Occurrence, release, and effects of multiple tachykinins in cat colonic tissues and nerves

Interaction between Pirenzepine and Ninjinto, a Traditional Japanese Herbal Medicine, on the Plasma Gut-Regulated Peptide Levels in Humans

The Japanese herbal medicine (Kampo) Ninjinto has been used for the treatment of gastroenteritis, esogastritis, gastric atony, gastrectasis, vomiting, and anorexia. The pharmacological effects of Ninjinto on the gastrointestine are due to changes in the levels of gut-regulated peptide, such as motilin, somatostatin, calcitonin gene-related peptide (CGRP), substance P, and vasoactive intestinal polypeptide (VIP). The release of these peptides is controlled by acetylcholine (ACh) from the preganglionic fibers of the parasympathetic nerve. Thus, we examined the effects of the selective M1 muscarinic receptor antagonist pirenzepine on the elevation of Ninjinto-induced plasma the area under the plasma gut-regulated peptide concentration-time curve from 0 to 240 min (AUC0→240 min) in humans. Oral pretreatment with pirenzepine significantly reduced the Ninjinto-induced elevation of plasma motilin and substance P release (AUC0→240 min). Combined treatment with Ninjinto and pirenzepine significantly increased the release of plasma somatostatin (AUC0→240 min) compared with administration of Ninjinto alone or placebo. Ninjinto appeared to induce the release of substance P and motilin into plasma mainly through the activation of M1 muscarinic receptors, and pirenzepine may affect the pharmacologic action of Ninjinto by the elevation of plasma substance P, motilin, and somatostatin.

Comparison of the effects of pantethine and fursultiamine on plasma gastrointestinal peptide levels in healthy volunteers

Pantethine and fursultiamine have been evaluated for their clinical usefulness in the treatment and prevention of uncomplicated postoperative adhesive intestinal obstruction. In recent years, the actions of drugs used to treat gastrointestinal diseases have been elucidated pharmacologically from the viewpoints of gastrointestinal peptide levels. We examined the effects of pantethine and fursultiamine on plasma levels of calcitonin gene-related peptide (CGRP)-, vasoactive intestinal polypeptide (VIP)-, motilin- and substance P (SP)-like immunoreactive substances (IS) in healthy subjects. An open-labeled study was conducted on five healthy volunteers. Each subject was administered a single oral dose of pantethine, fursultiamine and placebo at intervals of one month. Venous blood samples were collected before and at 20, 40, 60, 90, 120, 180 and 240 min after each administration. Plasma peptide levels were measured using a highly sensitive enzyme immunoassay. A single oral dose of pantethine resulted in significant increases of plasma CGRP- and VIP-IS levels compared to placebo. Furthermore, areas under the plasma concentration-time curves (AUC(0-240)) of CGRP- and VIP-IS were significantly higher after pantethine administration compared with placebo. On the other hand, fursultiamine had no effect on plasma levels and AUC(0-240) of CGRP-, VIP-, motilin- and SP-IS. This study demonstrated the different effects of pantethine and fursultiamine from the viewpoint of plasma gastrointestinal peptide changes. The pharmacological effects of pantethine may be closely related to the changes in plasma CGRP- and VIP-IS levels.

Ecabet sodium raises plasma levels of calcitonin gene-related peptide and substance P in healthy humans

Ecabet sodium (ecabet), a cytoprotective drug, produces an increase in mucosal blood flow. One of the gastrointestinal motility regulatory factors has been assumed to be the induction of changes in the levels of peptides (gastrin, somatostatin and motilin) in plasma. On the other hand, recently, capsaicin-sensitive afferent nerves were shown to play an important role in gastric mucosal defensive mechanism. Capsaicin stimulates afferent nerves and enhances the release of calcitonin gene-related peptide (CGRP) and substance P in the stomach. We studied the effect of ecabet on human plasma gastrin-, somatostatin-, motilin-, CGRP- and substance P-like immunoreactive substance (IS) in healthy subjects. Ecabet sodium at a dose of 3.0 g, or placebo, was orally administered in five healthy males. The blood samples were taken before and at 20, 40, 60, 90, 120, 180 and 240 min after administration, subjected to extracting procedures, and submitted to a highly sensitive enzyme immunoassay system. Single administration of ecabet caused significant (P < 0.05) increases in plasma CGRP-, substance P- and somatostatin-IS concentration compared with placebo. Ecabet significantly decreased plasma gastrin-IS levels compared with placebo. In this study, we hypothesized that ecabet might stimulate capsaicin-sensitive afferent nerves indirectly and improve mucosal blood flow; this might be a key mechanism underlying its gastroprotective action.

Effects of pirenzepine on Dai-kenchu-to-induced elevation of the plasma neuropeptide levels in humans

Dai-kenchu-to has been used for the treatment of abdominal obstructions, including bowel obstructions and a feeling of coldness in the abdomen. We reported that Dai-kenchu-to increases plasma neuropeptide [motilin, vasoactive intestinal polypeptide (VIP), serotonin, calcitonin gene-related peptide (CGRP), and substance P]-like immunoreactive substances (IS) levels and that its pharmacologic effects on the gastrointestine are due to changes in gastrointestinal mucosa-regulatory peptide levels. We examined the effects of the selective M(1) muscarinic receptor antagonist pirenzepine on the elevation of Dai-kenchu-to-induced plasma neuropeptide (gastrin, motilin, somatostatin, VIP, CGRP, substance P)-IS levels in human volunteers and the area under the plasma neuropeptide concentration-time curve from 0 to 240 min (AUC(0-->240 min)), which were calculated from the plasma neuropeptide concentration-time curves from each volunteers. Oral pretreatment with pirenzepine reduced the Dai-kenchu-to-induced elevation of plasma motilin and VIP-IS levels and AUC(0-->240 min). Combined treatment with Dai-kenchu-to and pirenzepine increased plasma somatostatin-IS levels and decreased plasma gastrin-IS levels and had no effects on plasma CGRP- and substance P-IS levels and AUC(0-->240 min) compared with administration of Dai-kenchu-to alone. Dai-kenchu-to appeared to induce the release of motilin and VIP into plasma mainly through the activation of M(1) muscarinic receptors, and pirenzepine may affect the pharmacologic action of Dai-kenchu-to by elevation of plasma motilin and VIP levels.

Omeprazole raises somatostatin and motilin in human plasma

Omeprazole, a proton pump inhibitor (PPI), is widely used in treatment of peptic ulcer, gastro esophageal reflux disease and eradication of Helicobacter pylori. PPIs inhibit final gastric acid secretion stage by blocking H+/K+-ATPase. But the mechanism except for gastric antisecretory effect has not understood clearly. So, we examined the effects of omeprazole on the levels of gastrointestinal peptides (somatostatin, motilin, gastrin, vasoactive intestinal peptide (VIP), substance P (SP) and calcitonin gene-related peptide (CGRP)) in plasma from healthy subjects. After a single oral administration of omeprazole, the plasma omeprazole concentration was highest at 120 min. Omeprazole caused a significant increase of plasma somatostatin-immunoreactive substance (IS) levels at 60-240 min and plasma motilin-IS levels at 120-180 min, compared with a placebo group, respectively. The physiological release of plasma gastrin-IS was reduced by the administration of omeprazole at 60 min, but the medicine did not alter the levels of VIP-, CGRP- and SP-IS. These results suggested that the pharmacological effects of omeprazole on regulation of gastrointestinal function are closely related to changes of somatostatin-, motilin- and gastrin-IS levels in human plasma.

Dai-kenchu-to raises levels of calcitonin gene-related peptide and substance P in human plasma

Sensory afferent neurons in the gastrointestinal mucosa regulate neuropeptides [calcitonin gene-related peptide (CGRP), substance P, etc.], which play various physiologic roles and are gastroprotective. To determine whether the pharmacologic effects of Dai-kenchu-to (DKCT) on the gastrointestine are due to changes in gastrointestinal mucosa regulatory peptide levels, we examined the effects of the DKCT on the levels of CGRP-like immunoreactive substances (IS) and substance P-IS in plasma taken from five healthy subjects. A single oral administration of DKCT 7.5 g caused significant increases in plasma CGRP-IS at 40 min, and in substance P-IS levels at 20 and 60 min, compared with a placebo group. The present study may indicate that the pharmacologic action of DKCT is closely related to changes in CGRP- and substance P-IS levels.

Cetraxate raises levels of calcitonin gene-related peptide and substance P in human plasma

Cetraxate hydrochloride (cetraxate), an anti-ulcer drug, produces a dose-related increase in mucosal blood flow. Recently, it was found that capsaicin-sensitive afferent nerves play an important role in gastric mucosal defence. Capsaicin stimulates afferent nerves and enhances the release of calcitonin gene-related peptide (CGRP) and substance P in the stomach. We studied the effect of cetraxate on human plasma CGRP and substance P in healthy subjects. Cetraxate (800 mg) or placebo were orally administered to five healthy males. Blood samples were taken before, and at 20, 40, 60, 90, 120, 180 and 240 min after administration, followed by the extracting procedure, and submitted to a highly sensitive enzyme immunoassay system for CGRP and substance P. Single administration of cetraxate caused significant increases in plasma CGRP concentration at 60-120 min compared with placebo. Cetraxate significantly increased plasma substance P levels at 40-90 min compared with placebo. In this study, we hypothesized that cetraxate might indirectly stimulate capsaicin-sensitive afferent nerves and increase mucosal blood flow, and that this may be a key mechanism underlying its gastroprotective action.

Effects of Hange-koboku-to (Banxia-houpo-tang) on neuropeptide levels in human plasma and saliva

Hange-koboku-to (Banxia-houpo-tang), a Chinese herbal (Kampo) medicine, has been used for improvement of hoarse voice, something foreign body sensation in the throat and/or esophagus, and swallowing reflex, among other conditions. One of the mechanisms of the empirical effects is assumed to be due to local changes in neuropeptide levels locally. We investigated the effects of Hange-koboku-to on neuropeptides, calcitonin gene-related peptide (CGRP), substance P, somatostatin, and vasoactive intestinal peptide (VIP) in plasma and saliva, as well as on salivary secretion in healthy subjects. A single oral administration of Hange-koboku-to caused significant increases in substance P-immunoreactive substance (IS) (40 min) in plasma, and slightly increased in CGRP-IS and somatostatin-IS in plasma compared with placebo. In saliva neuropeptides, Hange-koboku-to caused significant increases in substance P-IS (20 min) and somatostatin-IS (40, 60 min), and a slight increase in VIP-IS. However, a single Hange-koboku-to stimulation did not have a significant effect of sialosis volume. These results seem to suggest that Hange-koboku-to improves hoarse voice, something foreign body sensation in the throat and esophagus, and swallowing reflex disorder, by stimulation of neuropeptidergic nerves locally.

Tachykinin NK2 receptor antagonists for the treatment of irritable bowel syndrome

Tachykinin NK2 receptors are expressed in the gastrointestinal tract of both laboratory animals and humans. Experimental data indicate a role for these receptors in the regulation of intestinal motor functions (both excitatory and inhibitory), secretions, inflammation and visceral sensitivity. In particular, NK2 receptor stimulation inhibits intestinal motility by activating sympathetic extrinsic pathways or NANC intramural inhibitory components, whereas a modulatory effect on cholinergic nerves or a direct effect on smooth muscle account for the NK2 receptor-mediated increase in intestinal motility. Accordingly, selective NK2 receptor antagonists can reactivate inhibited motility or decrease inflammation- or stress-associated hypermotility. Intraluminal secretion of water is increased by NK2 receptor agonists via a direct effect on epithelial cells, and this mechanism is active in models of diarrhoea since selective antagonists reverse the increase in faecal water content in these models. Hyperalgesia in response to intraluminal volume signals is possibly mediated through the stimulation of NK2 receptors located on peripheral branches of primary afferent neurones. NK2 receptor antagonists reduce the hyper-responsiveness that occurs following intestinal inflammation or application of stressful stimuli to animals. Likewise, NK2 receptor antagonists reduce intestinal tissue damage induced by chemical irritation of the intestinal wall or lumen. In healthy volunteers, the selective NK2 antagonist nepadutant reduced the motility-stimulating effects and irritable bowel syndrome-like symptoms triggered by intravenous infusion of neurokinin A, and displayed other characteristics that could support its use in patients. It is concluded that blockade of peripheral tachykinin NK2 receptors should be considered as a viable mechanism for decreasing the painful symptoms and altered bowel habits of irritable bowel syndrome patients.

Effect of Sho-hange-ka-bukuryo-to on Gastrointestinal Peptide Concentrations in the Plasma of Healthy Human Subjects

Sho-hange-ka-bukuryou-to, a traditional Chinese herbal (Kampo) medicine, has been used to treat hyperemesis of pregnancy, nausea and vomiting. Most traditional herbal medicines are prepared from several herbs. For example, Sho-hange-ka-bukuryo-to is prepared from three herbs: Pinelliae Tuber, Zingiberis Rhizoma and Hoelen. Thus, to determine the precise mechanism of the pharmacological effects of Chinese herbal medicines is too difficult. So we have elucidated the effect of some Chinese herbal medicines by examining the change of the plasma levels of brain-gut peptides. In this study, we investigated the effects of Sho-hange-ka-bukuryo-to on the plasma levels of gut-regulated peptides (gastrin, somatostatin, motilin and vasoactive intestinal peptide (VIP)) and gastrointestinal mucosa regulatory neuropeptides (calcitonin gene-related peptide (CGRP) and substance P) in healthy human subjects. A single oral administration of Sho-hange-ka-bukuryo-to caused significant increases in plasma somatostatin-, CGRP- and substance P-immunoreactive substance (IS) levels, compared with a placebo group. Transient elevation of gastrin-IS levels in the placebo group was inhibited by the administration of Sho-hange-ka-bukuryo-to, but the medicine showed no effects on plasma motilin- or VIP-IS levels. In conclusion, these results might indicate that the pharmacological action of Sho-hange-ka-bukuryo-to is closely related to changes in gastrin-, somatostatin-, CGRP- and substance P-IS levels in human plasma.

Effects of Ninjin-to on Levels of Calcitonin Gene-Related Peptide and Substance P in Human Plasma

The herbal medicine Ninjin-to has been used for the treatment of gastroenteritis, esogastritis, gastric atony, gastrectasis, vomiting, and anorexia. One of the mechanisms of the empirical effects is assumed to be due to local changes in neuropeptide levels. Sensory afferent neurons in the gastrointestinal mucosa regulate neuropeptides [calcitonin gene-related peptide (CGRP), substance P, etc.], which play various physiologic roles. To determine whether the pharmacologic effects of Ninjin-to on the gastrointestine are due to changes in gastrointestinal mucosa regulatory peptide levels, we examined the effects of Ninjin-to on the levels of CGRP-like immunoreactive substances (IS) and substance P-IS in plasma taken from five healthy subjects. A single oral administration of 6.0 g of Ninjin-to caused significant increases in plasma CGRP-IS at 40 min and 60 min, and in substance P-IS levels at 90 min, compared with a placebo group. These results may indicate that the pharmacologic actions of Ninjin-to are closely related to changes in CGRP-IS and substance P-IS levels.

Comparison of the effects of hange-shashin-to and rikkunshi-to on human plasma calcitonin gene-related peptide and substance P levels

Regarding the gastroprotective function as a neural emergency system, sensory afferent neurons in the gastrointestinal mucosa regulate neuropeptide (calcitonin gene-related peptide (CGRP), substance P, etc.) levels, and those peptides play various physiological roles. To determine whether the pharmacological effects of Hange-shashin-to and Rikkunshi-to on the gastrointestine are due to changes in gastrointestinal mucosa regulatory peptides levels, we investigated the levels of CGRP-like immunoreactive substances (IS) and substance P-IS in plasma from healthy subjects. A single oral administration of Hange-shashin-to caused significant increases in CGRP-IS (40-60 min) and substance P-IS (60-180 min) levels in the plasma compared with the levels induced by a placebo. Rikkunshi-to and a 5.0 g Pinelliae tuber extract had no significant effect on CGRP-IS and substance P-IS levels. Extract of a 2.5 g Zingiberis rhizoma significantly caused increases in CGRP-IS at 40 min and in substance P-IS at 60 min. These results, in comparison with Kampo medicines, might indicate that the pharmacological actions of Hange-shashin-to closely are related to changes in CGRP-IS and substance P-IS levels, while Zingiberis rhizoma partially might participate in those effects of Hange-shashin-to.

An immunohistochemical screening of neurochemical markers in fungiform papillae and taste buds of the anterior rat tongue

The occurrence and distribution of several neurochemical markers were investigated. Numerous nerve fibres were shown, using antibodies to protein gene product (PGP) 9.5, neurone-specific enolase, calcitonin gene-related peptide (CGRP), substance P. neurokinin A or protein S-100. The presence of vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine amide (PHI), neuropeptide tyrosine, dopamine-beta-hydroxylase (DBH), cholecystokinin/gastrin, glutamate and galanin was more scarce. Nerve fibres containing these above-mentioned markers were found at several locations, i.e. in the epithelium, connective tissue, and around blood vessels. In the taste buds, numerous PGP 9.5, neurone-specific enolase-, CGRP-, substance P-, neurokinin A- and protein S-100-containing structures were found, but few VIP and galanin ones. No immunoreactivity was found with antibodies against somatostatin, bombesin, enkephalin or dynorphin. These findings extend knowledge about the general as well as the neurochemical messenger-based innervation of rat fungiform papillae, forming a firm basis for future functional investigations of normal, experimental and also clinical materials.

Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

The preprotachykinin-A gene-derived peptides substance (substance P; SP) and neurokinin (NK) A are expressed in intrinsic enteric neurons, which supply all layers of the gut, and extrinsic primary afferent nerve fibers, which innervate primarily the arterial vascular system. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Within the enteric nervous system, SP and NKA are likely to mediate, or comediate, slow synaptic transmission and to modulate neuronal excitability via stimulation of NK3 and NK1 receptors. In the intestinal mucosa, tachykinins cause net secretion of fluid and electrolytes, and it appears as if SP and NKA play a messenger role in intramural secretory reflex pathways. Secretory processes in the salivary glands and pancreas are likewise influenced by tachykinins. The gastrointestinal arterial system may be dilated or constricted by tachykinins, whereas constriction and an increase in the vascular permeability are the only effects seen in the venous system. Various gastrointestinal disorders are associated with distinct changes in the tachykinin system, and there is increasing evidence that tachykinins participate in the hypersecretory, vascular and immunological disturbances associated with infection and inflammatory bowel disease. In a therapeutic perspective, it would seem conceivable that tachykinin antagonists could be exploited as antidiarrheal, antiinflammatory and antinociceptive drugs.

Tachykinins in the gut. Part I. Expression, release and motor function

The preprotachykinin-A gene-derived peptides substance P and neurokinin (NK) A are expressed in distinct neural pathways of the mammalian gut. When released from intrinsic enteric or extrinsic primary afferent neurons, tachykinins have the potential to influence both nerve and muscle by way of interaction with three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Most prominent among the effects of tachykinins is their excitatory action on gastrointestinal motor activity, which is seen in virtually all regions and layers of the mammalian gut. This action depends not only on a direct activation of the muscle through NK1 and/or NK2 receptors, but also on stimulation of excitatory enteric motor pathways through NK3 and/or NK1 receptors. In addition, tachykinins can inhibit motor activity by stimulating either inhibitory neuronal pathways or interrupting excitatory relays. A synopsis of the available data indicates that endogenous substance P and NKA interact with other enteric transmitters in the physiological control of gastrointestinal motor activity. Derangement of the regulatory roles of tachykinins may be a factor in the gastrointestinal dysmotility associated with infection, inflammation, stress and pain. In a therapeutic perspective, it would seem conceivable, therefore, that tachykinin agonists and antagonists are adjuncts to the treatment of motor disorders that involve pathological disturbances of the gastrointestinal tachykinin system.

In vivo evidence for the involvement of tachykinin NK3 receptors in the hexamethonium-resistant inhibitory transmission in the rat colon

In urethane-anaesthetized rats, moderate colonic distention (0.5 ml) induced reflex rhythmic contractions (5 mm Hg amplitude and 1.1 cycles/min frequency). Senktide (1-10 nmol/kg, i.v.), a tachykinin NK3 receptor selective agonist, transiently suppressed distension-induced contractions. SR 142,801 (1-10 mumol/kg i.v.), a non-peptide tachykinin NK3 receptor antagonist, had no effect on distension-induced contractions but prevented the inhibitory effect of senktide. Infusion of N-omega-nitro-1-arginine methyl esther hydrochloride (L-NAME, 20 mumol/ml/h, i.v) increased the amplitude of colonic contractions and decreased the inhibitory effect of senktide. Hexamethonium (15 mumol/ml/h, i.v.) or atropine (1 mumol/ml/h, i.v.) inhibited the distension-induced contractions. In hexamethonium- or atropine-treated rats, senktide (10 nmol/kg) transiently and selectively enhanced the amplitude of contractions. Also SR 142,801 (10 mumol/kg), but not its inactive enantiomer SR 142,806, increased both amplitude and frequency of contractions. During continuous infusion of L-NAME and hexamethonium or atropine both frequency and amplitude of distension-induced colonic contractions were higher than when in hexamethonium or atropine only. Senktide (10 nmol/kg) had no effect and SR 142,801 (10 mumol/kg) produced a slight enhancement of colonic contractions. Infusion of sodium nitroprusside (3 mumol/ml/h, i.v.) decreased amplitude and frequency of distension-induced contractions. SR 142,801 had no effect in the presence of the nitric oxide (NO) donor. We conclude that tachykinins acting through NK3 receptors exert at least four different actions on colonic motility activated by distension: 1) a hexamethonium-resistant, NO-dependent, suppressant effect on contractions; 2) a hexamethonium-sensitive, NO-independent inhibitory effect on the amplitude of contractions; 3) a hexamethonium-resistant, NO-independent inhibitory effect on the amplitude of contractions and 4) a hexamethonium resistant and L-NAME-sensitive excitatory effect on amplitude of contractions. The prevalent inhibitory effect evoked in normal conditions along with the excitatory activity induced by SR 142,801 on hexamethonium-resistant colonic motility indicates that tachykinins, acting through neuronal NK3 receptors, activate NO-dependent and NO-independent inhibitory neurotransmission in the rat colon.

Neurochemical markers of human fungiform papillae and taste buds

The presence of distribution of several neurochemical markers in human fungiform papillae and taste buds were investigated by the immunohistochemical technique. The gustatory cells of the taste buds are in synaptic contact with sensory nerve endings, and considering the taste buds strictly as specialized sensory organs, the amounts and distribution of some of the neurochemical markers were different to what we expected. For example, few structures showed immunoreactivity to the tachykinins substance P (SP), calcitonin gene-related peptide (CGRP), and neurokinin A (NKA) also for the peptides vasoactive intestinal polypeptide (VIP), neuropeptide tyrosine (NPY) and galanin, low amounts of immunoreactivity occurred. On the other hand, using antibodies to protein gene product 9.5 (PGP 9.5), protein S-100, and glutamate, numerous nerve fibres and/or immunoreactive cells were found in the fungiform papillae, in the epithelium, in the connective tissue and around blood vessels, as well as in or near taste buds. Incubation with the antibodies against somatostatin, enkephalin, bombesin, peptide histidine isoleucine amide (PHI), cholecystokinin (CCK)/gastrin and dopamine-beta-hydroxylase (DBH) was negative for the fungiform papillae. In conclusion, the present study has shown several immunoreactive structures using antibodies against certain neurochemical markers. Further investigations will hopefully correlate these morphological findings with functional taste perception data. Future studies of patients with taste disorders or other pathological changes correlated with taste and tongue will also be of utmost importance.

Neuronal tachykinin NK2 receptors mediate release of non-adrenergic non-cholinergic inhibitory transmitters in the circular muscle of guinea-pig colon

The aims of this study were: (i) verify the usefulness of the recently described non-peptide antagonist, SR 142801, for blocking tachykinin NK3 receptors in the circular muscle of the guinea-pig colon and (ii) after occlusion of NK3 receptors by SR 142801, test the hypothesis that tachykinins may activate non-adrenergic non-cholinergic inhibitory neurons via non-NK3 receptors. In sucrose gap, we found that SR 142801 (0.1 microM) time-dependently inhibited the senktide-induced atropine (1 microM)-sensitive depolarization, action potentials and contractions of circular muscle of guinea-pig colon without affecting the cholinergic excitatory junction potential and contraction produced by single pulse electrical field stimulation. Likewise, SR 142801 (0.1 microM) time-dependently inhibited the senktide-induced non-adrenergic non-cholinergic hyperpolarization and relaxation of the circular muscle, without affecting the non-adrenergic non-cholinergic inhibitory junction potentials and relaxation produced by single pulse electrical field stimulation. Therefore, SR 142801 is a suitable tool to occlude neuronal NK3 receptors in guinea-pig colon. In the presence of SR 142801 (0.1 microM), atropine (1 microM), guanethidine (3 microM), indomethacin (3 microM) and nifedipine (1 microM) superfusion with neurokinin A (0.3 microM) produced depolarization on which a series of inhibitory junction potentials were superimposed. The incidence, number and amplitude of the inhibitory junction potentials evoked by neurokinin A was partly reduced by pretreatment with either apamin (0.1 microM) or L-nitroarginine (30 microM) and was totally blocked by pretreatment with apamin plus L-nitroarginine or by tetrodotoxin (1 microM). None of these treatments affected the depolarization and contraction produced by neurokinin A. The NK1 receptor selective antagonist, GR 82,334 (3 microM), did not affect the responses to neurokinin A, which were abolished by the NK2 receptor-selective antagonist GR 94,800 (0.1 microM). Substance P (0.3 microM) produced a large depolarization of the membrane but was poorly effective in producing superimposed inhibitory junction potentials. The NK1 receptor-selective agonist [Sar9]substance P sulfone (0.3 microM) produced large depolarization without inducing superimposed inhibitory junction potentials, while the NK2 receptor-selective synthetic agonist [beta-Ala8]neurokinin A(4-10) (0.3 microM) produced depolarization and superimposed inhibitory junction potentials. We conclude that neurokinin A, in addition to direct excitation and contraction of circular muscle activates, via neuronal NK2 receptors, inhibitory non-adrenergic non-cholinergic motorneurons. Thus, neuronal NK2 receptors should be considered as targets for endogenous tachykinins in enteric circuitries leading to descending relaxation in guinea-pig colon.

Tachykinin receptors in gastrointestinal motility

For a long time research on the action of TKs on gastrointestinal tissue has been demonstrating the importance of the TKs as non-cholinergic stimulators of motility in most parts of the mammalian gastrointestinal tract. The past years witnessed the development of TK agonists and antagonists selective for the various receptor types, which prompted a wealth of new insight into the pharmacology and molecular biology of the TK receptors. This knowledge now allows a more specific elucidation of the role of TKs and their receptors in the various aspects of gastrointestinal motility, not only in normal tissue but also under pathological conditions.

Nervous control of the release of substance P and neurokinin A from the isolated perfused porcine ileum

Using isolated perfused porcine ileum we studied the release of substance P (SP) and neurokinin A (NKA) in response to electrical stimulation of the mixed periarterial nerves and to infusion of different neuroactive agents. Nerve stimulation (8 Hz) had no significant effect on the release of SP and NKA. Nerve stimulation also had no effect on the release of SP and NKA during infusion of atropine (10(-6) M) or phentolamine (10(-5) M), whereas a significant increase (from 8.2 +/- 1.9 to 20.1 +/- 4.6 pmol/l for SP and from 12.3 +/- 2.7 to 34.2 +/- 7.7 pmol/l for NKA, n = 7) was observed during nerve stimulation after pretreatment with both atropine and phentolamine. This increase was abolished by hexamethonium (3 x 10(-5) M). Also acetylcholine infusion causes a significant release of SP and NKA after infusion of both atropine and phentolamine (to 172 +/- 56% and 232 +/- 69% of basal release, n = 7), an effect that was abolished by hexamethonium infusion. Infusion of atropine alone increased the release of SP and NKA significantly (to 337 +/- 92% and 386 +/- 124% of basal output, n = 5). Norepinephrine (10(-6) M) inhibited the release of SP and NKA (to 69 +/- 6% and 80 +/- 6% of basal release, n = 7). Our results suggest that the SP- and NKA-producing neurons receive intrinsic tonic muscarinic inhibitory impulses, extrinsic nicotinic excitatory impulses, and extrinsic adrenergic inhibitory impulses.