Inhibitory action of adenosine on synaptic transmission in the hippocampus of the guinea pig in vitro

Thin hippocampal slices were prepared from guinea pig brains. the postsynaptic field potential elicited in the pyramidal cell layer of CA3 region by mossy fiber stimulation was reversibly inhibited by application of adenosine to the perfusion medium. Among purine and pyrimidine derivatives, only adenosine and adenine nucleotides depressed the field potential with similar dose-response curves at concentrations of 10(-5).10(-3) M. In order to elucidate the mechanism of the inhibitory action of these agents, the effects of adenosine and adenine nucleotides on membrane events in pyramidal neurons were studied using intracellular recording techniques. Application of adenosine and adenine nucleotides hyperpolarized membrane potential and markedly depressed the EPSPs (excitatory postsynaptic potentials) elicited in the pyramidal cell by granular cell activation. However the spike generating mechanism of the neuron was not interfered with and membrane conductance was not increased by adenosine and adenine nucleotides. 4-Aminopyridine counteracted the inhibitory action of adenosine. These findings indicate that the mechanism of the inhibitory action of adenosine and adenine nucleotides is different from that of conventional inhibitory neurotransmitters such as gamma-aminobutyric acid and suggest a presynaptic action of adenosine and adenine nucleotides.     

肌松药物巴氯芬类似物的合成及其构效关系的研究

为研究解痉肌松药巴氯芬类似物的构效关系,合成了巴氯芬类似物15个,其中8个化合物是首次报道。采用小白鼠热板法及对抗吗啡竖尾反应实验评价目标化合物的镇痛和肌松作用。筛选结果表明:部分化合物有肌松和镇痛作用,其中Ⅰb,Ⅱb,Ⅲa和Ⅲc的镇痛作用较好,Ⅰd,Ⅱb,Ⅲa和Ⅲb的肌松作用较好,但均未超过巴氯芬。根据本研究及前人的研究结果,提出巴氯芬与GABA_B受体结合取决于巴氯芬分子中氨基、羧基和苯环三种基团。     

Characteristics of the relaxant response of adenosine and its analogs in intestinal smooth muscle

Several characteristics of the relaxant response of the isolated longitudinal muscle of the rabbit small intestine in response to the administration of adenosine and related compounds are studied. Following administration of adenosine or ATP the preparation responded with a rapid initial suppression of spontaneous contractile activity followed by a secondary sustained phase of inhibition of lower magnitude. Cumulative application of relaxant doses of adenosine or ATP caused a lesser total response than that obtained by single application of the cumulative dose. Neither procaine, lidocaine or guanethidine antagonized the responses to adenosine or ATP and the responsiveness of muscles obtained from reserpinized animals appeared unchanged. A number of adenosine derivatives and analogs was tested for the ability to relax the muscle. Generally, compounds containing a primary or secondary 6-amino group acted as agonists with the exception of 8-bromoadenosine. Those nucleosides found to be inactive did not modify the responsiveness of the muscle to adenosine. Responses to adenosine and ATP were not appreciably modified by papaverine, imidazole, dipyridamole, 6-(p-nitrobenzylthio)-purine riboside. Antagonism was observed, however, with phentolamine and theophylline. Theophylline at 100 μM inhibited responses to adenosine over a wide dose range; this antagonism was surmountable by high doses of adenosine. 1-Methyl-3-isobutylxanthine did not antagonize adenosine responses. A number of 1,3-alkyl-6-thioxanthines did not modify the adenosine response at doses that did not show any direct action. The results support the concept of an extracellular receptor site of adenosine and its analogs and the absence of an indirect mechanism of action via nerve stimulation.     

Effects of phencyclidine on cardiac action potential: pH dependence and structure-activity relationships

The effects of phencyclidine [1-(1-phenylcyclohexyl)-piperidine; PCP] on cardiac action potential duration (APD) were compared to those of some of its derivatives, in strips of isolated frog ventricular muscle perfused with normal Ringer solution. We studied compounds with PCP-like behavioral actions (N-ethyl-1-phenyl-cyclohexylamine: PCE; and m-amino-PCP) as well as behaviorally inactive analogs (m-nitro-PCP; the quaternary derivative PCP-methyl iodide; and various fragments of the PCP molecule). Exposure to PCP, 3 microM to 1 mM, produced reversible, dose- and pH-dependent prolongations, of the APD to over 100% above control. The observed effects of the drugs are compatible with a mechanism of blockade of potassium conductance. An intracellular site for this action is suggested by: (i) the inactivity of the quaternary analog; (ii) the marked increase in the potency of the compounds when the external pH is changed in the region of their respective pKa values to increase the concentration of the unionized species; and (iii) the pronounced acceleration of the termination of the PCP effect by washout with a series of buffer solutions with decreasing pH values. The rank order of potency of the compounds in lengthening APD (PCE greater than m-amino PCP greater than PCP much much greater than m-nitro-PCP) is the same as reported from other pharmacological studies of specific PCP actions, and matches the rank of behavioral activity of the drugs.     

Inhibitory effects of flavonoids on phosphodiesterase isozymes from guinea pig and their structure-activity relationships

The structure-activity relationships of flavonoids with regard to their inhibitory effects on phosphodiesterase (PDE) isozymes are little known. The activities of PDE1-5 were measured by a two-step procedure using cAMP with [(3)H]-cAMP or cGMP with [(3)H]-cGMP as substrates. In the present results, PDE1, 5, 2, and 4 isozymes were partially purified from guinea pig lungs in that order, and PDE3 was from the heart. The IC(50) values of PDE1-5 were greater than those reported previously for the reference drugs, vinpocetin, EHNA, milrinone, Ro 20-1724, and zaprinast, by 5-, 5-, 7-, 5-, and 3-fold, respectively. As shown in Table 2, luteolin revealed non-selective inhibition of PDE1-5 with IC(50) values in a range of 10-20 microM, as did genistein except with a low potency on PDE5. Daidzein, an inactive analogue of genistein in tyrosine kinase inhibition, showed selective inhibition of PDE3 with an IC(50) value of around 30 microM, as did eriodictyol with an IC(50) value of around 50 microM. Hesperetin and prunetin exhibited more-selective inhibition of PDE4 with IC(50) values of around 30 and 60 microM, respectively. Luteolin-7-glucoside exhibited dual inhibition of PDE2/PDE4 with an IC(50) value of around 40 microM. Diosmetin more-selectively inhibited PDE2 (IC(50) of 4.8 microM) than PDE1, PDE4, or PDE5. However, biochanin A more-selectively inhibited PDE4 (IC(50) of 8.5 microM) than PDE1 or PDE2. Apigenin inhibited PDE1-3 with IC(50) values of around 10-25 microM. Myricetin inhibited PDE1-4 with IC(50) values of around 10-40 microM. The same was true for quercetin, but we rather consider that it more-selectively inhibited PDE3 and PDE4 (IC(50) of < 10 microM). In conclusion, it is possible to synthesize useful drugs through elucidating the structure-activity relationships of flavonoids with respect to inhibition of PDE isozymes at concentrations used in this in vitro study.     

Muscarinic activity in the isolated guinea pig ileum of some carboxamides related to oxotremorine

A series of structural analogues of the potent oxotremorine-like agent N-(4-pyrrolidino-2-butynyl)-N-methyl-acetamide (1) was investigated for muscarinic activity in the isolated guinea pig ileum. Substitution of larger alkyl groups for the acetyl methyl group of 1 results in an attenuation of muscarinic potency. The observation that the agonist N-(4-dimethylamino-2-butynyl)-N-methylpropionamide (6) has a dissociation constant (K_A = 5.1 × 10^?5 M), estimated after elimination of spare receptors with dibenamine, similar to that of the antagonist N-(4-dimethylamino-2-butynyl)-N-methyl-2,2-dimethylpropionamide (11) suggests that the decrease in muscarinic agonist activity with increasing substitution is due mainly to a loss of efficacy. The N-methyl group of 1 is essential for muscarinic activity since its replacement by a hydrogen atom or an ethyl group yields antagonists.     

马钱子碱对豚鼠心脏乳头肌动作电位的影响

研究马钱子碱对心肌电生理方面的影响。采用常规微电极技术同步记录收缩力的方法，观察了马钱子碱对豚鼠心脏乳头肌动作电位（Ａｐ）及收缩力（Ｆｃ）的影响。实验结果表明：马钱子碱在浓度大于等于１×１０－６ｍｏｌ·Ｌ－１时，浓度依赖地延长快反应动作电位（ＦＡＰ）及高钾除极组织胺和氯化钡诱发的慢反应动作电位ＳＡＰ的ＡＰＤ５０、ＡＰＤ９０，在浓度大于等于３×１０－６ｍｏｌ·Ｌ－１时，抑制ＦＡＰ及ＳＡＰ的Ｆｃ，在浓度大于等于１×１０－５ｍｏｌ·Ｌ－１时，还可抑制ＦＡＰ及ＳＡＰ的ＡＰＡ、Ｖｍａｘ。提示马钱子碱具有阻断心肌Ｋ＋、Ｎａ＋、Ｃａ２＋通道的作用。     

赛庚啶对豚鼠乳头状肌的收缩性与动作电位的影响

Cyp对豚鼠孔头状肌有浓度依赖性负性肌力作用,提高浴液钙浓度此作用减弱,对高K~+除极后ISO恢复的收缩抑制作用更强。较高浓度的Cyp使频率依赖性正阶梯现象取消和翻转。对乳头状肌AP,Cyp浓度依赖性地使APD_(20),APD_(50),APD_(90)和ERP缩短。灌流液中Ca~(2+)降低或升高分别使该作用增强或减弱,K~+的改变对其作用影响较小。提示Cyp对豚鼠乳头状肌收缩性和AP的作用可能主要是抑制心肌跨膜Ca~(2+)内流所致。     

利福霉素类抗生素及其构效关系研究进展

本文综述了抗结核病利福霉素类抗生素的不同结构修饰方法、构效关系(SAR)及其典型衍生物。同时,本文阐述了这些衍生物体内外抗结核分枝杆菌(MTB)活性,甚至包括一些候选药物的临床试验结果。其中重点讲述了利福平、利福布汀和利福拉齐的结构修饰衍生物,而目前利福布汀和利福拉齐的衍生物是近年利福霉素类抗结核药物研究的热点,发现了一些有较好开发前景的新候选物,如RFA-2和RFA-2,且利福平衍生物rifalong和利福霉素类杂合物也值得关注。     

氨茶碱对豚鼠心脏乳头肌动作电位的影响

研究氨茶碱对豚鼠心脏乳头肌动作电位的影响。实验结果表明：１．８ｍｍｏｌ·Ｌ－１浓度的氨茶碱对心肌动作电位各项测试指标均无明显作用。当浓度达到３．６ｍｍｏｌ·Ｌ－１时，则ＡＰＤ、ＡＰＤ９０显著延长．复极斜率Ｋ５０、Ｋ７５明显变小，而静息电位（ＲＰ）、ＡＰＡ、Ｖｍａｘ无明显变化．该剂量药物所引起的最为明显的作用是动作电位第３期晚期复极延缓．呈现隆起现象或称长尾现象，后者在一定条件下可能导致触发发放，形成早后去极化．此现象的发生可能与氨茶碱使心肌细胞Ｋ＋电导（ＧＫ１）降低．Ｋ＋外流减少．进而促进某一种内向电流活动增强有关。     

IHC-66对豚鼠心室乳头状肌细胞缺氧与再给氧后跨膜电活动的影响

目的观察IHC-66对缺氧与再给氧后，豚鼠心室乳头状肌细胞电活动的影响，探讨其抗心律失常的机制。方法采用常规玻璃微电极技术，以离休豚鼠心室乳头肌为标本，研究IHC-66对豚鼠心室乳头肌细胞动作电位各参数的影响。结果IHC-66（10～30μmol·L-1）可呈现出浓度依赖性的对抗缺氧引起的动作电位时程（APD）的缩短。此外，IHC-66（10μmol·L-1）还可部分拮抗吡那地尔（pinacidil50μmol·L-1）缩短APD的作用，并可部分减少缺氧造成的豚鼠心室乳头状肌细胞组织中ATP水平的下降。结论IHC-66对缺氧与再给氧后豚鼠心室乳头状肌细胞电活动的影响，可能与其对K+-ATP通道的阻滞并部分减少心肌细胞ATP的消耗有关。     

Effect of adenosine on sinoatrial and ventricular automaticity of the guinea pig

Summary In isolated spontaneously beating right ventricular strips and right atrial preparations of guinea pigs adenosine was found to exert a concentration-dependent suppressing effect on the pacemaker activity. Responsiveness to adenosine was approximately 30-fold higher in ventricular than in atrial preparations. A decrease in the rate of slow diastolic (phase 4) depolarization of Purkinje and sinoatrial nodal fibers proved to be a major determinant of the adenosine-induced alteration in pacemaker activity. It is suggested that adenosine might exert its depressant effect on ventricular automaticity via direct excitation of purine receptors located in the specialized pacemaker fibres of the ventricular tissue.This work was supported by the Scientific Research Council, Ministry of Public Health, Hungary, Grant No. 2-06-0101-02-2/SzPreliminary report of this work was presented at the 7th International Congress of Pharmacology, Paris, 1978     

Antagonism between adenosine and bromobenzoyl-methyladamantylamine,A K+ channel blocker,in atrial myocardium of guinea pig

The effect of bromobenzoyl-methyladamantylamine (BMA) on the adenosine-induced changes in the electrical and mechanical activity of the atrial muscle, and the effect of adenosine on the slow action potentials induced by BMA in K⁺-depolarized atrial myocardium of guinea pig were studied. BMA was able to antagonize the adenosine-induced shortening of the action potential duration and negative inotropic effect. This action of BMA was potentiated by theophylline, and reduced by dipyridamole. Adenosine depressed the BMA-induced slow action potentials. The results suggest that there may be an antagonism between BMA and adenosine.     

丁咯地尔对豚鼠乳头肌快反应动作电位的影响

研究丁咯地尔(BUF)对豚鼠乳头肌快反应动作电位(AP)的影响。方法采用细胞内微电极技术 ,观察不同浓度BUF对AP的影响。结果各浓度BUF使动作电位幅度(APA)明显降低 ,使APD 30,APD 50缩短 ;BUF10-4M和10-3 使APD 90 也明显缩短。5×10-3M使AP消失之后 ,还使静息电位(RP)绝对值继续降低。结论(1)BUF对豚鼠乳头肌Ca2 、Na 通道有阻滞作用 ;对K 通道的影响较复杂。(2)BUF使豚鼠乳头肌对电刺激的兴奋性降低。(3)BUF对AP的作用是可逆的。     

苦参碱对豚鼠心肌电生理及机械特性的影响

目的　观察苦参碱对离体豚鼠右心室乳头状肌动作电位及收缩力 (Fc)的影响 ,以探讨其抗心律失常的作用机制。方法　采用标准玻璃微电极技术记录心肌细胞动作电位 ,肌力换能器同步记录心肌收缩力。结果　苦参碱 10、2 5、5 0 μmol·L-1可浓度依赖性地延长快反应动作电位(FAP)的复极 5 0 %时程 (APD50 )、复极 90 %时程 (APD90 )和有效不应期 (ERP) ,延长高钾除极组织胺及氯化钡诱发的慢反应动作电位 (SAP)的APD50 、APD90 ;但对FAP、SAP的动作电位振幅 (APA)、0期最大除极速率 (Vmax)及Fc无明显影响。结论　结果提示苦参碱对心肌细胞钠、钙离子通道无明显影响 ,其延长APD的作用可能是阻断心肌钾通道的结果。     

dl-四氢巴马汀对家兔窦房结和豚鼠心室肌慢反应电活动的影响

用细胞内固定微电极技术观察到dl-四氢巴马汀(THP)30～100μM使家兔窦房结细胞动作电位的振幅(APA)、零相去极化速率(SP_0)和舒张期4相去极化速率(SP_4)逐渐降低,小剂量使动作电位复极90％的时程(APD_(90))延长,大剂量使其缩短,并使心率(HR)减慢。THP 30～300μM使高K~+除极和河豚毒素(TTX)所致的豚鼠乳头状肌细胞慢反应动作电位的APA、零相最大上升速率(V_(max))逐渐降低,复极50％的时程(APD_(50))缩短。实验结果提示THP可能有钙拮抗作用。     

Protective effect of O-phenanthroline against mechlorethamine toxicity in the rat liver slice system and in the guinea pig skin

The effect of O-phenanthroline (OP) on mechlorethamine hydrochloride (HN2) toxicity was studied in in vitro and in vivo experiments. Incubation of HN2 with the in vitro rat liver slice system resulted in leakage of alanine aminotransferase (ALT) in a time-dependent manner. Exposure of the slices to HN2 for 4 h caused 79.2% ALT leakage. In the presence of OP enzyme leakage was reduced to 28.7%. OP-induced protection was shown to be dose dependent. Other metal chelators such as dithiothreitol (DTT) and EDTA (ethylenediaminetetraacetic acid) had a weak effect on HN2 cytotoxicity. The protective activity of OP was also demonstrated in in vivo skin toxicity studies in the guinea pig. The ulcerative effect of topically applied HN2 was inhibited by OP even when applied 10 min following the alkylator. Histology of NH2-treated skin showed epidermal ulceration associated with a covering layer of encrusted exudate. However, only a slight diffuse acanthosis of the epidermal layer was observed when OP was applied 10 min after the vesicant. It is suggested that OP may be used for the prevention of tissue damage caused by antineoplastic treatment with nitrogen mustard. It might also be employed in military medicine as an antidote to the chemical weapon sulfur mustard.     

7－氯苄基四氢巴马汀对豚鼠乳头肌迟后去极，触发活动及猫心单相动作电位的影响

７一氯苄基四氢巴马汀对豚鼠乳头肌迟后去极，触发活动及猫心单相动作电位的影响夏国瑾，曾维忠，姚伟星，戴水平，江明性，黄文龙，黄忱亚，彭司勋（同济医科大学药理学教研室，武汉４３００３０；中国药科大学药物化学研究室，南京２１０００９）７－氯苄基四氢巴马汀（...     

水杨酸及其类似物抑制β-内酰胺酶的构效关系研究

目的检测水杨酸及水杨酸的19个类似物对分离自铜绿假单胞菌的β-内酰胺酶的抑制活性，初步探讨它们的构效关系。方法采用Nitrocefin法。结果水杨酸对该酶的50%抑制浓度(IC₅₀)为22 mmol·L^-1； 4个类似物的IC₅₀比水杨酸低，其余类似物的活性比水杨酸差。结论水杨酸苯环上的羧基及邻位羟基是活性基团之一。水杨酸邻位上的羟基被羧基取代后能提高抑制活性。在水杨酸的苯环上增加磺酸基或硝基能提高抑制活性。苯环上的氨基可降低水杨酸的抑制活性。在苯甲酸的苯环上连接氯或氟与抑制活性无关。     

Advances in the structure-activity relationships,mechanisms of action,and therapeutic utilities of ATP-sensitive potassium channel openers

The presence of ATP-sensitive potassium channel (K_ATP) in a variety of tissues makes it an important therapeutic target for drug research. The existence of small molecules that modulate its activity has attracted a great deal of attention over the past several years. Progress achieved at understanding the structure-activity relationships of K_ATP openers, and their therapeutic utilities and mechanism of action are summarized in this review. The compounds combining the features of potent K_ATP openers cromakalim, pinacidil, and aprikalim retain the biological profiles of their predecessors, indicating the classical K_ATP openers may be expressing their biological effects through similar structural requirements. Based on these studies, a pharmacophore model which incorporates a lipophilic residue, an electron deficient aromatic ring, and a hydrogen bonding site has been proposed. Although the first generation compounds have served as extremely useful tools., their therapeutic utility is limited due to indiscriminate actions in a variety of tissues. Tissue selective K_ATP openers are required to advance these compounds into clinical practice. Progress made at the discovery of selective K_ATP openers that might be useful for the treatment of ischemic heart disease, urinary incontinence, and asthma is described in this article. The molecular mechanism of action of K_ATP openers is far from being understood. A binding site for these agents has been identified in the rat aortic smooth muscle cells and intact rat aortic tissue. However, the relationship of this binding site to K_ATP is not understood at the present time. Further work is needed to explore the clinical utility of tissue selective agents and understand their molecular mechanism of action. © 1994 Wiley-Liss, Inc.