N-Butyrate rectal transport in cirrhotic patients.

Data about colonic mucosa transport of short-chain fatty acids in cirrhotic patients are still lacking. The aim of the present study was to compare the rectal mucosa transport of n-butyrate and its effect on transport of other electrolytes and endoluminal pH in normal subjects and in cirrhotic patients by using a rectal dialysis technique. Thirteen subjects with normal hepatic function tests and 17 cirrhotic patients were enrolled. Dialysis bags containing 80 mmol/liter of butyrate in a neutral pH (6.8) electrolyte solution were placed in the rectum of enrolled subjects for 60 min. Net transport rate was calculated for butyrate, sodium, chloride, potassium, and bicarbonate. The differences in pH between initial and final dialysis solutions was also evaluated in the two groups in the study. Net butyrate absorption was significantly lower in cirrhotic patients than in controls (65.2 +/- 38.6 vs 101.2 +/- 45.3 nmol/min/cm2, respectively; P = 0.02). Furthermore, cirrhotic patients showed a lower HCO3 secretion than controls (-26.9 +/- 19.9 vs -45.1 +/- 20.0, respectively; P = 0.01). No differences were found in transport of the other electrolytes. The pH in the final dialysis solution in cirrhotic patients was not significantly lower than in the controls (7.15 vs 7.35; P = 0.1). In conclusion, the impairment of butyrate absorption and the concurrent reduction of bicarbonate secretion observed in cirrhotic patients may suggest a selective hypoactivity of apical HCO3-/SCFA- antiport located at the colonocyte apical membrane.

Contribution of NK3 tachykinin receptors to propulsion in the rabbit isolated distal colon.

The role of NK3 receptors in rabbit colonic propulsion has been investigated in vitro with the selective agonist, senktide, and two selective antagonists, SR142801 and SB222200. Peristalsis was elicited by distending a rubber balloon with 0.3 and 1.0 mL of water leading to a velocity of 2.2 and 2.8 mm s-1, respectively. At concentrations of 1 nM, senktide inhibited propulsion evoked by both distensions (range 25-40%), whereas at 6 and 60 nmol L-1 facilitated 'submaximal' propulsion by 30%. In the presence of Nomega-nitro-L-arginine (L-NNA, 200 micromol L-1), which per se caused a slight prokinetic effect, 1 nmol L-1 senktide markedly accelerated propulsion (range 35-50%). Hexamethonium (200 micromol L-1) had minor effects on propulsion. In its presence, 60 nmol L-1 senktide significantly inhibited propulsion induced by both stimuli (range 20-50%). SR142801 (0.3, 3 nmol L-1) and SB222200 (30, 300 nmol L-1) facilitated 'submaximal' propulsion (range 20-40%). Conversely, higher antagonist concentrations (SR142801: 30, 300 nM; SB222200: 1, 10 micromol L-1) inhibited propulsion to both distensions by 20%. A combination of SR142801 (300 nmol L-1) plus hexamethonium (200 micromol L-1) induced an approximately four-fold greater inhibition of propulsion than that induced by SR142801 alone. In conclusion, in the rabbit-isolated distal colon, a subset of NK3 receptors located on descending pathways mediates an inhibitory effect on propulsion by activating a NO-dependent mechanism. Another subset of NK3 receptors, located on ascending pathways mediates a facilitative effect involving a synergistic interaction with cholinergic nicotinic receptors.

Contribution of NK(2) tachykinin receptors to propulsion in the rabbit distal colon.

The role of the tachykinin neurokinin (NK)(2) receptors on rabbit distal colon propulsion was investigated by using two selective NK(2)-receptor antagonists, MEN-10627 and SR-48968. Experiments on colonic circular muscle strips showed that contractile responses to [beta-Ala(8)]NKA-(4-10) (1 nM-1 microM), a selective NK(2)-receptor agonist, were competitively antagonized by MEN-10627 (1-100 nM), whereas SR-48968 (0.1-10 nM) caused an insurmountable antagonism, thus confirming the difference in the mode of action of the two compounds. Colonic propulsion was elicited by distending a mobile rubber balloon with 0.3 ml (submaximal stimulus) or 1.0 ml (maximal stimulus) of water. The velocity of anal displacement of the balloon (mm/s) was considered the main propulsion parameter. At low concentrations (1.0-100 nM and 0.1-10 nM, respectively), MEN-10627 and SR-48968 facilitated the velocity of propulsion, whereas at high concentrations (100 nM and 1 microM, respectively) they decelerated propulsion. The excitatory and inhibitory effects of both antagonists were observed only with submaximal stimulus. We focused on the hypothesis that the facilitatory effect on propulsion may result from blockade of neuronal NK(2) receptors and the inhibitory effect from suppression of the excitatory transmission mediated by NK(2) receptors on smooth muscle cells. In the presence of N(G)-nitro-L-arginine (300 microM), a nitric oxide synthase inhibitor, MEN-10627, at a concentration (10 nM) that was found to accelerate propulsion in control experiments inhibited the velocity of propulsion. In the presence of threshold (1-10 nM) or full (1 microM) concentration of atropine, which inhibited to a great extent the velocity of propulsion, the inhibitory effect of MEN-10627 (1 microM) was markedly increased. In conclusion, in the rabbit distal colon NK(2) receptors may decelerate propulsion by activating a nitric oxide-dependent neuronal mechanism and may accelerate it by a postjunctional synergistic interaction with cholinergic muscarinic receptors.

[Different effects of subacute administration of S. Croce oligo-mineral water on colonic vs rectal constipation]. / Effetti differenziati sulla stipsi colica rispetto a quella rettale del trattamento subacuto con acqua oligominerale S. Croce Sponga.

OBJECTIVE: To evaluate the effect of a subacute administration of oligomineral water "S. Croce Sponga" in subjects affected by chronic constipation. PATIENTS AND METHODS: Hospitalized patients (13 females and 4 males) have been classified according to radiologically evaluated transit times if affected by colonic or rectal constipation, and by clinical interview if suffering from chronic colonic constipation due to increased resistance or hypomotility. Treatment consisted in the administration of 1.5 litres/day of S. Croce Sponga oligomineral water for 7 days or a control water of known composition. The study started after seven days of hospital stay. RESULTS: The results of the study showed that S. Croce Sponga oligomineral water was effective in resolving the condition of chronic colonic constipation in almost 80% of the subjects. No effect was observed in subjects with chronic rectal constipation. CONCLUSIONS: Treatment with S. Croce Sponga oligomineral water resolved chronic colonic constipation by enhancing velocity of the colonic transit.

Rectal and colonic mesalazine concentration in ulcerative colitis: oral vs. oral plus topical treatment.

AIM: To measure mucosal concentrations of mesalazine in ulcerative colitis patients treated with oral mesalazine alone, compared to patients treated with both topical and oral mesalazine. METHODS: Twenty-two patients with mild to moderate ulcerative colitis were randomized to receive 2.4 g/day of oral mesalazine (11 patients) or 2.4 g/day oral plus 4 g/day of topical mesalazine (11 patients). After 2 weeks of treatment, endoscopic biopsies specimens were taken from the rectum and in descending colon just distal of the splenic flexure and stored to -80 degrees C for later assay (HPLC). Wilcoxon's rank sum test for unpaired data was used for the statistical analysis. RESULTS: Mucosal levels of mesalazine in the rectum were significantly higher in patients who received oral plus topical treatment than in those who had oral treatment alone (52.1 ng/mg, range: 13.6-122.1 vs. 0.2 ng/mg, range: 0.2-9.7, respectively; P < 0.0001). Similarly, in the descending colon, the mucosal concentrations of mesalazine were significantly higher in patients who had oral plus topical treatment than in those receiving oral treatment alone (46.6 ng/mg, range: 6-112.6 vs. 15.9 ng/mg, range: 2.3-42.4, respectively; P=0.01). CONCLUSIONS: Topical treatment of mesalazine significantly increases mucosal concentrations of mesalazine up to the splenic flexure, supporting the rationale to treat left-sided ulcerative colitis with topical formulations of mesalazine.

Regulatory role of tachykinins on intestinal propulsive activity.

The role of NK1, NK2, NK3 tachykinin receptors in subserving intestinal peristalsis has been reviewed referring mainly to the latest advances in this field. The most interesting and intriguing notion emerging from recent and ongoing studies is that tachykinins present in enteric neurons may modulate propulsive activity in an opposite manner, by enhancing or inhibiting peristalsis via each of the three distinct tachykinin receptors. These studies unveiled the complexity of tachykinergic control of the intestinal motility which is due to interaction of endogenous tachykinins with receptors located on ascending excitatory and descending inhibitory pathways and on smooth muscle cells. In fact, the type of tachykinergic modulation may depend on the amount of released peptides, on the site of the bulk of peptide release along the enteric motor pattern and, consequently, on the cellular location of the activated receptor, i.e. muscular or neuronal cells. Furthermore, in the case of activation of neuronally located tachykinin receptors, the effect of tachykinins may depend on the relatively functional predominance of excitatory or inhibitory neural circuits subserving peristalsis in different intestinal tracts. Our findings obtained in a simple isolated model represent a promising start for the understanding of the complex tachykinergic modulatory role of intestinal motility even though the function of tachykinins studied "in vivo" is certainly more complex than that studied "in vitro".

[Effects of subacute treatment with S. Croce water from the Sponga Springs in a group of dyspeptic patients]. / Effetti di un trattamento subacuto con acqua S. Croce Sorgente Sponga in un gruppo di pazienti dispeptici.

The Authors have appraised, in a group of 20 patients suffering from "non-ulcer, non-reflux dyspepsia", the therapeutical action and tolerance of the oligomineral Santa Croce water from the Sponga spring administered at a dose of 500 mL with the main meals up to an overall quantity of 1.5 L per day for ten days. When compared with a comparable control group, taking fairly mineralized water of known composition and free of contaminants, the group of patients treated showed a significant reduction both in the number and intensity of the symptoms marking the dyspeptic condition including above all pyrosis and sensation of epigastric heaviness and laborious digestion. As a first hypothesis, the hydropinic treatment might have indirectly favoured post-prandial gastric emptying, through an action of reduction of endogastric osmolarity and pH. The only collateral effect, reported by only five subjects, consisted of an annoying pollakiuria and nycturia.

Effects of cisapride on abnormally prolonged endogastric alkalinity time and delayed gastric emptying in cirrhotic patients.

BACKGROUND/AIMS: An abnormally prolonged alkalinity time in endogastric long-term pH monitoring has been previously demonstrated in cirrhotic patients. Recently a growing body of evidence suggest the existence of severe abnormalities of gastric emptying in the same patients and more generally of gastrointestinal motility changes in many portal hypertensive animal models. Assuming that there was a good correlation between endogastric alkalinity and a delayed emptying of gastric bile reflux, the aim of this study was to evaluated the effect of a gastrokinetic drug, Cisapride, both on circadian gastric pH and on gastric emptying in cirrhotic patients compared with controls. MATERIALS AND METHODS: Ten in patients with chronic liver disease and portal hypertension (six males, four females, median age 49.5, range 28-59) were enrolled. The control group included twelve inpatients without cirrhosis (seven females and five males, average age 45 years, range 31-54) free from endoscopic esophagogastro-duodenal lesions. The subjects were submitted to a 24h endogastric pH monitoring and gastric emptying study before and after administration of Cisapride (10 mg tid for three days). To gastric emptying study we used an ultrasonographic method evaluating the ratio between the antropyloric region volume before and at a fixed time after a solid/liquid standard meal. RESULTS: Basal 24 h gastric pH monitoring in cirrhotic patients showed a significant prolonged time of alkalinity (pH conventionally over 4) during the entire registration and mainly in postprandial period vs controls. The same patients group showed also a delayed gastric emptying when compared to controls. Cisapride administration significantly reduced both the abnormally prolonged alkalinity time and delayed gastric emptying in cirrhotic group without affecting the same parameters in the control group. CONCLUSIONS: Cisapride significantly reduces both the delayed gastric emptying time and the abnormally prolonged alkalinity time in cirrhotic group. Taken together, the results offered an indirect evidence that abnormally prolonged alkalinity in cirrhotic patients may be due, at least in part, to changes in gastroduodenal motility leading to a reduced gastric clearance of potentially noxious duodeno-gastric alkaline reflux.

Ulcerative colitis: rectal dilations in a patient with refractory diarrhea. Report of a case.

UNLABELLED: A 45-year-old man with an eight-year history of ulcerative colitis was evaluated for severe, nonbloody diarrhea. Symptoms, which began two years earlier, were characterized by 15 bowel movements per day, accompanied by urgency and incontinence. A reduced rectal compliance was measured at manometry. All conventional treatments were not able to modify the symptoms despite improvement of inflammatory colonic lesions. PURPOSE: The aim was to reduce bowel movements and incontinence by increasing rectal compliance. METHODS: Gradual pneumatic dilations of the rectum were performed three times per week for three weeks. RESULTS: The patient's diarrhea improved dramatically, decreasing in frequency from approximately 15 to only 3 bowel movements per day, while contemporaneously increasing rectal compliance. Such effect, still evident 15 months after discontinuation of dilation, was probably obtained by improvement of viscoelastic features of the intestinal wall. CONCLUSIONS: Rectal pneumatic dilation may be a successful attempt in some forms of intractable diarrhea in long-lasting ulcerative colitis.

Treatment of type C chronic active hepatitis with interferon-alpha 2a. Treatment duration does not influence biochemical remission but does decrease the relapse rate.

Few data are as yet available on the influence of interferon (IFN) treatment duration on biochemical remission and posttreatment relapse of chronic type C hepatitis. We investigated whether duration of recombinant IFN-alpha 2a treatment influences the remission and relapse rates in type C chronic active hepatitis (CAH). Sixty-two CAH patients were randomly assigned to receive 3 MU of i.m. recombinant IFN-alpha 2a three times per week for either 3 (group A, 32 patients) or 6 (group B, 30 patients) months. A complete biochemical remission was cumulatively observed in 62.5 and 63.3% of patients in groups A and B, respectively (p = NS). One and two patients in groups A and B, respectively, showed a biochemical relapse during treatment. In all cases biochemical remission was observed within the first 3 months of treatment. Among responders, 84.2 and 52.9% (p = 0.04) cumulatively had relapses in groups A and B, respectively. We conclude that IFN treatment duration does not influence the biochemical remission rate in type C CAH, but lowers the relapse rate of those who are treated for a longer period. The IFN treatment should be stopped if the patient is a nonresponder after 3 months of treatment. In responders, treatment should be continued for at least 6 months.

Role of nitric oxide-dependent and -independent mechanisms in peristalsis and accommodation in the rabbit distal colon.

Previous findings, which have been confirmed in this study, indicate that nitric oxide (NO)-dependent and -independent (apamin-sensitive) mechanisms underlie the electrically induced non-adrenergic, noncholinergic (NANC) relaxation in the circular muscle of rabbit distal colon. Based on this evidence, we further investigated whether, and to what extent, these separate NANC components participate in the maintenance of circular muscle tone, reflex relaxations evoked by localized balloon distension or during peristalsis (descending inhibition) and in the accommodation of colonic wall in response to graded intraluminal fluid delivery. NG-nitro-L-arginine (L-NNA) (10-300 microM), apamin (100 nM) and tetrodotoxin (60 nM), enhanced the spontaneous low tone and phasic activity in circular muscle strips. In experiments on peristalsis, L-NNA (30 and 300 microM) shortened the latency of peristaltic wave initiation and increased the velocity of propulsion of an intraluminally distended balloon (range, 0.1-1 ml). The latter effect was mimicked by the NO scavenger oxyhemoglobin (30 microM). Velocity of propulsion was enhanced by apamin (100 nM) at low balloon distension (0.1 and 0.2 ml), whereas it was reduced at high distension volumes (1 ml), due to disruption of descending inhibition. A combination of L-NNA (300 microM) and apamin (100 nM) blocked peristalsis, due to persisting spasms of the circular muscle. L-NNA (300 microM) did not affect the amplitude of distension-evoked ascending reflex contraction and slightly inhibited the descending reflex relaxation. By contrast, the latter reflex was virtually abolished by apamin (100 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of neuronal 5-hydroxytryptamine receptor antagonists on non-cholinergic ganglionic transmission in the guinea-pig enteric excitatory reflex.

A partitioned bath made it possible to separate the site of recording of the ascending excitatory reflex of the ileal circular muscle (oral compartment) from the site of reflex induction (caudal compartment), evoked by inflating an intraluminal balloon. In the caudal compartment, blockade of cholinergic ganglionic transmission by hexamethonium (100 microM) and hyoscine (0.3 microM) caused an approximately 65% reduction in the amplitude of reflex contractions, suggesting that the remaining response was mediated by non-cholinergic transmission near the distension site. This non-cholinergic component of ganglionic transmission was insensitive to the action of methiothepin (1 microM), ondansetron (1 microM), tropisetron (1.5 microM), DAU 6285 (1 microM) and renzapride (1 microM), agents that antagonize the action of 5-hydroxytryptamine (5-HT) at neural 5-HT1-like, 5-HT3, 5-HT4 and putative 5-HT1P receptors. These findings suggest that the neural pathways subserving non-cholinergic ganglionic transmission in the ascending excitatory reflex in the guinea-pig ileum do not involve 5-HT as neurotransmitter.

Benzimidazolone derivatives: a new class of 5-hydroxytryptamine4 receptor agonists with prokinetic and acetylcholine releasing properties in the guinea pig ileum.

The influence of three azabicycloalkyl benzimidazolone derivatives, DAU 6236, BIMU 1 and BIMU 8, which act as agonists at central 5-hydroxytryptamine (5-HT)4 receptors, has been investigated on cholinergic neuromuscular transmission and peristalsis in the guinea pig small intestine. In the longitudinal muscle myenteric plexus preparations, these compounds caused a concentration-dependent (range 1-300 nM) enhancement of the amplitude of nerve-mediated cholinergic submaximal contractions to electrical stimulation. In comparison to the potentiating effect of 5-methoxytryptamine (a reference 5-HT4 receptor agonist), the rank order of agonist potency was BIMU 8 = BIMU 1 greater than DAU 6236 = 5-methoxytryptamine. In whole ileal segments, DAU 6236, BIMU 1 and BIMU 8 increased markedly (maximum increase, 200%) the frequency of peristalsis within the range of 0.1 to 3 microM. Micromolar concentrations of ICS 205-930, which is a low affinity antagonist of 5-HT4 receptors, were required to antagonize the facilitatory effect on cholinergic transmission caused by benzimidazolone derivatives and 5-methoxytryptamine (pA2 values, 6.5 in average) and to reverse the increase in the frequency of peristalsis induced by DAU 6236, BIMU 1 and BIMU 8. By contrast, the potent and selective 5-HT3 receptor antagonist ondansetron (1 microM) was ineffective. Our findings indicate that benzimidazolone derivatives act as agonists in the guinea pig ileum causing enhancement of acetylcholine release and peristaltic activity. The neural receptor site involved in the action of benzimidazolone derivatives and which showed low affinity for ICS 205-930 is probably identical to the putative 5-HT4 receptor subtype agonized by indoleamines and substituted benzamide derivative prokinetic agents.

5-hydroxytryptamine4 receptor agonists facilitate cholinergic transmission in the circular muscle of guinea pig ileum: antagonism by tropisetron and DAU 6285.

The effect of 5-hydroxytryptamine (5-HT), BIMU 8 (endo-N-(8-methyl-8-azabicyclo [3.2.1.] oct-3-yl)-2,3-dihydro-3-(1-methyl)ethyl-2-oxo-1H-benzimidazole-1- carboxamide hydrochloride) and cisapride was studied on the electrically-induced neurogenic cholinergic twitch contractions in the guinea pig ileum circular muscle. These compounds caused a concentration-dependent increase in the amplitude of submaximal twitch contractions with the following rank order of potency: 5-HT greater than BIMU 8 = cisapride. The effect of 5-HT was competitively antagonized by tropisetron (ICS 205-930) (apparent pA2 value: 6.4), suggesting an interaction at 5-hydroxytryptamine4 (5-HT4) receptors. The novel benzimidazolone derivative DAU 6285 (endo-6-methoxy-8-methyl-8-azabicyclo [3.2.1.] oct-3-yl-2,3-dihydro-2-oxo-1H-benzimidazole-1-carboxylate hydrochloride), antagonized the effect of 5-HT, BIMU 8 and cisapride with apparent pA2 values in the range 7.1-7.3. Our findings demonstrate that cholinergic neurones innervating the circular coat are endowed with excitatory 5-HT4 receptors. DAU 6285 is approximately 5-9-fold more potent than tropisetron as antagonist at these receptors.

An in vitro study of the relationship between GABA receptor function and propulsive motility in the distal colon of the rabbit.

1. The effects of gamma-aminobutyric acid (GABA), 3-aminopropane sulphonic acid (3-APS) and baclofen on spontaneous, electrically-induced and propulsive motility were investigated in rabbit distal colon. 2. In unstimulated longitudinal (LMPs) and circular muscle strip preparations (CMPs) 3-APS (10-200 microM) and GABA caused a clear-cut relaxation susceptible to desensitization. Baclofen (10-200 microM) caused relaxation in a minority (30%) of preparations. The 3-APS response was sensitive to tetrodotoxin (TTX; 1 microM), SR 95531 (a novel competitive GABAA-receptor antagonist) (10 microM), picrotoxinin (30 microM), and insensitive to hyoscine (1 microM) and to a combination of prazosin (1 microM) and propranolol (1 microM). The baclofen response was antagonized by 5-aminovaleric acid (DAVA, 500 microM), TTX and hyoscine and resistant to GABAA-receptor and adrenoceptor blockade. GABAA-receptors were therefore associated with non-adrenergic non-cholinergic (NANC) inhibitory nerve activation while GABAB-receptors were involved in depression of cholinergic tone of smooth muscle. GABA (10-200 microM) elicited both above mentioned effects. 3. In LMPs, baclofen (10-200 microM) dose-dependently inhibited submaximal responses to both cholinergic and NANC inhibitory nerve stimulation. This effect was resistant to SR 95531 and picrotoxinin and prevented by DAVA and baclofen desensitization. GABA (10-200 microM) mimicked the action of baclofen. GABA inhibitory effects persisted in the presence of GABAA-receptor blockade. 4. In segments of distal colon, GABA and baclofen (1-200 microM), but not 3-APS (1-200 microM), dose-dependently decreased the velocity of propulsion of an intraluminally-distended balloon. This effect was antagonized by DAVA and GABA or baclofen desensitization and resistant to SR 95531 and picrotoxinin. These antagonists per se had no effect on propulsion. In preparations in which propulsion was slowed by hyoscine (1 microM), baclofen caused no consistent further depression of propulsive activity. 5. Our results show that GABAA- and GABAB-receptors are present in rabbit colon. GABAA-receptor stimulation activates NANC inhibitory nerves without apparently affecting propulsion. GABAB-receptors are associated with a reduction of neural (mainly cholinergic) activity subserving muscular tone and peristalsis and appear to be located on both cholinergic and NANC inhibitory nerves. However, the persisting propulsive activity during suppression of GABAA- and GABAB-receptor function suggests that GABA in enteric neurones is not crucial for the neural circuitry subserving colonic peristalsis in this species.

The role of GABAA receptor function in peristaltic activity of the guinea-pig ileum: a comparative study with bicuculline, SR 95531 and picrotoxinin.

1. The peristaltic activity of the guinea-pig ileum was studied in the absence and in the presence of the blockade of GABAA receptors. 2. Bicuculline (1-30 microM), improved at the highest concentrations the efficiency of peristalsis by enhancing the frequency of propulsive contractions and the amount of fluid ejected per unit of time. 3. Neither SR 95531 (0.3-10 microM), a novel GABAA receptor antagonist, which competitively antagonized 3-aminopropane sulphonic acid induced contractions in myenteric plexus-longitudinal muscle preparations (pA2 value: 6.47), nor picrotoxinin (1-30 microM) modified peristaltic parameters or influenced the potentiating effect of bicuculline on peristaltic activity. 4. In myenteric plexus-longitudinal muscle preparations, bicuculline (1-30 microM) enhanced the amplitude of electrically-induced cholinergic contractions without modifying submaximal contractions to applied acetylcholine. SR 95531 and picrotoxinin had no effect on twitch amplitude. In the presence of each of these compounds, bicuculline retained its potentiating effect. 5. The results obtained with SR 95531 and picrotoxinin question the view that GABAA receptors may exert a critical role in intestinal propulsion by modulating the activity of nerve pathways subserving peristalsis. Bicuculline potentiates the peristaltic activity of the ileum probably via a facilitatory effect on enteric cholinergic transmission that is independent of GABAA receptor blockade.

Cholinergic contractions induced by GABA-A receptor activation in the guinea-pig ileum are inhibited by alpha-chymotrypsin and potentiated by diazepam.

The influence of alpha-chymotrypsin and diazepam on the phasic (mainly direct) and tonic (indirect, probably substance P-mediated) components of intestinal cholinergic contractions, induced by the GABA-A receptor agonist 3-aminopropane sulphonic acid (3-APS), was investigated in the guinea-pig ileum. alpha-Chymotrypsin, at a concentration (20 U/ml) not affecting submaximal Ach (0.1 microM) contractions, preferentially depressed the tonic component of the 3-APS (30 microM)-induced response. A brief exposure (10 or 60 sec) to diazepam (0.1 microM) potentiated both the phasic and the tonic contractions evoked by low (10, 30 microM) 3-APS concentrations. This potentiation was prevented by bicuculline (30 microM), hyoscine (1 microM) and flumazenil (1, 3 microM). These results provide further support for an involvement of a peptide neurotransmitter on GABA-A receptor-mediated cholinergic response in the ileum. The modulation of this response by diazepam is probably exerted through recognition sites resembling the "central type" benzodiazepine receptors.

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

The possible involvement of substance P (SP) in cholinergic contractions induced by GABAA agonists in the guinea-pig ileum was further investigated. 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. Capsaicin (0.2 microM) 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 microM (D-Pro4,D-Trp7.9)SP-(4-11), even though the degree of antagonism caused by this SP antagonist was consistently lower. These results indicate that depression of SP receptor function achieved by three different procedures decreases cholinergic contractile responses to GABAA agonists in the guinea-pig ileum. This provides further support for the hypothesis that GABAA 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.