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

Alterations of gut neuropeptides in gastroesophageal reflux disease are resolved after antireflux surgery

BACKGROUND

Gastroesophageal reflux disease (GERD) may cause alterations of gut neuropeptides such as motilin and neurotensin that are known to control foregut motility. The aim of this study was to investigate whether these alterations may be resolved following antireflux surgery.

METHODS

Basal and postprandial plasma levels of motilin and neurotensin were measured in 20 GERD patients preoperatively and 6 months after antireflux surgery. There were 9 patients with normal esophageal peristalsis and 11 with poor esophageal body motility. Eleven healthy subjects served as control group.

RESULTS

GERD patients with poor esophageal body motility had low basal plasma levels of motilin and high levels of neurotensin. Postprandial motilin levels were significantly increased in these GERD patients. After antireflux surgery, all observed alterations of gut neuropeptides returned to normal values.

CONCLUSION

Alterations of gut neuropeptides may be implicated in the pathophysiology of impaired esophageal peristalsis in GERD. Antireflux surgery restores normal physiology of gut neuropeptides. This may contribute to improvement of foregut motility in GERD, thus counteracting duodenogastric reflux.

Manometric and hormonal changes after distal partial gastrectomy

BACKGROUND

Alkaline oesophagitis attributable to duodenal mechanisms may induce oesophageal carcinogenesis in a rat reflux model.

AIM

To investigate the mechanism of the regurgitation after distal partial gastrectomy.

METHODS

Oesophageal manometry was used in 16 patients before and after distal partial gastrectomy with reconstruction by Bilroth methods. Serum concentrations of four gastrointestinal hormones were measured by radioimmunoassay in 10 gastrectomy patients and nine healthy volunteers before and after a standardized meal.

RESULTS

The lower oesophageal sphincter pressure was reduced to 83% after surgery. The amplitude and duration of the peristaltic waves tended to be increased, and the velocity tended to be less after surgery (amplitude 120%, duration 114%, velocity 88%). Interrupted waves appeared more frequently after surgery. The manometric changes in gastrectomized patients are considered to be disadvantageous relative to regurgitation. After surgery, gastrin and pancreatic polypeptide were completely abolished postprandially, whereas cholecystokinin and neurotensin were significantly increased.

CONCLUSION

The hormonal changes should have a suppressive effect on the lower oesophageal sphincter. Both the manometric and the hormonal changes may exacerbate reflux oesophagitis after distal partial gastrectomy.

Gastroesophageal reflux disease is associated with enteric hormone abnormalities

Basal and postprandial levels of the foregut hormones gastrin, cholecystokinin (CCK), motilin, and pancreatic polypeptide, and the distal gut hormones neurotensin and peptide YY were measured in 20 patients with gastroesophageal reflux disease (GERD). GERD was defined by abnormal esophageal exposure to pH less than 4. Ten GERD patients had decreased lower esophageal sphincter (LES) pressure (mean: 4.5 mm Hg, range: 0.8 to 6.8 mm Hg), and 10 patients had normal LES pressures (mean: 14.1 mm Hg, range: 9.7 to 22.4 mm Hg). Eight age-matched healthy subjects were also studied. Basal levels of peptide YY were moderately decreased in GERD patients compared with controls irrespective of LES pressure. In patients with abnormal LES pressure, basal levels of motilin and the postprandial response of CCK were significantly decreased compared with controls; and basal levels of neurotensin and the postprandial response of gastrin were significantly increased compared with controls. Pancreatic polypeptide levels were similar in all groups. These gut hormone changes, which are more marked in patients with poor LES pressure, may reflect primary or secondary abnormalities in GERD.

Effects of neurotensin-related peptides on the motility of the guinea pig oesophagus

Neurotensin, neuromedin N and xenopsin induced a monophasic and concentration-dependent contraction of the intact guinea pig oesophagus but kinetensin was without effect. The responses were completely abolished by tetrodotoxin and atropine but were unaffected by hexamethonium. The maximum response induced by neurotensin was reduced (20-30%) by somatostatin and by dynorphin-(1-13) in a naloxone-reversible manner. Neurotensin did not contract the isolated muscularis mucosae. The effects of neurotensin-related peptides on the motility of the oesophagus are mediated exclusively through the release of acetylcholine.

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)

Pharmacological analysis of the mechanism of action for colonic contraction induced by neurotensin, substance P and methionine-enkephalin

Infusion of neurotensin, substance P and methionine-enkephalin induces colonic contraction in the cat. The present study was performed to investigate the effect of various pharmacological blocking agents on colonic contraction evoked by these peptides infused by the i.a. or i.v. route. The contractions caused by infusions of neurotensin were blocked by tetrodotoxin (1 micrograms kg-1 i.a.), hexamethionium (10 mg kg-1 i.v.), atropine (0.1 mg kg-1 i.v.) or somatostatin (100 pmol min-1 i.a.), but not by haloperidol, methysergide, mepyramine, cimetidine or naloxone. The contractile effect of substance P on the colon was abolished by the substance P receptor antagonist (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-substance P (70 nmol min-1 i.a.). No other blockers used, such as tetrodotoxin, hexamethonium, atropine, mepyramine, cimetidine, methysergide, naloxone or somatostatin inhibited the response to substance P. Methionine-enkephalin produced a colonic contraction that was completely blocked by naloxone (1 mg kg-1 i.a.). Both atropine (0.1 mg kg-1 i.v.) and somatostatin (100 pmol min-1 i.a.) reduced the contractile response. However, tetrodotoxin, hexamethonium, mepyramine, cimetidine and methysergide did not affect the response to methionine-enkephalin. All adrenergic blockers tested, that is, guanethidine, propranolol and phentolamine, increased the contractile responses to the peptides. The results indicate that the colonic contraction induced by neurotensin is mediated via nervous cholinergic pathways. Substance P induces colonic contraction, probably by a direct effect on smooth muscle substance P receptors. Methionine-enkephalin induces colonic contraction which could be blocked by naloxone. However, a cholinergic or peptidergic link may also be involved in the response to methionine-enkephalin.