Purification, characterization, and spasmogenic activity of neurotensin from the toad Bufo marinus

Neurotensin (NT) was isolated from an extract of the intestine of the cane toad, Bufo marinus and its primary structure established as: pGlu-Ala-Ile-Val-Ser-Lys-Ala-Arg-Arg-Pro-Tyr-Ile-Leu. This amino acid sequence shows five substitutions (Leu2 --> Ala, Tyr3 --> Ile, Glu4 --> Val, Asn5 --> Ser, and Pro7 --> Ala) compared with bovine NT. Synthetic Bufo NT (pD2 = 8.05 +/- 0.28) was equipotent and equally effective as bovine NT (pD2 = 8.24 +/- 0.38) in producing spasmogenic contraction of isolated segments of toad small intestine. However, the maximum response produced by Bufo NT was only 35 +/- 2% of that produced by substance P. The potencies, but not the maximum responses, to Bufo and bovine NT were significantly (p < 0.05) attenuated by pre-treatment with atropine but neither parameter was significantly diminished by tetrodotoxin and indomethacin. The data suggest that the action of NT involves interaction with receptors on toad intestinal smooth muscle that recognize the C-terminal region of NT (residues 8-13) that has been fully conserved during evolution of tetrapods. Contractile activity is mediated, at least in part, by release of acetylcholine.

Huntingtin is a cytoplasmic protein associated with vesicles in human and rat brain neurons

The gene defective in Huntington's disease encodes a protein, huntingtin, with unknown function. Antisera generated against three separate regions of huntingtin identified a single high molecular weight protein of approximately 320 kDa on immunoblots of human neuroblastoma extracts. The same protein species was detected in human and rat cortex synaptosomes and in sucrose density gradients of vesicle-enriched fractions, where huntingtin immunoreactivity overlapped with the distribution of vesicle membrane proteins (SV2, transferrin receptor, and synaptophysin). Immunohistochemistry in human and rat brain revealed widespread cytoplasmic labeling of huntingtin within neurons, particularly cell bodies and dendrites, rather than the more selective pattern of axon terminal labeling characteristic of many vesicle-associated proteins. At the ultrastructural level, immunoreactivity in cortical neurons was detected in the matrix of the cytoplasm and around the membranes of the vesicles. The ubiquitous cytoplasmic distribution of huntingtin in neurons and its association with vesicles suggest that huntingtin may have a role in vesicle trafficking.

Physiological significance of neurotensin in pituitary glycoprotein hormone release as revealed by in vivo and in vitro studies with neurotensin antiserum

The neuropeptide, neurotensin, is localized to neurons within the hypothalamus which project to the median eminence. It is released from the terminals in the median eminence into the hypophyseal portal vessels and is carried to the gland. The content in the pituitary gland cells may be partly related to the delivery of the peptide via the portal vessels, but it also appears to be produced directly in pituitary cells. The peptide has actions on the release of glycoprotein hormones from the pituitary and in the present experiments, we attempted to determine whether these actions of the peptide were physiologically significant by microinjecting purified antiserum directed against neurotensin into the third cerebral ventricle or intravenously into conscious freely moving rats. Blood samples were withdrawn from an indwelling intra-right atrial catheter. In ovariectomized rats with high levels of plasma gonadotropins because of removal of ovarian steroid negative feedback, the intraventricular injection of the higher (3 microliters) dose of neurotensin antiserum (NT-AS) induced a more than 2-fold increase in plasma LH within 2 h which was maintained until 3 h after the injection and returned to basal values in the 4th and 5th hour. The lower 1-microliter dose was ineffective and there was no response to the control normal rabbit serum (NRS) injections into the third ventricle in this and the other experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of antiserum to neurotensin reveals a physiological role for the peptide in rat prolactin release

Previous studies have indicated that the brain peptide neurotensin can stimulate prolactin release by direct action on the pituitary gland, whereas its action within the hypothalamus is inhibitory. The inhibitory action is mediated by the release of dopamine into the hypophyseal portal veins, which deliver the neurotransmitter to the anterior pituitary gland to inhibit prolactin release. Our experiments were done to evaluate the physiologic significance of these neurotensin actions by injecting the globulin fraction of highly specific neurotensin antiserum either intravenously or intraventricularly. Injection into the third ventricle of either 1 or 3 microliter of neurotensin antiserum significantly increased plasma prolactin concentrations in (i) ovariectomized and (ii) ovariectomized estrogen- and progesterone-primed rats within 1 hr of injection. The response was more pronounced in the ovariectomized than in the ovariectomized estrogen- and progesterone-treated animals and was dose related. Intraventricular injection of these doses of neurotensin antiserum also evoked elevations in plasma prolactin in intact males, which were significant but smaller in magnitude than those seen in female rats. To evaluate the effect of the antiserum on the pituitary directly, the antiserum was injected intravenously at a dose of 40 microliter, which was sufficient to block the blood pressure-lowering effect of neurotensin. After the intravenous injection of antiserum, a highly significant suppression of plasma prolactin occurred, detectable when first measured at 1 hr after injection in both ovariectomized and ovariectomized estrogen- and progesterone-treated animals; however, the intravenous injection of antiserum had no significant effect on the prolactin release in males. These data indicate the physiological significance of the hypothalamic inhibitory actions of neurotensin on prolactin release, which are probably mediated by its stimulation of dopamine release that in turn, inhibits prolactin secretion by the lactotropes. The direct stimulatory effect of the peptide on prolactin release after its presumed release into portal vessels also appears to be physiologically significant in female but not in male rats.

Ganglion cells in the turtle retina contain the neuropeptide LANT-6

This study investigated the presence of the neurotensin-related hexapeptide, LANT-6, in retinal ganglion cells and their central projections in the turtle Pseudemys scripta elegans. Immunocytochemical techniques demonstrated that many of the cells in the ganglion cell layer of the turtle retina could be labeled with an antiserum specific for LANT-6. Radioimmunoassay and chromatographic analysis confirmed the presence of LANT-6-related peptides in retina, as well as brain. Several molecular forms of LANT-6 were observed, some larger than LANT-6. Characterization of the cells labeled in the ganglion cell layer in terms of their cell body size and their dendritic arborization patterns revealed that at least 6 specific LANT-6-positive cell types were present in the ganglion cell layer. Morphologically, the LANT-6-positive cells strongly resembled turtle ganglion cells, as previously described. In addition, two other lines of evidence supported this interpretation. First, double-label studies were performed in which retinal ganglion cells projecting to the tectum were retrogradely labeled by HRP injected into the tectum (using a cobalt chloride color-modified DAB reaction product) and immunocytochemically labeled with DAB using the antiserum against LANT-6. These double-label studies revealed that many of the LANT-6-positive cells in the ganglion cell layer in the portion of the retina labeled retrogradely by the HRP injection did project to the tectum. Within the retrogradely labeled portion of the retina, LANT-6-positive cells that were not labeled retrogradely, as well as neurons labeled retrogradely that did not contain LANT-6 were also observed. Second, the central projections of LANT-6-positive cells of the ganglion cell layer were examined by studying the effects of monocular enucleation on the distribution of LANT-6-positive fibers in the central projection targets of the turtle retina. Two to 8 weeks after enucleation, a substantial reduction in LANT-6-positive fibers was observed in all retinal target areas contralateral to the enucleated eye. Radioimmunoassay and chromatographic studies confirmed the presence of LANT-6-related peptides in the turtle brain and corroborated the reduction of LANT-6 observed in the contralateral tectum following monocular enucleation. Previous studies have demonstrated that LANT-6-related material is present in cells of the ganglion cell layer in a variety of vertebrates. The present results indicate that LANT-6 is in ganglion cells and that it may play a role in neurotransmission between retinal ganglion cells and their central target areas.

Reproduction of postprandial neurotensin plasma levels by intravenous neurotensin and the effect of neurotensin on exocrine pancreatic secretion in humans

A fatty meal releases neurotensin immunoreactivity from the small bowel in humans and dogs, and an infusion of synthetic neurotensin elicits exocrine pancreatic secretion in these species. It is not clear, however, which amount of exogenous neurotensin will reproduce endogenous neurotensin plasma levels as postprandial neurotensin immunoreactivity is composed of several fragments of neurotensin without biologic activity in addition to intact neurotensin. In order to clarify this question, we infused 1.25, 2.5, 5.0 and 7.5 pmol/kg/min synthetic Gln4-neurotensin in four volunteers, determined neurotensin plasma levels with a radioimmunoassay recognizing only intact neurotensin, and collected duodenal contents for estimation of pancreatic secretion. On another day, we determined neurotensin plasma levels after a fatty meal. Reverse-phase high-pressure liquid chromatography (HPLC) was performed on postprandial plasma samples. We found a stimulatory action of neurotensin on pancreatic secretion of volume enzymes and bicarbonate beginning with 1.25 pmol/kg/min neurotensin. The neurotensin plasma level after infusion of this dose of synthetic neurotensin was 69 pg/ml; after the meal, maximal neurotensin plasma concentration was 50 pg/ml (basal neurotensin plasma levels in both investigations were subtracted). HPLC indicated the presence of the tridecapeptide known to be the active molecular form of neurotensin in postprandial plasma. These results suggested that neurotensin plays a role as an endocrine hormone in the postprandial regulation of exocrine pancreatic secretion in humans.

Preparative electrophoresis of histones in solubilizable polyacrylamide gels

Histones from the mouse testis have been fractionated on 17% acrylamide gels containing 0.19% Bis-acrylylcystamine (BAC), 25 M urea and 0.4% Lubrol-WX at pH 2.7. Polyacrylamide gels which contain BAC, a cross-linking agent with disulfide bonds, can be solubilized in the presence of 2-mercaptoethanol, at pH 8.3. Polymerization is carried out at 40 degrees C and in the presence of 6.5--7.5% tetramethylethylenediamine (TEMED) at pH 8.3. Gels containing high acrylamide concentration (greater than 15%) are not soluble if polymerized at lower pH or TEMED concentrations. Following electrophoresis, the gels are stained with Coomassie brilliant blue R for the visualization of protein bands. The stained protein bands are excised and adjusted to pH 8.3 prior to their solubilization. The histones are recovered by ion-exchange chromatography and are free of soluble gel components and dye. Two variants of histone H2B (H2B . 1 and H2B . 2) have been isolated at approx. 95% purity using this single purification step.

Amphibian neurotensin (NT) is not xenopsin (XP): dual presence of NT-like and XP-like peptides in various amphibia

To clarify whether xenopsin (XP) is the amphibian counterpart of mammalian neurotensin (NT), extracts of skin, brain, and intestine from representative amphibians were subjected to immunochemical, chromatographic, and biological analyses. The results indicated the dual presence of NT- and XP-like peptides in extracts of tissues from Xenopus laevis, Rana catesbeiana, Rana pipiens, Bufo marinus, Bufo americanus, and Necturus maculosus, which were separated during gel chromatography on Sephadex G-25 and high pressure liquid chromatography on mu-Bondapak C-18. Immunochemical studies, employing three different region-specific antisera toward NT (ox and man) and one antiserum towards XP (Xenopus laevis), indicated that the NT-like peptides shared COOH-terminal homologies with NT and differed at their NH2-termini. TWo classes of NT-like peptides could be distinguished on the basis of their distributions in tissues and their cross-reactivities with the antisera; immunoreactive NT measured using antiserum HC-8 tended to be found primarily in brain and intestine, whereas that reactive with antiserum PGL-4 was most concentrated in stomach, liver, and pancreas. Although also present in brain and intestine, immunoreactive XP was highest in stomach, pancreas, and skin. Partially purified immunoreactive NT and XP obtained from gastrointestinal tissues of Xenopus laevis and Bufo marinus were shown to increase the hematocrit and induce cyanosis in anesthesized rats. These findings indicate the presence of both NT- and XP-like peptides in neural and gastrointestinal tissues from several amphibia and suggest the possibility that XP-like peptides (apart from NT) may exist in other animals.

Distribution and immunochemical character of neurotensin-like material in representative vertebrates and invertebrates: apparent conservation of the COOH-terminal region during evolution

Using a radioimmunoassay for bovine neurotensin (NT) and various region specific antisera which react selectively with different portions of the molecule, the presence of immunoreactive NT (iNT) in a wide range of vertebrate and invertebrate species has been demonstrated. While antisera directed towards the N-terminal region of NT recognized only mammalian forms of NT, antisera directed towards the C-terminal region of NT recognized materials from all species examined, including representatives of all vertebrates and invertebrate classes. When extracts of the brain and gut of the vertebrates examined were chromatographed on Sephadex G-25 multiple NT-like substances were observed, and the patterns of iNT obtained seemed to fall into three groups: (a) mammals, (b) birds and reptiles and (c) amphibians and fish. Extracts of invertebrates also exhibited multiple peaks of iNT on Sephadex G-25 and the profiles observed resembled those for lower vertebrates. Partially purified iNT obtained from chicken, turtle, dogfish and lobster was shown to increase hematocrit and induce cyanosis in anesthetized rats. These findings indicate (a) that NT-like substances appear to be present throughout the animal kingdom, (b) that the C-terminal region of NT is highly conserved while the N-terminal region varies, and (c) that in any one animal multiple substances sharing C-terminal homologies with NT exist. These findings are consistent with the notion that NT and related peptides participate in important processes basic to animal life and that their functioning depends highly upon elements located in their C-terminal regions. They further suggest the existence of an entire family of NT-related peptides in each animal form, possibly distributed differently and functioning differently in the various organs of the animal.

Neurotensin stimulates exocytotic histamine secretion from rat mast cells and elevates plasma histamine levels

1. Neurotensin stimulated histamine release and granule extrusion when applied to isolated rat peritoneal mast cells. 2. This secretory response was prevented by the removal of calcium or energy and was not accompanied by the release of lactic dehydrogenase. 3. The secretory response produced by neurotensin was prevented by prior treatment of mast cells with cromoglycate. 4. The intravenous injection of neurotensin into anaesthetized rats produced a rapid and significant increase in the level of blood histamine that was dependent upon the dose of neurotensin. 5. Treatment of rats with compound 48/80, 24 hr before neurotensin, abolished the elevation in blood histamine caused by neurotensin. The intravenous injection of cromoglycate 1-2 min before neurotensin greatly reduced the response to neurotensin. 6. The intradermal injection of neurotensin (0.03-30 p-mole) increased capillary permeability in rats pre-treated intravenously with Evans Blue. This response was abolished by the antihistamine, diphenhydramine. Increasing the dose of neurotensin to 300 p-mole partially overcame this inhibition by diphenhydramine. 7. Our results demonstrate that neurotensin can elicit an exocytotic secretory response from isolated rat peritoneal mast cells and elevate histamine levels in blood. It is suggested that some of neurotensin's physiological effects may be due to stimulation of mast cell secretion.

A multihormonal tumor of the pancreas producing neurotensin

In a pancreatic adenoma approximately 78.7% of the endocrine cells reacted specifically with antisera to neurotensin, 17.5% to gastrin, 2.8% to pancreatic polypeptide, and 1% to glucagon. The electron microscope revealed that the majority of the endocrine cells were N-cells--morphologically similar to the ileal N-cells which are known to represent the neurotensin-producing cells. Neurotensin was extracted from the tumor and identified by Sephadex, ion-exchange, and high-pressure liquid chromatography. Gastrin, pancreatic polypeptide, and glucagon cells were also identified by the electron microscope; the peptides were extracted and demonstrated by chromatography. The serum concentrations of these hormones were elevated. After total gastrectomy which was necessary because of Zollinger-Ellison syndrome, a jejunoesophageal alkaline reflux, reaching the upper esophagus appeared. As intravenous infusion of synthetic neurotensin in rats caused an increase of luminal enteric pressure, it is suggested that severe jejunoesophageal reflux after gastrectomy may be a clinical feature of a neurotensinoma.

Bacterial peptides with C-terminal similarities to bovine neurotensin

Using radioimmunoassay, peptides resembling the C-terminal region of bovine neurotensin (NT) have been demonstrated in acid/acetone extracts of Rhodopseudomonas palustris, Escherichia coli, and Caulaobacter crescentus. The NT-like bacterial components were shown to behave as peptides of small molecular weight (less than 2000) which were stable to acid and heat but labile to proteolytic digestion. In the radioimmunoassay toward NT they displayed dose-response curves parallel to standard and gave results indicating a competitive type of interaction with NT binding sites on antibody. The bacterial extracts did not register in a control radioimmunoassay toward rat luteinizing hormone. Some of the NT-like immunoreactivity could also be bound to an retrieved from anti-NT-antibody-Sepharose preparations. Since the C-terminal region of NT constitutes its biologically active core, these results suggest that presence of biologically important congeners of NT in bacteria.

Neurotensin in plasma: immunochemical and chromatographic character of acid/acetone-soluble material

Using a RIA, we have examined the character of the neurotensin-like (NT-like) peptides present in acid/acetone extracts of animal and human plasma. Plasma immunoreactivity was measured using four antisera with different specificities. Antisera which were directed against the COOH-terminus of NT measured higher levels of plasma immunoreactivity than did antisera with NH2-terminal or mixed specificity. Chromatographic fractionation of bovine plasma extracts revealed the presence of multiple substances, one of which was chromatographically and immunochemically indistinguishable from NT. We estimate the plasma level of this component to be about 15-25 fmol/ml, which is 30-50% of the measurement obtained on unfractionated extracts using antiserum HC-8. Several other components were also identified which behaved as though they were smaller than NT and seemed to share with NT four to eight of its COOH-terminal amono acids. One eluted from Sephadex G-25 in the region of the NT-like peptide previously identified in extracts of gastric mucosa. Infusion of synthetic NT into rats for 30 min did not result in the formation of these COOH-terminal relatives of NT. Our results argue strongly for the presence of NT in plasma and also indicate that other peptides, sharing COOH-terminal homologies with NT, appear in plasma, possibly from the stomach, liver, and other as yet unidentified source(s).

Neurotensin neurons in the rat hypothalamus: an immunocytochemical study

Neurotensin was localized in the hypothalamic tissues of adult Sprague-Dawley rats by immunoperoxidase techniques. Visualization of perikarya was greatly enhanced by intraventricular administration of colchicine. Many perikarya containing neurotensin-like immunoreactivity were seen in the medial preoptic area, the periventricular hypothalamus, the parvocellular portion of the paraventricular nucleus, the arcuate nucleus, and the lateral hypothalamus in the perifornical area. There were moderate numbers of cell bodies in the ventral portion of the anterior hypothalamus, the dorsomedial nucleus, and the posterior hypothalamus. No positive cells were seen in the suprachiasmatic, ventromedial, or mammillary nuclei. Reactive fibers were generally distributed in the same regions as cell bodies. Additional dense collections were seen in the lateral part of the zona externa of the median eminence, the pituitary stalk, the posterior mammillary nucleus, and the most lateral portions of the hypothalamus at the medial edge of the crura cerbri. There were smaller numbers of fibers found in the pre-mammillary and posterior hypothalamic nuclei and the posterior pituitary gland. These results indicate that the neurotensin system in the hypothalamus is very extensive and complex, as it is in many other brain regions. Neurons and fibers are found in many hypothalamic areas, including projections to the hypophysial portal system in the median eminence, suggesting that neurotensin may affect neuroendocrine mechanisms at several levels, including the anterior pituitary gland.

Isolation of human intestinal neurotensin

The biologically active peptide neurotensin (NT) has been isolated from fresh postmortem human small intestine and its identity with bovine hypothalamic and intestinal neurotensin has been established. Purification was achieved by gel filtration and two ion exchange chromatography steps; material was detected by radioimmunoassay (RIA). A substance was obtained that had integral molar ratios of amino acids and eluted in a single peak during reverse-phase high pressure liquid chromatography (HPLC). This material had an amino acid composition and COOH-terminal sequence identical with those of bovine NT. Human and bovine neurotensin gave rise to the same fragments when treated with papain; they were indistinguishable in RIAs using three different region-specific antisera and in their hypotensive effect on anesthetized rats. Using mucosal scrapings obtained immediately post-mortem from four subjects, the concentration of immunoreactive neurotensin was found to increase from duodenum to distal ileum, in agreement with results obtained in other mammalian species.

Distribution patterns of neurotensin-like immunoreactive cells in the gastro-intestinal tract of higher vertebrates

The endocrine system of the gastro-intestinal tract of selected species representing the five higher vertebrate classes was investigated with reference to occurrence and distribution of neurotensin-like immunoreactive cells. Using antibodies against C-terminal and N-terminal fragments of neurotensin and against the C-terminal sequence of xenopsin it was demonstrated that the intestine of all species studied contains endocrine, neurotensin-like immunoreactive cells. However, large differences in localization and frequency of these neurotensin-like immunoreactive cells were found. Except for a teleostean fish, neurotensin-like immunoreactive cells in the gastro-intestinal tract were more frequent in non-mamalian vertebrates than in mammals. In contrast to mammals, where the highest density of neurotensin-like immunoreactive cells was present in the ileal mucosa, in the non-mammalian vertebrates studied the corresponding cells were most abundant in the pyloric-duodenal junction. The exact mapping of neurotensin-like immunoreactive cells is presented throughout the entire gastro-intestinal tract of six species (Rattus, Coturnix, Lacerta, Rana, Xenopus, Carassius) including a quantitative evaluation of sequential serial sections.

Isolation, structure and biologic activity of chicken intestinal neurotensin

Using a radioimmunoassay towards bovine neurotensin(NT), chicken NT has been purified to homogeneity from extracts of intestine and its amino acid sequence determined to be: less than Glu-Leu-His-Val-Asn-Lys-Ala-Arg-Arg-Pro-Tyr-Ile-Leu-OH. The molecule is identical to the bovine peptide except for the 3 amino acid substitutions located in its NH2-terminal half and italicized above (His/Tyr: Val/Glu; Ala/Pro). The structure for chicken NT is consistent with earlier immunochemical studies which indicated a COOH-terminal homology with bovine NT [1]. The peptide isolated was shown to be near equipotent with bovine NT in its ability to induce hypotension, hyperglycemia, and cyanosis in the anesthesized rat, underscoring the importance of the COOH-terminal residues in NT for biological activity.

Immunochemical characterization of neurotensin-like peptides in chicken

Using radioimmunoassay and 3 region specific antisera toward bovine neurotensin (NT), the NT-like peptides in chicken have been shown to differ from NT but to strongly resemble its COOH-terminal region. Three substances were identified, one of which resembled NT biologically and appeared to share 7 or 8 of its COOH-terminal residues. The two other peptides were smaller than NT but seemed to possess 4-6 residue homologies with it. Tissue distribution studies indicated that the chicken pancreas and thymus had unusually high levels of this material (greater than 200 fold than in rat) and that the 3 substances were distributed differently in tissues. Chromatographic studies showed that the peptides obtained form brain, intestine, thymus, and pancreas were similar. These results, demonstrating evolutionary conservation of the COOH-terminal region of NT, are in keeping with the known importance of this region for biological activity. These finding also suggest the exstence of an NT-family of peptides serving multiple biological roles.

The amino acid sequence of bovine hypothalamic substance P. Identity to substance P from colliculi and small intestine

Bovine substance P has been isolated in pure form from hypothalamic fragments and its complete amino acid sequence determined by studies performed on the intact peptide and on its isolated papain-generated fragments. Direct evidence for the positioning of each residue was obtained, amide assignments were unequivocally established, and the COOH-terminal residue was isolated and identified as Met-NH2. The results of total enzymic digestion performed on each of the peptides obtained argue against the presence of any non-amino acid constituents in the molecule. The amino acid sequence obtained is identical with that previously reported for material isolated form bovine colliculi and from equine small intestine.

The amino acid sequence of radioimmunoassayable neurotensin from bovine intestine

The amino acid sequence of radioimmunoassayable neurotensin, isolated from bovine small intestinal extracts, has been shown to be the same as that of the peptide originally isolated from bovine hypothalamic extracts. This was accomplished by sequence studies on the intact peptide as well as on its chymotryptic and papain-generated fragments. Thus, neurotensin joins the group of biologically active peptides shown to be present in the same molecular form in both brain and intestine.

Ultrastructure of the gut neurotensin cell

In mammals, neurotensin cells occur scattered in the epithelium of the jejunum-ileum. In chicken, neurotensin cells are abundant in the region of the gizzard-duodenal junction (antrum) where they occur intermingled with numerous somatostatin and gastrin cells. The neurotensin cells in chicken, dog and man were identified at the electron microscopic level by immunocytochemistry, using the consecutive semithin/ultrathin section technique. They contain numerous electron dense cytoplasmic granules, pre-dominantly in the basal portion of the cell. It was shown that these granules are the storage site for neurotensin. The neurotensin granules are round, highly electron dense and of about the same size in the different species examined (mean diameter 260--290 nm). In dog and man the granules have a tightly applied surrounding membrane while in the chicken a relatively electron lucent zone separates the electron dense core from the granule membrane. The ultrastructure of the neurotensin granules in chicken is somewhat reminiscent of that of the gastrin granules. The mean diameter of the gastrin granules in chicken antrum is 230 nm; for the somatostatin granules the mean diameter is 305 nm.

Neurotensin: specific binding to synaptic membranes from rat brain

The binding of neurotensin to synaptic membranes from rat brain was studied at 24 degrees with the use of [3H]neurotensin. The binding was found to be highly specific, saturable, and reversible. Values for KD of 2 nM and 0.9 nM were derived from equilibrium and kinetic experiments, respectively. Virtually no degradation of neurotensin was observed in the incubation medium after exposure to synaptic membranes under the conditions of the binding studies. Competitive inhibition of [3H]neurotensin binding by partial sequences of neurotensin revealed that the addition of the residue arginine-8 to the neurotensin-(9-13)-pentapeptide increases about 500-fold the relative binding potency, whereas the remaining portion of the NH2-terminal region is mainly responsible for full pharmacological potency; the COOH-terminal leucyl residue is essential for binding.

Immunohistochemical localization of neurotensin in endocrine cells of the gut

Endocrine cells displaying neurotensin immunoreactivity are found scattered in the jejuno-ileum of all mammals studied, including man. They are rather scarce in rat, guinea pig, rabbit and pig and fairly numerous in cat, dog and man. In most mammals the neurotensin cells predominate on the villi. Only in the dog are they more numerous in the crypts. In the chicken, neurotensin cells occur all along the intestinal tract. They are particularly numerous in the zone that joins the gizzard with the duodenum. The ontogeny of the neurotensin cells in the gut was studied in rats and chickens. In the rat, the cells are first observed in the jejuno-ileum immediately before birth. The adult frequency is reached 4-5 days later. In the chicken, neurotensin cells first appear in the colon in the 18 day old embryo and in the small intestine two days later (i.e. one or two days before hatching). A few days after hatching, the gut has achieved the adult number of neurotensin cells per unit area.

Isolation of a tridecapeptide from bovine intestinal tissue and its partial characterization as neurotensin

Radioimmunoassayable neurotensin (R-NT) has been isolated from acid/acetone extracts of 50 kg of calf small intestine with an overall yield of approximately 15%. The concentration of R-NT in calf intestinal tissue was approximately 35 pmol/g wet weight. Throughout the purification procedures which involved adsorption onto sulfopropyl (SP)-Sephadex, chromatography on Sephadex G-25 and SP-Sephadex, immunoadsorption on neurotensin-antibody Sepharose and high voltage paper electrophoresis, R-NT displayed the chromatographic and electrophoretic properties of neurotensin. R-NT was found to contain a tridecapeptide with the same amino acid composition as neurotensin. This peptide yielded the same products as neurotensin when submitted to digestion by carboxypeptidase A or papain. Its immunological properties were indistinguishable from those of neurotensin and its potency in stimulating hypotension in anesthetized rats was comparable to that of synthetic neurotensin. If the amino acid sequence of this peptide proves to be the same as that of neurotensin, then neurotensin is another biologically active peptide isolated from both brain and intestinal tissues.

Characterization of radioimmunoassayable neurotensin in the rat. Its differential distribution in the central nervous system, small intestine, and stomach

Using radioimmunoassay, the distribution of radioimmunoassayable neurotensin (R-NT) has been determined in acid/acetone extracts of tissues from week-old and adult rats. Whereas only 10% of the R-NT in week-old rats was found in the head, 90% was found in extracts of the body, and 85% was present in the intestine. The distribution of R-NT in the central nervous system of adult male rats was as follows: hypothalamus (35%), brain stem (35%), cerebral cortex (17%), thalamus (11%), cerebellum (1%), and pituitary gland (1%). Concentrations of R-NT were highest in the hypothalamus (60 pmol/g) and lowest in the cerebellum (0.8 pmol/g). More than 10 times as much R-NT was found in extracts of adult rat small intestine than in brain. The concentration of R-NT was highest in the jejuno-ileal section of the intestine (approximately 50 pmol/g) but it was also detected in the esophogus, stomach, duodenum, and large intestine (approximately 1 to 8 pmol/g) than the remaining muscle layer (approximately 40 pmol/g). Rat jejuno-ileal R-NT co-chromatographed with neurotensin on Sephadex G-25, displayed equal immunological potency with the antisera utilized, and was destroyed by enzymes known to cleave neurotensin. High concentrations (approximately 400 pmol/g) of an R-NT of smaller molecular weight than neurotensin were found in rat stomach. This peptide reacted most strongly with a COOH-terminal-directed antiserum and appeared to be four to five amino acids in length; it might possibly be a breakdown product of neurotensin or a related peptide with biological activity. Acid/acetone extracts of rat and bovine plasma were found to contain an R-NT which displayed the properties of neurotensin (approximately 50 fmol/ml) as well as a substance which behaved similarly to the small molecular weight stomach R-NT (approximately 1000 fmol/ml).

Radioimmunoassay for neurotensin, a hypothalamic peptide

A highly sensitive and specific radioimmunoassay for neurotensin has been developed which utilizes 125I-labeled neurotensin and rabbit antisera raised toward synthetic neurotensin which has been coupled specifically through its lysine side chain to several proteins. The three antisera described have different specificities but are directed primarily towards the COOH-terminal region of neurotensin which is the biologically active portion of the molecule. Two of the antisera, poly(Glu60, Lys40) (from animal no. 4) and keyhole limpet hemocyanin (from animal no. 8), cross-react fully with COOH-terminal partial sequences of neurotensin while antiserum poly(Glu60, Lys40) (from animal no. 6) requires the entire molecule for full recognition. The assay can detect less than 3 fmol of neurotensin and the dose-response curves for synthetic and native neurotensin are superimposable, irrespective of the antiserum employed. Using these assay systems, the immunoactivity in acid/acetone extracts of 45 kg of bovine hypothalami was purified to homogeneity and shown to be attributable to intact neurotensin and not to fragments of neurotensin nor to related molecules. Radioimmunoassayable neurotensin (R-NT) obtained from bovine, rat, guinea pig, and rabbit hypothalami also gave dose-response curves which paralleled that of neurotensin and the neurotensin equivalents per g of wet tissue were in the range 45 to 70 pmol/g. Measurements with the three antisera were in agreement, especially after the extracts were chromatographed on Sephadex G-25; R-NT in these hypothalamic extracts has also been shown to be destroyed by treatment with various enzymes known to cleave neurotensin.

Synthesis and activities of neurotensin, and its acid and amide analogs: possible natural occurrence of [Gln4]-neurotensin

It was considered, a priori, that the isolation of the tridecapeptide, neurotensin, might have inadvertently sllowed the hydrolysis of either the [Gln4]- or the [Leu13-NH2]-moieties. Neurotensin and its three acid and amide analogs, i.e., [Gln4]-neurotensin, neurotensin-NH2, and [Gln4]-neurotensin-NH2 were synthesized. Neurotensin and [Gln4]-neurotensin were indistinguishable by the hypotensive assay, hyperglycemic assay, contraction of the ileum, and radioimmunoassay. Neurotensin-NH2 and [Gln4]-neurotensin-NH2 showed less than 1% of these neurotensin activities. Present information does not elucidate whether the glutamic acid residue in position 4 of neurotensin in situ is present as Glu4 or as Gln4. At high levels, neurotensin released the luteinizing hormone, follicle stimulating hormone, and thyrotropin; [Gln4]-neurotensin-NH2 released thyrotropin, and [Gln4]-neurotensin released luteinizing hormone and follicle stimulating hormone, but these activities do not appear biologically significant.

The synthesis of neurotensin

A tridecapeptide having the amino acid sequence, less than Glu-Leu-Tyr-Glu-Asn-Pro-Arg-Arg-Pro-Tyr-Iie-Leu-OH, (The nomenclature and symbols follow the suggestions of the IUPAC-IUB Commission on Biochemical Nomenclature (1972) J. Biol. Chem. 247, 977).) has been synthesized by the Merrifield solid-phase procedure. The synthetic scheme chosen involved synthesis of the peptide in the (Gln) form and cyclization to the less than Glu) form. After purification, the (Gln) peptide was obtained in a 7% yield and the (greater than Glu) peptide was obtained in a 35% yield. The (greater than Glu) was found to be chemically and biologically indistinguishable from the tridecapeptide, neurotensin, recently isolated from bovine hypothalami.

The amino acid sequence of a hypothalamic peptide, neurotensin

The amino acid sequence of neurotensin, a hypotensive peptide isolated from acid-acetone extracts of bovine hypothalami, has been established as less than Glu-Leu-Tyr-Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu-Oh. (The nomenclature and symbols follow the suggestions of the IUPAC-IUB Commission on Biochemical Nomenclature (1972) J. Biol. Chem. 247, 977). This was accomplished by sequence analyses performed on the intact peptide as well as its isolated tryptic, chymotryptic, and papain-generated fragments. The results of enzymic hydrolyses were consistent with the specificities of the enzymes used and indicated that all of the amino acids are unsubstituted and in the L configuration. The absence of non-amino acid constituents was further supported by analyses of electrophoretic mobility-molecular weight relationships of neurotensin and its fragments.