Antitransit Effects Research Articles

Cyclic derivatives of morphiceptin possess anti-transit effect in the gastrointestinal tract and alleviate abdominal pain in mice

BackgroundIrritable bowel syndrome (IBS) is a chronic condition with recurring gastrointestinal (GI) symptoms: altered motility and abdominal pain. As endogenous opioid system participates in pain perception and in the control of GI peristalsis, opioids have been proposed as a promising therapy in IBS. In a previous study, we observed that morphiceptin derivative, P-317 (Dmt-cyclo-(d-Lys-Phe-d-Pro-Asp)-NH2), presents promising features to be applied in IBS. In this project, we tested whether modifications in cyclic morphiceptin-based structure: fluorination (compound 1) or peptide bond reduction (compound 2) improve pharmacological effect.MethodsWe evaluated tested derivatives in the mouse GI system under physiological (GI transit) and pathophysiological (castor oil diarrhea, stress-induced hypermotility, visceral pain) conditions.ResultsBoth compounds prolonged GI transit. Compound 1 and P-317 inhibited upper GI transit and motility of the colon; compound 2 remained inactive. Compound 1 and P-317 inhibited hypermotility in stressed mice and delayed the acute diarrhea in comparison to control. Only P-317 exerted antinociceptive effect. None of tested derivatives, similar to P-317, affected locomotor activity.ConclusionsCompound 1 is equally effective as P-317 in the mouse GI tract. The peptide bond reduction decreased the activity of compound 2. Fluorination appears to be an efficient way to increase the effects of morphiceptin analogs in the GI tract.

Mixed MOP/DOP agonist biphalin elicits anti-transit effect in mouse models mimicking diarrhea-predominant irritable bowel syndrome symptoms.

Opioid receptors play a crucial role in the maintenance of homeostasis in the gastrointestinal (GI) tract. The aim of this study was to characterize the effect of biphalin, a mixed MOP/DOP agonist, on mouse intestinal contractility in vitro and GI motility in vivo and in animal models mimicking symptoms of diarrhea-predominant irritable bowel syndrome (IBS-D). The effect of biphalin on muscle contractility in vitro was characterized in the ileum and colon. The anti-transit activity of biphalin in vivo was assessed in the following tests: whole gastrointestinal transit, colonic bead expulsion, fecal pellet output and castor oil-induced diarrhea, alone and in the presence of naloxone, and MOP and DOP antagonists. In vitro, biphalin (10(-10)-10(-6)M) inhibited colonic and ileal smooth muscle contractions in a concentration-dependent, opioid antagonist-reversible manner. In vivo, biphalin at the dose of 5mg/kg ip prolonged the whole GI transit and inhibited colonic bead expulsion. Biphalin reversed hypermotility and exerted anti-diarrheal effect in mouse models mimicking IBS-D symptoms. Biphalin is an interesting template for novel opioid-based agents to be used in therapy of functional GI diseases.

Effect of centrally administered apelin-13 on gastric emptying and gastrointestinal transit in mice

Apelin, as the endogenous ligand for the APJ, regulates many biological functions, including blood pressure, neuroendocrine, drinking behavior, food intake and colonic motility. The present study was designed to investigate the effect of central apelin-13 on gastric emptying and gastrointestinal transit in mice. Intracerebroventricular (i.c.v.) injection of apelin-13 (3 and 10 μg/mouse) decreased gastric emptying rate by 10.9% and 17.1%. This effect was significantly antagonized by the APJ receptor antagonist apelin-13(F13A) and the opioid receptor antagonist naloxone, respectively. However, intraperitoneal (i.p.) injection of apelin-13 (10–100 μg/mouse) did not affect gastric emptying. Apelin-13 (0.3, 1 and 3 μg/mouse, i.c.v.) inhibited gastrointestinal transit by 16.8%, 23.4% and 19.2%. Apelin-13(F13A) and naloxone could also reverse this antitransit effect induced by apelin-13. Taken together, these results suggest that i.c.v. injected apelin-13 inhibits gastric emptying and gastrointestinal transit and it seems that APJ receptor and opioid receptor might be involved in these processes.

The Effects of Tramadol and Fentanyl on Gastrointestinal Motility in Septic Rats

In this study, we investigated the effects of tramadol and fentanyl on gastrointestinal transit (GIT) during acute systemic inflammation in an experimental model of cecal ligation and perforation (CLP). One-hundred-twenty male Swiss-Albino rats were divided randomly into 6 groups: Group I = sham-operated + saline; Group II = sham-operated + fentanyl; Group III = sham-operated + tramadol; Group IV = CLP + saline; Group V = CLP + fentanyl; Group VI = CLP + tramadol. Suspension of charcoal was administered as an intragastric meal to measure the GIT. GIT% (mean +/- sd) were 46.1% +/- 9.8%, 43.2% +/- 9.8%, 45.9% +/- 10.2%, 33.2% +/- 9.2%, 24.9% +/- 4.1%, and 31.8% +/- 8.4% in Groups I, II, III, IV, V, and VI, respectively. GIT% was significantly less in Group V than in Groups I, II, III, and IV (P < 0.05). The Group VI mean value was significantly lower than those of Groups I, II, and III (P < 0.05) but not different from those of Groups IV and V (P > 0.05). The antitransit effect of fentanyl was shown to have increased in the experimental sepsis model, but no decrease in GIT was obtained with tramadol. This was thought to be the result of an associated endogenic opioid system activation and receptor upregulation in sepsis.

Interaction between tramadol and two anti-emetics on nociception and gastrointestinal transit in mice

Background Clinical studies suggest that tramadol-induced analgesia is partially antagonized by ondansetron. Aims To investigate the type of interaction between tramadol and two anti-emetics on antinociception and gastrointestinal transit in mice. Methods We assessed the antinociceptive (acetic acid writhing test, plantar test) and antitransit (charcoal meal) effects of tramadol individually, and combined with ondansetron or droperidol in female Swiss CD-1 mice. Isobolograms and analysis of variance were used to determine the type of interaction. Results In the writhing test, tramadol, ondansetron and droperidol, each induced dose-related inhibition of nociception. The ED 50’s were: tramadol 4.2 ± 0.33 mg kg −1; ondansetron 1.03 ± 0.05 mg kg −1, and droperidol 1.00 ± 0.14 mg kg −1. Dose-response curves were also obtained with tramadol combined with ondansetron or droperidol at 1:1 fixed ratios. The isobolographic analysis demonstrated antagonism for both combinations. In the plantar test, the ED 50 for tramadol was 51.4 ± 2.3 mg kg −1, but no dose-response curves could be obtained with ondansetron or droperidol individually. The interaction was assessed from dose-response curves to tramadol in the presence of a fixed dose of ondansetron (0.1 mg kg −1) or droperidol (0.05 mg kg −1). The results show antagonism between tramadol–ondansetron ( p < 0.05) and no interaction for the tramadol–droperidol combination. Both anti-emetics antagonized the antitransit effects of tramadol. Conclusions The interaction of tramadol with ondansetron or droperidol on antinociception can be antagonistic or additive, depending on the type of stimuli. Both anti-emetics antagonize the anti-transit effects of tramadol. The results demonstrate antagonism between tramadol and the two anti-emetics for analgesia and inhibition of gastrointestinal transit, supporting previous clinical studies.

The involvement of nitric oxide in the enhanced expression of μ‐opioid receptors during intestinal inflammation in mice

Intestinal inflammation enhances the potency of mu-opioid receptor (MOR) agonists inhibiting gastrointestinal transit and increases the expression of MOR in mice intestine. The precise mechanisms implicated in the increased expression of MOR during intestinal inflammation are not known. The aim of the study is to evaluate if nitric oxide released during intestinal inflammation could modulate MOR gene expression and affect gastrointestinal transit. Intestinal inflammation was induced by the intragastric administration of croton oil. In CD-1 mice, with and without inflammation, we evaluated the anti-transit effects of morphine in animals treated with NOS inhibitors (L-NAME and L-NIL) and the intestinal levels of iNOS enzyme mRNA. The anti-transit effects of morphine and the expression of MOR mRNA in the gut of wild-type (WT) and iNOS-/- mice were also assessed. Gastrointestinal transit was measured with charcoal meal and mRNA levels determined by real-time PCR. In CD-1 mice, inflammation induced a 10-fold increase (P<0.0001) in iNOS mRNA levels in the gut. The absence of iNOS gene and treatment of CD-1 mice with L-NAME or L-NIL abolished the increased antitransit effects of morphine observed during inflammation. Moreover, although the basal levels of MOR mRNA were similar in WT and iNOS animals (-/-), intestinal inflammation only increased the MOR expression in the gut of WT (P<0.01) but not in iNOS-/- mice. The results suggest that nitric oxide derived from the increased expression of iNOS is implicated in the enhanced effects of morphine and in the upregulation of MOR gene transcription observed during intestinal inflammation.

Expression of Opioid Receptors During Peripheral Inflammation

Opioid receptors (OR) and their mRNA are present in the central and peripheral nervous system of mammals. In this review we examine the behavioral effects of opioids and the expression of their receptors during peripheral inflammation in two experimental models: the rat paw and the mouse intestine. Inflammation increased the antinociceptive (paw) and the inhibitory effects of opioids in the gut (transit, permeability and plasma extravasation) by interaction with OR located at peripheral sites. Based on agonist efficacy, micro > delta >> kappa-OR mediate the antinociceptive and antitransit effects of opioids during inflammation. Intestinal permeability is modulated by delta = micro >> kappa-OR, while kappa > delta >> micro-OR are involved in the inhibition of plasma extravasation. Intestinal inflammation increased the transcription of micro and delta-OR (but not kappa) genes in the gut, thus explaining the enhanced antitransit and antisecretory effects of micro and delta-OR agonists; however, the increased inhibitory effects of kappa-OR agonists on plasma extravasation could result from post-transcriptional regulation of the receptor. Similarly, the increased expression of peripheral micro-OR observed in the rat paw during inflammation, occurs at post-transcriptional levels and is related to an increased axonal transport from the dorsal root ganglia to peripheral terminals. The sites and mechanisms implicated in the increased transcription of micro and delta-OR during intestinal inflammation are under investigation.

Antisense oligodeoxynucleotides to μ- and δ-opioid receptor mRNA block the enhanced effects of opioids during intestinal inflammation

Intestinal inflammation enhances the inhibitory effects of μ- and δ-opioids in the gut, possibly related to an increased receptor expression. We evaluated the effects of opioids after intraperitoneal administration of antisense oligodeoxynucleotides to μ- and/or δ-opioid receptor mRNA. Inflammation was induced in mice by intragastric administration of croton oil; gastrointestinal transit was assessed with charcoal and permeability with [ 51Cr]etylenediaminetetraacetate ([ 51Cr]EDTA). Baseline values were unaltered after antisense oligodeoxynucleotides. In controls, antisense oligodeoxynucleotides to μ-opioid receptor mRNA decreased the antitransit effects of morphine (27%) and [ N-MePhe 3, d-Pro 4]morphiceptin (PL017) (26%), and the reduction was significantly greater during inflammation (50% and 47%). A similar effect was observed on permeability (control: 41–21% decrease; inflamed: 66–45%). In both assays, antisense oligodeoxynucleotides to δ-opioid receptor mRNA also reduced the effects of [ d-Pen 2,5]enkephalin (DPDPE) in a higher percentage during inflammation (43–32% controls, 60–49% inflamed). We show that antisense oligodeoxynucleotides to μ- and/or δ-opioid receptor mRNA are efficiently blocking the intestinal effects of opioids during inflammation, suggesting that an increased transcription of these receptors in the gut mediates the enhanced effects of opioids during inflammation.

Anti-diarrheal effect of water extract of Evodiae fructus in mice

Our previous study showed that Evodiae fructus (the dried, unripe fruit of Evodia rutaecarpa) has an inhibitory effect on the intestinal transit (anti-transit effect) in mice. In the present study, a water extract of Evodiae fructus was used to examine its effect on castor oil-induced diarrhea and to compare with its anti-transit effect in mice. The results indicated that Evodiae fructus had both anti-transit and anti-diarrheal effects with comparable ID 50 (the dose for 50% inhibition) values of 54±7 and 76±17 mg/kg. The time-courses of Evodiae fructus pretreatment for both anti-transit and anti-diarrheal effects were very similar. Because no significant influences of both nitric oxide (NO) precursor l-arginine (600 mg/kg, i.p.) and NO synthase inhibitor N G-nitro- l-arginine methyl ester (25 mg/kg, i.p.) pretreatment, the NO system was not involved in both the anti-transit and anti-diarrheal effects of Evodiae fructus. Like Evodiae fructus, a muscarinic acetylcholine receptor antagonist atropine inhibited castor oil-induced increase in fecal weight and loss of body weight. However, the potencies or time-courses of atropine pretreatment for both anti-transit and anti-diarrheal effects were different. Furthermore, the anti-diarrheal effect of atropine was independent of its anti-transit effect at the lower dose (0.5 mg/kg, i.p.). Therefore, the action of Evodiae fructus appeared to be something different from atropine, suggesting that an action other than the anti-muscarinic action, as previously proposed for Evodiae fructus, may be involved.

Intestinal inflammation and morphine tolerance alter the interaction between morphine and clonidine on gastrointestinal transit in mice.

Morphine and clonidine show synergy or antagonism inhibiting gastrointestinal transit depending on their proportion and level of effect. Their interaction during morphine tolerance and intestinal inflammation were assessed. Gastrointestinal transit in mice was evaluated with charcoal and antitransit effects expressed as percent mean values +/- SEM. Tolerance was induced with a morphine pellet (75 mg) implanted for 72 h, and inflammation with intragastric croton oil. Dose-response curves for morphine and clonidine alone and combined at a 1:1 potency ratio were obtained, and doses producing a 50% and 60% inhibition were calculated (ED50, ED60). Interaction was established by isobolograms, interaction indexes, and analysis of variance. In naive and tolerant mice, the combination induced linear dose-response curves up to the ED60 and then reached a plateau. In naive mice, ED50 values were as follows: morphine 1.52 +/- 0.15 mg/kg, clonidine 0.09 +/- 0.008 mg/kg, and combined 0.506 +/- 0.084 mg/kg (0.478 +/- 0.08 mg/kg morphine plus 0.028 +/- 0.004 mg/kg clonidine). During tolerance, ED50 values were as follows: morphine 9.73 +/- 0.8 mg/kg, clonidine 0.09 +/- 0.007 mg/kg, combination 0.131 +/- 0.09 mg/kg (morphine 0. 13 +/- 0.09 mg/kg plus clonidine 0.0013 +/- 0.0005 mg/kg). In both groups, the interaction was synergistic up to the ED60 and antagonistic thereafter; synergy was enhanced during tolerance. During inflammation, ED50 values were as follows: morphine 0.17 +/- 0.04 mg/kg, clonidine 0.015 +/- 0.006 mg/kg, combined 0.62 +/- 0.04 mg/kg (morphine 0.568 +/- 0.04 mg/kg plus clonidine 0.052 +/- 0.004 mg/kg); thus, potencies of morphine and clonidine increased 9.3 and 7.1 times, while the combination remained unaltered. Moreover, inflammation transformed synergy into antagonism. The interaction between morphine and clonidine was significantly altered during tolerance and inflammation. During tolerance, synergy was present up to 60% effect and then became antagonistic. Inflammation converted synergy to antagonism. A common pathway in signal transduction could partially explain the results.

Central effect of SNC 80, a selective and systemically active δ-opioid receptor agonist, on gastrointestinal propulsion in the mouse

We investigated the effects of SNC 80 ((+)-4-[ α R)- α-((2 S,5 R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]- N, N-diethylbenzamide), a new highly selective, non-peptidic and systemically active δ-opioid receptor agonist, on gastrointestinal and colonic propulsion in mice. Intraperitoneally (i.p.) SNC 80 (1, 10 and 30 mg/kg) significantly decreased gastrointestinal propulsion measured as transit of an orally administered charcoal meal. Pretreatment with the δ-opioid receptor antagonist, naltrindole (1 mg/kg) subcutaneously (s.c.), with the non-selective opioid antagonist, naloxone (5 mg/kg, s.c.) or the μ 1-opioid receptor antagonist, naloxonazine (10 mg/kg, i.p.), significantly decreased the antitransit effect of SNC 80 but pretreatment with the non-selective opioid antagonist, naloxone methiodide (5 mg/kg, s.c.), a quaternary salt of naloxone that does not cross the blood–brain barrier, did not. SNC 80 (1, 5 and 10 mg/kg, i.p.), produced dose-related inhibition of colonic propulsion measured as the increase in mean expulsion time of a 3 mm glass bead placed in the distal colon. Naloxone (5 mg/kg, s.c.) and naltrindole (1 mg/kg, s.c.), completely antagonized the colonic antipropulsive effect of SNC 80. In contrast, naloxone methiodide (5 mg/kg, s.c.), left the inhibitory effect of i.p. SNC 80 on colonic function unchanged. These results suggest that peripherally injected SNC 80 inhibits gastrointestinal transit and colonic propulsion. It does so mainly through a central mechanism. Although the gastrointestinal antitransit effect of SNC 80 is naltrindole- and naloxonazine-sensitive, we cannot exclude an opioid-independent mechanism. The colonic antipropulsive effect of SNC 80 confirms the inhibitory role of the central δ-opioid receptor system on colonic motility.

Reversal of tolerance to the antitransit effects of morphine during acute intestinal inflammation in mice.

1. The aim of investigation was to establish and compare the reversibility of tolerance to the antitransit effects of morphine by three different procedures: (a) acute inflammation of the gut, (b) lorglumide a cholecystokininA (CCKA) receptor antagonist, or (c) MK-801, an N-methyl-D-aspartate (NMDA) receptor ion channel blocker. The type of interaction between morphine and lorglumide or MK-801 on the inhibition of gastrointestinal transit (GIT) in naive animals was also evaluated. 2. Male Swiss CD-1 mice were implanted with 75 mg of morphine base or placebo pellets. Gastrointestinal transit was assessed with a charcoal meal and results expressed as % inhibition of GIT. Inflammation was induced by the intragastric (p.o.) administration of croton oil (CO), while controls received castor oil (CA) or saline (SS). Morphine was administered by subcutaneous (s.c.) or intracerebroventricular (i.c.v.) injection, to naive and tolerant animals treated with CO, CA or SS. Dose-response curves for s.c. morphine were also performed in naive and tolerant mice receiving 5.2 or 7.4 nmol (s.c.) lorglumide or MK-801, respectively. 3. The ED50 values for inhibition of GIT by s.c. morphine were: 45.9 +/- 2.7 and 250.1 +/- 3.1 nmol in naive and tolerant animals, respectively, demonstrating a five fold decrease in the potency of morphine. In naive animals, inflammation (CO) decreased the ED50 of morphine three times (14.4 +/- 2.2 nmol). However, no tolerance to s.c. morphine (ED50 16.4 +/- 2.6 nmol) was manifested during intestinal inflammation. After i.c.v. administration, a similar degree of tolerance to morphine was observed (4.8 fold decrease in potency). Intestinal inflammation had no effect on the ED50 values of i.c.v. morphine in naive and tolerant animals, showing that reversal of tolerance is related to local mechanism/s. Mean values for intestinal pH were 6.9 +/- 0.04 and 6.2 +/- 0.04 in SS and CO treated mice, respectively. In addition, morphine was 74 times more potent by the i.c.v. than by the s.c. route (naive-SS). 4. Morphine and lorglumide interacted synergistically in naive animals; in addition, the administration of lorglumide reversed tolerance to s.c. morphine. No interaction (additivity) was observed in naive animals when morphine and MK-801 were administered in combination. However, the drug completely reversed tolerance to the antitransit effects of morphine. 5. The present investigation shows that acute inflammation of the gut reverses tolerance to the antitransit effects of s.c. morphine by a peripheral mechanism. Qualitatively similar results were obtained after the administration of lorglumide or MK-801. Our results suggest that a local decrease in pH could play an important role during inflammation, while antagonism of endogenous compensatory systems would explain the reversal of tolerance induced by lorglumide or MK-801.

81 EFFICACY AND TOLERANCE OF ACETORPHAN IN INFANT ACUTE DIARRHEA. A MULTICENTRIC DOUBLE BLIND STUDY.

Acetorphan A is an enkephalinase inhibitor efficient in adult acute diarrhea via a purely instestinal antisecretory mechanism without associated antitransit effect. The efficacy of A (1.5 mg/kg TID) versus placebo P was compared in 172 infants (1.6 mths - 3.6 yrs; mean 13 mths) with severe acute diarrhea < 3 days. Other treatments were excluded except oral rehydratation solution ORS ad libitum, normal feeding for age and paracetamol (60 mg/kg/d) in case of fever. IV rehydrated patients (IRP) were included at the end of IR if they responded to the inclusion criteria. Data were analyzed by Student t test or non parametric Wilcoxon test. There was no difference between A and P groups for age, duration of diarrhea, number of stools, IRP,% of dehydrated infants, viral or bacterial infection before inclusion. A highly significant difference was observed in group A compared to P on stool output (g/kg) during the first 24 and 48h of treatment (20 ± 3.3 A vs 45 ± 6.2 P, p = 0.004; 25 ± 3.8 A vs 76 ± 11 P, p = 0.002) the difference was even higher between groups A and P with rotavirus (46% of acute diarrhea) regarding stool output (27 ± 7 A vs 102 ± 18 P at 48h, p = 0.001). A significative difference was also observed in duration of liquid stool (6.9 h A vs 36 h P, p = 0.02) and treatment duration (35 ± 4.3 h A vs 49 ± 4.6 h P, p = 0.02). Suspicion of intolerance (mild symptoms) was found with the same frequency in A and P groups (10.1% A vs 10.9% P). This study demonstrates for the first time the efficacy and safety of Acetorphan as an adjuvant therapy to ORS in the treatment of severe acute diarrhea in infants.

Pertussis and cholera toxins modulate κ-opioid receptor agonists-induced hypothermia and gut inhibition

In mice pretreated intracerebroventricularly (i.c.v.) with either saline (1 μl/mouse), pertussis (1 μg/mouse) or cholera (2.5 μg/mouse) toxins, effect of κ-opioid receptor agonists on the colonic temperature and charcoal meal transit time were assessed. The κ-opioid receptor agonist, trans-(+)-3,4-dichloro- N-methyl-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide methane sulfonate hydrate (U-50488H, 50, 100 and 200 μg/mouse, i.c.v.) produced dose dependent hypothermia. Pertussis toxin pretreatment (72 and/or 144 h before) antagonized ( P < 0.05) the hypothermic effect of U-50488H (100 μg/mouse) and (±)- trans- N-methyl- N-[2-(1-pyrrolidinyl)cyclohexyl[benz[b]-thio-phene-4-acetamide (PD 117302, 30 μg/mouse). In contrast, cholera toxin pretreatment (48 and/or 96 h before) did not antagonize the hypothermic effect of the κ-opioid receptor agonists. Moreover, both i.c.v. and intrathecal (i.t.) administration of κ-opioid receptor agonists, U-50488H, {[5 R-(5 α,7 α,8 β)]-(±)- N-methyl- N-[7-(1-pyrrolidinyl)-1-oxaspirol[4,5]dec-8-yl]-benzeneacetamide} (U-65593) and PD 117302, produced dose dependent inhibition of the charcoal meal transit. Cholera toxin pretreatment (48 and 96 h before) augmented ( P < 0.05) the antitransit effect of i.c.v. administered U-50488H (100 μg/mouse), U-69593 (100 μg/mouse) and PD 117302 (50 μg/mouse). However, pertussis toxin previous pretreatment did not affect the gastrointestinal inhibitory effect of the κ-opioid receptors agonists. The present results extend our previous results on the affect of κ-selective agonists on gastrointestinal motility and indicate, like the prototype opiate agonist morphine, κ-opioid receptor agonists are effective in inhibiting the gastrointestinal motility when administered either by intrathecal or intracerebroventricular routes. Thus, for the antitransit effect of κ-opioid receptor agonists, both spinal and supra spinal site could be implicated. Furthermore, these results also suggest that pertussis and cholera toxin-sensitive transducer G-proteins may be involved in the central κ-opioid receptor mediated hypothermia and gastrointestinal transit inhibition respectively.

The Role of Dopamine (D 2), α and β-adrenoceptor Receptors in the Decrease in Gastrointestinal Transit Induced by Dopamine and Dopamine-Related Drugs in the Rat

This study analyses the effects of dopamine receptor agonists and antagonists on rat gastrointestinal transit (GIT) in an attempt to identify the mechanisms involved. Dopamine (DA), apomorphine, quinpirole, bromocriptine and fenoldopam were given by subcutaneous (s.c.), intrathecal (i.t.), intracisternal (i.c.) and/or intraperitoneal (i.p.) routes. In general, DA (200 μg, i.t.), apomorphine (3, 5 and 10mg/kg, s.c.; or 10, 30 and 100 μg, i.t.), and bromocriptine (1, 5 and 10 mg/kg, s.c.) elicited decreases in gastrointestinal transit which were significantly antagonized by the D 2 receptor antagonists domperidone or alizapride (both 5 mg/kg, s.c.), but remained unaffected by the D 1 receptor antagonist SCH 23390 (5 mg/kg, s.c.). Similarly, DA (50, 100 and 200 μg, i.c.) and apomorphine (12 and 50 μg; i.c.) produced dose-dependent decreases in gastrointestinal transit amenable to blockade by the classical DA receptor antagonist haloperidol (10 μg, i.c.). The responses to apomorphine (3, 5 and 10 mg/kg, s.c.) were unaltered by 6-hydroxydopamine (100 mg/kg, i.p.)-induced sympathectomy but were antagonized by both propranolol (1 mg/kg, s.c.) and phentolamine (5 mg/kg, s.c.). Significantly, after bilateral (cervical) vagotomy, gastrointestinal transit was markedly reduced, but apomorphine (5 mg/kg, s.c.) apparently further reduced gastrointestinal transit. The D 1 agonists fenoldopam (5, 10 and 20 mg/kg, s.c.) significantly reduced GIT. Fenoldopam-induced antitransit effects were markedly modified by the D 1 receptor antagonist, SCH 23390 (5 mg/kg, s.c.); only the response induced by 5 mg/kg of fenoldopam was apparently antagonized by SCH 23390. The mixed D 2 and D 3 receptor agonist quinpirole (4 and 8 mg/kg, s.c.; or 8 mg/kg, i.p.; 200 μg, i.t.) did mimic DA eliciting significant reductions in gastrointestinal transit which, however, were not antagonized by domperidone (5 mg/kg, s.c.). Taken together, the present results support the contention that the decrease in rat gastrointestinal transit induced by DA and apomorphine may be mediated by an interaction with central and/or peripheral D 2 receptors. The presence of dopamine receptors (D 2) in the alimentary canal are strengthened by antitransit effect of fenoldopam and bromocriptine in the gastrointestinal tract.

&amp;kappa;-Opiate Agonist-Induced Inhibition of Gastrointestinal Transit in Different Strains of Mice

The effects of kappa-opiate agonists on gastrointestinal motility was assessed in Swiss Webster, C57BL/6, BALB/c and DBA/2 strains of mice. The kappa-agonists, PD 117302, U-69593 and U-50488H (3 mg kg-1), were injected subcutaneously and the distance travelled by a charcoal meal in the gastrointestinal tract was measured. All kappa-agonists induced significant inhibition of charcoal meal transit; however, there were significant strain differences in the antitransit effect. It is concluded that kappa-receptors are involved in the inhibition of gastrointestinal transit and that the negative data reported in the literature may be due to a genotype-dependent effect of kappa-agonists.

Streptozotocin‐diabetes attenuates α2‐adrenoceptor agonist‐induced delay in small intestinal transit in mice*

1. The effect of alpha 2-adrenoceptor agonists on gastrointestinal motility was assessed in normoglycaemic and streptozotocin-diabetic mice. 2. The alpha 2-adrenoceptor agonists used were: clonidine (0.1, 0.3 and 1 mg kg-1, azepexole (10, 20 and 40 mg kg-1), tizanidine (1, 3 and 10 mg kg-1) and ST-91 (10, 20 and 30 mg kg-1). 3. Acute hyperglycaemia was induced by D-(+)-glucose (5 g kg-1) and chronic hyperglycaemia by streptozotocin (200 mg kg-1) injection. 4. The gut motility was quantitated using the charcoal meal test. 5. The results indicate that in normoglycaemic and acutely hyperglycaemic mice, all of the alpha 2-adrenoceptor agonists used produced significant inhibition of meal transit. 6. However, in streptozotocin-diabetic mice, the anti-transit effect of alpha 2-adrenoceptor agonists was attenuated. 7. Since streptozotocin-induced diabetes but not acute hyperglycaemia was associated with the attenuation of anti-transit effect, elevated blood sugar is not the mechanism for the observed effect. 8. As with groups treated with clonidine, azepexole or tizanidine, the anti-transit effect of a peripherally acting alpha 2-adrenoceptor agonist, ST-91, was attenuated in streptozotocin-diabetic mice. This suggests the involvement of peripheral mechanism(s) in attenuating the anti-transit effect of alpha 2-adrenoceptor agonists. 9. These results identify the need for critical evaluation of the role and efficacy of alpha 2-adrenoceptor agonists in the therapeutic management of diabetic diarrhoea.

Pertussis toxin modifies the effect of central morphine on rat intestinal motility

To find whether the antipropulsive effect of morphine administered intracerebroventricularly (i.c.v.) depends on a G-protein-mediated mechanism, we studied the effect of i.c.v. pertussis toxin (PTX) pretreatment on morphine-induced inhibition of intestinal motility. The influence of PTX was evaluated on intestinal transit (charcoal meal test) and by monitoring of intestinal myoelectrical activity. The antitransit effect of morphine (10 μg/rat) was antagonized by about 70% 3, 6, 9 and 12 days after PTX pretreatment (1 μg/rat) and it was partially restored after 25 days. I.c.v. morphine abolished the regular appearance of the myoelectric migrating complex (MMC) recorded in the rat jejunum and this effect was completely antagonized by PTX pretreatment. When orphine was injected 25 days after PTX, it significantly reduced MMC frequency, confirming the partial recovery seen in the transit experiments. The pertussis toxin-catalyzed ADP ribosylation of a 39–41 kDa substrate in membranes prepared from hypothalamus and midbrain of rats injected with toxin 6 days before was strongly reduced as compared to the controls. On the contrary, after 25 days, ADP ribosylation was the same in treated and control rats. Thus the antipropulsive effect of central morphine could be initiated at receptor sites which interact with G-protein substrates of pertussis toxin.

Hyperglycaemia as a factor affecting κ-opiate agonist-induced inhibition of the gastrointestinal transit in mice

The effects of highly selective kappa-opiate agonists were assessed on the gastrointestinal motility in normoglycaemic and hyperglycaemic conditions in mice. Chronic hyperglycaemia was induced by streptozocin injection (200 mg kg-1 i.p.), 7-8 days before the experiment. Acute hyperglycaemia was induced by glucose injection (5 g kg-1 i.p.) at the time of opiate administration. The kappa-opiate agonists, U-50488H and U-69593 (1, 3 and 10 mg kg-1) were injected (i.p.) just before the charcoal meal. The animals were killed 45 min later and the distance travelled by the test meal was measured. In the normoglycaemic mice, both kappa-agonists significantly (P less than 0.05) inhibited the meal transit and this effect was significantly (P less than 0.05) augmented in acute hyperglycaemic animals. However, in chronic hyperglycaemic animals U-50488H failed to inhibit the charcoal meal transit, while U-69593 produced anti-transit effect comparable to that observed in normoglycaemic mice. These results demonstrate that kappa-opiate agonists produce anti-transit effects in mice that these effects are enhanced during acute hyperglycaemia. The disparity of anti-transit effects of kappa-opiate agonists in acute vs chronic hyperglycaemia supports the hypothesis that elevated glucose levels are not the primary mechanism for the altered response to opiates observed in the experimental models of diabetes.

Sites of clonidine action to inhibit gut propulsion in mice: Demonstration of a central component

The role of central (supraspinal and spinal) and peripheral α-adrenoceptors in the regulation of gastrointestinal propulsion in the mouse was studied using clonidine, an α2-adrenoceptor agonist. Clonidine produced a dose-dependent inhibition of propulsion when given intracerebroventricularly, intrathecally, or subcutaneously, but was most potent when given intracerebroventricularly. The antitransit effects of centrally given clonidine were antagonized by intracerebroventricular (i.c.v.) yohimbine, but higher doses were required when this antagonist was given peripherally. Whereas i.c.v. and s.c. administration of clonidine were effective in inhibiting gut transit in spinally transected mice, intrathecal (i.th.) administration of this agonist was not. A supraspinal site of clonidine action is suggested based upon (a) the higher central to peripheral potency of clonidine; (b) the greater potency of i.c.v., compared with s.c., administration of yohimbine in blocking i.c.v. clonidine; (c) the lack of effect of i.th. administration of clonidine in spinally transected mice; and (d) the reduced potency of i.c.v., but not s.c., administration of clonidine in spinally transected mice. Additionally, a peripheral site of clonidine action is suggested by (a) the lower potency of i.c.v. yohimbine in blocking s.c., compared with i.c.v., clonidine; (b) the lower potency of i.c.v. yohimbine in blocking i.c.v. clonidine in transected mice (compared with normal mice); (c) the equal potency of s.c. clonidine in slowing propulsion in normal and spinally transected mice; and (d) the equal potency of i.c.v. yohimbine in blocking s.c. clonidine in normal and spinally transected mice. These data in mice would thus support the concept that normal (peripheral) therapeutic administration of clonidine would affect gut motor function by interactions within the brain and directly at the level of the gut.