, aortae and tail arteries were removed for experiments on vascular reactivity. Acute and chronic losartan treatment had no effect on KCl and norepinephrine reactivity. Endothelial-dependent and independent relaxation responses were also unaltered. A significant decrease in the maximal contractile response to angiotensin II was observed in aorta from acute and chronic losartan treated rats. Electrical stimulation-induced responses were unaltered in tail arteries from rats acutely treated with losartan but were potentiated in rats chronically treated with losartan. Exogenously applied angiotensin II, in concentrations which did not elicit contractile responses, potentiated electrical stimulation-induced responses of tail arteries from control rats but did not influence responses in arteries from acute and chronic losartan treated rats. These results demonstrate that.