Development of an isolated, pulsatile blood-perfused rat lung model for evaluating the preserved lung functions

The purpose of this study was to develop an isolated, pulsatile blood-perfused rat lung model that allows us to evaluate the preserved lung functions. Lungs isolated from Sprague-Dawley rats, were perfused with venous whole blood by either a pulsatile or constant flow. The effuent was continuously deoxygenated with a 95% N₂/5% CO₂ gas mixture. Airway resistance, lung compliance, elastic work, flow resistive work, pulmonary vascular resistance, and blood gas analysis were assessed. Pressor responses toN ^G -monomethyl-l-arginine (l-NMMA) were compared between pulsatile and constant blood flow. At a flow of 0.1 ml/g body weight/min, pulsatile perfusion allowed for stable perfusion at least for 2h (mean 162.5±15.1 min) with stable aerodynamic and hemodynamic variables including blood gas tensions, whereas constant perfusion resulted in immediate lung failure. Whenl-NMMA was added to the perfusate, the mean pulmonary artery pressure did not show any change in the constant flow (6.0±2.6% increase), but did show a significant increase in the pulsatile flow (45±11% increase). Pulsatile blood flow reduced the pulmonary vascular resistance relative to the constant flow and allowed for a 2-h perfusion period to evaluate the lung function. The vasorelaxant mechanism in the pulsatile perfusion is related in part to the endothelial-dependent relaxation observed in the nitric oxide pathway. Presented in part at the 79th, Annual Clinical Congress of the American College of Surgeons (ACS) held in San Francisco, CA USA, 1993.     

Involvement of cyclic nucleotide-dependent protein kinases in cyclic AMP-mediated vasorelaxation

1. The involvement of cyclic AMP-dependent protein kinase (PKA) and cyclic GMP-dependent protein kinase (PKG) in the effects of cyclic AMP-elevating agents on vascular smooth muscle relaxation, cyclic nucleotide dependent-protein kinase activities and ATP-induced calcium signalling ([Ca²⁺]_i) was studied in rat aorta. Cyclic AMP-elevating agents used were a β-adrenoceptor agonist (isoprenaline), a phosphodiesterase 3 (PDE3) inhibitor (SK&F 94120) and a PDE4 inhibitor (rolipram).
2. In rat intact aorta, the relaxant effect induced by isoprenaline (0.01–0.3 μM) was decreased by a specific inhibitor of PKA, H-89, whereas a specific inhibitor of PKG, Rp-8-Br-cyclic GMPS, was without effect. No significant difference in PKA and PKG activity ratios was detected in aortic rings when isoprenaline 10 μM was used. At the same concentration, isoprenaline did not modify ATP-induced changes in [Ca²⁺]_i in smooth muscle cells. Neither H-89 nor Rp-8-Br-cyclic GMPS modified this response. These findings suggest that PKA is only involved in the relaxant effect induced by low concentrations of isoprenaline (0.01–0.3 μM), whereas for higher concentrations, other mechanisms independent of PKA and PKG are involved.
3. The relaxant effects induced by SK&F 94120 and rolipram were inhibited by Rp-8-Br-cyclic GMPS with no significant effect of H-89. Neither SK&F 94120, nor rolipram at 30 μM significantly modified the activity ratios of PKA and PKG. Rolipram inhibited the ATP-induced transient increase in [Ca²⁺]_i. This decrease was abolished by Rp-8-Br-cyclic GMPS whereas H-89 had no significant effect. These results suggest that PKG is involved in the vascular effects induced by the inhibitors of PDE3 and PDE4. Moreover, since it was previously shown that PDE3 and PDE4 inhibitors only increased cyclic AMP levels with no change in cyclic GMP level, these data also suggest a cross-activation of PKG by cyclic AMP in rat aorta.
4. The combination of 5 μM SK&F 94120 with rolipram markedly potentiated the relaxant effect of rolipram. This relaxation was decreased by H-89 and not significantly modified by Rp-8-Br-cyclic GMPS. Moreover, the association of the two PDE inhibitors significantly increased the activity ratio of PKA without changing the PKG ratio. The present findings show that PKA rather than PKG is involved in this type of vasorelaxation. The differences in the participation of PKA vs PKG observed when inhibitors of PDE3 and PDE4 were used alone or together could be due to differences in the degree of accumulation of cyclic AMP, resulting in the activation of PKA or PKG which are differently localized in the cell.
5. These findings support a role for both PKA and PKG in cyclic AMP-mediated relaxation in rat aorta. Their involvement depends on the cellular pathway used to increase the cyclic AMP level.

     

附子水煎剂对家兔离体肺动脉血管的舒张作用

目的:研究附子Monkshood Root(DMR)水煎剂对肺动脉环的舒张作用及机制.方法:采用家兔离体肺动脉平滑肌标本,以去甲肾上腺素(NA)预收缩肺动脉后,给予不同剂量的附子观察其张力变化,并探讨去除血管内皮、给予NO合酶抑制剂左旋硝基精氨酸(L-NNA)、甲烯蓝(MB)、环氧酶抑制剂吲哚美辛和β肾上腺素能受体阻断剂普萘洛尔对血管张力变化的影响.结果:附子对血管环静息张力无明显影响,但不同剂量的附子可使10-6mol·L-1NA预收缩血管产生明显舒张(r=0.71,P＜0.001).去除血管内皮、10-4mol·L-1L-NNA或10-5mol·L-1MB可减弱附子的舒张作用.另外,1 mg·mL-1DMR对无内皮血管环NA和KCl的量效曲线无明显影响,DMB温育前后NA的PD2值为7.56±0.95和7.30±0.83,P＞0.05;KCl的PD2值为1.74±0.48和1.71±0.51,P＞0.05.结论:附子水煎剂对肺动脉的舒张作用是内皮依赖性,与内皮细胞释放的NO有关,而与平滑肌细胞膜上的受体依赖性Ca2 通道和电压依赖性Ca2 无关.     

High-conductance calcium-activated potassium channels

High-conductance, calcium-activated potassium (Maxi-K) channels represent a group of proteins with diverse physiologic functions. Although the role of Maxi-K channels in the CNS is complex and still an area of active academic research, there appears to be better agreement concerning the contribution of these channels to the regulation of smooth muscle tone and, thus the expectations remain high for Maxi-K channel openers having use in the treatment of hypertension, overactive bladder, asthma or erectile dysfunction. Despite this consensus view, at the present time, there is only one compound that targets Maxi-K channels in clinical development for overactive bladder conditions. In the present review, the latest developments in the identification of potent and selective Maxi-K channel openers and their utility in the treatment of smooth muscle disorders will be discussed.     

映山红花总黄酮对全脑缺血再灌注大鼠脑基底动脉超极化反应的诱导作用

目的 探讨映山红花总黄酮（TFR）对内皮源性超极化因子（EDHF）介导的全脑缺血再灌注大鼠脑基底动脉（CBA）血管舒张和平滑肌细胞膜静息电位超极化反应的诱导作用。方法 采用四血管结扎法建立大鼠全脑缺血再灌注模型，测定离体大鼠CBA平滑肌细胞膜静息电位和血管舒张功能。结果 在3×10^?5 mol/L L–NAME和1×10^?5 mol/L吲哚美辛存在时，全脑缺血再灌注可明显促进乙酰胆碱（Ach，1×10^?7～1×10^?5 mol/L）诱导大鼠CBA产生非NO、非PGI₂介导的血管舒张和平滑肌细胞膜静息电位超极化；TFR 11～2 700 mg/L可使全脑缺血再灌注大鼠CBA产生较明显的非NO、非PGI₂介导的血管舒张和平滑肌细胞膜静息电位超极化反应，并能被Ca²⁺激活的K通道阻断剂四乙胺（TEA，1 mmol/L）和内源性硫化氢（H₂S）生成抑制剂dl-炔丙基甘氨酸（PPG，1×10^?4 mol/L）显著抑制。结论 全脑缺血再灌注明显增强大鼠CBA中非NO、非PGI₂介导的血管舒张和平滑肌细胞超级化。TFR明显诱导全脑缺血再灌注大鼠CBA产生此种血管舒张和超级化，即EDHF反应，并可能与H₂S有关。     

黄芪甲甙对大鼠离体肠系膜动脉血管舒缩功能的影响

目的：观察黄芪甲甙对大鼠离体肠系膜动脉舒缩功能的影响，并探讨其可能机制。方法：分离肠系膜动脉1—2级分支制备离体肠系膜血管环固定于微血管张力测定仪，观察黄芪甲武对血管环舒缩功能的影响。结果：①不同浓度的黄芪甲甙（30mg／L和100mg／L）孵育后，苯肾上腺素引起的血管收缩较对照组明显下降（尸〈0．05或P〈0．01）。②累积浓度的黄芪甲甙对苯肾上腺素（2×10^-6mol／L）预收缩的内皮完整或去内皮肠系膜动脉血管环均产生浓度依赖性的舒张作用，中高浓度的黄芪甲甙（10mg／L、30mg／L和100mg／L）对内皮完整组的舒张作用明显强于去内皮组（P〈0．05或P〈0．01）。③累积浓度的黄芪甲甙对KCl预收缩的肠系膜动脉血管环张力无明显影响（P〉0．05）。④L-NAME（10^-4mol／L）预处理能显著减弱黄芪甲甙的舒血管作用（P〈0．05或P〈0．01）。结论：黄芪甲甙具有一定的内皮依赖性舒张血管作用，且主要通过NO途径发挥作用。     

Effects of an aqueous extract of Terminalia arjuna on isolated rat atria and thoracic aorta

Terminalia arjuna (Combretaceae) is used traditionally in ayurveda, to treat a variety of cardiovascular disorders. The aims of this study were to characterize the positive inotropic effect of the aqueous extract of T. arjuna bark in isolated paced rat left atria and to study its effects on a vascular smooth muscle preparation, the rat thoracic aorta. The crude and semipurified aqueous extracts produced a positive inotropic effect of rat atria and the maximum contraction was comparable to that produced by isoprenaline. The positive inotropic effect of the extract was completely blocked by a β-adrenoceptor blocker, propranolol, and an uptake-1 blocker, cocaine. In precontracted aorta, the aqueous extract produced a contraction followed by relaxation. Propranolol did not block the relaxant effect of the aqueous extract. It is concluded that the positive inotropic effect of the aqueous extract was mediated via an action on β₁-adrenoceptors and was likely to be due to the release of noradrenaline from the sympathetic nerve endings. The vasorelaxant effect of the extract, however, was not mediated via an action on β₂ adrenoceptor.     

体外反搏对高胆固醇血症猪颈动脉内膜形态和功能的影响

目的 探讨长期体外反搏对高胆固醇血症猪颈动脉内膜形态和内皮依赖血管舒张功能的影响.方法 18头雄性乳猪被随机分为3组,每组6只.用喂养高脂饲料乳猪复制高胆固醇血症模型(高脂饲养组);采用增强型体外反搏(EECP)治疗模型动物36 h(EECP组);以正常饲养组作为对照.取各组动物颈总动脉血管.用扫描电镜和透射电镜观察颈动脉内膜的形态,并测定离体颈动脉血管环对不同浓度梯度乙酰胆碱(Ach)的舒张反应.结果 扫描电镜下观察高脂饲养组血管内皮细胞排列紊乱,内皮细胞有明显脱落,部分细胞胞膜皱缩.体积明显减小,符合凋亡细胞的外形特征;EECP组血管内皮细胞排列紊乱的情形明显减轻,内皮细胞大小不一的程度减轻,皱缩脱落细胞较高脂饲养组明显减少.透射电镜下观察高脂饲养组血管内皮细胞凋亡、脱落,内膜破损明显,平滑肌细胞侵入和增生,泡沫细胞形成;EECP组内皮细胞呈梭形,内皮完整,内皮与内皮下结构连接紧密,平滑肌细胞轻度增生,少见泡沫细胞.在10-8～10-5mol/L Ach时,高脂饲养组和EECP组的血管舒张率较正常饲养组显著降低(P均＜0.05);在10-7～10-5mol/L Ach时,EECP组的血管舒张率较高脂饲养组明显提高(P均＜0.05).结论 高胆固醇血症动物颈动脉内皮超微结构改变提示有动脉粥样硬化形成,内皮依赖血管舒张功能明显受损;长期EECP干预可以显著改善内皮结构损伤和内皮依赖血管舒张功能,这可能是其发挥抗动脉粥样硬化作用的机制之一.     

大豆异黄酮心血管作用的研究进展

异黄酮是一类具有雌激素样作用的生物活性物质。大豆中的异黄酮主要有两种形式：染料木黄酮和黄豆苷原。近年来发现，大豆异黄酮具有较强的扰动脉粥样硬化和舒血管效应，影响细胞增殖和新生血管的形成，对心血管有保护和调节作用。