肾血管性高血压大鼠肠系膜动脉内皮细胞型一氧化氮合酶磷酸化变化的研究

目的在肾血管狭窄诱发高血压大鼠模型上,探讨肾血管性高血压大鼠肠系膜动脉内皮型一氧化氮合酶(eNOS)磷酸化变化的机制。方法 24只雄性大鼠随机分为假手术组和手术组,每组又分为2周组和4周组(n=6)。手术组采用双肾双狭的方法复制大鼠慢性肾血管性高血压模型,Westernblot印迹法检测肠系膜动脉eNOS蛋白的表达、eNOS丝氨酸(Ser1179)位点磷酸化水平以及磷酸酶2Ac(PP2Ac)的表达。硝酸还原酶法检测血浆一氧化氮(NO)的水平。结果与假手术组相比,双肾双狭高血压大鼠4周后肠系膜动脉eNOS蛋白表达、eNOSSer1179磷酸化水平明显降低,分别为42%和64%,PP2Ac蛋白水平明显增加(P均<0.05)。血浆NO水平在2周、4周时均明显降低(P<0.05)。结论肾血管性高血压大鼠肠系膜动脉eNOS总蛋白表达降低,同时eNOSSer1179磷酸化明显减弱,导致血浆NO水平降低,促进高血压的发生发展;而且PP2Ac水平升高可能是eNOSSer1179磷酸化水平降低的机制之一。     

高血压SD大鼠心脏结构及功能的超声评价

目的：建立肾血管性高血压大鼠模型并应用高分辨率超声评价高血压ＳＤ大鼠心脏结构及功能。方法：采用二肾一夹型（２Ｋ１Ｃ）肾血管性高血压大鼠模型,应用７．５ＭＨｚ线阵探头,２－ＤＥ结合Ｍ型探测高血压ＳＤ大鼠心脏获得结构及功能指标,并与对照组进行比较。结果与结论：高分辨率超声可以清晰地显示高血压ＳＤ大鼠心脏结构并获得多项结构及功能指标,可以鉴别高血压左心室肥厚类型,是评价高血压ＳＤ大鼠心脏结构及功能的理想     

大鼠小肠移植术后血清一氧化氮及小肠组织一氧化氮合酶和诱导型一氧化氮合酶活性的变化

目的:研究同种大鼠小肠移植后内源性一氧化氮、一氧化氮合酶(nitricoxidesynthase,NOS)及诱导型一氧化氮合酶(induciblenitricoxidesyn-thase,iNOS)的变化及一氧化氮与急性排斥反应的关系。方法:以大鼠小肠移植为研究对象,16只SD大鼠进行同系移植作为对照组,8只SD大鼠和8只Wistar大鼠进行同种移植作为实验组,两组移植后分别于第3,5,7天同时取血液及小肠组织,病理为常规苏木精-伊红染色观察,血清一氧化氮采用硝酸还原酶法测定,NOS和iNOS采用分光光度法测定。结果:在急性排斥反应发生的早期实验组血清一氧化氮水平与对照组比较显著升高(术后第3,5,7天t值分别为9.7900,9.0073,6.3159,P<0.01),小肠组织NOS及iNOS活性亦显著高于对照组(NOS术后第3,5,7天t值分别为5.9318,9.1237,3.0457,iNOS术后第3,5,7天t值分别为3.2008,5.4930,4.8170,P<0.01)。结论:大鼠小肠移植后NOS及iNOS变化与排斥反应相关,血清一氧化氮水平的检测可作为干预移植措施始动的指标之一。     

参龙健脑胶囊对脑缺血损伤大鼠学习记忆能力及皮层反应性氮中介物的影响

目的探讨参龙健脑胶囊对脑缺血大鼠学习记忆能力以及大脑皮层反应性氮中介物的影响。方法利用永久性结扎大鼠双侧颈总动脉的方法制备脑缺血模型,50只大鼠分为假手术组、模型组、脑复康阳性对照组、参龙健脑胶囊大、小剂量组。4周后分别进行Morris水迷宫实验及测定大脑皮层一氧化氮(NO)、诱导型一氧化氮合酶(iNOS)含量。结果参龙健脑胶囊能明显提高脑缺血大鼠的学习记忆能力,降低NO、iNOS含量。结论参龙健脑胶囊能降低脑缺血大鼠大脑皮层NO、iNOS含量,对学习记忆能力有明显提高作用。     

诱导型一氧化氮合酶在血管性痴呆大鼠海马中的表达

目的 探讨诱导型一氧化氮合酶在血管性痴呆(vascular dementin，VD)大鼠海马中的表达。方法 将60只大鼠随机分为5组：对照组、模型12h组(VD12h)、模型1d组(VD1d)、模型3d组(VD3d)、模型7d组(VDTd)，每组12只。采用反复夹闭双侧颈总动脉再灌注方法建立血管性痴呆大鼠模型。用HE染色观察各组大鼠海马CA1区神经元数目的变化；应用免疫组织化学染色和Western Blot方法检测诱导型一氧化氮合酶在大鼠海马中的表达。结果 大鼠海马CA1区神经元数在12h组、1d组、3d组、7d组均明显下降。Western印迹显示在VD12h组iNOS的表达上调，VD1d组进一步升高，保持这一水平至第7天。免疫组化见iNOS在正常组大鼠海马CA1区中有很弱的表达，在VD12h组、1d组、3d组、7d组表达逐渐增强。结论 iNOS可能参与缺血后海马神经元的损害，是构成血管性痴呆的机制之一。     

大鼠小肠移植术后血清一氧化氮及小肠组织一氧化氮合酶和诱导型一氧化氮合酶活性的变化

目的：研究同种大鼠小肠移植后内源性一氧化氮、一氧化氮合酶(nitric oxide synthase，NOS)及诱导型一氧化氮合酶(inducible nitric oxide synthase，iNOS)的变化及一氧化氮与急性排斥反应的关系。方法：以大鼠小肠移植为研究对象，16只SD大鼠进行同系移植作为对照组．8只SD大鼠和8只Wistar大鼠进行同种移植作为实验组，两组移植后分别于第3，5，7天同时取血液及小肠组织，病理为常规苏木精一伊红染色观察，血清一氧化氮采用硝酸还原酶法测定，NOS和iNOS采用分光光度法测定。结果：在急性排斥反应发生的早期实验组血清一氧化氮水平与对照组比较显著升高(术后第3，5，7天t值分别为9．7900，9．0073，6．3159，P&;lt;0．01)，小肠组织NOS及iNOS活性亦显著高于对照组(NOS术后第3，5，7天t值分别为5．9318，9．1237，3．0457，iNOS术后第3，5，7天t值分别为3．2008，5．4930，4．8170，P&;lt;0．01)。结论：大鼠小肠移植后NOS及iNOS变化与排斥反应相关，血清一氧化氮水平的检测可作为干预移植措施始动的指标之一。     

大鼠脊髓损伤后诱导型一氧化氮合酶的表达及动态改变

目的:探讨大鼠急性脊髓损伤后不同时段髓内诱导型一氧化氮合酶(iNOS)mRNA动态表达。方法:36只SD大鼠抽签法随机分组,任选一组作为对照。采用Allen法制作急性脊髓损伤模型,在损伤后2,6,12,24,48h等时段,以反转录酶聚合酶链式反应(RT-PCR)分析iNOSmRNA表达。在脊髓损伤后24h,用免疫组化方法分析iNOS在脊髓不同类型神经细胞中的表达与分布,并以比色法测定脊髓损伤后血清NOS及一氧化氮的含量。结果:脊髓损伤后,神经元、星形细胞和小胶质中均可见iNOS表达,以神经元表达为主。脊髓损伤后2h可见iNOS表达0.56±0.02,24h达高峰1.20±0.05,48h开始降低0.70±0.06。血清中NOS及一氧化氮的动态改变与损伤组织iNOSmRNA变化趋势相一致。结论:研究资料提示脊髓损伤后脊髓内iNOS表达增高,过量产生的一氧化氮加重了继发性脊髓损伤。     

肾性高血压患者肾素、血管紧张素及醛固酮测定的临床价值

目的探讨肾性高血压患者肾素(PRA)、血管紧张素Ⅱ(AngⅡ)、醛固酮(ALD)测定对临床诊断与治疗价值。方法收集2014年4月至2016年10月来该院就诊肾性高血压患者134例,其中肾实质性高血压患者114例,肾血管性高血压患者20例,健康体检正常志愿者50例(对照组),均在普通饮食下卧位、立位时采血测定血浆中PRA、AngⅡ、ALD水平。结果肾实质性高血压组卧位、立位血浆PRA、AngⅡ、ALD水平均高于对照组,两组比较,差异有统计学意义(P0.05);肾血管性高血压组卧位、立位血浆PRA、AngⅡ、ALD水平明显高于对照组,两组比较,差异有统计学意义(P0.05);肾血管性高血压组卧位、立位血浆PRA、AngⅡ、ALD水平高于肾实质性高血压组,两组比较,差异有统计学意义(P0.05)。结论肾性高血压患者血浆PRA、AngⅡ及ALD的测定有一定的临床诊断治疗价值。     

铅对大鼠海马和大脑皮质NOS活性的影响

目的 观察实验性铅中毒对大鼠海马和大脑皮质一氧化氮合酶（NOS）性的影响，探讨NOS在铅中毒中枢系统损害中的作用机制。方法 4周龄Wistar雄性大鼠按45mg/kg剂量行醋酸铅灌胃30d；大鼠海马和大脑皮质总NOS和诱导型一氧化氮合酶（iNOS）活性测定采用NOS催化L-Arg和氧分子生成NO法。结果 与空白对照纽大鼠比较，染铅组大鼠海马和大脑皮质总NOS活性明显降低，而iNOS活性均升高，差异有显著性（P〈0．01）。结论 铅可以使大鼠海马和大脑皮质总NOS活性降低，iNOS活性升高。     

大鼠脊髓损伤后诱导型一氧化氮合酶的表达及动态改变

目的：探讨大鼠急性脊髓损伤后不同时段髓内诱导型一氧化氮合酶(iNOS)mRNA动态表达。方法：36只SD大鼠抽签法随机分组，任选一组作为对照。采用Allen法制作急性脊髓损伤模型，在损伤后2，6，12，24，48h等时段，以反转录酶聚合酶链式反应(RT-PCR)分析：iNOS mRNA表达。在脊髓损伤后24h，用免疫组化方法分析iNOS在脊髓不同类型神经细胞中的表达与分布，并以比色法测定脊髓损伤后血清NOS及一氧化氮的含量。结果：脊髓损伤后，神经元、星形细胞和小胶质中均可见iNOS表达，以神经元表达为主。脊髓损伤后2h可见iNOS表达0．56&;#177;0．02，24h达高峰1．20&;#177;0．05，48h开始降低0．70&;#177;0．06。血清中NOS及一氧化氮的动态改变与损伤组织iNOS mRNA变化趋势相一致。结论：研究资料提示脊髓损伤后脊髓内iNOS表达增高，过量产生的一氧化氮加重了继发性脊髓损伤。     

Imbalance in endothelial vasoactive factors as a possible cause of cyclosporin toxicity: a role for endothelin-converting enzyme

Cyclosporin A (CsA) is a powerful, widely used immunosuppressant, but it is not devoid of serious clinical side effects such as hypertension and nephrotoxicity. To clarify the mechanisms involved in the genesis of these side effects, we studied the effects of chronic CsA administration on the expression of some endothelial vasoactive factors in the aorta and kidney. For this purpose rats were treated for 30 days with 50 mg/kg/day CsA, and hypertension and renal insufficiency developed. In rats receiving CsA, the mRNA expression of pre-pro-endothelin-1 increased, whereas that of endothelial nitric oxide (NO) synthase decreased, both in the aorta and in the renal cortex (increases in pre-pro-endothelin-1 mRNA in aorta and renal cortex, respectively: 275%+/-18%, 300%+/-27%; decreases in endothelial NO synthase mRNA in aorta and renal cortex respectively: 40%+/-8%, 42%+/-6%). Moreover, long-term CsA treatment also induced an up-regulation of the endothelin-converting enzyme 1 mRNA expression (156% vs. control rats) in the renal cortex, with a significantly increased protein content and enzyme activity. In contrast, no changes were detected in endothelin-converting enzyme 1 mRNA expression in aortas from rats receiving the drug. This imbalance between endothelin-1 and NO systems could explain the hypertension and the deranged kidney function observed after long-term CsA treatment in rats.     

Exhaled nitric oxide and acute lung injury in a rat model of extracorporeal circulation

Exhaled nitric oxide (NO) concentration, a marker of pulmonary inflammation, has been shown to be elevated in various models of acute lung injury (ALI). This study was undertaken to evaluate the pulmonary NO production in a rat model of postextracorporeal circulation (ECC) ALI. Wistar rats underwent either a partial femorofemoral ECC in normothermia for 3 h (n = 10) or a sham procedure (n = 10). The extracorporeal circuit consisted of a roller pump and a membrane oxygenator. Exhaled NO concentration was monitored with a chemiluminescence analyzer. After sacrifice, lungs were harvested for microscopic studies and to analyze the inducible nitric oxide synthase (iNOS) activity and expression (Western blot). ECC was responsible for an ALI characterized by a decreased arterial blood oxygen saturation (88.9% [51.7-94.2] vs. 93.7% [91.4-98.6] P = 0.005) and pulmonary histological changes (marked alveolar neutrophil infiltration; interstitial edema; intraalveolar hemorrhage). The lung injury score was significantly higher in the ECC group (n = 5; 3.0 [2-4]) in comparison to the sham group (n = 5; 1.0 [0-2]). Exhaled NO concentration remained stable throughout the experiment in all sham rats whereas it significantly increased in the ECC group from baseline (2 ppb [1-5]) until the end of experiment (33.5 ppb [1-47]). Lung iNOS activity and expression were also significantly increased in the ECC group. An increase in exhaled NO, however, did not correlate with the decrease in arterial oxygen pressure. ECC was responsible for an ALI in rats and for an elevated pulmonary NO production. Determination of the relationship between exhaled NO and the severity of the inflammatory process in ALI will require further studies.     

八肽缩胆囊素对脂多糖诱导血管内皮细胞诱生型一氧化氮合酶表达变化的抑制作用

目的探讨八肽缩胆囊素（CCK-8）对脂多糖（LPS）诱导血管内皮细胞诱生型一氧化氯合酶（iNOS）表达变化的影响。方法培养人脐静脉内皮细胞株ECV-304细胞。用0．01、0．1和1mg／L LPS处理2～24h，用生理盐水、10mol／LCCK-8和0．1mg／L LPS＋10^-8、10^-7、10^-8mol／L CCK-8处理16h；用比色法检测培养液中一氧化氮（NO）含量、细胞NOS活性，免疫细胞化学及蛋白质免疫印迹法检测iNOS蛋白表达。结果与生理盐水处理的对照组比较，LPS诱导培养液NO含量增多、细胞NOS活性增高、iNOS蛋白表达上调；CCK-8剂量依赣性抑制LPS的上述效应。而单独作用对iNOS蛋白表达、NOS活性和NO含量均无明显影响。结论CCK-8可以明显抑制LPS引起ECV-304细胞iNOS蛋白表达上调。减少NO生成。     

Incidence of renal artery stenosis in a population having cardiac catheterization

Patients with renovascular hypertension comprise only a small percentage of those with hypertension. In our study 102 consecutive patients who had cardiac catheterization were screened at the time of the procedure for renal artery stenosis. Only 65 (64%) of the 102 patients were hypertensive, and 14 of the total population (13.7%) had renal artery stenosis. Of these 14 patients, only five had more than 50% narrowing of the arterial lumen. By renal vein renin determination, only four of the five patients with significant renal artery stenosis had lateralizing renins. The frequency of significant renovascular hypertension does not justify the routine search for this problem during catheterization procedures, though it may be worthwhile if the patients are hypertensive. This area deserves further evaluation.     

电针对脑缺血再灌注损伤大鼠海马诱导型一氧化氮合酶mRNA表达的影响

背景诱导型一氧化氮合酶mRNA在脑缺血再灌注脑损伤中具有减轻血脑屏障的破坏,保护血管内皮和脑组织的作用.目的观察电针水沟、内关、足三里对脑缺血再灌注大鼠海马诱导型一氧化氮合酶mRNA表达的影响.设计随机对照实验.单位上海中医药大学、上海市针灸经络研究所及复旦大学华山医院.方法实验于2003-12/2004-12在上海中医药大学实验动物中心、上海市针灸经络研究所针灸免疫学实验室和复旦大学华山医院完成.40只SD大鼠随机分为4组正常组、假手术组、模型组和电针治疗组,每组10只.用双肾双夹法复制易卒中型肾血管性高血压模型,在此基础上,运用栓线法制备大鼠局灶性脑缺血再灌注模型;假手术组除不插入栓线外,其余步骤同模型组;电针治疗组取水沟(唇裂鼻尖下1 mm正中处,向上斜刺1 mm)、双侧内关(前肢内侧,离腕关节约3 mm处的尺桡骨缝间,直刺1 mm)、双侧足三里(膝关节下侧,在腓骨小头下约5 mm处,直刺7 mm)水沟穴与右耳根部皮肤、内关与足三里接G6805电针治疗仪,连续波,频率120次/min,强度1 mA,留针30 min.缺血后即时治疗1次,再灌注后每12 h治疗1次.所有动物于再灌注后24h断头处死,取出脑组织,分离海马,应用荧光定量逆转录聚合酶链反应技术观察电针对实验性脑缺血再灌注大鼠海马诱导型一氧化氮合酶mRNA表达的影响.主要观察指标大鼠海马诱导型一氧化氮合酶mRNA的表达.结果40只SD大鼠均进入结果分析.大鼠海马诱导型一氧化氮合酶mRNA的表达[1]模型组明显高于电针治疗组{[(4.85±1.29)×1 000,(3.19±1.38)×1 000]拷贝,(t=2.77,P＜0.05)};[2]模型组明显高于假手术组{[(4.85±1.29)×1 000,(4.93±2.17)×10]拷贝,(t=97.38,P＜0.01)};[3]模型组显著高于正常组{[(4.85±1.29)×1 000,(3.13±1.68)×10]拷贝,(t=11.81,P＜0.01)}.结论电针可以显著抑制脑缺血再灌注后大鼠海马诱导型一氧化氮合酶mRNA表达,从而减少一氧化氮的产生,有助于减轻脑缺血再灌注损伤.     

Presence of nitrotyrosine with minimal inducible nitric oxide synthase induction in lipopolysaccharide-treated pigs

The production of large amounts of nitric oxide (NO) by the inducible form of nitric oxide synthase (iNOS) and the subsequent production of peroxynitrite (OONO-) are believed to be major factors in the hemodynamic abnormalities of sepsis. This finding is based on data from rats and mice but has not been established in other species. Therefore, we examined the role of iNOS in lipopolysaccharide (LPS)-treated pigs, which have a hemodynamic pattern with sepsis that is more similar to humans than rats. Pigs were anesthetized, ventilated, and given LPS (n = 12), 20 microg/kg over 2 h, or saline (n = 7). They were killed after 2 (n = 8 LPS, 7 control) or 4 h (4 LPS). We measured cardiac output (CO), mean arterial (Part), and pulmonary and central venous pressures. We evaluated NO production by measuring expired NO, and plasma nitrate/nitrite concentration, NOS activity (in lung tissue), and iNOS protein by Western analysis, and immunohistochemistry (lung and liver), as well as iNOS mRNA by Northern analysis (liver and lung). We also measured nitrotyrosine as evidence of OONO- production by slot blot, Western analysis, and immunohistochemistry. By 2 h, Part fell and CO did not change so that systemic vascular resistance decreased from 21.5+/-2.9 to 12.7+/-3.1 mmHg x L(-1) x min (P < 0.05) and remained at 11.3+/-1.7 mmHg x L(-1) x min in the animals observed for 4 h. Plasma nitrate/nitrite, expired NO, and NOS activity did not change. We found no iNOS in tissues by Western analysis with 5 different antibodies but detected a small amount of iNOS by immunohistochemistry in inflammatory cells and small vessels. There was a small increase in iNOS mRNA in liver and lung. Despite the minimal increase in iNOS, nitrotyrosine was increased in small vessels and in inflammatory cells. In conclusion, caution should be used when extrapolating the septic response in rodents to other species, for the pattern of iNOS induction is very different.     

Protein kinase A- and C-dependent modulation of murine inducible nitric oxide synthase

Effects of pharmacological modulation of protein kinase A, C and G (PKA, PKC and PKG) were examined on inducible form of nitric oxide synthase (iNOS) expressed in COS cells to elucidate regulatory mechanism of iNOS by protein kinases. Formation of nitric oxide (NO), as an index of NOS activity, was assessed by measurement of nitrite in incubation medium in long term observation and by hemoglobin assay method in kinetic study. In long term observation (18 hours), activation of PKA by 8-Br-cAMP increased NO formation that was inhibited by N-(2-[p-bromocinnamylamino] ethyl)-5-isoquinolinesulfonamide (H89). Though activation of PKC by 12-O-tetradecanoyl phorbol-13-acetate (TPA) decreased NO formation, PKC inhibitor, chelerythrine, failed to inhibit the decrease. Activation of PKG with 8-Br-cGMP and inhibition with KT5823 resulted in no change in NO formation. Western blot analysis revealed that neither 8-Br-cAMP nor TPA affect iNOS expression. In kinetic study (short term perfusion study), no change in NO formation was observed by 8-Br-cAMP and TPA. These results indicate that, in living cells, PKG does not play a regulatory role in iNOS activity and that PKA and PKC do not directly modulate iNOS activity. However, PKA and PKC would possibly modify NOS activity indirectly via cofactors necessary for NO formation.     

Intravascular infusion of acid promotes intrapulmonary inducible nitric oxide synthase activity and impairs blood oxygenation in rats

OBJECTIVE: To test the hypothesis that intravascular acid infusion promotes intrapulmonary nitric oxide formation by promoting inducible nitric oxide synthase (iNOS) and inhibiting endothelial nitric oxide synthase (eNOS) expression in rats. DESIGN: Prospective, placebo controlled, randomized laboratory study. SETTING: University laboratory. SUBJECTS: Twelve male Sprague-Dawley rats weighing 317 +/- 30 g served as study subjects. All animals were anesthetized, paralyzed, and mechanically ventilated throughout the experiment. INTERVENTIONS: The animals were randomized to receive either 0.1 N hydrochloric acid or 0.9% saline intravenously. The infusions were initially given at a rate of 11 mL/kg/hr for 15 mins and then at a rate of 0.95 mL/kg/hr for the remainder of the experiment. Exhaled nitric oxide concentrations and hemodynamic measurements were monitored throughout the experiment. Lung tissues were harvested for Western blot analysis and immunostaining 4 hrs after starting the intravascular infusion. MEASUREMENT AND MAIN RESULTS: At the end of the experiment, we found more than a four-fold higher concentration of exhaled nitric oxide in the acid-treated animals than in the saline-treated animals (p <.001). Western blot analysis revealed that the acid infusion increased intrapulmonary iNOS concentrations (p <.001), yet it decreased intrapulmonary eNOS concentrations (p =.009). Acid-related lung injury manifested as a decrease in blood oxygen tensions (p =.045) and as an increase in lung homogenate interleukin-6 concentrations (p =.003). CONCLUSIONS: Our results reveal that hydrochloric acid infusion stimulates intrapulmonary nitric oxide formation at least in part by promoting the expression of iNOS. Our findings suggest that correcting acidosis should attenuate iNOS formation. Our data also support the idea that metabolic acidosis itself can lead to impaired intrapulmonary gas exchange and increased expression of pro-inflammatory cytokines such as interleukin-6. Whether the induction of intrapulmonary nitric oxide formation mediates or simply indicates lung injury warrants further investigation.     

Differential involvement of guanylate cyclase and potassium channels in nitric oxide-induced hyporesponsiveness to phenylephrine in endotoxemic rats.

This study evaluated the involvement of nitric oxide (NO), guanylate cyclase, and potassium channels in the long-lasting vascular hyporesponsiveness to phenylephrine induced by Escherichia coli lipopolysaccharide (LPS) in vitro and in vivo. Experiments in rat aorta rings with endothelium incubated with LPS (10 microg/mL) for 12 h showed that the hyporesponsiveness depends on guanylate cyclase activity and tetraethylammonium-sensitive, but not voltage- or ATP-dependent, potassium channels. Pressor responses to phenylephrine were reduced by 50% in rats injected 8 and 24 h before with LPS (10 mg/kg, intraperitoneally). Pretreatment with NO synthase inhibitors (iNOS; Nomega-nitro-L-arginine methyl ester [L-NAME], 55 micromol/kg or aminoguanidine, 244 micromol/kg, intraperitoneally) fully prevented LPS-induced hyporesponsiveness. When administered just before phenylephrine, L-NAME (11 micromol/kg, intravenously) reversed the hyporesponsiveness in rats injected 8 h, but not in those injected 24 h before with LPS, whereas 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1 (ODQ, 11 micromol/kg, intravenously) reversed the hyporesponsiveness in animals injected 24 h, but not in those injected 8 h before with LPS. Tetraethylammonium (360 micromol/kg, intravenously) reestablished normal responses to phenylephrine in rats injected 8 and 24 h before with LPS. Again, neither voltage- nor ATP-dependent potassium channels appears to be involved. Western blot showed that iNOS expression peaked at 8 h, decreasing to low levels 24 h after LPS injection. Therefore, NO is important in initiating LPS-induced hyporesponsiveness to vasoconstrictors, but not in maintaining it for long periods. Once NO has exerted its effects and even when iNOS expression is minimal, the long-lasting hyporesponsiveness appears to depend on a complex interplay between guanylate cyclase and potassium channel activation.