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  • 1
    Electronic Resource
    Electronic Resource
    Isolation of Cholinergic Synaptic Vesicles from the Myenteric Plexus of Guinea-Pig Small Intestine (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 35 (1980), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The acetylcholine-rich myenteric plexus-longitudinal muscle preparation of the guinea-pig small intestine has been subjected to subcellular fractionation using modifications of both classical methods and that originally devised for bulk isolation of cholinergic synaptic vesicles from the electromotor nerve terminals of Torpedo marmorata by means of density gradient centrifugation in a zonal rotor. The latter method gave a vesicle fraction with the highest acetylcholine content so far recorded for a mammalian particulate fraction, 30.9 × S.E.M. 1.8 (5) nmol of acetylcholine × mg of protein−1. Electron-microscopical examination showed that it consisted of a homogeneous preparation of vesicles of mean spherical diameter 61 ×sd 4 (108) nm, with little or no contamination with other lipoprotein membrane structures, mixed how-ever with considerable amounts of actomyosin fibrils, presumably derived from the longitudinal muscle. Slab-gel electrophoresis in sodium dodecyl sulphate showed that, in addition to prominent peaks attributable to actin and myosin, there was a relatively simple pattern of (presumably) vesicle protein among which all the proteins thought to be characteristic of Torpedo synaptic vesicles were present. Dowe G. H. C. et al. Isolation of cholinergic synaptic vesicles from the myenteric plexus of guinea-pig small intestine. J. Neurochem.35, 993–1003 (1980).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1980.tb07099.x
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  • 2
    Electronic Resource
    Electronic Resource
    Pre- and postsynaptic effects of muscarinic agonists in the guinea-pig ileum (1980)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 314 (1980), S. 259-266 
    Details
    ISSN: 1432-1912
    Keywords: Myenteric plexus ; Muscarinic agonists ; Inhibition of acetylcholine release ; Smooth muscle contraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of several muscarinic agonists on smooth muscle (postsynaptic effect) and on acetylcholine release (presynaptic effect) were compared in the longitudinal muscle-myenteric plexus preparation of the guinea-pig ileum. 1. For release experiments the acetylcholine stores of the preparation were labelled with 3H-choline. Electrical field stimulation in the absence of a cholinesterase inhibitor caused an outflow of tritium that reflected release of 3H-acetylcholine. The agonists oxotremorine, arecaidinepropargylester, methylfurmethide, muscarine, carbachol, arecoline and pilocarpine inhibited the stimulation-induced outflow in a concentration-dependent manner. At the highest concentrations used, the drugs depressed the evoked outflow by 83–96%. Scopolamine (10nM) antagonized the inhibitory effects of all agonists which suggests that the reduction of outflow was mediated by muscarine receptors. 2. Oxotremorine (100nM) depressed the twitch response to field stimulation at 0.1 Hz. The inhibitory effect was overcome by scopolamine (3nM). The twitch-inhibitory effect of oxotremorine is thought to result from stimulation of presynaptically located muscarine receptors. 3. All agonists contracted the longitudinal muscle in a concentration-dependent fashion. The rank orders of potencies for pre- and postsynaptic effects were dissimilar. Furthermore, the potency ratios (measured as EC 50 presynaptic: EC 50 postsynaptic) were not constant but varied from 0.37 (oxotremorine) to 2.9 (acetylcholine). The results suggest that pre-and postsynaptic muscarine receptors in the longitudinal muscle-myenteric plexus preparation differ slightly in their pharmacological properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00498547
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  • 3
    Electronic Resource
    Electronic Resource
    Inhibition by oxotremorine of acetylcholine resting release from guinea pig-ileum longitudinal muscle strips (1975)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 287 (1975), S. 47-60 
    Details
    ISSN: 1432-1912
    Keywords: Guinea-Pig Ileum Longitudinal Muscle Strips ; Acetylcholine Resting Release ; Acetylcholine Content ; Oxotremorine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Longitudinal muscle strips of the guinea-pig ileum were incubated in Tyrode solution containing either DFP or physostigmine as cholinesterase inhibior. After a 90 min preincubation period the acetylcholine resting release into the medium was determined. Acetylcholine was estimated by gas chromatography. 2. The resting release was 0.39 nmol/g×min irrespective of the cholinesterase inhibitor used. In the presence of hexamethonium, or after omission of external calcium, the resting release fell by 50 and 55%, respectively. 3. Oxotremorine (10−5 and 10−4 M) significantly inhibited the resting release of acetylcholine by 25 and 33%, respectively. The inhibitory effect of oxotremorine was completely reversed by atropine (3×10−7M). Oxotremorine did not reduce the spontaneous release of acetylcholine that occurred either in the presence of hexamethonium or in the absence of external calcium. 4. The acetylcholine content of the muscle strips was approximately doubled during the preincubation with a cholinesterase inhibitor. The subsequent incubation with oxotremorine did not lead to a further increase in the endogenous acetylcholine content. However, incubation of the muscle strips with oxotremorine in the absence of a cholinesterase inhibitor led to a rise in the endogenous acetylcholine concentration. Inin vivo experiments, oxotremorine also caused an increase in the acetylcholine content of the muscle strips. The possibility is discussed that the rise in the acetylcholine concentration following the administration of oxotremorine is a consequence of the decreased release. 5. It is concluded that oxotremorine inhibits the resting release of acetylcholine by activation of neuronal muscarinic receptors. The inhibitory effect of oxotremorine is linked to that fraction of the acetylcholine resting release that is calcium-dependent and that arises from propagated activity in cholinergic neurones. The results are consistent with the hypothesis of a feed-back control of acetylcholine release mediated by inhibitory muscarinic receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00632637
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  • 4
    Electronic Resource
    Electronic Resource
    Modulation by oxotremorine and atropine of acetylcholine release evoked by electrical stimulation of the myenteric plexus of the guinea-pig ileum (1977)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 300 (1977), S. 145-151 
    Details
    ISSN: 1432-1912
    Keywords: Myenteric plexus ; Presynaptic muscarine receptors ; Acetylcholine release ; Oxotremorine ; Atropine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. The effects of oxotremorine and atropine on the release of acetylcholine from longitudinal muscle strips of the guinea-pig ileum stimulated at frequencies between 0.1 and 3 Hz in the presence of eserine were investigated. In control experiments the acetylcholine output per stimulus declined with increasing frequencies of stimulation. 2. Oxotremorine inhibited the release of acetylcholine in a concentration-dependent fashion. At a concentration of 10−6 M oxotremorine, the release evoked by 0.1 Hz was reduced by 54%. With increasing frequencies of stimulation the inhibitory effect of oxotremorine became smaller. 3. Atropine enhanced the output of acetylcholine evoked by electrical stimulation. In the presence of 10−8 M atropine, the concentration-effect curve for the inhibitory action of oxotremorine was shifted to the right in a parallel manner. From the dose-ratio a pA2 value for atropine against oxotremorine of 8.8 was calculated. 4. Hexamethonium (2.8×10−4 M) did not affect the modulating effects of oxotremorine or atropine on acetylcholine output. 5. It is concluded that the guinea-pig ileum myenteric plexus contains inhibitory muscarine receptors whose stimulation by oxotremorine or by liberated endogenous acetylcholine leads to a diminished output of transmitter. Atropine, by blocking these receptors facilitates acetylcholine release. Further, the results suggest that the depression of acetylcholine release per stimulus with increasing frequencies of stimulation is due to the presence of the inhibitory muscarine receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00505045
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  • 5
    Electronic Resource
    Electronic Resource
    Increase by α-adrenolytic drugs of acetylcholine release evoked by field stimulation of the guinea-pig ileum (1979)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 309 (1979), S. 255-257 
    Details
    ISSN: 1432-1912
    Keywords: Myenteric plexus ; Acetylcholine release ; Yohimbine ; Tolazoline ; Phentolamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The release of acetylcholine evoked by field stimulation of the guinea-pig ileum (3 Hz) is increased by yohimbine and tolazoline but not affected by phentolamine. It is proposed that yohimbine and tolazoline by blocking α-adrenoceptors of the cholinergic nerves abolish the inhibition caused by endogenous noradrenaline, and thus facilitate the output of acetylcholine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00504758
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  • 6
    Electronic Resource
    Electronic Resource
    Choline inhibits acetylcholine release via presynaptic muscarine receptors (1981)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 316 (1981), S. 131-134 
    Details
    ISSN: 1432-1912
    Keywords: Myenteric plexus ; Choline ; Presynaptic muscarine receptors ; Acetylcholine release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of exogenous choline on the outflow of 3H-acetylcholine evoked by field stimulation was studied on the myenteric plexus-longitudinal muscle preparation of the guinea pig. Choline at concentrations of 100 μM and higher depressed the evoked outflow of 3H-acetylcholine in a concentration-dependent manner. The EC 50 for the inhibitory action was 300 μM. Scopolamine (10 nM) antagonized the effect of choline which indicates that the inhibition of 3H-acetylcholine outflow is mediated by muscarine receptors. The findings imply that choline at high concentrations does not improve cholinergic synaptic neurotransmission in tissues that are endowed with presynaptic muscarine receptors (e.g. myenteric and central cholinergic neurones). Furthermore, it is suggested that the increase in tissue acetylcholine content that has been observed after choline administration is probably due to the depression of acetylcholine release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00505306
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  • 7
    Electronic Resource
    Electronic Resource
    Absence of muscarinic modulation of vasopressin release from the isolated rat neurohypophysis (1975)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 287 (1975), S. 391-397 
    Details
    ISSN: 1432-1912
    Keywords: Isolated Rat Neurohypophysis ; Vasopressin Release ; Acetylcholine ; Atropine ; Oxotremorine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Isolated rat neurohypophyses were incubated in Locke solution at 37°C and the vasopressin output into the medium determined by bioassay. 2. Potassium chloride 60 mM caused a 9-fold increase in the rate of vasopressin release that was abolished when calcium chloride was omitted from the Locke solution. 3. Acetylcholine 5.5×10−4 M neither alone nor in the presence of atropine 2.9×10−6 M changed the “resting” release of vasopressin. 4. Neither acetylcholine 5.5×10−4 M nor oxotremorine 10−4 and 3×10−4 M altered the vasopressin release evoked by potassium chloride 60 mM. 5. In contrast to the peripheral adrenergic nerve fibres, the secretory terminal fibres of the neurohypophysis do not appear to contain muscarinic inhibitory or nicotinic excitatory receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00500040
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  • 8
    Electronic Resource
    Electronic Resource
    Some pharmacological properties of the false cholinergic transmitter acetylpyrrolidinecholine and its precursor pyrrolidinecholine (1976)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 295 (1976), S. 81-87 
    Details
    ISSN: 1432-1912
    Keywords: Acetylpyrrolidinecholine ; Pyrrolidinecholine ; Muscarine receptors ; Nicotine receptors ; Neuromuscular transmission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The acetylcholine analogue acetylpyrrolidinecholine as well as the chline analogue pyrrolidinecholine were synthesized and the cholinergic properties of both substances were investigated on the guinea-pig ileum, rat blood pressure and frog rectus abdominis muscle. Acetylpyrrolidinecholine was 3–5 times less potent than acetylcholine on the three preparations tested. The dose-response curves to acetylpyrrolidinecholine were shifted to the right in a parallel manner by atropine and (+)-tubocurarine. The dissociation constants for atropine and (+)-tubocurarine obtained with acetylpyrrolidinecholine as agonist were not different from those obtained with acetylcholine. This indicates that acetylpyrrolidinecholine specifically stimulates muscarine and nicotine receptors. Eserine potentiated the effects of acetylcholine more than those of acetylpyrrolidinecholine. Pyrrolidinecholine was only a weak agonist on the guinea-pig ileum. It caused a rise of rat blood pressure in doses higher than 10 μmol per rat. Neuromuscular transmission of the phrenic nerve-diaphragm preparation of the rat was not impaired during a 150 min incubation period with 1 mM pyrrolidinecholine. It is suggested that the possible formation and release of acetylpyrrolidinecholine as a false cholinergic transmitter does not modify neuromuscular transmission in skeletal muscle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00509777
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  • 9
    Electronic Resource
    Electronic Resource
    The effects of metoclopramide on acetylcholine release and on smooth muscle response in the isolated guinea-pig ileum (1982)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 319 (1982), S. 231-238 
    Details
    ISSN: 1432-1912
    Keywords: Guinea-pig ileum ; Metoclopramide ; Acetylcholine release ; 5-Hydroxytryptamine receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of metoclopramide on smooth muscle contraction and on release of acetylcholine were studied in the guinea-pig myenteric plexus longitudinal muscle preparation. Acetylcholine was determined either as endogenous acetylcholine, or as labelled transmitter from strips preloaded with 3H-choline. Metoclopramide caused an increase in resting tension of longitudinal muscle as well as an increase in resting output of either endogenous or labelled acetylcholine. Tetrodotoxin abolished the metoclopramide-evoked increase in transmitter release. The increase in smooth muscle tension was clearly related to the increase in resting output. The effects of metoclopramide on both longitudinal muscle contraction and resting release of labelled acetylcholine were prevented in the presence of a concentration of 5-hydroxytryptamine (5-HT) that desensitized 5-HT receptors. This suggests that metoclopramide stimulates neuronal 5-HT receptors and, thereby, facilitates acetylcholine release. Metoclopramide augmented the twitch-like contractions induced by field stimulation at 0.1 Hz. Contractions elicited at 1 Hz were only slightly enhanced. Similarly, metoclopramide facilitated only the release of labelled acetylcholine evoked by electrical stimulation at 0.1 Hz, but not that at 1 Hz. The facilitatory effetts of metoclopramide on twitch height and evoked release could not be attributed to a blockade of presynaptic inhibitory α-adrenoceptors, dopamine or muscarine receptors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00495871
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  • 10
    Electronic Resource
    Electronic Resource
    The inhibition by dopamine of cholinergic transmission in the isolated guinea-pig ileum (1982)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 318 (1982), S. 308-312 
    Details
    ISSN: 1432-1912
    Keywords: Guinea-pig ileum ; α-Adrenoceptors ; Dopamine ; Tolazoline ; Metoclopramide ; Sulpiride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 1. Segments of the guinea-pig ileum were incubated in Tyrode's solution containing 3 μM propranolol. Dopamine, like noradrenaline and clonidine, inhibited the twitch response to field stimulation. The inhibitory action of dopamine remained unchanged in the presence of the dopamine uptake inhibitor nomifensine (1 μM). Tissue from reserpine-pretreated amimals was insensitive to tyramine but the response to dopamine was not affected. It is, therefore, assumed that the effect of dopamine is due to a direct receptor stimulation and not to the release of noradrenaline. 2. The inhibitory action of dopamine was not antagonized by the dopamine receptor antagonists cis-flupenthixol, pimozide or domperidone. 3. Metoclopramide, sulpiride and tolazoline were competitive antagonists of the inhibitory effects of dopamine. The pA2-values for metoclopramide against dopamine (5.64) noradrenaline (5.52), and clonidine (5.57) did not differ significantly. Likewise, there was no significant difference between the pA2-values for sulpiride (5.30, 5.29, 5.50) and those for tolazoline (6.52, 6.69, 7.02) determined against dopamine, noradrenaline and clonidine. 4. Apomorphine inhibited the twitch response, and this inhibition was not affected by tolazoline, sulpiride or pimozide. 5. It is concluded that dopamine inhibits the twitch response in the guinea-pig ileum through stimulation of neuronal α-adrenoceptors. Metoclopramide and sulpiride are weak antagonists at these receptors. The results provide no evidence for the existence of specific inhibitory dopamine receptors in the guinea-pig ileum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00501170
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