Intestinal Strips Research Articles

Structure-activity relationships of anthraquinones in the decrease of intestinal motility.

The effects of substituted anthraquinones on intestinal motility were evaluated in-vitro using rabbit small intestinal strips. This structure-activity relationship study revealed the critical requirement of a hydroxy group at R2 position. The intestinal motility was inhibited 50% (IC50) by emodine (8 microM), 2-hydroxy anthraquinone (20 microM), 2,6-dihydroxy anthraquinone (25 microM), 2,7-dihydroxy anthraquinone (10 microM), 1,2,4-trihydroxy anthraquinone (80 microM) and 1,2,5,8-tetra-hydroxyanthraquinone (9 microM). The presence of other polar groups at R2 position such as an amino, aldehyde and carboxylic acid group significantly reduced the activity (IC50 360-400 microM). The presence of a methyl group and esterification of the carboxylic acid at R2 position was found to abolish the activity. These data are useful for the future development of anthraquinones as laxative agents.

Identification of histaminic (H1-type) receptors in small intestine of broilers by application of histamine and some of its agonists and antagonists

Histamine is a biologically active amine (biogenic amine) that has a broad spectra of physiologic and pathologic reactions in the organism. Its effects are shown through 4 types of specific receptors (H1, H2, H3 and H4). Histamine is one of the main causes of intestine disorders and the occurrence of diarrhea, both of which are very common in broilers. Whilst there is no information in scientific literature about the presence of histaminic receptors in smooth muscles of the small intestine wall of broilers (duodenum, jejunum and ileum), we tried to determine their presence, distribution and type in this kind of muscles. Investigations were carried out on isolated smooth muscles of the circular and longitudinal layer of the broiler small intestine (strip dimension 3-4 mm x 2 cm). The muscle strip was then placed in an isolated organ bath and the contractions obtained were registered with isometric transducers on a two-channel printer. This was done following the addition of histamine, betahistine (H1 agonist), and mepiramine (H1 antagonist). Muscle vitality was checked by adding acethylcholine chloride. Using the obtained results, it can be concluded that H1 types of histaminergic receptors are present in smooth muscles of the small intestine of broilers. .

Direct vasodilative effect of FK506 on porcine mesenteric artery in small bowel transplantation

Background Tacrolimus (FK506) is widely used as an immunosuppressive drug in small bowel transplantation. However, its precise effects on the vascular tone of the transplanted organ have not been studied. This study aimed to clarify the effects of FK506 on the porcine mesenteric artery. Methods The effects of FK506 on the changes in cytosolic Ca 2+ concentration ([Ca 2+]i) and force using fura-2 fluorometry were investigated in mesenteric arterial strips of the porcine small intestine. The effects of FK506 on the activity of voltage-dependent Ca 2+ channels and receptor-operated Ca 2+ channels using high K + (118 mmol/L K +) depolarization and thromboxane A 2 analog (U46619) stimulation were also examined. Results FK506 inhibited the force development induced by 118 mmol/L K + depolarization and 1 μmol/L U46619 stimulation in a concentration-dependent manner. The extent of inhibition of this contraction was greater than that of the K +-induced contraction, and its inhibitory potency was about 10-fold. FK506 (10 μmol/L) inhibited the increases in [Ca 2+]i (24.9% ± 7.4%) and the force development (52.0% ± 5.6%) induced by 1 μmol/L U46619, respectively. Conclusions FK506 induces arterial relaxation by decreasing [Ca 2+]i. Pretreatment of a graft with FK506 may reduce the risk of vasospasm, ischemia-reperfusion injury, and thrombosis in small bowel transplantation.

Melatonin attenuates the acetylcholine-induced contraction in isolated intestine of a teleost fish

The present study investigates the possible direct actions of melatonin (N-acetyl-5-methoxytryptamine) on intestinal motility in goldfish (Carassius auratus) using an in vitro system of isolated intestine in an organ bath engaged to an isometric transducer. The longitudinal strips from goldfish intestine in the organ bath showed a resting spontaneous myogenic rhythmic activity which is not altered by melatonin. The addition of acetylcholine (1 nmol l(-1)-10 mmol l(-1)) to the organ bath induces a significant contraction of the intestinal strips in a concentration-dependent manner. The addition of melatonin and its agonist, 2-iodomelatonin, induced a concentration-dependent attenuation of acetylcholine-induced contractile response. The specificity of this effect is tested by the preincubation of the intestine strips in the presence of two melatoninergic antagonists, luzindole (a non-selective MT(1)/MT(2) melatonin receptor antagonist) and 4-P-PDOT (preferred antagonist of MT2 receptor subtype), which counteracted the melatonin-induced relaxation in a concentration-dependent manner. Finally, present results demonstrate that this melatoninergic effect on intestinal strips is a process highly dependent on extracellular calcium. In conclusion, this is the first study demonstrating the role of melatonin in the control of gut motility in a non-mammalian vertebrate. The melatonin effects on isolated intestine from goldfish are mediated by melatoninergic membrane receptors, and could suggest a delay in food transit time, supporting its anorectic effect reported on in vivo studies.

Effects of essential oil from Croton tiglium L. on intestinal transit in mice

Aim of the Study Croton tiglium ( Croton tiglium L., Euphorbiaceae) is widely used as a herb for treatment of gastrointestinal disturbances. Previous studies established its purgative and inflammational properties. The present study aimed to investigate the effects of Croton tiglium oil (CO) on intestinal transit in mice. Materials and Methods Gastrointestinal transit in mice and contractile characteristics of isolated intestinal strips from mice were evaluated. Intestinal inflammation was confirmed by histological examination. Results Low dose of CO increased the gastrointestinal transit of charcoal and barium meal as well as the production of fecal pellets in mice. In contrast, high dose exerted inhibitory effects. For normal colonic circular strips, both high and low dose of CO inhibited the contractile frequency. Low doses (0–20 μg/ml) of CO enhanced the phasic contractions, while high doses (>40 μg/ml) reduced them. Colonic longitudinal strips in CO-treated mice were less sensitive to electrical field stimulation than those in control mice. The contraction of colonic longitudinal, colonic and jejunal circular strips in CO-treated mice was more sensitive to atropine than that in control mice. Conclusions CO might modulate gastrointestinal motility and induce intestinal inflammation related to immunological milieu and motor activity. Our findings may highlight the ethno-medical uses of Croton tiglium on intestinal disorders.

Sildenafil delays the intestinal transit of a liquid meal in awake rats

Sildenafil slows down the gastric emptying of a liquid test meal in awake rats and inhibits the contractility of intestinal tissue strips. We studied the acute effects of sildenafil on in vivo intestinal transit in rats. Fasted, male albino rats (180-220 g, N = 44) were treated (0.2 mL, iv) with sildenafil (4 mg/kg) or vehicle (0.01 N HCl). Ten minutes later they were fed a liquid test meal (99m technetium-labeled saline) injected directly into the duodenum. Twenty, 30 or 40 min after feeding, the rats were killed and transit throughout the gastrointestinal tract was evaluated by progression of the radiotracer using the geometric center method. The effect of sildenafil on mean arterial pressure (MAP) was monitored in a separate group of rats (N = 14). Data (medians within interquartile ranges) were compared by the Mann-Whitney U-test. The location of the geometric center was significantly more distal in vehicle-treated than in sildenafil-treated rats at 20, 30, and 40 min after test meal instillation (3.3 (3.0-3.6) vs 2.9 (2.7-3.1); 3.8 (3.4-4.0) vs 2.9 (2.5-3.1), and 4.3 (3.9-4.5) vs 3.4 (3.2-3.7), respectively; P < 0.05). MAP was unchanged in vehicle-treated rats but decreased by 25% (P < 0.05) within 10 min after sildenafil injection. In conclusion, besides transiently decreasing MAP, sildenafil delays the intestinal transit of a liquid test meal in awake rats.

Effect of Aqueous Extract of Alstonia Congensis on Glucose Transport and Na+-K+-ATPase Activity in the Everted and Non-Everted Guinea Pig Intestine and Erythrocyte Fragility

The seed of Alstonia congensis has been used as purgative by traditional doctors. It is not known if glucose transport and Na+-K+ ATPase activity are affected during the purging process. The effect of the plant on erythrocytes fragility is also not known. This study was designed to provide this information. The effect of aqueous extract (1:25w/v) of Alstonia congensis on the transportation of glucose ranging from 0.10 to 0.40M from normal and everted guinea pig intestinal strips into the surrounding 0.5M TrisEDTA saline buffer pH 8.2; on Na+-K+- ATPase activity and erythrocytes fragility were measured. Results showed that the aqueous extract reduced glucose transportation; inhibited Na+-k+-ATPase activity and specific activity at higher enzyme protein concentration and activated the enzyme activity and specific activity at lower enzyme protein concentration. Glucose transport reduction was linked to the effect of the extract on the Na+-k+-ATPase system. The extract also increased erythrocytes fragility. The active ingredient(s) in the extract is not known yet and research work is in progress to ascertain it. Keywords: Alstonia congensis, glucose transport, Na+-K+-ATPase activity Nigerian Journal of Health and Biomedical Science Vol. 6 (1) 2007: pp. 5-9

IgA from HIV+ haemophilic patients triggers intracellular signals coupled to the cholinergic system of the intestine.

IgA was obtained from HIV-infected haemophilic patients and the intracellular signals triggered by its reaction with isolated rat intestinal strips were studied. HIV+ IgA stained intestinal microvilli with a granular immunofluorescence pattern and bound to the muscarinic acetylcholine receptor (mAChR), displacing the specific muscarinic cholinergic antagonist QNB in a non-competitive manner. It triggered the signals that are the consequence of mAChR stimulation in the intestine. Thus, it decreased cAMP synthesis and increased guanosine 3':5'-cyclic monophosphate (cGMP) formation and phosphoinositide (PI) turnover of the intestine. In addition, it stimulated prostaglandin E2(PGE2) synthesis by intestinal strips. Through its effect on PGE2 synthesis, HIV+ IgA could have a dual action. On the one hand, it could enhance immunosuppression at a local level, favouring pathogen growth and subsequent intestinal dysfunction. On the other hand, PGE2 could directly increase intestinal motility and electrolyte/fluid loss. Both effects could be involved in intestinal damage in AIDS.

Effects of haloperidol and clotrimazole on synaptic transmission in and contractile activity of smooth muscles of the guinea-pig intestine

In muscle strips of the guinea-pig large intestine, haloperidol and clotrimazole increased spontaneous electrical and contractile activities and decreased ATP-evoked hyperpolarization of smooth-muscle cells and the amplitude of inhibitory synaptic potentials. The pattern of effects of haloperidol on hyperpolarization induced by intramural stimulation of muscle strips was preserved under conditions of pre-incubation of the preparations in Krebs solutions containing pyridoxal-5′-phosphate, Nω-nitro-L-arginine, or apamin, as well as both apamin and tetraethylammonium.

In vitro evaluation of gut contractile response to histamine in rainbow trout ( Oncorhynchus mykiss Walbaum, 1792)

The contractile response of intestinal strips in rainbow trout ( Oncorhynchus mykiss Walbaum, 1792) to the administration of histamine was assessed by means of the organ bath technique. Intestinal strips were isolated from 16 clinically healthy fish and mounted in organ baths. Histamine was compared with the full agonist serotonin, to evaluate their contractile efficacy and potency. Serotonin elicited a concentration-related contraction in all examined intestinal strips, whereas histamine induced the contraction only in 14 exemplars. Of these, seven exhibited a concentration-related response. A sigmoidal curve was fitted from data ( R 2 = 0.55) and its best fit values were compared with those of serotonin. Interestingly, histamine exhibited the same efficacy ( E max) as serotonin ( F-test, p > 0.05), but showed lower potency (by an order of magnitude) ( F-test, p < 0.01). Moreover, the effect of the H1 antagonist, pyrilamine, has been tested to exclude aspecific contraction due to other agonists eventually released in situ following histamine administration. Pyrilamine showed a marked concentration-related antagonist action on the contractility induced by histamine with complete contractility antagonism at 10 −4 M. The authors suggest that the responses to histamine measured in the present study reflect a less sensitive response to an exogenous source of histamine, possibly due to bacterial metabolism.

ADRENALINE &amp; ITS ANTAGONIST

Objective: This research work deals with the mechanism involved in determining the therapeuticpotential of adrenaline and its blockers in gastrointestinal motility. Method: The classical method of Craig &amp; Clark wasused for obtaining the longitudinal and circular muscles strip of rabbit intestine for in-vitro studies. Each muscle stripseparately was subjected to the effect of adrenaline and its blockers. The results were recorded on polygraphapparatus. Results: The effects were recorded in vice versa fashion i.e. agonist v/s antagonist and antagonist v/sagonist on each muscle strip separately. Adrenaline had significant effect on the force of contraction of muscle strip.On addition of antagonist in the presence of agonist the effects were increased. Longitudinal muscle showed morepronounced effects i.e. 69% with beta-blocker in comparison to the effect with alpha-blocker, which was only 27%.Circular muscle showed reduction in the force of contraction with adrenaline, which was further reduced on additionof beta-blocker, whereas the effects were increased when treated with alpha-blocker. Conclusion: This studyconcluded that adrenaline released in vitro in response to sympathetic stimulation or given from external source,increases the force and reduces the rate of contraction. Hence decreases the intestinal motility due to its antispasmodiceffect. The result of this study can be utilized in the development of new drug related to G.I. motility mediated throughadrenoceptors.

Effect of somatostatin on gastrointestinal contractility in Schistosoma mansoni infected mice

Schistosoma mansoni infection induces severe gastrointestinal motility disturbances which are characterised by hyperactivity of intestinal muscle, abdominal pain, diarrhoea, vomiting and nausea. During schistosomiasis, the neuropeptide somatostatin is generated within inflammatory granulomas. However, somatostatin is also an important inhibitory modulator of gastrointestinal motility. In the present study, we have investigated the potential of somatostatin to reduce schistosomiasis-induced hyperactivity of gastrointestinal smooth muscle. Organ bath experiments were performed to study the contractility of isolated smooth muscle strips of intestine from control mice and from mice that were infected with S. mansoni for 2, 4, 8 and 16 weeks. Electrical field stimulation (0.5–8 Hz) of enteric nerves induced frequency-dependent neurogenic contractions of cholinergic origin in all regions of the small intestine. Somatostatin (0.1–1 μM) concentration-dependently inhibited the contractions to enteric nerve stimulation in the small intestine from uninfected control mice and from acutely S. mansoni infected mice (2 and 4 weeks of infection). After 8 weeks of infection with S. mansoni, this inhibitory effect of somatostatin was less pronounced and after 16 weeks of infection it was completely abolished. Histology demonstrated that chronic infection of mice with S. mansoni was associated with significant alterations in the musculature of the small intestine. These alterations may be associated with physiological changes in the responsiveness to somatostatin and suggest that the somatostatin neuroregulatory circuit of enteric neurotransmission in the small intestine is disturbed during chronic schistosomiasis mansoni.

Direct inhibitory effect of erythromycin on human alimentary tract smooth muscle

Background: Erythromycin was found to stimulate motor activity in the upper gastrointestinal tract. However, in several smooth muscle preparations, it also elicited an inhibitory effect. Our aim was to study the effect of erythromycin in various human alimentary tract smooth muscles. Methods: Using force measurements, we assessed the effect of erythromycin on electrically and chemically evoked contractions of isolated muscle strips of human gallbladder, small intestine, and colon. Results: The muscarinic receptor agonist carbachol evoked contraction in gallbladder, ileum, and colonic smooth muscle that were reduded by erythromycin at 10 −4 M to 72% ± 24%, 77% ± 22%, and 76% ± 22% of control values, respectively. Erythromycin did not affect contractions evoked by noncholinergic agents. Erythromycin’s inhibitory effects were not altered by nerve blockade, indicating a direct muscle effect. Eryrthromycin also reduced contractions evoked by electrical stimulation at frequencies of 5, 10, and 20 Hz in the human gallbladder, ileum, and colon preparations. These contractions were reduced by erythromycin in a reversible and dose-dependent manner. Conclusions: Erythromycin antagonized direct cholinergic effects on various smooth muscles from the human alimentary tract in a concentration-dependent manner.

Effect of Ectopic Expression of Rat Trefoil Factor Family 3 (Intestinal Trefoil Factor) in the Jejunum of Transgenic Mice

To further examine the function of the trefoil factor family (TFF), the expression of which is up-regulated at sites of injury, we have produced transgenic mice that chronically express rat TFF3 within the jejunum (using a rat fatty acid-binding protein promoter). The expression of rat TFF3 was limited to the villi of the jejunum and had no effect on base-line morphology. Rat TFF3 expression did result, however, in a reduced sensitivity to indomethacin (85 mg/kg subcutaneously), which only caused a 29% reduction in villus height in transgenics versus 51% reduction in controls (p < 0.01). Indomethacin increased initial intestinal epithelial cell proliferation and migration, but the presence of rat TFF3 caused no additional change in proliferation (bromodeoxyuridine), cell migration ([(3)H]thymidine and bromodeoxyuridine), apoptosis (terminal deoxyuridine nucleotidyl nick end labeling), or E-cadherin immunostaining. In vitro studies following changes in resistance of intestinal strips in Ussing chambers (voltage-clamp technique) showed increased base-line resistance in the rat TFF3-expressing region (326 +/- 60 versus 195 +/- 48 ohm.cm(2) in controls, p < 0.05) and reduced the fall in resistance following HCl exposure by about 40% (p < 0.01). Overexpression of TFF3 stabilizes the mucosa against noxious agents, supporting its role in mucosal protection/repair. It may therefore provide a novel approach to the prevention and/or treatment of intestinal ulceration.

5-HT(4) receptors on cholinergic nerves involved in contractility of canine and human large intestine longitudinal muscle.

5-HT(4) receptors mediate circular muscle relaxation in both human and canine large intestine, but this phenomenon alone can not explain the improvement in colonic motility induced by selective 5-HT(4) receptor agonists in vivo. We set out to characterize 5-HT(4) receptor-mediated effects in longitudinal muscle strips of canine and human large intestine. Electrical field stimulation (EFS) was applied providing submaximal isotonic contractions. L-NOARG (0.1 mM) was continuously present in the organ bath to preclude nitric oxide-induced relaxation to EFS. The selective 5-HT(4) receptor agonist prucalopride (0.3 microM) enhanced EFS-evoked contractions, that were antagonized in both preparations by the selective 5-HT(4) receptor antagonist GR 113808 (0.1 microM). The prucalopride-induced increase was present in canine ascending and descending colon, but absent in rectum. Regional differences in response to prucalopride were not observed in human ascending and sigmoid colon and rectum. Incubation with atropine (1 microM) or tetrodotoxin (0.3 microM) inhibited EFS-induced contractions, which were then unaffected by prucalopride (0.3 microM) in both tissues. In the presence of methysergide (3 microM; both tissues) and granisetron (0.3 microM; only human tissues), 5-HT (0.3 microM) enhanced EFS-induced contractions, an effect that was antagonized by GR 113808 (0.1 microM). In the presence of atropine or tetrodotoxin, EFS-induced contractions were inhibited, leaving 5-HT (0.3 microM) ineffective in both preparations. This study demonstrates for the first time that in human and canine large intestine, 5-HT(4) receptors are located on cholinergic neurones, presumably mediating facilitating release of acetylcholine, resulting in enhanced longitudinal muscle contractility. This study and previous circular muscle strip studies suggest that 5-HT(4) receptor agonism facilitates colonic propulsion via a coordinated combination of inhibition of circumferential resistance and enhancement of longitudinal muscle contractility.

Regulation of pacemaker currents in interstitial cells of Cajal from murine small intestine by cyclic nucleotides.

1. Electrical rhythmicity (slow waves) in gastrointestinal muscles (GI) is generated by interstitial cells of Cajal (ICC). Cultured ICC from the murine small intestine were studied with the patch-clamp technique to characterize regulation of pacemaker currents by cyclic nucleotides. Cyclic nucleotide agonists were also tested on intact strips of murine small intestine. 2. Nitric oxide donors slowed the frequency of pacemaker currents in a concentration-dependent manner. These effects depended on cGMP formation and were reduced by 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The effects of nitric oxide donors were mimicked by membrane-permeable analogues of cGMP. The specific cGMP phosphodiesterase inhibitor zaprinast reduced the frequency of spontaneous pacemaker currents. 3. The cGMP-dependent effects on pacemaker currents were not affected by okadaic acid or KT-5823, an inhibitor of protein kinase G. 4. Forskolin, but not dideoxy forskolin, reduced the frequency of spontaneous pacemaker activity and activated a sustained outward current. The latter was likely to be due to ATP-dependent K+ channels because it was blocked by glibenclamide. 5. The effects of forskolin were not mimicked by membrane-permeable cAMP analogues. A membrane-permeable inhibitor of protein kinase A, myristoylated PKA inhibitor, and the adenylyl cyclase inhibitor SQ-22536, had no effect on responses to forskolin. 6. Responses of intact muscles to cGMP and cAMP agonists were similar to the responses of pacemaker cells. Changes in resting membrane potential and slow wave amplitude, however, were noted in intact jejunal muscles that were not observed in ICC. Differences in responses may have been due to the effects of cyclic nucleotide agonists on smooth muscle cells that would sum with responses of ICC in intact jejunal muscle strips. 7. A cGMP-dependent mechanism regulates slow wave frequency, but this occurs through direct action of cGMP not via protein phosphorylation. Regulation of pacemaker currents by cAMP-dependent mechanisms was not observed.

In vivo recording of gastrointestinal motility in Ws/Ws mutant rats

Background: WslWs rat (Ws) has a mutation at the c-kit gene which has a critical role in the development of interstitial cells of Cajal (ICC). In the gastrointestinal tract of Ws ICCs are either absent or markedly reduced. In vitro studies using intestinal muscle strips showed that regularity of contractions is severely impaired in Ws. Interestingly, however, Ws rats can live and be fertile, while the WlWv mouse with a mutation at the c-kit gene can not survive. In the present study we recorded gastrointestinal mechanical contractions in vivo in Ws and control (wild type: (+1+» rats. Methods: Ws (8weeks old, approximately 250g, n=9) and control rats (Cont, n=8) were operated under nembuthal anesthesia. Miniature strain gauge force transducers developed specifically for in vivo rat motility studieswere sutured onto the serosal side of the gastric antrum and jejunum (5cmto 8cm distal to pylorus). In order to confirm the migration of intestinal phase 3s, two transducers were attached in proximal jejunum 5 em apart in Ws (n=2) and Cont (n=3). After 4 to 7 days recovery period and 24-36 h fasting, lead wires of transducers were connected to transducers and contractions were recorded in computer through an amplifier and an AID converter. Rats were free of any body restrictions. Results: (I) In Ws sporadic or short c1usters( 1 min) clusters of rhythmic contractions were the dominant pattern in Cont. Migration of those gastric clusters to the duodenum were not clearly observed. (2) In the duodenum and jejunum, MMC patterns were present in 4 out of II Ws and in 6 out of II Cont. The mean duration, interval, and frequency of contractions of phase 3 were 2.3+/-0.6 min, 28.7+1-8.7 min, 29.5+1-2.0 min'! and 4.5+1-0.9 min, 12.3+1-1.6 min, 34.3+1-2.2 min'! in Ws and Cont, respectively. (3) In phase 2 of small intestine, clusters of contractions with various length were the dominant contraction pattern in borh Ws and Cont. (4) Feeding immediately changes motility patterns both in Ws and in Cont. Conclusion: Unlike normal rats, clusters of rhythmic contractions are rare in the stomach of Ws. Although phase 3-like clustered contractions were present in the small intestine in Ws, they are quantitatively different from those in Cont.

Substrate utilization by intestinal mucosal tissue strips from patients with inflammatory bowel disease

A primary metabolic disorder may be present in the colonic mucosa of patients with ulcerative colitis. Preserving the epithelium in situ, we evaluated the metabolism of the colonic mucosa of contro...

Muscarinic M3-like receptors, cyclic AMP and L-type calcium channels are involved in the contractile response to cholinergic agents in gut smooth muscle of the rainbow trout, Oncorhynchus mykiss

Cholinergic signalling in mammalian gut smooth muscle usually involves M3 muscarinic receptors for direct contraction via phospholipase C activation and M2 muscarinic receptors to reduce cyclic AMP levels. However, the proportion of receptor subtypes and second messengers involved varies among tissues and animals and studies in non-mammalian species will provide information on the conservation of pathways and consequently on their importance for signal transduction. In the present study we investigated receptor subtypes, involvement of calcium, phospholipase C and cyclic AMP in the cholinergic contraction of the rainbow trout gut. Intestinal and gastric smooth muscle strip preparations, with the mucosa removed, were used in functional studies, and homogenised strips were used for measurements of cyclic AMP. Calcium-free medium, the L-type calcium-channel inhibitor verapamil, the cyclic AMP-phosphodiesterase inhibitor IBMX + isoprenaline, and the M3-antagonist 4-DAMP methiodide all caused a partial or marked reduction of the response to cholinergic agonists. Neomycin, an inhibitor of phospholipase C, and SKF96365, an inhibitor of receptor-operated calcium channels, had no effect. Carbachol (0.1 mM) reduced the levels of cyclic AMP transiently. It is concluded that the cholinergic signal transduction in rainbow trout gut smooth muscle involves (1) binding to M3-like receptors, (2) a transient reduction in cyclic AMP levels, (3) influx of extracellular calcium, in part through L-type calcium-channels and (4) no involvement of phospholipase C.

Neural mediation of vasoactive intestinal polypeptide inhibitory effect on jejunal alanine absorption.

It was recently shown that vasoactive intestinal polypeptide (VIP) inhibits rat jejunal alanine absorption, an effect that was significantly reduced by vagotomy. This study assesses the role of capsaicin-sensitive primary afferents (CSPA) and the myenteric plexus in the inhibition of rat jejunal alanine absorption by VIP. Continuous intravenous infusion of VIP (11.2 ng . kg-1 . min-1) reduced alanine absorption by 60% in sham control rats and by 20% in rats neonatally treated with capsaicin (P < 0.01). In in vitro experiments, VIP decreased alanine uptake by jejunal strips isolated from sham control rats in a dose-dependent manner. In the presence of 40 nM VIP, alanine uptake by full-thickness jejunal strips was reduced by 54% in sham control rats and by 25% in rats neonatally treated with capsaicin (P < 0.001). On the other hand, VIP reduced alanine uptake by mucosal scrapings by 25% in sham rats compared with 9% reduction in neonatally treated rats. Chemical ablation of the extrinsic innervation and jejunal myenteric plexuses by pretreatment with benzalkonium chloride significantly (P < 0.001) reduced basal alanine absorption and the inhibitory effect of VIP. Moreover, incubation of intestinal strips with tetrodotoxin and atropine reduced significantly (P < 0.05) the inhibitory effect of VIP on alanine absorption. These data suggest that VIP exerts its inhibitory effect on alanine absorption through the CSPA fibers and the myenteric plexus. The neuronal circuitry of this inhibitory process may involve cholinergic muscarinic mechanisms.