Effects of cholecystokinin and bombesin on the expression of preprosomatostatin-encoding genes in goldfish forebrain

It was previously demonstrated that both cholecystokinin (CCK) and bombesin (BBS) stimulate growth hormone (GH) secretion in goldfish. Both peptides induce satiety and it was speculated that they integrate satiation and the postprandial increase in GH circulating levels. In the present paper we investigated the effects of CCK and BBS on the forebrain expression of the somatostatin gene family in goldfish to analyze if somatostatin peptides may be part of the effector mechanisms of CCK and BBS. We found that peripherally as well as centrally administered CCK decreases mRNA levels of preprosomatostatin (PSS)-I that encodes for SRIF-14, having no effects on PSS-II and PSS-III, which encode for gSRIF-28 and [Pro2] SRIF-14, respectively. In addition, a direct action on the pituitary to stimulate GH release, this inhibition of PSS-I expression provides a possible mechanism for CCK to increase postprandial GH levels. On the other hand, BBS inhibits the forebrain expression of PSS-I and PSS-II but does not affect PSS-III regardless of the route of administration. We conclude that this could be the most likely mechanism of action of BBS to increase GH secretion, since there are few BBS-immunoreactive (IR) fibers and BBS binding sites in the anterior pituitary of goldfish.

The bombesin/gastrin releasing peptide receptor antagonist RC-3095 blocks apomorphine but not MK-801-induced stereotypy in mice

Bombesin (BN)-like peptides might be involved in the pathogenesis of neuropsychiatric disorders such as schizophrenia. Stereotyped behaviors induced by the dopamine receptor agonist apomorphine or the N-methyl-D-aspartate glutamate receptor antagonist dizocilpine (MK-801) in rodents have been proposed as animal models of schizophrenic psychosis. In the present study we evaluated the effects of the BN/gastrin-releasing peptide receptor (GRP) antagonist (D-Tpi6, Leu13 psi[CH2NH]-Leu14) bombesin (6-14) (RC-3095) on apomorphine and MK-801-induced stereotyped behavior in mice. An intraperitoneal (i.p.) injection of RC-3095 (1.0, 10.0 or 100.0 mg/kg) blocked apomorphine-induced stereotypy. The inhibitory effect of RC-3095 on apomorhine-induced stereotypy was similar to that induced by haloperidol (0.5 mg/kg). RC-3095 did not affect stereotyped behavior induced by MK-801 (0.5 mg/kg). The results provide the first evidence that BN/GRP receptor antagonism blocks stereotyped behavior induced by a dopamine agonist. Together with previous evidence, the present study indicates that the BN/GRP receptor can be considered a drug target in the investigation of potential new agents for treating neuropsychiatric disorders.

Intrahippocampal infusion of the bombesin/gastrin-releasing peptide antagonist RC-3095 impairs inhibitory avoidance retention

Bombesin (BN)-like peptides regulate cell proliferation and cancer growth as well as neuroendocrine and neural functions. We evaluated the effects of the BN/gastrin-releasing peptide (GRP) antagonist RC-3095 on memory formation. Male Wistar rats were given a bilateral infusion of saline or RC-3095 (0.2, 1.0 or 5.0 microg) into the dorsal hippocampus either immediately or 2 h after training in an inhibitory avoidance (IA) task. Retention test trials were carried out 1.5 h (short-term memory) and 24 h (long-term memory) after training. RC-3095 impaired both short- and long-term retention only when given immediately after training. The results suggest that the hippocampal BN/GRP receptor system modulates IA memory formation.

Somatostatin receptor type 2 mediates bombesin-induced inhibition of gastric acid secretion in mice

Studies in isolated mouse stomach showed that bombesin releases somatostatin. We characterized the effects of exogenous bombesin on gastric acid secretion in mice and determined the involvement of somatostatin and somatostatin receptor type 2 (SSTR2) by using somatostatin immunoneutralization, the SSTR2 antagonist, PRL-2903, and SSTR2 knockout mice. Gastric acid secretion was monitored under basal and pentagastrin-, histamine- or bethanechol-stimulated conditions in urethane-anaesthetized mice. Bombesin (10-40 micro g kg-1 h-1) and somatostatin-14 (20 micro g kg-1 h-1) were infused I.V. 10 and 30 min after PRL-2903 or somatostatin antibody pretreatment, respectively. Urethane-anaesthetized wild-type mice had low basal acid secretion (0.12 +/- 0.01 micro mol (10 min)-1) compared with SSTR2 knockout mice (1.43 +/- 0.10 micro mol (10 min)-1). Somatostatin antibody and PRL-2903 increased basal secretion in wild-type mice but not in SSTR2 knockout animals. In wild-type mice, bombesin inhibited secretagogue-stimulated acid secretion in a dose-dependent manner, and somatostatin-14 inhibited pentagastrin-stimulated secretion. In wild-type mice pretreated with somatostatin antibody or PRL-2903 and in SSTR2 knockout mice, bombesin and somatostatin-14 I.V. infusion did not alter the increased gastric acid secretion. These results indicate that, in mice, bombesin inhibits gastric acid secretion through the release of somatostatin and the activation of SSTR2. These observations strengthen the important role of SSTR2 in mediating somatostatin inhibitory actions on gastric acid secretion.

Pharmacological characteristics of bombesin receptor mediating hypothermia in the central nervous system of rats

Bombesin (BN) and structurally related peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB), injected into the lateral ventricle produce multiple effects such as hypothermia, anorexia and hormone release. In this study, the pharmacological characteristics of BN receptors mediating hypothermia in the central nervous system (CNS) were investigated using free-moving male Wistar rats. Intracerebroventricular injections of BN, GRP and NMB produced hypothermia in a dose-dependent manner. The BN (0.3 microg)-induced effect showed a short latency and a 4-h duration with a potency increased by more than 100 times compared to the NMB-induced effect. Pretreatment with [D-Tyr(6)]BN(6-13)methylester, a GRP receptor antagonist, inhibited the BN (0.3 microg)- and NMB (7 microg)-induced hypothermia. On the other hand, BIM23127, an NMB receptor antagonist, did not influence the hypothermia. Of the protein kinase C (PKC) inhibitors, chelerythrine, Go6983, staurosporine and GF109203X, the first two partially blocked the BN-induced hypothermia. A PKC activator, phorbol-12,13-dibutyrate, decreased the rectal temperature. Genistein (a tyrosine kinase inhibitor), Y-27632 (a Rho kinase inhibitor) and PD98059 (a MAPK inhibitor) tended to suppress the BN-induced hypothermia, however, these were not significant. The inhibitory effect of a mixture of the three inhibitors, chelerythrine, genistein and Y-27632, on the BN-induced hypothermia was of a similar degree to that of chelerythrine alone. The BN receptor mediating the hypothermia seem to be the GRP subtype, and the effect involves activation of PKC.

Small bowel allografts maintained by administration of bombesin while under immunosuppression

BACKGROUND/PURPOSE

The aim of this study was to determine if Bombesin (BBS) could help maintain the mucosal villus state in small bowel allografts without inducing acute rejection under immunosuppression.

METHODS

Allogeneic small bowel transplantation was performed heterotopically in rats (n = 12). All rats received daily administration of FK506 from postoperative day 0 to day 28. On postoperative day 14, rats were divided into 2 groups of 6 rats each, and administered BBS or normal saline as a control. After 2 weeks of treatment, the rats were killed, and the graft mucosal villus state was evaluated by H&E staining, and crypt cell proliferation analysis was performed using immunohistochemistry with proliferative cell nuclear antigen (PCNA).

RESULTS

Villi were thin, and villus blunting was marked in the control group. The BBS group showed that the villi of the grafts were well maintained, and the volume of the lamina propria mucosa was adequately preserved. The PCNA labeling index of crypt cells in the control group was 40.06 +/- 3.36 (mean +/- SD) and that in the BBS group was 61.02 +/- 4.27. There was a significant difference (P <.001) between the 2 groups.

CONCLUSIONS

BBS maintained allograft epithelial cells and the volume of the lamina propria intestinal mucosa, stimulating proliferation of crypt cells under immunosuppression without inducing acute rejection.

Healing-promoting effect of bombesin treatment on chronic gastric ulcer in rats

To evaluate whether bombesin treatment has a facilitatory effect on the healing of chronic gastric ulcer, following the induction of ulcer by serosal application of acetic acid, rats were given bombesin (30 microg/kg/day; subcutaneously) or vehicle three times a day for 7, 14 or 21 days until they were decapitated. Neither food intake nor gastric emptying rate in either vehicle-treated or bombesin-treated groups was not statistically different from control rats. Similarly, ulcer indices and gastric myeloperoxidase (MPO) activities at the first and second weeks of injury were not different among the groups. However, in the 3-week ulcer group, bombesin treatment reduced tissue MPO level significantly back to control levels. Moreover, the analysis of the surface epithelium by scanning electron and light microscopy demonstrated a significant reduction in the severity of ulcers by bombesin treatment. Pretreatment with CCK antagonists (L-364,718 or L365,260; 25 micromol/kg/day) before bombesin treatment showed that neither of the CCK antagonists had a significant effect on the bombesin-mediated healing process, suggesting that CCK receptors are not involved in the action of bombesin. In accordance with the previous studies that show its acute gastroprotective effects, bombesin is also effective in promoting the healing process of chronic gastric ulcer in rats.

Tobacco smoke exposure and bombesin-like peptides in guinea pigs

Bombesin-like peptides (BLPs) are associated with tobacco smoke (TS)-induced diseases. We sought to determine if acute TS exposure releases BLPs into the pulmonary circulation. Sensitized and non-sensitized guinea pigs were chronically exposed to TS or compressed air. Thereafter, the lungs were acutely challenged with TS while perfused. Perfusates were analyzed for BLPs. TS increased BLPs in non-sensitized guinea pigs. A separate study determined daily bombesin exposure increased lung cell counts but not airway hyperresponsivensess. TS exposure releases BLPs into the pulmonary circulation but can be modified by host factors and bombesin itself does not induce airway hyperresponsiveness.

Octreotide-induced suppression of the hyperglycemic response to neostigmine or bombesin: relationship to hypothalamic noradrenergic drive

Neostigmine (cholinesterase inhibitor) or bombesin, when injected into the third cerebral ventricle of awake rat, dose-dependently increased serum glucose with the simultaneous rise in hypothalamic noradrenergic neuronal activity (NAA). Co-administration of octreotide with neostigmine or bombesin suppressed the hypothalamic NNA response with the simultaneous inhibition of the hyperglycemic response. There was a close relationship between hypothalamic NNA and serum glucose in these studies. On the basis of the concept that hypothalamic noradrenergic drive plays an important role in mediating the hyperglycemic response to stressful stimuli, the present findings suggest that the hyperglycemic response to neostigmine or bombesin is mediated via the interaction with hypothalamic noradrenergic neurons.

Secretion of the trefoil factor TFF3 from the isolated vascularly perfused rat colon

The trefoil factor TFF3 is a peptide predominantly produced by mucus-secreting cells in the small and large intestines. It has been implicated in intestinal protection and repair. The mechanisms that govern TFF3 secretion are poorly understood. The aim of this study was, therefore, to evaluate the influence of neurotransmitters, hormonal peptides and mediators of inflammation on the release of TFF3. For this purpose, an isolated vascularly perfused rat colon preparation was used. After a bolus administration of 1 ml isotonic saline into the lumen, TFF3 secretion was induced by a 30-min intra-arterial infusion of the compounds to be tested. TFF3 was evaluated in the luminal effluent using a newly developed radioimmunoassay. TFF3 was barely detected in crude luminal samples. In contrast, dithiothreitol (DTT) treatment of the effluent revealed TFF3 immunoreactivity, which amounted to about 0.3 pmol min(-1) cm(-1) in the basal state. Gel chromatography of DTT-treated luminal samples revealed a single peak that co-eluted with the monomeric form of TFF3. TFF3 was not detected in the portal effluent. Bethanechol (10(-6)-10(-4) M), vasoactive intestinal peptide (VIP, 10(-8)-10(-7) M) or bombesin (10(-8)-10(-7) M) induced a dose-dependent release of TFF3. In contrast, substance P evoked a modest release of TFF3, whereas calcitonin gene-related peptide (CGRP), somatostatin, neurotensin or peptide YY (PYY) did not modify TFF3 secretion. The degranulator compound bromolasalocid, 16,16-dimethyl PGE2 (dmPGE2) or interleukin-1-beta (IL-1-beta) also evoked a marked release of TFF3. In conclusion, TFF3 in the colonic effluent is present in a complex. This association presumably involves a disulfide bond. Additionally, the present results suggest a role for enteric nervous system and resident immune cells in mediation of colonic TFF3 secretion.

Blockade of GRP receptors inhibits gastric emptying and gallbladder contraction but accelerates small intestinal transit

BACKGROUND & AIMS

This study was designed to characterize [D-F(5)Phe(6)D-Ala(11)]Bn(6-13)OMe (BIM26226) as a gastrin-releasing peptide (GRP)-preferring bombesin receptor antagonist and to determine whether GRP physiologically regulates gastrointestinal motility. Intravenous BIM26226 (5-500 microg. kg(-1). h(-1)) inhibits GRP-induced gallbladder contraction and plasma cholecystokinin (CCK) release in a dose-dependent fashion.

METHODS

Gastric emptying and small bowel transit of a solid meal were quantified using scintigraphy. Meal-stimulated gallbladder contraction was measured by sonography in a 2-period crossover design.

RESULTS

Intravenous BIM26226 potently inhibited gastric lag time (114 +/- 7 vs. 41 +/- 6 minutes [control]) and gastric emptying rate (0.11 +/- 0.02%/min vs. 0.26 +/- 0.04%/min [control]), whereas concomitant infusion of BIM26226 accelerated small bowel transit time (153 +/- 41 vs. 262 +/- 20 minutes [control]). A continuous liquid meal perfusion into the duodenum induced complete gallbladder contraction (t(50%), 35 +/- 4 minutes), which BIM26226 inhibited significantly (t(50%), 64 +/- 8 minutes). BIM26226 did not alter plasma CCK response, indicating that circulating CCK did not mediate these effects.

CONCLUSIONS

These data show that BIM26226 is a potent antagonist of exogenous and endogenous GRP and suggest that GRP is a major physiologic regulator of gastric emptying, small bowel transit, and gallbladder contraction.

Attenuation of the anorectic effects of cholecystokinin and bombesin by the specific amylin antagonist AC 253

Previous studies provided evidence for an interaction between the satiety effects of cholecystokinin (CCK), bombesin (BBS), and amylin. Amylin released in response to CCK (or BBS) was supposed to mediate part of CCK's (or BBS's) anorectic effect since the amylin and calcitonin gene-related peptide (CGRP) antagonist CGRP 8-37 attenuated their anorectic action. Due to the low specificity of CGRP 8-37 for amylin vs. CGRP binding sites, the aim of the present study was to test whether the specific amylin antagonist AC 253 also influenced the anorectic effects of CCK and BBS. Injections took place at dark onset in 24-h food-deprived rats. At a dose that attenuated the anorectic effect of amylin (5 microg/kg), the amylin antagonist AC 253 (500 microg/kg) significantly attenuated the anorectic effects of CCK and BBS (0.5 microg/kg). It can therefore be concluded that amylin, rather than CGRP, mediates part of the anorectic effects of CCK and BBS.

Central bombesin inhibits food intake and the orexigenic effect of neuropeptide Y in the neonatal chick

It is well known that central injection of bombesin (BN) suppresses feeding in mammalian and avian species, but the anorexigenic effect of central BN are still open with special reference to the chick. The dose response (0, 0.1 and 0.5 microg) of intracerebroventricular (ICV) injection of BN was examined in Experiment 1. ICV injection of BN inhibited food intake in a dose-dependent manner. Experiment 2 was done to determine whether BN interacts with the orexigenic effect of neuropeptide Y (NPY) in the neonatal chick. Central administration of NPY (2.5 microg) greatly enhanced food intake, but co-injection of BN (0.5 microg) suppressed food intake. The dose response of NPY (2.5 microg) co-injected with three levels of BN (0, 0.1 and 0.5 microg) was examined in Experiment 3. ICV injection of BN attenuated the hyperphagia by NPY in a dose-related fashion. It is suggested that central BN may interact with NPY for the regulation of feeding in the neonatal chick.

Impact of gastrin-releasing peptide on intestinal microcirculation after ischemia-reperfusion in rats

We investigated the effect of gastrin-releasing peptide (GRP) and its antagonist RC-3095 on intestinal microcirculation after ischemia-reperfusion. Intestinal ischemia was induced in female Wistar rats by occlusion of the superior mesenteric artery for 40 min. Ten minutes prior to reperfusion, infusion of GRP or RC-3095 was started. A jejunal segment was exteriorized and the microhemodynamics of the mucosa and submucosa were examined by intravital microscopy and compared both with normal and ischemic controls (without application of the regulatory peptide). Ischemia-reperfusion significantly decreased functional capillary density from 891.2 +/- 14.1 to 398.3 +/- 11.4 cm(-1). Capillary red blood cell velocity was reduced from 0.46 +/- 0.01 to 0.37 +/- 0.01 mm/s (p < 0.05). Furthermore, both sticking and rolling of leukocytes were enhanced. 3.4 +/- 1.1% of the villi were not perfused at all. GRP infusion reversed the microcirculatory ischemia-reperfusion injury by increasing functional capillary density to 669.8 +/- 8.3 cm(-1) and red blood cell velocity to 0.62 +/- 0.01 mm/s (p < 0.05). In addition, application of GRP resulted in a complete absence of stasis (0%) in the villi. Leukocyte-endothelium adherence remained unchanged when compared to the ischemic controls. In contrast, application of RC-3095 caused an aggravation of microcirculatory disturbances demonstrated by a markedly increased number of non-perfused villi (42.5 +/- 4.2%; p < 0.05 vs. ischemic controls) and a significantly reduced functional capillary density (346.2 +/- 8.4 cm(-1), p < 0.05 vs. ischemic controls). In addition, RC-3095 led to an increased permanent leukocyte adherence in postcapillary venules whereas rolling was significantly reduced when compared to normal controls. We conclude that GRP in pharmacological doses has a protective effect on intestinal microcirculation during reperfusion. Furthermore, these data suggest that endogenous GRP may play a decisive role in the maintenance of microvascular integrity during reperfusion.

Inhibition of growth of MDA-MB-468 estrogen-independent human breast carcinoma by bombesin/gastrin-releasing peptide antagonists RC-3095 and RC-3940-II

BACKGROUND

The growth of breast carcinoma is promoted by autocrine growth factors such as the bombesin (BN)-like peptides and epidermal growth factor (EGF). The stimulatory action of BN-like peptides can be blocked by the use of BN/gastrin-releasing peptide (GRP) antagonists.

METHODS

The authors investigated the effects of synthetic BN/GRP antagonists RC-3095 and RC-3940-II on tumor growth and the expression of mRNA for EGF receptors and three BN receptor subtypes in MDA-MB-468 human breast carcinoma. Athymic nude mice with xenografts of MDA-MB-468 human breast carcinoma were injected subcutaneously for 6 weeks with RC-3940-II at doses of 20 or 40 microg/day. In another study, the effects of RC-3940-II and RC-3095 were compared.

RESULTS

RC-3940-II caused a significant and dose-dependent growth inhibition of MDA-MB-468 tumors in nude mice; therapy with either dose of RC-3940-II significantly (P<0.01) reduced the mean final tumor volume and weight compared with controls. RC-3940-II induced a persistent regression of > 50% of all tumors. One of 3 tumors treated with 20 microg of RC-3940-II and 3 of 5 tumors treated with 40 microg were found to have regressed completely by the end of the study. When RC-3940-II and RC-3095 were compared at the dose of 20 microg/day, both powerfully suppressed growth of MDA-MB-468 tumors, with RC-3940-II causing a complete regression of 2 tumors and RC-3095 a complete regression of 1 tumor. Receptor analyses of untreated MDA-MB-468 tumors revealed an overexpression of EGF receptors and two classes of binding sites for BN/GRP. mRNAs for receptors of GRP, neuromedin B, and BN receptor subtype-3 were detected by reverse transcriptase-polymerase chain reaction.

CONCLUSIONS

A virtual arrest of growth or regression of MDA-MB-468 human breast carcinoma after therapy with RC-3940-II and RC-3095 indicates that these BN/GRP antagonists could provide a new treatment modality for breast tumors expressing BN and EGF receptors.

Role of central oxytocin in the inhibition by endotoxin of distension-stimulated gastric acid secretion

The gastric acid hyposecretory state associated with endotoxemia is mediated by a nervous reflex involving the central nervous system. The aim of the present study was to analyse the central effects of different peptides on distension-stimulated gastric acid secretion and the endogenous role of such peptides on the hyposecretory effects of endotoxin. The effect of an intracisternal (i.c.) administration of oxytocin, vasopressin, corticotropin releasing factor (CRF), bombesin, somatostatin and the opioid receptor agonist BW443C or an intravenous (i.v.) injection of a small dose of endotoxin on distension-stimulated gastric acid secretion was studied in the continuously perfused stomach of anaesthetised rats. In some animals, specific receptor antagonists for oxytocin (Compound VI [d(CH2)5, Tyr(Me)2, Thr4, Tyr-NH2(9)]-OVT, 0.01-1 microg/rat), vasopressin (des-Gly9-[beta-Mercapto-beta,beta-cyclopentamethylene-propiony l1, O-Et-Tyr2, Val4, Arg8]-VP, 20 microg/rat), CRF (alpha-helical CRF [9-41], 50 microg/rat) or bombesin (D-Phe12-Bombesin, 20 microg/rat) were administered i.c. before endotoxin. Distension-stimulated acid secretion was significantly inhibited by central oxytocin (0.2, 2 or 4 nmol/rat, 45+/-16%, 69+/-10% and 79+/-5% reduction, respectively), CRF (0.5, 1 or 2 nmol/rat, 52.2+/-15.6%, 74.3+/-9.1% and 93.2+/-1.6% reduction, respectively) and bombesin (2 nmol/rat, 79.1+/-5.8% reduction). The hyposecretory effect induced by endotoxin (5 microg/kg, 60.2+/-2.3% reduction) was reversed in a dose-dependent manner by pretreatment with the oxytocin receptor antagonist (0.01, 0.1 and 1 microg/rat, 65.2+/-14.4%, 88.0+/-22.5% and 112.4+/-25.2% of control response, respectively) while the vasopressin (20 microg/rat), CRF (50 microg/rat) or bombesin (20 microg/rat) receptor antagonists had no effect. The present results support a role for the endogenous release and action in the central nervous system of oxytocin in the inhibitory effect of endotoxin on gastric acid secretion.

Synthesis of nitric oxide in the dorsal motor nucleus of the vagus mediates the inhibition of gastric acid secretion by central bombesin

1. Central administration of bombesin inhibits gastric acid production independently of the centrally or peripherally-acting stimuli employed. This study evaluates the role and location of the cerebral nitric oxide (NO) implicated in the inhibitory effect of central bombesin on in vivo rat gastric acid secretion, as induced by distension with 15 cm H2O, insulin (0.75 u.i. kg-1 i.p.) TRH (1.2 microg kg-1, i.c.) or pentagastrin (100 microg kg-1, i.p.). 2. The acid-inhibitory effect of i.c. bombesin (40 ng kg-1) was prevented by prior administration of L-NAME (80 microg kg-1) in the dorsal motor nucleus of the vagus (DMN). This dose of L-NAME when administered into the nucleus of the tractus solitarious (NTS) did not influence the effects of bombesin. Administration of L-arginine (400 microg kg-1) into the DMN restored the acid-inhibitory effect of i.c. bombesin in animals treated with L-NAME. 3. Microinjection of bombesin (12 ng kg-1) into the paraventricular nucleus of the hypothalamus (PvN) inhibits acid secretion stimulated by pentagastrin. This inhibitory effect was prevented by a previous injection of L-NAME (80 microg kg-1) into the DMN. 4. The release of NO in the DMN following i.c. administration of bombesin was confirmed by in vivo electrochemical detection. 5. Administration by microdialysis in the DMN of the NO-donor SNAP (25 mM in 1.5 microl min-1) into the DMN inhibits pentagastrin-stimulated gastric acid secretion. 6. The present study suggests that nNOS-containing neurons in the DMN have an inhibitory role in the control of gastric acid responses.

Capsaicin-sensitive fibers are required for the anorexic action of systemic but not central bombesin

Bombesin (BN) suppresses food intake in rats whether given centrally or systemically. Although the brain BN-sensitive receptors are known to be essential for the anorexic effect of systemic BN, the mode of communication between the gut and the brain remains unclear. This study assessed whether the anorexic effect of systemic BN is mediated humorally or via neural circuits. Afferent neurons were lesioned using capsaicin (50 mg/kg sc) on postnatal day 2, and responses to BN were assessed during adulthood. Capsaicin treatment decreased body weight gain significantly from postnatal age 4-7 wk. Peripheral BN (4-16 micrograms/kg ip) dose dependently suppressed food intake in control animals. However, this effect was completely blocked in capsaicin-treated rats. In contrast to systemic effects, feeding-suppressant effects of centrally administered BN (0.01-0.5 microgram icv) were not affected by capsaicin treatment. This research suggests that peripheral BN communicates with the brain via a neuronal system(s) whose afferent arm is constituted of capsaicin-sensitive C and/or Adelta-fibers, whereas the efferent arm of this satiety- and/or anorexia-mediating circuitry is capsaicin resistant.

Effect of bombesin at low doses on the secretion of the exocrine pancreas and on plasma gastrin concentration in the conscious pig

We investigated the role of low-doses of bombesin in the regulation of exocrine secretion in the pancreas of the conscious pig. In ten growing castrated male Large White pigs, bombesin was infused intravenously for 1 h at doses of 0 to 500 pmol/kg/h under a stimulation of secretin (36 pmol/kg/h). In six pigs, bombesin (50 pmol/kg/h) was administered alone for 2 h and its effect on pancreatic secretion was compared to that of an infusion of secretin. The pancreatic juice and the blood were collected at 15-min intervals for use in assays of protein in the juice and gastrin in the plasma. When bombesin was infused alone or in combination with secretin, the volume secreted was not altered. The protein output was not altered by secretin, but was increased by the infusion of bombesin, in a dose-dependent manner, reaching a plateau at 250 pmol/kg/h. The plasma gastrin levels were increased by bombesin, starting with the 50 pmol/kg/h dose. This effect was maximal at a dose of 100 pmol/kg/h. The levels remained below those measured after a standard meal, demonstrating that the effect of bombesin on the studied parameters is of physiological significance.

Effect of the gastrin-releasing peptide antagonist BIM 26226 and lanreotide on an acinar pancreatic carcinoma

The effects of a potent specific gastrin-releasing peptide receptor antagonist, BIM 26226 ([D-F5 Phe6, D-Ala11] bombesin (6-13) OMe), and the long-acting somatostatin analogue, lanreotide (BIM 23014), on the growth of an acinar pancreatic adenocarcinoma growing in the rat or cultured in vitro were investigated. Lewis rats bearing a pancreatic carcinoma transplanted s.c. in the scapular region, were treated with gastrin-releasing peptide (30 microg/kg per day), BIM 26226 (30 and 100 microg/kg per day) and lanreotide (100 microg/kg per day) alone or in combination for 14 successive days. Chronic administration of BIM 26226 and lanreotide significantly inhibited the growth of pancreatic tumours stimulated or not by gastrin-releasing peptide (GRP), as shown by a reduction in tumour volume, protein, ribonucleic acid, amylase and chymotrypsin contents. This effect was more pronounced with 100 microg/kg per day BIM 26226 than with 30 microg/kg per day. However, BIM 26226 and lanreotide, given together, did not exert any additive effect on GRP-treated and -untreated tumours. In cell cultures, both BIM 26226 and lanreotide (10(-6) M) inhibited [3H]thymidine incorporation in tumour cells induced or not by GRP, but no increased effect was observed after combined treatment with both agents. Binding studies showed that BIM 26226 had a high affinity for GRP receptors in tumour cell membranes (IC50 = 6 nM). These results from in vivo and in vitro experiments suggest that BIM 26226 and lanreotide are able to reduce the growth of an experimental acinar pancreatic tumour. Thus, these agents represent interesting steps toward the development of new approaches for treatment of pancreatic carcinomas.

Effect of cerebroventricular perfusion of bombesin on gastrointestinal myoelectric activity

The effect of intracerebroventricular (i.c.v.) perfusion of bombesin (BBS) on the interdigestive migrating myoelectric complex (MMC) activity was examined in conscious dogs with electrodes implanted on the stomach and small intestine. Cannulas and a catheter were chronically positioned in the lateral and fourth cerebral ventricles, respectively. i.c.v. perfusion of BBS, which failed to increase plasma BBS levels, replaced phase I activity in the stomach and duodenum by intense irregular spike activity and decreased the occurrence rate of MMCs, whereas intravenous infusion of BBS evoked phase II-like activity, mainly in the jejunum and ileum, and suppressed phase III activity. These data suggest that the effect of i.c.v. administration of BBS was mediated by direct activation of central brain structures. During i.c.v. perfusion of BBS, cycling in plasma levels of motilin persisted even when phase III activity was absent and plasma levels of epinephrine rose significantly. Epinephrine infusion, however, did not affect myoelectric gastrointestinal activity except for prolonging phase II. Thus it is unlikely that the central action of BBS is exerted by motilin or epinephrine.

Plasma cholecystokinin and gallbladder responses to increasing doses of bombesin in celiac disease

Impaired postprandial gallbladder emptying in celiac disease has been attributed to an absence of appropriate cholecystokinin release. To determine if a flat jejunal mucosa in celiac patients is related to a reduced cholecystokinin-secreting capacity, increasing doses of bombesin were infused into six patients with celiac disease and a flat jejunal mucosa (group A), in seven celiac patients with a normal jejunal mucosa while on a gluten-free diet (group B), and in seven healthy controls (group C). Bombesin induced significant (P < 0.05) increments of plasma CCK to a maximum value of 1.0 +/- 0.3 pM in group A, to 1.5 +/- 0.3 pM in group B, and to 1.2 +/- 0.3 pM in group C (NS between groups), that were accompanied by significant (P < 0.05) gallbladder emptying responses of 70 +/- 4% in group A, 47 +/- 10% in group B and 65 +/- 5% in group C. Dose-response relationships were not different between groups. We conclude that there is no major impairment of gallbladder responsiveness to bombesin or of cholecystokinin-secreting capacity in patients with a flat jejunal mucosa due to celiac disease.

Brain histamine mediates the bombesin-induced central activation of sympatho-adrenomedullary outflow

Intracerebroventricular (i.c.v.) administration of bombesin (0.3 nmol) increased plasma levels of both adrenaline and noradrenaline in urethane anesthetized rats. These bombesin-induced increases were inhibited by i.c.v. pretreatment with pyrilamine, an H1-receptor antagonist. Ranitidine, an H2-receptor antagonist also inhibited the increase of adrenaline, however, its effective dose was much larger than that of pyrilamine. Furthermore, the bombesin-induced increase of noradrenaline was not effectively inhibited by ranitidine. In the next series, turnover of histamine was assessed by measuring accumulation of tele-methylhistamine (t-MH), a major metabolite of brain histamine. I.c.v. administration of bombesin (0.3-3 nmol) increased turnover of hypothalamic histamine, while its intravenous administration was without effect. The present results suggest that the bombesin-induced central activation of sympatho-adrenomedullary outflow is probably, at least in part, mediated through brain histaminergic neurons.