Plasma Neurotensin-like Immunoreactivity Research Articles

Inhibitory effect of neurotensin on gastric acid secretion in rats

Neurotensin has been shown to inhibit gastric acid secretion when administered in pharmacological doses, but no information has been available concerning its possible dose-related effect during intravenous infusion. In this study, a dose-related and reversible inhibitory effect of neurotensin was demonstrated in pentobarbital-anesthetized female Sprague-Dawley rats. The rats underwent continuous gastric perfusion with saline, 1 ml/min, and intravenous infusion of both pentagastrin and neurotensin. Inhibition of acid secretion did not depend upon the occurrence of hypotension, and ranged from 35 +/- 7% of maximal acid output at 0.24 nmol/kg/hr to 60 +/- 10% at 7.2 nmol/kg/hr of neurotensin. Blood levels of C-terminal neurotensin-like immunoreactivity were proportional to the dose of peptide infused and were 52 fmol/ml during infusion of 0.24 nmol/kg/hr, a dose that significantly inhibited pentagastrin-induced acid secretion. Thus, a model has been developed to study the effect of neurotensin infusion on acid secretion; the concentration of plasma neurotensin-like immunoreactivity at which inhibition occurs in this model is similar to the concentration reported to occur after a nutrient stimulus.

The localization of the site(s) of neurotensin release in man and dog

AbstractThe major source of neurotensin in the gut is the ‘N’ cell and this is found in the highest density in the ileum. The ingestion of food, particularly fat, causes the biphasic release of neurotensin‐like immunoreactivity (NTLI) into the circulation. The early peak occurs sooner than expected if it is due to the presence of chyme in the ileum, suggesting that the early release of neurotensin is due to a more proximal concentration of N cells or that neurotensin is released from the ileum by a more proximal stimulus. This paper investigates the site(s) of neurotensin release by studying: three groups of patients with various resections of the small intestine and the fashioning of duodenostomies, jejunostomies and ileostomies; and the dog with chronic gastric, duodenal and ileal fistulae, and following ileal resection. The results indicate that the jejunum and ileum are critical in the release of neurotensin following fat stimulation and that the stomach and duodenum have no direct role. The stimulation of the jejunum by fat causes the early rise of plasma NTLI by releasing neurotensin from the ileum. If chyme is prevented from passing to the distal jejunum the magnitude of the early peak is diminished and the second, later, peak is abolished. The second peak of plasma NTLI is due to the direct luminal stimulation of the distal jejunum and ileum by the products of fat digestion. Ileal resection completely abolishes any release of plasma NTLI in response to fat. It was concluded that the source of neurotensin released by the ingestion of food is the ileum. The release of neurotensin from the distal gut is dependent upon a signal from the proximal to the distal gut. The identity of the signal is unknown, but it is either neural or humoral and previous studies suggest a cholinergic‐dependent reflex.

Local effect of neurotensin on canine ileal blood flow, and its release by luminal lipid.

This study was performed to determine whether the level of neurotensin in mesenteric venous blood after lipid perfusion is sufficient to establish neurotensin as a mediator of lipid-induced mesenteric vasodilation. In anesthetized dogs, arterial flow to segments of the ileum was recorded, and blood was collected for measurement of neurotensin-like immunoreactivity, and neurotensin and metabolites. Perfusion of the lumen with micellar lipid resulted in an increase in blood blow from 37.7 +/- 4.1 to 44.5 +/- 3.9 ml/min/100 g (p less than 0.01; n = 8); flow to a control segment did not change. Venous plasma neurotensin-like immunoreactivity doubled, and neurotensin also increased (to 11.3 +/- 3.9 fmol/ml; p less than 0.05). Close intra-arterial infusion of neurotensin at 5 pmol/min increased blood flow to 44.3 +/- 3.4 ml/min/100 g (p less than 0.025; n = 5); flow to a control segment did not change. Neurotensin-like immunoreactivity increased to the same extent as with lipid perfusion, and neurotensin increased to 28.6 +/- 6.1 fmol/ml (p less than 0.05). No accumulation of metabolites was detected in either experiment. Thus, infused neurotensin caused increased ileal blood flow at a level in venous plasma comparable to that present after lipid perfusion, suggesting that neurotensin may have a role in the local regulation of ileal blood flow.

Regulation of gastric acid secretion by neurotensin in man. Evidence against a hormonal role.

The present study was designed to evaluate neurotensin as a hormonal regulator of gastric acid secretion in man. After a fat-rich meal, the strongest known stimulus of neurotensin release, plasma neurotensin-like immunoreactivity (NTLI) was elevated from 7.6 +/- 1.9 to 15.5 +/- 2.5 pM. Plasma NTLI was measured with antiserum L170, which requires the biologically active carboxyl-terminal hexapeptide of the neurotensin molecule for recognition and does not crossreact significantly with any known natural catabolite in human plasma. Intravenous infusion of neurotensin at 25 pmol X kg-1 h-1 resulted in a plasma level of 14.7 +/- 2.1 pM, similar to the maximal physiological level observed after the fat-rich meal. Intravenous infusion of neurotensin at 25 pmol X kg-1 h-1 during 2 h, however, failed to significantly inhibit peptone meal-stimulated gastric acid secretion measured by intragastric titration. The 2-h acid output to peptone was 40.8 +/- 6.2 and 41.3 +/- 6.9 mmol during the vehicle and the neurotensin infusion, respectively. Intravenous infusion of neurotensin at 100 or 400 pmol X kg-1 h-1 did not affect acid output, whereas at 1,600 pmol X kg-1 h-1, which resulted in a plasma neurotensin concentration of 725 +/- 80 pM, significantly reduced peptone meal-stimulated gastric acid secretion. The neurotensin-induced inhibition of acid output was independent of the hormone gastrin. The present results provide evidence against a hormonal role for neurotensin in the regulation of meal-stimulated gastric acid secretion in man.

The role of the liver in the metabolism of neurotensin‐like immunoreactivity in man and dog

Abstract To assess the role of liver in the metabolism of neurotensin‐like immunoreactivity (NTLI) basal and meal‐stimulated levels of plasma NTLI were measured by radioimmunoassay, employing a specific C‐terminal antiserum in: healthy control subjects; patients with cirrhosis of the liver who had previously undergone a portacaval shunt; and patients with cirrhosis of the liver and hepatic failure, without a portacaval shunt. Neurotensin (1–13) was infused into the portal vein of the dog for 60 min, at a dose of 100 pmol/kg per min, and blood sampled simultaneously from the portal, hepatic and peripheral venous systems to determine the hepatic extraction and clearance of NTLI. The results revealed that: the liver is a major site of neurotensin metabolism; transhepatic extraction of exogenous neurotensin was 39%; hepatic clearance of NTLI was about 13 ml/kg per min and the total metabolic clearance of NTLI was 36.8 ml/kg per min (s.e.m. = 4.8) and the t½ of NTLI was 2.8 min.

Neurotensin-like immunoreactivity released into the portal vein by duodenal acidification in the dog.

The present study in the dog evaluates neurotensin as a potential hormone, mediating the inhibition of gastric acid secretion by duodenal acidification. Histamine-stimulated acid output was determined before and during duodenal acidification. Portal vein blood was obtained and assayed for carboxy-terminal neurotensin-like immunoreactivity (NTLI). Duodenal perfusion with 15 mmol HCL for 30 min significantly inhibited histamine-stimulated acid output to 67% of control output. This inhibition was not associated with any change in the peripheral plasma NTLI, but the portal plasma NTLI was significantly elevated from 27 to 78 pM. The effect of duodenal acidification on liver extract meal-stimulated acid secretion was determined in a second group of dogs without portal vein catheter. Duodenal perfusion with 15 mmol HCl for 30 min significantly inhibited meal-stimulated acid secretion to 37% of control output. Intravenous infusion of synthetic neurotensin to a plasma level of 130 pM was required to inhibit meal-stimulated acid output significantly. In summary, NTLI is elevated in portal, but not peripheral, plasma after duodenal acidification. The associated inhibition of acid secretion is not due to hormonal action of neurotensin.

The effect of atropine and vagal stimulation on the release of neurotensin-like immunoreactivity in man.

This study investigated the food stimulated release of neurotensin-like immunoreactivity (NTLI) in man with and without the administration of atropine, and the influence of vagal stimulation by modified sham feeding and insulin hypoglycaemia. NTLI was measured, after ethanol extraction, by specific C- and N-terminally directed antisera. With both a liquid fat meal and a mixed meal an early peak of NTLI occurred. The mixed meal also produced a second sustained rise in plasma NTLI. An intramuscular injection of 0.6 mg atropine sulphate abolished the early peak, but had no effect on the late peak. Modified sham feeding and insulin hypoglycaemia did not release NTLI. We conclude that it is possible that a cholinergic non-vagal mechanism is responsible for the early phase of food stimulated release of NTLI in man, and that the second sustained rise may be cholinergically independent.

Quantitation and characterization of human plasma neurotensin-like immunoreactivity in response to a meal.

The secretion and metabolism of endogeneous neurotensin-like immunoreactivities after a test meal were studied in five healthy human subjects. Intact neurotensin and the N-terminal metabolic fragment, neurotensin 1-8, were quantified by radioimmunoassay with C- and N-terminally directed antisera in conjunction with gel filtration of plasma samples obtained at timed intervals. Both C- and N-terminal neurotensin-like immunoreactivities rose after the meal, reaching a plateau level after 20 and 30 min, respectively. During the plateau phase, which lasted for the rest of the experimental period of 180 min, the molar ratio of intact neurotensin to neurotensin 1-8 remained approximately constant at 1:4.6. Meal-stimulated immunoreactive neurotensin appeared to be metabolized in a manner comparable to that of exogenously infused neurotensin in man. The results suggest that intact neurotensin is secreted at an approximately constant rate during the plateau phase. The relatively low plateau level of neurotensin 1-8, which has a much longer half-life than intact neurotensin in the circulation, implies that only a fraction of the secreted intact neurotensin is metabolized to neurotensin 1-8, indicating the existence of alternative pathways of neurotensin metabolism.

Postprandial release of neurotensin-like immunoreactivity and its mechanism.

The effects of various ingested materials on plasma neurotensin-like immunoreactivity (NTLI) in humans were investigated using a newly developed, specific radioimmunoassay. Plasma NTLI was determined after its extraction with acid/acetone (recovery 77 +/- 4%). The intraassay and interassay coefficients of variation were 3.6% and 8.9%, respectively. The plasma concentration of human NTLI in normal subjects was 5.6 +/- 2.9 pmol/l and showed no significant sex difference. Ingestion of a test meal (150 g of Campbell's condensed meat soup) caused a biphasic rise in plasma NTLI from a basal level of 5.7 +/- 1.0 pmol/l to 10.8 +/- 1.2 pmol/l after 30 min and 9.6 +/- 1.1 pmol/l after 120 min. Ingestion of 5.5 g fat resulted in a biphasic rise in plasma NTLI from a basal level of 4.8 +/- 0.3 pmol/l to 8.9 +/- 0.3 pmol/l after 15 min and 11.9 +/- 0.4 pmol/l after 90 min. When 100-150 mg of ileal mucosa was perfused with a solution of 2 mEq/l fatty acids, 1 mM or 5 mM sodium taurocholate or 154 mM sodium bicarbonate (NaHCO3), the release of NTLI from the mucosa into the perfusate was 2.3-fold, 4.3-fold and 7.5-fold, respectively, over the base level. These results indicate that NTLI release is stimulated by ingestions of meat soup and fat and that NTLI present in the human ileum is released by the direct actions of solutions of fatty acid, sodium taurocholate, and NaHCO3 on the ileal mucosa. These findings strongly suggest that neurotensin (NT) has a physiological role in gut physiology.

Chromatographic characterization of plasma and tumour neurotensin-like immunoreactivity in a hepatoma patient

Chromatographic characterization of plasma and tumour neurotensin-like immunoreactivity in a hepatoma patient

Nervous control of the release of neurotensin-like immunoreactivity from the small intestine of the rat.

Intraduodenal administration of oleic acid increased plasma neurotensin-like immunoreactivity (p-NTLI). The integrated responses to saline and oleic acid were 5.7 and 9.7 nM0-180 min, respectively. The integrated response was not significantly altered by i.v. administration of atropine, guanethidine, mepyramine, cimetidine, methysergide or a substance P antagonist, but it was abolished by hexamethonium and morphine (5.9 and 6.3 nM0-180 min, respectively). An exogenous supply of bile and pancreatic juice did not alter the integrated response in morphine- and hexamethonium-treated rats. Haloperidol significantly increased the p-NTLI response to oleic acid (13 nM0-180 min). The results suggest that the release of neurotensin is influenced by nervous pathways involving nicotinic and opioid receptors. Catecholamines and 5-HT receptors may exert an inhibitory influence on the release of NTLI.

Secretion of Neurotensin and Its Effects on the Jejunum in the Dog

The triple-lumen perfusion technique was used to assess the effect of neurotensin on the canine jejunum; net water and electrolyte fluxes were measured during intravenous infusion of neurotensin and during preceding and succeeding control infusions of sodium chloride. A pharmacologic dose of neurotensin (70 pmol X kg-1 X min-1) converted basal net jejunal water and electrolyte absorption to net secretion (p less than 0.02); 3.2 pmol X kg-1 X min-1 of the peptide significantly inhibited net water and electrolyte absorption (p less than 0.05), and induced a transient but consistent increase in jejunal transmural potential difference; however, 1.3 pmol X kg-1 X min-1 had no significant effect on net jejunal water and electrolyte fluxes. Neurotensin (1.3 pmol X kg-1 X min-1) induced a rise in plasma neurotensinlike immunoreactivity which was greater than the increment occurring after a normal meal, but which could be reproduced in the same animals by infusion of oleic acid into the ileum. This latter stimulus, however, had no effect on jejunal potential difference, or net water and electrolyte fluxes. These observations do not support a hormonal role for neurotensin in the postprandial regulation of intestinal function in the dog, although they do not rule out the possibility of physiologic paracrine activity.

Effect of Intravenous and Intrajejunal Fat Infusion on Gastric Acid Secretion and Plasma Neurotensin-like Immunoreactivity in Man

The effects of intrajejunal and intravenous infusion of fat (100 ml Intralipid 20%) on pentagastrin-stimulated gastric acid secretion and on the concentrations of plasma neurotensin-like immunoreactivity (p-NTLI) were studied in eight healthy subjects. Gastric acid secretion was studied for a 1.5-h period at 15-min intervals after fat administration. Acid secretion was reduced by 58% and 36%, respectively, after intrajejunal and intravenous administration. The concentration of p-NTLI rose significantly from 29 to 177 pmol/l at 45 min after intrajejunal administration but did not change after intravenous infusion. The results indicate that large volumes of fat inhibit gastric acid secretion by a neurotensin-independent postabsorptive mechanism and by an intestinal mechanism that may in part be mediated by neurotensin.

Neurotensinlike immunoreactivity in plasma and tumor tissue from patients with endocrine tumors of the pancreas and gut

Nine of 34 (26%) consecutive patients with different endocrine gastrointestinal tumors had increased levels of plasma neurotensinlike immunoreactivity in the fasting state. This was the case in 6 of 18 (33%) patients with endocrine pancreatic tumors and in 3 of 16 (19%) patients with gut tumors. Only 1 of 13 patients with midgut tumors had increased plasma-neurotensinlike immunoreactivity, despite the fact that most of the normal neurotensin-containing cells are located in the midgut. In 3 of 4 cases the concentration of plasma-neurotensinlike immunoreactivity decreased after streptozotocin or surgical treatment. In 1 patient, increasing levels of plasma-neurotensinlike immunoreactivity were found several months before the onset of clinical symptoms or signs of relapse after surgical treatment. Neurotensin was found in extracts of primary tumors and metastases. Plasma-neurotensinlike immunoreactivity in patients with “neurotensinomas” represents more than one molecular form, including neurotensin(1–13) and neurotensin(1–8). Neurotensin(1–8) in plasma may be a degradation product of neurotensin(1–13) released from the tumor tissue. We have not been able to relate any specific symptoms to elevated plasma-neurotensinlike immunoreactivity.

Cholinergic inhibition of meal stimulated plasma neurotensin like immunoreactivity in man

Meal stimulated plasma neurotensin like immunoreactivity (NTLI) was compared during saline or atropine infusion in six volunteers over six hours. Plasma gastrin and pancreatic polypeptide were also measured to compare the timing of their release to that of NTLI. Like plasma gastrin and PP, plasma NTLI rose rapidly following the meal, rising from 27±7 pmol/1 to a peak of 45±8 pmol/1 at 20 minutes (p < 0.05). Also, like that of pancreatic polypeptide, the release of NTLI was biphasic. Sixty minutes after the meal, plasma NTLI had returned to basal values, followed by a rise to a prolonged peak of 64±10 pmol/1 between 90–180 minutes (p < 0.05) returning once more to basal values by 240 minutes. Following atropine, basal plasma NTLI fell from 22±4 pmol/1 to 11±2 pmol/1 (p < 0.05), but rose to basal levels 30–60 minutes after the meal, where it remained unaltered for the remainder of the study. We conclude that both basal and meal stimulated plasma NTLI are inhibited by cholinergic blockade. Further, the similar temporal relationship between plasma NTLI and pancreatic polypeptide in the late phase of the meal response, suggests that a component of NTLI may mediate part of the intestinal phase of pancreatic polypeptide release.

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.

Characterization of human plasma neurotensin-like immunoreactivity after fat ingestion

The concentration of neurotensin-like immunoreactivity in plasma (p-NTLI) increases after the ingestion of food, and fat seems to be the most important nutrient. It is essential to characterize the NT species that are responsible for this postprandial rise of p-NTLI. After an overnight fast, two male and two female subjects therefore ingested 300 ml of cream (containing 40% (w/w) milk fat). Unextracted plasma samples were subjected to column chromatography and the eluates were analysed using four NT antisera having different specificities. The concentration of chromatographically identified NT(1–13) in peripheral plasma increased significantly from 3 pM in the fasting state to 26 pM 30 min after the ingestion of fat. The concentration of NT(1–8), which is probably a metabolite of NT(1–13), also increased markedly. No significant increase of smaller COOH-terminal sequences of NT was found. The results show that the plasma concentration of NT(1–13) may increase about tenfold following the ingestion of fat. This is further support for the hypothesis that NT(1–13) may function as a hormone.

Plasma neurotensin release and gastric emptying in the dumping syndrome

Seventy-three patients were studied after ingesting a liquid glucose meal, tagged with 113Indium. Nineteen of these patients were awaiting surgery for their duodenal ulcer, while 54 were studied postoperatively, 25 of whom experienced troublesome postprandial (dumping) symptoms in their daily lives. The radioactive marker emptied significantly faster in the symptomatic patients than in the symptomfree, pre and post-operative groups (initial emptying rate 3.45 ± 0.23, compared with 1.16 ± 0.19 and 1.27 ± 0.15% fall in counts/min respectively; p < 0.01). Initial (20 min) rises in the plasma concentrations of neurotensin-like immunoreactivity measured during the test correlated significantly with the rate of gastric emptying in all patients, being greatest in patients with dumping symptoms. Physiological concentrations of neurotensin have been shown to delay gastric emptying. The excessive rise in plasma neurotensin-like immunoreactivity in patients with dumping symptoms, presumably occuring as a result of the rapid passage of nutrients to the neurotensin-rich ileum, may possibly have a compensatory role in slowing further emptying from the stomach.

Plasma neurotensin-like immunoreactivity (P-NTLI) in the rat after duodenal administration of fatty acids, triolein, lecithin and paraffin oil

Plasma neurotensin-like immunoreactivity (P-NTLI) in the rat after duodenal administration of fatty acids, triolein, lecithin and paraffin oil

The effect of intraduodenal installation of oleic acid on plasma neurotensin-like immunoreactivity and on gastric acid secretion stimulated by betazole and sham feeding in man.

Intraduodenal administration of oleic acid has previously been shown to inhibit gastric acid secretion induced by pentagastrin in man. This inhibition was dose-dependent and significantly correlated to a rise in plasma concentration of neurotensin-like immunoractivity (NTLI). Maximal inhibition occurred with a volume of oleic acid of 20 ml. In the present study intraduodenal instillation of 20 ml. of oleic acid inhibited acid secretion evoked by sham feeding in healthy subjects but did not significantly inhibit the near-maximal acid secretion stimulated by the histamine analogue betazole. The inhibition of acid secretion induced by sham feeding was the same (about 45%) as the inhibition of pentagastrin-stimulated secretion. Plasma NTLI rose significantly in both the sham feeding and betazole experiments and peaked at about 145 pM. The results are in agreement with the inhibitory characteristics of neurotensin and support the hypothesis that the inhibition of gastric acid secretion by small amounts of intestinal fat is at least partly mediated by neurotensin.