Effects of peripheral and central bombesin on feeding behavior of rats

Intraperitoneal injections of tetradecapeptide bombesin (BBS) produced large, dose-related suppressions of liquid and solid food intake in rats, with threshold doses of 1--2 micrograms-kg-1. The feeding-associated behaviors of rats receiving BBS by this route at a test meal were normally sequenced, and several other observations suggested that the effect of BBS was specific and not due to malaise. The structurally related amphibian peptide litorin and the structurally related mammalian gastrin-releasing peptide (GRP) produced similar suppressions of food intake. The satiety effect of BBS administered intraperitoneally did not require the accumulation of food in the gut, the presence of intact adrenals, the abdominal vagus, or the release of cholecystokinin. When BBS and cholecystokinin were administered simultaneous, the suppressive effects on food intake were additive. Lateral cerebroventricular injections of BBS also produced large, dose-related suppressions of food intake, with a threshold dose of 100 ng per rat. The effect by this route, however, was not behaviorally specific: BBS produced equivalent inhibitions of food and water intake at every point on the dose-response curve, and produced a marked increase in grooming which dominated the behavioral display. Thus, (1) peripheral BBS is a putative satiety signal in the rat; (2) the class (endocrine, paracrine, or neural) and mechanism of this satiety action is not established; and (3) the differences in specificity and behavior following intraperitoneal and cerebroventricular routes indicate that peripheral BBS does not act solely via the cerebrospinal fluid to elicity satiety.

Behavioral effects of bombesin administration in rats

Bombesin (BBS, 0.1-4.0 micrograms) administered to the lateral cerebral ventricle (IVT) of rats decreased food intake and feeding behavior. Grooming behavior increased and resting behavior decreased as doses greater than or equal to 0.01 microgram. IVT BBS (4.0 micrograms) caused greater suppression of food-deprivation-induced food intake and feeding behavior than the same dose and volume administered intraperitoneally (IP). After IVT BBS, rats displayed more grooming and less resting than normal, but after IP BBS, rats displayed a normal frequency of grooming and more resting. IVT BBS (greater than or equal to 0.01 microgram) also decreased drinking behavior, and drinking-associated feeding, and suppressed (greater than or equal to 0.1 microgram) water-deprivation-induced water intake. When neither food nor water was present, non-deprived rats displayed increased grooming and decreased resting after IVT BBS (1.0 microgram). The results show that IVT BBS inhibits feeding markedly, but the inhibition of feeding by IVT BBS does not resemble normal satiety or the effect of IP BBS because the central inhibition of feeding is always accompanied by excessive grooming and little resting. Furthermore, since IVT BBS decreases drinking at a dose lower than that required to reduce food intake, and IP BBS does not, the specific satiety effect of IP BBS on feeding cannot be mediated solely by increasing bombesin in the cerebrospinal fluid.

Inhibition of growth of androgen-independent DU-145 prostate cancer in vivo by luteinising hormone-releasing hormone antagonist Cetrorelix and bombesin antagonists RC-3940-II and RC-3950-II

The aim of this study was to test the antagonist of LH-RH (Cetrorelix), agonist [D-Trp6]LH-RH (triptorelin) and new bombesin antagonists RC-3940-II and RC-3950-II for their effect on the growth of an androgen-independent prostate cancer cell line, DU-145, xenografted into nude mice. Xenografts were grown in male nude mice, and after 4 weeks, the animals were treated either with saline (control) or with one of the analogues. One group of mice was given a combination of Cetrorelix and RC-3950-II. Treatment was given for 4 weeks. Tumour and body weights, and tumour volumes were measured. At sacrifice, tumours were dissected for histological examination and receptor studies. Serum was collected for measurement of hormone levels. The final tumour volume in control animals injected with saline was 577 +/- 155 mm3 and that of animals treated with Cetrorelix only 121.4 +/- 45 mm3 (P < 0.01). Bombesin antagonists RC-3940-II and RC-3950-II also significantly reduced DU-145 tumour volume in nude mice to 84.9 +/- 19.9 and 96.8 +/- 28 mm3, respectively. Agonist [D-Trp6]LH-RH did not significantly inhibit tumour growth. Serum levels of LH were decreased to 0.08 +/- 0.02 ng/ml (P < 0.05) in the Cetrorelix treated group as compared to 1.02 +/- 0.1 ng/ml for the controls, and testosterone levels were reduced to castration levels (0.01 +/- 0.01 ng/ml). Specific receptors for EGF and LH-RH in DU-145 tumours were significantly downregulated after treatment with Cetrorelix, RC-3940-II and RC-3950-II. Although LH-RH could be a local regulator of growth of prostate cancer, the fall in LH-RH receptors is not fully understood and the inhibitory effects of Cetrorelix and bombesin antagonists on DU-145 tumour growth might be attributed at least in part to a downregulation of EHF receptors. Since Cetrorelix and bombesin antagonists inhibit growth of androgen-independent DU-145 prostate cancers, these compounds could be considered for the therapy of advanced prostate cancer in men, especially after relapse.

High potency of bombesin for stimulation of human gastrin release and gastric acid secretion

Dose-response studies were performed in 6 human volunteer subjects to determine the threshold and optimal doses of intravenous bombesin for stimulation of gastric acid secretion and gastrin release. A significant stimulation of both acid and gastrin was obtained with a very low dose, 3 pmol x kg-1 x h-1. Peak stimulation of acid secretion (67% of pentagastrin PAO) was obtained at 12.5 pmol x kg-1 x h-1. Serum gastrin response to this dose of bombesin was similar to that obtained after a high protein meal. Higher doses of bombesin caused further increases in serum gastrin but not in acid secretion. Since very low doses of bombesin, too small to produce detectable increases in immunoreactive serum bombesin, caused parallel increases in gastrin and acid secretion, it is possible that the bombesin-like peptides present in human gastrointestinal tissues contribute to regulation of human gastric secretion.

Inhibition of growth of PC-82 human prostate cancer line xenografts in nude mice by bombesin antagonist RC-3095 or combination of agonist [D-Trp6]-luteinizing hormone-releasing hormone and somatostatin analog RC-160

The effects of treatment with a bombesin receptor antagonist [D-Tpi6, Leu13 psi (CH2NH) Leu14]BN(6-14)(RC-3095) and the combination of an agonist of luteinizing hormone-releasing hormone [D-Trp6]-LH-RH and somatostatin analog D-Phe-Cys-Tyr-D-Trp-Lys-Val- Cys-Trp-NH2 (RC-160) were studied in nude mice bearing xenografts of the hormone-dependent human prostate tumor PC-82. During the 5 weeks of treatment, tumor growth was decreased in all treated groups compared with controls. Bombesin antagonist RC-3095 and the combination of [D-Trp6]-LH-RH and RC-160 caused a greater inhibition of tumor growth than [D-Trp6]-LH-RH or RC-160 alone as based on measurement of tumor volume and percentage change in tumor volume. The largest decrease in tumor weight was also seen in the groups treated with the bombesin antagonist and with the combination of RC-160 and [D-Trp6]-LH-RH. Serum prostatic-specific antigen levels were greatly decreased, and insulin-like growth factor I (IGF-I) as well as growth hormone levels were reduced in all treated groups. Specific binding sites for [D-Trp6]-LH-RH, epidermal growth factor (EGF), IGF-I, and somatostatin (SS-14) were found in the tumor membranes. Receptors for EGF were significantly down-regulated by treatment with the bombesin antagonist or RC-160. Combination of LH-RH agonists with somatostatin analog RC-160 might be considered for improvement of hormonal therapy for prostate cancer. The finding that bombesin antagonist RC-3095 inhibits the growth of PC-82 prostate cancer suggests the merit of further studies to evaluate the possible usefulness of antagonists of bombesin in the management of prostatic carcinoma.

Inhibition by ginsenoside Rg3 of bombesin-enhanced peritoneal metastasis of intestinal adenocarcinomas induced by azoxymethane in Wistar rats

The effects of concomitant use of bombesin and ginsenoside Rg3 on the incidence of peritoneal metastasis of intestinal adenocarcinomas induced by azoxymethane were investigated in male inbred Wistar rats. From the start of the experiment, rats were given weekly s.c. injections of azoxymethane (7.4 mg/kg body weight) for 10 weeks and s.c. injection of bombesin (40 microg/kg body weight) every other day, and from week 20, s.c. injections of ginsenoside Rg3 (2.5 or 5.0 mg/kg body weight) every other day until the end of the experiment in week 45. Bombesin significantly increased the incidence of intestinal tumors and cancer metastasis to the peritoneum in week 45. It also significantly increased the labeling index of intestinal cancers. Although administration of a higher dose of ginsenoside Rg3 with bombesin had little or no effect on the enhancement of intestinal carcinogenesis by bombesin, the location, histologic type, depth of involvement, infiltrating growth pattern, labeling and apoptotic indices and tumor vascularity of intestinal cancers, it significantly decreased the incidence of cancer metastasis. These findings indicate that ginsenoside Rg3 inhibits cancer metastasis through activities that do not affect the growth or vascularity of intestinal cancers.

Studies on bombesin-induced grooming in rats

The gross behavior induced by centrally administered bombesin in rats was compared to that elicited by ACTH-(1-24) and the somatostatin analog, des AA1,2,4,5,12,13[D-Trp8]-somatostatin (ODT8-SS). Bombesin (0.001-1 microgram, ICV) caused dose-related excessive scratching which was qualitatively different from that associated with the other two groom-inducing agents. Bombesin-induced grooming was not markedly affected by behaviorally nondepressant doses of haloperidol, morphine, naloxone or neurotensin. Bombesin was active in genetically hypotrichotic (essentially furless) rats; and, again in such animals, even after numbing the area caudal to the shoulders with lidocaine. Tolerance and cross-tolerance studies with bombesin and ODT8-SS indicated that they produce scratching through different mechanisms. Bombesin caused scratching when injected directly into the periaqueductal gray, but not when administered intravenously. Neither hypophysectomy nor adrenalectomy markedly affected bombesin-induced grooming. This behavior appears to be initiated in the central nervous system and is produced independently of the pituitary-adrenal axis.

Targeting Cytotoxic Conjugates of Somatostatin, Luteinizing Hormone- Releasing Hormone and Bombesin to Cancers Expressing Their Receptors: A “Smarter” Chemotherapy

Chemotherapy is one of the main modalities in the therapy of cancer. However, an improvement in the efficacy and a reduction in the toxicity of chemotherapeutic agents remains a great challenge to oncologists. A specific delivery of cytotoxic drugs to cancerous cells may help improving both aspects. Peptide hormones, for which receptors have been found in various human cancers, can serve as carriers for a local delivery of cytotoxic agents or radiopharmaceuticals to the tumors, as demonstrated by the successful clinical use of radiolabeled somatostatin analog Octreoscan for the detection and treatment of some somatostatin receptor-positive tumors. Thus, in recent years we developed a series of cytotoxic peptide hormone conjugates based on derivatives of hypothalamic hormones such as somatostatin and luteinizing hormone-releasing hormone (LHRH), and the brain-gut hormone bombesin. To create targeted conjugates with high cytotoxic activity, a derivative of doxorubicin (DOX), 2-pyrrolino-DOX (AN-201), which is 500-1, 000 times more active than its parent compound, was developed. This agent was coupled to somatostatin octapeptide RC-121 to form cytotoxic conjugate AN-238, and to [D-Lys6]LHRH carrier to produce analog AN-207. Cytotoxic bombesin hybrid AN-215 also contains AN-201. DOX was likewise linked to [D-Lys6]LHRH to form AN-152. A comprehensive testing of these cytotoxic conjugates in experimental models of various human and rodent cancers led to their selection as candidates for clinical trials.

Central nervous system action of bombesin to inhibit gastric acid secretion

Bombesin or gastrin releasing peptide injected into the lateral, third, or fourth ventricle, or into the cisterna magna, inhibited gastric acid secretion induced by a wide variety of gastric acid stimulants in several animal models. Studies of bombesin microinfusion into specific hypothalamic nuclei of intact rats, or injection into the cisterna magna of midbrain transected rats, indicated that the peptide can trigger inhibition of gastric acid secretion from both forebrain and hindbrain structures. The neural pathways mediating bombesin action required the integrity of the cervical spinal cord; the vagus did not play an important role. Spantide, a substance P and bombesin receptor antagonist, was not useful in studying the physiological role of bombesin. This was due both to its inability to reverse the central action of bombesin on gastric secretion, and to its in vivo toxicity.

Bombesin-induced anorexia: sites of action in the rat brain

To determine the brain sites at which centrally injected bombesin (BBS) may act to suppress feeding behavior, this peptide (1.0 micrograms/0.3 microliter) was microinjected into one of twelve brain regions in 6 hr food deprived rats, and food intake was measured 45 min postinjection. Bombesin produced its strongest suppression of feeding (47-65%) when injected into hypothalamic areas, namely, the paraventricular, dorsomedial, ventromedial nuclei and lateral hypothalamus, and also when administered into the amygdala and the periaqueductal gray. Insensitive areas included the septum, ventral tegmental area and reticular formation. In contrast to these somewhat site-specific effects on feeding behavior, observation of BBS' effects on other behaviors revealed that, in all brain areas tested, there was a significant increase in grooming behavior and decrease in time spent resting and sleeping. In conjunction with high levels of BBS-like immunoreactivity and BBS receptors in the brain areas where injected BBS suppresses feeding, these results suggest that the effects of centrally administered BBS on feeding behavior may be mediated by multiple hypothalamic and extra-hypothalamic brain regions.

Bombesin-induced behavioural changes: antagonism by neuroleptics

Adult male Sprague-Dawley rats were administered bombesin (BN) intracerebroventricularly (ICV), at a dose of 0.001, 0.01, 0.1, or 1.0 microgram, and the behavioural effects monitored longitudinally across time for up to 24 hr. Administration of BN significantly increased the locomotor, rearing and grooming activity at all doses. The time-course of behavioural activation was dose-related (lasting up to 2.5 hr). There was no significant difference in the behavioural response of rats receiving the BN doses in an ascending or descending order. To test the effects of dopamine receptor blockade on the BN-induced behavioural changes, groups of animals were treated with fluphenazine or haloperidol (0.1 to 2.5 mg/kg, IP) 30 min prior to BN (1 microgram, ICV) administration. The results revealed that the neuroleptics could effectively antagonize the BN-induced activation of locomotor, rearing and grooming activity. These data are concordant with the view that centrally administered BN stimulates spontaneous exploratory and grooming behaviours in rats, in a time- and dose-related manner. Furthermore, since neuroleptics block these effects, it remains possible that the BN-induced behavioural changes may be mediated, at least in part, through the dopaminergic system(s).

Peripheral bombesin induces c-fos protein in the rat brain

Bombesin injected intraperitoneally induces c-fos protein-like immunoreactivity in the medial nucleus tractus solitarius and the parvocellular part of the paraventricular nucleus of the hypothalamus in the rat brain. C-fos expression induced by bombesin is less densely represented compared with CCK. Capsaicin pretreatment did not influence c-fos-immunoreactivity induced by bombesin and significantly reduced that induced by CCK.

Physiological function of gastrin-releasing peptide and neuromedin B receptors in regulating itch scratching behavior in the spinal cord of mice

Pruritus (itch) is a severe side effect associated with the use of drugs as well as hepatic and hematological disorders. Previous studies in rodents suggest that bombesin receptor subtypes i.e. receptors for gastrin-releasing peptide (GRPr) and neuromedin B (NMBr) differentially regulate itch scratching. However, to what degree spinal GRPr and NMBr regulate scratching evoked by intrathecally administered bombesin-related peptides is not known. The first aim of this study was to pharmacologically compare the dose-response curves for scratching induced by intrathecally administered bombesin-related peptides versus morphine, which is known to elicit itch in humans. The second aim was to determine if spinal GRPr and NMBr selectively or generally mediate scratching behavior. Mice received intrathecal injection of bombesin (0.01-0.3 nmol), GRP (0.01-0.3 nmol), NMB (0.1-1 nmol) or morphine (0.3-3 nmol) and were observed for one hour for scratching activity. Bombesin elicited most profound scratching over one hour followed by GRP and NMB, whereas morphine failed to evoke scratching response indicating the insensitivity of mouse models to intrathecal opioid-induced itch. Intrathecal pretreatment with GRPr antagonist RC-3095 (0.03-0.1 nmol) produced a parallel rightward shift in the dose response curve of GRP-induced scratching but not NMB-induced scratching. Similarly, PD168368 (1-3 nmol) only attenuated NMB but not GRP-induced scratching. Individual or co-administration of RC-3095 and PD168368 failed to alter bombesin-evoked scratching. A higher dose of RC-3095 (0.3 nmol) generally suppressed scratching induced by all three peptides but also compromised motor function in the rotarod test. Together, these data indicate that spinal GRPr and NMBr independently drive itch neurotransmission in mice and may not mediate bombesin-induced scratching. GRPr antagonists at functionally receptor-selective doses only block spinal GRP-elicited scratching but the suppression of scratching at higher doses is confounded by motor impairment.

Anorectic effect of calcitonin, neurotensin and bombesin infused in the area of the rostral part of the nucleus of the tractus solitarius in the rat

The three neuropeptides calcitonin, neurotensin and bombesin can decrease food intake in the rat when injected into the cerebral ventricles or into the paraventricular nucleus of the hypothalamus. The paraventricular nucleus of the hypothalamus is an important site for the integration of visceral and endocrine systems, and has connections with the nucleus of the tractus solitarius which is a major locus for visceral afferents. Since calcitonin, neurotensin and bombesin, or their receptors, have been found to be present in the nucleus of the tractus solitarius, we tested the effects of local infusions of these peptides on food intake. The peptides were microinjected in a 0.25 microliter volume in rats trained to eat for only 3 hours per day. The injections were made in the rostral part of the nucleus and surrounding areas, through the lateral vestibular nuclei, to avoid leakage of the peptides into the cerebrospinal fluid. In the nucleus of the tractus solitarius the three peptides decreased food intake by more than 50%. The peptides were also active in the spinal trigeminal nucleus oralis, and, for calcitonin and bombesin, in the reticular formation under the nucleus of the tractus solitarius. A local diffusion from the point of injection may explain some of these results. Therefore, the area of the nucleus of the tractus solitarius is a nonhypothalamic site where these peptides can act to produce anorexia.

Bombesin inhibits alveolarization and promotes pulmonary fibrosis in newborn mice

RATIONALE

Bombesin-like peptides promote fetal lung development. Normally, levels of mammalian bombesin (gastrin-releasing peptide [GRP]) drop postnatally, but these levels are elevated in newborns that develop bronchopulmonary dysplasia (BPD), a chronic lung disease characterized by arrested alveolarization. In premature baboons with BPD, antibombesin antibodies reduce lung injury and promote alveolarization.

OBJECTIVES

The present study tests whether exogenous bombesin or GRP given perinatally alters alveolar development in newborn mice.

METHODS

Mice were given peptides intraperitoneally twice daily on Postnatal Days 1-3. On Day 14 lungs were inflation-fixed for histopathologic analyses of alveolarization.

MEASUREMENTS AND MAIN RESULTS

Bombesin had multiple effects on Day 14 lung, when alveolarization was about half complete. First, bombesin induced alveolar myofibroblast proliferation and increased alveolar wall thickness compared with saline-treated control animals. Second, bombesin diminished alveolarization in C57BL/6 (but not Swiss-Webster) mice. We used receptor-null mice to explore which receptors might mediate these effects. Compared with wild-type littermates, bombesin-treated GRP receptor (GRPR)-null mice had increased interstitial fibrosis but reduced defects in alveolarization. Neuromedin B (NMB) receptor-null and bombesin receptor subtype 3-null mice had the same responses as their wild-type littermates. GRP had the same effects as bombesin, whereas neither NMB nor a synthetic bombesin receptor type 3 ligand had any effect. All effects of GRP were abrogated in GRPR-null mice.

CONCLUSIONS

Bombesin/GRP can induce features of BPD, including interstitial fibrosis and diminished alveolarization. GRPR appears to mediate all effects of GRP, but only part of the bombesin effect on alveolarization, suggesting that novel receptors may mediate some effects of bombesin in newborn lung.

Effect of bombesin on feeding behavior

Peripherally-administered bombesin and gastrin-releasing peptide produce potent, dose-related, and specific reductions of food intake at test meals in rats. Similar effects on meal size are observed after intraperitoneal injections in mice and after intravenous infusions in baboons and humans. The mechanism for this effect is unknown, but the action of bombesin is not blocked by complete subdiaphragmatic vagotomy, by a variety of peripheral endocrine and neural ablations, or by lesions of the area postrema or hypothalamus. Hypothalamic injections of bombesin produce small but specific reductions of food intake; the relationship of this central effect to the peripheral effect of the peptide is unknown. Bombesin and bombesin-like peptides may play roles in the regulation of meal size.

Inhibitory effect of bombesin/gastrin-releasing peptide antagonist RC-3095 and luteinizing hormone-releasing hormone antagonist SB-75 on the growth of MCF-7 MIII human breast cancer xenografts in athymic nude mice

BACKGROUND

The results of several clinical trials using various luteinizing hormone-releasing hormone agonists for treatment of advanced breast cancer are encouraging. However, only about 30% of breast cancers are estrogen-dependent and can be treated by hormonal manipulation. New therapeutic approaches combining estrogen ablation therapy with other compounds must be explored. Various studies suggest that bombesin or gastrin-releasing peptide acts as an autocrine growth factor and may play a role in the initiation and progression of some cancers, including that of the breast.

METHODS

Female athymic nude mice bearing xenografts of the MCF-7 MIII human breast cancer cell line were treated for 7 weeks with bombesin/gastrin-releasing peptide antagonist (D-Tpi6, Leu13 psi[CH2NH]-Leu14) bombesin(6-14) (RC-3095) injected subcutaneously daily at a dose of 20 micrograms and luteinizing hormone-releasing hormone antagonist SB-75 (Cetrorelix) administered biweekly in the form of microgranules releasing 45 micrograms/day.

RESULTS

After 2 weeks of treatment, a significant inhibition of tumor volume was observed in the groups treated with RC-3095 alone or in combination with SB-75 but not in those treated with SB-75 as a single agent. After 7 weeks, tumor growth as measured by tumor volume and percentage changes in tumor volume and tumor weight was greatly inhibited in all of the treated groups. Uterine and ovarian weights were reduced and serum luteinizing hormone levels decreased by administration of SB-75 alone or in combination with RC-3095. Histologically, a significant decrease in argyrophilic nucleolar organizer region count in tumor cell nuclei was observed in all of the treated groups, indicating a lower proliferation of these cells. High-affinity binding sites for bombesin were detected in cultured MCF-7 MIII cells. Chronic treatment with RC-3095 caused a significant down-regulation of epidermal growth factor receptors in tumor cell membranes, which might be related to tumor inhibition. In studies in vitro, SB-75 inhibited proliferation of MCF-7 cells in culture but not proliferation of MCF-7 MIII cells.

CONCLUSIONS

Because previously we demonstrated that RC-3095 inhibits the proliferation of MCF-7 MIII cells in vitro, it appears that the major antitumoral effect of RC-3095 on the MCF-7 MIII cancer line is direct, whereas that of SB-75 is indirect, and that it is mediated by suppression of the pituitary-gonadal axis. In view of its immediate and powerful inhibitory effect on MCF-7 MIII tumors, bombesin/gastrin-releasing peptide antagonist RC-3095 might be considered as a possible new agent for the treatment of breast cancer.

Periprandial changes in growth hormone release in goldfish: role of somatostatin, ghrelin, and gastrin-releasing peptide

In goldfish, growth hormone (GH) transiently rises 30 min after meals, returning to baseline at 1 h postmeal. Somatostatin (SRIF) is the major inhibitor of GH release. Three cDNAs encoding pre-pro-SRIF (PSS) have been previously cloned from goldfish brain: PSS-I, which encodes SRIF-14; PSS-II, which is potentially processed into gSRIF-28 that has [Glu1,Tyr7,Gly10]SRIF-14 at the COOH terminus; and PSS-III, which encodes [Pro2]SRIF-14 at its COOH terminus. In goldfish, bombesin (BBS), mimicking the endogenous gastrin-releasing peptide (GRP), acutely suppresses food intake and also stimulates GH release. Ghrelin was recently characterized in goldfish as a GH secretagogue and an orexigen. In this paper, we studied the changes in SRIF mRNA levels during feeding and analyzed the influences of BBS and ghrelin peptides on forebrain PSS expression. The results showed a 60% reduction in PSS-II mRNA after meals, but no changes in the expression of PSS-I and PSS-III were found. Intraperitoneal injections of 100 ng/g body wt of BBS increased GH secretion and decreased PSS-I and PSS-II gene expression. Intraperitoneal injection of goldfish ghrelin (100 ng/g body wt) transiently increased the serum GH levels and increased PSS-I, while decreasing PSS-II mRNA levels. Ghrelin (50 ng/g body wt) blocked the effects of BBS (100 ng/g body wt) on PSS-I but not on PSS-II expression. Coadministration of BBS and ghrelin decreased only the PSS-II gene expression. We conclude that the interactions between BBS/GRP and ghrelin can account for the postprandial variations in serum GH levels and the forebrain expression of PSS-II. Furthermore, we demonstrate that intraperitoneal administration of BBS reduces the ghrelin expression levels in the gut. Thus the inhibition of production of ghrelin in the gut may contribute to the satiety effects of BBS/GRP peptides.

Effect of bombesin infused intrapancreatically on glucagon and insulin secretion

Synthetic bombesin was infused at a dose of 20 pmoles/kg/min for 10 min into the cranial pancreaticoduodenal artery of anesthetized dogs. Plasma immunoreactive glucagon concentrations in the cranial pancreaticoduodenal vein as well as in the femoral artery were concurrently and slowly elevated. However, the net release of glucagon from the pancreas did not increase significantly during infusion of bombesin. Plasma immunoreactive insulin concentrations in the pancreatic vein were transiently raised, and a delayed rise was noted in arterial plasma IRI. Net release of insulin was significantly augmented during infusion of the tetradecapeptide. Plasma glucose levels did not change after bombesin. These results indicate that the gastrointestinal tetradecapeptide may stimulate secretion of both insulin and gut glucagonlike immunoreactivity in the dog.

Gastrin-releasing peptide induces itch-related responses through mast cell degranulation in mice

Gastrin-releasing peptide (GRP), secreted from the central terminals of primary afferents, is involved in the transmission of itch signals in the spinal dorsal horn. Although primary afferents containing GRP are distributed throughout the skin, the role of peripherally released GRP in the itch response is unknown. We investigated whether GRP acts on the skin to induce an itch response in mice. Intradermal injections of GRP(18-27) (1-300 nmol/site) elicited scratching. GRP(18-27)-induced scratching was inhibited by the μ-opioid receptor antagonist naltrexone hydrochloride, the BB(2) bombesin receptor antagonist RC-3095, the H(1) histamine receptor antagonists fexofenadine hydrochloride and chlorpheniramine maleate, and the PAR(2) proteinase-activated receptor antagonist FSLLRY-NH(2). Mast cell deficiency significantly, but not completely, reduced the GRP(18-27)-induced scratching. BB(2) bombesin receptors are present in mast cells in the skin, and intradermal injection of GRP(18-27), not only induced scratching, but also led to mast cell degranulation. GRP(18-27)-induced mast cell degranulation was inhibited by the BB(2) bombesin receptor antagonist RC-3095. These results suggest that peripherally released GRP can induce an itch response, at least partly, through activation of BB(2) receptors present in the mast cells, triggering their degradation and the release of histamine and the serine proteinase, tryptase.