Contractile activity of synthetic neurotensin and related polypeptides on guinea-pig ileum

Mechanical and current responses to neurotensin in the smooth muscle of guinea-pig intestine

1. The effects of neurotensin (NT) on the mechanical activity of the smooth muscle and membrane currents of enzymatically-dispersed single smooth muscle cells of guinea-pig intestine were investigated by the isometric tension recording method and the whole-cell patch clamp technique, respectively. 2. NT (0.3-670 nM) produced an initial relaxation followed by a contraction in segment preparations of the jejunum and ileum. Atropine (0.2 microM) abolished the contraction. In 30% of ileal segments, NT produced a slowly-developed contraction in the presence of atropine. The atropine-resistant contraction was insensitive to tetrodotoxin (TTX, 0.2 microM). The relaxant effect of NT was unaffected by TTX (0.2 microM) and guanethidine (2 microM), but markedly reduced or abolished by apamin (67 nM). 3. In segment preparations of the colon and rectum, NT produced a biphasic response, similar to that in the small intestine, or a triphasic one (relaxation, contraction and relaxation). The contractile effect of NT was affected neither by atropine (0.2 microM) nor by TTX (0.2 microM). The first relaxation in response to NT was similar in pharmacological properties to that in the small intestine. 4. Responses to NT in longitudinal muscle strips were similar to those in segment preparations. The taenia caecum responded to NT with a contraction alone and the effect was unaffected by atropine (0.2 microM) and TTX (0.2 microM). 5. NT had little or no effect on the mechanical activity in the circular muscle of the small intestine. In the circular muscle of the large intestine, NT had a weak inhibitory effect on the spontaneous activity which was followed by a small rise in muscle tone. Apamin (67 nM) converted the biphasic response to a contraction. 6. In cells dialysed with a KCl-based solution under voltage clamp at 0 mV, NT (5 microM) produced a brief, outward current in a very small fraction of cells (4 out of 40 cells). When cells were dialysed with a CsCl-based solution under voltage clamp at -50 or -60 mV, no current response to NT (5 microM) was observed in all 37 cells, but NT increased inward Ca2+ currents evoked upon depolarization. 7. From these results, it appears that there is a regional difference in the mode of action of NT to contract and relax the smooth muscle of guinea-pig intestine, and NT acts on its receptors on the smooth muscle to enhance activation of voltage-dependent Ca2+ channels, which underlies the slow contraction in the longitudinal muscle of the intestine.

Current contributions of peptide synthesis to studies on brain-gut-skin triangle peptides

The usefulness of a strong acid, such as MSA or TFMSA/TFA, as a deprotecting reagent in peptide synthesis was examined. By synthesizing several structurally related brain-gut-skin triangle peptides, a number of advantageous features of the thioanisole-mediated deprotecting procedure were demonstrated. New amino acid derivatives, Arg(Mts), Trp(Mts) and Asp(OChp), were introduced to improve the synthetic methodology of complex peptides and the superior properties of Cys(Ad) were evaluated.

Suppression of norepinephrine-elicited feeding by neurotensin: evidence for behavioral, anatomical and pharmacological specificity

Neurotensin (NT) injected into the paraventricular hypothalamic nucleus (PVN) has been shown to suppress feeding behavior. To investigate whether this suppression generalizes to feeding elicited by norepinephrine injection, rats with bilateral PVN cannulas were injected with NT (3.0 nmol/cannula) or vehicle followed by norepinephrine (20.0 nmol/cannula). Pretreatment with NT caused a 48% reduction in feeding elicited by norepinephrine. To determine whether NT's effect resulted from non-specific behavioral effects or leakage into the periphery, NT (0.25, 1.25 or 6.0 nmol) was injected ipsilateral or contralateral to a unilateral norepinephrine (40.0 nmol) injection. Ipsilateral NT produced a dose-dependent suppression of norepinephrine-elicited feeding which was significantly greater than the effect of contralateral NT, suggesting that NT's effect was at least partially behaviorally and anatomically specific. To investigate the pharmacological specificity of the suppression, rats that ate in response to PVN norepinephrine (40.0 nmol) were given prior injections of NT or one of six NT fragments at 0.25, 1.25, 6.0 or 30.0 nmol. NT and the C-terminal fragments 3-13 and 6-13 caused a dose-dependent suppression of feeding. In contrast, none of the N-terminal fragments (i.e. 1-8, 1-11 or 1-12) were effective. This specificity rules out non-specific changes in parameters such as pH or osmotic pressure and suggests that the anorectic effect may have been mediated by NT receptors.

Structure-activity studies with carboxy- and amino-terminal fragments of neurotensin on hypothalamic neurons in vitro

The purpose of this study was to determine the structural requirements for the activity of neurotensin (NT1-13) on preoptic/anterior hypothalamic (POAH) neurons in vitro. Standard explant culture electrophysiological techniques were employed. NT was administered to POAH cultures through the superfusion fluid, or, to the vicinity of individual neurons by pressure ejection (0.5-10 psi) from micropipettes. Computer-generated, peri-event histograms were used to quantitate neuronal responses. Pressure ejection of NT1-13 (50 pM to 1 microM) consistently produced an excitatory effect on 30 of 42 neurons. The remaining cells were either inhibited or unaffected. Application of the C-terminal hexapeptide, NT8-13, but not the N-terminal octapeptide, NT1-8 (less than or equal to 1 mM), produced an excitatory response in 21 of 30 neurons, but was less potent than NT1-13. Application of an N-acetylated NT8-13 fragment (NTAC8-13) produced a response that was similar to that produced by NT8-13. The excitatory effects of NT1-13 and NT8-13 were maintained in medium which effectively blocked synaptic transmission (0 mM Ca2+/12 mM Mg2+ 1 mM EGTA). These data indicate that the C-terminal hexapeptide, but not the N-terminal octapeptide, produces a dose-related, excitatory effect on single neurons in the POAH in vitro. The persistence of these effects in Ca2+-free medium supports a postsynaptic site of action for these peptides.

Neo-kyotorphin (Thr-Ser-Lys-Tyr-Arg), a new analgesic peptide

The amino acid sequence of a newly isolated pentapeptide, neo-kyotorphin from bovine brain was synthetically verified to be Thr-Ser-Lys-Tyr-Arg corresponding to the C-terminal portion of hemoglobin alpha-chain. The synthetic neo-kyotorphin showed the dose-dependent analgesia in mice which was approximately equal to that of Leu-enkephalin.

Isolation from bovine brain of a novel analgesic pentapeptide, neo-kyotorphin, containing the Tyr-Arg (kyotorphin) unit

A novel analgesic peptide, isolated from the bovine brain, was found to contain the Tyr-Arg (kyotorphin) unit at the C-terminal portion. This peptide, in the methanol-soluble fraction, was isolated by gel filtration and cation exchange chromatography. This peptide was termed "neo-kyotorphin" and the amino acid sequence is Thr-Ser-Lys-Tyr-Arg. The synthetically prepared neo-kyotorphin proved to have a dose-dependent analgesic effect in mice. The median analgesic dose, ED50 of neo-kyotorphin was 195 nmol/mouse (intracisternal injection), with the tail pinch test, and the potency was approximately equal that of Leu-enkephalin.

[TRP11]-neurotensin and xenopsin discriminate between rat and guinea-pig neurotensin receptors

The binding and biological activities of neurotensin and two analogues, [TRP11]-neurotensin and xenopsin, in which a tryptophan replaces the neurotensin residue Tyr11, were compared in rat and guinea-pig. The binding activity of three peptides was measured as their ability to inhibit the binding of [3H]neurotensin to rat and guinea-pig brain synaptic membranes. Their biological activities were measured as their effects on the contractility of rat and guinea-pig ileal smooth muscle preparations. In binding as well as biological assays, it was found that [Trp11]-neurotensin and xenopsin were as potent as neurotensin in the rat. In contrast, the two analogues were about 10 times less potent than neurotensin in the guinea-pig. These findings reveal differences between rat and guinea-pig neurotensin receptors should be considered when comparing the activity of neurotensin analogues in assays using tissue preparations from various animal species.

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

The purpose of the present experiments was to study the effect of neurotensin and neurotensin analogues on the migrating myoelectrical complexes in the small intestine of rats. Four bipolar electrodes were implanted into the muscular wall of the small intestine. The electrodes were placed 5, 15, 25 and 35 cm distal to the pylorus. 7-10 days after the operation the animals were fasted for 48 h with free access to water. Some experiments were performed on conscious rats and in others the rats were anesthetized with pentobarbital, 30 mg/kg. I.v. infusion of either neurotensin (NT) or (Gln4)-neurotensin at doses of 1.8, 3.6 and 7.1 pmol X kg-1 X min-1 abolished the migrating myoelectric complexes, which were replaced by increased spiking activity along the whole length of the small intestine from which activity was recorded. The changes in myoelectrical activity were observed within 2-4 min after commencement of the infusion. The activity returned to control levels within 5-15 min after the end of the infusion period. The neurotensin sequences NT 9-13, NT 8-13, NT 4 -13, NT 1-9 and (Gln4)-NT 1-11 did not induce any changes in the electrical activity in the small intestine. The effects of NT and (Gln4)-neurotensin on the myoelectrical activity in the small intestine were indistinguishable. The changes induced by NT or (Gln4)-NT resemble those found after the ingestion of food. The present data indicate that the intact NT sequence, rather than smaller NT fragments, is necessary to induce changes in myoelectrical activity in the small intestine.

Pharmacological studies of neurotensin, several fragments and analogous in the isolated perfused rat heart

Neurotensin (NT) induced a dose-dependent increase of the coronary perfusion pressure (CPP) in the isolated perfused rat heart. This effect was not modified by pretreating the organ with methysergide (8.5 x 10(-6) M), atropine (3.4 x 10(-6) M), a mixture of phentolamine (3.1 x 10(-6) M) and practolol (1.5 x 10(-5) M), 8-leucine-angiomine (2.9 x 10(-5) M) thus suggesting the existence of specific NT receptors in the coronary vessels of rat. The structure-activity studies performed using several NT fragments and analogues in the isolated perfused rat heart led us to the following conclusions: (1) the minimum structure required for the full expression of the biological activity of NT is H-Arg9-Pro10-Tyr11-Ile12-Leu13-OH; (2) the amino acid Tyr in position 11 appears to play a key role in the process of NT receptor activation. The replacement of Tyr11 with Tyr(Me) gave a compound which inhibits selectively the increase in coronary perfusion pressure induced by NT, but still exhibits some NT-like activity, specially when used in concentrations higher than 10(-6) M. [Tyr(Me)11]NT did not antagonize the stimulant effects of NT in rat stomach strips and guinea pig atria, thus suggesting that the receptors mediating the constrictor effect of NT in coronary vessels of the rat are pharmacologically different from those subserving the stimulant effect of NT in rat stomach strip and guinea pig atria.

Pharmacological characterization of neurotensin receptors in the rat isolated portal vein using analogues and fragments of neurotensin

The contractile effects of the tridecapeptide neurotensin (NT) and several NT fragments and analogues were evaluated and compared in the rat isolated portal vein. The removal of the sequence pGlu1-Leu2-Tyr3-Glu4-Asn5-Lys6-Pro7 produced practically no change in the myotropic activity of NT while the deletion of Leu13 or the last 3 C-terminal amino acids (e.g. Tyr11, Ile12 and Leu13) gave compounds with very low agonist activity (NT(1-12)) or devoid completely of affinity and intrinsic activity (NT(1-10)). Replacing Tyr11 with Ala, Leu, D-Tyr or D-Phe markedly decreased the stimulant effect of NT but did not confer to the molecule antagonistic properties. On the other hand, the substitution of Try11 with D-Trp or Tyr(Me) gave NT analogues which behave as specific and competitive antagonist of the contractile effect of NT in the portal vein. pA2 values of [D-Trp11]-NT and [Tyr(Me)11]-NT measured in the venous preparation were similar to those found in the coronary vasculature of the rat. Taken all together, these results suggest that: (1) the minimum structure required for the full expression of the myotropic activity of NT in the rat portal vein is -Arg9-Pro10-Tyr11-Ile12-Leu13-OH; (2) Tyr11 appears to be closely involved in the process of NT receptor activation since its replacement with D-Trp or Tyr(Me) produced specific and competitive antagonist of NT; (3) the receptors mediating the contractile effect of NT in the rat portal vein appear to be pharmacologically similar to those found in the coronary vessels of the rat. The possibility for the existence of different types of NT receptor in other tissues is discussed.

Selective blockade of neurotensin-induced coronary vessel constriction in perfused rat hearts by a neurotensin analogue

[D-Trp11]-NT, an analogue of neurotensin (NT) in which Tyr11 was replaced with D-Trp, was found to antagonize selectively NT-induced coronary vessel constriction in perfused rat hearts, in concentrations varying between 1.3 x 10(-7) and 1.1 x 10(-6) M. Higher concentrations of [D-Trp11]-NT displayed NT-like activity. In rat stomach strips and guinea pig atria, [D-Trp11]-NT exhibits full intrinsic activity, markedly reduced affinity for NT receptors, but no inhibitory effect against NT. These results suggest that the receptors mediating the constrictor action of NT in the coronary vessels of rat hearts are pharmacologically distinct from those subserving the stimulant effects of NT in rat stomach strips and guinea pig atria.

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.

The stimulatory effects of neurotensin and related peptides in rat stomach strips and guinea-pig atria

1 The stimulatory effects of neurotensin (NT) and several NT fragments were evaluated in two pharmacological preparations: rat stomach strips and isolated spontaneously beating atria of guinea-pigs.2 In rat stomach strips, NT elicited a dose-dependent contractile effect in concentrations varying between 1.3 x 10(-9) and 5.4 x 10(-7) M.3 The contractile effect of NT (1.3 and 5.4 x 10(-8) M) in this tissue was not modified by atropine (3.4 x 10(-7) M), methysergide (2.0 x 10(-6) M), a mixture of cimetidine (8.0 x 10(-6) M) and diphenhydramine (7.8 x 10(-6) M), indomethacin (1.4 x 10(-5) M), 8-Leu-angiotensin II (1.0 x 10(-6) M), glucagon (2.0 x 10(-6) M) or somatostatin (3.0 x 10(-7) M).4 Rat stomach strips desensitized by bradykinin (6.1 x 10(-6) M) or substance P (7.4 x 10(-6) M) maintained their sensitivities to NT (1.3 and 5.4 x 10(-8) M).5 In guinea-pig atria, NT produced a dose-dependent positive inotropic action in concentrations varying between 5.4 x 10(-10) and 2.7 x 10(-7) M.6 The inotropic effect of NT (2.7 x 10(-9) M) was not influenced by methysergide (2.8 x 10(-6) M), atropine (3.4 x 10(-7) M), practolol (1.5 x 10(-5) M), 8-Leu-angiotensin II (1.0 x 10(-6) M), or indomethacin (1.4 x 10(-5) M), but it was reduced by 37% by cimetidine (4.0 x 10(-5) and 2.0 x 10(-4) M). A combination of cimetidine (4.0 x 10(-5) M) and diphenhydramine (3.9 x 10(-6) M) did not produce a greater inhibition of NT than cimetidine alone.7 Atria desensitized by bradykinin (6.1 x 10(-6) M) or glucagon (2.0 x 10(-6) M) maintained their sensitivities to NT (2.7 x 10(-9) M). Substance P was inactive both as an agonist or antagonist of NT.8 These results suggest the existence of specific NT receptors in rat stomach strips and guinea-pig atria.9 The data derived from our structure-activity study suggest that the minimum structure required for the full stimulation of NT receptors in these two preparations is H-Arg(9)-Pro(10)-Tyr(11)-Ile(12)-Leu(13)-OH. The sequence PyroGlu(1)-Leu(2)-Tyr(3)-Glu(4)-Asn(5)-Lys(6)-Pro(7)-Arg(8)- and the amino acids Ile(12) and Leu(13) appear to contribute mainly to the affinity or binding of NT to its receptor. The chemical groups responsible for the full activation (intrinsic activity) of NT receptors seem to be located in the sequence -Arg(9)-Pro(10)-Tyr(11).

Regioal distribution of immunoreactive neurotension in monkey brain

The regional distribution of immunoreactive neurotensin (IRNT) in 66 different areas of the monkey brain and spinal cord was studied by radioimmunoassay using specific rabbit antisera to synthetic neurotensin. Each area was found to contain IRNT in uneven concentrations. Highest concentrations were present in the hypothalamic areas and the interpeduncular nucleus, values reaching around 80 pg IRNT/mg wet tissue weight. The habenula, subthalamus and preoptic area were also rich in IRNT. A relatively selective distribution of IRNT was found in the thalamic regions. Low values were obtained in the cerebral and cerebellar cortex, striatum, substantia nigra and white matter areas. Among the fiber bundle studied, the olfactory tract contained a significant amount of IRNT. The present finding of a selective distribution of IRNT suggests a specific neuronal action of neurotensin in primate central nervous system.

Biological activity of neurotensin and its C-terminal partial sequences

A hypothalamic tridecapeptide, neurotensin, and its C-terminal partial sequences down to the dipeptide were synthesized. These peptides were assayed for smooth muscle contracting and blood pressure lowering properties using preparations of isolated stomach fundus, uterus and duodenum of the rat, isolated guinea pig ileum and rabbit carotid artery. Sequences of 6 or more terminal amino acids produced a strong stomach fundus contracting effect, the potencies of the fragments being approximately equivalent to or slightly more than that of the parent tridecapeptide. These fragments also elicited the ileum contracting activity, but the potencies were only one fifth to one tenth that of neurotensin. The tetra- or dipeptide hardly stimulated either the fundus or the ileum. The stimulating effect on the uterus or relaxing effect on the duodenum of neurotensin was not consistent. Rabbit blood pressure was lowered markedly by neurotensin and weakly by its dodecapeptide. From these results, the arginine or arginine-arginine residue down to the C-terminal leucine appears to be essential for the smooth muscle contracting activity of neurotensin. The full length sequence may be needed for the hypotensive effect.

Effects of neurotensin on isolated intestinal smooth muscles

The effects of neurotensin were investigated in intestinal smooth muscle preparations. Neurotensin relaxed the rat ileum, and contracted the guinea-pig ileum and taenia. Neurotensin induced a biphasic response (relaxation followed by contraction) in the contracted guinea-pig ileum. In all systems, half-maximal effects were obtained with 4--5 nM neurotensin and maximal responses with 30--60 nM; tachyphylaxis occurred with higher concentrations. Tetrodotoxin did not affect the responses to neurotensin in the rat ileum and the guinea-pig taenia. Tetrodotoxin abolished the contraction or the contraction phase (but not the relaxation phase) of the biphasic response induced by neurotensin in the guinea-pig ileum. Atropine partially inhibited the Neurotensin-induced contraction in the guinea-pig ileum. These results suggest that neurotensin acts on intestinal smooth muscle both directly (relaxation of the rat and guinea-pig ileum, and contraction of the guinea-pig taenia) and through a nerve-mediated, partly cholinergic, process (contraction of the guinea-pig ileum).

Ultrastructural identification of a new cell type--the N-cell as the source of neurotensin in the gut mucosa

The neurotensin-cell is identified immunohistochemically and ultrastructurally by differential counting of endocrine cells in the gut of a primate (Tupaia belangeri). Utilizing light microscopy, the EC-cells are identified by the Masson-Fontana silver stain; with the same method the neurotensin cells are not stained. The other endocrine cells have been quantified in the small intestine using the peroxidase-antiperoxidase stain with antisera against glucagon, somatostatin, cholecystokinin, gastrin, secretin, pancreatic polypeptide, gastric inhibitory peptide and neurotensin. In the ileal mucosa of Tupaia, the most frequent endocrine cell is the EC-cell followed by the glucagonoid cell, (L-cell). The immunoreactive neurotensin cell represents the third most frequent endocrine cell in this region. On the ultrastructural level, this third most frequent endocrine cell is a heretofore undescribed cell, the N-cell, containing electron dense secretory granules measuring 335 +/- 87 nm in diameter.

Localization of neurotensin-immunoreactive cells in the small intestine of man and various mammals

Antibodies against synthetic bovine neurotensin were raised in rabbits and used to demonstrate neurotensin-immunreactive cells by immunohistochemical methods. In the jejunum and ileum of all species investigated (man, dog, monkey, cat, rabbit, sheep, rat, mouse, hamster, chinese hamster, gerbil, pig and guinea pig) cells were present in the mucosa, which reacted specifically with antineurotensin serum using the indirect immunofluorescence and peroxidase-antiperoxidase methods. In the monkey Tupaia the distribution of neurotensin-immunoreactive cells was examined by investigating serial sections through the entire gastro-entero-pancreatic (GEP) endocrine system, again showing most neurotensin-immunoreactive cells in the jejunum and ileum. The functional role of the presence of neurotensin immunoreactivity in the gut is discussed.