PGE2对巨噬细胞摄取氧化修饰LDL影响的形态计量学观察

应用图象分析仪及抗氧化物酶活性检测方法，研究了ＰＧＥ２对ＬＤＬ氧化悠和巨噬细胞摄脂的影响。结果显示：１．氧化ＬＤＬ组的ＬＰＯ含量明显升高而ＰＧＥ２组明显降低。２．氧化ＬＤＬ组的ＧＳＨ－Ｐｘ活性降低而ＰＧＥ２组明显升高。３．氧化ＬＤＬ组的巨噬细胞含脂量明显高于ＰＧＥ２组。     

松果腺褪黑素对大鼠腹腔巨噬细胞化学发光和脾,下丘脑PGE2含量…

采用松果腺切除术、母多糖调理的鲁米诺依赖的化学发光法及前列腺素Ｅ２（ＰＧＥ２）放射免疫测定方法观察了松果腺和褪黑素（ＭＴ）对大鼠腹腔巨噬细胞化学发光及脾、下丘脑ＰＧＥ２含量的影响。结果表明：松果腺切除后大鼠腹腔巨噬细胞化学发光值降低，脾及下丘脑ＰＧＥ２含量升高，１０－１０００μｇ．ｋｇ＾－１ＭＴ分别恢复之。其中以１０μｇ．ｋｇ＾－１ＭＴ作用最强；１０μｇ．ｋｇ＾－１ＭＴ还抑制正常大鼠脾及下丘脑ＰＧ     

银杏细胞培养物多糖与银杏叶多糖的研究

对药用植物银杏悬浮细胞培养物多糖及银杏叶多糖进行较为系统的研究。方法：用银杏悬浮细胞培养方法得到细胞培养物,对细胞培养物中的多糖进行常规提取处理和离子交换凝胶色谱分离,用凝胶过滤色谱法和聚丙烯酰胺凝胶色谱法验证其纯度。结果：从细胞培养物得到五个多糖（ＩＣＰ－１、ＩＣＰ－ ２、ＥＣＰ－１、ＥＣＰ－２、ＥＣＰ－３）,从银杏叶中分得两个多糖（ＬＧＰ－１、ＬＧＰ－２）。确定了其分子量、旋光度、糖含量和糖醛酸含量、单糖组成及其摩尔比。结论：初步分析了ＥＣＰ－１的糖基连接位置和苷键构型;药理实验证明ＬＧＰ具有抗炎和耐缺氧活性,ＩＣＰ具有较强的耐缺氧活性,ＥＣＰ具有显著的抗炎活性。     

PGE2对^65Zn在大鼠肠道吸收和体内分布的影响

采用麻醉大鼠十二指肠袢法研究ＰＧＥ２对＾６５Ｚｎ吸收和分布的影响。结果０．１％ＰＧＥ２对＾６５Ｚｎ的吸收率无明显影响，但可使十二指肠壁内含量增高。而肠袢腔内残留量显著减少，与对照组比较Ｐ〈０．０１。提示ＰＧＥ２可促进＾６５Ｚｎ向肠壁内转运。     

褪黑素对大鼠松果腺细胞产生前列腺素E_2的影响

采用松果腺细胞培养、前列腺素Ｅ２（ＰＧＥ２）放射免疫测定等方法，研究了松果除分泌的褪黑素（ＭＴ）对松果腺细胞产生ＰＧＥ２的影响。结果表明：ＭＴ０．１～１０μｍｏｌ·Ｌ－１抑制松果腺细胞产生ＰＧＥ２，０．０１～１０μｍｏｌ·Ｌ－１对抗去甲肾上腺素刺激松果腺细胞产生ＰＧＥ２，且以１μｍｏｌ·Ｌ－１的作用最为明显。提示ＭＴ对松果腺细胞功能有负性调节作用。Ｐ＜０．０１图２ＭＴ对去甲肾上腺素刺激松果腺细胞（１０５ｃｅｌｌｓ）转引产生ＰＧＥ２的影响●－●：ＮＥ；○－○：ＮＥ＋ＭＴ；ｎ＝４与对照组比较，Ｐ＜０．０５，Ｐ＜０．０１；与对应的去甲肾上腺素比较，△Ｐ＜０．０５，△△Ｐ＜０．０１３讨论支配松果腺细胞的交感神经纤维在暗相时产生与释放大量去甲肾上腺素，作用于松果腺细胞膜上的β１、α１受体，双重受体激动后通过Ｇ蛋白使蛋白激酶Ｃ激活，Ｃａ２＋、Ｋ＋、花生四烯酸增多，继而使ｃＡＭＰ、ｃＧＭＰ产生明显增加，松果腺细胞内特有的合成ＭＴ的限速酶Ｎ－乙酰转移酶和羟基吲哚－０－甲基转移酶被激活，从血液中摄取的色氨酸迅速转化为ＭＴ。在ＭＴ合成过程中，ＰＧ起很重要作用，因α１受体激动可使ＰＧ产生增多，ＰＧ进而促进ｃＧＭＰ生成和ＭＴ的合成?     

凯时治疗糖尿病周围神经病变临床研究

目的：研究前列腺素Ｅ１脂微球载体制剂（Ｌｉｐｏ ＰＧＥ１，凯时）治疗糖尿病周围神经病变的临床疗产及观察其不良反应。方法：对确诊为糖尿病合并周围神经病变的１８例患者，给予Ｌｉｐｏ ＰＧＥ１１０μｇ／ｄ，共２周。对照组２２例给予维生素Ｂ１ １０ｍｇ、维手素Ｂ１２０．５ｍｇ／ｄ。结果：治疗组应用Ｌｉｐｏ ＰＧＥ１治疗２周后，患者主观太和体征有效明显改善，总有效率达８８．９％，而对照组有效率仅达４０．９％     

前列腺素E1治疗原发性肾病综合征蛋白尿的临床研究

为探讨前列腺素Ｅ４（ＰＧＥ４）对原发性肾病综合征（ＰＮＳ）病人蛋白尿的影响，对１０６例ＰＮＳ病人分组观察，ＰＧＥ４组４８例，用２００μｇ的ＰＧＥ１每日１次静滴，连用１５天为１疗程，共用２个疗程，强的松组４０例，给强的松每日１ｍｇ／ｋｇ连用４周，联合治疗组已用强的松４周以上尿蛋白消退下明显者，继续强的松应用的同时联用ＰＧＥ４，结果发现，ＰＧＥ４强的松对ＰＮＳ单纯型有效率分别为３０．５％，８１．８％，     

国产静注前列腺素E1（PGE1）质量研究

本文对国产及进口ｉｖ前列腺素Ｅ１（ＰＧＥ１）的质量进行了研究。试验药任意取国内三个药厂（简称Ａ、Ｂ、Ｃ）和德国ＳＣＨＷＡＲＺ药厂产品。分别取二、三个批号，每个批号各取三支采用高效液相色谱法进行测定。结果表明，Ａ药厂的前列腺素Ｅ１含量均高于标示量，内批号内含量大差２９．４％。各支被测样品间含量最大差３１．３％。Ｂ药厂的前列腺素Ｅ１含最均低于标示量，各支被测样品之间含量大差２２．８％。Ｃ药厂的前列腺素     

前列腺素 E_1 治疗原发性肾病综合征蛋白尿的临床研究

为探讨前列腺素Ｅ１（ＰＧＥ１）对原发性肾病综合征（ＰＮＳ）病人蛋白尿的影响，对１０６例ＰＮＳ病人分组观察。ＰＧＥ１组４８例，用２００μｇ的ＰＧＥ１每日１次静滴，连用１５天为１疗程，共用２个疗程；强的松组４０例，给强的松每日１ｍｇ／ｋｇ连用４周；联合治疗组为已用强的松４周以上尿蛋白消退不明显者，继续强的松应用的同时联用ＰＧＥ１。结果发现，ＰＧＥ１、强的松对ＰＮＳ单纯型有效率分别为３０．５％、８１．８％，两者间有非常显著性差异；对肾炎型有效率分别为８８０％和５５．６％，两者间有显著性差异，而两者的疗效与单纯型相反；联合应用时降尿蛋白作用加强。说明ＰＧＥ１比强的松对ＰＮＳ肾炎型患者的降尿蛋白作用更有效。     

消旋（15R）－15甲基PGE_2甲酯（PG_6E）对大鼠实验性胃溃疡的保护作

用实验性胃溃疡模型研究了ＰＧ＿６Ｅ的抗溃疡作用，结果表明ＰＧ＿６Ｅ有抗胃酸分泌作用，而对胃肠运动无明显影响；ＰＧ＿６Ｅ在剂量为１０一８０μｇ·ｋｇ－１时，对无水乙醇型、盐酸型、消炎痛型、慢性醋酸型和幽门结扎型胃溃疡有明显保护作用，并能显著减少幽门结扎大鼠的胃液体积、胃酸分泌、胃蛋白酶活性和ＤＮＡ含量。小鼠ｐｏＰＧ＿６Ｅ３０～６０μｇ·ｋｇ－１，３ｄ后粘膜氨基己糖含量显著增加。研究结果提示ＰＧ＿６Ｅ能抑制对胃粘膜的攻击性因素，增加保护性因素的作用，可望成为一种新型抗胃溃疡药     

Increase in atrial contractility induced by PGE2 in diabetic rats

Contractile response to exogenous prostaglandin E2 (PGE2) was studied in auricles from normal and acutely-diabetic (streptozotocin-treated) rats. In normal atria, PGE2 induced a biphasic inotropic effect negative at low concentrations and positive at higher ones. In diabetic, PGE2 only elicited a positive inotropic action which was greater in efficacy and potency than in normal controls. Incubation of diabetic atrial preparations with alpha-adrenoceptor antagonists (phentolamine, phenoxybenzamine or Prazosin) diminished the prostaglandin effect. However, blockade of beta-adrenoceptors with propranolol did not modify the response. Blockers of arachidonic acid metabolism via cyclo-oxygenase (indomethacin and acetylsalicylic acid) or via lipoxygenase(s) (nordihydroguaiaretic acid and dithizone) were able to reduce the positive inotropism of PGE2. A significant blockade of the stimulant action of PGE2 was seen in the presence of inhibitors of thromboxane synthesis (L-8027 and imidazole). These results suggest that in diabetic atria PGE2 effect could be associated to an involvement of cardiac alpha-adrenergic stimulation which promotes endogenous arachidonic acid release with diversification of its metabolism towards cyclo- and lipoxygenase(s)- pathway and direct to an increased thromboxane formation which could account for the positive inotropic effect induced by PGE2.     

Selective cytotoxicity of indomethacin and indomethacin ethyl ester-loaded nanocapsules against glioma cell lines: an in vitro study

Gliomas are the most common and devastating tumors of the central nervous system. Several studies have suggested that nonsteroidal anti-inflammatory drugs (NSAIDs) are promising anticancer agents. Biodegradable nanoparticulate systems have received considerable attention as potential drug delivery vehicles. The aim of this study was to evaluate the effects of indomethacin-loaded nanocapsules and indomethacin ethyl ester-loaded nanocapsules on glioma cell lines. In addition, the effect of these formulations on normal neural tissue was also evaluated. In order to investigate this, glioma cell lines (U138-MG and C6) and hippocampal organotypic cultures were used. The main finding of the present study is that indomethacin-loaded nanocapsules formulation was more potent than a solution of indomethacin in decreasing the viability and cell proliferation of glioma lines. Indomethacin and indomethacin ethyl ester associated together in the same nanocapsule formulation caused a synergic effect decreasing glioma cell proliferation. In addition, when the glioma cells were exposed to 25 microM of indomethacin-loaded nanocapsules or indomethacin ethyl ester-loaded nanocapsules, a necrotic cell death was observed. Interestingly, 5 microM of indomethacin-loaded nanocapsules was able to cause an antiproliferative effect without promoting necrosis in glioma cells. Another important finding was that the cytotoxic effect induced by 25 microM or 50 microM of indomethacin-loaded nanocapsules or indomethacin ethyl ester-loaded nanocapsules, in glioma cells was not observed in the organotypic cultures, indicating selective cytotoxicity of those formulations for tumoral cells. Further investigations using in vivo glioma model should be helpful to confirm the distinct effects of indomethacin-loaded nanocapsules and indomethacin ethyl ester-loaded nanocapsules, in normal versus tumoral cells.     

Cysteinyl leukotrienes mediate the enhancing effects of indomethacin and aspirin on eosinophil production in murine bone marrow cultures

BACKGROUND: Prostaglandin E(2) (PGE(2)) suppresses, while indomethacin and aspirin enhance, eosinophil production in murine liquid bone-marrow cultures. Because cysteinyl leukotrienes (cys-LTs) enhance human eosinophil colony formation, we investigated whether the effects of indomethacin and aspirin on murine bone-marrow were due to blockade of PGE(2) production alone, or involved further promotion of cys-LTs production/signalling. EXPERIMENTAL APPROACH: BALB/c liquid bone-marrow cultures were established with IL-5, alone or associated with indomethacin, aspirin, or cys-LTs. The effects of preventing cys-LT production or signalling were assessed. KEY RESULTS: Indomethacin and aspirin counteracted the suppression of eosinophil production by exogenous PGE(2). LTD(4), LTC(4) and LTE(4) enhanced IL-5-dependent eosinophil production and further counteracted the effect of exogenous PGE(2). The 5-lipoxygenase activating protein (FLAP) inhibitor, MK886, a leukotriene synthesis inhibitor, zileuton, the CysLT(1) receptor antagonists, MK571 and montelukast, or inactivation of the LTC(4) synthase gene, abolished effects of indomethacin and aspirin. MK886 and zileuton were ineffective but MK571 and montelukast were effective, against LTD(4). Indomethacin, aspirin and LTD(4) failed to enhance eosinophil production in bone-marrow from CysLT1 receptor-deficient mice. Indomethacin, aspirin and LTD(4) no longer counteracted the effects of exogenous PGE(2) in the presence of MK571 and montelukast. MK886, MK571 and montelukast had no effect by themselves, or in association with PGE(2). CONCLUSIONS AND IMPLICATIONS: Dependence on the FLAP/5-lipoxygenase/LTC(4) synthase pathway and receptor signalling shows that cyclo-oxygenase inhibitors act here through endogenous cys-LTs. While PGE(2) does not act by suppressing cys-LT production, cys-LTs override PGE(2) signalling. Eosinophil production is therefore coordinately regulated by both pathways.     

美洲大蠊提取物Ento-A对湿热型溃疡性结肠炎模型大鼠的改善作用研究

目的:研究美洲大蠊提取物Ento-A对湿热型溃疡性结肠炎(UC)模型大鼠的改善作用。方法:将70只大鼠随机分为正常对照组(n=8)和造模组(n=62),造模组大鼠采用高糖高脂、辛辣饮食联合2,4,6-三硝基苯磺酸灌肠法复制湿热型UC动物模型。将造模成功的48只大鼠随机分为模型对照组、美沙拉嗪组(300 mg/kg)、肠炎宁(300 mg/kg)和Ento-A低、中、高剂量组(50、100、200 mg/kg,以提取物计),每组8只。正常对照组和模型对照组大鼠灌胃生理盐水,其余各组大鼠灌胃相应药物,每天1次,连续给药14 d。末次给药后,对大鼠疾病活动指数(DAI)、结肠黏膜损伤指数(CMDI)及病理组织学(HS)进行评分,测定大鼠脾指数、肝指数和结肠指数,并采用酶联免疫吸附法测定大鼠血清中白细胞介素8(IL-8)、IL-17、超氧化物歧化酶(SOD)、丙二醛(MDA)水平和结肠组织中IL-2、前列腺素E2(PGE2)、髓过氧化物酶(MPO)水平。结果:与正常对照组比较,模型对照组大鼠DAI评分、CMDI评分、HS评分、结肠指数以及血清中IL-8、IL-17、MDA水平和结肠组织中MPO、PGE2水平显著升高(P<0.01),血清中SOD水平和结肠组织中IL-2水平显著降低(P<0.01)。与模型对照组比较,Ento-A高剂量组大鼠DAI评分、CMDI评分及血清中IL-17、MDA水平和结肠组织中PGE2水平显著降低(P<0.05或P<0.01),血清中SOD水平和结肠组织中IL-2水平显著升高(P<0.01);Ento-A中剂量组大鼠CMDI评分、HS评分以及血清中IL-8、IL-17、MDA水平和结肠组织中PGE2、MPO水平显著降低(P<0.05或P<0.01),结肠组织中IL-2水平显著升高(P<0.01);Ento-A低剂量组大鼠HS评分以及血清中IL-17、MDA水平和结肠组织中MPO、PGE2水平显著降低(P<0.05或P<0.01),血清中IL-2水平显著升高(P<0.01)。结论:美洲大蠊提取物Ento-A可能通过调节免疫系统平衡、减少炎症损伤,发挥其对湿热型UC模型大鼠的改善作用。     

Evidence that the histamine sensitivity and responsiveness of guinea-pig isolated trachea are modulated by epithelial prostaglandin E2 production.

1. Guinea-pig isolated tracheal preparations in which the epithelium had been removed exhibited a greater contractile response to histamine (intact: 1.91 +/- 0.12 g; n = 6 and rubbed: 2.76 +/- 0.15 g; n = 11; P less than 0.001). The histamine sensitivity (pD2 value) of these preparations was also significantly greater (intact: 4.80 +/- 0.04 and rubbed: 5.40 +/- 0.08; P less than 0.01). 2. Indomethacin suppressed the basal tone of both intact and rubbed preparations but was more effective in the former tissues (intact: -0.70 +/- 0.14 g; n = 22 and rubbed: -0.17 +/- 0.05 g; n = 12; P less than 0.02). 3. Arachidonic acid (AA; 10 microM) suppressed the basal tone of intact tissues but contracted such preparations following indomethacin treatment (1.7 microM; 30 min). However, in rubbed tissues AA (10 microM) induced a contraction which was attenuated following indomethacin treatment. 4. Prostaglandin E2 (PGE2; 0.01 and 0.1 microM) suppressed the basal tone of intact preparations and always evoked contraction of rubbed tissues. Following indomethacin treatment PGE2 (0.01 and 0.1 microM) generally evoked spasm of intact and rubbed tissues while at higher concentrations (1 microM) relaxant effects were observed. 5. Removal of the epithelium did not alter the relaxant effect of PGE2 (pD2 value) on histamine (50 microM)-contracted tissues (intact: 6.86 +/- 0.08 and rubbed: 7.10 +/- 0.3; n = 4; P greater than 0.1). 6. In rubbed preparations treated with indomethacin, PGE2 (0.01 and 0.1 microM) evoked spasm. However, when added to preparations contracted with 5 microM histamine, PGE2 always caused relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)     

康复新栓对慢性阴道炎大鼠血清MDA、SOD及组织PGE2的影响

目的探讨康复新栓对慢性阴道炎大鼠血清中丙二醛(malondialdehyde,MDA)、超氧化物歧化酶(superoxide dismutase,SOD)及阴道组织中前列腺素E2(prostaglandin E2,PGE2)含量的影响。方法以大肠埃希菌、白色假丝酵母菌、金黄色葡萄球菌混合菌液和8%苯酚胶液交叉感染建立大鼠阴道炎模型。经阴道给予空白栓,双唑泰栓(37.84 mg·kg^-1),高剂量(80mg·kg^-1)、低剂量(40mg·kg^-1)康复新栓治疗。通过酶联免疫法检测大鼠血清中MDA、SOD和阴道组织PGE2含量,通过病理组织学评分判断其阴道炎程度。结果与正常对照组比较,模型对照组大鼠血清中MDA和阴道组织匀浆中PGE2含量显著升高(P<0.01),SOD活力显著降低(P<0.01);大鼠阴道病理组织学评分显著增高(P<0.01),说明大鼠阴道炎模型造模成功。与模型对照组比较,双唑泰栓组、康复新栓高、低剂量组血清SOD活性显著升高(P<0.01),MDA及PGE2含量显著降低(P<0.01);大鼠阴道病理组织学评分显著降低(P<0.01)。结论康复新栓能有效治疗大鼠的慢性阴道炎,可能与降低大鼠血清中MDA的表达及提高阴道组织中SOD的活性,改善阴道组织病变程度有关。     

Prevention of ocular inflammation by matrine, prednisolone, and cyclooxygenase and lipoxygenase inhibitors.

Lens protein-induced ocular inflammation in rabbits was used to study the action mechanism of some anti-inflammatory agents. Indomethacin, a cyclooxygenase inhibitor, markedly reduced PGE2 and PGF2 alpha in the iris and ciliary body at 2 h but PGE2 only at 4 h. REV 5901, a lipoxygenase inhibitor, only significantly reduced PGE2 levels in the ciliary body at 4 h. PGF2 alpha levels were not affected by REV 5901. When indomethacin and REV 5901 were combined, both PGE2 and PGF2 alpha were suppressed at 2 and 4 h in both iris and ciliary body. Neither matrine nor prednisolone produced significant effects on the levels of PGE2 and PGF2 alpha. However, prednisolone exhibited the greatest reduction in chemotaxis of leukocytes followed by REV 5901. Indomethacin, on the contrary, produced a significant increase in chemotaxis of leukocytes. Matrine produced a decrease in leukocyte counts but was not statistically significant. These results indicate that indomethacin is effective in the early phase of inflammation to reduce PG's production whereas prednisolone and REV 5901 were more effective in the late phase of inflammation. Combined use of REV 5901 and indomethacin could become a drug of choice for the treatment of ocular inflammation without inducing corticosteroidal side effects.     

Production of PGE2 by bovine cultured airway smooth muscle cells and its inhibition by cyclo-oxygenase inhibitors.

1. Prostaglandin E2 (PGE2) is thought to be an important inhibitory modulator of inflammatory processes in the airway. It inhibits inflammatory cell function and cholinergic neurotransmission in vitro and roles have been postulated in vivo in refractoriness and in the mechanism of action of the diuretic agent, frusemide. 2. The production of PGE2 by bovine cultured airway smooth muscle cells has been studied under a range of conditions. The effects of cyclo-oxygenase inhibitors (flurbiprofen, indomethacin, acetyl salicylic acid) on serum-induced production of PGE2 were assessed over a range of concentrations (10(-7)-10(-4) M). 3. Serum-stimulated production of PGE2 in control wells ranged from 350 to 800 ng PGE2 ml-1 in cells from different animals. All three cyclo-oxygenase inhibitors inhibited PGE2 production with an order of potency, flurbiprofen > indomethacin > acetyl salicylic acid. Log IC50 values were -6.24 for flurbiprofen, -5.23 for indomethacin and -3.50 for acetyl salicylic acid. 4. PGE2 production was stimulated by arachidonic acid (10(-5) M) or addition of the proinflammatory mediator, bradykinin (10(-8)-10(-5) M). 5. Incubation of cells for 24 h with 5 bromo deoxyuridine (BRDU) (10(-4) M) to prevent DNA synthesis did not alter PGE2 production in response to serum, suggesting that it was not a function of proliferation per se. 6. Our study suggests that airway smooth muscle may be an important source of PGE2. Production of PGE2 may be a novel feedback mechanism whereby airway smooth muscle cells can negatively modulate airways inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Indomethacin increases plasma lithium.

The effects of indomethacin on plasma lithium concentrations and renal lithium clearance were investigated in three psychiatric patients and four normal volunteers. After steady-state plasma lithium concentrations had been reached, the subjects received indomethacin placebo for three to seven days, indomethacin (50 mg thrice daily) for seven days, and placebo again for three to seven days. Indomethacin increased plasma lithium concentrations by 59% in the psychiatric patients and 30% in the volunteers. Renal lithium clearance was reduced by indomethacin by 31% in the group as a whole, and prostaglandin synthesis, determined by measuring the major metabolite of PGE2 with mass spectrometry, was reduced by 55%. These results show that indomethacin reduces renal lithium clearance to an extent which may be clinically important. They also suggest that the renal clearance may be affected by a prostaglandin-dependent mechanism, possibly located in the distal tubule.     

Role of PGE2 in neurotransmission from pre- to post-ganglionic hypogastric nerves of guinea pigs.

The hypogastric nerve to guinea pig vas deferens was stimulated pre- or post-ganglionically by adjusting the position of the suction electrode. Both stimulations induced a biphasic contraction consisting of a rapid transient phase and a delayed tonic phase. Indomethacin partially inhibited the contraction induced by pre-ganglionic stimulation, but did not inhibit that induced by post-ganglionic stimulation. Prostaglandin (PG) E2 counteracted the inhibitory effect of indomethacin. Mepacrine also inhibited the contraction induced by pre-ganglionic stimulation. Arachidonic acid and PGE2 both reversed the inhibition. The PGE2-receptor antagonist SC-19220 inhibited the contraction induced by pre-ganglionic, but not post-ganglionic nerve stimulation. These results suggested that endogenous PGE2 is important in neurotransmission in the pelvic ganglion of guinea pigs.