Inhibitory Effect Of Neurotensin Research Articles

The inhibitory effect of neurotensin on synaptosomal membrane Na +, K +-ATPase is altered by antipsychotic administration

Synaptosomal membrane Na +, K +-ATPase is inhibited by neurotensin, an effect which involves its high affinity receptor (NTS1) [López Ordieres MG, Rodríguez de Lores Arnaiz, G. Peptides 2000; 21:571–576.]. Herein, the effect of neurotensin on synaptosomal membrane Na +, K +-ATPase of rats 18 h after i.p. administration of antipsychotic haloperidol (2 mg/kg) or clozapine (10 mg/kg) was studied. Basal enzyme activity after these treatments did not differ from that in vehicle-treated rats. It was observed that 3.5×10 −6 M neurotensin reduced roughly 40% cerebral cortex Na +, K +-ATPase from vehicle-injected rats, produced no effect on the enzyme from rats injected with haloperidol but enhanced 26% that from rats injected with clozapine. The peptide decreased 40% striatal Na +, K +-ATPase from vehicle-injected rats or from rats injected with clozapine, whereas it failed to alter this enzyme activity from rats injected with haloperidol. Haloperidol and clozapine (1×10 −6 M) added in vitro failed to alter Na +, K +-ATPase activity in cerebral cortex synaptosomal membranes. Results obtained after antipsychotic administration may well offer an alternative explanation for the particular side effects recorded in therapeutics by typical (haloperidol) versus atypical (clozapine) antipsychotic drugs.

The neurotensinergic synaptic innervation of vasopressin containing neurons in the rat hypothalamic paraventricular nucleus

A recent physiological report suggested that neurotensin could inhibit the vasopressin releasing from vasopressin-producing neurons in the hypothalamic paraventricular nucleus but not in the supraoptic nucleus. In the present study, the synaptic relationship between the neurotensin-like immunoreactive and vasopressin-like immunoreactive neurons has been examined using a pre-embedding double immunostaining technique in the rat hypothalamic paraventricular nucleus. At the light microscopic level, many neurotensin-like immunoreactive fibers were found near the vasopressin-like immunoreactive neurons. At the electron microscopic level, the neurotensin-like immunoreactive fibers were identified as axon terminals that made many synapses on the vasopressin-like immunoreactive perikarya and dendrites. The synapses were both asymmetrical and symmetrical. These findings of the present study suggest that the inhibitory effect of neurotensin on the vasopressin neurons in the hypothalamic paraventricular nucleus may be due to the direct synapses made by neurotensin-like immunoreactive axon terminals on the vasopressin-like immunoreactive neurons.

Neurotensin decreases pepsin output and gastrointestinal motility in chickens

Two experiments were conducted to determine the effect of neurotensin on gastric secretion and gastrointestinal motility in conscious chickens. Chickens were surgically fitted with a cannula to collect secretions from the proventriculus and strain gauge transducers sutured to the gizzard, duodenum, and ileum in order to detect contractions. Peripheral intravenous infusion of physiological levels of neurotensin inhibited pepsin output from the proventriculus, but had no effect on the volume or pH of gastric secretions. Neurotensin also inhibited both the frequency and strength of gastrointestinal contractions when compared to motility patterns following infusion of isotonic 0.9% (wt/vol) saline. The frequency of occurrence of small intestinal refluxes was not affected by neurotensin. These results coupled with our earlier work, which demonstrated that neurotensin is released by the presence of oleic acid in the duodenum, indicate that neurotensin may function as an enterogastrone released by lipids in the gastrointestinal tract of the chicken. This overall inhibitory effect of neurotensin on the avian gut indicates that it is involved in the postprandial regulation of digestion, especially lipid digestion.

Inhibition of mechanical activity by neurotensin in rat proximal colon: involvement of nitric oxide.

The aim of the present study was to define the nature of inhibitory action of neurotensin in rat proximal colon. Mechanical activity was detected as changes of intraluminal pressure. Neurotensin (10(-10) to 10(-7) M), in the presence of atropine (10(-6) M), guanethidine (10(-6) M), and nifedipine (10(-8) M), induced a tetrodotoxin-insensitive inhibitory effect characterized by the complete disappearance of the spontaneous phasic contractions. The inhibitory effect of neurotensin (10(-7) M) was abolished by scorpion venom (Leiurus quinquestriatus hebraeus) (10(-6) g/ml) or high K+ (40 mM KCl), whereas it persisted in the presence of omega-conotoxin GVIA, (10(-7) M). N omega-nitro-L-arginine methyl ester (L-NAME) (10(-4) M to 3 x 10(-4) M) antagonized the inhibitory response to neurotensin but did not affect the response to norepinephrine. L-Arginine (5 x 10(-3) M) prevented the effect of L-NAME. The contractile action of neurotensin, observed in the absence of atropine and nifedipine, was potentiated by L-NAME (10(-4) M); L-arginine (5 x 10(-3) M) prevented the L-NAME effect. The present results suggest that in rat proximal colon the inhibitory action of neurotensin is largely due to production of nitric oxide (NO), likely released from neural prejunctional sites. Ca2+ influx through N-type channels is not a required step in the mechanism of neurotensin inhibitory action.

Mediation by neurotensin-receptors of effects of neurotensin on self-stimulation of the medial prefrontal cortex.

1 Intracortical microinjections of neurotensin (NT) selectively decreased intracranial self-stimulation (ICSS) of the medial prefrontal cortex in the rat. 2 To elucidate whether this effect is mediated by NT receptors or by the formation of NT-dopamine complexes, we investigated the effects on ICSS of intracortical microinjections of neurotensin (1-11), an NT fragment that forms extracellular complexes with dopamine but does not bind to NT receptors. 3 We also studied the effects of the peripheral administration of SR 48692, a selective antagonist of NT receptors, on the inhibition of ICSS produced by the intracortical administration of NT. 4 Unilateral microinjections of neurotensin (1-11) at doses of 10, 20 and 40 nmol into the medial prefrontal cortex did not change the basal ICSS rate of this area. 5 The intraperitoneal administration of SR 48692 at doses of 0.08 and 0.16 mg kg-1 30 min before microinjection of 10 nmol of NT into the medial prefrontal cortex, antagonized the inhibition of ICSS produced by the neuropeptide. 6 These results demonstrate that the inhibitory effect of NT on ICSS is mediated by NT receptors.

Neurotensin in the Gut of the Amphibian Necturus maculosus and the Effects of Neurotensin on Stomach Motility

Neurotensin-like material was found throughout the gut of the amphibian Necturus maculosus, in both muscle layers and mucosa, and with the highest levels in the intestine. Ion-exchange high-performance liquid chromatography (HPLC) and reversed-phase HPLC revealed several peaks of immunoreactive material, with one closely related to neurotensin 1-6 occurring by both methods. Exogenous neurotensin was excitatory on longitudinal stomach muscle; this excitation was unaffected by tetrodotoxin, indicating a direct effect on the smooth muscle. An inhibitory effect of neurotensin on circular muscle preparations was abolished by tetrodotoxin, revealing an excitatory effect. Noradrenaline and adrenaline were in many cases inhibitory on the circular preparations, an effect that was blocked by the β-adrenergic anztagonist propranolol. Propranolol also blocked the inhibitory effect of neurotensin in approximately 50% of the tests, which suggests an involvement of an adrenergic link in the inhibitory effect of neurotensin on the circular muscle. The results are compatible with the view that a neurotensin-like peptide is involved in a simultaneous phase of shortening and widening of a segment of the stomach.

Inhibitory effect of neurotensin on proline.

The effect of neurotensin (NT) on proline absorption across rat jejunum was investigated using the single-pass perfusion technique. This study showed that intravenous administration of NT produced a dose-dependent inhibition of proline absorption. Thus, NT at a 0.16 pmol/kg/min concentration gave 10% decrease in proline absorption while 0.32 and 1.6 pmol/kg/min concentration gave 31% and 45% decrease, respectively. In the absence of Na, proline absorption decreased to 77% from control values. No change in proline absorption was noticed when NT at a concentration of 0.32 pmol/kg/min was intravenously injected in the absence of sodium from the perfusion solution. Water absorption did not show significant changes (P > 0.05) in presence or absence of NT. Moreover, NT did not produce a significant change (P > 0.2) in intracellular proline accumulation. NT inhibited proline absorption through an indirect mechanism that is Na-dependent and independent of changes in water absorption.

Direct inhibitory effect of neurotensin on isolated gastric smooth muscle cells of guinea pig via the cyclic GMP system.

Smooth muscle cells isolated from the gastric muscle layers of the guinea pig were used to determine whether neurotensin can inhibit the contractile response produced by 10(-6) M carbachol by exerting a direct action on muscle cells. In addition, the inhibitory effect of 2',5'-dideoxyadenosine, an inhibitor of adenylate cyclase, and methylene blue, an inhibitor of guanylate cyclase, on the neurotensin-induced relaxation of gastric smooth muscle cells were examined. Neurotensin inhibited the contractile response produced by carbachol in a dose-dependent manner, with an IC50 value of 5 nM. 2',5'-Dideoxyadenosine did not have any significant effect on the neurotensin-induced relaxation. On the other hand, methylene blue significantly inhibited the relaxation produced by neurotensin. These results strongly suggest that the action of neurotensin is mediated by cyclic GMP.

Mechanisms of neurotensin-induced inhibition in rat ileal smooth muscle.

The aim of the present study was to determine the mechanisms of neurotensin-induced inhibition in ileal smooth muscle. Isolated rat ileal smooth muscle strips were stimulated in an organ bath using carbachol (CCH) or by KCl depolarization. Neurotensin produced a concentration-dependent inhibition of muscle contraction [mean inhibitory concentration (IC50): 2.8 x 10(-9) M], which was not blocked by phentolamine (10(-6) M), hexamethonium (10(-4) M), indomethacin (10(-6) M), nordihydroguaretic acid (10(-6) M), or tetrodotoxin (10(-6) M). The inhibitory effect of neurotensin during CCH stimulation was blocked concentration dependently in the presence of the K(+)-channel blocker apamin. By contrast, other K(+)-channel blockers such as 9-aminoacridine (10(-6) M to 3 x 10(-5) M), 4-aminopyridine (10(-4) M to 5 x 10(-3) M), tetraethylammonium (10(-4) M to 10(-1) M), or glibenclamide (10(-5) M) were ineffective. The presence of the Ca(2+)-channel antagonist nitrendipine (IC50: 2.4 x 10(-9) M) or verapamil (IC50: 1.1 x 10(-7) M) also blocked the neurotensin inhibitory effect. Ileal contraction, induced by the Ca(2+)-channel activator BAY K 8644 (10(-7) M), was completely inhibited by neurotensin. After depletion of internal Ca2+ stores by repetitive stimulation with CCH and caffeine in Ca(2+)-free buffer, reintroduction of external Ca2+ restored neurotensin inhibition of the contraction induced by CCH. These results demonstrate that the inhibitory effect of neurotensin in rat ileum longitudinal muscle is apamin sensitive and cannot be observed in the presence of the Ca(2+)-channel blockers nitrendipine or verapamil.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuromedin N decreases self-stimulation of the medial prefrontal cortex.

Intracerebral microinjections of neurotensin (NT) decrease intracranial self-stimulation (ICSS) of the medial prefrontal cortex (MPC) in the rat. This effect could be due to the ability of NT to bind dopamine. To test this hypothesis we studied the effects of intracerebral microinjections of neuromedin N, a natural NT analogue that does not bind dopamine, on ICSS of the rat MPC. Unilateral microinjections of neuromedin N into the MPC at doses of 2.5, 5, 10, 20 and 40 nmol produced a dose-related decrease in ICSS of the ipsilateral MPC. ICSS of the contralateral MPC, used as a control, was not affected by the microinjections. These results suggest that the inhibitory effect of NT on ICSS is independent of NT-dopamine binding. Because neuromedin N is also present in the MPC, these results also suggest a possible neuromodulatory role of this neuropeptide on ICSS of the prefrontal cortex.

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.

Heterologous desensitization of bradykinin-induced phosphatidylinositol response and Ca 2+ mobilization by neurotensin in NG108-15 cells

The heterologous desensitization of the bradykinin (BK)-induced increase in intracellular Ca 2+ concentration ([Ca 2+] i) by neurotensin was studied in neuroblastoma × glioma hybid NG108-15 cells. The addition of neurotensin to the cells resulted in an increase in [Ca 2+] i and an increase in the formation of inositol phosphates in Ca 2+ -free medium. Pretreatment of the cells with neurotensin resulted in 43% decrease in the BK-induced increase of [Ca 2+] i. The increase in [Ca 2+] i induced by ionomycin, which causes Ca 2+ release from the intracellular pool, was not decreased by pretreatment with neurotensin. This indicates that the inhibitory effect of neurotensin on the BK-induced increase of [Ca 2+] i was not due to depletion of the intracellular Ca 2+ pool. Pretreatment with neurotensin also caused a 47% decrease in the BK-induced formation of inositol trisphosphates (IP 3). This decrease was not due to depletion of phosphatidylinositol bisphosphates. Neurotensin did not inhibit [ 3H]BK binding to cell membranes. These results show that neurotensin desensitizes the BK responses of NG108-15 cells, heterologously, perhaps by changes in phospholipase C and/or guanine nucleotide-binding protein (G-protein).

Inhibitory effect of neurotensin on pentagastrin-stimulated gastric acid secretion in pylorus-ligated rats

Neurotensin is a known inhibitor of gastrin-stimulated acid secretion in dogs and humans. In order to study the dose-related effect of neurotensin, we prepared pentobarbital-anesthetized rats by pyloric ligation and collected gastric secretions one hour after injection of saline (Basal), pentagastrin, 6 micrograms/Kg subcutaneously (PG Alone), or pentagastrin plus neurotensin by tail vein injection (PG + NT). Acid output was calculated from the volume and pH of the samples, which correlated well with the output determined by titration with 0.02 N NaOH (r = 0.92). Basal output was 36 +/- 4 muEq/hr; stimulated output (PG Alone) was 64 +/- 5 muEq/hr, and output after PG + NT, 250 pmol/Kg, was 33 +/- 3 muEq/hr (p less than 0.001). The effect of neurotensin was dose-related over a range from 125 to 500 pmol/Kg. This technique may be useful in the biological evaluation of neurotensin-related peptides.

Extracellular calcium dependence of the neurotensin-induced relaxation of intestinal smooth muscles: Studies with calcium channel blockers and BAY K-8644

To investigate whether the neurotensin-induced relaxation of the rat duodenum and ileum is dependent on the external concentration of calcium, the effect of the neuropeptide was studied in isolated intestinal segments superfused with Tyrode solution containing no calcium, 1 or 2.5 mM Ca 2+. The neurotensin-induced intestinal relaxation was reduced when the extracellular calcium concentration was lowered. In addition, the inhibitory effect of neurotensin was cancelled when the tissues were incubated in the presence of diltiazem, methoxyverapamil or nifedipine. BAY K-8644, a structural analog of nifedipine that functions as an agonist of the calcium channel, potentiated the neurotensin-induced smooth muscle relaxation. The facilitatory effect of BAY K-8644 was antagonized by nifedipine, indicating competition between the 2 dihydropyridines. Apamin, the K + channel blocker, antagonized the neurotensin-induced visceral relaxation, displacing the concentration-response curve of the peptide to the right. Furthermore, apamin also blocked the effect of neurotensin when the neuropeptide was assayed in the presence of BAY K-8644. It is concluded that the smooth muscle relaxation induced by neurotensin is dependent on external calcium, suggesting that the activation of the neuropeptide receptor causes an influx of calcium which leads to the opening of K + channels before smooth muscle relaxation is triggered.

Neurotensin induced inhibition of gastric acid secretion in duodenal ulcer patients before and after parietal cell vagotomy.

The influence of the vagal nerve on the inhibitory effect of neurotensin on pentagastrin stimulated gastric acid secretion was investigated in seven duodenal ulcer patients before and after parietal cell vagotomy without drainage. Preoperatively, neurotensin inhibited gastric acid secretion, whereas no effect was found postoperatively. Plasma concentration of neurotensin was identical pre-and postoperatively. This study shows that the inhibitory effect of neurotensin on gastric acid secretion is dependent on an intact vagal innervation of the parietal cell area.

Analysis of the Control of Intestinal Motility in Fasted Rats, with Special Reference to Neurotensin

Migrating myoelectric complexes (MMC) in the small intestine of fasted rats were monitored by means of four bipolar electrodes chronically implanted at 5, 15, 25, and 35 cm distal to the pylorus. In intact rats the MMC occurred at regular intervals. Truncal abdominal vagotomy did not influence the initiation and propagation of the MMC. Administration of atropine, hexamethonium, or somatostatin significantly decreased the spiking activity of the MMC by 30-45% in the duodenum and jejunum. Infusion of neurotensin at two different doses (3.6 or 7 pmol X kg-1 X min-1) interrupted the activity front of the MMC and induced irregular spiking activity at all recording levels in control rats. In vagotomized rats neurotensin interrupted the activity front inconsistently. After atropine or hexamethonium administration, infusion of neurotensin did not interrupt the distal propagation of the activity front in the jejunum. Guanethidine, naloxone, cimetidine, mepyramine, haloperidol, and a substance P antagonist did not change the MMC or alter the normal response to neurotensin. The results suggest that the inhibitory effect of neurotensin on the propagation of the jejunal activity front involves activation of enteric cholinergic mechanisms. Neurotensin seems to induce irregular spiking activity by a direct myogenic action. The enteric cholinergic innervation of the small intestine partially contributes to the occurrence of the spiking activity of the MMC in fasted rats.

Effect of neurotensin on mechanical and intracellular electrical activity of the canine stomach.

Intracellular microelectrode and standard organ bath techniques were used to study in vitro the effects of neurotensin on the electrical and mechanical activities of canine antral circular smooth muscle. Neurotensin reduced or abolished spontaneous contractions. Muscarinic and adrenergic antagonists and tetrodotoxin did not block the effects of neurotensin, suggesting that the action of neurotensin was due to a direct action on the smooth muscle cell. Although the inhibitory effect of norepinephrine and neurotensin was similar, the effect of neurotensin did not appear to occur by an adrenergic mechanism because alpha- and beta-receptor blockade had no effect. Neurotensin also reduced or abolished contractions stimulated by pentagastrin and acetylcholine. The inhibitory effect of neurotensin on spontaneous acetylcholine- and pentagastrin-stimulated contractions was associated with a decrease in the amplitude and duration of the plateau potential of the gastric action potential. The data suggest that modulation of antral contractions by neurotensin occurs through a voltage-dependent mechanism that operates during the plateau potential.

Interaction of neurotensin with the substance P receptor mediating histamine release from rat mast cells and the flare in human skin.

1 Substance P induced histamine release from rat peritoneal mast cells in a dose-dependent manner over the concentration range 1 to 10 microM. 2 At concentrations in the range 2.5 to 1 0 microM, neurotensin produced only about 5% release of histamine, which was substantially less than the maximum effect obtained with substance P. 3 Neurotensin, 2.5 to 10 microM produced graded inhibition of histamine release induced by substance P. The inhibitory effect of neurotensin was not seen when histamine release was induced by an antigen-antibody effect of neurotensin was not seen when histamine release was induced by an antigen-antibody reaction or by the ionophore, A 23187. Some evidence was obtained to suggest that compound 48/80 may interact with the same receptor as substance P and neurotensin. 4 [D-Arg8]neurotensin, [D-Arg9]neurotensin, xenopsin and the C-terminal octapeptide of substance P (SP4-11) all inhibited histamine release by substance P, but physalaemin did not. 5 Neurotensin inhibited the wheal and flare reactions induced by substance P in human skin. 6 [D-Trp7,9]substance P released histamine from rat mast cells and was about 12 times more potent than substance P itself. [D-Trp7,9]SP1-11 also produced wheal and flare responses in human skin, being 1.8 times more potent than substance P in the production of flare.