ATP通过P2受体调节大鼠近端结肠纵行肌的舒张与收缩反应(英文)

目的腺苷三磷酸(ATP)对大鼠离体远端结肠纵行肌运动的影响已明确,对近端结肠纵行肌的影响可能不同,但未有报告,为此对此进行观察并探讨其受体机制。方法观察静息张力时或预收缩时0.1μmol·L-1～1mmol·L-1ATP和1～100μmol·L-1腺苷对大鼠近端结肠纵行肌的抑制和兴奋作用。结果在静息张力下,1μmol·L-1～1mmol·L-1ATP对大鼠近端结肠纵行肌产生3种效应,即抑制自发性收缩反应,一过性轻度降低基础张力(0.05～0.08g),随后产生浓度依赖性收缩反应(0.04～0.44g)。0.1μmol·L-1河豚毒素不影响ATP的上述作用。在静息张力下,1～100μmol·L-1腺苷对近端结肠纵行肌未产生明显的收缩反应。应用5羟色胺(5HT)或乙酰胆碱(ACh)预收缩标本时,1μmol·L-1～1mmol·L-1ATP产生明显的浓度依赖性舒张反应(23.2%～94.6%,5HT预收缩;24.8%～92.4%,ACh预收缩),而腺苷引起的舒张反应明显小于ATP。结论在大鼠离体近端结肠纵行肌,ATP主要通过嘌呤嘧啶(P)2受体介导收缩反应,部分通过P1受体介导舒张反应。     

腺苷三磷酸对大鼠离体胃平滑肌运动的影响

目的观察腺苷三磷酸(ATP)对大鼠离体胃平滑肌运动的调节作用。方法制备大鼠离体胃体纵行肌、胃体环行肌、胃窦纵行肌、胃窦环行肌标本,观察ATP(01,1,10,100μmol·L-1和1mmol·L-1)的作用。结果在胃体纵行肌标本,ATP诱发微弱的舒张反应,继而出现收缩反应;在高钾预收缩条件下,ATP则引起较大舒张反应后续较小的收缩反应。ATP对胃体环行肌诱发单相收缩反应。1~100μmol·L-1ATP抑制胃窦纵行肌的自发性收缩幅度,同时加快收缩频率;1mmol·L-1ATP则完全抑制自发性收缩反应;在高钾预收缩条件下,ATP产生浓度依赖性舒张反应。1~10μmol·L-1ATP先增大后减低胃窦环行肌的自发性收缩幅度,同时加快收缩频率;100μmol·L-1~1mmol·L-1ATP则抑制自发性收缩反应。结论本文首次报道了ATP影响大鼠离体胃体纵行肌、胃体环行肌、胃窦纵行肌、胃窦环行肌四种平滑肌的运动,且对各种标本的作用特点互不相同,提示ATP在生理条件下对大鼠胃的运动功能发挥重要的调节作用。     

腺苷的血管效应与腺苷三磷酸敏感性钾通道的关系

目的 研究大鼠主动脉腺苷受体和腺苷三磷酸（ＡＴＰ）敏感性钾通道间的关系。方法 在离体大鼠主动脉上观察内皮完整和内皮去除后腺苷受体介导的血管效应及吡那尔与格列苯脲对腺苷作用的影响。结果：腺苷３－３００μｍｏｌ．Ｌ＾－１浓度依赖地松弛ＫＣｌ２０ｍｍｏｌ．Ｌ＾－１预收缩的离体大鼠主动脉环,在４８／９９的标本,腺苷产生先短暂收缩后持续舒张的双向反应,格列本脲１和１００μｍｏｌ．Ｌ＾－１阻断ＡＴＰ敏感性通道     

匹维溴胺对束缚应激大鼠结肠不同部位和肌层平滑肌条的作用

目的评价匹维溴胺对束缚应激大鼠离体结肠平滑肌条的影响并探讨其对各型IBS可能的作用机理.方法成年SD大鼠随机分为模型组和对照组,模型组用自制硬塑胶模具束缚 2 h.分别制作两组大鼠近端及远端结肠的环行肌和纵行肌条共64条(每组肌条32个,各肌层8个).采用离体平滑肌条器官浴槽实验方法,观察不同浓度匹维溴胺对平滑肌条自发性收缩活动的影响.结果匹维溴胺对模型组和对照组离体结肠平滑肌条自发性收缩活动均表现为抑制作用,但对模型组效应较对照组显著(近端结肠 28.54±4.82 vs 7.48±1.65,21.75±1.00 vs 12.56±3.15;远端结肠 15.71±5.27 vs 3.89±1.16,20.16±3.16 vs 7.56±1.96)(P<0.05).匹维溴胺对近端结肠平滑肌收缩的抑制作用较远端结肠显著(P<0.05).匹维溴胺对相同部位结肠环行肌与纵行肌的抑制作用无显著性差异(P>0.05).结论匹维溴胺能抑制束缚应激大鼠离体结肠平滑肌的收缩,且对近端结肠收缩的抑制作用显著高于远端结肠;但在相同部位,对环行肌和纵行肌收缩的抑制作用无显著性差异.     

Relationship between adenosine induced vascular effects and ATP sensitive K channels

目的：研究大鼠主动脉腺苷受体和腺苷三磷酸（ＡＴＰ）敏感性钾通道间的关系．方法：在离体大鼠主动脉环上观察内皮完整和内皮去除后腺苷受体介导的血管效应及吡那地尔与格列苯脲对腺苷作用的影响．结果：腺苷３－３００μｍｏｌ·Ｌ－１浓度依赖地松弛ＫＣｌ２０ｍｍｏｌ·Ｌ－１预收缩的离体大鼠主动脉环,在４８／９９的标本,腺苷产生先短暂收缩后持续舒张的双向反应．格列本脲１和１００μｍｏｌ·Ｌ－１阻断ＡＴＰ敏感性钾通道后腺苷的舒张作用被取消而收缩作用仍存在;腺苷１００μｍｏｌ·Ｌ－１与吡那地尔１μｍｏｌ·Ｌ－１合用时未产生协同作用;去除内皮不影响腺苷的缩血管效应,但舒血管作用减弱且变慢．结论：ＡＴＰ敏感性钾通道的激活参与腺苷受体介导血管扩张作用,但与血管收缩无关．     

P2Y受体介导大鼠胃体环行肌收缩反应的药理学特点

观察大鼠离体胃体环行肌和胃底环行肌不同的药理学特征，分析核苷及核苷酸类物质诱发胃体环行肌收缩反应的作用特点和受体机制。制备大鼠离体胃体环行肌和胃底环行肌标本，利用受体药理学技术观察药物诱发的收缩反应。在胃体环行肌KCl所致收缩反应与胃底环行肌无显著性差别；但是，CCh收缩胃体环行肌的EC₅₀值 [(0.45 ± 0.15) μmol·L⁻¹] 显著高于胃底环行肌 [(0.20 ± 0.09) μmol·L⁻¹, P < 0.01]。5-HT和His收缩两种标本的EC₅₀值无显著差异 (P > 0.05); 但是, 在胃体环行肌5-HT和His产生收缩反应的E_max值 [(0.81 ± 0.26) 和 (0.88 ± 0.27) g] 显著小于胃底环行肌 [(2.67 ± 0.61) 和 (1.90 ± 0.68) g, P < 0.01]。在预收缩胃体环行肌，ATP (0.1～3 000 μmol·L⁻¹) 诱发浓度依赖性收缩反应，未见舒张反应；在预收缩胃底环行肌标本，同浓度ATP诱发先舒张后收缩的双相反应，并呈浓度依赖性。ATP、UTP、ADP、2-MeSATP和α, β-MeATP浓度依赖性诱发大鼠胃体环行肌收缩反应，2-MeSATP的EC₅₀值为 (7.2 ± 5.2) nmol·L⁻¹比Ach [(3.47 ± 1.20) μmol·L⁻¹] 低500倍；各药物产生收缩反应的效价序列为：2-MeSATP>>ADP>ATP=UTP>α, β-MeATP>>腺苷。酚妥拉明、普萘洛尔、阿托品及河豚毒素不影响ATP和UTP诱发的胃体环行肌收缩反应。研究结果表明, 大鼠胃体环行肌的药理学特征明显不同于胃底环行肌; 核苷酸类物质通过某种特殊的P2Y受体介导胃体环行肌收缩反应，是调节胃体环行肌收缩功能的重要介质。
     

糖尿病结肠动力障碍与几种胃肠激素变化的意义

目的　研究糖尿病大鼠模型离体近端结肠平滑肌的收缩运动 ,及其与血浆和结肠组织中生长抑素 (SS)、血管活性肠肽 (VIP)、胃动素 (MTL)、P物质 (SP)在糖尿病结肠动力障碍中的作用。方法　建立糖尿病大鼠模型 ,制备试验组和对照组大鼠离体近端结肠环行肌及纵行肌肌条 ,应用张力换能器测定其静息张力、平均振幅、收缩频率等运动指标 ;用放免法同批测定两组大鼠血浆和近端结肠组织中SS、VIP、MTL和SP含量。结果　 (1)糖尿病组结肠肌条收缩运动的多项指标均较对照组明显降低 (P <0 0 1) ;(2 )糖尿病组血浆中SS、VIP、MTL增加 ,SP降低 ,结肠组织中SS和VIP降低 ,SP增加 ,MTL无变化 ;(3)血浆和肠组织SS与结肠运动指标无显著相关 ;血浆VIP和MTL与结肠运动呈负相关 ,而组织中VIP与结肠运动呈正相关 ;血浆SP和结肠运动呈正相关。结论　 (1)糖尿病多伴有结肠运动功能障碍 ;(2 )血浆和结肠组织中胃肠激素含量变化在糖尿病结肠动力障碍的发病中有一定作用     

一种新型大鼠结肠纵行肌细胞分离培养方法的建立

目的对大鼠结肠纵行肌细胞分离培养的方法进行改进,建立一种取材方便,纯度高的新型大鼠结肠纵行肌细胞的原代分离培养方法,并观察乙酰胆碱和去甲肾上腺素对结肠纵行肌细胞的作用,为结肠纵行肌生理、病理的研究提供细胞模型。方法取Wistar大鼠结肠,从外侧刮去外膜层,剥离外膜下结肠纵行肌,消化后过滤所剩组织进行贴块培养。观察乙酰胆碱和去甲肾上腺素对纵行肌细胞的作用,用NTS-Elements BR3.60分析软件进行分析。结果经α-SM-actin免疫组织化学染色确定培养的细胞为平滑肌细胞,且纯度高;乙酰胆碱对大鼠结肠纵行肌细胞具有收缩作用,当浓度为5.5×10-1μmol.L-1时,收缩作用最强。去甲肾上腺素对纵行肌细胞具有舒张作用,当浓度为4.86×10-2mmol.L-1时,舒张作用最强。结论从结肠外膜分离肠纵行肌层,消化后过滤,所剩组织进行贴块培养,此方法简便易行、纯度高,且对乙酰胆碱和去甲肾上腺素反应良好。     

雷尼替丁和西咪替丁对大鼠结肠平滑肌条收缩活动的影响(英文)

通过大鼠离体结肠平滑肌条实验 ,观察雷尼替丁 ( 0 .0 2 ,0 .2 ,2和 10mmol·L- 1)和西咪替丁 ( 0 .0 .8和 4mmol·L- 1)对结肠收缩活动的影响 .结果表明 :雷尼替丁和西咪替丁增加结肠头端环行肌和结肠尾端纵行肌的平均收缩幅度以及结肠尾端环行肌的运动指数 ,减小结肠头端纵行肌的平均收缩幅度 ,并均有一定的剂量效应关系 ;雷尼替丁增加结肠头端纵行肌的静息张力和结肠尾端纵行肌的收缩频率 ,西咪替丁则降低结肠肌条的收缩频率 .阿托品( 0 .0 1μmol·L- 1)部分阻断雷尼替丁 ( 0 .2mmol·L- 1)对结肠肌条的兴奋作用 ,但不影响西咪替丁 ( 0 .8mmol·L- 1)的作用 ;六甲溴铵 ( 10 μmol·L- 1)不影响雷尼替丁和西咪替丁对结肠肌条的作用 .提示 ,雷尼替丁和西咪替丁对结肠肌条主要表现兴奋作用 ,雷尼替丁对结肠的作用与M受体有关     

S-腺苷蛋氨酸对子宫平滑肌收缩的影响

目的 探究S-腺苷蛋氨酸对子宫平滑肌收缩的影响,为寻找安全有效的新型子宫收缩调节药物提供理论依据。方法 取未妊娠、妊娠早期(6.5d)、妊娠中期(12.5~13.5d)和妊娠晚期(16.5~17.5d)ICR小鼠,分离子宫肌条,两端分别固定于张力换能器,采用氨甲酰胆碱诱导收缩,累积给药法给予沙丁胺醇、S-腺苷蛋氨酸、蛋氨酸、牛磺酸等药物,记录、测量并分析离体子宫收缩曲线。结果 沙丁胺醇和S-腺苷蛋氨酸对未孕、妊娠早期(6.5d)、妊娠中期(12.5~13.5d)和妊娠晚期(16.5~17.5d)四个时间点的小鼠离体子宫平滑肌的收缩均有较强的抑制作用,分别在10-7mol/L和1.0mmol/L的溶液浓度下显著抑制收缩。蛋氨酸、牛磺酸在实验浓度下对ICR小鼠离体子宫平滑肌的收缩影响不明显。结论 S-腺苷蛋氨酸可有效抑制不同阶段离体子宫的收缩,提示S-腺苷蛋氨酸可能是一个有效且安全的子宫收缩调节药物。     

Effects of adenosine and related compounds on adenylate cyclase and cyclic AMP levels in smooth muscle.

The hypotheses were tested that the relaxant effect of adenosine and related compounds in the longitudinal muscle of the rabbit small intestine involves interaction with adenylate cyclase and/or the elevation of tissue cAMP levels. Adenylate cyclase was prepared by gentle homogenization of an isolated smooth muscle cell fraction obtained after collagenase digestion of longitudinal muscle strips. A number of analogs and derivatives of adenosine possessing a primary or secondary 6-amino group were found to inhibit the enzyme similarly to adenosine; however, there was no correlation between compounds known to relax the intact tissue and the existence, or the degree of, cyclase inhibition. Isolated muscle strips were exposed to adrenaline, isoprenaline, adenosine or ATP, at doses causing 30-60% relaxation, for 60 sec prior to sampling and analysis of cAMP content. While small increments in cAMP levels were found after administering adrenaline or isoprenaline, no change was found with adenosine in the absence or presence of theophylline of 1-methyl-3-isobutylxanthine. Neither adenylate cyclase inhibition nor changes in cAMP levels appear to be part of the mechanism of the smooth muscle relaxant action of adenosine or ATP.     

Antagonism by SR 48692 of mechanical responses to neurotensin in rat intestine.

1. The effects of SR 48692 on neurotensin (NT)-induced mechanical responses were investigated in rat duodenum and proximal colon by use of isometric, isovolumic preparations. 2. SR 48692 inhibited the relaxant responses to NT in duodenal circular and longitudinal muscle. It also antagonized the NT-induced contractile effects in duodenal circular muscle and in proximal colon (both muscular layers). 3. From Schild analysis and pA2 value for SR 48692 was 8.2 in tissues where NT induced relaxant effects and 7.5 in tissues where NT induced contractile effects and the slope of the regression line was not significantly different from unity, indicating competitive antagonism. 4. SR 48692 did not antagonize the duodenal relaxant effect induced by noradrenaline and the contractile response to carbachol or substance P in duodenum and colon. 5. Our results demonstrate that SR 48692 selectively antagonizes the mechanical actions of NT in rat intestine and confirm the existence of specific NT receptors. Receptors that subserve a relaxant effect seem to be related, but not identical, to those that mediate contractile effects.     

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.     

Contraction and prostaglandin biosynthesis by myometrium from non-pregnant and pregnant rabbits in response to adenosine 5'-triphosphate

In both non-pregnant and pregnant rabbit myometrial strips, adenosine 5'-triphosphate (ATP) produced contractions in a concentration-dependent manner. Furthermore, ATP (100 microM and 1 mM) produced an initial rapid twitch-like contraction followed by augmented spontaneous motility. These contractile responses of strips from pregnant rabbits to ATP were more marked than those of strips from non-pregnant rabbits. The pD2 values for the contractile response to ATP were 5.20 and 6.70 in strips from non-pregnant and pregnant rabbits, respectively. Treatment with indomethacin did not affect the initial rapid twitch-like contraction, but inhibited the augmented spontaneous motility. ATP also increased the synthesis of prostaglandins (PGs) and thromboxane B2 (TXB2) in a concentration-dependent manner in the following order: 6-keto-PGF1 alpha greater than PGE2 greater than PGF2 alpha greater than TXB2. The increase in the synthesis of cyclooxygenase products induced by ATP was more marked in strips from pregnant rabbits than in strips from non-pregnant rabbits. ATP and melittin stimulated arachidonic acid, phosphatidic acid and diacylglycerol formation in strips from both non-pregnant and pregnant rabbits. These results indicate that ATP stimulates PGs and TXB2 synthesis and phosphatidylinositol hydrolysis through an effect on P2-purinoceptors and consequently augments myometrial contractility in both non-pregnant and pregnant rabbits.     

Two phases of contractile response in rat isolated vas deferens and their regulation by adenosine and alpha-receptors

Contractions to transmural electrical stimulation and exogenous norepinephrine were recorded in isolated longitudinal segments of rat vas deferens. Electrical stimulation for 30 s produced a biphasic contraction in the vas deferens consisting of a rapid, transient response (Phase I), followed by a slowly developing, sustained contraction (Phase II). N6-Cyclohexyladenosine (CHA), a selective adenosine1 (A1)-receptor agonist, attenuated in a concentration-dependent manner the Phase I contractile response, while having little effect on the Phase II response. In contrast, 2-(phenylamino)adenosine (CV-1808), a selective adenosine2 (A2)-receptor agonist had little effect on either contractile phase. CHA did not inhibit the contraction to exogenous norepinephrine, suggesting that A1-receptors were located at a presynaptic site. The relatively selective alpha 2-receptor agonist clonidine produced the same pattern of contractile inhibition as CHA. The inhibitory effect of CHA on the Phase I contractile response in the vas deferens could be antagonized by the selective A1-receptor antagonist 8-cyclopentyltheophylline, while the selective alpha 2-receptor antagonist idazoxan preferentially antagonized the inhibitory effect of clonidine on the Phase I response. Both the Phase I and Phase II contractile responses were reduced by the selective alpha 1-adrenoceptor antagonist prazosin and the ATP analog alpha, beta-methylene adenosine triphosphate (alpha, beta-methylene ATP), suggesting that norepinephrine and ATP are coreleased as neurotransmitters for both responses. The results of the present study demonstrate that in the rat vas deferens the presynaptic inhibitory effects of adenosine is mediated by the A1-receptor subtype, and that both A1- and alpha 2-receptor agonists exert a selective inhibitory effect on the Phase I contractile response to electrical stimulation.     

Postnatal changes in response to adenosine and adenine nucleotides in rat duodenum.

1. The effects of adenosine and adenine nucleotides were studied in rat duodenum from postnatal day 1 to day 70. The mechanical activity of duodenal segments was recorded through an isotonic transducer connected to a polygraphic recorder. 2. In rat duodenal segments, adenosine-5'-triphosphate (ATP, 10(-4) M) and adenosine-5'-diphosphate (ADP, 10(-4) M) produced a contractile response on postnatal day 1. This response increased with age, peaking on day 7, followed by a gradual decrease and was non-existent by day 21. In contrast, a relaxant response to ATP and ADP was apparent on day 21, and continued to increase up to day 70. 3. The contraction caused by ATP was inhibited by indomethacin or the P2y-purinoceptor antagonist, reactive blue-2 but not by tetrodotoxin or hyoscine. Thus, it may be mediated by production of prostaglandin through the P2y-purinoceptor. The relaxation produced by ATP was inhibited by reactive blue-2 but not by tetrodotoxin, guanethidine or the P1-purinoceptor antagonist, 8-phenyltheophylline indicating that ATP acts on smooth muscle directly through the P2y-purinoceptor. The pD2 for the contractile response to ATP was 5.15 on day 7 and that for the relaxant response, 6.64 on day 70. 4. Adenosine (10(-4) M) and adenosine-5'-monophosphate (AMP, 10(-4) M) elicited no response before day 14. On day 14, both adenosine and AMP produced a small relaxant response which increased with age. The relaxation produced by adenosine was inhibited by 8-phenyltheophylline but not by tetrodotoxin or guanethidine, indicating that it is mediated by an action on the P1-purinoceptor of smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of an antihypertensive agent, nipradilol, on isolated coronary artery of the dog

Effects of nipradilol on proximal, middle and distal portions of left coronary arteries of the dog were investigated in vitro. Nipradilol (10(-7)-10(-3) M) produced a concentration-dependent relaxation in helical strips of isolated coronary artery under potassium contracture. The relaxation in the middle portions was most pronounced, it was 10% of the equimolar concentrations of nitroglycerin and significantly greater than that of propranolol. In the proximal portions of the coronary arteries, nipradilol (3 X 10(-8)-3 X 10(-7) M) showed a tendency to augment the contractile responses to norepinephrine; in the middle portions it reversed the relaxant responses to norepinephrine into contractile effects in a concentration-dependent manner. In distal portions, nipradilol significantly decreased the relaxant responses of the strips to norepinephrine. The findings demonstrate direct vasodilating and beta-adrenoceptor blocking actions of nipradilol in isolated coronary arteries of the dog.     

Stimulation of lumbar sympathetic nerves evokes contractions of cat colon circular muscle mediated by ATP and noradrenaline.

1. The action of the lumbar sympathetic nerves to cat colon was studied in vitro using isolated muscle strips with attached lumbar colonic nerves (LCN) orientated in the axis of circular muscle layer. Electrical stimulation of LCN caused frequency-dependent increases in resting tension and in amplitude of spontaneous contractions. Contractile responses were abolished by tetrodotoxin (3 microM) and by guanethidine (30 microM), indicating that they were neurogenic, involving the release of neurotransmitter from sympathetic fibres. 2. Propranolol (1-9 microM), a beta-adrenoceptor antagonist, caused a concentration-dependent potentiation of LCN-evoked contractile responses. Propranolol (3 microM) potentiated contractile responses to exogenously applied noradrenaline but not to phenylephrine. 3. Phentolamine (1-9 microM), an alpha-adrenoceptor antagonist, and prazosin (1-9 microM), an alpha 1-adrenoceptor antagonist, caused a concentration-dependent reduction of amplitude but did not abolish LCN-evoked contractile responses. Prazosin (3 microM) or phentolamine (3 microM) antagonized contractile responses to noradrenaline and phenylephrine. 4. Desensitization of purinoceptors with the P2x-receptor agonist, alpha,beta-methylene ATP, caused a decrease in amplitude of LCN-evoked contractile responses and abolished contractile responses to ATP. In muscle strips where alpha 1-adrenoceptors were blocked with prazosin (3 microM) and P2-purinoceptors were desensitized with alpha,beta-methylene ATP, the amplitude of contractile responses was reduced by 82-100%. 5. The P2x-purinoceptor antagonists, arylazido amino propyl adenosine triphosphate (ANAPP3) and 5. The P2x-purinoceptor antagonists, arylazido amino propyl adenosine triphosphate (ANAPP3) and suramin, affected LCN-evoked contractile responses. ANAPP3 (50-100 microM) caused a concentration-dependent reduction in the amplitude of contractile response. Suramin (100 microM) caused a small reduction in amplitude of contractile responses but potentiated their amplitude at a concentration of 500 microM. 6. ANAPP3 (100 microM) irreversibly inhibited contractions to alpha,beta-methylene ATP or ATP. Suramin (100-500 microM) inhibited contractions to alpha,beta-methylene ATP (0.5-1 microM) or low concentrations of ATP (10-50 microM) but potentiated contractions at higher concentrations. ANAPP3 (100 microM) and suramin (100, 500 microM) had no effect on contractile responses to noradrenaline. 7. Clonidine (0.05-1 microM), a selective alpha 2-adrenoceptor agonist, caused a concentration-dependent reduction in amplitude of LCN-evoked contractile responses, at 10 Hz, while yohimbine (0.1-1 microM), a selective alpha 2-adrenoceptor antagonist, increased them. At 1 microM, both compounds affected LCN-evoked contractions at all frequencies. This suggests that prejunctional alpha 2-receptors are involved in autoinhibition at sympathetic terminals.(ABSTRACT TRUNCATED AT 400 WORDS)