A comparison of the central gastrointestinal antitransit effects of morphine and bombesin in the mouse

The gastrointestinal motor effects of centrally-given morphine and bombesin were compared in mice. Both compounds produced a dose-related decrease in the propulsion of a marker along the gut when given by the intracerebroventricular (i.c.v.) or intrathecal (i.th.) routes. Co-administration of the same compound by both routes was found to produce a marked increase in potency for morphine, but only a slight increase in potency for bombesin. Isobolographic analysis of the gut effects of these compounds revealed a multiplicative brain-spinal cord interaction for morphine, but an additive interaction for bombesin. These results are consistent with the interpretation that morphine can act at either the level of the brain or the spinal cord, activating independent pathways which ultimately converge to alter gut propulsion. In contrast, spinal bombesin requires communication to supraspinal sites in order for its gut effects to occur, suggesting activation of a common outflow pathway from the central nervous system.     

Pituitary-adrenal mediation of bombesin-induced inhibition of gastrointestinal transit in rats

Centrally administered bombesin (0.1-3.5 micrograms, i.c.v.) inhibits gastrointestinal transit of a charcoal meal in a dose-related manner in rats. The roles of pituitary and adrenal glands in the mediation of this effect were assessed. The inhibition of gastrointestinal transit associated with bombesin (0.5 microgram, i.c.v.) was prevented by either hypophysectomy or adrenalectomy. Bombesin-induced inhibition of gastrointestinal transit is therefore mediated through the pituitary-adrenal axis. This is in contrast to bombesin-induced scratching and inhibition of gastric acid secretion which are not markedly influenced by either hypophysectomy or adrenalectomy.     

Intrathecal bombesin-induced inhibition of gastrointestinal transit: requirement for an intact pituitary-adrenal axis

The role of the pituitary-adrenal axis in the inhibition of gastrointestinal transit caused by intrathecal administration of bombesin was examined. Bombesin (0.3-10 micrograms) slowed transit by this route in a dose-related manner. Either hypophysectomy or adrenalectomy prevented the inhibition of gastrointestinal transit associated with bombesin (10 micrograms, i.th.). The inhibitory gut effects of this peptide were not prevented in sham-operated rats. Intrathecal bombesin-induced inhibition of gastrointestinal transit is thus dependent upon an intact pituitary-adrenal axis.     

Regulation of gastrointestinal function by multiple opioid receptors

Agonist and antagonist drugs possessing selectivity for individual types of opioid receptors have been employed in vitro and in vivo to determine the mechanisms by which opioids regulate gastrointestinal functions. Selective mu opioid agonists given by intracerebroventricular (i.c.v.) injection, by intrathecal (i.t.) injection, or by peripheral (s.c. or i.v.) injection in rats or mice decreased gastrointestinal transit and motility, inhibited gastric secretion, and suppressed experimentally-induced diarrhea. Selective delta agonists, by contrast, inhibited gastrointestinal transit after i.t., but not after i.c.v. or s.c. administration. Delta agonists also did not alter gastric secretion after i.c.v. or s.c. injection. However, delta agonists exhibited antidiarrheal effects after i.c.v., i.t., or s.c. administration. Kappa agonists given i.c.v. had no effect on gastrointestinal transit in rats or mice or on gastric secretion in rats, but exhibited antidiarrheal effects in mice. The kappa agonist U-50, 488H given peripherally increased gastric acid secretion. Different types of opioid receptors in different anatomical sites influence differently gastrointestinal motility and propulsion, gastric secretion, and mucosal transport. Brain, spinal cord, enteric neural and smooth muscle opioid receptors represent chemosensitive sites for regulation of gastrointestinal function.     

Effects of bombesin on behavior

This report describes the influence of bombesin on the gross behavior of goldfish, frogs, mice, rats, guinea pigs, rabbits, chicks, pigeons and monkeys. Goldfish, frogs, chicks and pigeons were overtly unaffected by bombesin given centrally and/or peripherally. Mice, rats, guinea pigs, rabbits and monkeys responded quickly to intracerebroventricular (i.c.v.) and/or intrathecal (i.th.) administration of bombesin by displaying a range of behaviors suggestive of altered skin sensation. In mice, bombesin was essentially equipotent as a scratch inducer by i.c.v. and i.th. routes (A50 = 0.010-0.019 microgram) but 6800 times less potent i.p. In rats, bombesin-induced grooming and scratching behaviors were shown to be qualitatively different from those associated with ACTH-(1-24) and thyrotropin releasing hormone. Spantide and [D-Arg1, D-Pro2, D-Trp7,9, Leu11]substance P (both at 0.20, 0.50 and 0.80 microgram i.c.v.), two proposed bombesin receptor antagonists, did not markedly influence bombesin-induced scratching or hypothermia in rats.     

Intracerebroventricular administration of neuronostatin delays gastric emptying and gastrointestinal transit in mice

Neuronostatin is a 13-amino acid amidated peptide widely distributed in various organs including gastrointestinal tract. However, the effect of neuronostatin on gastrointestinal motility has not been well characterized. In the present work, effects of central administration of neuronostatin on gastric emptying and gastrointestinal transit were investigated. The results indicated that intracerebroventricular (i.c.v.) administration of neuronostatin (1, 5, 10 or 20nmol/mouse) delayed gastric emptying and gastrointestinal transit in a dose-related manner in mice. The effects were significantly reversed by melanocortin 3/4 receptor antagonist SHU9119 or classical opioid receptor antagonist naloxone, suggesting that the central melanocortin system and opioid system may be involved in the gastrointestinal effects elicited by i.c.v. administration of neuronostatin. In addition, we found that C-terminal amidation modification of neuronostatin is essential to exert its gastrointestinal effects. These results indicated that neuronostatin may play an important role in regulating gastrointestinal function.     

Peripheral versus central components of the effects of dermorphin on intestinal motility in the fed rat

The effects of subcutaneous (s.c.), intraperitoneal (i.p.), intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of dermorphin (DER) on intestinal myoelectrical activity were examined in fed rats with chronically implanted electrodes on the small and large bowel. DER s.c. restored the 'fasting' pattern of duodenal activity, i.e., the migrating myoelectric complex (MMC), corresponding to an inhibition by about 40% of the fed pattern for 120 min at a dose as small as 0.5 nM per rat. DER i.p. strongly inhibited (about 65%) the fed pattern for 120 min. A fasting pattern lasting 80 min, or a marked inhibition lasting 150 min were recorded after 0.5 nM DER i.t. or i.c.v., respectively. On the contrary, the colonic pattern of activity was inhibited by DER whatever the route used, although the duration of inhibition was different from each other. For both the small and large intestine, similar doses of DER were more efficient by i.c.v. than by i.t. routes, and by i.p. than by s.c. routes. A plurality of sites of action is suggested, including local receptors which are activated, particularly at the duodenal level by i.p. DER (0.5 nM). The supraspinal component of the immediate effects of i.c.v. DER (0.1 nM) were demonstrated by a preferential effect on the colon that was even more intense than after i.t. DER.     

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.     

Antinociception produced by systemic, spinal and supraspinal administration of amiloride in mice.

This study investigates the antinociceptive and antihyperalgesic action caused by i.p., i.t. or i.c.v. injections of amiloride when assessed against formalin, capsaicin-induced licking, acetic acid-induced writhing and glutamate-induced hyperalgesia in mice. The systemic, spinal and supraspinal administration of amiloride causes dose-related antinociception when assessed against acetic acid-induced writhing, formalin and capsaicin-induced licking. In addition, amiloride administered by the same routes produced graded inhibition of glutamate-induced hyperalgesia in mice. Together, these results suggest, that amiloride or its derivatives may constitute a strategy for the development of new antinociceptive drugs.     

Endogenous nitric oxide modulates morphine-induced constipation.

Administration of morphine in mice causes inhibition of the gastrointestinal transit of a charcoal meal. Morphine-induced constipation in mice seems to depend predominantly on action(s) on the central nervous system since N-methyl morphine, a quaternary derivative, inhibits intestinal transit only when administered intracerebroventricularly (i.c.v.). L- but not D-arginine, given intraperitoneally, reversed the constipation induced by both morphine and its quaternary analogue. L-arginine was ineffective when given i.c.v. and did not reverse atropine-induced constipation. These results suggest that L-arginine preferentially modulates opioid-induced constipation through a stereospecific and peripheral action(s). It is possible that the effect of L-arginine is achieved by increasing the amount of nitric oxide released by non-adrenergic, non-cholinergic nerves in the gut. Thus, L-arginine may represent a useful agent for the treatment of undesirable constipation associated with the use of narcotic analgesics.     

Prostaglandin stimulation of gastrointestinal transit in post-operative ileus rats

The prostaglandins PGF_2α, PGE₂ and 16,16-dimethyl PGE₂, when administered intravenously, orally, subcutaneously or intraduodenally to laparotomized rats, decreased gastric emptying, small intestinal transit and colonic transit as compared to unoperated controls. All three prostaglandins increased colonic transit above that found with unoperated controls. This activity was independent of small intestinal fluid accumulation (i.e., enteropooling) since ligating the ileal-cecal junction had no effect on colonic transit. Small intestinal transit was increased, but not normalized, by PGE₂ and 16,16-dimethyl PGE₂. 16,16-Dimethyl PGE₂ completely restored gastric emptying when given intravenously to laparotomized rats at doses greater than 5.0 μg/kg. This effect on gastric emptying lasted approximately 4 hrs. Thus, 16,16-dimethyl PGE₂, when given intravenously, normalized gastric emptying, significantly increased small intestinal transit, and made the colon hypermotile. Prostaglandins may be beneficial in the treatment of post-operative ileus and other conditions of sluggish gastrointestinal propulsion.     

In vivo modulation of intestinal motility and sites of opioid effects in the rat

The effects of subcutaneous (s.c.), intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of fentanyl and D-Ala2,D-Leu5-enkephalin (DADLE) on intestinal myoelectrical activity were examined in fed rats. In rats with chronically implanted electrodes on the small and large bowel, i.c.v. fentanyl and DADLE restored the 'fasted' pattern of duodenal activity, i.e. the migrating myoelectric complex (MMC) for 8-12 h at a dose as small as 1 nM/kg. In addition, the colonic pattern of activity evaluated as the number of migrating spike bursts (MSB) per min was nearly halved for 1 h following i.c.v. fentanyl (10 nM/kg). Pretreatment with naloxone, but not methylnaloxone prevented these effects on the small and large bowel. Fentanyl (100 nM/kg s.c.) significantly reduced small and large bowel motility, but DADLE (100 nM/kg s.c.) which induced a transient 'fasted pattern' on the duodenum strongly stimulated colonic motor activity. Pretreatment with methylnaloxone prevented the inhibitory effects of s.c. fentanyl but not the colonic excitatory effects of DADLE. The i.t. administration of fentanyl and DADLE did not modify the activity pattern of the bowel. Again, i.t. DADLE stimulated the colon, even after methylnaloxone treatment and at doses 100 times less than the smallest active s.c. dose. The long-lasting changes in small bowel motility and the important delay following DADLE and fentanyl i.c.v., reinforces the hypothesis of a central opioid control of the gastrointestinal motor pattern with possible involvement of released substances.(ABSTRACT TRUNCATED AT 250 WORDS)     

Calcitonin gene-related peptide: Brain and spinal action on intestinal motility

The effects of intracerebroventricular (ICV) and intrathecal (IT) administration of calcitonin gene-related peptide (CGRP) on intestinal motility were examined in conscious rats chronically fitted with intraparietal electrodes in the duodeno-jejunum and a cannula in a cerebral lateral ventricle or catheter in the subarachnoid space. ICV administration of CGRP (0.5–10 μg) restores the fasted pattern of intestinal motility in fed rats in a dose-related manner. Intrathecal administration of CGRP or calcitonin also induces fasted pattern but after a 30 min delay. These effects persisted after transection of the spinal cord and no change in intestinal motility appeared after intravenous administration of CGRP at a dose effective when given IT. This study suggests that CGRP, as calcitonin, has a neuromodulatory role in the control of intestinal motility at both brain and spinal cord levels.     

Spinal δ2 but not δ1 opioid receptors are involved in intracereboventricular β-endorphin-induced antinociception in the mouse

The antinociception induced by β-endorphin given intracerebroventricularly (i.c.v.) has been previously demonstrated to be mediated by the release of Met-enkephalin and subsequent stimulation of δ receptors in the spinal cord for antinociception. The present study was designed to determine what type of opioid receptor, δ1 or δ2, in the spinal cord is involved in i.c.v. β-endorphin-induced antinociception. Antinociception was assessed by the tail-flick test in male ICR mice. NTB (0.2–20 nmol) and NTI0 (0.22–2.2 nmol),selective δ2 receptor antagonists, given intrathecally (i.t.) dose-dependently attenuated i.c.v. β-endorphin-induced inhibition of the tail-flick response. On the other hand, BNTX (0.02–2.2 nmol), a selective δ1 receptor antagonist, given i.t., did not block i.c.v. β-endorphin-induced antinociception. The tail-flick inhibition induced by DAMGO, a μ receptor agonist, or U50,488H, a к receptor agonist, was not blocked by i.t. BNTX, NTB or NTI. It is concluded that δ2 but not δ1 receptors in the spinal cord are involved in i.c.v. β-endorphin-induced antinociception.     

Centrally administered bombesin modulates gastric motility

Intracerebroventricular bombesin alters arterial pressure and gastrointestinal transit in rats. In order to evaluate the influence of bombesin on arterial and gastric intraluminal pressure in a specific site in the central nervous system, we microinjected bombesin into the medial subnucleus of the nucleus tractus solitarius (mNTS) in 28 rats anesthetized with choralose. Bombesin (78 pmole in 25 nl), but not vehicle, caused an increase of tonic gastric intraluminal pressure (2.6 +/- 0.5 cm H2O) and of phasic gastric intraluminal pressures but did not acutely alter arterial pressure. The effect on tonic and phasic gastric intraluminal pressure was dose-dependent. The threshold dose was 7.8 pmole. Intravenous bombesin caused a similar dose-dependent rise in tonic gastric intraluminal pressure but did not significantly change the mean amplitude of phasic gastric intraluminal pressures. Transection of the cervical spinal cord and both cervical vagus nerves blocked the effect of centrally but not peripherally administered bombesin. We conclude that bombesin microinjected into the mNTS does not influence arterial pressure but does raise tonic and phasic gastric intraluminal pressures. Bombesin may act in the NTS as a central modulator of gastric motility.     

Nociceptin and dynorphin A(1-17) produce antianalgesia through independent systems in mice

The administration of dynorphin A(1-17), Dyn, intrathecally (i.t.) or of nociceptin, intracerebroventricularly (i.c.v.) produces antianalgesic actions against i.t. morphine in the tail flick test in mice. The antianalgesic action of nociceptin is mediated by spinal PGE2 and attenuated by i.t. PGD2 or indomethacin. The Dyn response is mediated by release of IL1beta in the spinal cord to activate an ascending pathway to the brain and in turn releases IL1beta in the brain which activates a descending pathway to the spinal cord. The present work investigated the possibility that the action of IL1beta in the Dyn system might release prostaglandins so that the Dyn and nociceptin antianalgesic systems would overlap at these points. The results indicated that in the Dyn system neither the IL1beta in the spinal cord or brain implicated prostaglandin release because i.t. and i.c.v. PGD2 and indomethacin did not affect Dyn-induced antianalgesia. In addition, nociceptin-induced antianalgesia did not involve components in the Dyn system. Thus, the Dyn and nociceptin antianalgesic systems did not overlap and each were independent systems.     

In vitro and in vivo opioid activity of [DPro(6)]dermorphin,a new dermorphin analogue

To study the effects of inducing stereo-chemical modifications in the structure of dermorphin (DM) so as to improve its mu-opioid receptor affinity and its resistance to C-terminal enzymatic degradation, in the Institute of Molecular Genetics of Moscow, we synthesized a new DM analogue ([DPro(6)]DM) and analyzed the changes induced in the biological activities of DM by substituting the Pro(6) residue with DPro(6). We compared the activity of the new DM analogue and DM in in vitro assays and in in vivo tests of analgesia, thermoregulation, heart rate recordings, and gastrointestinal motility in rats. In the in vitro tests, guinea pig ileum (GPI) and mouse vas deferens (MVD), although the opioid activities of [DPro(6)]DM indicated that the peptide was always less potent than DM, its lower IC(50) ratios (mu/delta) showed that it had higher mu-opioid receptor selectivity. In the in vivo analgesic test, [DPro(6)]DM, when injected intraperitoneally (i.p.) (0.5-5 and 10mg/kg) in rats, had the same antinociceptive efficacy as DM and when injected intranasally (i.n.) (0.005 and 0.02 mg/kg) it induced a more stable and long-lasting analgesia than DM (the AUC was about 91% higher for [DPro(6)]DM than for DM). Moreover, these data confirm that the intranasal route is advantageous for peripheral drug administration. In the heart rate study, [DPro(6)]DM and DM (0.5mg/kg, i.p.), induced a similar, weak bradycardia. The only difference was that [DPro(6)]DM induced a longer-lasting effect than DM. Conversely, in body temperature regulation [DPro(6)]DM induced weaker inhibitory activity than DM (56% of the DM-induced response); it did so only in a cold environment and at the maximal used dose (0.5mg/kg, i.p.) without inducing vasomotor effects. In the gastrointestinal study, [DPro(6)]DM and DM (0.005, 0.05, and 0.5mg/kg, i.p.) significantly slowed upper gastrointestinal transit of a charcoal meal and inhibited colonic propulsion. Comparison of the ED(50) values of [DPro(6)]DM (0.03 mg/kg) and DM (0.009 mg/kg) showed that the DM analogue was about three times less potent than DM in slowing gastrointestinal and colonic transit. In conclusion, all these data overall suggest that structural maneuvering in the Pro(6)-residue of the DM molecule changes its affinity for mu-opioid receptor subtypes and confirms the usefulness of experimental studies involving structural modifications in obtaining new therapeutic agents.     

Centrally-mediated antinociceptive action of RWJ-22757 (formerly McN-5195): involvement of spinal descending inhibitory pathways (an hypothesis)

The present studies were an attempt to examine the mechanism of action of the novel antinociceptive compound RWJ-22757, (+/-)-trans-3-(2-bromophenyl)-octahydroindolizine (McN-5195). Intracerebroventricular (i.c.v.) administration of RWJ-22757 produced dose-related antinociception in the mouse tail-flick (48 degrees C) and rat hot-plate (51 degrees C) tests (ED50 = 243.3 and 261.3 micrograms, respectively). In contrast, intrathecal (i.t.) administration was without effect. The antinociception produced by peripherally (i.p.) or centrally (i.c.v.) administered RWJ-22757 was attenuated by i.t. administration of 2 micrograms phentolamine, 5 micrograms yohimbine, or 10 micrograms methysergide. I.t. administration of naloxone, at a dose (0.5 micrograms) that significantly attenuated the antinociceptive effects of peripherally or centrally administered morphine, had no effect on RWJ-22757-induced antinociception. We conclude from these results, coupled with the overall pharmacological and neurochemical profile of RWJ-22757, that the data are consistent with the hypothesis that RWJ-22757 produces antinociception predominantly at a site or sites located supraspinally with little or no activity at the spinal level and that RWJ-22757 activates adrenergic and serotonergic descending inhibitory pathways, increasing the tonic activity of endogenous antinociceptive systems.     

Slowing intestinal transit by PYY depends on serotonergic and opioid pathways

Slowing of intestinal transit by fat is abolished by immunoneutralization of peptide YY (PYY), demonstrating a key role for this gut peptide. How PYY slows intestinal transit is not known. We tested the hypothesis that the slowing of intestinal transit by PYY may depend on an ondansetron-sensitive serotonergic pathway and a naloxone-sensitive opioid pathway. In a fistulated dog model, occluding Foley catheters were used to compartmentalize the small intestine into proximal (between fistulas) and distal (beyond midgut fistula) half of gut. Buffer (pH 7.0) was perfused into both proximal and distal gut, and PYY was delivered intravenously. Ondansetron or naloxone was mixed with buffer and delivered into either the proximal or distal half of gut. Intestinal transit was measured across the proximal half of the gut. The slowing of intestinal transit by PYY was abolished when either ondansetron or naloxone was delivered into the proximal, but not the distal gut, to localize the two pathways to the efferent limb of the slowing response. In addition, 5-HT slows intestinal transit with marker recovery decreased from 76.2 +/- 3.6% (control) to 33.5 +/- 2.4% (5-HT) (P < 0.0001) but was reversed by naloxone delivered into the proximal gut with marker recovery increased to 79.9 +/- 7.2% (P < 0.0005). We conclude that the slowing of intestinal transit by PYY depends on serotonergic neurotransmission via an opioid pathway.     

Interleukin-6 is a centrally acting endogenous pyrogen in the rat.

Intracerebroventricular (i.c.v.) injection of human recombinant interleukin-6 (IL-6; 20-100 ng) caused significant increases in colonic temperature and resting oxygen consumption (VO2) in conscious rats. These effects were prevented by pretreatment with a cyclooxygenase inhibitor (flurbiprofen, 1 mg/kg, i.p.) or a corticotrophin-releasing factor antagonist (alpha-helical CRF9-41, 25 micrograms, i.c.v.). Higher doses of IL-6 (i.c.v.) caused only small changes in VO2 and temperature, and very high doses given intravenously (i.v.) (4 micrograms/kg) were required to stimulate these parameters. Central injection of anti-rat IL-6 antibody inhibited the effects of interleukin-1 beta (i.c.v.) or endotoxin injection (i.p.) on colonic temperature and VO2 in conscious rats. These data indicate that IL-6 is an important endogenous pyrogen that acts within the central nervous system.