慢性间歇性低压低氧对大鼠动脉血管收缩功能的影响

本研究旨在探讨慢性间歇性低压低氧(chronicintermittent hypobaric hypoxia,CIHH)对大鼠胸主动脉和肺动脉收缩功能的影响及其机制.雄性Sprague-Dawley大鼠随机分为4组:CIHH处理14天组(CIHH 14)、28天组(CIHH 28)、42天组(CIHH 42)和对照组(...     

多巴胺对急性间歇性低氧诱导的大鼠颈动脉体低氧敏感性的影响*

目的: 观察急性间歇性低氧刺激后大鼠颈动脉体对低氧的敏感性以及多巴胺对颈动脉体低氧敏感性的影响。方法: 将分离SD大鼠的颈动脉体-窦神经移入到孵育槽,然后把分离的窦神经吸入到记录的玻璃电极中行电信号记录。记录基线部分缓冲液充入气体为95% O₂+ 5% CO₂混合气,低氧应激给予5% O₂+ 5% CO₂+ 90% N₂混合气,低氧刺激给予30 s,95% O₂ + 5% CO₂给予90 s,共10个循环,每组实验大鼠数量n大于等于5。结果: 大鼠离体的颈动脉体,给予急性间歇性低氧应激,再给予低氧刺激,窦神经较之前低氧刺激放电活动增强。但加入多巴胺后,可以抑制窦神经对低氧的反应,急性间歇性低氧后,多巴胺对窦神经的低氧放电活动抑制作用加强。结论: 大鼠颈动脉体给予急性间歇性低氧可增强窦神经对低氧的反应,多巴胺可抑制急性低氧诱导的颈动脉体对低氧敏感性的增强。     

间歇性低压低氧通过促进细胞凋亡抗大鼠胶原诱导性关节炎

本文旨在研究慢性间歇性低压低氧(chronic intermittent hypobaric hypoxia,CIHH)对大鼠胶原诱导性关节炎(collagen-induced arthritis,CIA)影响.雄性成年Sprague-Dawley大鼠50只,随机分为5组:CIHH预处理组(Pre-T)、预处理对照组(...     

银杏苦内酯B抑制麻醉大鼠颈动脉窦压力感受性反射

本研究在30只麻醉雄性Sprague-Dawley大鼠隔离灌流颈动脉窦区观察了银杏苦内酯B(ginkgolide B)对颈动脉窦压力感受性反射的影响.结果显示:(1)银杏苦内酯B(0.1,1,10 pmol/L)隔离灌流序侧颈动脉窦区,使压力感受性机能曲线向右上方移位,曲线最大斜率(peak slop,PS)减小,血压反射性下降(reflex decrease,RD)幅度减小(P<0.01),阂压(threshold pressure,TP)、平衡压(equilibrium pressure,EP)和饱和压(saturation pressure,SP)均升高(P<0.05,P<0.01).其中PS、RD、TP、EP和sP呈明显的剂量依赖性;(2)预先应用钙通道开放剂Bay K8644(500 nmol/L),可以完伞取消银杏苦内酯B的抑制作用.(3)预先应用钾通道阻断剂四乙铵(tetraethylammonium,TEA,1 mmol/L),银杏苦内酯B的上述作用也被完全取消.结果表明,银杏苦内酯B对大鼠颈动脉实压力感受性反射有抑制作用,此作用与银杏苦内酯B减少颈动脉窦压力感受器神经末梢钙离子内流和增加钾离子外流有关.     

Endothelin-1 mediates attenuated carotid baroreceptor activity by intermittent hypoxia

The objectives of the present study were to examine the effects of intermittent hypoxia (IH) on arterial baroreflex function and assess the underlying mechanism(s). Experiments were performed on adult male rats treated with 14 days of IH (15 s of hypoxia, 5 min of normoxia; 8 h/day) or normoxia (control). Arterial blood pressures were elevated in IH-treated rats, and this effect was associated with attenuated heart rate and splanchnic sympathetic nerve responses to arterial baroreflex activation. In IH-treated rats, carotid baroreceptor responses to elevated sinus pressures were attenuated. Endothelin-1 (ET-1) levels were elevated in the carotid sinus region of IH-treated rats, and this effect was associated with increased endothelin converting enzyme (ECE) activity, which generates biologically active ET-1. ET(A) receptor antagonist prevented the effects of IH on carotid baroreceptor activity. In IH-treated rats, reactive oxygen species (ROS) levels were elevated in the carotid sinus region, and antioxidant treatment prevented the effects of IH on ET-1 levels, ECE activity, carotid baroreceptor activity, and baroreflex function. These results demonstrate that 1) IH attenuates arterial baroreflex function, which is in part due to reduced carotid baroreceptor responses to elevated carotid sinus pressure, and 2) IH-induced carotid baroreceptor dysfunction involves reactive oxygen species-dependent upregulation of ET-1 signaling in the carotid sinus region.     

Preservation of TSPO by chronic intermittent hypobaric hypoxia confers antiarrhythmic activity

Abnormal activation of mitochondrial translocator protein (TSPO) contributes to arrhythmogenesis during cardiac metabolic compromise; however, its role in the antiarrhythmic activities of chronic hypoxia adaptation remains unclear. Our results demonstrated that 80% of normoxic rats developed ischaemic VF, whereas this condition was seldom observed in rats with 14 days of chronic intermittent hypobaric hypoxia (CIHH). TSPO stimulation or inhibition affected the arrhythmias incidence in normoxic rats, but did not change the CIHH‐mediated antiarrhythmic effects. Abrupt and excessive elevation of TSPO activity was positively linked to ischaemic VF, and CIHH preserved TSPO activity during ischaemia. The preservation of TSPO activity by CIHH also contributed to the maintenance of intracellular Ca homeostasis. These results suggest that the blunt sensitivity of TSPO to ischaemic stress may be responsible for the antiarrhythmic effects by CIHH.     

Ventilatory and carotid body chemoreceptor responses to purinergic P2X receptor antagonists in newborn rats

Adenosine triphosphate, acting through purinergic P2X receptors, has been shown to stimulate ventilation and increase carotid body chemoreceptor activity in adult rats. However, its role during postnatal development of the ventilatory response to hypoxia is yet unknown. Using whole body plethysmography, we measured ventilation in normoxia and in moderate hypoxia (12% fraction of inspired O?, 20 min) before and after intraperitoneal injection of suramin (P2X? and P2X? receptor antagonist, 40 mg/kg) in 4-, 7-, 12-, and 21-day-old rats. Suramin reduced baseline breathing (～20%) and the response to hypoxia (～30%) in all rats, with a relatively constant effect across ages. We then tested the effect of the specific P2X? antagonist, A-317491 (150 mg/kg), in rats aged 4, 7, and 21 days. As with suramin, A-317491 reduced baseline ventilation (～55%) and the hypoxic response (～40%) at all ages studied. Single-unit carotid body chemoreceptor activity was recorded in vitro in 4-, 7-, and 21-day-old rats. Suramin (100 μM) and A-317491 (10 μM) significantly depressed the sinus nerve chemosensory discharge rate (～80%) in normoxia (Po? ～150 Torr) and hypoxia (Po? ～60 Torr), and this decrease was constant across ages. We conclude that, in newborn rats, P2X purinergic receptors are involved in the regulation of breathing under basal and hypoxic condition, and P2X?-containing receptors play a major role in carotid body function. However, these effects are not age dependent within the age range studied.     

Enhancement of Na/K pump activity by chronic intermittent hypobaric hypoxia protected against reperfusion injury

Chronic intermittent hypobaric hypoxia (CIHH) has been shown to attenuate intracellular Na(+) accumulation and Ca(2+) overload during ischemia and reperfusion (I/R), both of which are closely related to the outcome of myocardial damage. Na/K pump plays an essential role in maintaining the equilibrium of intracellular Na(+) and Ca(2+) during I/R. It has been shown that enhancement of Na/K pump activity by ischemic preconditioning may be involved in the cardiac protection. Therefore, we tested whether Na/K pump was involved in the cardioprotection by CIHH. We found that Na/K pump current in cardiac myocytes of guinea pigs exposed to CIHH increased 1.45-fold. The K(1) and f(1), which reflect the portion of α(1)-isoform of Na/K pump, dramatically decreased or increased, respectively, in CIHH myocytes. Western blot analysis revealed that CIHH increased the protein expression of the α(1)-isoform by 76%, whereas the protein expression of the α(2)-isoform was not changed significantly. Na/K pump current was significantly suppressed in simulated I/R, and CIHH preserved the Na/K pump current. CIHH significantly improved the recovery of cell length and contraction during reperfusion. Furthermore, inhibition of Na/K pump by ouabain attenuated the protective effect afforded by CIHH. Collectively, these data suggest that the increase of Na/K pump activity following CIHH is due to the upregulating α(1)-isoform of Na/K pump, which may be one of the mechanisms of CIHH against I/R-induced injury.     

Effect of chronic hypoxia on purinergic synaptic transmission in rat carotid body.

Recent studies indicate that chemoafferent nerve fiber excitation in the rat carotid body is mediated by acetylcholine and ATP, acting at nicotinic cholinergic receptors and P2X2 purinoceptors, respectively. We previously demonstrated that, after a 10- to 14-day exposure to chronic hypoxia (CH), the nicotinic cholinergic receptor blocker mecamylamine no longer inhibits rat carotid sinus nerve (CSN) activity evoked by an acute hypoxic challenge. The present experiments examined the effects of CH (9-16 days at 380 Torr) on the expression of P2X2 purinoceptors in carotid body and chemoafferent neurons, as well as the effectiveness of P2X2 receptor blocking drugs on CSN activity evoked by hypoxia. In the normal carotid body, immunocytochemical studies demonstrated a dense plexus of P2X2-positive nerve fibers penetrating lobules of type I cells. In addition, type I cells were lightly stained, indicating P2X2 receptor expression. After CH, the intensity of P2X2 receptor immunostaining was maintained in chemosensory type I cells and in the soma of chemoafferent neurons. P2 receptor expression on type I cells was confirmed by demonstrations of ATP-evoked increased intracellular Ca2+; this response was modulated by simultaneous exposure to hypoxia. In normal preparations, CSN activity evoked by hypoxia in vitro was 65% inhibited in the presence of specific P2X2 receptor antagonists. However, unlike the absence of mecamylamine action after CH, P2X2 antagonists remained effective against hypoxia-evoked activity after CH. Our findings indicate that ATP acting at P2X2 receptors contributes to adjusted chemoreceptor activity after CH, indicating a possible role for purinergic mechanisms in the adaptation of the carotid body in a chronic low-O2 environment.     

Chronic sustained and intermittent hypoxia reduce function of ATP-sensitive potassium channels in nucleus of the solitary tract

Activation of neuronal ATP-sensitive potassium (K(ATP)) channels is an important mechanism that protects neurons and conserves neural function during hypoxia. We investigated hypoxia (bath gassed with 95% N(2)-5% CO(2) vs. 95% O(2)-5% CO(2) in control)-induced changes in K(ATP) current in second-order neurons of peripheral chemoreceptors in the nucleus of the solitary tract (NTS). Hypoxia-induced K(ATP) currents were compared between normoxic (Norm) rats and rats exposed to 1 wk of either chronic sustained hypoxia (CSH) or chronic intermittent hypoxia (CIH). Whole cell recordings of NTS second-order neurons identified after 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (DiA) labeling of the carotid bodies were obtained in a brain stem slice. In Norm cells (n = 9), hypoxia (3 min) induced an outward current of 12.7 +/- 1.1 pA with a reversal potential of -73 +/- 2 mV. This current was completely blocked by the K(ATP) channel blocker tolbutamide (100 muM). Bath application of the K(ATP) channel opener diazoxide (200 muM, 3 min) evoked an outward current of 21.8 +/- 5.8 pA (n = 6). Hypoxia elicited a significantly smaller outward current in both CSH (5.9 +/- 1.4 pA, n = 11; P < 0.01) and CIH (6.8 +/- 1.7 pA, n = 6; P < 0.05) neurons. Diazoxide elicited a significantly smaller outward current in CSH (3.9 +/- 1.0 pA, n = 5; P < 0.05) and CIH (2.9 +/- 0.9 pA, n = 3; P < 0.05) neurons. Western blot analysis showed reduced levels of K(ATP) potassium channel subunits Kir6.1 and Kir6.2 in the NTS from CSH and CIH rats. These results suggest that hypoxia activates K(ATP) channels in NTS neurons receiving monosynaptic chemoreceptor afferent inputs. Chronic exposure to either sustained or intermittent hypoxia reduces K(ATP) channel function in NTS neurons. This may represent a neuronal adaptation that preserves neuronal excitability in crucial relay neurons in peripheral chemoreflex pathways.     

间歇性低压低氧对过氧化氢心肌细胞损伤的保护作用

目的:观察慢性间歇性低压低氧对过氧化氢所致心肌细胞损伤的保护作用及其机制。方法:雄性豚鼠20只,随机分为两组(n=10):对照组(non-IHH)、低氧组(IHH)。低氧组豚鼠于低压氧舱接受28 d(海拔5 000 m、每天6 h)的低压低氧处理。胶原酶方法急性分离心肌细胞。细胞动缘探测系统测定过氧化氢对各组细胞收缩力的变化。生化方法测定各组丙二醛(MDA)、乳酸脱氢酶(LDH)及超氧化物歧化酶(SOD)和过氧化氢酶(CAT)的变化。结果:①过氧化氢可使心肌细胞出现收缩、舒张紊乱,但IHH处理使其出现的潜伏期明显延长。②给予过氧化氢(300μmol/L,10 min)使来自于non-IHH或IHH的心肌细胞LDH、MDA含量均明显增加,但IHH心肌细胞LDH、MDA含量明显低于non-IHH心肌细胞的LDH、MDA含量。③经IHH处理组的心肌细胞SOD,CAT活性均明显高于non-IHH组。给予过氧化氢使来自于non-IHH或IHH的心肌细胞SOD,CAT活性均明显降低,但IHH心肌细胞SOD,CAT活性明显高于non-IHH心肌细胞的SOD,CAT活性。结论:IHH具有对抗过氧化氢心肌细胞损伤的作用,可能与其增强抗氧化酶活性有关。     

KATP通道开放剂对颈动脉窦压力感受器反射的易化作用

在30只隔离灌流颈动脉窦区的麻醉大鼠, 观察了KATP通道开放剂(cromakalim, Cro)对颈动脉窦压力感受器反射的影响.结果如下: (1)以Cro (10 μmol/L)隔离灌流大鼠左侧颈动脉窦区时, 压力感受器机能曲线向左下方移位, 曲线最大斜率 (PS) 由0.36±0.01增至0.48±0.01 kPa/kPa (P<0.001), 反射性血压下降幅度(RD)由5.78±0.14增至7.87±0.12 kPa (P<0.001);阈压(TP)、平衡压(EP)和饱和压(SP)则分别从8.34±0.35, 12.71±0.25和24.89±0.25下降至6.41±0.09 kPa, 11.78±0.24 kPa, 22.56±0.16 kPa (P<0.01～0.001).其中RD, PS和TP的变化呈明显的剂量依赖性.(2)用KATP通道阻断剂格列苯脲(glibenclamide, 10 μmol/L)预处理后, Cro的上述反射效应即被阻断.(3)先给予腺苷(adenosine, 125 μmol/L)则可以加强Cro对压力感受器反射的影响.以上结果表明, KATP通道开放剂Cro对大鼠颈动脉窦压力感受器反射有易化作用, 此作用是由KATP通道开放剂引起窦壁扩张而牵张压力感受器所致.     

白细胞介素-1β对实验性急性缺氧诱导的大鼠窦神经放电的影响

最近的研究显示,颈动脉体（carotid body,CB）除具有缺氧等化学感受功能外,还对白细胞介素-1B（IL-1β）的刺激起反应。但是,IL-1β刺激对颈动脉体的缺氧感受功能有何影响还不清楚。本研究运用在体（in vivo）细胞外神经干电位记录的方法,利用麻醉大鼠,观察了CB局部给予IL-1β对实验性急性缺氧（experimental acute hypoxia,EAH）诱导的CB传入神经窦神经（carotid sinus nerve,CSN）放电频率的影响。结果发现,EAH可以诱导麻醉状态下大鼠的CSN放电频率增高;颈动脉体局部给予ATP（0、1mmol／L）和ACh（0,5mmol／L）在一定程度上可模拟缺氧诱导的CSN放电;局部给予ILlp（40μg／L）可诱导窦神经放电频率增加。但同时给予IL-1B和EAH,所引起的放电频率增高效应与单独给予EAH或IL-1β所诱导的放电频率的增高效应间无显著性差别,且IL-1β对ATP和ACh诱导的窦神经放电的增高效应也无显著影响。这些结果提示,IL-1β对EAH诱导的窦神经放电无调节作用。     

黄连对正常氧和慢性间歇性低压低氧大鼠离体胸主动脉收缩活动的影响

目的：观察黄连对正常氧和慢性间歇性低压低氧（CIHH）大鼠离体胸主动脉收缩活动的影响并探讨其作用机制。方法：取青年雄性SD大鼠,随机分为正常氧组和CIHH组。前者不予任何处理,后者于低压氧舱接受28d模拟海拔5000m高度的低压低氧（PB=404mmHg,PO2=84mmHg,11．1％O2）处理,每天6h。制备大鼠离体胸主动脉环并将其恒温灌流,记录黄连对动脉环收缩活动的影响并研究其作用机制。结果：黄连使去甲肾上腺素（NE）和氯化钾（KCl）诱发的正常氧和CIHH大鼠离体动脉环收缩活动明显减弱,但其对两组大鼠动脉收缩的抑制作用无明显差异。除去内皮后各组收缩幅度均无显著变化。以收缩幅度为指标,用Logit法计算正常氧组黄连对NE和KCl诱发收缩的ICso分别为2．99g／L和6．14g／L,CIHH组则分别为3．45g／L和5．81g／L。格列苯脲、左旋硝基精氨酸甲酯可部分阻断黄连对两组大鼠动脉环收缩活动的抑制作用,吲哚美辛还能抑制黄连对正常氧大鼠动脉的舒张作用。黄连明显抑制NE诱发的两组血管细胞内钙性和细胞外钙性收缩。结论：黄连对正常氧和CIHH大鼠离体胸主动脉环具有明显舒张作用,该作用不依赖血管内皮,且在两组之间无显著差异。其抑制CIHH大鼠血管收缩的机制可能是通过激活ATP敏感型钾通道,增加一氧化氮浓度,抑制肌浆网释放Ca2＋及细胞外Ca2＋内流;对正常氧大鼠动脉的舒张作用可能还通过增加局部前列环素。     

Alteration of ATP-sensitive K+ channels in rabbit aortic smooth muscle during left ventricular hypertrophy

We investigated the impairment of ATP-sensitive K(+) (K(ATP)) channels in aortic smooth muscle cells (ASMCs) from isoproterenol-induced hypertrophied rabbits. The amplitude of K(ATP) channels induced by the K(ATP) channel opener pinacidil (10 μM) was greater in ASMCs from control than from hypertrophied animals. In phenylephrine-preconstricted aortic rings, pinacidil induced relaxation in a dose-dependent manner. The dose-dependent curve was shifted to the right in the hypertrophied (EC(50): 17.80 ± 3.28 μM) compared with the control model (EC(50): 6.69 ± 2.40 μM). Although the level of Kir6.2 subtype expression did not differ between ASMCs from the control and hypertrophied models, those of the Kir6.1 and SUR2B subtypes were decreased in the hypertrophied model. Application of the calcitonin-gene related peptide (100 nM) and adenylyl cyclase activator forskolin (10 μM), which activates protein kinase A (PKA) and consequently K(ATP) channels, induced a K(ATP) current in both control and hypertrophied animals; however, the K(ATP) current amplitude did not differ between the two groups. Furthermore, PKA expression was not altered between the control and hypertrophied animals. These results suggests that the decreased K(ATP) current amplitude and K(ATP) channel-induced vasorelaxation in the hypertrophied animals were attributable to the reduction in K(ATP) channel expression but not to changes in the intracellular signaling mechanism that activates the K(ATP) current.     

Mitochondrial BKCa channels contribute to protection of cardiomyocytes isolated from chronically hypoxic rats

Chronic hypoxia protects the heart against injury caused by acute oxygen deprivation, but its salutary mechanism is poorly understood. The aim was to find out whether cardiomyocytes isolated from chronically hypoxic hearts retain the improved resistance to injury and whether the mitochondrial large-conductance Ca2+-activated K+ (BKCa) channels contribute to the protective effect. Adult male rats were adapted to continuous normobaric hypoxia (inspired O2 fraction 0.10) for 3 wk or kept at room air (normoxic controls). Myocytes, isolated separately from the left ventricle (LVM), septum (SEPM), and right ventricle, were exposed to 25-min metabolic inhibition with sodium cyanide, followed by 30-min reenergization (MI/R). Some LVM were treated with either 30 μM NS-1619 (BKCa opener), or 2 μM paxilline (BKCa blocker), starting 25 min before metabolic inhibition. Cell injury was detected by Trypan blue exclusion and lactate dehydrogenase (LDH) release. Chronic hypoxia doubled the number of rod-shaped LVM and SEPM surviving the MI/R insult and reduced LDH release. While NS-1619 protected cells from normoxic rats, it had no additive salutary effect in the hypoxic group. Paxilline attenuated the improved resistance of cells from hypoxic animals without affecting normoxic controls; it also abolished the protective effect of NS-1619 on LDH release in the normoxic group. While chronic hypoxia did not affect protein abundance of the BKCa channel regulatory β1-subunit, it markedly decreased its glycosylation level. It is concluded that ventricular myocytes isolated from chronically hypoxic rats retain the improved resistance against injury caused by MI/R. Activation of the mitochondrial BKCa channel likely contributes to this protective effect.     

辣椒素对颈动脉窦压力感受性反射的易化作用

在30只隔离灌流颈动脉窦区的麻醉大鼠,观察了辣椒素(capsaicin,CAP)对颈动脉窦压力感受性反射的影响.结果显示(1)以CAP(1 μmol/L)隔离灌流大鼠左侧颈动脉窦区时,颈动脉窦压力感受性机能曲线向左下方移位,曲线最大斜率(peak slope,PS)由0.34±0.01增至0.42±0.01(P＜0.01),反射性血压下降幅度(reflex decrease,RD)由36.51±1.26增至45,01±0.71 mmHg(P＜0.01).阈压、平衡压和饱和压分别从70.43±2.09、95.5±1.71和177.60±1.37 mmHg下降至52.86±2.80、87.00±1.58、163.55±2.12 mmHg(P＜0.01).其中PS和RD的变化呈明显的剂量依赖性.(2)用香草酸受体亚型(vanilloid receptor subtypel,VRl)阻断剂钌红(ruthenium red,100 μmo1/L)预处理后,CAP的上述反射效应即被阻断.(3)先给予KArp通道阻断剂格列苯脲(glibenclamide,20 μmo1/L)也取消了CAP对压力感受性反射的影响.结果表明,CAP对大鼠颈动脉窦压力感受性反射有易化作用,此作用似与VR1介导的KATP通道开放有关.     

ATP inhibits the hypoxia response in type I cells of rat carotid bodies

Summary During hypoxia, ATP was released from type I (glomus) cells in the carotid bodies. We studied the action of ATP on the intracellular Ca(2+) concentration ([Ca(2+)](i)) of type I cells dissociated from rat carotid bodies using a Ca(2+) imaging technique. ATP did not affect the resting [Ca(2+)](i) but strongly suppressed the hypoxia-induced [Ca(2+)](i) elevations in type I cells. The order of purinoreceptor agonist potency in inhibiting the hypoxia response was 2-methylthioATP > ATP > ADP > alpha, beta-methylene ATP > UTP, implicating the involvement of P2Y(1) receptors. Simultaneous measurements of membrane potential and [Ca(2+)](i) show that ATP inhibited the hypoxia-induced Ca(2+) signal by reversing the hypoxia-triggered depolarization. However, ATP did not oppose the hypoxia-mediated inhibition of the oxygen-sensitive TASK-like K(+) background current. Neither the inhibition of the large-conductance Ca(2+)-activated K(+) (maxi-K) channels nor the removal of extracellular Na(+) could affect the inhibitory action of ATP. Under normoxic condition, ATP caused hyperpolarization and increase in cell input resistance. These results suggest that the inhibitory action of ATP is mediated via the closure of background conductance(s) other than the TASK-like K(+), maxi-K or Na(+) channels. In summary, ATP exerts strong negative feedback regulation on hypoxia signaling in rat carotid type I cells.