Contrasting effects of tachykinins and guanethidine on the acetylcholine output stimulated by nicotine from guinea-pig bladder [corrected]

1. Contractile responses and acetylcholine release evoked by nicotine in guinea-pig detrusor strips were determined by isotonic transducer and radioimmunoassay, respectively. Nicotine stimulated acetylcholine release and a contractile response in guinea-pig detrusor strips treated with the cholinesterase inhibitor, methanesulphonyl fluoride (MSF). Both actions evoked by nicotine were antagonized by the nicotinic receptor antagonist, hexamethonium but were insensitive to tetrodotoxin. 2. A sympathetic nerve blocker, guanethidine and a tachykinin antagonist, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-substance P (rpwwL-SP) partially inhibited the acetylcholine release evoked by nicotine to much the same degree. The inhibitory effects of guanethidine and rpwwL-SP on acetylcholine release were significantly greater than corresponding effects on the contraction evoked by nicotine. 3. In preparations treated with rpwwL-SP to block the tachykinin receptors, guanethidine had no effect on the response to nicotine. Conversely, after treatment with guanethidine to block release of a mediator from sympathetic nerve endings, nicotine-induced responses were not affected by rpwwL-SP. 4. Nicotine-induced contraction was reduced to 30% by the muscarinic cholinoceptor antagonist, atropine and completely abolished after desensitization of P2-purinoceptors with alpha,beta-methylene ATP in the presence of atropine. 5. A concentration-contractile response curve to neurokinin A (NKA) was shifted to the left after cholinesterase inhibition with MSF. Atropine abolished the facilitatory effect of MSF and partially inhibited contractions induced by NKA at 100 nM to 1 microM. The contractile responses to substance P methyl ester (SPOMe) and Tyr0-neurokinin B (Tyr0-NKB) were not influenced by MSF or atropine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacological action of nicotine in the isolated urinary bladder from rabbit: special reference to the chronic nicotine treatment

1. A mode of action of nicotine and a change of the responsiveness to nicotine following chronic nicotine treatment in the urinary bladder of rabbit were investigated. 2. Nicotine induced only a contraction in the urinary bladder of rabbit, and the response to nicotine was reduced by hexamethonium, atropine and capsaicin. These findings suggest that the contractile response to nicotine was mediated through an action on the nicotinic receptors and partially due to the release of acetylcholine and tachykinins. 3. Tetrodotoxin did not inhibit the contractile response to nicotine in the rabbit detrusor muscle, suggesting that the nicotine-induced response may be produced mainly through a sodium action potential-independent process. 4. Nicotine-induced contraction was reduced following the chronic nicotine treatment without a change of its pharmacological properties. These findings suggest that chronic nicotine treatment might cause a decrease of the amounts of nicotinic receptors and also receptors for mediators released by nicotine.     

Tachykinin-independent activity of capsaicin on in-vitro lamb detrusor

The capsicum alkaloid capsaicin is an afferent fibre exciter. In the vesical bladder, capsaicin acts by releasing peptides stored in afferent fibres. The aim of this work was to verify the activity of capsaicin on in-vitro lamb urinary bladder and to ascertain whether this alkaloid evokes peptide release. Capsaicin relaxed about 80% of the lamb detrusor muscle preparations tested and contracted about 20%. Whereas neurokinin A and substance P antagonists, administered alone or together, left the contractile responses to capsaicin unchanged, atropine and tetrodotoxin totally inhibited contraction. Ruthenium red and indometacin abolished contractions and relaxation. The substance P and neurokinin A antagonists and the NO-synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) left relaxation unchanged; conversely, the calcitonin gene-related peptide antagonist alpha h-CGRP (8-37) abolished this response. These results suggest that capsaicin relaxes lamb detrusor muscle not through tachykinins but by releasing CGRP from afferent fibres. Our observation that indometacin blocks the capsaicin response in in-vitro lamb urinary bladder also suggests a role of prostanoids.     

Significant role of neuronal non-N-type calcium channels in the sympathetic neurogenic contraction of rat mesenteric artery

1. The possible involvement of pre-junctional non-N-type Ca2+ channels in noradrenaline (NA)-mediated neurogenic contraction by electrical field stimulation (EFS) was examined pharmacomechanically in the isolated rat mesenteric artery. 2. EFS-generated contraction of endothelium-denuded mesenteric artery was frequency-dependent (2 - 32 Hz) and was abolished by tetrodotoxin (TTX, 1 microM), guanethidine (5 microM) or prazosin (100 nM), indicating that NA released from sympathetic nerve endings mediates the contractile response. 3. NA-mediated neurogenic contractions to lower frequency stimulations (2 - 8 Hz) were almost abolished by an N-type Ca2+ channel blocker, omega-conotoxin-GVIA (1 microM) whereas the responses to higher frequency stimulations (12 - 32 Hz) were less sensitive to omega-conotoxin-GVIA. The omega-conotoxin-GVIA-resistant component of the contractile response to 32 Hz stimulation was inhibited partly (10 - 20%) by omega-agatoxin-IVA (10 - 100 nM; concentrations which are relatively selective for P-type channels) and to a greater extent by omega-agatoxin-IVA (1 microM) and omega-conotoxin-MVIIC (3 microM), both of which block Q-type channels at the concentrations used. 4. omega-Agatoxin-IVA (10 - 100 nM) alone inhibited 32 Hz EFS-induced contraction by 10 approximately 20% whereas omega-conotoxin-MVIIC (3 microM) alone inhibited the response by approximately 60%. 5. These omega-toxin treatments did not affect the contractions evoked by exogenously applied NA. 6. These findings show that P- and Q-type as well as N-type Ca2+ channels are involved in the sympathetic neurogenic vascular contraction, and suggest the significant role of non-N-type Ca2+ channels in NA release from adrenergic nerve endings when higher frequency stimulations are applied to the nerve.     

Contractile response of the human isolated urinary bladder to neurokinins: involvement of NK-2 receptors

The contractile response to substance P (SP), neurokinin A (NKA) and arginin-neurokinin B (Arg-NKB) (a water soluble analogue of NKB) was investigated in detrusor muscle strips from the dome of the urinary bladder obtained from patients undergoing total cystectomy for carcinoma of the bladder base. Spontaneous activity and response to nerve stimulation indicated that the material used in this study has characteristics similar to those described for 'normal' human detrusor muscle. All neurokinins induced a concentration-related contraction with sensitivity at nM concentrations and the following rank order of potency: NKA (90) greater than Arg-NKB (22) greater than SP (1). These findings indicate the involvement of NK-2 receptors in the contractile response of human detrusor muscle to neurokinins.     

Evidence for a capsaicin-sensitive, tachykinin-mediated, component in the NANC contraction of the rat urinary bladder to nerve stimulation.

1. In the presence of atropine (1 microM) and guanethidine (3 microM), electrical field stimulation (EFS) of the rat isolated urinary bladder for 30 s induced a frequency-dependent (1-30 Hz) nonadrenergic non-cholinergic (NANC) triphasic contraction characterized by a peak response (within 10 s from onset of stimulation), a late response (determined as the tension developed at the end of the stimulation period) and a prolonged post-stimulus 'off' response. The latter peaked at 2-6 min from the end of the stimulation period. At 10 Hz, the amplitude of the three responses averaged 89 +/- 6, 76 +/- 6 and 18 +/- 3% of the response to 40 mM KCl, respectively. Tetrodotoxin (1 microM) abolished all contractile responses to EFS. 2. In capsaicin-pretreated bladder strips (10 microM for 15 min) the amplitude of the peak response to EFS (1-30 Hz for 30 s) was unchanged, the 'late' response to EFS was significantly reduced as compared to controls, and the post-stimulus response was absent, being replaced by a transient relaxation. 3. When varying train duration from 1 to 120 s at a frequency of 10 Hz, the differences between control and capsaicin-treated strips became evident for periods of stimulation > 10 s. 4. The tachykinin NK1 receptor antagonist, SR 140,333 (0.1-1 microM) had no effect on the peak response to EFS (10 Hz for 30 s) while it decreased significantly the late response at both concentrations tested (16 +/- 3 and 33 +/- 3% inhibition).(ABSTRACT TRUNCATED AT 250 WORDS)     

A regional difference of the effect of tachykinin on cholinergic response evoked by electrical field stimulation in the rabbit airway

1. Experiments were designed to determine whether regional differences exist in the effects of phosphoramidon (a metalloprotease inhibitor) and [d-Arg, ¹d-Pro,²d-Trp,^7,9Leu,¹¹]-substance P (a tachykinin antagonist: rpwwL-SP) on contractile responses to electrical field stimulation (EFS) in rabbit airways.2. EFS contractions were potentiated by phosphoramidon and were attenuated by rpwwL-substance P at low frequencies (less than 10 Hz).3. Potentiating effect of phosphoramidon was more pronounced in distal bronchus than trachea and was proportional to total proteinase activity.4. The rank order of inhibitory effect of rpwwL-SP was: trachea > proximal bronchus > distal bronchus, and inverse relationship was observed between the drug's inhibitory effect of drug and total proteinase activity in three different regions.5. Good correlation was observed between total proteinase activity and pD₂ value of neurokinin A in each airway region.6. In conclusion, tachykinin modulates acetylcholine release in the contractile response to EFS at low frequencies (less than 10Hz), and regional differences in the effects of the inhibitor and the antagonist on EFS-evoked contractions in the rabbit airway were suggested to be due to heterogenous distribution of the metalloprotease which metabolized tachykinins.     

Substance P-containing nerves mediate nicotine-induced contractions of rabbit bronchial smooth muscle

1. A possible role of substance P-containing nerves in the contractile response to nicotine was investigated in isolated rabbit bronchial smooth muscle preparation. 2. Nicotine caused a contraction which was attributed to the release of acetylcholine in the rabbit bronchus. The response was reduced by capsaicin (10(-5) M) and a substance P antagonist, [D-Arg1, D-Pro2, D-Trp7.9, Leu11] substance P (10(-5) M). 3. Substance P (10(-7) M)-induced contraction was reduced by atropine (10(-6) M) and potentiated by physostigmine (10(-6) M). Furthermore, substance P (10-7 M) enhanced the release of tritium or acetylcholine from the [3H]choline labelled bronchi. 4. Results suggest that substance P-like tachykinin accelerates the nicotine-evoked prejunctional endogenous neural release of acetylcholine on the nervous cells in the rabbit bronchial preparation.     

Pharmacological characterization of the excitatory innervation to the guinea-pig urinary bladder in vitro: evidence for both cholinergic and non-adrenergic-non-cholinergic neurotransmission.

1 Field stimulation of strips of guinea-pig isolated urinary bladder with 5 s trains at 0.1 to 15 Hz resulted in frequency-dependent, reproducible contractions. 2 At concentrations of 1 and 4 x 10(-7) M and 1 x 10(-6) M, atropine produced a variable, partial inhibition of contractions at all frequencies but was most effective at frequencies of 3 Hz or more. 3 Tetrodotoxin (TTX), 5 x 10(-7) M, inhibited contractions at all frequencies by 80 to 90%. 4 Physostigmine, 2 x 10(-6) M, significantly enhanced the contractile response to frequencies of less than 10 Hz but did not enhance responses resistant to inhibition by atropine. Hexamethonium, 1 x 10(-4) M, slightly enhanced the contractile response to frequencies of 4 Hz or greater. 5 (+/-)-Propranolol (5 x 10(-6)M), guanethidine (1 x 10(-6)M), phentolamine (5 x 10(-6)M) and clonidine (3 x 10(-8)M) each enhanced the contractile response to field stimulation. 6 Contractile responses obtained in the presence of atropine (4 x 10(-7) M) and guanethidine (1 x 10(-6) M) increased with time and were inhibited 60 to 80% by TTX (5 x 10(-7)M. 7 It is concluded that the cholinergic nervous system contributes, in part, to electrically-induced excitatory contractions of the isolated urinary bladder of the guinea-pig. Concomitant sympathetic stimulation appears to serve an inhibitory role. In addition, a major portion of the contractile response appears to be due to a non-cholinergic non-adrenergic, as yet unidentified, substance.     

The hamster isolated trachea: a new preparation for studying NK-2 receptors

Mammalian tachykinins (substance P, neurokinin A and neurokinin B) produced a concentration-related contraction of the hamster isolated trachea with the following order of potency: NKA congruent to NKB much greater than substance P (SP). NKA and NKB were 280 and 203 times more potent than SP, respectively. The action of NKA, NKB or SP was not significantly modified in presence of thiorphan (10 microM), atropine (1 microM), mepyramine (1 microM) or indomethacin (5 microM). [Nle10]NKA-(4-10) or [beta Ala8]NKA-(4-10), two selective NK-2 receptor agonists, displayed good activity while other synthetic agonists, selective for NK-1 or NK-3 receptors, had little or no effect. The contractile response to tachykinins did not undergo appreciable desensitization and was promptly reversed by washing out. These data indicate that NK-2 receptors are the main if not the sole mediators of the response of the hamster isolated trachea to tachykinins, whose action is independent from cholinergic nerves, histamine release or prostaglandin production. Further, no significant peptide degradation by a thiorphan-sensitive mechanism occurs in this organ.     

Substance P, nicotinic acetylcholine receptors and antinociception in the rat

Intracerebroventricular injections of both nicotine and substance P (SP) induced antinociception in the tail-flick test in rats. The antinociceptive effect was blocked in both cases by mecamylamine and by naloxone, suggesting that central nicotinic acetylcholine receptors and endogenous opioids are implicated in the action of these drugs. A link between substance P neurones and central cholinergic systems, involving nicotinic receptors, was also suggested by the quickly developed cross-tolerance between the antinociceptive effect of substance P and nicotine. A smaller, subeffective dose of substance P was able to block, on acute administration, the antinociceptive action of nicotine, an effect not shared by the two other mammalian tachykinins, neurokinin A or neurokinin B. The results obtained in the present study appear to indicate a dual action of substance P on central nicotinic cholinoceptors.     

Neurogenic mechanisms in control of the rabbit iris sphincter muscle

The iris sphincter muscle is supplied with cholinergic, adrenergic and substance P-containing nerve fibers, all with a possible role in the control of pupil size. The functional significance of the various nervous components in the rabbit iris sphincter muscle was examined in vitro and in vivo. The contractile response to electrical stimulation is composed of several contractions, occurring along different time scales. Single pulse stimulation produced an atropine-sensitive twitch. Pulse train stimulation revealed two successive atropine-sensitive twitches followed by a slow, long-lasting contraction, sensitive to Spantide, an antagonist of tachykinins such as substance P. A guanethidine- and phentolamine-sensitive contractile response to pulse train stimulation could be demonstrated in the presence of both atropine and Spantide. Only the Spantide-sensitive response could be completely exhausted by prolonged electrical stimulation. In vivo, neither the adrenergic nor the substance P-containing nerve fibres appeared to contribute to the miotic response to light since Spantide and guanethidine were without effect. This response was inhibited by atropine only.     

Comparison of the responses to the sensory neuropeptides, substance P, neurokinin A, neurokinin B and calcitonin gene-related peptide and to trigeminal nerve stimulation in the iris sphincter muscle of the rabbit

Three mammalian tachykinins (substance P, neurokinin A and B) and two non-mammalian ones (eledoisin and physalaemin) produced potent contractions of the isolated rabbit iris sphincter muscle. The rank order of potencies was eledoisin greater than neurokinin B = physalaemin greater than substance P greater than neurokinin A. The maximum efficacy was much the same. The contractile responses to neurokinin A and eledoisin developed more rapidly than did those to the other tachykinins used and were selectively attenuated by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Electrical transmural stimulation produced a contraction consisting of cholinergic and tachykininergic components. The tachykininergic component was abolished by pretreatment with capsaicin or by trigeminal denervation (Fujiwara et al., 1984). [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP attenuated the tachykininergic component, but not the cholinergic one. KCl and capsaicin also produced a tachykininergic contraction which was inhibited by [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP. Calcitonin gene-related peptide affected neither the iris sphincter muscle nor the response to electrical transmural stimulation. These results suggest that the tachykininergic responses induced by electrical transmural stimulation, KCl and capsaicin are predominantly mediated by neurokinin A, probably released from the peripheral endings of trigeminal nerves.     

NK-1 receptor mediation of neurogenic plasma extravasation in rat skin.

1. Plasma extravasation was induced by electrical nerve stimulation and by perfusion of tachykinins over a vacuum-induced blister base on rat footpad. 2. Stimulation of the sciatic nerve (18 V, 15 Hz, 0.5 ms) for 20 min produced a significant increase in the protein content of the perfusate. The response in capsaicin pretreated rats was only 4% of the control response. This indicates that the electrically-induced plasma extravasation response was mediated by capsaicin-sensitive sensory fibres. 3. Exogenous perfusion of the mammalian tachykinins substance P, neurokinin A and neurokinin B and the non-mammalian tachykinins physalaemin, kassinin and eledoisin was used to determine the tachykinin receptor type mediating the plasma extravasation response. Dose-response curves of the tachykinins (10(-9) M-10(-4) M) gave a rank order of potency of substance P = physalaemin greater than eledoisin greater than or equal to kassinin greater than neurokinin B = neurokinin A. 4. In addition, specific agonists of neurokinin receptors were perfused. Perfusion of [Glp6, D-Pro9] SP6-11 and [Glp6, L-Pro9]SP6-11 demonstrated that the L-Pro isomer was much more potent than the D-Pro isomer. 5. The rank order of potency and the greater potency of [Glp6, L-Pro9]SP6-11 over its D-isomer indicate an NK-1 neurokinin receptor mediates plasma extravasation in rat footpad skin.     

Nerve-induced tachykinin-mediated vasodilation in skeletal muscle is dependent on nitric oxide formation.

Nerve-induced vasodilatation was studied by intravital microscopy of the rabbit tenuissimus muscle, pretreated with pancuronium, phentolamine, and guanethidine. Nerve stimulation of the tenuissimus nerve induced a vasodilatation which was frequency and pulse duration-dependent and insensitive to atropine and propanolol but abolished by tetrodotoxin. The nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME, 100 microM), but not its enantiomer, D-NAME, markedly inhibited the vasodilation induced by nerve stimulation or by exogenous substance P or neurokinin A. Vasodilatation due to calcitonin gene-related peptide, prostaglandin E2 or nitroprusside was unaffected. The substance P antagonist, spantide (30 microM), significantly attenuated nerve-induced vasodilatation, in parallel with L-NAME. Our results indicate that nerve-induced vasodilatation in skeletal muscle can be attributed to the release of substance P and/or other tachykinins and that nitric oxide subsequently mediates the response to endogenous tachykinins released from nerves.     

A comparison of the excitatory and inhibitory effects of non-adrenergic, non-cholinergic nerve stimulation and exogenously applied ATP on a variety of smooth muscle preparations from different vertebrate species

1. The responses to non-adrenergic, non-cholinergic nerve stimulation have been compared with those to exogenously applied ATP on seventeen different tissues from a number of vertebrate classes.2. Stimulation of all the mammalian gut preparations studied (with the exception of the guinea-pig ileum) after blockade of the effects of adrenergic and cholinergic nerve stimulation by guanethidine (3.5 muM) and hyoscine (1.3 muM) caused inhibition; exogenously applied ATP mimicked this inhibitory response.3. Stimulation of the guinea-pig ileum in the presence of hyoscine and guanethidine, usually caused a diphasic response, relaxation followed by contraction; exogenously applied ATP mimicked this response, in contrast to acetylcholine and noradrenaline which caused excitation and relaxation respectively.4. Stimulation of preparations of lower vertebrate gut and guinea-pig bladder in the presence of hyoscine and guanethidine caused contraction; exogenously applied ATP mimicked this contractile response.5. In each preparation the time course of the response to ATP was similar or identical to the response to non-adrenergic, non-cholinergic nerve stimulation.6. The results are consistent with the hypothesis that a purine nucleotide may be the transmitter substance released from non-adrenergic, non-cholinergic nerves supplying smooth muscle preparations from a number of vertebrate classes.     

Regulation of the substance P-induced contraction via the release of acetylcholine and gamma-aminobutyric acid in the guinea-pig urinary bladder.

1. The action of substance P (SP) on the release of gamma-aminobutyric acid (GABA) and acetylcholine (ACh) and on contraction were studied in strips of the guinea-pig urinary bladder. Substance P induced a dose-dependent contraction of strips of guinea-pig urinary bladder (EC50 = 1.2 x 10(-9) M). This contraction was not altered by tetrodotoxin, but with a dose of 10(-9) M and less, there was a complete inhibition by 10(-6) M) atropine. Contractions initiated by 3 x 10(-9) M) SP or more were partly inhibited by atropine. The EC50 value of substance P in the presence of atropine was 7.0 x 10(-9) M. 2. Substance P induced a Ca2+-dependent and tetrodotoxin-resistant release of [3H]-acetylcholine (ACh) from strips of urinary bladder preloaded with [3H]-choline (EC50 = 4.9 x 10(-10) M), and this release was antagonized by [D-Pro2,D-Trp7,9] substance P. 3. Bicuculline increased the substance P-induced contraction and the release of [3H]-ACh from the strips. 4. Substance P induced a Ca2+-dependent and tetrodotoxin-sensitive release of [3H]-gamma-aminobutyric acid (GABA) from strips preloaded with [3H]-GABA (EC50 = 2.6 x 10(-9) M), and this release was antagonized by [D-Pro2,D-Trp7,9] substance P. 5. Therefore, substance P appears to exert excitatory effects on the contractility of urinary bladder predominantly by stimulating its own receptor located on the cholinergic nerve terminals. GABA released by substance P inhibits stimulation of the cholinergic neurone. However, the direct action of substance P on the cholinergic neurone is more potent that the indirect action via GABA release.     

Investigation of enhancement effects of nicotine on cholinergic neurotransmission in isolated rabbit gastric fundus: role of antioxidants

1 Nicotine, which is tobacco alkaloid, still induces interests for researchers because of smokers addiction to nicotine. Nicotine having influence on the neuronal acetylcholine receptors (nAChRs) increases release of most certain neurotransmitters from the nerve endings. Also, nicotine, affecting the mitochondrial respiratory chains, contributes to the formation of reactive oxygen species. 2 In the present study, we investigated the effects of nicotine on smooth muscles of gastric fundus on the electrical field stimulation (EFS) that induces transition contraction via stimulation nAChRs. In addition, we aimed to investigate the interaction between release of acetylcholine, induced by nicotine, and the effects of reactive oxygen species. 3 Therefore, the effects of allopurinol (10^?6–10^?5 m ), deferoxamine (10^?4 m ) and mannitol (10^?4–5 × 10^?3 m ) were tested on the transient contraction induced by nicotine. 4 In conclusion, mannitol (5 × 10^?3 m ) significantly reduced contractile response to nicotine on EFS only in high concentration. Whereas in small concentrations mannitol (10^?4 m ) statistically did not cause any results. Deferoxamine and allopurinol also did not have any significant response.     

Further studies on the mechanisms of the tachykinin-induced activation of micturition reflex in rats: evidence for the involvement of the capsaicin-sensitive bladder mechanoreceptors

The relative ability of substance P, neurokinin A, neurokinin B and kassinin to activate the micturition reflex was investigated in urethane-anaesthetized rats. When administered topically neurokinin A, neurokinin B and kassinin were 14, 36 and 280 times, respectively, more potent than substance P to activate micturition. On the other hand substance P, neurokinin A and kassinin were practically equipotent (and neurokinin B was about 3-4 times less potent than substance P) to stimulate the contraction of the rat isolated bladder and to potentiate the contractions induced by electrical field stimulation. This indicates that neither a direct action on muscle cells nor a potentiating effect on efferent neurotransmission can account for the rank order of potency of tachykinins for activation of the micturition reflex. The ability of topical tachykinins to activate the micturition reflex was largely impaired in 2 months old rats pretreated with capsaicin (50 mg/kg s.c.) on their second day of life, indicating that integrity of the capsaicin-sensitive bladder mechanoreceptors is essential for the production of this effect. These findings indicate that an NK-B receptor, possibly located on sensory nerves in the bladder wall, participates in the tachykinin-induced activation of reflex micturition.     

Antagonist discrimination between subtypes of tachykinin receptors in the guinea-pig ileum

The effects of substance P and eledoisin on spontaneous and electrically-evoked release of [3H]acetylcholine, and on smooth muscle were studied in the guinea-pig myenteric plexus-longitudinal muscle preparation preloaded with [3H]choline. Substance P and eledoisin caused transient increases in spontaneous release of [3H]-acetylcholine and in longitudinal muscle tone. Both tachykinins were equipotent in contracting the muscle, but eledoisin was more potent than substance P in eliciting [3H]acetylcholine release. The release caused by substance P was enhanced in the presence of naloxone and scopolamine which suggests that the release is modulated through opioid and muscarinic receptors. Substance P and eledoisin inhibited the release of [3H]acetylcholine evoked by electrical stimulation at 0.1 Hz. The inhibition was not due to an activation of alpha-adrenoceptors, histamine or opioid receptors. The substance P antagonists (D-Pro2, D-Trp7,9)SP (10 and 30 microM) and (Arg5, D-Trp7,9, Nle11)SP5-11 (1 and 10 microM) competitively antagonized both the contractile effects of substance P and eledoisin, and the inhibition by the tachykinins of the electrically-evoked release of [3H]acetylcholine. The increase in spontaneous [3H]acetylcholine release elicited by substance P and eledoisin was not prevented by the substance P antagonists. The results suggest that the neuronal receptor whose activation causes inhibition of acetylcholine release and the smooth muscle receptor correspond to the SP-P type, whereas the neuronal receptor mediating an increase in spontaneous acetylcholine release is of the SP-E type. The two antagonists, (D-Pro2, D-Trp7,9)SP and (Arg5, D-Trp7,9, Nle11)SP5-11, selectively block only the SP-P receptor.