紫菀乙醇提取物对豚鼠离体气管平滑肌收缩功能的影响

本试验旨在研究紫菀乙醇提物对豚鼠离体气管平滑肌收缩功能的影响。采用离体气管恒温灌流的方法,将豚鼠气管制成气管螺旋条,通过 BL-420F 生物机能实验系统测定其张力的变化,观察紫菀乙醇提物对离体气管平滑肌静息状态下的舒张作用,以及在氯化乙酰胆碱(Ach)、磷酸组胺(His)、CaCl₂条件下和无钙下Ach诱导细胞内钙释放和外钙内流所致两种收缩条件下对离体气管平滑肌张力变化的影响。试验结果显示,低浓度紫菀乙醇提取物(0.002~0.008 g/mL)对静息状态下豚鼠离体气管平滑肌具有一定的收缩作用,高浓度(0.008~0.196 g/mL)时具有舒张作用;低、中、高3个剂量组均可抑制Ach、His和CaCl₂引起的气管平滑肌收缩强度,使各致痉剂的量效曲线非平行右移并降低最大效应。紫菀乙醇提取物对His的抑制作用强度最大,其次为Ach,最后是CaCl₂,且均呈剂量依赖性。以上结果表明紫菀乙醇提物具有舒张气管平滑肌的作用,其机制可能与抑制豚鼠气管平滑肌M受体、H₁受体和阻断Ca²⁺通道从而抑制细胞Ca²⁺内流有关。     

中药产复康对大鼠离体子宫平滑肌收缩功能的影响

为了观察中药制剂产复康对离体子宫平滑肌的收缩功能,测定了产复康对大鼠离体子宫平滑肌收缩功能和催产素引起的大鼠离体子宫平滑肌收缩功能的影响。结果发现低剂量产复康可以促进大鼠离体子宫平滑肌的收缩功能,提高子宫的活动性,高剂量则对子宫呈抑制作用;产复康对催产素引起的大鼠离体子宫平滑肌收缩功能具有抑制作用,且呈剂量-效应关系。产复康对大鼠离体子宫具有双向调节作用。     

麻叶荨麻醇提液对大鼠离体子宫运动的影响

为探究荨麻对子宫运动的影响及其可能机制,本试验用生物信号处理系统测定了浓度递增(0.5%、1.0%、2.0%、4.0%、8.0%和16.0%)的麻叶荨麻(Urtica cannabina,UC)醇提液对未孕大鼠离体子宫收缩频率、收缩张力和收缩幅度的影响,并用特异性M-受体阻断剂硫酸阿托品(atropine,A,2.5 μg/mL)和2.0% UC联合用药,分为3个处理: UC单独处理、UC+A和A+UC,观察UC对子宫收缩的影响是否与M-受体有关.结果显示,在UC浓度递增到4.0%时收缩频率较用药前显著增加(P <0.05);浓度递增到4.0%、8.0%时,收缩幅度较用药前极显著降低(P <0.01);但浓度递增UC对子宫收缩张力影响不显著(P >0.05).一次性加入2.0% UC后子宫收缩张力迅速增加并接近僵直,之后逐渐降低.无论UC+A或A+UC处理都使子宫收缩频率较用药前明显加快,收缩张力极显著增加(P <0.01),但2个联合用药处理组之间差异不显著(P >0.05);UC+A和A+UC处理组收缩张力较UC单独用药组均极显著降低(P <0.01).结果表明,UC可兴奋未孕大鼠离体子宫,A可缓解UC引起的子宫僵直或张力增加,但不能阻断UC引起的子宫收缩频率增加.提示UC对未孕大鼠离体子宫的兴奋作用和激动与M-受体有一定关系,但可能还存在其他机制.     

小裂芽梅衣对兔离体肠平滑肌的舒张作用及其机制

采用兔离体肠肌试验,应用BL-420E生物机能实验系统比较小裂芽梅衣对正常肠肌及乙酰胆碱、氯化钡、组胺所致肠平滑肌运动的影响。应用IP3受体阻断剂肝素、肌浆网ryanodine受体阻断剂钌红、一氧化氮合酶抑制剂左旋硝基精氨酸甲酯,探讨小裂芽梅衣对兔离体肠平滑肌的作用机制。结果表明,小裂芽梅衣可浓度依赖性抑制兔小肠平滑肌的收缩,且对乙酰胆碱、氯化钡、组胺诱导的肠平滑肌收缩有明显抑制作用(P0.05)。肝素能显著增强小裂芽梅衣对兔小肠平滑肌运动的抑制作用(P0.05),左旋硝基精氨酸甲酯和钌红能部分增强小裂芽梅衣对兔小肠平滑肌运动的抑制作用(P0.01)。小裂芽梅衣乙醇提取物对兔小肠平滑肌收缩的抑制作用机制可能与增加NO浓度、抑制IP3受体和肌浆网ryanodine受体介导的内钙释放有关。     

菊花水提物对家兔离体小肠平滑肌收缩性的影响

研究菊花水提物在有乙酰胆碱、组胺和阿托品的条件下对家兔离体小肠平滑肌收缩性的影响。以家兔离体小肠平滑肌条为模型,考察在正常克氏液条件下分别加入乙酰胆碱、组胺和阿托品后家兔平滑肌条的收缩状况及在该条件下分别加入0.5g/mL菊花水提液物后家兔小肠平滑肌条的收缩状况。结果:菊花水提物对家兔离体小肠平滑肌的收缩具有一定的促进作用,菊花水提物能协同促进乙酰胆碱对家兔离体小肠平滑肌的收缩作用,拮抗阿托品的作用,对组胺的小肠收缩振幅影响不显著。菊花水提物对家兔小肠平滑肌收缩活动具有明显的兴奋作用,这种兴奋作用可由M受体介导。     

松萝酸对兔离体肠平滑肌运动的舒张作用

以兔离体肠平滑肌为研究对象,考察松萝酸对兔离体肠平滑肌运动的影响,并探讨其作用机制。利用BL-420E生物机能实验系统,观察松萝酸对兔离体小肠平滑肌自主收缩的影响;采用工具药乙酰胆碱、组胺、氯化钡诱导小肠平滑肌收缩,并记录小肠平滑肌收缩频率和振幅。采用IP3受体阻断剂肝素、肌浆网ryanodine受体阻断剂钌红(RR)和一氧化氮合酶抑制剂左旋硝基精氨酸甲脂(L-NAME),探明松萝酸对兔离体肠平滑肌作用的机制。结果发现,松萝酸可抑制兔离体小肠平滑肌收缩,具有浓度依赖性,且对乙酰胆碱、组胺、氯化钡诱导的肠肌收缩具有显著的抑制作用。IP3受体阻断剂肝素可增强松萝酸舒张肠平滑肌运动的频率(P0.01)和振幅(P0.05),肌浆网ryanodine受体阻断剂钌红和一氧化氮合酶抑制剂左旋硝基精氨酸甲酯可显著增强松萝酸舒张兔离体肠平滑肌运动的频率,对振幅影响不显著。说明松萝酸可显著抑制兔离体小肠平滑肌收缩的频率和振幅,其机制可能与增加一氧化氮浓度,抑制IP3受体和肌浆网ryanodine受体介导的内钙释放有关。     

硫氧还蛋白对过氧化氢诱导的BRL-3A细胞损伤的保护作用

本试验利用不同浓度过氧化氢（H₂O₂）作用于BRL-3A大鼠肝细胞,用四甲基偶氮唑蓝（MTT）比色法检测BRL-3A细胞存活数量以确定H₂O₂最适损伤浓度。试验随机分为正常对照组、H₂O₂处理组和硫氧还蛋白(2.5和5 μmol/L) 预处理组,用脂质过氧化物丙二醛（MDA）、超氧化物歧化酶（SOD）、过氧化氢酶（CAT）试剂盒测定细胞的氧化应激变化。结果显示1000 μmol/L H₂O₂对BRL-3A细胞增殖具有显著的抑制作用（P<0.05）;2.5 μmol/L 硫氧还蛋白对H₂O₂损伤的BRL-3A细胞具有保护作用,能显著抑制H₂O₂诱导的BRL-3A细胞损伤产生MDA（P＜0.05）,并显著增加细胞SOD及CAT的活性（P＜0.05）,从而保护肝细胞。本试验结果表明,硫氧还蛋白对H₂O₂诱导BRL-3A细胞的氧化应激损伤具有保护作用。     

奶牛子宫内膜上皮细胞氧化应激模型的建立及奶牛脂肪间充质干细胞对其迁移的影响

【目的】探讨奶牛脂肪间充质干细胞（bovine adipose-derived mesenchymal stem cells,bAD-MSCs）对氧化应激条件下奶牛子宫内膜上皮细胞迁移能力的影响。【方法】使用0、5、25、50、100、200 μmol/L H₂O₂处理奶牛子宫内膜上皮细胞2、4、6、8、12 h后,通过MTT试验检测细胞存活率、流式细胞术检测细胞内活性氧（ROS）水平来筛选H₂O₂诱导奶牛子宫内膜上皮细胞氧化应激模型的最佳条件。在细胞划痕试验中设立对照组、H₂O₂组、bAD-MSCs共培养组（1∶0.5）、bAD-MSCs共培养组（1∶1）、奶牛乳腺上皮细胞（MACT）共培养组（1∶0.5）和MACT共培养组（1∶1）共6组,分析奶牛子宫内膜上皮细胞迁移能力,并利用Western blotting检测细胞外蛋白调节激酶（Erk）和磷酸化细胞外蛋白调节激酶（pErk）蛋白的表达水平。【结果】MTT试验结果显示,4~12 h内50 μmol/L H₂O₂组细胞存活率为50%~80%,适用于构建氧化应激模型。流式细胞术结果显示,用50 μmol/L H₂O₂刺激奶牛子宫内膜上皮细胞2 h时,ROS水平显著高于对照组与4、6、8、12 h组（P<0.05）。划痕试验结果显示,与对照组相比,H₂O₂组奶牛子宫内膜上皮细胞的迁移能力显著降低（P＜0.05）;与H₂O₂组相比,bAD-MSCs共培养组奶牛子宫内膜上皮细胞的迁移能力均显著增加（P＜0.05）,MACT共培养组细胞迁移能力均显著降低（P＜0.05）。Western blotting结果显示,与对照组相比,H₂O₂组奶牛子宫内膜上皮细胞中pErk蛋白表达水平显著降低（P＜0.05）;与H₂O₂组相比,bAD-MSCs共培养组奶牛子宫内膜上皮细胞中pErk蛋白表达水平均显著升高（P＜0.05）,MACT共培养组细胞中pErk蛋白表达水平均显著降低（P＜0.05）。【结论】50 μmol/L H₂O₂处理2 h可成功构建奶牛子宫内膜上皮细胞氧化应激模型,bAD-MSCs可促进氧化应激条件下奶牛子宫内膜上皮细胞的迁移并参与调控Erk蛋白的表达。     

维生素E对H2O2诱导的奶牛乳腺上皮细胞氧化损伤及紧密连接相关基因表达的影响

试验通过研究维生素E （VE）对H₂O₂诱导的奶牛乳腺上皮细胞（MAC-T cells）氧化损伤及紧密连接相关基因表达的影响,旨在揭示维生素E对缓解奶牛乳腺细胞氧化应激的作用。试验设对照组（完全培养基处理组）、H₂O₂组和H₂O₂＋VE组。利用MTT法检测奶牛乳腺细胞存活率,比色法检测奶牛乳腺细胞培养液中超氧化物歧化酶（SOD）和过氧化氢酶（CAT）活性、丙二醛（MDA）和活性氧（ROS）含量;通过实时荧光定量PCR检测紧密连接基因ZO-1、occludin、claudin-1的相对表达量。结果显示,与对照组相比,H₂O₂组的奶牛乳腺上皮细胞存活率显著下降（P<0.05）,ROS和MDA含量显著增加（P<0.05）,SOD和CAT活性显著下降（P<0.05）;与H₂O₂组相比,H₂O₂＋20 μmol/L VE组的细胞存活率显著上升（P<0.05）,ROS和MDA含量显著下降（P<0.05）,SOD和CAT活性显著增加（P<0.05）。此外,与对照组相比,H₂O₂组极显著抑制了紧密连接基因的相对表达量（P<0.01）;而与H₂O₂组相比,添加维生素E极显著缓解了H₂O₂对紧密连接基因相对表达的抑制作用（P<0.01）。本研究结果证明,维生素E不仅能够减轻H₂O₂诱导的奶牛乳腺上皮细胞氧化损伤,还能缓解H₂O₂对紧密连接基因相对表达的抑制作用。     

外源H2O2引发对燕麦种胚线粒体AsA-GSH循环的影响

本试验为了探究外源H₂O₂引发对燕麦（Avena sativa）种胚线粒体抗坏血酸-谷胱甘肽（Ascorbic acid-glutathione,AsA-GSH）循环的影响,设置浓度为0 mol·L^-1,0.96 mol·L^-1,1.92 mol·L^-1,3.84 mol·L^-1和7.68 mol·L^-1 H₂O₂引发燕麦种子0 h （CK）,6 h,12 h和18 h后,分析燕麦种胚线粒体AsA-GSH循环抗氧化酶活性及其脂质过氧化作用的变化规律。结果表明：外源H₂O₂引发导致了燕麦种胚线粒体H₂O₂及丙二醛含量的显著升高（P<0.05）,其H₂O₂的清除则由其线粒体AsA-GSH循环来发挥主要作用,但其抗氧化能力的变化与外源H₂O₂引发的浓度和时间密切相关,低浓度（<0.96 mol·L^-1）外源H₂O₂引发时间越短对燕麦种胚线粒体AsA-GSH循环抗氧化酶活性的促进效果就越小,而引发时间越长则其促进效果就越大;相反,高浓度（>3.84 mol·L^-1）外源H₂O₂引发时间越短则对其抗氧化酶活性的抑制作用就越弱,而引发时间越长则其抑制作用就越强。因此,利用外源H₂O₂对燕麦种子进行引发时,H₂O₂浓度应低于1.92 mol·L^-1、引发时间应少于12 h。     

Effect of Sanguinarine on Active Capacity of Isolated Rat Uterine Smooth Muscle in vitro and Its Mechanism

The study was aimed to explore the effects of the sanguinarine on activity of isolated rat uterine smooth muscle in vitro. The effect of the sanguinarine on activity of the isolated myometrium of non-pregnant Sprague-Dawley rats eight weeks old was recorded by BL-420F four channels physiological recorder. Four antagonists, atropine sulfate, ranitidine hydrochloride, propranolol hydrochloride and diphenhydramine hydrochloride were used to study their mechanism, respectively. The results showed that sanguinarine and Yuan hu painkillers markedly inhibited the frequency, amplitude and activity of uterine contractions induced by oxytocin injection (P<0.05). The inhibitory effect of sanguinarine on uterine muscle contractions was blocked after using diphenhydramine hydrochloride (H₁-receptor antagonist) and ranitidine hydrochloride (H₂-receptor antagonist). However, after using atropine sulfate (M-receptor antagonist) and propranolol hydrochloride (β-receptor antagonist), sanguinarine also significantly inhibited the contractions of rat uterine smooth muscle (P<0.05). It was concluded that the effect of sanguinarine on activity of uterine smooth muscle in rats was mainly associated with H₁ receptor or H₂ receptor but not M receptor or β receptor.     

Pharmacological evaluation of sheep lung strip

Isolated sheep lung parenchymal strips responded to histamine > carbachol > PGF_2a > 5-HT with contractions, and to isoproterenol (Isop), and to large doses of epinephrine (E), norepinephrine (NE) and phenylephrine (PE) with relaxations. PGF_2a-contracted lung strip responded to PGE₁ and PGE₂ with relaxation. The strips which were partially contracted to histamine, PGF_2a, 5-HT and carbachol also responded to isop, E and NE with relaxations. Histamine responses were not modified by metiamide (an H₂-receptor antagonist). Mepyramine and atropine selectively antagonized contractions to histamine and carbachol, respectively. After β-blockade with propranolol, lung strips responded to NE > E > PE > isop with contractions, which were inhibited or reversed by phentolamine and dibenzyline. It is concluded that H₁ receptors are present in sheep peripheral airway smooth muscles, and that a- and β-adrenoceptors mediate contraction and relaxation, respectively, in sheep lung strips.     

Diazepam potentiates the positive inotropic effects of histamine and forskolin in guinea-pig papillary muscles

There have been diverse reports on the effects of diazepam on cardiac contractility. The purpose of this study was to examine whether diazepam modifies the inotropic response elicited by histamine on an isolated guinea-pig papillary muscle. The responses of electrically driven papillary muscle to histamine and cyclic AMP-related inotropic agents were recorded in the absence and in the presence of diazepam. Histamine and forskolin, which directly stimulate adenylate cyclase, significantly increased the contractile force in the papillary muscle in a concentration-dependent manner. A histaminergic H₂-receptor antagonist, cimetidine, but not a H₁-receptor antagonist, diphenhydramine, at 10 μ M produced a rightward shift in the concentration-response curve for histamine. Diazepam (10 μ M ) shifted the concentration-response curve for histamine and forskolin to the left by 1.8 and 1.6 times, respectively. Neither a central type (fulmazenil) nor a peripheral type (PK11195) of benzodiazepine receptor antagonist modified the effect of diazepam on the histaminergic-evoked contraction. Phosphodiesterase blockade by 3-isobutyl-1-methylxanthine shifted the concentration-dependent curve for histamine to the left. A combination of 3-isobutyl-1-methylxanthine also produced a leftward shift of the curve. However, there was no significant difference between the 3-isobutyl-1-methylxanthine only group and the combination group. These results indicate that diazepam potentiates the positive inotropic effect produced by histamine, probably mediated via an increase in cyclic AMP levels induced by histamine.     

Characterization of muscarinic receptor subtype mediating contraction and relaxation in equine coronary artery in vitro

In coronary arterial rings isolated from horses, 10-^-8-10^-6 mol/l acetylcholine (ACh) induced concentration-dependent contractions which were potentiated by the removal of endothelium and by pretreatment with I,-nitro-arginine (LNAG) or methylene blue (MB). Relatively lower concentrations of Ach 10-¹⁴-10-⁸ mol/l) induced relaxation when the coronary rings were contracted by phenylephrine (PE). ACh-induced contractions in the coronary rings without endothelium were competitively inhibited by each muscarinic subtype selective antagonist in the following order of potency: 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) > pirenzepine ≥ parafluoro-hexahydrosiladiphenidol (pFHHSiD) > methoctramine. ACh-induced relaxation in the rings with endothelium was inhibited by LNAG or MB, and by each selective antagonist in the following order of potency: 4-DAMP < pFHHSiD ≥ pirenzepine ≥ methoctramine. These results suggest that the ACh-induced contraction and relaxation in equine coronary arteries are mediated mainly by an M₃-receptor located on the smooth muscle cells and endothelial cells, respectively, and that the stimulation of the M₃-receptor on the endothelial cells liberates nitric oxide.     

Functional characterization of the muscarinic receptors involved in endothelium-dependent relaxation in isolated canine uterine artery

Acetylcholine interacts with endothelial muscarinic receptors releasing nitric oxide and causing vasodilatation. To identify the receptor subtype responsible for acetylcholine-induced relaxation in canine uterine artery, the usual organ bath method for in vitro investigation on isolated blood vessels was applied. Using a range of muscarinic receptor antagonists such as atropine (nonselective), pirenzepine (M₁-selective), methoctramine (M₂-selective) and p -fluoro-hexahydro-sila-difenidol ( p -FHHSiD) (M₁/M₃) and determining pA2 value of those antagonists through Shild analysis, we aimed at establishing a precise receptor mechanism underlying acetylcholine-induced relaxation in isolated canine uterine artery. The relaxation of uterine arterial rings in response to acetylcholine in the presence or absence of selective muscarinic receptors antagonists was calculated using concentration response curves. Acetylcholine induced concentration-dependent and endothelium-dependent relaxation of arterial rings precontracted with phenylephrine (pEC₅₀ = 6.90 ± 0.02). Muscarinic receptors antagonists atropine, pirenzepine, methoctramine and p -FHHSiD competitively antagonized the response to acetylcholine and obtained pA₂ values were 9.91 ± 0.06, 6.60 ± 0.04, 6.21 ± 0.08 and 8.05 ± 0.1, respectively. This study showed that acetylcholine induced endothelium-dependent relaxation of canine uterine artery by stimulation of muscarinic receptors localized on the endothelial cells. On the basis of differential antagonist affinity, we suggest that the muscarinic receptors involved in the acetylcholine-induced relaxation of canine uterine artery are predominantly of M₃ subtype.     

Characterization of bradykinin-induced endothelium-independent contraction in equine basilar artery

We investigated the effect of bradykinin (BK) on isolated equine basilar arterial rings with and without endothelium. BK induced concentration-dependent contraction of resting arterial rings and no relaxation when the rings were precontracted by prostaglandin F_2α. The maximal response and pD₂ value were 161.2 ± 28.1% (to 60 m m KCl-induced contraction) and 8.24 ± 0.25 respectively. The cumulative concentration–response curve for BK was not shifted to the right by des-Arg⁹-[Leu⁸]-BK (a B₁-receptor antagonist), HOE140 (a B₂-receptor antagonist) or NPC567 (another B₂-receptor antagonist). In four of six basilar arteries, NPC567 induced concentration-dependent contraction. Indomethacin (a cyclooxygenase inhibitor), nordihydroguaiaretic acid (a lipoxygenase inhibitor), quinacrine (a phospholipase A₂ inhibitor), tetrodotoxin (a selective blocker of Na⁺ channels), guanethidine (a nor-adrenergic neuron blocking drug), phentolamine (an α-adrenoceptor antagonist), Nω-nitro- l -arginine ( l -NNA, a nitric oxide (NO) synthase inhibitor) and endothelial denudation did not affect the BK-induced contraction. l -NNA and indomethacin induced contraction and relaxation under resting vascular tone respectively. These results suggest that endothelial cells are not involved in BK-induced contraction and that the contraction is not mediated via activation of known B₁ and B₂ receptors. Arachidonic acid metabolites and neurotransmitters like norepinephrine and NO might not play a role in BK-induced contraction in equine basilar artery.     

Equine coronary artery responds to 5-hydroxytryptamine with relaxation in vitro

Isolated equine coronary arteries responded to 5-hydroxytryptamine (5-HT) with relaxations in both endothelium-dependent and endothelium-independent mechanisms. Experiments were designed to characterize the 5-HT receptor sub type mediating these relaxations. Both 5-HT and alpha-methyl-5-HT (α-Me-5- HT; 5-HT₂ agonist) produced concentration-dependent relaxations in equine coronary arteries precontracted with a thromboxane A₂ derivative (0N011113). The degree of the maximal relaxation induced by α t-Me-5-HT was about one-half of that induced by 5-HT. In the coronary arteries without endothelium, α -Me-5-HT produced no relaxation, but 5-HT caused relaxation, which was inhibited by a 5-HT₁ antagonist (methysergide, mianserin and methiothepin), but was inhibited neither by ketanserin (5-HT₂ antagonist) nor by MDL72222 (5-HT₃ antagonist). In the coronary arteries with endothelium, however, the relaxation induced by α -Me-5-HT was inhibited by ketanserin, L-nitro-arginine (NO synthase inhibitor) and methylene blue (soluble guanylate cyclase inhibitor). These results suggest that the relaxation induced by 5-HT in equine coronary arteries depends mainly on the stimulation of both 5-HTi receptor subtype on smooth muscle cells directly, and 5-HT₂ receptor subtype on endothelial cells indirectly by liberating endothe-lium-derived NO.     

Localization of CCK-1R in the omasum and role of CCK in the regulation of omasal contractions in sheep

The present study examined localization of cholecystokinin receptor (CCK-R) mRNA in the muscle layer of the ovine omasum and role of CCK-R type 1 (CCK-1R) in the regulation of muscle contraction of the omasum. We demonstrated that not only CCK-R type 2 (CCK-2R) mRNA but also CCK-1R mRNA is highly expressed in the muscle layer of the ovine omasum. Application of CCK-8 to muscle strips of the greater curvature of the ovine omasum at 1-100 nM induced tonic contraction in a concentration-dependent manner, and the contractile effect of CCK-8 was inhibited by both CCK-1R antagonist lorglumide (IC(50) 2.7 and 7.9 microM in the longitudinal and circular muscle, respectively) and CCK-2R antagonist PD135,158 (IC(50) 51.4 microM in the longitudinal muscle), indicating that not only CCK-2R but also CCK-1R is functionally expressed in the plasma membrane of smooth muscles in the omasum and mediates action of exogenous CCK. Contractile effect of intravenous infusion of CCK-8 (1-30 pmol/kg/min) on omasal contraction was also confirmed in the in vivo experiments using conscious sheep in the absence and presence of atropine infusion (14.4 nmol/kg/min), and showed that circulating CCK increases omasal electromyographic (EMG) activity at lower plasma concentration than that it inhibits ruminal contractions. Taking account of our previous results in the in vivo study using other CCK-1R antagonist, it is suggested that circulating CCK, even at normal range of plasma concentration, plays a physiological role as a regulator of omasal contractions in sheep and CCK-1R mediates the action of CCK.     

Effects of Pasteurella haemolytica culture supernate on bovine tracheal smooth muscle.

Pasteurella haemolytica leukotoxin is a ruminant specific leukotoxin that has been implicated in the pathogenesis of shipping fever in cattle. The present study was undertaken to determine the effect of this toxin on bovine airway smooth muscle. In vitro, the addition of culture supernate containing leukotoxin to bovine tracheal smooth muscle resulted in contraction of 55% of the muscle strips tested. Maximum responses were reached rapidly during cumulative additions of this material. In 95% of the muscle strips that responded, maximum responses were obtained after the addition of one or two cumulative doses. Repeated additions of culture supernate resulted in decreased responsiveness. Since responsiveness to other agonists was not affected, these results suggest the development of a condition similar to tachyphylaxis. The contractions were inhibited by antihistamines. Diphenhydramine, at a concentration of 10(-6) M (dose-ratio 7), and mepyramine, at a concentration of 2 x 10(-7) M (dose-ratio 56), blocked the contractions by 84% and 100% respectively. In addition, the contractions were blocked by the muscarinic antagonist atropine, but this inhibition was much weaker (46%) and was present at high concentrations only. Inhibition of the contractions by H1 receptor antagonists suggests that the contractions are mediated via H1 receptors. Since the dose-response relationship is not typical of a drug-receptor interaction, it appears unlikely that the leukotoxin is a direct agonist of H1 receptors. It is proposed that an indirect mechanism of action involving the release of histamine by tissue mast cells is responsible for the leukotoxin-induced contractions.