Opioid/Dopamine Receptor Binding Studies, NMR and Molecular Dynamics Simulation of LENART01 Chimera, an Opioid-Bombesin-like Peptide

The design and development of hybrid compounds as a new class of drug candidates remains an excellent opportunity to improve the pharmacological properties of drugs (including enzymatic stability, efficacy and pharmacokinetic and pharmacodynamic profiles). In addition, considering various complex diseases and/or disorders, the conjugate chemistry approach is highly acceptable and justified. Opioids have long been recognized as the most potent analgesics and serve as the basic pharmacophore for potent hybrid compounds that may be useful in pain management. However, a risk of tolerance and physical dependence exists. Since dopamine receptors have been implicated in the aforementioned adverse effects of opioids, the construction of a hybrid with dual action at opioid and dopamine receptors is of interest. Herein, we present nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics simulation results for LENART01, an opioid-ranatensin hybrid peptide. Apart from molecular docking, protein-ligand interactions were also assessed in vitro using a receptor binding assay, which proved LENART01 to be bound to mu-opioid and dopamine receptors, respectively.

Side-by-side comparison of the two widely studied GRPR radiotracers, radiolabeled NeoB and RM2, in a preclinical setting

INTRODUCTION

NeoB and RM2 are the most investigated gastrin-releasing peptide receptor (GRPR)-targeting radiotracers in preclinical and clinical studies. Therefore, an extensive side-by-side comparison of the two radiotracers is valuable to demonstrate whether one has advantages over the other. Accordingly, this study aims to compare the in vitro and in vivo characteristics of radiolabeled NeoB and RM2 to guide future clinical studies.

METHOD

The stability of the radiolabeled GRPR analogs was determined in phosphate buffered saline (PBS), and commercially available mouse and human serum. Target affinity was determined by incubating human prostate cancer PC-3 cells with [177Lu]Lu-NeoB or [177Lu]Lu-RM2, + / - increasing concentrations of unlabeled NeoB, RM2, or Tyr4-bombesin (BBN). To determine uptake and specificity cells were incubated with [177Lu]Lu-NeoB or [177Lu]Lu-RM2 + / - Tyr4-BBN. Moreover, in vivo studies were performed to determine biodistribution and pharmacokinetics. Finally, radiotracer binding to various GRPR-expressing human cancer tissues was investigated.

RESULTS

Both radiotracers demonstrated high stability in PBS and human serum, but stability in mouse serum decreased substantially over time. Moreover, both radiotracers demonstrated high GRPR affinity and specificity, but a higher uptake of [177Lu]Lu-NeoB was observed in in vitro studies. In vivo, no difference in tumor uptake was seen. The most prominent difference in uptake in physiological organs was observed in the GRPR-expressing pancreas; [177Lu]Lu-RM2 had less pancreatic uptake and a shorter pancreatic half-life than [177Lu]Lu-NeoB. Furthermore, [177Lu]Lu-RM2 presented with a lower tumor-to-kidney ratio, while the tumor-to-blood ratio was lower for [177Lu]Lu-NeoB. The autoradiography studies revealed higher binding of radiolabeled NeoB to all human tumor tissues.

CONCLUSION

Based on these findings, we conclude that the in vivo tumor-targeting capability of radiolabeled NeoB and RM2 is similar. Additional studies are needed to determine whether the differences observed in physiological organ uptakes, i.e., the pancreas, kidneys, and blood, result in relevant differences in organ absorbed doses when the radiotracers are applied for therapeutic purposes.

NEUROENDOCRINE PEPTIDES IN THE PATHOGENESIS OF COLORECTAL CARCINOMA

Colorectal carcinoma (CRC) is the third most frequent neoplasm worldwide and the second leading cause of mortality. Neuroendocrine peptides such as glucagon, bombesin, somatostatin, cholecystokinin, and gastrin as well as growth factors such as platelet-derived growth factor, epidermal growth factor, insulin-like growth factor, and fibroblast growth factor have been postulated as being involved in carcinogenesis. The fact that these neuroendocrine peptides are involved in the development of CRC through the activation of growth factors that stimulate a series of molecular pathways that activate oncogenic signaling mechanisms is emphasized in this review. Peptides such as CCK1, serotonin, and bombesin have been found to be over-expressed in human tumor tissues. Meanwhile, the expression of peptides such as GLP2 has been seen mainly in murine models. The information contained in this review provides a better understanding of the role these peptides play in the pathogenesis of CRC for basic and clinical science studies.

PET Probes for Preclinical Imaging of GRPR-Positive Prostate Cancer: Comparative Preclinical Study of [68Ga]Ga-NODAGA-AMBA and [44Sc]Sc-NODAGA-AMBA

Gastrin-releasing peptide receptors (GRPR) are overexpressed in prostate cancer (PCa). Since bombesin analogue aminobenzoic-acid (AMBA) binds to GRPR with high affinity, scandium-44 conjugated AMBA is a promising radiotracer in the PET diagnostics of GRPR positive tumors. Herein, the GRPR specificity of the newly synthetized [⁴⁴Sc]Sc-NODAGA-AMBA was investigated in vitro and in vivo applying PCa PC-3 xenograft. After the in-vitro assessment of receptor binding, PC-3 tumor-bearing mice were injected with [⁴⁴Sc]Sc/[⁶⁸Ga]Ga-NODAGA-AMBA (in blocking studies with bombesin) and in-vivo PET examinations were performed to determine the radiotracer uptake in standardized uptake values (SUV). ⁴⁴Sc/⁶⁸Ga-labelled NODAGA-AMBA was produced with high molar activity (approx. 20 GBq/µmoL) and excellent radiochemical purity. The in-vitro accumulation of [⁴⁴Sc]Sc-NODAGA-AMBA in PC-3 cells was approximately 25-fold higher than that of the control HaCaT cells. Relatively higher uptake was found in vitro, ex vivo, and in vivo in the same tumor with the ⁴⁴Sc-labelled probe compared to [⁶⁸Ga]Ga-NODAGA-AMBA. The GRPR specificity of [⁴⁴Sc]Sc-NODAGA-AMBA was confirmed by significantly (p ≤ 0.01) decreased %ID and SUV values in PC-3 tumors after bombesin pretreatment. The outstanding binding properties of the novel [⁴⁴Sc]Sc-NODAGA-AMBA to GRPR outlines its potential to be a valuable radiotracer in the imaging of GRPR-positive PCa.

Bombesin Peptide Conjugated Water-Soluble Chitosan Gallate-A New Nanopharmaceutical Architecture for the Rapid One-Pot Synthesis of Prostate Tumor Targeted Gold Nanoparticles

PURPOSE

We report herein bombesin peptide conjugated water-soluble chitosan gallate as a template for rapid one-pot synthesis of gold nanoparticles (AuNPs) with capabilities to target receptors on prostate cancer cells.

METHODS

Water-soluble chitosan (WCS), anchored with gallic acid (GA) and LyslLys3 (1,4,7,10-tetraazacyclo dodecane-1,4,7,10-tetraacetic acid) bombesin 1-14 (DBBN) peptide, provides a tumor targeting nanomedicine agent. WCS nanoplatforms provide attractive strategies with built-in capabilities to reduce gold (III) to gold nanoparticles with stabilizing and tumor-targeting capabilities. WCS-GA-DBBN encapsulation around gold nanoparticles affords optimum in vitro stability.

RESULTS

The DBBN content in the WCS-GA-DBBN sample was ~27%w/w. The antioxidant activities of WCS-GA and WCS-GA-DBBN nanocolloids were enhanced by 12 times as compared to the nascent WCS. AuNPs with a desirable hydrodynamic diameter range of 40-60 nm have been efficiently synthesized using WCS-GA and WCS-GA-DBBN platforms. The AuNPs were stable over 4 days after preparation and ~3 days after subjecting to all relevant biological fluids. The AuNPs capped with WCS-GA-DBBN peptide exhibited superior cellular internalization into prostate tumor (PC-3) cells with evidence of receptor mediated endocytosis.

CONCLUSION

The AuNPs capped with WCS-GA-DBBN exhibited selective affinity toward prostate cancer cells. AuNPs conjugated with WCS-GA-DBBN serve as a new generation of theranostic agents for treating various neoplastic diseases, thus opening-up new applications in oncology.

Recent advances in the biology of bombesin-like peptides and their receptors

PURPOSE OF REVIEW

The current review aims to update the important findings about molecular and cellular biology of mammalian bombesin-like peptides (BLPs) and their receptors.

RECENT FINDINGS

Recent identification of synaptic communication between gastrin-releasing peptide (GRP) neurons and GRP receptor (GRPR) neurons in spinal itch relay provides us novel insights into physiology of itch sensation. Neuromedin B (NMB) neurons were found to form connections with subcortical areas associated with arousal, hippocampal theta oscillation, and premotor processing and project to multiple downstream stations to regulate locomotion and hippocampal theta power. In addition to researches regarding the roles of BLPs and their receptors in central nervous system, recent findings reveal that NMB receptor is expressed on helminth-induced type 2 innate lymphoid cells and is regulated by basophils, suggesting an important function of NMB in helminth-induced immune responses. Bombesin transactivates epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER2), and HER3 receptors on human nonsmall-cell lung cancer (NSCLC) cells and elicits downstream signaling cascades and induces formation of both human epidermal growthfactor receptor 3 (HER3)/EGFR and HER3/HER2 heterodimers. Several high-affinity ligands for bombesin receptors were characterized, providing useful tools in investigation of biological roles of those peptides and their receptors.

SUMMARY

The most exciting findings of BLPs and their receptors in the past year come from studies in central nervous system. In addition, more researches are still underway to probe the molecular mechanisms of those peptides in peripheral tissues and characterize novel synthetic ligands with high affinity for mammalian bombesin receptors.

Synthesis and Biochemical Evaluation of Samarium-153 Oxide Nanoparticles Functionalized with iPSMA-Bombesin Heterodimeric Peptide

Developments in the design of lanthanide oxide nanoparticles (NPs) have unleashed a wide variety of biomedical applications. Several types of hepatic cancer cells overexpress two proteins: the gastrin-releasing peptide receptor (GRPr), which specifically recognizes the bombesin (BN) peptide, and the prostate-specific membrane antigen (PSMA), which specifically binds to several peptides that inhibit its activity (iPSMA). This research synthesized and physicochemically characterized Sm₂O₃ nanoparticles functionalized with the iPSMA-BN heterodimeric peptide and studied the effects on their structural, biochemical and preclinical properties after activation by neutron irradiation for possible use in molecular dual-targeted radiotherapy of hepatocellular carcinoma. The Sm₂O₃ NPs were synthesized by the precipitation-calcination method and functionalized with iPSMA-BN peptide using the DOTA macrocycle as a linking agent. Analysis of physicochemical characterization via TEM, EDS, XRD, UV-Vis, FT-IR, DSL, and zeta potential results showed the formation of Sm₂O₃-iPSMA-BN NPs (94.23 ± 5.98 nm), and their physicochemical properties were not affected after neutron activation. The nanosystem showed a high affinity with respect to PSMA and GRPr in HepG2 cells ( K_d = 6.6 ± 1.6 nM) and GRPr in PC3 cells ( K_d = 10.6 ± 1.9 nM). ¹⁵³Sm₂O₃-iPSMA-BN NPs exhibited radioluminescent properties, making possible in vivo optical imaging of their biodistribution in mice. The results obtained from this research support further preclinical studies designed to evaluate the dosimetry and therapeutic efficacy of ¹⁵³Sm₂O₃-iPSMA-BN nanoparticles for in vivo imaging and molecular dual-targeted radiotherapy of liver tumors overexpressing PSMA and/or GRPr proteins.

[Central regulation mechanisms for stress-induced frequent urination]

Psychological stress can induce not only frequent urination but also exacerbation of bladder dysfunctions. However, the brain pathophysiological mechanisms underlying stress-induced effects on the micturition reflex are still unknown. Bombesin (BB)-related peptides and BB receptors in the brain have been reported to mediate and integrate stress responses. We have found that centrally administered BB induced frequent urination in rats through brain BB₁ and BB₂ receptors, serotoninergic nervous system/5-HT₇ receptors and corticotropin-releasing factor (CRF) type1 (CRF₁) receptors. Interestingly, the BB-induced frequent urination was independent of the BB-induced activation of the sympatho-adrenomedullary outflow, a representative response to stress. Because the outflow is well known to regulate micturition, the finding was very surprising. These findings indicate that brain BB₁, BB₂, 5-HT₇ and CRF₁ receptors could be new therapeutic targets for bladder dysfunction exacerbated by stress exposure.

Rationale for the use of radiolabelled peptides in diagnosis and therapy

Nuclear medicine techniques are becoming more important in imaging oncological and infectious diseases. For metabolic imaging of these diseases, antibody and peptide imaging are currently used. In recent years peptide imaging has become important, therefore the rationale for the use of peptide imaging is described in this article. Criteria for a successful peptide tracer are a high target specificity, a high binding affinity, a long metabolic stability and a high target-to-background ratio. Tracer internalization is also beneficial. For oncological imaging, many tracers are available, most originating from regulatory peptides, but penetrating peptides are also being developed. Peptides for imaging inflammatory and infectious diseases include regulatory peptides, antimicrobial peptides and others. In conclusion, for the imaging of oncological, imflammatory and infectious diseases, many promising peptides are being developed. The ideal peptide probe is characterized by rapid and specific target localization and binding with a high tumour-to-background ratio.

Differentiation between malignant transformation and tumour recurrence by (68)Ga-bombesin and (18)F-FDG-PET, in patients with low grade gliomas

Treatment of gliomas is multimodal. Magnetic resonance imaging (MRI) in the posttreatment course is of limited value due to therapy-induced changes. In low-grade gliomas (LGG) malignant transformation is of special interest. Our patients and methods were as follows: In nine consecutive patients with LGG we examined the role of bombesin labelled with gallium-68 ((68)Ga-bombesin) studied with positron emission tomography (PET), in addition to fluoro-18-fluorodeoxyglucose ((18)F-FDG) in the differential diagnosis of tumour recurrence versus malignant transformation. We used (68)Ga-bombesin combined with (18)F-FDG-PET in these patients with suspicious new contrast enhancement at the original tumour site or resection cavity in MRI. Eight patients were operated. In one patient, tumour recurrence was most likely as shown by the PET findings and chemotherapy was administered. Our results have shown that in this last mentioned patient after the follow-up period, MRI contrast enhancement was definitively regressive. In the operated patients the tumour was graded as glioblastoma multiforme, gliosarcoma and WHO grade III tumour. In two patients histological grading confirmed the PET findings without malignant transformation. In all of the 9 patients the combination of (68)Ga-bombesin and (18)F-FDG-PET predicted correctly malignant transformation or recurrence of the initial tumour grade which shows that (68)Ga-bombesin-PET can provide additional important information to detect a malignant transformation. In conclusion it is crucial for the patient to differentiate the nature of the new lesion in order to endorse an aggressive or non-aggressive treatment.

Fluorescein isothiocyanate–hapten immunoassay for determination of peptide–cell interactions

We have developed a fluorescein isothiocyanate (FITC)-hapten immunoassay, where a FITC-labeled peptide binding to a cell is assayed as the amount of immunoreactive fluorescein present in a cell lysate. An antifluorescein-horseradish peroxidase conjugate binds to either a fluoresceinated peptide in the lysate or a fluorescein attached to the wells of a microtiter plate in a competitive fashion. After washing, solid-phase peroxidase activity is measured and inversely related to the amount of FITC-labeled peptide present. To demonstrate the assay, the interaction of a FITC-labeled bombesin-like peptide with the gastrin-releasing peptide receptor on PC-3 and HT-29 cells was investigated. Using PC-3 cells, we obtained similar displacement curves and numbers of binding sites per cell by both the FITC-hapten immunoassay and a reference radioreceptor assay. The FITC-hapten immunoassay is a sensitive and versatile method, since the same commercially available reagents can be used to assess interactions between any peptide and any receptor. In addition, the FITC-labeled peptide can be used to visualize receptors in fluorescent-activated cell sorting or fluorescent microscopy.

Development of high affinity camptothecin-bombesin conjugates that have targeted cytotoxicity for bombesin receptor-containing tumor cells

Mammalian bombesin (BN) receptors are among those most frequently overexpressed by a number of common tumors including prostate, breast, lung, and colon cancers. The aim of this study was to develop a camptothecin-bombesin (CPT-BN) conjugate that interacts with all classes of BN receptors and possibly functions as a prodrug via a labile linker with site-specific cytotoxicity for cancer cells bearing these receptors. CPT was coupled to analogs of [D-Tyr6,beta-Ala11,Phe13,Nle14]BN-(6-14) (BA0) using carbamate linkers (L1 and L2) with built-in nucleophile-assisted releasing groups for intracellular cleavage of free cytotoxic agents. One conjugate, CPT-L2-BA3, bound to all three BN receptor classes with high affinity and functioned as a full agonist at each. 125I-CPT-L2-BA3 was rapidly internalized by cells expressing each BN receptor class and, using fluorescent imaging, was found to co-localize with BN receptors initially and later to be internalized in cytoplasmic compartments. HPLC analysis of internalized ligand showed that 40% was intact, 25% was metabolized by releasing free CPT, and 35% was metabolized to other breakdown products. CPT-L2-BA3 inhibited the growth of NCI-H1299 non-small cell lung cancer cells in 3-(4,5-dimethylthiazol-2-yl)-2.5-diphenyl-2H-tetrazolium bromide (MTT) and clonal growth assays. CPT-L2-BA3 was cytotoxic in an MTT assay for cells transfected with each class of BN receptor; however, it had significantly less effect in cells lacking BN receptors. These results indicate that CTP-L2-BA3 is a potent agonist that is cytotoxic for cells overexpressing any of the three BN receptor classes and functions as a prodrug for receptor-mediated cytoxicity. It therefore should be a useful prototype to explore the effectiveness of tumor-specific cytotoxicity delivery using a receptor-mediated mechanism.

Immunohistochemistry, histopathology and ultrastructure of Gasterosteus aculeatus tissues infected with Glugea anomala

Immunohistochemical and histopathological studies were conducted on a population of 3-spined sticklebacks Gasterosteus aculeatus (L.) from Loch Airthrey (Stirling, Scotland) naturally infected with the microsporean Glugea anomala (Moniez 1887). Of the 55 host specimens that were examined, 16 (29.09%) were infected, the intensity of infection ranging from 1 to 4 xenomas per fish, which were principally located within the central portion of the body lateral flank musculature. All 32 G. anomala xenomas examined were mature, their diameter ranging from 936 to 2232 Pum, and their walls of presented a laminar structure. Subcutaneously situated xenomas protruded from the fish body surface, whilst xenomas encountered within the intestine were seen to cause distortion. Light and electron microscopical observations confirmed a host cellular reaction around the xenoma, seen by the presence of eosinophile granule cells (EGCs), and some neutrophils. The occurrences of rodlet cells among the intestinal epithelial cells, and in close proximity to the xenoma wall, were observed in certain specimens. Outside the xenoma wall, macrophage aggregates (MAs) were commonly encountered. Within the xenoma wall, the presence of eosinophile granular cells immunoreactive to the anti-serotonin serum was also recorded. Further immunohistochemical tests revealed that a high number of nerve fibres running along the white lateral muscle fibres were immunoreactive to bombesin-, galanin-, and leu-enkephalin-antisera. Nerve fibres containing bombesin- and leu-enkephalin-like substances were also observed in the connective inflammatory tissue around the protozoan cyst, while neurons in the spinal ganglia were immunoreactive to met-enkephalin, and serotonin antisera. The control for the specificity of immunohistochemical reactions was performed using preabsorption tests of each antiserum with the corresponding antigen, and no immunoreactivity was noticed. The data presented are discussed in relation to the occurrence of G. anomala, which alters the pattern of nerve fibres present in the host. Specifically, the protozoan induces a response in the stickleback nervous system, the reaction of which is revealed through the application of immunohistochemical techniques.

Role of 99mTc-Bombesin Scan in Diagnosis and Staging of Prostate Cancer

Aim of this work was to asses whether a novel 99mTc labeled Bombesin (BN) can play a clinical role in diagnosis and staging of prostate cancer. 14 patients were studied with trans-rectal ultrasonography-guided biopsy, CT and MRI and with 99mTc BN Scintigraphy. Five patients were also imaged by 111In Octreotide (O) scan. All the patients but one were submitted to surgery and final diagnosis was reached by pathology, taken as the gold standard method. Two patients showed benign adenoma and 12 patients showed cancer at biopsy. 99mTc BN SPECT was positive in all 12 patients with cancer. Four of these patients also showed pelvic focal uptake, referred to inguinal lymph-nodal involvement. MRI and CT provided similar findings in only three cases. Pathologic evaluation after operation confirmed the invasion of nodes in all four subjects. Both 99mTc BN and 111In O scans provided normal findings in the two subjects affected by benign adenoma, while 111In O was positive in only two of three patients with cancer and was always unable to detect nodal invasion. These preliminary data suggest that 99mTc BN SPECT scan could be useful to detect primary prostate cancer and to reveal loco-regional node involvement.

Oxidative stress increases internal calcium stores and reduces a key mitochondrial enzyme

Fibroblasts from patients with genetic and non-genetic forms of Alzheimer's disease (AD) show many abnormalities including increased bombesin-releasable calcium stores (BRCS), diminished activities of the mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC), and an altered ability to handle oxidative stress. The link between genetic mutations (and the unknown primary event in non-genetic forms) and these other cellular abnormalities is unknown. To determine whether oxidative stress could be a convergence point that produces the other AD-related changes, these experiments tested in fibroblasts the effects of H(2)O(2), in the presence or absence of select antioxidants, on BRCS and KGDHC. H(2)O(2) concentrations that elevated carboxy-dichlorofluorescein (c-H(2)DCF)-detectable ROS increased BRCS and decreased KGDHC activity. These changes are in the same direction as those in fibroblasts from AD patients. Acute treatments with the antioxidants Trolox, or DMSO decreased c-H(2)DCF-detectable ROS by about 90%, but exaggerated the H(2)O(2)-induced increases in BRCS by about 4-fold and did not alter the reduction in KGDHC. Chronic pretreatments with Trolox more than doubled the BRCS, tripled KGDHC activities, and reduced the effects of H(2)O(2). Pretreatment with DMSO or N-acetyl cysteine diminished the BRCS and either had no effect, or exaggerated the H(2)O(2)-induced changes in these variables. The results demonstrate that BRCS and KGDHC are more sensitive to H(2)O(2) derived species than c-H(2)DCF, and that oxidized derivatives of the antioxidants exaggerate the actions of H(2)O(2). The findings support the hypothesis that select abnormalities in oxidative processes are a critical part of a cascade that leads to the cellular abnormalities in cells from AD patients.

Is there a role for agonist gastrin-releasing peptide receptor radioligands in tumour imaging?

Gastrin-releasing peptide (GRP) has been shown to be a tumour growth stimulating agent for a number of normal and human cancer cell lines. The tumour growth effect is a direct result of GRP binding to membrane G-protein coupled GRP receptors (GRP-R) on the cell surface. Available data on the role of GRP and GRP-R in human lung, prostate, breast, colorectal and gastric carcinoma are reviewed and it is suggested that radiolabelled agonists are preferable to antagonists for imaging and therapy as they appear to be internalised, yielding a higher target/background ratio. The use of rhenium or indium radiolabels for therapy may provide a new approach to GRP/bombesin expressing tumours.

Individual neuropeptides regulate gut-associated lymphoid tissue integrity, intestinal immunoglobulin A levels, and respiratory antibacterial immunity

BACKGROUND

Total parenteral nutrition (TPN) leads to atrophy of the gut-associated lymphoid tissue (GALT) and a significant decrease in intestinal immunoglobulin A (IgA) levels, a major constituent of mucosal immunity. Bombesin (BBS) prevents TPN-induced GALT atrophy and maintains intestinal IgA levels. BBS, a neuropeptide analogous to gastrin-releasing peptide in humans, stimulates the release of other gut neuropeptides including cholecystokinin (CCK), gastrin, and neurotensin (NT). This study investigates the ability of CCK, gastrin, or NT to individually prevent TPN-induced GALT atrophy and preserve respiratory immunity.

METHODS

Experiment 1: Male mice were randomly assigned to receive chow, TPN, TPN plus CCK, TPN plus gastrin, or TPN plus NT. After 5 days of feeding, Peyer's patches (PP) from the proximal and distal small bowel were harvested and analyzed for cell yields. PP cells were also analyzed for GALT cell type. Small bowel IgA levels were measured by enzyme-linked immunosorbent assay (ELISA). Experiment 2: Mice were randomly assigned to receive either liposomes containing Pseudomonas antigen or liposomes without antigen. After 10 days, mice were randomly assigned to the same five treatment groups, fed for 5 days, and then given intratracheal Pseudomonas. Mortality was assessed after 48 hours.

RESULTS

Experiment 1: GALT cell reductions due to IV-TPN were greater in the distal than proximal small bowel. All three neuropeptides prevented most TPN-induced GALT atrophy due mainly to the maintenance of the B-cell and T-cell populations in the PP of the distal bowel. Intestinal IgA levels were significantly higher in the animals treated with neuropeptides than animals treated with TPN only; however, these IgA levels were not maintained at levels observed in chow-fed animals. Experiment 2: Immunization resulted in significantly lower mortality in animals fed chow, TPN plus CCK, and TPN plus gastrin. TPN alone and TPN plus NT resulted in loss of immunity and mortality rate at comparable levels to unimmunized animals.

CONCLUSIONS

Supplementation of IV-TPN with CCK, gastrin, and NT prevents GALT atrophy, primarily in the distal bowel. Intestinal IgA levels improve but not to normal levels. CCK and gastrin reversed IV-TPN-induced effects on antibacterial pneumonia in immunized animals while NT did not.

Cholecystokinin secretion in patients with chronic pancreatitis and after different types of pancreatic surgery

Cholecystokinin (CCK) secretion may be affected in patients with chronic pancreatitis (CP), but little is known on the effect of pancreatic surgery on CCK secretion. We measured CCK secretion (radioimmunoassay, RIA) in response to bombesin infusion (100 ng/kg/20 min) for 120 min to test CCK secretory capacity, to ingestion of a liquid diet (400 kcal) for 120 min, and in response to a solid fat-rich meal (500 kcal) for 120 min. These studies were performed in 45 patients with CP (25 with exocrine insufficiency), 15 patients after duodenum-preserving pancreatic head resection (DPRHP), 18 patients after the Whipple operation, 12 patients after distal pancreatectomy (DP), and 35 control subjects. In CP patients, the CCK secretory capacity was preserved, but the postprandial CCK response was reduced, depending on meal composition and the presence of exocrine insufficiency. In patients after Whipple's operation, CCK secretory capacity and postprandial CCK secretion were significantly (p < 0.05) reduced. In patients after DPRHP, CCK secretory capacity was not affected, but the postprandial CCK response was significantly (p < 0.05) reduced, depending on meal composition and the presence of exocrine insufficiency. In patients after DPRHP, fasting plasma CCK levels were significantly (p < 0.01) increased, pointing to the absence of feedback inhibition on CCK secretion by intraluminal enzymes. After DP, the CCK secretory capacity was not affected.

IN CONCLUSION

alterations in CCK secretion are observed in patients with chronic pancreatitis and after pancreatic surgery. These alterations are related not only to the disease process (exocrine insufficiency) but also to the type of surgery and type of stimulus.

Multifocal peripheral bronchial carcinoid tumour

Peripheral bronchial carcinoids sometimes arise as single solid or nodular lesions in the periphery of the lung. We encountered a 74-year-old Japanese male with bronchial carcinoids that were widely disseminated throughout the lung parenchyma. Pulmonary function tests revealed mild airflow obstruction. A metastatic process was ruled out from primary malignancy and a histological examination revealed findings consistent with a peripheral bronchial carcinoid. Based on these findings, we concluded that this patient had a primary multifocal peripheral bronchial carcinoid. An immunohistochemical examination revealed immunoreactivity for chromogranin A and bombesin. The present case appears to be an unusual case of diffuse multifocal peripheral bronchial carcinoid, confirmed by immunohistochemistry.

Marked rebound acid hypersecretion after treatment with ranitidine

OBJECTIVES

Dyspeptic symptoms frequently recur rapidly after withdrawal of H2 antagonists, and this might be related to rebound acid hypersecretion. We have studied this phenomenon in healthy volunteers with and without Helicobacter pylori infection.

METHODS

Basal and gastrin-releasing peptide (GRP) (40 pmol/kg/h) stimulated acid output, and gastrin concentration were measured in 18 healthy volunteers (nine were H. pylori positive). Studies were performed before and at 60 h and 10 days after completion of a 60-day course of ranitidine 300 mg nocte.

RESULTS

In the H. pylori-negative healthy volunteers, basal acid output increased by a median of 137% 2 days after stopping ranitidine therapy compared with pretreatment values (p = 0.01) and returned to pretreatment values by day 10 posttreatment. Their GRP-stimulated acid output increased by a median of 108% 2 days post ranitidine (p < 0.01) and remained slightly increased at day 10. In H. pylori-positive healthy volunteers, basal acid output increased by a median of 96% 2 days after ranitidine therapy ceased (p < 0.01) and returned to pretreatment values by day 10 posttreatment. Their GRP-stimulated acid output also increased by a median of 56% 2 days posttreatment and returned to pretreatment values by day 10. The increase in acid output both basal and in response to GRP was not accompanied by any rise in gastrin concentration in either the H. pylori-positive or -negative subjects.

CONCLUSIONS

Ranitidine therapy is associated with marked rebound hypersecretion of acid, and this may contribute to rapid resurgence of symptoms after therapy has been discontinued.

Plasma cholecystokinin and pancreatic polypeptide secretion in response to bombesin, meal ingestion and modified sham feeding in lean and obese persons

Disturbed satiety mechanisms may contribute to obesity. There has been speculation that cholecystokinin (CCK) and pancreatic polypeptide (PP) are involved in the regulation of satiety. We have therefore investigated whether there are differences between healthy lean and healthy non-diabetic obese volunteers in plasma CCK or PP release after a neuropeptidergic stimulation with bombesin and after infusion of a mixed meal. There were no differences in plasma CCK between groups either basally or in response to either form of stimulation. However, the plasma PP concentrations after the meal were significantly less in obese (2845 +/- 404 pM.min) than in lean subjects (5569 +/- 997 pM.min), whereas the plasma PP concentrations during bombesin were similar in both groups. We tested two other groups of nine obese and lean subjects to determine whether a disturbed vagal function could be the cause of the diminished plasma PP in obese persons, by studying the effect of modified sham feeding (MSF) on plasma PP. However, there were no significant differences in the plasma PP response to MSF between lean and obese subjects. We conclude that there are no differences between lean and obese persons in plasma CCK secretion in response to infusion of the neuropeptide bombesin or to ingestion of a mixed meal. However, the plasma PP after a mixed meal, is markedly diminished in obese subjects. This could not be attributed to a disturbed vagal cephalic stimulation.

Neurons containing gastrin releasing peptide-like immunoreactivity in the human pancreas

Gastrin releasing peptide (GRP) is known to stimulate pancreatic enzyme and islet hormone secretion. In the present immunohistochemical study, the localization and distribution of GRP-like immunoreactivity were investigated in the human pancreas using two antisera with different specificities. GRP-like immunoreactivity (GRP-LI) was observed in numerous nerve fibers diffusely distributed to the exocrine pancreas, but was not seen in intrapancreatic nerve cells of normal pancreatic specimens examined. Nerve fibers and terminals with GRP-LI were found in abundance around pancreatic acini and capillaries, with moderate density around ductules and in the walls of arterioles, and a few were seen in islets. This distribution pattern was quite similar to that of vasoactive intestinal polypeptide (VIP)-LI nerve fibers. The study, using the antibody elution method, strongly suggests the co-localization of GRP- and VIP-LIs within a part of VIP-containing nerve fibers. In the chronic pancreatitis specimens, neurons with GRP-LI were frequently found, and > 90% of intrapancreatic nerve cells were VIP-immunoreactive. Immunostainings for GRP and for VIP on serial adjacent sections of intrapancreatic ganglia from chronic pancreatitis specimens suggested the co-localization of the two immunoreactivities in > 70% of intrapancreatic neurons. The present findings may provide a morphological basis for neurotransmitter and/or neuromodulator roles of GRP in the human pancreas.

Opioid agonist properties of two oxime derivatives of naltrexone, NPC 831 and NPC 836

Two novel oxime derivatives of naltrexone, 6-[2-phenylethyl]-oximino naltrexone (NPC 831) and 6-[3-phenylpropyl]-oximino naltrexone (NPC 836) were potent agonists at opioid receptors. Both compounds inhibited binding to all three opioid receptor subtypes with nanomolar affinities. In vivo, NPC 831 and NPC 836 were equipotent to morphine and more potent than the kappa-selective agonist U-50,488H to produce analgesia. ED50 values of 4.02 mg/kg for NPC 831 and 2.24 mg/kg for NPC 836 were generated for inhibition of the tail-flick response in the rat, and ED50 values of 0.05 mg/kg for NPC 831 and 0.02 mg/kg for NPC 836 were calculated for inhibition of the writhing response in the mouse. Bombesin-induced scratching was used to evaluate NPC 831 and NPC 836 for kappa-agonist properties, and the A50, defined as the percent antagonism of the bombesin-induced response, was 1.86 mg/kg for NPC 831 and 0.08 mg/kg for NPC 836, compared to an A50 of 1.54 mg/kg for U-50,488H. These data suggest that NPC 831 and NPC 836 possess potent mu- and kappa-agonist properties in vivo, with NPC 836 being approximately twice as potent as NPC 831 to produce analgesia and 20 times as potent as NPC 831 to inhibit the scratching response produced by bombesin.

Gastrin releasing peptide immunoreactivity is present in ovine amniotic fluid and fetal and maternal circulations. MRC Group in Fetal and Neonatal Health and Development

Using antisera directed towards the C-terminal region of gastrin releasing peptide (GRP), significant quantities of GRP-like immunoreactivity (GRPLI) were detected in ovine amniotic fluid and in the fetal and maternal circulations. The highest GRPLI levels were found in amniotic fluid (2135 +/- 829 fmol/ml, n = 12; mean +/- SEM), followed by those in ovine fetal (604 +/- 267 fmol/ml, n = 13) and maternal plasma (229 +/- 89 fmol/ml, n = 13). On gel filtration chromatography, the predominant GRPLI form in each fluid eluted in an identical position consistent with the entity being of apparently larger molecular size than porcine GRP1-27. Certain fetal plasma samples contained a second GRPLI peak eluting at the void volume. Hence, during ovine pregnancy a GRPLI entity circulates in fetal and maternal plasma; the entity is of apparently larger molecular size than GRP1-27 but contains a structure immunologically indistinguishable from the bioactive c-terminal region of GRP1-27. Given the recognized bioactivities of GRP, this entity may be an important hormone during ovine fetal life.

Destruction of different fiber tracts underlies development of lateral hypothalamic lesion-induced hyperthermia and loss of bombesin-induced hypothermia

The relative roles of lateral hypothalamic cell bodies and fibers of passage were assessed in the development of lesion-induced hyperthermia and bombesin-induced hypothermia. Electrolytic lesions or discrete fiber transections were combined with intracisternal bombesin injection to show that each of these two thermoregulatory effects involves fibers crossing the borders of the lateral hypothalamus; however, the two effects primarily involve fibers crossing different borders. Thus, the hyperthermia and the abolition of bombesin-induced hypothermia which follow lateral hypothalamic damage appear to result from disruption of separate thermoregulatory pathways.

The effect of bombesin infusion and urea ingestion

Recent studies have shown that the exaggerated meal-stimulated gastrin release in patients with duodenal ulcer abates after eradication of Helicobacter pylori infection. Bombesin-stimulated gastrin release was compared in 11 H. pylori-infected patients with chronic duodenal ulcer and 8 uninfected healthy volunteers both before and after therapy to eradicate H. pylori. Bombesin infusion significantly increased the gastrin release both in control subjects and in patients with duodenal ulcer. Antimicrobial therapy (bismuth, tetracycline, and metronidazole) to eradicate the H. pylori infection was associated with a significant reduction in bombesin-stimulated gastrin release in patients with duodenal ulcer (from 116.9 +/- 19 pg/mL to 69.5 +/- 7 pg/mL following 50 pmol.kg-1.h-1 bombesin; and from 158 +/- 29 to 83.4 +/- 10 following 200 pmol.kg-1.h-1 bombesin: P = 0.01 for each). Antimicrobial therapy had no effect on gastrin release in uninfected volunteers, thus excluding a nonspecific effect of antimicrobial therapy on antral G-cell function. Serum gastrin was also not increased by feeding 500 mg of urea to 5 H. pylori-infected volunteers. This suggests that access of hydrogen ion to the pH-sensitive sites governing gastrin release by mucosal ammonia produced by H. pylori urease is not a critical factor. These data suggest that exaggerated gastrin release present in patients with duodenal ulcer disease is secondary to H. pylori infection.

Role of cholecystokinin in bombesin- and meal-stimulated pancreatic polypeptide secretion in dogs

This study was undertaken to delineate the role of cholecystokinin (CCK) in bombesin- and meal-stimulated pancreatic polypeptide (PP) secretion in seven conscious dogs by studying: (1) the stimulatory effect of similar plasma levels of CCK induced by a meal and infusions of bombesin and the synthetic CCK analog cerulein on plasma PP, and (2) the inhibition of PP secretion by the CCK-receptor antagonist CR-1409 during these three stimuli. The stimulation of PP secretion during bombesin (11.0 +/- 1.6 nM/hr) and after the meal (8.9 +/- 2.0 nM/hr) were significantly (P less than 0.05) greater than during infusion of the CCK analog cerulein (2.7 +/- 0.4 nM/hr). CR-1409 significantly inhibited the bombesin- and meal-stimulated PP secretion to 2.0 +/- 0.4 nM/hr (81%; P less than 0.05) and 3.1 +/- 1.2 nM/hr (47%; P less than 0.05), respectively, while the cerulein-stimulated PP release was almost abolished to 0.2 +/- 0.1 nM/hr (93%; P less than 0.05) by the drug. These findings point to an important role for CCK in the regulation of bombesin- and meal-stimulated PP secretion.

NMR identification of a partial helical conformation for bombesin in solution

The conformation of bombesin in trifluoroethanol/water mixtures has been studied using 1H-NMR spectroscopy. By a combination of two-dimensional 1H-NMR techniques and measurement of vicinal NH-alpha-CH spin-spin coupling constants, the secondary structure of the molecule has been determined. Bombesin adopts a helical structure in the region from Asn-6 to Met-14 with the remaining N-terminal portion existing as a more extended structure. The structure is very similar to that proposed from Fourier-transform infrared spectroscopic measurements for bombesin inserted into lipid bilayers [D. Erne & R. Schwyzer (1987) Biochemistry 26, 6316-6319]. The absence of a hydrogen bond between the sidechains of Trp-8 and His-12 is discussed in terms of the ionization state of His-12. Stabilisation of the helix results when His-12 is in the ionized state.

Effect of parietal cell vagotomy and cholinergic blockade on gastrin release in man induced by gastrin-releasing peptide

The influence of cholinergic blockade as well as vagal denervation of the oxyntic gland mucosa on the gastrin response to gastrin-releasing peptide (GRP) have been studied in patients with duodenal ulcer disease. The gastric luminal content was neutralized during the experiments. GRP induced a substantial increase in gastrin levels with a peak response already after 15 min of infusion. Vagal denervation of the parietal cell area induced a significant increase in basal gastrin concentrations and a significant enhancement of the GRP response. Two different doses of benzilonium bromide were studied and neither influenced the basal concentrations of gastrin. A significantly increased gastrin response to GRP was, however, observed after administration of both a high and a very low dose of the anticholinergic drug. Our results delineate a vagal, noncholinergic inhibitory influence on the basal gastrin release. In addition a vagally dependent oxyntopyloric mechanism inhibits the gastrin release stimulated by GRP. This inhibitory mechanism may hypothetically be a cholinergic reflex mechanism.

Differential mechanisms of inositol phosphate generation at the receptors for bombesin and platelet-derived growth factor

We investigated the mechanism(s) whereby activation of a growth-factor receptor typically endowed with tyrosine kinase activity, such as the platelet-derived growth factor (PDGF) receptor, triggers phosphoinositide hydrolysis. In Swiss 3T3 cells permeabilized with streptolysin O, an analogue of GTP, guanosine 5'-[gamma-thio]triphosphate, was found to potentiate the coupling of the bombesin receptor to phospholipase C. In contrast, the activation of the enzyme by PDGF occurred in a GTP-independent manner. Moreover, the inactive analogue of GTP, guanosine 5'-[beta-thio]diphosphate, significantly inhibited the bombesin-induced InsP3 generation, whereas it did not decrease the same effect when stimulated by PDGF.

Carboxyl-terminal modification of a gastrin releasing peptide derivative generates potent antagonists

Gastrin releasing peptide (GRP) is a 27-residue peptide hormone which is analogous to the amphibian peptide bombesin. GRP serves a variety of physiological functions and has been implicated as an autocrine factor in the growth regulation of small cell lung cancer cells. We have developed a series of potent GRP antagonists by modification of the COOH terminus of N-acetyl-GRP-20-27. The most potent member of this series, N-acetyl-GRP-20-26-OCH2CH3, exhibits an IC50 of 4 nM in a competitive binding inhibition assay. This compound blocks GRP-stimulated mitogenesis in Swiss 3T3 mouse fibroblasts, inhibits GRP-dependent release of gastrin in vitro, and blocks GRP-induced elevation of [Ca2+]i in H345 small cell lung cancer cells. These results demonstrate that while residues 20-27 of GRP influence binding of the parent peptide to its receptor, the COOH-terminal amino acid is primarily responsible for triggering the subsequent biological response.

Conformation of bombesin in buffer and in the presence of lysolecithin micelles: NMR, CD, and fluorescence studies

The conformation of the tetradecapeptide hormone bombesin has been studied in buffer and in the presence of lysolecithin micelles, using static and dynamic fluorescence, CD, and one- and two-dimensional nmr. The results obtained show that in buffer bombesin is present in an extended flexible chain, with no evidence for any ordered secondary structure. A marked change in the CD spectrum is observed changing from buffer to the lipid suspension. Concomitantly, the 1H-nmr spectrum of bombesin, in a D2O lipid dispersion, shows the persistence of resonances due to exchangeable protons and in similar conditions the fluorescence intensity increases. We think therefore that these results strongly support the hypothesis that bombesin interacts with the lipid phase, assuming ordered secondary structure. Finally, the marked dependence of tryptophan fluorescence quantum efficiency and order parameter from the hormone concentration in the presence of lysolecithin but not in buffer leads to the conclusion that bombesin can associate into the lipid matrix.

Gastrin cell function in familial multiple endocrine neoplasia type I

Recent studies have suggested that patients with multiple endocrine neoplasia type I (MEN I) may have abnormal serum gastrin secretion in the absence of gastrin producing tumours. G-(gastrin) cell function by three provocation tests in 20 patients with hyperparathyroidism from six MEN I-families were studied: each patient was an obligate carrier of the MEN I-gene. The serum gastrin response to secretin was used to identify the presence of gastrinoma, that to a test meal of G-cell hyperfunction of the antral and/or duodenal mucosa, and that to bombesin to differentiate antral from duodenal G-cell hyperfunction. Seven patients had basal hypergastrinaemia and hyperchlorhydria. These patients had increased serum gastrin responses to secretin (p less than 0.01) and to bombesin (p less than 0.02), but normal postprandial responses. In the 13 normogastrinaemic patients the responses to the three stimuli were normal. In families with MEN-I gastrinoma is the only endocrine disorder accounting for abnormal gastrin secretion. G-cell function is normal in obligate carriers of the MEN I-gene.

Decreased gastrin secretion in patients with late-onset hypogammaglobulinemia

We undertook this study to determine whether patients with late-onset hypogammaglobulinemia, who are at very high risk for gastric cancer, have a reduced secretion of gastrin after stimulation with food or bombesin, a potent gastrin-releasing stimulus. We compared the plasma gastrin responses to bombesin and to a standard test meal in 18 patients with late-onset hypogammaglobulinemia with those in patients with X-linked agammaglobulinemia, early-onset hypogammaglobulinemia, or hypogammaglobulinemia due to lymphoproliferative cancer, and in 30 normal control subjects. Thirteen of 18 patients with late-onset hypogammaglobulinemia (72 percent) had an abnormally low gastrin response to bombesin, as compared with none of 21 patients with other forms of hypogammaglobulinemia (P less than 0.05). After a test meal, abnormally low gastrin secretion was found in 6 of 14 patients with late-onset hypogammaglobulinemia (43 percent) and in 1 of 18 patients with other forms of the disease (6 percent) (P not significant). The plasma gastrin responses to stimulation with bombesin or food distinguished late-onset hypogammaglobulinemia from other forms, with sensitivities of 72 and 43 percent and specificities of 100 and 94 percent, respectively. Stimulated gastrin response can therefore be used as a marker for this type of immunodeficiency. The test responses also showed heterogeneity among patients with late-onset hypogammaglobulinemia and may help to identify patients with an increased risk for gastric cancer.

Evidence for the direct action of gastrin-releasing peptide (GRP) on amylase secretion from rat pancreatic acini: an assessment using a perifusion system

We examined the effects of porcine gastrin-releasing peptide (GRP) on exocrine secretion from dispersed rat pancreatic acini using a perifusion system. GRP stimulated amylase secretion, in a dose-dependent manner in the range of 10(-10)-10(-5) M. The submaximum response was observed at 10(-8) M. Stimulation with 10(-8) M GRP caused a biphasic release of amylase. Amylase secretion by GRP stimulation was not affected by the addition of carbachol, dibutyryl cyclic GMP, or atropine. W-7, a calmodulin antagonist, inhibited the amylase secretion induced by GRP. The addition of isobutylmethylxanthine or secretin increased amylase secretion caused by GRP stimulation. These observations suggest that GRP facilitates enzyme secretion by a direct action on pancreatic acini and not through muscarinic and cholecystokinin receptors. The interaction by the Ca2+-calmodulin complex was suggested.

Different responses of serum cationic trypsinogen to secretin and bombesin in normal subjects and patients with chronic alcoholic pancreatitis

We evaluated the behavior of serum cationic trypsinogen (SCT), an enzyme of solely pancreatic origin, in 30 patients with chronic pancreatitis and 25 healthy subjects as a control, after secretin and bombesin stimulation. After both the stimulations, serum cationic trypsinogen is unable to distinguish between the healthy control subjects and the patients with chronic pancreatitis. On the other hand, after secretin, the enzyme is able to separate chronic pancreatitis patients with different levels of exocrine function insufficiency. It does so with a greater statistical significance than that obtained by the rapid injection of bombesin and equal to that of trypsin into the duodenal juice during duodenal intubation. For these reasons, as well as the absence of any side-effects, secretin is preferred to bombesin stimulation in the evaluation of the exocrine pancreatic function in patients with chronic pancreatitis.

Prediction of membrane interactions of gastrin-releasing peptide, neuromedin B, and neuromedin C

Bombesin, in contact with flat phospholipid bilayer membranes, was shown to adopt a membrane structure similar to that of substance P, dynorphin-(1-13)-tridecapeptide, and adrenocorticotropin-(1-24)-tetracosapeptide. The C-terminal message segment, comprising 8-10 amino acid residues, is inserted into a relatively hydrophobic membrane compartment as an alpha-helical domain oriented perpendicularly on the membrane surface. The N-terminal, hydrophilic tetrapeptide segment remains in the aqueous compartment as a random coil. This was shown with IR and IR attenuated total reflection spectroscopy. Equilibrium thermodynamic estimations confirmed the observed membrane structure with respect to helix length, strength of hydrophobic membrane association, and orientation (caused by favorably oriented molecular amphiphilic and helix electric dipole moments). The membrane structure may explain why Trp-8 and His-12 are essential for biologic activity. Neuromedin B is predicted to be able to adopt a membrane structure similar to that of bombesin. However, gastrin-releasing peptide and neuromedin C are predicted not to behave in the same manner. The molecular mechanism of receptor subtype selection by bombesin-like peptides may prove to be similar to that observed earlier for opioid peptides and the neurokinins.

The conformation of bombesin in solution as determined by two-dimensional 1H-NMR techniques

The 1H nuclear magnetic resonance spectrum of the tetradecapeptide, bombesin, has been assigned in (2H6)dimethyl sulphoxide solution and aqueous solution using two-dimensional techniques. The chemical shifts in both solvents indicate that the molecule has little secondary structure and adopts a random coil conformation. A comparison is made between the spectra of various smaller bombesin fragments and the intact polypeptide.

Conformational flexibility of the hormonal peptide bombesin and its interaction with lipids

The conformational flexibility of the tetradecapeptide hormone bombesin has been studied using circular dichroism and fluorescence of its single tryptophan residue. The spectral changes observed indicate that the peptide changed from a random flexible coil in solution to a helical structure in lysolecithin micelles and dimyristoylphosphatidylserine vesicles. The tryptophan residue in the lipid complexes was located in a hydrophobic environment. The interaction with lipids was shown to involve both hydrophobic and electrostatic forces.

Neuromedin B-like peptides in rat brain: biochemical characterization, mechanism of release and localization in synaptosomes

Neuromedin B-like peptides were characterized in the rat brain. A rabbit antisera was utilized which recognized neuromedin B but not bombesin or GRP. Using gel filtration and HPLC techniques, a major and minor peak of immunoreactivity was present in rat brain extracts. In both cases the main peak of immunoreactivity coeluted with synthetic neuromedin B. The density of neuromedin B-like peptides ranged 50-fold being greatest in the olfactory bulb and hypothalamus, intermediate in the hippocampus, spinal cord, medulla/pons, pituitary, midbrain, thalamus, striatum and cortex and lowest in the cerebellum. Release studies indicated that neuromedin B-like peptides were secreted from hypothalamic, olfactory bulb and thalamic slices in a Ca++-dependent manner when KCl (75 mM) was present. Also, the neuromedin B-like peptides in the rat brain were localized to synaptosomes. These data indicate that neuromedin B-like peptides may function as regulatory peptides in the CNS distinct from bombesin/GRP.

Evocative test of serum pancreatic enzymes to bombesin in chronic pancreatitis

The levels of serum immunoreactive trypsinogen and P-isoamylase in response to Bombesin intravenous infusion were evaluated in 25 controls, 18 patients with documented chronic pancreatitis, and nine subjects with nonpancreatic gastroenterological diseases. Mean immunoreactive trypsinogen peak values were significantly higher in controls and gastroenterological diseases than in chronic pancreatitis, but there was marked overlap in individual values between the three groups. As for P-isoamylase, a statistical difference was detected only between mean peak concentrations of control versus chronic pancreatitis. Integrated responses for both enzymes did not result in a better discrimination between controls, chronic pancreatitis, and gastroenterological diseases. This study confirms that evocative tests are of limited value in the diagnosis of pancreatic disease.

Bombesin and G-17 dose responses in duodenal ulcer and controls

Gastric acid and pepsin secretion and serum gastrin concentrations were measured in nine patients with uncomplicated duodenal ulcer (DU) and 10 normal controls in the fasting state and in response to graded doses of bombesin, a tetradecapeptide gastrin releaser, and, for reference, synthetic gastrin G-17. Serum gastrin with bombesin stimulation was significantly greater in duodenal ulcer (maximum 467 pg/ml) than in controls (153 pg/ml), while in seven of the DU group tested gastrin levels after a meal were not different from that seen in five of the normal controls. Gastric acid concentrations and outputs were greater in duodenal ulcer with both stimuli. Secretory responses were then related to serum gastrin levels; despite increasing gastrin levels with bombesin stimulation, peak outputs achieved with bombesin were only 50% of G-17 maximum in normals and up to 90% of maximum in duodenal ulcer. Up to the point of peak response to bombesin, acid and pepsin outputs were the same with exogenous and endogenous gastrin, ie, bombesin acted only via G-17. Furthermore, in direct comparison of duodenal ulcer and normals with G-17 infusion, acid and pepsin outputs related to serum gastrin were congruent up to 75% of duodenal ulcer maximum, at which point normals reached their maximum level. These data have shown that duodenal ulcer patients are not more sensitive to either exogenous or endogenous gastrin; we have also shown regulatory defects in duodenal ulcer patients not previously described: an exaggerated release of gastrin with bombesin stimulation, and a defective inhibition of acid and pepsin secretion with higher doses of bombesin.

The diagnosis and management of gastrinoma

Initial reports of patients with Zollinger-Ellison syndrome were characterized by a long history of recurrent peptic ulcer and multiple operations. Diagnosis was usually made by a combination of clinical history and roentgenograms of the upper aspect of the gastrointestinal tract. Diagnosis was confirmed by the demonstration of elevated basal plasma gastrin levels. The management of the disease included either tumor excision or gastric resection, but more often it included a total gastrectomy. The mortality was high, often because of late recognition of the disease or operative problems related to inadequate control of the hypersecretion of acid. This review is a brief synopsis of the evolution and status of the different diagnostic and therapeutic techniques involved in the contemporary management of patients with gastrinomas. The diagnostic emphasis has shifted away from gastrointestinal contrast studies. Techniques have been developed both for the biochemical diagnosis of the condition and for the topographic localization of the site of the lesion. The use of acid secretory data has declined in value with the development of more elegant techniques for the detection of elevated levels of plasma gastrin in the systemic circulation and the use of portal venous sampling for identifying the source. Thus, the results of sophisticated procedures such as percutaneous transhepatic portopancreatic venous sampling or selective angiography provide additional information. The biochemical diagnosis of gastrinoma is best supported by the evaluation of provocative testing with either calcium or secretin rather than measurement of the basal levels of plasma gastrin. The introduction of potent H2 receptor antagonists has produced support for more conservative management of the disease. The incidence of significant complications during such therapy limits its over-all efficacy. The use of these drugs has, however, facilitated both the conservative and the operative management of patients with extensive sequelae of acid hypersecretion due to a gastrin-secreting tumor. It is probably reasonable to surgically stage the disease of all patients with hypergastrinemia of neoplastic origin since a small percentage (10 per cent) may have a solitary benign lesion which is curable by resection. Total gastrectomy under elective circumstances still has considerable merit. Preliminary data have indicated that alternative, lesser surgical procedures, such as proximal gastric vagotomy, may be therapeutic options if the patient is compliant and sensitive to the appropriate dosage of H2 receptor antagonist.(ABSTRACT TRUNCATED AT 400 WORDS)

Bombesin and insulin-stimulated pancreatic polypeptide release as a discriminator of vagal integrity

Intact vagi after ulcer operations are often implicated in the cause of recurrent ulcer. The stimulation of gastric acid by insulin hypoglycemia is dangerous and the measurement of acid secretion after gastrectomy unreliable. This study was undertaken to assess and compare PP release by bombesin or insulin as an indicator of vagal integrity. Eight dogs with a chronic gastric fistula were tested with bombesin (100 nanograms per kilogram) and insulin (0.1 unit per kilogram) intravenous bolus after unilateral and, then, bilateral truncal vagotomy. Each study was 120 minutes, and blood was taken at one, three, five, seven and then ten minute intervals. Gastric acid was measured by autobiuret titration. Plasma was stored at minus 20 degrees C. until assayed for PP by radioimmunoassay. Bombesin-stimulated gastric acid secretion was not significantly altered by vagotomy (p greater than 0.05), whereas that stimulated by insulin was significantly inhibited by bilateral truncal vagotomy (p less than 0.05). Bilateral and right hemivagotomy significantly inhibited PP release by bombesin (p less than 0.05), however, only bilateral truncal vagotomy significantly inhibited PP release by insulin (p less than 0.05). These results suggest that the measurement of PP release by insulin or bombesin is a sensitive index of vagal integrity and that bombesin-released PP may specifically delineate the integrity of the right vagus. Since the measurement of gastric acid secretion after operation is both uncomfortable and often difficult to interpret, the value of a simple blood test to determine vagal integrity may be of considerable clinical relevance.