The role of prostaglandins in cholinergic neurotransmission in the guinea pig.

Prostaglandins have contrasting effects on neurotransmission at different cholinergic nerve endings. This is a report on the role of prostaglandins in a number of cholinergic preparations from the guinea pig. In the isolated ileum PGE1 (2 X 10(-10) to 5 X 10(-8) M) potentiated the response to electrical stimulation of the cholinergic nerves. PGE1 (10(-7 M) caused an increase in tone followed by a period of transient inhibition of twitch height. Responses to simulation of the ileum with drugs were not potentiated by PGE1. Responses of atropinized or plexus-free muscle to electrical stimulation were also not potentiated by PGE1. Acetylsalicylic acid (2.5 X 10(-4) M) diminished the twitch response and the output of acetylcholine from the ileum. Both effects were reversed by PGE1. Qualitatively similar observations were made on the trachea. It is concluded that prostaglandins facilitate acetylcholine release in the ileum and trachea. PGE1 diminished the effect of vagal stimulation on the heart rate. The response to stimulation of the phrenic nerve was not affected.     

Contraction of isolated guinea-pig ileum by urotensin II via activation of ganglionic cholinergic neurons and acetylcholine release

Urotensin II and its receptor are expressed in the gastrointestinal tract of mice, but the effects of urotensin II on the gastrointestinal functions have not been established. In the present study, we investigated the effects of human urotensin II on a segment of the guinea-pig ileum. The addition of urotensin II induced contraction of the ileum in concentration-manner (-log EC(50) value was 8.13+/-0.21). The response by urotensin II was extracellular CaCl(2)-dependent and easily desensitized. Like nicotine, the contraction induced by 100 nM urotensin II was inhibited by treatment with atropine, hexamethonium, D-tubocurarine, tetrodotoxin or hemicholinium-3, and enhanced by physostigmine. Treatment with omega-conotoxin GVIA (an inhibitor of N-type Ca(2+) channels, 300 nM) inhibited 100 nM urotensin II- and 4 microM nicotine-, but not 3 microM acetylcholine-, induced contraction. Both urotensin II and nicotine stimulated [(3)H]choline release in a tetrodotoxin-sensitive manner from the prelabeled slices of the ileum. These findings suggest that urotensin II stimulated acetylcholine release from the ganglionic cholinergic neurons and thus stimulated contraction via muscarinic acetylcholine receptors in the guinea-pig ileum. Urotensin II receptor system in the myenteric neurons may regulate the gastrointestinal functions.     

Characteristics of post-tetanic contraction induced by naloxone in guinea pig ileum

The characteristics of isolated guinea-pig ileal contractions of basal tension after tetanic stimulation in the presence of a high concentration of naloxone (NLX) [post-tetanic contraction] were investigated. The post-tetanic contraction did not occur in the absence of NLX, but did occur in a concentration-dependent manner in the presence of a high concentration of NLX (5 x 10(-7), 10(-6), 10(-5) and 5 x 10(-5) M), the concentration of which was higher than that required for antagonizing post-tetanic twitch inhibition. The contraction in the presence of 10(-6) M NLX was diminished by washing NLX from the preparation with Krebs-bicarbonate solution. The contraction under 10(-6) M NLX occurred in a frequency-dependent manner (5, 10 and 20 Hz), but not at 0.1 Hz. Tetanic stimulation (5, 10 and 20 Hz) without NLX did not induce this contraction. The post-tetanic contraction with 10(-6) M NLX had a tendency to be antagonized in the presence of 5 x 10(-6) M atropine. Methysergide (5 x 10(-5) M) had no effect on this contraction. Spantide (10(-5) M) largely inhibited the contraction, and indomethacin (5 x 10(-6) M) and tetrodotoxin (5 x 10(-7) M) completely inhibited this contraction. These results indicate that tetanic stimulation in the presence of a high concentration of NLX induces contraction of the ileal muscle due to the release of endogenous ileal contractile substances (substance P, prostaglandins and acetylcholine), and suggests that these contractions are closely linked to the endogenous opioid system induced by tetanic stimulation in the ileum.     

Effect of l-ephedrine on cholinergic neurotransmission in the isolated guinea pig ileum

In the isolated guinea pig ileum, the effects of I-ephedrine on the twitch response to field stimulation were investigated in the presence of propranolol. Ephedrine and clonidine inhibited the twitch response but not the contraction to exogenous acetylcholine. The inhibitory effect of clonidine was significantly diminished by yohimbine pretreatment. However, the inhibitory effect of ephedrine was not influenced by yohimbine, sulpiride or 6-hydroxydopamine (6-OHDA) pretreatment. Most of this action of ephedrine appeared to be cholinergic prejunctional in nature, but unrelated to activation of prejunctional alpha 2-adrenoceptors and dopamine sensitive receptors on the cholinergic nerves in this preparation.     

Mechanism of atropine-resistant contraction induced by Dai-kenchu-to in guinea pig ileum.

To clarify the contractile mechanism of Dai-kenchu-to, the effects of hydroxy beta-sanshool (an ingredient of Zanthoxylum fruit), Zanthoxylum fruit (a constituent herb of Dai-kenchu-to) and Dai-kenchu-to were studied in mucosa-free longitudinal muscle of guinea pig ileum. Hydroxy beta-sanshool at 10(-7)-10(-5) g/ml induced dose-related contractions accompanied by autonomous contraction and produced an initial contraction at a concentration of 10(-4) g/ml or more. The contraction induced by hydroxy beta-sanshool (10(-5) g/ml) was significantly inhibited by tetrodotoxin or the capsaicin-receptor antagonist capsazepine. Although atropine or the substance P antagonist spantide tended to inhibit the contraction, a combination of atropine and spantide almost abolished the contraction by hydroxy beta-sanshool. The P2-purinoceptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid did not affect hydroxy beta-sanshool-induced contraction in the presence or absence of spantide. The tonic contractions by Zanthoxylum fruit (2 x 10(-4) g/ml) and Dai-kenchu-to (10(-3) g/ml) were significantly inhibited or tended to be inhibited by atropine, spantide, tetrodotoxin or capsazepine and were remarkably suppressed by the combination of atropine and spantide. These results suggested that acetylcholine release from intrinsic cholinergic nerves and tachykinins from sensory neurons are involved in the contractions induced by hydroxy beta-sanshool and that tachykinins may be involved in the atropine-resistant contraction by Dai-kenchu-to.     

Contractile effect of prolactin on guinea pig isolated ileum

Prolactin (PRL) at high concentrations contracted the guinea pig isolated ileum. The maximum response elicited by PRL was 44% of that of histamine-induced responses. There was no significant difference in potency between PRL preparations obtained from two different sources. PRL responses were nullified by denaturation or proteolytic digestion of the hormone. The contractile response was antagonised by atropine and potentiated by neostigmine, but unaffected by the prostaglandin antagonist SC-19220. The pA2 values of atropine against PRL and ACh were similar. Preincubation with morphine, which inhibits ACh release, produced slight inhibition of PRL-evoked contractions. Even high concentrations of PRL failed to produce any response in neostigmine-treated frog rectus muscle preparations. This suggests that PRL may produce contractions through a cholinergic mechanism involving muscarinic receptors. Enhanced gut motility reported earlier for hyperprolactinemic states may be attributed to this cholinomimetic effect of PRL on the intestinal tract.     

Histamine receptors in the guinea pig ileum

Summary Histamine and some related compounds acting selectively on H₂-or H₁-receptors were tested for their ability to contract the guinea pig ileum, in the usual whole ileum preparation and in the longitudinal muscle preparation. The concentrations elicited by histamine in both kinds of preparations were not potentiated by cimetidine or metiamide and were not inhibited by administration of H₂ receptor selective agonists in doses which were subthreshold for contracting the guinea pig ileum; higher doses of the H₂ agonists could actually potentiate the effect of histamine. The results obtained suggest that H₂ receptors with relaxing effect do not occur in the guinea pig ileum or at least that they are not involved in the contraction of the longitudinal muscle layers. The possibility that a sub-type of H₂ receptors with properties different from those of the classical H₂ receptors so far known, exists in the guinea pig ileum, cannot be excluded.     

A comparison of the actions of acetylcholine and bradykinin on the guinea pig ileum

Summary Procaine (8.5×10^–5 M) inhibited the action of acetylcholine but not that of bradykinin on the guinea pig ileum. Attempts were made to identify the difference in stimulus-response coupling which would explain this difference in sensitivity. The responses to both agonists were dependent upon the presence of Ca²⁺ in the extracellular fluid, were inhibited to approximately the same extent by the addition of 0.25 mM Mn²⁺ to the bathing fluid and were equally sensitive to reduction in Na⁺ concentration of the extracellular fluid. Neither acetylcholine nor bradykinin could provoke ileal contraction when Sr²⁺ was substituted for Ca²⁺. Thus there was no indication of the difference in the stimulus-response pathways for the two agonists which must exist to explain the differential sensitivity to procaine.     

庆大霉素对组胺所致豚鼠离体肠肌收缩的拮抗作用

目的观察庆大霉素对组胺所致豚鼠离体回肠的拮抗作用。方法离体豚鼠回肠经庆大霉素预处理后加入不同浓度组胺,记录肠肌收缩的幅度。结果发现庆大霉素能部分对抗组胺诱发的肠肌收缩,对组胺的减活指数为4.45,甚至对肠肌也有直接的舒张作用。结论庆大霉素对肠肌具有舒张作用,此作用在庆大霉素口服治疗感染性胃肠炎方面具有减轻症状的意义。     

干酪菌发酵产物对豚鼠离体回肠平滑肌收缩功能的影响

目的 观察干酪菌发酵产物对豚鼠离体回肠平滑肌收缩功能的影响。方法采用豚鼠离体回肠平滑肌标本,观察加入干酪菌发酵产物前后肌紧张的变化以及加入几种受体阻断剂对其药效的影响。结果 干酪菌发酵产物能提高豚鼠离体回肠平滑肌肌紧张,且呈剂量-效应依赖关系,组织胺H1受体阻断剂苯海拉明能阻断其兴奋作用。结论 干酪菌发酵产物能提高豚鼠离体回肠平滑肌肌紧张,其作用途径与组织胺H1受体有关。     

Prejunctional M1 and postjunctional M3 muscarinic receptors in the circular muscle of the guinea-pig ileum

The effects of subtype-selective muscarinic receptor antagonists on electrically evoked release of acetylcholine and muscle contraction were compared in circular muscle preparations of the guinea-pig ileum. Incubation of the preparation with [³H]choline resulted in the formation of [³H]acetylcholine. Electrical stimulation caused the release of [³H]acetylcholine which was abolished by tetrodotoxin and omission of calcium from the medium. 5-Hydroxytryptamine (10 M) and the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (300 M) did not change acetylcholine release. The muscarinic antagonists pirenzepine (M1 selective), AF-DX 116 (M2 selective) and hexahydrosiladifenidol (M3 selective) caused concentration-dependent increases in the evoked release of acetylcholine, and inhibitions of the circular muscle contraction. The postjunctional affinity constants (pA₂ values) obtained for hexahydrosiladifenidol (8.06), pirenzepine (6.95) and AF-DX 116 (6.60) identified the muscular receptor as an M3 subtype. Pirenzepine was more potent in facilitating the evoked release than hexahydrosiladifenidol and AF-DX 116. These findings suggest that the release of acetylcholine in the circular muscle is inhibited by M1 muscarinic autoreceptors whereas muscle contraction is mediated by M3 receptors.     

Pinacidil suppression on 5-HT_3 receptor-mediated contraction of guinea pig ileum in vitro

目的：研究钾通道开放剂吡那地尔对５ＨＴ３受体介导的离体豚鼠回肠（ＧＰＩ）收缩反应的影响．方法：以等长换能器记录ＧＰＩ收缩反应．以［３Ｈ］ＧＲ６５６３０结合试验检测大鼠内嗅皮层５ＨＴ３受体的结合特性．结果：（１）２甲基５ＨＴ及５ＨＴ以剂量依赖方式引起ＧＰＩ的收缩；托品色创竞争性抑制此反应．（２）吡那地尔以剂量依赖方式抑制２甲基５ＨＴ和５ＨＴ引起的ＧＰＩ收缩，并增强托品色创或Ｂｅｎｅｓｅｔｒｏｎ对５ＨＴ诱发ＧＰＩ收缩的抑制作用，但不影响卡巴胆碱引起的ＧＰＩ收缩；吡那地尔对大鼠内嗅皮层５ＨＴ３受体与［３Ｈ］ＧＲ６５６３０的结合无影响．结论：吡那地尔可能通过激活突触前神经元ＡＴＰ敏感钾通道抑制由５ＨＴ３受体介导的ＧＰＩ收缩反应．     

Cholinergic modulation of the release of 5-hydroxytryptamine from the guinea pig ileum

Summary Isolated segements of the guinea pig ileum were vascularly perfused and the release of 5-HT and its metabolite 5-HIAA into the portal venous effluent determined by HPLC with electrochemical detection. Test substances were applied via the arterial perfusion medium. Oxotremorine inhibited concentration-dependently the release of 5-HT and 5-HIAA (by 47% at 1 mol/l). Scopolamine (0.1 mol/1) did not affect the release of 5-HT and 5-HIAA, but antagonized the effect of oxotremorine. In the presence of TTX (1 mol/1) oxotremorine (1 pmol/1) increased the release of 5-HT by 150% and that of 5-HIAA by 220%. This increase was completely blocked by scopolamine. Hexamethonium (100 pmol/1) and TTX (1 pmol/1) reduced the release of 5-HT by 32 and 40%, respectively. DMPP (10 pmol/1) increased the release of 5-HT by 57%, and this effect was prevented by hexamethonium. Neither DMPP nor hexamethonium significantly affected the release of 5-HIAA. The enhancing effect of DMPP on 5-HT release was increased and prolonged in the presence of TTX or scopolamine. Nicotine (1, 10 or 30 mol/l) alone did not cause a consistent increase in the release of 5-HT. However, in the presence of scopolamine nicotine increased the release of 5-HT by 57%. In conclusion, the release of intestinal 5-HT is facilitated via muscarine and nicotine receptors located on the enterochromaffin cells. Indirect evidence suggests that the release of 5-HT is additionally modulated by an as yet unknown inhibitory neurotransmitter released by muscarine receptor activation.Abbreviations DMPP 1,1-dimethyl-4-phenylpiperazinium - 5-HT 5-hydroxytryptamine - 5-HIAA 5-hydroxyindoleacetic acid - TTX tetrodotoxin Send offprint requests to H. S. at the above address     

Evidence for the involvement of P2-purinoceptors in the cholinergic contraction of the guinea-pig ileum

In the isolated ileum of the guinea-pig the P₂-purinoceptor antagonists PPADS and suramin: (a) strongly inhibited the cholinergic contractile effect of α,β-methylene ATP, (b) did not influence contractions evoked by exogenous acetylcholine (ACh) but, (c) moderately (by about 30%) inhibited cholinergic contractions due to electrical field stimulation (EFS), in a non-additive manner. These results suggest that an endogenous ligand that stimulates P₂-purinoceptors (possibly ATP) is involved in the contractile effect of EFS, as a positive modulator of ACh release.     

吡那地尔对5—HT3受体介导的离体豚鼠回肠收缩反应的抑制

AIM: To study the effects of the K+ channel opener pinacidil on 5-HT3 receptor-mediated contractions of the isolated guinea pig ileum (GPI) longitudinal muscle-myenteric plexus strip preparations. METHODS: GPI contractions were recorded with a chart recorder through isometric transducers. The effect of pinacidil on binding properties of 5-HT3 receptors was assessed using [3H]GR65630 binding assay in membrane preparations of rat entorhinal cortex. RESULTS: (1) A selective 5-HT3 receptor agonist 2-methyl-5-HT 0.1-300 mumol.L-1 and 5-HT 0.001-50 mumol.L-1 elicited GPI contractile responses in concentration-dependent manners, the EC50 values (and 95% confidence limits) for 2-methyl-5-HT and 5-HT were 10.0 (8.9-11.2) mumol.L-1 and 1.6 (1.3-1.9) mumol.L-1, respectively. Selective 5-HT3 receptor antagonist tropisetron 0.1 mumol.L-1 competitively inhibited the responses to 2-methyl-5-HT and 5-HT. (2) Pinacidil 0.5-5 mumol.L-1 inhibited 5-HT3 receptor-mediated contractions. (3) Pinacidil 1 mumol.L-1 enhanced the inhibitory effects of tropisetron 0.1 mumol.L-1 or another selective 5-HT3 receptor antagonist benesetron 1 mumol.L-1 on 5-HT-induced GPI contractile responses. (4) Pinacidil 1-5 mumol.L-1 did not affect GPI contractile responses evoked by a selective M-ACh receptor agonist carbachol 1 mumol.L-1. (5) Pinacidil 1-5 mumol.L-1 had no effect on binding properties of 5-HT3 receptors with selective 5-HT3 receptor radioligand [3H]GR65630 in the entorhinal cortex of rat brain. CONCLUSION: The inhibition by pinacidil of 5-HT3 receptor-mediated GPI contractile responses may be mediated through activation of ATP-sensitive K+ channels located in prejunctional myenteric neurons.     

Direct evidence for a release of acetylcholine from the myenteric plexus of guinea pig small intestine by substance P

Myenteric plexus-longitudinal muscle strips from guinea pig small intestine were labeled with [3H]choline while under continuous field stimulation. Release of newly synthesized [3H]acetylcholine was studied in the presence of substance P afterwards. Substance P evoked release of [3H]acetylcholine in a dose-related fashion. Both tetrodotoxin and [D-Pro2,D-Phe7,D-Trp9]substance P, a synthetic antagonist of substance P, completely blocked this release and provided evidence for a cholinergically mediated mechanism of substance P on enteric neurons.     

介导豚鼠腹腔神经节细胞5-羟色胺去极化反应的受体亚型

目的在豚鼠腹腔神经节(CG)细胞上鉴定介导5-羟色胺(5-HT)去极化反应的受体亚型。方法应用离体细胞内记录技术。结果赛庚啶(cyproheptad ine,5-HT1/2受体拮抗剂)和BRL 24924(5-HT1P受体拮抗剂)可逆地阻抑5-HT慢去极化反应,而sp iperone(5-HT1A受体拮抗剂),和m ian-serin(5-HT2受体拮抗剂),对5-HT慢去极化反应无明显影响;MDL 72222(5-HT3受体拮抗剂)对5-HT慢去极化反应无明显影响,却能够可逆地阻抑5-HT快去极化反应;压力注射MCPP(5-HT1P受体激动剂)可使5-HT敏感的CG神经元出现慢去极化反应且此反应能够被BRL 24924可逆地阻抑。结论豚鼠CG细胞的5-HT快、慢去极化反应分别由5-HT3和5-HT1P受体介导的。     

Involvement of substance P in the excitatory action of GABAA agonists on cholinergic neurons in the guinea-pig ileum

Summary 1. The possible involvement of substance P (SP) in cholinergic contractions induced by GABA_A agonists in the guinea-pig ileum was further investigated. 2. Responses evoked by 3-aminopropane sulphonic acid (3-APS) or muscimol consisted of a rapid phasic contraction followed in 70% of preparations by a tonic contraction, usually smaller in amplitude but considerably longer in duration. Phasic and tonic components were sensitive to bicuculline, neurogenic (cholinergic) in nature and susceptible to desensitization. 3. Capsaicin (0.2 M) pretreatment and SP receptor desensitization caused by 3 different priming SP concentrations (10 nM, 30 nM, 100 nM), depressed both components of the 3-APS-induced response, the magnitude of antagonism being greater for tonic contractions. Similar findings were obtained by using 10 M (d-Pro⁴, d-Trp^7,9)SP-(4–11), even though the degree of antagonism caused by this SP antagonist was consistently lower. 4. These results indicate that depression of SP receptor function achieved by three different procedures decreases cholinergic contractile responses to GABA_A agonists in the guinea-pig ileum. This provides further support for the hypothesis that GABA_A receptor activation evokes both direct and indirect stimulation of enteric cholinergic neurons and that SP and/or a related peptide play an important role in mediating the indirect component of the cholinergic response. Send offprint requests to M. Tonini at the above address