gastrin-releasing-peptide and ranatensin

The mammalian bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB), are structurally related neuropeptides that elicit a wide spectrum of biological activities including regulation of smooth muscle contraction, stimulation of secretion, modulation of neural activity, and growth regulation. Earlier studies have shown that GRP and NMB are expressed in different regions of both the CNS and peripheral organs. Recent ligand-binding and molecular-cloning studies have revealed two pharmacologically distinct G-protein-coupled receptor subtypes for mammalian bombesin-like peptides that have different relative affinities for GRP, NMB and bombesin receptor antagonists. Similar to the peptide ligands, the two receptor subtypes are expressed in a distinct but overlapping set of CNS regions, some of which have been identified in functional studies as sites where bombesin peptides elicit defined biological responses. Delineation of these peptide ligands and receptor subtypes will be important in future studies that explore the molecular basis for the heterogeneous nature of the responses to bombesin observed in mammalian systems.

Topics: Amino Acid Sequence; Animals; Bombesin; Brain Chemistry; Brain Mapping; Cloning, Molecular; DNA; Gastrin-Releasing Peptide; Mice; Molecular Sequence Data; Neurokinin B; Oligopeptides; Peptides; Protein Binding; Pyrrolidonecarboxylic Acid; Rats; Receptors, Bombesin; Receptors, Neurotransmitter; Sequence Homology, Nucleic Acid

Topics: Amino Acid Sequence; Animals; Bombesin; DNA; Gastrin-Releasing Peptide; Genes; Humans; Molecular Sequence Data; Neurokinin B; Oligopeptides; Peptides; Pyrrolidonecarboxylic Acid; Rana pipiens; Sequence Homology, Nucleic Acid

The effects of bombesin, gastrin-releasing peptide, neuromedin C, ranatensin, and neuromedin B on hypothalamic arcuate neurons were tested in this study using extracellular single-unit recording in fresh brain tissue slices. Adult ovariectomized Sprague-Dawley rats were used for preparation of brain slices. All bombesin-like peptides in pmol ranges exhibited potent stimulatory effects on the firing of arcuate neurons, i.e., gastrin-releasing peptide stimulated 90.9% (n = 22), bombesin 78.0% (n = 41), neuromedin C 63.2% (n = 19), ranatensin 58.0% (n = 22), and neuromedin B 50.0% (n = 6) of arcuate neurons tested. Pretreatments with either [Leu13-psi(CH2NH)-Leu14]-bombesin or [D-Phe6,Des-Met14]-bombesin6-14 ethylamide, two bombesin antagonists, significantly blocked most of the actions of bombesin-like peptides tested. The present results further support the notion that bombesin-like peptides may play a significant role in the arcuate nucleus.

Topics: Animals; Arcuate Nucleus of Hypothalamus; Bombesin; Female; Follow-Up Studies; Gastrin-Releasing Peptide; In Vitro Techniques; Neurokinin B; Neurons; Oligopeptides; Peptide Fragments; Peptides; Pyrrolidonecarboxylic Acid; Rats; Rats, Sprague-Dawley; Stimulation, Chemical

The effect of the bombesin-like peptides, gastrin-releasing peptide (GRP) and neuromedin-C (NMC), and the ranatensin-like peptides, neuromedin-B (NMB), neuromedin-B30 (NMB30), and neuromedin-B32 (NMB32), on pituitary GH and PRL release was studied in perifused anterior pituitary aggregate cell cultures from 9- to 12-week-old male rats cultured in serum-free defined medium supplemented with 0.05 nM T3 and 4 nM dexamethasone (DEX). All peptides stimulated PRL and GH release. GRP and NMC stimulated hormone release in a concentration-dependent manner between 0.1-10 nM. NMB was slightly more potent than NMB30 and NMB32, but was significantly less potent than GRP and NMC. The magnitude of the PRL response to GRP and NMC inversely correlated with that of the GH response. Cultures with relatively low PRL response levels displayed high GH responses, whereas the opposite was found in cultures with high PRL response levels. The stimulatory actions of GRP, NMC, and NMB were blocked by the bombesin receptor antagonist Leu13 psi (CH2NH) Leu14-bombesin, supporting the specificity of the findings. Addition of 1 nM estradiol (E2) to the culture medium provoked an impressive (4- to 10-fold) increase in the magnitude of the GH response to NMC without changing the EC50 value (0.5 nM). In contrast, E2 significantly decreased the stimulation of GH release by rat GH-releasing factor. In the E2-treated aggregates 3 nM NMC stimulated GH release to a comparable extent as 0.1 nM GRF. 5 alpha-Dihydrotesterone (10 and 100 nM) and DEX (80 nM) also enhanced the GH response to NMC, but to a much smaller extent than E2. E2 had also a stimulatory effect on the PRL response to NMC, particularly in cultures with a low intrinsic PRL response. The PRL response to NMC was decreased by DEX and slightly augmented by 5 alpha-dihydrotestosterone. It is concluded that bombesin- and ranatensin-like peptides have a stimulatory effect on GH and PRL release at the pituitary level. Since their action on GH release is strongly potentiated by E2 and much less so by glucocorticoids, these peptides clearly distinguish their activity and specificity from that of the protagonist releasing factor GH-releasing factor, suggesting a role in sex-related differences in GH release or in the control of GH secretion during sexual maturation.

Topics: Animals; Bombesin; Cells, Cultured; Dexamethasone; Dihydrotestosterone; Drug Synergism; Estradiol; Gastrin-Releasing Peptide; Growth Hormone; Male; Neurokinin B; Oligopeptides; Peptide Fragments; Peptides; Pituitary Gland, Anterior; Prolactin; Pyrrolidonecarboxylic Acid; Rats; Rats, Inbred Strains

To examine the biochemical basis for growth factor-induced responses in human lung cancer cells, we used the quin2 technique to study the effect of the amphibian peptide bombesin and its congeners including mammalian gastrin-releasing peptide (GRP) on the intracellular free calcium level [Ca2+]i in small cell lung cancer cell lines. In five of eleven cell lines tested, Tyr4-bombesin or GRP elicited a rapid and transient increase in [Ca2+]i. The response was seen with as little as 1 nM ligand, was not affected by membrane depolarization, and derived in part from internal calcium stores. Desensitization to a second addition of active bombesin congeners occurs subsequent to initial addition of Tyr4-bombesin. Structure-activity analysis showed the carboxyl-terminal octapeptide was the active portion of the peptide. Analogs in which the carboxyl terminus was oxidized or deamidated were inactive. Ranatensin, litorin, alytesin, and GRP, but not physalaemin, were as active as Tyr4-bombesin. A monoclonal antibody to the carboxyl terminus of bombesin selectively blocked the increased [Ca2+]i elicited by Tyr4-bombesin. These studies suggest that bombesin congeners can act on some small cell lung cancer cell lines by a pathway utilizing increased [Ca2+]i.

Topics: Amino Acid Sequence; Bombesin; Calcium; Carcinoma, Small Cell; Cell Line; Dose-Response Relationship, Drug; Gastrin-Releasing Peptide; Humans; Kinetics; Lung Neoplasms; Oligopeptides; Peptides; Pyrrolidonecarboxylic Acid; Structure-Activity Relationship

When dispersed acini from mouse pancreas are first incubated with bombesin, washed, and then reincubated with fresh incubation solution containing no bombesin, there is significant residual stimulation of amylase release. Induction of residual stimulation is relatively rapid in that significant stimulation occurs as early as after 15 s of first incubation with bombesin. Induction of residual stimulation of amylase release per se is temperature independent, but induction does occur more rapidly when acini are first incubated at 37 degrees C than when they are first incubated at 4 degrees C. Residual stimulation of amylase release persists for at least 75 min in acini that have been first incubated with bombesin at 37 degrees C. The maximal residual stimulation of amylase release obtained with pancreatic acini that have been first incubated with bombesin and then washed is 45% greater than the maximal stimulation obtained when bombesin is added directly to the incubation medium. In terms of their abilities to cause residual stimulation of amylase release, litorin and ranatensin are equal to bombesin in potency and efficacy. Gastrin-releasing peptide is approximately 70% as efficacious as bombesin in causing residual stimulation of amylase release.

Topics: Amylases; Animals; Bombesin; Dose-Response Relationship, Drug; Gastrin-Releasing Peptide; Male; Mice; Mice, Inbred Strains; Oligopeptides; Pancreas; Peptides; Pyrrolidonecarboxylic Acid; Stimulation, Chemical; Time Factors

The amphibian skin tetrapeptide bombesin shows potent action in reducing gastric acid secretion by intracerebral ventricular (ICV) administration in rats. In order to establish a relationship between this action and the amino acid composition of the bombesin-like peptides, most of the natural bombesin-like peptides and some synthetic analogues were tested on their ability to reduce gastric acid secretion by ICV administration. The amphibian peptides bombesin, its [Tyr4]-bombesin analogue, alytesin, ranatensin and litorin, and the mammalian peptide GRP significantly reduced gastric acid output 2 hr after peptide administration (p less than 0.01). The data support the following prerequisites for the maximal neuromodulatory role of bombesin-like peptides on gastric secretion: Trp is required at position 8; Gln and His are important at positions 7 and 12, respectively; Leu replacement by Phe, which occurs in the litorin subfamily, modifies the response; and unspecified amino acids or sequences are also involved in the N-terminal region of bombesin-like peptides. Synthetic analogues are currently being tested to confirm and extend these conclusions.

Topics: Amino Acid Sequence; Animals; Bombesin; Gastric Juice; Gastrin-Releasing Peptide; Hydrogen-Ion Concentration; Male; Neurokinin B; Oligopeptides; Peptide Fragments; Peptides; Pyrrolidonecarboxylic Acid; Rats; Secretory Rate

An antibody to des-pyroglutamyl ranatensin (RT 2-11) has been prepared and has been used to histochemically and biochemically identify ranatensin-like immunoreactivity (irRT) in the rat brain. The most most prominent stained cell group was situated in the dorsal tegmental pons. Areas of immunoreactive fibers were found in the ventral hippocampus, septal area and the hypothalamus. A similar distribution was found by radioimmunoassay data. The distribution of irRT was compared to that of bombesin-like immunoreactivity (irBN). The two peptides have different though partly overlapping distributions. Gel filtration of brain extracts show that the molecular size of irRT is similar to that of synthetic RT. However, HPLC characterization of irRT indicated that the immunoreactive material is different from synthetic RT and also different from irBN and irGRP. These results indicate the presence of two separate peptide systems, one RT-like, the other BN-like, in the mammalian CNS.

Topics: Animals; Bombesin; Brain Chemistry; Chromatography, High Pressure Liquid; Fluorescent Antibody Technique; Gastrin-Releasing Peptide; Male; Molecular Conformation; Nerve Fibers; Nerve Tissue Proteins; Oligopeptides; Peptides; Pyrrolidonecarboxylic Acid; Radioimmunoassay; Rats; Rats, Inbred Strains