Effects of neurotensin and neurotensin analogues on the migrating myoelectrical complexes in the small intestine of rats

Importance of the enteric nervous system in the control of the migrating motility complex

The migrating motility complex (MMC), a cyclical phenomenon, represents rudimentary motility pattern in the gastrointestinal tract. The MMC is observed mostly in the stomach and gut of man and numerous animal species. It contains three or four phases, while its phase III is the most characteristic. The mechanisms controlling the pattern are unclear in part, although the neural control of the MMC seems crucial. The main goal of this article was to discuss the importance of intrinsic innervation of the gastrointestinal tract in MMC initiation, migration, and cessation to emphasize that various MMC-controlling mechanisms act through the enteric nervous system. Two main neural regions, central and peripheral, are able to initiate the MMC. However, central regulation of the MMC may require cooperation with the enteric nervous system. When central mechanisms are not active, the MMC can be initiated peripherally in any region of the small bowel. The enteric nervous system affects the MMC in response to the luminal stimuli which can contribute to the initiation and cessation of the cycle, and it may evoke irregular phasic contractions within the pattern. The hormonal regulators released from the endocrine cells may exert a modulatory effect upon the MMC mostly through the enteric nervous system. Their central action could also be considered. It can be concluded that the enteric nervous system is involved in the great majority of the MMC-controlling mechanisms.

On the effect of xenin and xenin fragments on exocrine pancreas secretion in vivo

A stimulatory effect on exocrine pancreas secretion could be demonstrated with high concentrations of the 25-amino-acid peptide xenin in non-anesthetized dogs. This peptide has been isolated from gastric mucosa and it is part of a structural coat protein. It has close structural similarities to neurotensin. The longer C-terminal fragments xenin-(13--25) and xenin-(18--25) are essential for the stimulation of exocrine pancreas secretion in vivo. The smaller peptide fragments xenin-(21--25) and xenin-(22--25) failed to stimulate the pancreas as well as the N-terminal peptide fragment xenin-(1--23). The stimulatory effects of xenin may be mediated via neural neurotensin pathways, because neurotensin receptor blockade abolished the stimulatory effect on pancreatic secretion. Cholinergic pathways are not involved, because atropine had no inhibiting effect.

Peripheral neurotensin participates in the modulation of pre- and postprandial intestinal motility in rats

The present study was undertaken to determine whether neurotensin is involved in the regulation of the intestinal postprandial motor response and, if so, whether the regulatory pathway depends upon peripheral or central neurotensin secretion. Neurotensin, injected by the i.v. route (5 micrograms/kg) during the fasting state, induced firstly an increased irregular spiking activity during 30-40 min. This effect was followed by an increase of frequency of the myoelectrical complexes during 60 min. When injected by the i.c.v. route, neurotensin (0.5 microgram/kg) reinforced the fasting motility pattern of the small intestine after a latency of 70 min. Neurotensin was ineffective on the colon. The neurotensin receptor antagonist SR 48692 (200 micrograms/kg i.v.) reduced the duration of the postprandial motor response of the small intestine and blocked the late postprandial phase on the proximal colon while it suppressed the early postprandial phase on the distal colon. When administered i.c.v. (20 micrograms/kg), SR 48692 had no effect. It is concluded that neurotensin modulates intestinal postprandial motility essentially by a peripheral regulatory pathway. Endogenous neurotensin is involved in the maintenance of the postprandial motility pattern on the small intestine and the proximal colon while it is involved in the initiation of this response on the distal colon. This suggests that endogenous neurotensin acts via both endocrine and nervous mechanisms.

Antagonism by SR 48692 of mechanical responses to neurotensin in rat intestine

1. The effects of SR 48692 on neurotensin (NT)-induced mechanical responses were investigated in rat duodenum and proximal colon by use of isometric, isovolumic preparations. 2. SR 48692 inhibited the relaxant responses to NT in duodenal circular and longitudinal muscle. It also antagonized the NT-induced contractile effects in duodenal circular muscle and in proximal colon (both muscular layers). 3. From Schild analysis and pA2 value for SR 48692 was 8.2 in tissues where NT induced relaxant effects and 7.5 in tissues where NT induced contractile effects and the slope of the regression line was not significantly different from unity, indicating competitive antagonism. 4. SR 48692 did not antagonize the duodenal relaxant effect induced by noradrenaline and the contractile response to carbachol or substance P in duodenum and colon. 5. Our results demonstrate that SR 48692 selectively antagonizes the mechanical actions of NT in rat intestine and confirm the existence of specific NT receptors. Receptors that subserve a relaxant effect seem to be related, but not identical, to those that mediate contractile effects.

Immunological recognition of different forms of the neurotensin receptor in transfected cells and rat brain

In this work, the molecular forms of the rat neurotensin receptor (NTR) expressed in transfected Chinese hamster ovary (CHO) cells, in infected Sf9 insect cells and in rat cerebral cortex were immunologically detected by means of an anti-peptide antibody raised against a fragment of the third intracellular loop of the receptor. Immunoblot experiments against a fusion protein indicated that the anti-peptide antibody recognized, under denaturing conditions, the corresponding amino acid sequence within the NTR. In immunoblot analysis of membranes from NTR-transfected CHO cells, high levels of immunoreactivity were observed between 60 and 72 kDa, while only a faint labelling was observed at 47 kDa, the molecular mass deduced for the rat NTR cDNA. The bands of high molecular mass were no longer observed after deglycosylation of membrane proteins by peptide N-glycosidase F, indicating that they represented glycosylated forms of the receptor. Extracts of membranes derived from baculovirus-infected Sf9 insect-cells expressing the NTR provided a quite different immunoblot pattern, since the major band detected in that case was at 47 kDa, the molecular size of the non-glycosylated receptor. Taken together, these data show that, while most of the NTR protein was glycosylated in CHO cells, it was unglycosylated in Sf9 insect-cells. In addition, molecular sizes of the receptor proteins observed in these two cell lines differed from those obtained for the NTR endogenously expressed in the rat cerebral cortex of 7 day-old rats, where bands at 56 and 54 kDa were detected. Binding experiments carried out on membrane preparations obtained from baculovirus-infected Sf9 cells demonstrated that the immunogenic sequence was still accessible to the antibody when the receptor was embedded in the cell membrane. Immunohistochemical studies carried out on both transfected CHO cells and infected Sf9 cells confirmed this interpretation and further indicated that the antibody could be applied in the visualization of the receptor.

Binding and biologic activity of neurotensin in guinea pig ileum

Experiments were performed to relate receptor binding to biologic activity for the contractile effect of neurotensin (NT) in guinea pig ileum. The contractile response was examined on pieces of ileum under 1 g tension in a 5 ml bath of oxygenated Tyrode's at 38 degrees C. NT contracted the longitudinal muscle (ED50, approximately 0.3 nM), the 2-3 g response peaking at 1 min and fading rapidly. In the presence of atropine (1 microM), > or = 50% of the response was blocked and the residual effect gave an ED50 of approximately 1.4 nM. In the presence of atropine and CP-96,345, a substance P receptor antagonist (0.2 microM), no contraction was observed at 20 nM NT. Thus, there were two components to the response, one involving acetylcholine (ED50, 0.3 nM) and one substance P (ED50, 1.4 nM). Using membrane preparations and 125I-labeled NT, specific, high affinity receptors for NT were demonstrated in the muscle and myenteric plexus. Scatchard analyses indicated the presence of two binding sites (Kds: approximately 0.1 nM and approximately 2 nM). Sodium ion and GTP analogs inhibited binding. Binding and biologic activity were similar in regard to dependence on specific groups within NT and sensitivity to metal ions. The high potency of Hg++ was consistent with an involvement of free sulfhydryl group(s) in the binding reaction; this was supported by work with SH-directed agents. The results suggest that two receptor types or configurations may mediate the two components of the contractile effect of NT on guinea pig ileum.

Dihydropyridine calcium channel antagonists disrupt migrating myoelectric complexes and counteract intestinal disorders associated with morphine withdrawal diarrhea

The effects of two dihydropyridine (DHP) calcium channel antagonists, nifedipine and nimodipine, on migrating myoelectric complexes (MMCs) of the small intestine were studied in naive and morphine-dependent rats. In addition, the effects of two other calcium channel antagonists, verapamil and diltiazem, on the MMCs were investigated. Nifedipine (1.0-4.0 mg kg-1 intravenously) or nimodipine (1.0-4.0 mg kg-1 intravenously) had an inhibitory effect on the spontaneously occurring MMCs, whereas verapamil (2.5-5.0 mg kg-1 intravenously) or diltiazem (2.5-5.0 mg kg-1 intravenously) had no effect. Bay K 8644 (0.25 mg kg-1 intravenously), a DHP calcium channel agonist, instantly reversed the inhibition induced by nifedipine or nimodipine. When given alone, Bay K 8644 induced irregular spiking activity. In morphine-dependent rats with regular MMCs naloxone (1.0 mg kg-1 intravenously) induced intense spiking activity and profuse diarrhea. Nifedipine (2.0 and 4.0 mg kg-1 intravenously) and nimodipine (2.0 and 4.0 mg kg-1 intravenously) given before naloxone prevented the intense, abstinence-evoked spiking and associated diarrhea. In healthy volunteers nimodipine at an infusion rate of 2 mg h-1 for 4 h did not inhibit the fasting motility pattern. Our findings indicate that DHP-binding sites are involved in the regulation of MMC in the rat and that drugs acting as antagonists at these sites can be used to suppress morphine withdrawal diarrhea and, tentatively, other functional disorders of the intestine.

Neurotensin: dual effect on the motor activity of rat duodenum

The effects of neurotensin on mechanical activity of rat duodenum were investigated using an isometric-isovolumic preparation. Neurotensin (1 pM to 10 nM) induced a concentration-dependent, tetrodotoxin (TTX)-insensitive fall in both endoluminal pressure and isometric tension. At higher concentrations of neurotensin (1 nM to 1 microM) the relaxation was followed by a concentration-dependent TTX-insensitive contraction, detected only by an increase in endoluminal pressure. Different concentrations of neurotensin were required to desensitize the relaxant and the contractile actions of the neuropeptide. The relaxation was antagonized by apamin, while the contractile response was blocked by nifedipine. Neurotensin, when tested separately on longitudinal and circular muscular strips, caused relaxation of the longitudinal strips. Circular strips showed contractions in response to neurotensin, following an inhibitory phase, if the strips were spontaneously or pharmacologically activated. The results suggest the presence of two sets of neurotensin receptors with a differential localization between the two muscular layers in rat duodenum.

Neuromedin-N inhibits migrating myoelectric complex and induces irregular spiking in the small intestine of rats; comparison with neurotensin

The effects of neuromedin-N on migrating myoelectric complexes in the small intestine of rats were studied. As neuromedin-N and neurotensin are structurally related peptides a comparison with neurotensin was made. Myoelectric activity was recorded by means of three bipolar electrodes implanted into the wall of the small intestine at 5, 15 and 25 cm distal to the pylorus. The peptides were administered as intravenous infusions to fasted conscious rats. Neuromedin-N at doses of 100-800 pmol kg-1 min-1 caused a dose-dependent disruption of the migrating myoelectric complexes and induced irregular spiking activity (n = 7, P less than 0.05). Neurotensin induced a similar response, but at doses of 1.0-8.0 pmol kg-1 min-1 (n = 5, P less than 0.05). Thus, on a molar basis, neuromedin-N appeared to be about 100-times less potent than neurotensin. Hexamethonium (20 mg kg-1 i.v.) inhibited the migrating motor complexes and induced quiescence, but did not block the effect of neuromedin-N at a dose of 800 pmol kg-1 min-1. Atropine (1 mg kg-1 i.v.) and mepyramine (2 mg kg-1 i.v.) did not affect the migrating motor complexes, nor did they block the effect of neuromedin-N. Simultaneous infusion of neuromedin-N and neurotensin in a 1:1 molar ratio at doses of 2 pmol kg-1 min-1 showed inhibition of the response to neurotensin in eight out of ten experiments. In conclusion, neuromedin-N changes the myoelectric activity in the small intestine from a fasting to a fed pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of castor oil-induced diarrhoea by alpha 2-adrenoceptor agonists

The effects of systemic administration of alpha 2-adrenoceptor agonists on migrating myoelectric complexes and castor oil-induced diarrhoea of the small intestine were studied in conscious rats. Castor oil (1 mg/kg, intraduodenally) disrupted the migrating myoelectric complexes and induced irregular spiking activity with sporadic bursts of myoelectric activity. This change of motility pattern was present concomitant with diarrhoea 1-2 h after instillation of castor oil and during the whole period of diarrhoea. Pre-treatment with clonidine (5-10 micrograms/kg i.v.) or oxymetazoline (5.6-11.2 micrograms/kg i.v.), a peripherally active alpha 2-agonist, inhibited the irregular spiking induced by castor oil and no diarrhoea occurred during the experimental period of 6 h. Thus, the antidiarrhoeal action of peripherally acting alpha 2-adrenoceptor agonists such as oxymetazoline, may be of clinical value in the treatment of diarrhoea.

Involvement of dopamine in the central effect of neurotensin on intestinal motility in rats

The effects of intracerebroventricular (ICV) administration of neurotensin (NT) before a meal on intestinal postprandial motility were examined in conscious rats chronically fitted with intraparietal Nichrome electrodes in the duodeno-jejunum. The effects were compared with those of two analogues, [D-Tyr11]NT and [D-Trp11]NT, resistant to degradation by brain peptidases. NT (10 micrograms ICV) delayed the occurrence of postprandial disruption of duodenal motility and blocked it on the jejunum. [D-Tyr11]NT and [D-Trp11]NT (1 microgram ICV) elicited the same effects but at a ten-fold lower dose. NT administered peripherally just before a meal significantly lengthened the duration of the postprandial motor pattern. The central effect of NT on the fed pattern involved dopaminergic neurons as it was mimicked by dopamine, blocked by haloperidol and partly antagonized by either sulpiride or (+) SCH 23390. It is concluded that: 1) both D1 and D2 receptors are involved in the blocking effect of the postprandial disruption induced by central NT; 2) that [D-Tyr11]NT and [D-Trp11]NT are potent agonists at NT receptors in the brain.

Effects of cholera toxin, Escherichia coli heat stable toxin and sodium deoxycholate on neurotensin release from the ileum in vivo

Neurotensin (NT) is a biologically active peptide found in specialized epithelial cells (N-cells) in the distal small intestine. In this study we tested the hypothesis that NT may be released by luminal secretagogues, i.e., cholera toxin, Escherichia coli heat-stable toxin and sodium deoxycholate. Cholera toxin elicited net fluid secretion in anesthetized cats. This secretion was accompanied by an increased release of NT-like immunoreactivity (NTLI) into the mesenteric vein when NTLI was measured with either a C-terminally or a N-terminally directed antibody. An increasing plasma NTLI concentration (N-terminally directed antibody) was recorded in the mesenteric vein and femoral artery in cholera experiments. These results indicate that cholera toxin releases NT from the small intestine. Since neurotensin causes intestinal fluid secretion at least in part via an activation of enteric nerves we propose that the N-cell functions as a 'receptor cell' which activates an intramural secretory reflex upon luminal stimulation by cholera toxin. This study does not support a similar role for NT in the secretion elicited by the heat stable toxin of Escherichia coli or by sodium deoxycholate since we were unable to demonstrate any intestinal release of NTLI after exposing the intestine to these secretory agents.

Suppression of small intestinal motility and morphine withdrawal diarrhoea by clonidine: peripheral site of action

The effects of systemic administration of morphine (4.0 mg kg-1) and clonidine (2.5-10.0 micrograms kg-1), as well as the peripherally active alpha 2-adrenoceptor agonist oxymetazoline (2.8-11.2 micrograms kg-1), were studied on the migrating myo-electric complexes (MMCs) of the small intestine in conscious, naive rats. Furthermore, the effects of naloxone (1.0 mg kg-1) and the peripherally acting opioid antagonist, methylbromide naloxone (1.0-2.0 mg kg-1) were studied on the MMCs in morphine-dependent animals. Similar doses of clonidine or oxymetazoline inhibited the MMCs of the small intestine, which suggests a peripheral site of action of clonidine. Since naloxone (1.0 mg kg-1) did not antagonize the effect of clonidine, and yohimbine (1.0 mg kg-1) failed to antagonize the effect of morphine on the MMC, the inhibitory effects on intestinal motility of clonidine and morphine are mediated through different receptors. Morphine-dependent rats showed a prolonged interval between activity fronts and decreased propagation velocity of the activity fronts. Both naloxone (1.0 mg kg-1) and methylbromide naloxone (1.0-2.0 mg kg-1) induced intense spiking activity and profuse diarrhoea. Clonidine (5.0-10.0 micrograms kg-1) as well as oxymetazoline (5.6-11.2 micrograms kg-1) given prior to naloxone prevented the intense spiking as well as the concomitant diarrhoea. We conclude that the potent inhibition of small intestinal myoelectric activity by alpha 2-adrenoceptor agonists is mainly executed via peripheral mechanisms. This effect may contribute to their beneficial action in morphine withdrawal diarrhoea, and partly underlie a general antidiarrhoeal action.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotensin changes the motor pattern in canine ileum from propulsive to segmenting

Modulation of ileal propulsive motility by different doses of neurotensin has been determined in detail. In conscious dogs neurotensin (2.5, 5, and 10 pmol/kg/min) was intravenously infused during the propulsive motor pattern induced by an acaloric viscous meal. Motor patterns were recorded by seven closely spaced strain gauge transducers and analyzed by a computerized method. Luminal transit was measured fluoroscopically. Neurotensin changed the propulsive motor pattern induced by the acaloric meal into a segmenting pattern. Effects were dose-dependent and most striking at a dose of 10 pmol/kg/min. The transit of luminal contents decreased from 20 to 8 cm/min. This was achieved by the increase in the number of stationary contractions (31 vs 55%), the reduction in the length of contraction spread (3.8 vs 1.8 cm), and the decrease in the number of contractions (11.5 vs 9.2 contractions/min). The contraction force was enhanced from 67 to 107 mN. Because of the marked effects on ileal motor patterns, neurotensin might be involved in the regulation of digestive motility in the distal small intestine.

The electrophysiological effects of neurotensin on neurones of guinea-pig prevertebral sympathetic ganglia

1. The membrane effects of neurotensin on neurons of guinea-pig prevertebral ganglia were investigated by means of intracellular recording techniques in vitro. 2. Neurotensin (2-5 microM) applied by superfusion caused depolarizing responses in fifty-seven of seventy-four neurones tested in the inferior mesenteric ganglion and thirty-seven of forty-seven neurones tested in the coeliac plexus. The remaining neurones tested showed no membrane response. 3. Responses to neurotensin could be discriminated into two different types of membrane depolarizations on the basis of their different time courses and pharmacological characteristics: a steady-state type of depolarization and a transient type of depolarization. Seven of fifty-seven responsive neurones tested in the inferior mesenteric ganglion and ten of thirty-seven responsive neurones tested in the coeliac plexus responded to neurotensin with a depolarization which was maintained constant as long as neurotensin was superfused over the preparation (steady-state type). Forty-eight of fifty-seven responsive neurones tested in the inferior mesenteric ganglion and twenty of thirty-seven responsive neurones tested in the coeliac plexus responded with a transient depolarization which was followed by a repolarization in the maintained presence of neurotensin (transient type). A combination of both types of responses was observed in two neurones tested in the inferior mesenteric ganglion and in seven neurones tested in the coeliac plexus. 4. Steady-state type responses were characterized by a slowly developing membrane depolarization which reached a plateau and lasted throughout the presence of neurotensin. Amplitude and time course of this response were not altered in a solution containing hexamethonium (10 microM) and atropine (10 microM) or by a solution low in calcium (1 mM) and high in magnesium (15 mM). 5. Transient type depolarizations evoked by neurotensin were faster in reaching their maximum and were followed by a repolarization during the maintained presence of neurotensin. Responses similar in time course and amplitude were obtained in solutions containing hexamethonium (10-100 microM) and atropine (10 microM). However, transient responses were abolished in a solution low in calcium (1 mM) and high in magnesium (15 mM) and were markedly attenuated in ganglia treated with capsaicin (3 microM). 6. Both types of depolarizations were associated with increases in membrane input resistance. Both responses converted subthreshold depolarizing electrotonic potentials and subthreshold fast EPSPs to action potentials. 7. Both types of depolarizations were observed when the C-terminal hexapeptide fragment neurotensin 8-13 was used.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism of action of neurotensin at the ileocecal sphincter region

Neurotensin, a neuropeptide identified in the distal small intestine, plays an unclear role in ileocecal sphincter regional function. The purpose of this study was to determine the effect and mechanism of action of neurotensin on the feline ileocecal sphincter (ICS), proximal colon, and distal ileum. Intraluminal pressures were recorded at these sites in anesthetized cats after superior mesenteric artery injection of neurotensin. Dose dependent tonic and phasic contractions were seen at all sites. Peak pressure responses were seen at the maximal dose used and were greater for the ICS than the distal ileum and the proximal colon. The threshold dose for peak pressures for neurotensin was 0.05 microgram/kg for all sites with the maximal peak pressures occurring at the maximal dose used (100 micrograms/kg). The motility index (MI [number of contractions x mean amplitude of contractions]) was determined for three minutes before and after neurotensin injection. The change in the motility index after neurotensin increased at doses above 0.05 micrograms/kg for the ileum and the ICS and 0.25 microgram/kg for the colon. Maximal responses for the motility index were seen at 1 microgram/kg for the distal ileum, and 10 micrograms/kg for the ICS and the proximal colon, with the greatest response seen at the ICS. Neurotensin-induced ICS relaxation was seen at 1 microgram/kg (50 +/- 10%, p less than 0.01) in 33% of cats. The contractile responses of the distal ileum and the proximal colon were not inhibited by naloxone, trimethaphan, tetrodotoxin, or atropine. The ICS contractile response was decreased by tetrodotoxin by 53%, p less than 0.05. The alpha 2 antagonist, yohimbine reduced the neurotensin induced ICS contraction from 31.6 +/- 3.4 to 21.9 +/- 3.3 mm Hg, p less than 0.05. Prazosin had no effect on neurotensin-induced contractions. In the presence of cimetidine and diphenhydramine, trimethaphan did not affect the neurotensin-induced contractile response at all three sites. However, neurotensin inhibited contractions induced by trimethaphan alone at all three sites.

CONCLUSIONS

1. Neurotensin causes a dose-dependent contractile response at the distal ileum, ICS, and proximal colon. 2. Neurotensin has an inhibitory effect at all three sites. 3. The contractile response at the distal ileum and the proximal colon is mediated via smooth muscle receptors. 4. The contractile response of neurotensin at the ICS is mediated partly via alpha 2 receptors and partly via smooth muscle receptors.

Adaptive changes in postprandial motility after intestinal resection and bypass. Electromyographic study in rats

An electromyographic technique was used to study the changes in postprandial motility induced by jejunal and ileal resection and jejunal bypass (50% reduction of total length of small bowel). Electrodes were implanted in rats throughout the intestine. Compared to control animals, the duration of postprandial interruption of the myoelectric complex (DIMC) was rapidly increased after jejunal resection, more gradually augmented after jejunal bypass, and remained constant after ileal resection. The frequency of occurrence of spike bursts during the postprandial period was significantly decreased in the short remaining proximal segment after jejunal resection and was not changed in the ileum. The jejunal bypass induced no change in the frequency throughout the remaining bowel. Ileal resection was followed by a decrease on the jejunum. The percentage of slow waves superimposed by a spike burst remained constant after jejunal resection and bypass but was significantly decreased after ileal resection on the whole remaining intestine. These results show important modifications in postprandial motor activity of the small bowel, which appear rapidly after jejunal resection, more gradually after jejunal bypass, and which are less pronounced after ileal resection. This electromyographic study emphasizes the role of intestinal motility in the development of adaptation after small bowel resection or bypass.

Secretion of neurotensin from isolated perfused porcine ileum

The secretion and molecular nature of immunoreactive neurotensin (NT) was studied following stimulation of an isolated perfused porcine ileal segment with glucose, triglyceride and intra-arterial infusion of gastrin-releasing peptide (GRP). Secreted peptides were separated using gel chromatography and analyzed with 3 sequence-specific radioimmunoassays towards NT. Glucose (5%) and GRP both stimulated NT secretion from the ileal segment whereas pure triglyceride did not. Maximal secretion of NT during glucose perfusion was 0.448 nmol/min and 6.9 nmol/min during GRP infusion (medians, n = 5). GRP infused in doses from 10(-10) to 10(-8) M stimulated NT release in a dose-related manner. Following gel chromatography only the intact peptide and no smaller or larger molecular size immunoreactive components were observed. The study showed that both luminal and humoral stimuli release NT from the isolated pig ileum. Apparently no fragments or other NT-related immunoreactive components were cosecreted with the peptide.

Mechanisms of neurotensin-induced fluid secretion in the cat ileum in vivo

Neurotensin (NT) is released from N cells in the small intestinal epithelium. Among other effects NT is known to elicit fluid secretion in the small intestine. This study was carried out in order to elucidate the mechanism by which NT elicits this secretion. Neurotensin infusions at two rates (4.5 and 45 pmol min-1 kg-1 body wt) to isolated segments of cat ileum in vivo, caused a steady rate of net fluid secretion and a release of vasoactive intestinal polypeptide into the mesenteric vein. The secretion was totally inhibited by tetrodotoxin. Hexamethonium, a nicotinic receptor antagonist, inhibited the secretion elicited by the lower but not by the higher dose of NT. Met-enkephalin also inhibited the induced secretion while pyrilamine, a histamine-I receptor antagonist had no effect. No significant change in enteric blood flow was caused by the NT infusion. These results indicate that NT elicits a nervous reflex in the enteric nervous system which, accordingly, turns the transport of the enterocytes into net fluid secretion.

Vagotomy inhibits the effect of neurotensin on gastrointestinal transit in the rat

Neurotensin has previously been shown to delay gastric emptying, gastrointestinal transit and ileo-caecal emptying in the rat. To investigate the vagal influence on these effects of neurotensin, separate groups of rats were operated with combined vagotomy and pyloroplasty or with pyloroplasty alone and compared to a group of normal rats. All animals were supplied with a permanent gastrointestinal catheter and a venous catheter. After operation the rats were allowed to recover for 7 days, and were fasted for 24 h prior to the experiments. A radioactive marker of 1.0-0.5 ml Na2(51)CrO4 in isotonic polyethylene glycol 400 was instilled intraluminally in the stomach, proximal or distal the small intestine. Saline (control animals) or neurotensin (test animals) was given i.v. in each group studied. The animals were killed at 15, 30, 60, and 120 min after administration of the marker. The distribution of the marker in the gastrointestinal tract was registered with a scintillation detector and quantitative analysis of the amount of radioactivity retained in separate gastrointestinal segments was carried out. Gastric emptying was delayed by combined vagotomy and pyloroplasty (P less than 0.01) compared to pyloroplasty alone and normals. Neurotensin at doses of 6 (P less than 0.05) and 12 (P less than 0.01) pmol kg-1 min-1 retarded gastric emptying dose-dependently in normals and rats with pyloroplasty alone, but did not further slow the gastric emptying in rats with vagotomy and pyloroplasty. However, at a dose of 24 pmol kg-1 min-1 neurotensin delayed gastric emptying (P less than 0.01) compared to controls. Gastrointestinal transit was slowed down by neurotensin at a dose of 6 pmol kg-1 min-1 in normals (P less than 0.01) and rats with pyloroplasty alone (P less than 0.05). In rats with vagotomy and pyloroplasty, neurotensin at doses of 6 and 12 pmol kg-1 min-1 had no effect on gastrointestinal transit.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of neurotensin and neurotensin fragments on gastric acid secretion in man

The effect of intravenous infusion of neurotensin (NT) and NT-fragments on pentagastrin stimulated gastric acid secretion was investigated in healthy subjects. Neurotensin was infused in three doses (72, 144 and 288 pmol/kg per h). An N-terminal fragment (NT 1-8), a C-terminal fragment (NT 8-13) and an NT-analogue, substituted at the C-terminal tyrosine residue (Phe11-NT) were infused in two doses (72 and 144 pmol/kg per h). Concentrations of the infused peptides were measured in peripheral venous blood by radioimmunoassay. Plasma levels of NT 1-13, NT 1-8 and Phe11-NT increased in a dose-dependent manner; NT 1-13 to 50 (34-69), 78 (54-113) and 143 (112-242) pmol/l (medians and range) at 72, 144 and 288 pmol/kg per h, NT 1-8 to 405 (340-465) and 1215 (915-1300) pmol/l, and Phe11-NT to 200 (110-245) and 390 (250-410) pmol/l at 72 and 144 pmol/kg per h, respectively. Increases in plasma levels of NT 8-13 could not be detected during the infusion, suggesting that the fragment is rapidly metabolized in man. Neurotensin 1-13 inhibited gastric acid secretion in a dose-dependent manner and the decrease in gastric acid secretion was linearly related to plasma levels of NT 1-13. Neurotensin 1-8 and NT 8-13 inhibited gastric acid secretion only at 144 pmol/kg per h, while the analogue Phe11-NT had no effect. The results showed that the inhibition of gastric acid secretion produced by NT was dose-dependent and linearly related to circulating levels of NT, and that under physiological conditions this effect presumably is elicited by the C-terminal part of the peptide.

Effect of neurotensin in the dumping syndrome

The possibility that the gut peptide, neurotensin, may contribute to the dumping syndrome was investigated in 17 patients with a long history of dumping after a Billroth II gastrectomy for duodenal ulcer. After a test meal plasma levels of neurotensin were higher than in normal subjects, but no correlation to the severity of symptoms was found. In eight of the patients with meal-provoked dumping symptoms, intravenous infusion of neurotensin in relevant doses produced neither symptoms nor changes in blood glucose, blood pressure, or pulse rate. The apparent plasma half-life of neurotensin (t1/2 = 2.3 min) did not differ from that previously found in normal subjects. The results indicate that it is unlikely that neurotensin alone has a pathogenetic role in the dumping syndrome in gastrectomized patients.

Neurotensin increases colonic motility

The effects of neurotensin on colonic motility were investigated in 6 healthy volunteers (rectosigmoid area) and 7 patients (ascending colon and at the splenic flexure). Neurotensin (12 pmol/kg X min) infused intravenously for 30 min increased the duration of the contractions to 76% in the ascending colon and 46% in the rectosigmoid area. In the postinfusion period, the values were 42% and 67%, respectively. The motor activity did not change significantly at the splenic flexure. During the infusion period, the motility index increased from 870 to 4500 in the ascending colon and from 332 to 1700 in the rectosigmoid area. In the rectosigmoid area, however, a statistically significant increase was recorded first after cessation of the infusion. All subjects reported increased sensation of intestinal movement after intravenous infusion of neurotensin, and the patients discharged a median volume of 600 ml of bowel contents 20 min after cessation of the infusion. The data show that neurotensin causes an increase in colonic motility in the ascending colon of patients and also, after a latent period, in the rectosigmoid area of healthy subjects.

Neurotensin-like immunoreactivities in human plasma: feeding responses and metabolism

Feeding responses and day and night levels of plasma concentration of neurotensin (NT) and NT-fragments were studied in healthy subjects. Plasma levels were measured by three radioimmunoassays recognizing intact NT in addition to C- and N-terminal immunoreactivity. The metabolism of NT was studied following intravenous administration. In 106 subjects fasting levels of intact NT (median 18 pmol/l), C-terminal (median 30 pmol/l) and N-terminal immunoreactivity (median 95 pmol/l) were unrelated to sex or age. Postprandially plasma levels in seven subjects measured with all assays increased by a factor 1-3. Following a mixed meal the increase was biphasic, whereas the response to dairy cream was monophasic. Repetitive measurements during 24 hours showed that levels of N-terminal immunoreactivity fluctuated in a manner related to meal ingestion and were elevated throughout the daytime, whereas intact NT and C-terminal immunoreactivity changed little. Following intravenous infusion of 2.4 pmol/kg/min NT in 5 subjects the chromatographic pattern was similar to that seen postprandially. The plasma half life of intact NT and C-terminal immunoreactivity was 1.5 and 1.2 min, whereas that of N-terminal immunoreactivity was 10.0 min. The differences in circulating levels could be explained by these differences in metabolism, but the physiological significance remains to be elucidated.

Dexamethasone reduces fat-induced release of neurotensin in the rat

The effect of glucocorticoids on the release of neurotensin (NT) was studied in the rat. Oleic acid (200 microliters) was instilled into the duodenum of fasted rats given saline or 1 mg . kg-1 dexamethasone subcutaneously 16 h prior to the experiment. Neurotensin-like immunoreactivity (p-NTLI) was analysed in unextracted plasma with the C-terminal directed NT antiserum 6-8206. Pretreatment with dexamethasone almost totally abolished the fat-induced increase in p-NTLI. The data suggest that glucocorticoids may modulate the post-prandial release of NT. Since NT is known to constrict the vascular beds of subcutaneous adipose tissue, this effect of glucocorticoids may be one of the factors responsible for the abnormal distribution of fat caused by high levels of glucocorticoids, e.g. in Cushing's syndrome.

Plasma levels of neurotensin in gastroplasty for morbid obesity

Fasting and postprandial plasma levels of the tridecapeptide neurotensin were determined in ten women before and three months after gastroplasty for morbid obesity. Measurements were by radioimmunoassay in unextracted plasma with two antisera recognizing intact neurotensin (NT1-13) or intact neurotensin together with small C-terminal fragments, which may circulate as metabolites of neurotensin. Levels of both intact neurotensin and C-terminal immunoreactivity in obese women were in the same order of magnitude as those found previously in lean persons. Fasting levels measured with both antisera were significantly reduced following gastroplasty (P less than 0.01). Meal-stimulated levels and increments were unchanged. The cause of this prolonged reduction is at present unknown, but may be a reduced luminal stimulation of the small intestine or an altered vagal tonus following gastroplasty.

Somatostatin inhibits bombesin-induced effects on migrating myoelectric complexes in the small intestine of the rat

The effect of i.v. infusions of bombesin and somatostatin, administered either separately or in combination, on migrating myoelectric complexes (MMCs) in the small intestine were studied in conscious, fasted rats. The myoelectrical activity was recorded by means of three bipolar electrodes chronically implanted into the duodenum and jejunum. Infusion of bombesin (0.5, 0.9 and 3 pmol . kg-1 . min-1) interrupted the MMC and induced irregular spiking activity similar to that observed on feeding. Only after the highest dose a consistent inhibition of the MMCs and a significant increase (P less than 0.05) of the spiking activity were achieved at all recording levels. Somatostatin (90 pmol . kg-1 . min-1) did not interrupt the MMC, but reduced significantly the incidence of the activity fronts and spiking activity of the MMCs (P less than 0.05). The effects of bombesin (3 pmol . kg-1 . min-1) on the MMC pattern were inhibited by simultaneous infusion of somatostatin (P less than 0.05). In a second series of experiments, using anesthetized rats, infusion of bombesin (0.5 and 3 pmol . kg-1 . min-1) increased the plasma concentration of neurotensin- gastrin-like immunoreactivities in a dose-dependent manner. The results show that bombesin alters the myoelectrical activity of the small intestine from a fasting to a fed pattern. Since the effect of bombesin was inhibited by the hormone release inhibitor somatostatin, it is suggested that the effect of bombesin on MMC may be secondary to the release of gastrointestinal peptides, such as neurotensin or gastrin.

The use of a rat isolated ileal preparation to investigate the release of neurotensin

An isolated and perfused preparation of rat ileum was used to investigate the effects of cholinergic, adrenergic and bombesin stimuli on neurotensin release into the vascular compartment. A vigorous release of neurotensin like immunoreactivity (NTLI) to 200% above basal values in response to intraluminal infusions of emulsified soybean oil (Intralipid) demonstrated the physiological responsiveness of the preparation. Carbachol significantly stimulated the release of both NTLI and bombesin like immunoreactivity (BLI), with maximal responses at 5 X 10(-9) mol/l carbachol of 100% and 400% above basal values for NTLI and BLI, respectively. Noradrenaline at 10(-6) and 10(-4) mol/l caused no significant release of NTLI but markedly inhibited spontaneous BLI release. Synthetic amphibian bombesin caused a marked release of NTLI to 81% and 100% above basal at infusion concentrations of 5 X 10(-11) and 5 X 10(-10) mol/l respectively. These results suggest that there is either a direct effect of cholinergic agents on the N cells bringing about NTLI release, or an indirect effect via the release of bombesin like peptides from intrinsic gut neurones. This preparation provides a useful model to study the complex neural, paracrine and endocrine interactions in the gastrointestinal tract.

[Neurotensin--what is known about its role as a hormone in the gastrointestinal tract?]

Neurotensin is a tridecapeptide originally isolated and characterized from bovine hypothalamus and later, in identical form, from bovine and human intestine. In the rat about 85% of immunoreactive neurotensin is found in the gut and about 10% in the brain. When an antibody specific for the amino terminal region of neurotensin was used the highest concentrations were found in the mucosa of the ileum, while an antibody specific for the biologically active region, the carboxyl terminus, also detected large amounts in the mucosa of the upper gastrointestinal tract. After a meal neurotensin - as measured by carboxyl terminal antibodies - rises after 5 min, a time in which the chymus has not yet reached the ileum, the main source of whole neurotensin. It is therefore possible that the carboxyl terminal molecules of neurotensin, found in the upper gastrointestinal tract, play an important physiological role. In plasma, neurotensin is rapidly degraded into smaller amino terminal and therefore biologically inactive molecules. Increases of carboxyl terminal neurotensin have been found in plasma in only a very few studies. The nature of this immunoreactive material has not yet been established. Therefore, the physiological role of neurotensin as a circulating hormone is unknown. Potential actions of neurotensin include thermoregulation, regulation of hormone release from brain (pituitary hormones) and gut (glucagon, insulin, somatostatin, pancreatic polypeptide), increase of vascular permeability, vasodilatation, inhibition of gastric acid secretion, stimulation of pancreatic secretion and changes of gut motility from the fasting to the fed type.

Cigarette smoking potentiates fat-induced elevation of neurotensin-like immunoreactivity in human plasma

The aim of the present study in man was to investigate the influence of cigarette smoking on basal plasma concentrations of neurotensin-like immunoreactivity (p-NTLI), as well as on fat-induced elevation of p-NTLI levels. On three separate occasions, habitual tobacco smokers either ingested fat (55 ml Intralipid 20%) or smoked three cigarettes, or ingested fat and smoked. The subjects were fasted overnight and told no to smoke during the fasting period. Smoking of one cigarette at one hour intervals (0, 60, and 120 min) did not change the p-NTLI levels (n = 6). Ingestion of fat caused a significant increase (n = 16) and when these two procedures were combined (n = 16), the mean integrated p-NTLI response (nM0-180 min) was 56% larger than the response after fat ingestion alone. The results show that cigarette smoking potentiates the fat-induced elevation of p-NTLI levels, whereas cigarette smoking per se has no effect.

Intestinal motility after infusion of arachis oil into duodenum and ileum of dogs

Arachis oil and a mixture of arachis oil with bile and pancreatic enzymes were infused into the duodenum and ileum of dogs via surgically positioned catheters in order to study the mechanism of disruption of the migrating complex by intraluminally infused triglycerides, the importance of cholecystokinin and neurotensin in this event, and the pattern of digestive myoelectrical activity during fat digestion. When infused into the duodenum both arachis oil and the oil-bile-pancreatic enzyme mixture disrupted the migrating myoelectric complex (MMC). When infused into the ileum, only the oil-bile-pancreatic enzyme mixture disrupted the MMC. The duration of the disruption lasted as long as when the same amount of oil was administered orally. Triglyceride-induced digestive activity was characterized by the frequent alternation of short periods of spiking activity and short periods of quiescence. It is concluded that the triglyceride-induced disruption of the MMC-pattern is not caused by the triglyceride itself but by some emulsion or digestion product. We further suggest that the disruption is hormonally mediated and due to fat-stimulated neurotensin, rather than cholecystokinin (CCK), release.

Neurotensin increases net fluid secretion and transit rate in the small intestine of man

In a double-blind study with six patients, who previously had undergone proctocolectomy for ulcerative colitis, the ileostomy discharge significantly increased from 110 to 295 ml X 4 h-1 during infusion of neurotensin, 3 pmol X kg-1 X min-1 for 4 h. Transit defined as the passage of a perorally ingested unabsorbable marker (polyethylene glycol, PEG 4000) was significantly increased during the last hour of neurotensin infusion. The dose of neurotensin used in this study has previously been shown to result in plasma levels of neurotensin-like immunoreactivity within the range obtained after a fatty meal. Thus, the present data indicate that neurotensin in man may exert a physiological function by increasing net fluid secretion in the small intestine as well as increasing the intestinal transit rate.

Antroduodenal motor response induced by (Gln4)-neurotensin in man

The effect of (Gln4)-neurotensin on antroduodenal motor activity was investigated in 7 healthy volunteers. Motor activity was monitored by measuring the intraluminal pressure in the antrum and in the proximal and middle part of the duodenum. Intravenous infusion of (Gln4)-neurotensin (6 pmol X kg-1 X min-1) for 20 min significantly increased the number of contractions in the duodenum, from 13.8 +/- 1.1 to 33.2 +/- 3.0 contractions X 5 min-1, and changed the motility pattern in the duodenum to irregular pressure waves similar to those seen after the ingestion of food. The contractile activity (amplitude X number of contractions) in the antrum and duodenum changed significantly from 230 +/- 29 to 148 X 39 and from 288 +/- 21 to 556 X 62 mmHg X 5 min-1, respectively, despite the fact that the baseline pressure gradient was unchanged. The number of antral contractions migrating to the duodenum was significantly reduced from 3.3 +/- 0.4 to 0.1 +/- 0.1 contractions X 5 min-1 and their velocity was also significantly decreased, from 18.2 +/- 1.7 to 11.1 +/- 1.7 mm X sec-1. The concentration of p-NTLI rose from 39 +/- 11 pM to a maximum of 150 +/- 14 pM at 20 min; these latter levels are within the range found after a fatty meal. Thus, (Gln4)-neurotensin changes antroduodenal motility to a pattern seen after a meal. This suggests that neurotensin, or a neurotensin metabolite, may carry the information to the antroduodenal area to decrease the rate of gastric emptying after a fatty meal.

Studies on the mechanisms by which (Gln4)-neurotensin reduces lower esophageal sphincter (LES) pressure in man

The mechanisms behind the reduction of lower esophageal sphincter (LES) pressure by (Gln4)-neurotensin were investigated in 17 healthy volunteers. LES pressure was measured with a continuous pull-through technique. Intravenous infusion of (Gln4)-neurotensin (6, 12 or 18 pmol X kg-1 X min-1) caused a significant, prompt and dose-related fall in LES pressure from a mean basal value of 35.2 +/- 3.4 mmHg to 29.2 +/- 3.0, 27.3 +/- 3.5 and 25.9 +/- 2.7 mmHg, respectively. Atropine (1 mg) administered as a single i.v. bolus injection did not change the mean pressure significantly. After atropine, the LES pressure response to 12 pmol X kg-1 X min-1 of (Gln4)-neurotensin was abolished. The increase in LES pressure following a bolus injection of pentagastrin (0.6 microgram X kg-1) was not inhibited by 12 pmol X kg-1 X min-1 of (Gln4)-neurotensin. The concentration of plasma neurotensin-like immunoreactivity (p-NTLI) in all experiments was lower than, or in the same order of magnitude as, that obtained postprandially. Thus, the data indicate that reduction of LES pressure by neurotensin may occur postprandially and that this effect seems to involve a cholinergic nervous pathway, rather than being due to a direct myogenic action.

Neurotensin: effects of hypothalamic and intravenous injections on eating and drinking in rats

To investigate a role for the brain-gut peptide neurotensin (NT) in ingestive behavior, changes in food and water intake of food-deprived rats were examined following injection of NT into the paraventricular hypothalamic nucleus (PVN) or the mesenteric vein. Unilateral PVN NT (2.5, 5.0, 10.0 micrograms/0.3 microliter) produced substantial dose-dependent reductions in total food intake 0.5, 1, and 4 hr postinjection. In contrast, PVN NT had no effect on water intake and produced no change in grooming, rearing, sleeping, resting or locomotor activity. Bilateral PVN NT at a high dose (10.0 micrograms/side) suppressed consumption of solid or liquid diet in food-deprived rats, but did not affect water intake in water-deprived rats. This specificity is consistent with a role for CNS NT in feeding behavior. Intravenous NT (1-1000 pmole/kg/min for 30 min) did not specifically suppress food intake; however, low doses did increase water intake in food-deprived rats. These findings do not support a role for plasma NT in feeding, but do suggest that it may play a role in drinking behavior.

Effects of intracerebroventricular administration of neurotensin, substance P and calcitonin on gastrointestinal motility in normal and vagotomized rats

The effects of intracerebroventricular (ICV) vs. intravenous (IV) injection of neurotensin, substance P and calcitonin on intestinal myoelectrical activity were examined in fed rats. ICV administered neurotensin and calcitonin restored the 'fasted' pattern of intestinal activity, i.e. the migrating myoelectric complex (MMC) at a dose as low as 12 and 0.2 pmol, respectively, whereas substance P only reduced significantly (P less than 0.01) the duration of the postprandial pattern when injected ICV (48 pmol). Administered systemically at doses 100 times higher than the smallest active doses by the ICV route, calcitonin induced a fasted pattern, while neurotensin and substance P did not modify the fed pattern. The effects of ICV administration of neurotensin and calcitonin were abolished after vagotomy but the shortening effect of substance P on the duration of the postprandial pattern was still present. It is concluded that these three neuropeptides act centrally to control the pattern of intestinal motility in fed rats by shortening the 'fed' pattern for substance P and by restoring the MMC pattern for calcitonin and neurotensin, this last effect being mediated by the vagus.

Effects of neurotensin on small bowel propulsion in intact and vagotomized rats

The effects of intravenous infusion of neurotensin on small bowel motility was studied in conscious rats. During 1 h a standardized test meal of glucose, polyethyleneglycol (PEG) 3000, phenol red and 125I-labelled polyvinylpyrrolidone was administered via a permanent gastric catheter and simultaneously the bile-excreted radio-pharmaceutic 99Tcm-Solco-HIDA was infused intravenously. Immediately after the infusions the gastrointestinal specimen was excised and examined for distribution of radioactivity. Both doses of neurotensin (0.1 and 0.3 microgram . kg-1 . h-1) resulted in an increase in the neurotensin-like immunoreactivity (NTLI) of plasma to levels similar to that found after a fatty meal. Concurrently the small bowel transport pattern was changed from an interdigestive state to one similar to that found after a meal. In animals not receiving the gastric test meal, neurotensin (0.1-0.5 microgram . kg-1 . h-) had no effect on motility. Infusion of the gastric test meal alone did not change the interdigestive motility or the NTLI value. This indicates that the presence of gastric infusates potentiates the effect of neurotensin on small bowel motility. The motility response to neurotensin did not differ between intact and vagotomized animals. This contrasts to earlier findings that the small bowel motility response to a fatty meal is dependent on intact vagal function. Thus, a difference in the mechanism responsible for the motility responses between a fatty meal and neurotensin exists. In view of this finding it seems reasonable to assume that neurotensin cannot be the only factor responsible for the shift in motility found after a fatty meal.

Blood flow in human adipose tissue after infusion of (Gln4)-neurotensin

(Gln4)-neurotensin, 18 pmolXkg-1Xmin-1, was infused i.v. during 20 min in 10 healthy male volunteers. Adipose tissue blood flow was continuously monitored by measuring the disappearance rate of 99mTc-pertechnetate injected s.c. on the abdomen and thigh. Heart rate and blood pressure were measured and calf blood flow studied by venous occlusion plethysmography. Neurotensin-like immunoreactivity (NTLI) in serum was determined. Infusion of isotonic saline served as control. During intravenous infusion of (Gln4)-neurotensin the first order rate constants of 99mTc-pertechnetate from the abdomen decreased by 21.9 +/- 5.9% from a basal value of 8.3 +/- 0.5% min-1 (p less than 0.01). The reduction in blood flow started after a latent period of 5-10 min and persisted throughout the thirty minute observation period following infusion. A significant correlation (r=0.87, p less than 0.001) was found between the percentage decrease in blood flow from abdominal fat and the body fat content of the subjects as determined from the sum of four skinfolds. Blood flow from thigh fat did not change significantly, nor did heart rate, blood pressure or calf blood flow. During infusion of (Gln4)-neurotensin plasma neurotensin-like immunoreactivity (NTLI) increased successively. Ten minutes after starting the infusion the mean plasma NTLI level had increased from 20 +/- 5 pM to 302 +/- 31 pM; at 20 min it was 473 +/- 51 pM. These concentrations are within the range found after eating a fatty meal. The results indicate that neurotensin plays a physiological role in the regulation of human adipose tissue blood flow and may be of importance for the postprandial uptake of substrates in adipose tissue in certain regions. We suggest that neurotensin deserves consideration as an endocrine hormone affecting the regional deposition of fat postprandially.