Dose-response comparisons of canine plasma gastroenteropancreatic hormone responses to bombesin and the porcine gastrin-releasing peptide (GRP)

Neuromedin: An insight into its types, receptors and therapeutic opportunities

Neuropeptides are small protein used by neurons in signal communications. Neuromedin U was the first neuropeptide discovered from the porcine spinal and showed its potent constricting activities on uterus hence was entitled with neuromedin U. Following neuromedin U another of its isoform was discovered neuromedin S which was observed in suprachiasmatic nucleus hence was entitled neuromedin S. Neuromedin K and neuromedin L are of kanassin class which belong to tachykinin family. Bombesin family consists of neuromedin B and neuromedin C. All these different neuromedins have various physiological roles like constrictive effects on the smooth muscles, control of blood pressure, pain sensations, hunger, bone metastasis and release and regulation of hormones. Over the years various newer physiological roles have been observed thus opening ways for various novel therapeutic treatments. This review aims to provide an overview of important different types of neuromedin, their receptors, signal transduction mechanism and implications for various diseases.

Insulinotropic action of bombesin-like peptides mediated by gastrin-releasing peptide receptors in steers

The present study characterizes the receptor that mediates the insulinotropic action of bombesin-like peptides (BLP) in ruminants. Eight Holstein steers were randomly and intravenously injected with synthetic bovine gastrin-releasing peptide (GRP; 0.9 nmol/kg BW), neuromedin B (NMB; 0.9 nmol/kg BW), or neuromedin C (NMC; 0.9 nmol/kg BW), each alone or combined with the antagonist of GRP receptors N-acetyl-GRP-OCHCH (N-GRP-EE; 22.5 nmol/kg BW) or the antagonist of GH secretagogue receptor type 1a (GHS-R1a) [D-Lys]-GHRP-6 (21.5 nmol/kg BW). Blood samples were collected at -10, 0 (just before injection), 5, 10, 15, 20, 30, 45, 60, 75, and 90 min relative to injection time. Levels of injected peptides, insulin, and glucose in plasma were analyzed. Results showed that the peak of insulin levels was seen at 5 min after injection of NMC or GRP. Plasma glucose was observed in 2 phases; a significant rise followed a remarkable fall after NMC or GRP administration compared with injection of the vehicle ( < 0.05). On a same molar basis, effects of GRP on insulin and glucose were more potent than those of NMC ( < 0.05). The NMC-induced changes of insulin and glucose were completely blocked by N-GRP-EE, but [D-Lys]-GHRP-6 did not block any of these changes. Administration of NMB or N-GRP-EE alone did not change the circulating levels of insulin or glucose during any of the sampling time points ( > 0.05). These results indicated that the insulinotropic action of BLP is mediated by GRP receptors but not through a ghrelin/GHS-R1a pathway and that BLP may be involved in the regulation of glucose homeostasis in ruminants.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Modulation of gastrin-releasing peptide (GRP) receptors in insulin secreting cells

Gastrin-releasing peptide (GRP) receptors are present in pancreatic islets, though their regulation is unknown except for homologous desensitization. The modulation of binding of GRP to mouse pancreatic islets and INS-1 cells was studied. At 60 min (steady-state), total binding of [(125)I-Tyr(15)] GRP was 1.62 per cent of total radioactivity per 50 islets; non-specific binding (presence of 1 mM unlabelled GRP(1-27)) was 0.05 to 0.61 per cent of total radioactivity. A preincubation with 1000 nM cholecystokinin (CCK(8)) or with 1000 nM glucose-dependent insulinotropic peptide (GIP) augmented the number of GRP binding sites but not their affinity. [(125)I-Tyr(15)]GRP binding to INS-1 cells was saturable (90 min) and specific with respect to compounds that are not chemically related to GRP (e.g. calcitonin gene-regulated peptide-CGRP and atrial natriuretic peptide-ANP). Displacement studies showed one binding site with a K(d) of 0.39 nM and a B(max) of 13.2 fmoles mg(-1) protein. When the cells were pretreated for 24 h with 10 nM GIP or CCK(8), only GIP but not CCK(8) increased the B(max) of the GRP binding site. The affinity (K(d)) was not changed by either compound. This effect of GIP pretreatment was not affected by downregulating PKC by TPA (phorbol ester; long-term pretreatment). These data indicate that: (1) specific binding sites for GRP are present in mouse pancreatic islets and INS-1 cells; (2) the GRP binding is upregulated by GIP in both islets and INS-1 cells and additionally by CCK(8 ), albeit only in islets; and (3) PKC does not seem to be involved in the up-regulation process. Thus a positive interplay between both the incretins GIP and CCK(8) and the neurotransmitter GRP is obvious.

Growth stimulation of normal melanocytes and nevocellular nevus cells by gastrin releasing peptide (GRP)

In order to know the possible effects of gastrin releasing peptide (GRP) on nevus cells and melanocytes, we studied the effect of GRP on the proliferation of cultured human nevus cells and normal melanocytes. MTS assay showed that GRP stimulated the growth of viable melanocytes at 1000 ng/ml. GRP also stimulated the growth of nevus cells in a dose dependent manner and maximum stimulation was obtained at 100 ng/ml of GRP. GRP was less effective for growth stimulation of normal melanocytes than nevus cells. The cytoplasm of nevus cells were positively stained by polyclonal anti-GRP antibody. We also detected the expression of GRP and GRP receptor mRNAs in these cells by RT-PCR. These results suggest that GRP acts as an autocrine growth factor for nevus cells and normal melanocytes.

A rhesus monkey model to characterize the role of gastrin-releasing peptide (GRP) in lung development. Evidence for stimulation of airway growth

Gastrin-releasing peptide (GRP) is developmentally expressed in human fetal lung and is a growth factor for normal and neoplastic lung but its role in normal lung development has yet to be clearly defined. In this study we have characterized the expression of GRP and its receptor in fetal rhesus monkey lung and determined the effects of bombesin on fetal lung development in vitro. By RNA blot analysis, GRP mRNA was first detectable in fetal monkey lung at 63 days gestation, reached highest levels at 80 days gestation, and then declined to near adult levels by 120 days gestation; a pattern closely paralleling GRP expression in human fetal lung. As in human lung, in situ hybridization localized GRP mRNA to neuroendocrine cells though during the canalicular phase of development (between 63-80 days gestation) GRP mRNA was present not only in classic pulmonary neuroendocrine cells, but also in cells of budding airways. Immunohistochemistry showed that bombesin-like immunoreactivity was present in neuroendocrine cells, but not in budding airways, suggesting that in budding airways either the GRP mRNA is not translated, is rapidly secreted, or a related, but different RNA is present. RNase protection analysis using a probe to the monkey GRP receptor demonstrated that the time course of receptor RNA expression closely paralleled the time course of GRP RNA expression. In situ hybridization showed that GRP receptors were primarily expressed in epithelial cells of the developing airways. Thus GRP would appear to be secreted from neuroendocrine cells to act on target cells in developing airways. This hypothesis was confirmed by organ culture of fetal monkey lung in the presence of bombesin and bombesin antagonists. Bombesin treatment at 1 and 10 nM significantly increased DNA synthesis in airway epithelial cells and significantly increased the number and size of airways in cultured fetal lung. In fact, culturing 60 d fetal lung for 5 d with 10 nM bombesin increased airway size and number nearly to that observed in cultured 80 d fetal lung. The effects of bombesin could be blocked by specific GRP receptor antagonists. Thus this study demonstrates that GRP receptors are expressed on airway epithelial cells in developing fetal lung and that the interaction of GRP with the GRP receptor stimulates airway development.

Determination of the structural requirements for the inhibitory action of gastrin-releasing peptide on growth hormone release

We have previously determined that gastrin-releasing peptide (GRP) suppresses plasma growth hormone (GH) levels and blocks the response to growth hormone releasing factor (GRF) following its injection into the third ventricle (3V) of conscious male rats. To determine the portion of the peptide required for this action, fragments of the peptide were injected at various doses to determine their effect on plasma growth hormone and the response to a test dose of GRF (1 microgram/kg IV). The GRP 1-16 lowered plasma GH and blocked the response to GRF following an intraventricular injection of 2 micrograms but not 0.2 microgram of the peptide. Carboxy-terminal fragments were more effective. AcGRP20-27 was partially effective at a 100 times lower dose of 2.0 ng, a result similar to that obtained with the related peptide, bombesin. Even the C-terminal heptapeptide AcGRP-27 was effective at a dose of 2 ng. The results indicate that the C-terminal heptapeptide is the minimal requirement for intraventricularly injected GRP to suppress plasma GH levels and block the response to GRF.

Bombesin stimulates intracellular Ca2+ mobilization but not proliferation on human colon cancer cells

Increases in intracellular Ca2+ ([Ca2+]i) levels mediated by bombesin (BBS) are believed to be important signals leading to stimulation of DNA synthesis and an increase in cellular proliferative rate. Since the role of BBS on growth of normal or malignant cells in the GI tract is still unclear, we examined whether BBS affects in vitro growth of human colon cancer cells (COLO 320, HCT116 and LoVo). We also examined the effect of BBS on intracellular Ca2+ levels to determine if the growth-regulatory effect of BBS is mediated through increases in [Ca2+]i. Levels of [Ca2+]i in response to BBS were measured by single cell fluorescence after loading with fura-2. BBS stimulated the mobilization of [Ca2+]i in COLO 320, LoVo, and HCT116 cells in a dose-dependent fashion, but did not affect in vitro growth. These findings suggest that the BBS-mediated increase in [Ca2+]i does not always correlate with the growth-regulatory effect of BBS.

Bombesin stimulates growth of colon cancer in mice and decreases their survival

Bombesin (BBS) stimulates cellular proliferation of both normal and transformed cells. The mouse colon cancer cells (MC-26) possess specific binding sites for BBS. The purpose of this study, therefore, was to examine the effect of chronic administration of BBS on in vivo growth of MC-26 tumours in Balb/c mice and on survival of tumour-bearing mice. Three groups of mice (n = 10 each) inoculated with MC-26 cells received either saline containing 0.1% bovine serum albumin (BSA), or BBS (5 micrograms kg-1 or 20 micrograms kg-1) dissolved with 0.1% BSA saline by intraperitoneal route three times a day for 15 days. BBS increased weight, DNA and RNA contents of MC-26 tumours. To examine the effect of BBS on survival rates of mice with MC-26 tumours, three groups of mice (n = 20 each) were treated for 31 days, as above. One group of mice inoculated with MC-26 cells received 0.1% BSA saline; the other group of MC-26-inoculated mice and the control group without tumour received BBS (5 micrograms kg-1) dissolved with 0.1% BSA saline. BBS significantly decreased the survival rate of mice bearing MC-26 tumours (median survival; saline group: 42.5 days, BBS group: 32.0 days, P = 0.037). None of the mice in the control group died during the experiment. BBS may stimulate in vivo growth of MC-26 cells through specific receptors.

Direct effect of bombesin on pancreatic and gastric growth in suckling rats

Bombesin stimulates growth of the stomach and pancreas in adult rats. Part of this effect is thought to be through the release of CCK following bombesin treatment. We studied the effect of long term administration of bombesin on the pancreas and stomach in suckling rats and examined the action of bombesin using specific CCK antagonist (CR-1409) and bombesin antagonists (GRP19-26, D-Phe19, Leu26CH2NHCOCH3 = cpd 17; L-686,095-001C002 = cpd 23). Rat pups (7-days-old) were given bombesin (20 micrograms/kg body wt. twice a day) or vehicle (1% gelatin) for 9 days. Bombesin stimulated pancreatic and gastric growth (tissue weight, total protein and DNA content all increased). Pancreatic trypsinogen concentration and content showed a 2-3-fold increase. CR-1409 at 6 mg/kg body wt., a dose that blocked the trophic action of CCK-33 when given to pups at similar ages, did not affect the bombesin-stimulated growth of the pancreas or the increase in trypsinogen level. At 2.4 mg/kg body wt., cpd 17 partially blocked and cpd 23 completely blocked the trophic effect of bombesin on the pancreas and stomach and the increase in trypsinogen level in the pancreas. RU-486, a type II glucocorticoid receptor antagonist, given at a dose sufficient to block the physiological action of glucocorticoid, had no effect on bombesin-stimulated growth of the pancreas. Thus, in vivo, bombesin acts directly on the neonatal pancreas and stomach.

Gastrin releasing peptide, but not pentagastrin, stimulates ACTH and cortisol secretion in conscious dogs

Gastrin releasing peptide (GRP) is the mammalian equivalent of bombesin. Bombesin has been shown to stimulate canine ACTH and cortisol secretion in a dose-related manner. In the present study, following a 30-40 min saline infusion, a progressively-increasing, stepwise infusion of GRP (60, 600, 1200 pmol/kg per h) or pentagastrin (PG) (2, 4, 8 micrograms/kg per h) was administered. Each drug dose was infused for 40-45 min and blood samples were drawn at 20-22.5 min intervals. GRP caused significant, dose-dependent increases in plasma ACTH (145 +/- 6%, 242 +/- 49%, 270 +/- 78% of control) and cortisol (158 +/- 16%, 218 +/- 26%, 250 +/- 62% of control). The dose of GRP required for a half-maximal cortisol response was 120 pmol/kg per h, while that for ACTH was 140 pmol/kg per h. PG had no effect on either ACTH or cortisol. While PG is apparently not involved in GRP/bombesin release of ACTH or cortisol, similar mechanisms of action for GRP and bombesin are suggested by their equimolar potencies.

Release of ileal neurotensin in the rat by neurotransmitters and neuropeptides

To investigate the functional relationship between the enteric nervous system and the intestinal neurotensin (N) cells, the release of neurotensin (NT) was measured upon vascular 8-min infusion periods of various neurotransmitters and neuropeptides in an isolated vascularly perfused rat jejunoileum. NT-like immunoreactivity (NT-LI) was measured with an antiserum that specifically recognizes intact NT. The cholinergic agonists methacholine and carbachol produced a strong release of NT-LI (250% and 700% of basal, respectively at 10(-5) M). The infusion of a lower dose (10(-7) M) was less effective in both cases. The nicotinic receptor agonist DMPP (10(-4) M) had no significant effect on NT-LI release. Norepinephrine (10(-6) M) produced a moderate and well-sustained secretion of NT (200% of basal). Infusion of higher doses of these neurotransmitters dramatically increased the arterial pressure. G-amino-n-butyric acid (GABA), histamine, serotonin and dopamine administered at final concentrations up to 10(-5) M had no effect on NT-LI release. In contrast, gastrin-releasing peptide and bombesin induced a dose-dependent transient increase of portal NT-LI (maximal value at 10(-7) M: 1000% of basal) followed by a rapid return to near basal values. Substance P (10(-7) M) evoked a prompt release of NT-LI with a peak at 600% of basal followed by a decline to 200% of basal at the end of the session. Leu-enkephalin and calcitonin-gene-related-peptide (CGRP, 10(-7) M) produced a small rise in portal NT-LI, while Met-enkephalin, dynorphin, vasoactive intestinal peptide (VIP), galanin, neuropeptide Y (NPY), peptide histidine isoleucine (PHI), neuromedin U and thyrotropin releasing hormone (TRH) had no stimulatory effect. Our results indicate that additionally to the secretion of NT induced by cholinergic agents and bombesin, substance P and to a lesser extent Leu-enkephalin are capable of stimulating NT release in the rat.

Cloning of cDNAs encoding amphibian bombesin: evidence for the relationship between bombesin and gastrin-releasing peptide

Bombesin is a tetradecapeptide originally isolated from frog skin; its mammalian homologue is the 27-amino acid peptide gastrin-releasing peptide (GRP). cDNAs encoding GRP have been cloned from diverse species, but little is yet known about the amphibian bombesin precursor. Mass spectrometry of HPLC-separated skin exudate from Bombina orientalis was performed to demonstrate the existence of authentic bombesin in the skin of this frog. A cDNA library was prepared from the skin of B. orientalis and mixed oligonucleotide probes were used to isolate cDNAs encoding amphibian bombesin. Sequence analysis revealed that bombesin is encoded in a 119-amino acid prohormone. The carboxyl terminus of bombesin is flanked by two basic amino acids; the amino terminus is not flanked by basic amino acids but is flanked by a chymotryptic-like cleavage site. Northern blot analysis demonstrated similarly sized bombesin mRNAs in frog skin, brain, and stomach. Polymerase chain reaction was used to show that the skin and gut bombesin mRNAs encoded the identical prohormones. Prohormone processing, however, differed between skin and gut. Chromatography showed the presence of only authentic bombesin in skin whereas gut extracts contained two peaks of bombesin immunoreactivity, one consistent in size with bombesin and one closer in size to mammalian GRP. Thus the same bombesin prohormone is processed solely to bombesin in skin but is processed to a peptide similar in size to bombesin and to a peptide similar in size to mammalian GRP in stomach.

The effect of bombesin-related peptides on the phagocytic function of mouse phagocytes in vitro

Bombesin (BBS) at doses of 0.1, 1.0, 10.0 and 100.0 nM stimulated chemiluminescence (CL) production by phagocytic cells (monocytes, macrophages and polymorphonuclear leucocytes) in mice in the presence of ZAP (opsonized zymosan particles containing luminol). These data suggest that BBS increased the phagocytic function of mouse phagocytes. BBS-related peptides, gastrin-releasing peptides (GRP)-27, GRP-14, GRP-10 and neuromedin B, also induced similar CL responses compared with BBS. The CL response elicited by BBS was depressed dramatically by various concentrations of EGTA (a Ca++ chelator), indicating that a Ca++ pathway may play a key role in the BBS-stimulated CL response.

Gastrin releasing peptide stimulates the secretion of insulin, but not that of glucagon or somatostatin, from the isolated perfused dog pancreas

Gastrin releasing peptide (GRP) is an intrapancreatic peptide, but its physiological function is unknown. Previously, the peptide has been shown to increase plasma levels of insulin and glucagon in vivo in dogs, but no studies on the possible direct actions on islet hormone secretion from the dog pancreas have been undertaken. Therefore, we examined the effects of a 10-min perfusion of synthetic porcine GRP at four different dose rates over a wide range (0.1-50 nmol l-1) on the islet hormone release from the isolated dog pancreas (n = 5-6 in each group) at 5.5 mM glucose. We found that, at all four concentrations tested, GRP rapidly and markedly stimulated insulin secretion. The stimulation was, however, transient: the increased insulin secretion returned to basal levels within 7-8 min despite the ongoing GRP perfusion for 10 min. In contrast, GRP did not affect the pancreatic secretion of glucagon or somatostatin. We conclude that GRP stimulates insulin secretion by a direct pancreatic action without affecting the secretion of glucagon or somatostatin.

Bombesin stimulates growth of human prostatic cancer cells in vitro

Cell proliferation of the human prostatic carcinoma cell line PC3 and of the epithelial cell strain PMU 23 derived from a primary culture of a stage III prostatic carcinoma was enhanced dose dependently by adding 0.1 nM to 10.0 nM bombesin (BMBS) to the culture medium. The growth stimulation was specifically inhibited by antibodies versus Gastrin Releasing Peptide (GRP) crossreacting with BMBS. Presence of BMBS-positive neuroendocrine cells in human prostate and measurable amounts of BMBS-like peptides in prostatic fluid were reported previously. In a binding assay using 125I-GRP, it was possible to demonstrate the presence of saturable specific receptors on PC3 cells, numerically comparable with those measured on small cell lung cancer cell lines. By immunofluorescence, however, no BMBS immunoreactivity on PC3 cells could be demonstrated. These observations suggest that BMBS plays a role in prostatic epithelium growth and that prostatic carcinoma may have an autocrine or paracrine proliferation stimulus within the gland microenvironment.

Effects of synthetic human gastrin-releasing peptide on pancreatic exocrine secretion and release of pancreatic polypeptide in conscious rats

The effects of a newly synthesized peptide, human gastrin-releasing peptide (hGRP), on the pancreatic exocrine secretion and the release of pancreatic polypeptide (PP) were examined in the conscious rat. Plasma PP concentrations were determined by a recently established specific radioimmunoassay for rat PP. Amounts of 0.18, 0.35, and 3.5 nmol/kg/h hGRP significantly stimulated both pancreatic exocrine secretion and 0.35 nmol/kg/h of hGRP increased PP release. Simultaneously infused proglumide (300 mg/kg/h) did not affect either pancreatic exocrine secretion or PP release. However, simultaneous infusion of atropine (100 micrograms/kg/h) slightly inhibited PP release, but did not restrict the incremental response of pancreatic protein secretion to hGRP. These results suggest that hGRP directly stimulates pancreatic exocrine secretion and PP release.

Dual effect of bombesin and gastrin releasing peptide on gastric emptying in conscious cats

The effect of bombesin (BBS) and gastrin releasing peptide (GRP) on gastric emptying was studied in conscious cats. This effect was measured simultaneously with antral motility. Acid and pepsin secretions as well as blood hormonal peptide release were additionally measured. A dual effect was observed. First, BBS and GRP slowed gastric emptying of liquids, while antral motility was decreased, then after 60 minutes of continuous intravenous infusion, antral motility returned to basal values and gastric emptying effect reversed. The mechanism of this peculiar action is independent of gastrin, pancreatic polypeptide, somatostatin and motilin release and most probably connected with a cholinergic stimulation induced by the peptides, the late predominance of which counterbalances the inhibitory effect of bombesin-like peptides on antral motility.

The effect of gastrin-releasing peptide on the endocrine pancreas

Infusion of GRP into conscious sheep and dogs produced elevations of systemic plasma levels of insulin, glucagon, and pancreatic polypeptide (PP). In the dog, infusions of GRP produced dose-dependent decreases in plasma glucose levels, whereas, in the sheep, dose-dependent increases in plasma glucose levels occurred. Glucose turnover studies demonstrated that infusions of GRP produce prompt increases in the rate of appearance of glucose in sheep, but previous studies demonstrated a transient decrease in the rate of appearance of glucose in dogs, suggesting that sheep and dogs differ in hepatic responses to the elevated levels of insulin and glucagon. GRP was a potent PP secretagogue in the sheep, whereas, in contrast to results in the dog, infusions of GRP did not result in elevations of plasma levels of gastrin in sheep. GRP has multiple complex stimulatory effects on the endocrine pancreas, and there exist species-dependent differences in responses, which affect the potency and spectrum of the hormone-releasing activity of GRP. Further studies are required to determine the precise anatomical relation of GRP-containing nerve fibers to islet cells and to elucidate the pathways by which GRP activates endocrine pancreatic hormone release.

Expression and electrophysiological identification of the receptor for bombesin and gastrin-releasing peptide in Xenopus laevis oocytes injected with polyA+ RNA from rat brain

The receptor for bombesin and the related peptide, gastrin-releasing peptide (GRP) has been induced in frog oocytes by injection of polyA+ RNA from rat brain. The primed oocytes responded to peptides of the bombesin family (GRP, neuromedin C of bombesin) by showing dose-dependent oscillations in membrane currents as recorded by the voltage-clamp method. The induced membrane changes were suppressed when oocytes were pretreated with a bombesin-receptor antagonist.

Gastrin-releasing peptide (GRP) immunoreactivity in the rat retina: a radioimmunoassay, immunohistochemical and chromatographic study

Using radioimmunoassay, reverse phase high pressure liquid chromatography (rp HPLC) and immunohistochemistry, we have identified gastrin releasing peptide-immunoreactivity (GRP-IR) in the rat retina. The concentration of GRP-IR in retinal extracts was 7.4 +/- 0.6 ng/g wet wt. (mean +/- S.E.M. n = 15). There was no significant difference between the levels of immunoreactivity in 12-h light and 12-h dark adapted retinae. rp HPLC analysis of retinal extracts demonstrated that two main immunoreactive components were present which corresponded in retention time to GRP10 (neuromedin C) and GRP14 (GRP14-27). A small amount of material also co-eluted with GRP27. Using immunohistochemistry, the immunoreactivity has been localised in the inner retinal layers. Immunoreactive somata were present in the proximal inner nuclear layer and in the ganglion cell layer. Fibre staining was present in laminae 2 and 4 of the inner plexiform layer. Somatal staining was increased by pretreatment of retinae with vincristine while the laminar staining was markedly reduced. These results demonstrate the existence of GRP-like peptides in the rat retina which has not previously been reported.

The effects of intravenously administered bombesin on pentagastrin-stimulated acid secretion in cats

The effects of bombesin (BBS) infusion or BBS injection on the plateau gastric secretion stimulated by pentagastrin (Pg) were compared in cats fitted with gastric fistula (GF) and Heidenhain pouch (HP). Injection of 81 pmol/kg of BBS inhibited Pg-stimulated acid secretion in both GF and HP by 47 +/- 5% and 37 +/- 5% (P less than 0.01), respectively. Infusion of 324 pmol/kg.h of BBS did not significantly modify acid secretion, but as soon as the infusion stopped, an inhibition appeared which lasted 1 h (37 +/- 5% in GF and 53 +/- 4% in HP P less than 0.01). The inhibition was reversed in GF by infusion of BBS 324 pmol/kg.h. In HP, reversion of inhibition required the addition in the Pg infusion of subthreshold dose of carbachol. We suggest that under non-steady state conditions (i.e. injection or after the end of the infusion) a concentration gradient of BBS is created which favors the response of D-cells over that of G-cells, whereas under steady-state conditions (i.e. during infusion) the effects of BBS on G- and D-cells are balanced. This finding argues for a physiological role of BBS in the regulation of gastric acid secretion.

Transient elevation of messenger RNA encoding gastrin-releasing peptide, a putative pulmonary growth factor in human fetal lung

Gastrin-releasing peptide (GRP), the mammalian homologue of the amphibian peptide bombesin, is present in pulmonary neuroendocrine cells and appears to be a growth factor for both normal and neoplastic pulmonary cells. Previously we have reported the cloning of the messenger RNAs (mRNAs) and gene that encode human GRP. We now report that GRP mRNAs are markedly elevated in human fetal lung during the canalicular phase of pulmonary development (from approximately 16 to 30 wk gestation). By RNA blot and in situ hybridization analyses, GRP mRNAs were first detectable in fetal lung at 9-10 wk, plateaued at levels 25-fold higher than in adult lungs from 16 to approximately 30 wk and then declined to near adult levels by 34 wk gestation. By contrast, GRP peptide levels remain elevated until several months after birth. Consistent with this, in situ hybridization and immunohistochemical studies showed that GRP mRNA and peptide consistently colocalized in early gestation lung but that in neonatal lung, many cells that contained GRP peptide no longer contained GRP mRNA. The transient expression of high levels of GRP mRNAs during an approximately 12-wk phase of fetal lung development suggests that the secretion of GRP or its COOH-terminal peptides from pulmonary neuroendocrine cells may play a role in normal lung development.

Origin of gastrin liberated by gastrin releasing peptide in man

Gastrin release induced by gastrin releasing peptide (GRP) in man has been studied in patients before and after complete resection of the antrum and duodenal bulb, as well as after pancreaticoduodenectomy according to Whipple. Studies in healthy subjects showed that 400 pmol/kg an hour of GRP induced a maximal release of gastrin. Infusion of this dose of GRP after a complete resection of the antrum and duodenal bulb induced a small, but significant increase in gastrin concentrations. After pancreaticoduodenectomy, however, GRP infusion had no effect on serum gastrin concentrations. In patients previously subjected to an incomplete antrectomy, GRP infusion was followed by a gastrin response considerably higher than after a complete antrectomy. Our results would suggest that GRP is capable of releasing gastrin predominantly from the antrum and the duodenal bulb, but also a small amount of gastrin from the remaining part of the duodenum. Gastrin releasing peptide infusion and determination of gastrin release may be of clinical significance in showing remaining significant gastrin pools in patients with recurrent ulceration after previous gastric resections.

Inhibition of insulin release by galanin and gastrin-releasing peptide in the anaesthetized rat

The present study was designed to determine the effects of intravenously administered galanin or gastrin-releasing peptide (GRP) on glucose- and/or glucose-dependent insulinotropic peptide (GIP)-stimulated insulin release in the anaesthetized rat. Galanin inhibited glucose-stimulated insulin responses in a dose-related manner. Galanin also inhibited insulin release in response to glucose administered with GIP; this effect was due largely to inhibition of the glucose-stimulated component since galanin did not inhibit GIP-stimulated insulin release. Galanin also inhibited insulin responses to ingestion of a mixed meal. GRP inhibited glucose-stimulated insulin responses, and the insulin responses to glucose plus GIP; unlike galanin, GRP inhibited both glucose- and GIP-stimulated insulin release. GRP also inhibited insulin release following ingestion of a mixed meal. The results suggest a possible modulatory role for these neuropeptides in regulation of insulin secretion.

Effect of porcine gastrin releasing peptide on gastric secretion and motility and the release of hormonal peptides in conscious cats

The effect of porcine gastrin releasing peptide (GRP) was compared to those of bombesin (BBS) and pentagastrin (PG) in conscious cats. GRP and BBS augmented acid and pepsin secretions, as well as antral motility with an early effect comparable to that produced by pentagastrin with an elevation of low amplitude contractions and a diminution of high amplitude contractions. BBS and GRP increased plasma gastrin and pancreatic polypeptide (PP) levels and decreased motilin levels measured by a C terminus-directed antiserum. In all cases, BBS and GRP displayed parallel dose-response curves. PG showed slight differences in the slopes of the dose-response curves slopes of the dose-response curves except for acid secretion stimulation where no difference was noted (PG was the most effective) and for pepsin stimulation where the difference was large (PG was much less effective). According to the different targets studied, BBS was 4 to 9 times more potent than GRP, 6 to 200 times more than PG. Gastrin release, elicited by the lowest ED50 of both BBS and GRP, should be considered as their primary effect in the cat.

The effect of gastrin-releasing peptide on the endocrine pancreas

The 27-amino acid peptide gastrin releasing peptide (GRP-(1-27] was infused at 4 dose levels (0.01, 0.1, 1.0, and 10 nM) into the arterial line of the isolated perfused porcine pancreas. Infusions were performed at 3 different perfusate glucose levels (3.5, 5.0, and 8.0 mM) and at two levels of amino acids (5 and 15 mM). GRP-(1-27) stimulated insulin and pancreatic polypeptide secretion and inhibited somatostatin secretion in a dose-dependent manner. Glucagon secretion was unaffected by infusion of GRP under all circumstances. The effect of GRP-(1-27) on insulin secretion was enhanced with increasing perfusate glucose levels, whereas the effects upon somatostatin and pancreatic polypeptide secretion were independent of perfusate glucose levels. The responses to GRP were unaffected by elevation of the concentration of amino acids in the perfusate. The effects of GRP were unaffected by atropine at 10(-6) M. The localization of GRP within the porcine pancreas, its release during electrical stimulation of the vagus nerve, and its potent effects upon pancreatic endocrine secretion make it conceivable that the peptide participates in parasympathetic regulation of pancreatic endocrine secretion.

Human gastrin-releasing peptide gene is located on chromosome 18

Gastrin-releasing peptide (GRP), a bombesin-like peptide, increases plasma levels of gastrin, pancreatic polypeptide, glucagon, gastric inhibitory peptide, and insulin. GRP is produced in large quantities by small-cell lung cancer and acts as a growth factor for these cells. To determine if chromosomal changes in small-cell lung cancer are related to the expression of GRP, we chromosomally mapped the gene using human-mouse somatic cell hybrids. Twenty hybrids, characterized for human chromosomes, were analyzed by Southern filter hybridization of DNA digested with EcoRI. Human DNA cut with EcoRI yields a major band of 6.8 kb and a minor band of 11.3 kb. The 6.8 kb band segregated concordantly with chromosome 18 and the marker peptidase A. The chromosome 3 abnormalities seen in small-cell lung cancer do not correlate with the chromosomal location of GRP, suggesting that the elevated expression of this gene may be due to mechanisms other than chromosomal rearrangement.

Distribution of bombesin-like peptides in the alimentary canal of several vertebrate species

The objective of this study was to quantitate and characterize the variants of bombesin-like immunoreactivity in the alimentary canal of the rat, rabbit, hawk, owl, dog, monkey and human. Bombesin-like immunoreactivity was found throughout the entire gastrointestinal tract of all species studied. In the rat, the highest concentration of bombesin-like immunoreactivity was found in the colon. Gel chromatography showed that bombesin-like immunoreactivity corresponded to gastrin-releasing peptide (GRP-27) and GRP-10. In the dog, the greatest concentration of bombesin-like immunoreactivity was observed in the mucosal layer of the fundus, whereas the concentration of bombesin-like immunoreactivity in the muscle layer of the dog did not vary significantly from region to region. Gel chromatography showed that bombesin-like immunoreactivity in the dog corresponded to GRP-27, bombesin, GRP-10, and a smaller fragment. In the human, the concentration of bombesin-like immunoreactivity did not vary significantly from region to region in the mucosal and muscular layers. Gel chromatography of human fundal mucosa showed that bombesin-like immunoreactivity peaks occur in the regions of GRP-27, bombesin and GRP-10. These findings substantiate the observation that bombesin-like peptides play a variety of roles in the regulation of gut function.

Central versus peripheral effects of bombesin on the release of gastrointestinal hormones in dogs

This study compared the effects of bombesin given intracerebroventricularly and intravenously on circulating levels of gastrin, pancreatic polypeptide (PP), and cholecystokinin (CCK-33). Bilateral cannulas were implanted permanently into the lateral cerebral ventricles of five dogs. An intravenous (IV) bolus injection of bombesin (0.25 microgram/kg) significantly elevated circulating levels of gastrin, PP, and CCK-33. Vagotomy inhibited the release of PP that was induced by IV bombesin, but vagotomy did not affect gastrin and CCK-33 responses. Intracerebroventricular injection of bombesin (5.0 micrograms) significantly elevated circulating gastrin levels but did not affect circulating levels of CCK-33 and PP. Vagotomy did not alter gastrin release induced by intracerebroventricular injection of bombesin.

Two prohormones for gastrin-releasing peptide are encoded by two mRNAs differing by 19 nucleotides

In our studies on the molecular biology of human gastrin-releasing peptide (GRP), we have discovered an example of a change in translational reading frame apparently produced through alternative RNA splicing. Complementary DNAs prepared from a pulmonary carcinoid tumor rich in GRP immunoreactivity had one of two different-sized internal DNA fragments after digestion with the restriction enzyme Pvu II. Nucleotide sequences of the two DNA fragments were identical except for 19 additional nucleotides present in the larger fragment. The region of the mRNA containing the 19 nucleotides corresponded to the carboxyl-terminal region of the human GRP precursor. The resulting shift in reading frame causes a difference of 10 amino acids in size and an overall sequence difference of 27 amino acids between the two GRP prohormones so formed. The change in reading frame described here is unusual in eukaryotes and is yet another mechanism to produce diversity in the generation of biological peptides.

Influence of CCK and bombesin on ACTH and cortisol secretion in the conscious dog

Bombesin and cholecystokinin (CCK) have a variety of similar actions. Previous investigations have demonstrated that IP injections of bombesin and CCK-33 increased corticosterone secretion in conscious, freely-moving, fed rats. In this study bombesin or CCk-8 was administered by continuous, intravenous infusion to conscious, awake, fasted, mongrel dogs. Following a 30-40 minute control infusion, a progressively-increasing, stepwise infusion of either bombesin (0.1, 1.0 and 2.0 micrograms/kg-hr) or CCK-8 (62.5, 125, and 250 ng/kg-hr) was administered. Each drug dose was infused for 40-45 minutes and blood samples were drawn at 20-22.5 minutes intervals. Bombesin caused significant, dose-dependent increases in plasma cortisol (286 +/- 39% of control) and plasma ACTH (176 +/- 33% of control). CCK-8 had no consistent effect on either cortisol or ACTH secretion. Whether the lack of effect of CCK-8 in dogs, as compared to rats, is due to species variations or to the differing experimental designs is unknown.

Evidence that bombesin releases extragastric gastrin in man

Bombesin-induced gastrin release from extragastric sources has been investigated in two groups of patients without gastric antrum: 11 patients with total gastrectomy and 11 patients with subtotal (Billroth II) gastrectomy. A 30-min bombesin infusion (5 ng . kg-1 . min-1) caused a prompt significant gastrin increase (P less than 0.05) in both groups of patients. The gastrin response to bombesin was significantly (P less than 0.005) lower in patients without antral tissue than in the control group (n = 7). The individual peak gastrin responses, in totally (TG) and subtotally (SG) gastrectomized patients, were significantly over basal levels (TG: peak 100.3 +/- 12 vs. basal 62.8 +/- 9.1, P less than 0.005; SG: peak 96.9 +/- 9.4 vs. basal 72.4 +/- 6.8, P less than 0.001; pg/ml, mean +/- S.E.M.). These data indicate that bombesin acts not only on antral G cells, but on all gastrin cells in the gastrointestinal tract.

The role of vagal integrity in gastrin releasing peptide stimulated gastroenteropancreatic hormone release and gastric acid secretion

The role of the vagus nerve in the control of gastrin releasing peptide (GRP) stimulated gastroenteropancreatic hormone release and gastric acid secretion was investigated in four conscious gastric fistula dogs using a technique of bilateral cryogenic vagal blockade. A 90-min infusion of GRP at a dose of 400 pmol X kg-1. h-1 produced significant elevations in plasma levels of gastrin, motilin, GIP, enteroglucagon, insulin, pancreatic glucagon, pancreatic polypeptide and VIP. Vagal blockade reversibly inhibited the rise of plasma PP and significantly blunted the elevation of plasma VIP. However, the GRP stimulated response of the other hormones investigated was not modified by vagal blockade. Similarly, the substantial secretion of gastric acid observed with GRP was not influenced by vagal blockade. Thus GRP acts predominantly via mechanisms which are independent of vagal integrity, findings that are in support of a major role for the local neuromodulation of hormone release and gastric acid secretion.

Mammalian bombesin-like peptides: neuromodulators of gastric function and autocrine regulators of lung cancer growth

Peptides corresponding closely in structure to the biologically active carboxyl terminal region of the amphibian peptide bombesin have now been isolated from several mammalian species, including man. Two principal forms have been found: one contains 27 amino acids and exhibits variations in amino acid sequence in the amino terminal region; the other is the carboxyl terminal decapeptide and probably does not vary among mammals. These peptides exhibit full immunoreactivity with most bombesin antisera and account for "bombesin-like immunoreactivity" that has been described in mammalian brain, sympathetic ganglia, and nerve fibers in the gut as well as in fetal lung endocrine cells and certain lung tumors, especially small cell lung carcinoma. The name gastrin releasing peptide (GRP) was given to the porcine and avian heptacosapeptides by McDonald and Mutt. The larger and smaller mammalian peptides now often are called GRP27 and GRP10. Both forms exhibit the full spectrum of activity shown by bombesin. Evidence has been obtained that neural release of mammalian bombesin-like peptides is physiologically important in regulation of gastrin release from the stomach. Lung tumors that produce bombesin-like peptides also have receptors for bombesin. These receptors appear to be involved in the autocrine regulation of tumor cell proliferation.