Bombesin stimulates human gastric function by gastrin-dependent and independent mechanisms

Gastrointestinal hormones and regulation of gastric emptying

PURPOSE OF REVIEW

In this review, we evaluate recent findings related to the association between gastrointestinal hormones and regulation of gastric emptying.

RECENT FINDINGS

Motilin and ghrelin, which act during fasting, promote gastric motility, whereas most of the hormones secreted after a meal inhibit gastric motility. Serotonin has different progastric or antigastric motility effects depending on the receptor subtype. Serotonin receptor agonists have been used clinically to treat dyspepsia symptoms but other hormone receptor agonists or antagonists are still under development. Glucagon-like peptide 1 agonists, which have gastric motility and appetite-suppressing effects are used as a treatment for obesity and diabetes.

SUMMARY

Gastrointestinal hormones play an important role in the regulation of gastric motility. Various drugs have been developed to treat delayed gastric emptying by targeting gastrointestinal hormones or their receptors but few have been commercialized.

Gastrin-releasing peptide and cancer

Over the past 20 years, abundant evidence has been collected to suggest that gastrin-releasing peptide (GRP) and its receptors play an important role in the development of a variety of cancers. In fact, the detection of GRP and the GRP receptor in small cell lung carcinoma (SCLC), and the demonstration that anti-GRP antibodies inhibited proliferation in SCLC cell lines, established GRP as the prototypical autocrine growth factor. All forms of GRP are generated by processing of a 125-amino acid prohormone; recent studies indicate that C-terminal amidation of GRP18-27 is not essential for bioactivity, and that peptides derived from residues 31 to 125 of the prohormone are present in normal tissue and in tumors. GRP receptors can be divided into four classes, all of which belong to the 7 transmembrane domain family and bind GRP and/or GRP analogues with affinities in the nM range. Over-expression of GRP and its receptors has been demonstrated at both the mRNA and protein level in many types of tumors including lung, prostate, breast, stomach, pancreas and colon. GRP has also been shown to act as a potent mitogen for cancer cells of diverse origin both in vitro and in animal models of carcinogenesis. Other actions of GRP relevant to carcinogenesis include effects on morphogenesis, angiogenesis, cell migration and cell adhesion. Future prospects for the use of radiolabelled and cytotoxic GRP analogues and antagonists for cancer diagnosis and therapy appear promising.

Biomarkers of satiation and satiety

This review's objective is to give a critical summary of studies that focused on physiologic measures relating to subjectively rated appetite, actual food intake, or both. Biomarkers of satiation and satiety may be used as a tool for assessing the satiating efficiency of foods and for understanding the regulation of food intake and energy balance. We made a distinction between biomarkers of satiation or meal termination and those of meal initiation related to satiety and between markers in the brain [central nervous system (CNS)] and those related to signals from the periphery to the CNS. Various studies showed that physicochemical measures related to stomach distension and blood concentrations of cholecystokinin and glucagon-like peptide 1 are peripheral biomarkers associated with meal termination. CNS biomarkers related to meal termination identified by functional magnetic resonance imaging and positron emission tomography are indicators of neural activity related to sensory-specific satiety. These measures cannot yet serve as a tool for assessing the satiating effect of foods, because they are not yet feasible. CNS biomarkers related to satiety are not yet specific enough to serve as biomarkers, although they can distinguish between extreme hunger and fullness. Three currently available biomarkers for satiety are decreases in blood glucose in the short term (<5 min), which have been shown to be involved in meal initiation; leptin changes during longer-term (>2-4 d) negative energy balance; and ghrelin concentrations, which have been implicated in both short-term and long-term energy balance. The next challenge in this research area is to identify food ingredients that have an effect on biomarkers of satiation, satiety, or both. These ingredients may help consumers to maintain their energy intake at a level consistent with a healthy body weight.

New molecular targets for treatment of peptic ulcer disease

Most patients with peptic ulcer disease are currently treated with proton pump inhibitors or histamine H(2) receptor antagonists. The long-term use of these compounds has been associated with two potential problems. Firstly, proton pump inhibitors may induce enterochromaffin-like (ECL) cell hyperplasia. Secondly, ulcers may relapse despite maintenance therapy with histamine H(2) antagonists. This has been the rationale for the development of new antisecretory agents, including antagonists against gastrin and gastrin releasing peptide (GRP), as well as ligands to histamine H(3) receptors. Several potent, high affinity cholecystokinin (CCK)-2 receptor antagonists have recently been identified such as L-365260, YM-022, RP-73870, S-0509, spiroglumide and itriglumide (CR-2945). Current data suggest that they all have antisecretory and anti-ulcer effects. In addition to reducing acid production, CCK-2 receptor antagonists may possibly also accelerate gastric emptying, a combination of functions which could potentially be beneficial in patients with functional dyspepsia. Receptors for bombesin and its mammalian counterpart GRP have been localised in the brain, spinal cord and enteric nerve fibres of the gut as well as on secretory cells and smooth muscle cells of the intestinal tract. Current data clearly indicate that endogenous GRP is involved in the regulation of basal and postprandial acid secretion. However, at this stage it is not clear whether GRP agonists or GRP antagonists can be developed into useful drugs. The peptide has a wide range of biological effects and it is likely that analogues of GRP or antagonists of the peptide affect not only gastric acid secretion but also induce considerable side effects. Histamine plays a central role in the stimulation of acid secretion. After their detection in the brain, H(3) receptors have been identified in a variety of tissues including perivascular nerve terminals, enteric ganglia of the ileum and lung, and ECL cells. Despite many studies, the role of H(3) receptors in the regulation of gastric acid secretion is still unclear. Controversial data have been presented, and study results largely depend on the species and experimental models. It seems unlikely that proton pump inhibitors or H(2) receptor antagonists will be replaced in the near future by new antisecretory agents. The current shortcomings of the new compounds include mainly their reduced clinical effectiveness and pharmacological limitations. However, the development of these new antisecretory compounds provides interesting tools to assess the physiological and pharmacological role of different receptors within the gastrointestinal tract. The use of CCK-2 receptor antagonists in patients with functional dyspepsia and Zollinger-Ellison syndrome should be examined in randomised, controlled trials.

Measurement of meal-stimulated gastric acid secretion by in vivo gastric autotitration

Measurement of meal- stimulated gastric acid secretion using manual intragastric titration is demanding in terms of personnel and specialized equipment. In the present study, we used a new method, in vivo gastric autotitration, to determine meal-stimulated gastric acid secretion. Gastric pH was measured every 4 s before, during, and after ingestion of a standard meal in 24 healthy subjects. Placebo, ranitidine (150 mg), ranitidine (75 mg), or famotidine (10 mg) was given 1 h after the beginning of the meal. Meal-stimulated gastric acid secretion was calculated from the amount of HCl required to titrate the homogenized standard meal to pH 2 in vitro (119 mmol) and the time required for the pH of the ingested meal to decrease to pH 2 in vivo. Values for pH were also converted to acid concentration (mM), and integrated acidity was calculated from the cumulative, time-weighted means of the acid concentrations for every fourth second of the postprandial recording period. Control meal-stimulated gastric acid secretion was 60 (40-71) mmol/h (median; interquartile range), and each histamine H(2)-receptor antagonist significantly decreased secretion by approximately 50%. Meal-stimulated acid secretion correlated directly with postprandial integrated gastric acidity (r = 0.72; P = 0.0001). Thus intragastric autotitration is a convenient, reproducible method for measuring gastric acid secretion after ingestion of a solid meal and offers several advantages over manual intragastric titration.

Capsaicin-sensitive vagal fibres and 5-HT3-, gastrin releasing peptide- and cholecystokinin A-receptors are involved in distension-induced inhibition of gastric emptying in the rat

The present study was undertaken to investigate how the activation of gastric mechanoreceptors by distension of the stomach in conscious gastric fistula rats influences gastric emptying; and the roles of capsaicin sensitive vagal afferent fibres and the 5-HT3, GRP and CCK-A receptors involved in mediating these responses. To activate mechanoreceptors by non-nutrient dependent pathways, methylcellulose in saline was used to distend the stomach (5 cm H2O) and the subsequent emptying of saline was examined immediately, and at 3, 5 and 10 min following distension. Prior distension delayed the subsequent emptying of saline instilled into the stomach compared with non-distended controls (2.28+/-0.09 ml/5 min; P < 0.001). Topical application of capsaicin, completely abolished the distension-induced inhibition of gastric emptying when compared with vehicle treated rats (2.82+/-0.09 vs. 2.38+/-0.04 ml/5 min; P < 0.001). Peripheral administration of a GRP antagonist (2258 U89UJ, 1 mg/kg), and a 5-HT3 antagonist (BRL4369UA, 50 microg/kg) significantly reversed (2.56+/-0.14 ml/5 min; P < 0.05 and 2.61+/-0.07 ml/5 min; P < 0.01; respectively) the delay in gastric emptying induced by distension. When the rats were treated with the CCK-A antagonist, gastric emptying of saline following distension was also significantly facilitated (2.56+/-0.07 ml/5 min; P < 0.001). In contrast, the CCK-B/gastrin receptor antagonist had no significant effect on the distension induced delay in gastric emptying (1.95+/-0.12 ml/5 min). The present results suggest that gastric distension in conscious gastric fistula rats delays gastric emptying by activating capsaicin-sensitive extrinsic afferent nerve fibres. Moreover, the results also indicate that distension-induced mechanisms involve GRP, 5-HT3 and CCK-A receptors, but not CCK-B receptors.

Bombesin inhibits histamine release from the rat oxyntic mucosa by a somatostatin-dependent mechanism

BACKGROUND AND METHODS

This study examines the effect of bombesin on endogenous somatostatin and the histamine-synthesizing enterochromaffin-like cells. Somatostatin and histamine were measured in the venous effluent of isolated/antrectomized vascularly perfused rat stomachs after administration of bombesin and gastrin alone or combined. Histidine decarboxylase (HDC) enzyme activity and mRNA abundance were measured in the gastric corpus after intravenous administration of bombesin to conscious rats.

RESULTS

Bombesin released somatostatin from the isolated stomachs and reduced basal and gastrin-stimulated venous histamine. Somatostatin antiserum partially reversed the effect of bombesin on basal and gastrin-stimulated histamine release. In conscious fed rats, intravenous bombesin doubled serum gastrin concentrations and increased HDC activity.

CONCLUSION

We conclude that endogenous (paracrine) somatostatin inhibits basal and gastrin-stimulated histamine release from the ECL cell. In intact animals this effect is surmountable by simultaneously released gastrin, suggesting that a balance between the effects of gastrin and somatostatin determines the activation of the ECL cell.

Inhibitory effects of gastrin releasing peptide on gastric emptying in rats

Gastrin-releasing peptide (GRP) has a wide range of biological actions, including stimulation of the frequency of antral contractions and delaying gastric emptying. The present study was designed to evaluate the role of GRP in the control of gastric emptying of liquid test meals in the rat. The emptying of methyl cellulose given by gavage to fasted rats, or of saline given via the fistula to conscious gastric fistula rats was not influenced by the GRP antagonists, NC-8-89 (Leu13-psi-(CH2NH)-Leu14-bombesin) and 2258U89 ((de-NH2)Phe19, D-Ala24, D-Pro26 psi (CH2NH)Phe27(-GRP (19-27)), at 2 mg/kg, s.c. However, both antagonists (0.02, 0.2 and 2 mg/kg) reversed the inhibitory effect of HCI on gastric emptying in gastric fistula rats (P < 0.05-0.001). When peptone was administered after a preload, but not otherwise, the inhibition of emptying was also partly reversed by both antagonists at all doses used (P < 0.05-0.001). Interestingly, the delay in the emptying of hyperosmolal saline compared to saline, was enhanced at a dose of 0.2 mg/kg of both antagonists (P < 0.05 and P < 0.01). Food intake did not change significantly with the two lower doses of antagonists, but was decreased by the highest dose of NC 8-89. We conclude that GRP specifically inhibits gastric emptying of acid and peptone solutions in the conscious rat.

Helicobacter pylori infection and abnormalities of acid secretion in patients with duodenal ulcer disease

BACKGROUND & AIMS

The mechanism by which Helicobacter pylori predisposes to duodenal ulcers (DUs) remains unclear. The aim of this study was to investigate the effect of the infection on acid secretion.

METHODS

Acid output was examined basally and in response to gastrin-releasing peptide (GRP) and gastrin in healthy volunteers with and without H. pylori infection and in patients with DUs before and after eradication of the infection.

RESULTS

Compared with H. pylori-negative healthy volunteers, patients with DUs with H. pylori had the following abnormalities of acid secretion: (1) threefold increase in basal acid output, (2) sixfold increase in acid response to GRP, (3) increased maximal acid response to exogenous gastrin, (4) increased ratio of basal acid output to maximal gastrin-stimulated output, and (5) increased ratio of maximal GRP-stimulated acid output to maximal gastrin-stimulated output. All of these abnormalities resolved fully after H. pylori eradication except for increased maximal acid output to gastrin, which was unchanged. Infected healthy volunteers showed a threefold increase in acid response to GRP that resolved after eradication of H. pylori infection.

CONCLUSIONS

These disturbances in acid secretion caused by H. pylori infection are consistent with impaired inhibitory control and are likely to be relevant to the mechanism by which the infection predisposes to DU.

Review article: gastrin releasing peptide and its value in assessing gastric secretory function

Gastrin releasing peptide (GRP) has proved to be a particularly valuable tool in detecting disturbances of gastric secretory function associated with duodenal ulcer disease and Helicobacter pylori infection, and it has furthered understanding of the pathophysiology of these conditions. Its attractiveness lies in the fact that it simultaneously activates many physiological control processes, both stimulatory and inhibitory. This facilitates the detection of a defect in any of the many controls involved in regulating biological function. Other gastrointestinal functions such as gall-bladder contraction, pancreatic secretion and gastrooesophageal motility are also subject to complex regulatory controls, and GRP may also be of value in investigating disturbances of these processes.

Bombesin does not stimulate pepsinogen release in isolated gastric chief cells

Bombesin (BN)-related peptides, such as gastrin-releasing peptide (GRP), have been shown in vivo to stimulate release of pepsinogen. However, whether this is due to a direct interaction with chief cells is not clear. To clarify this we prepared isolated chief cells (> 90% pure) from guinea pig stomach. BN, GRP, or neuromedin B (NMB), at concentrations up to 1 microM, did not stimulate pepsinogen release or affect the stimulation caused by vasoactive intestinal peptide (VIP) (100 nM) or CCK-8 (10 nM), respectively. In addition, BN, GRP, or NMB at a concentration of 1 microM did not increase cAMP nor did they alter the increase in cAMP caused by VIP or secretin. BN (1 microM) did not alter basal cytosolic calcium [Ca2+]i or affect the increase in [Ca2+]i caused by CCK-8 (1 microM). Furthermore, BN, GRP, or NMB at a concentration of 1 microM did not increase the generation of inositol phosphates (IP) or alter the increase in [3H]IP1, [3H]IP2, or [3H]IP3, caused by CCK-8 (1 microM) or carbachol (1 mM). Binding studies demonstrated no saturable binding of either [125I][Tyr4]BN or [125I][D-Tyr0]NMB using experimental conditions where binding with other peptide ligands to other receptors on chief cells is seen. We conclude that BN-related peptides do not interact directly with specific receptors on chief cells to stimulate or alter stimulated pepsinogen secretion, increase the breakdown of inositol phosphates, or alter [Ca2+]i or cAMP.

Gut hormones in gastric function

This chapter has focused on many of the gut hormones that regulate gastric function. Gastrin remains the principal, and only, gastric hormone controlling gastric acid secretion during the cephalic, gastric and intestinal phases of secretion. Several other hormones, including cholecystokinin, peptide YY and secretin, released from intestinal endocrine cells in response to food substrates, have significant inhibitory effects on gastric acid secretion. Many of these hormones, including enteroglucagon and glucagon-like peptide, may act through paracrine release of somatostatin, which in turn acts as the final mediator of acid inhibition. In addition, several peptides contained in nerves, including gastrin releasing peptide and vasoactive intestinal peptide, have been shown to regulate gastric acid secretion and motor function. With the creation of specific monoclonal antibodies for use in in vivo immunoneutralization studies, and the development of selective chemical antagonists for use in receptor blockade experiments, the specific contributions of the different gut hormones in the regulation of gastric function, can be assessed.

Gastrin-releasing peptide: neuronal distribution and spatial relation to endocrine cells in the human upper gut

By using immunocytochemical techniques, we have studied the distribution of gastrin releasing peptide (GRP)-containing neurons as well as the spatial relationship between these neurons and the endocrine cells in the human stomach and duodenum. Moderate numbers of immunoreactive fibers were distributed in the smooth muscle and submucosa of the stomach; they were more rare in the duodenal wall. Numerous GRP-containing nerve fibers were found in the oxyntic mucosa, the antral mucosa harboured only few GRP immunoreactive nerve fibers. The mucosa of the proximal duodenum was found to be virtually devoid of such fibers. Only occasionally did we observe signs of a direct contact between GRP-containing nerve fibers and gastrin and somatostatin cells in the antral mucosa. In the oxyntic mucosa GRP-containing nerve fibers sometimes seemed to contact endocrine cells, including somatostatin cells as well as individual parietal cells. In conclusion, although GRP-containing nerve fibers were quite numerous in the wall of the human upper gastro-intestinal (GI)-tract, we observed a lack of intimate spatial relationship between these fibers and endocrine cells in the antral mucosa, suggesting additive mechanisms to a direct innervation of gastrin cells and somatostatin cells by GRP nerve fibers explaining the physiological effects on hormonal release.

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

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

The effect of gastrin-releasing peptide on acid secretion and the release of gastrin, somatostatin, and histamine in the totally isolated, vascularly perfused rat stomach

We have studied the effect of gastrin-releasing peptide (GRP) on exocrine and endocrine secretion in the totally isolated, vascularly perfused rat stomach with or without concomitant infusion of a potent somatostatin antiserum. GRP (1 nM) showed a marginal acid-stimulatory effect (base line, 11.6 +/- 2.3 mumol/60 min, and after GRP, 20.0 +/- 2.2 mumol/60 min; p = 0.05). GRP significantly increased gastrin and somatostatin release to the venous effluent, and the venous gastrin concentration increased significantly during concomitant infusion of somatostatin antiserum. Furthermore, GRP inhibited histamine liberation, and somatostatin antiserum reversed this effect. The antiserum did not significantly stimulate acid secretion. Thus, the present study shows that GRP directly or indirectly affects both acid secretion and the release of gastrin, somatostatin, and histamine in the rat stomach.

Autoradiographic demonstration of gastrin-releasing peptide-binding sites in the rat gastric mucosa

The location of [125I]iodotyrosyl gastrin-releasing peptide-binding sites in the rat fundic mucosa was studied. Peptide specificity was demonstrated by competitive binding studies using the addition of a large amount of cold gastrin-releasing peptide or substance P. Autoradiography of the stomach tissue was carried out by freeze-drying, embedding in Epon, wet-sectioning with ethylene glycol, and dry-mounting the emulsion film by the wire-loop method to prevent loss of the labeled substance. Specific binding sites of gastrin-releasing peptide were found on D cells, surface mucus cells, and parietal cells, whereas few binding sites were seen on the chief or mucus neck cells.

Retardation of gastric emptying of solid food by secretin

The effect of secretin at nearly physiologic plasma concentrations on the gastric emptying rate of solid food was studied in 12 healthy men. A 99mTc colloid-labeled pancake was used as the test meal. The gastric emptying rate was measured during 1 h using a dual-headed gamma-camera, and was expressed as the half-time of the emptying curve. To prevent endogenous secretin release, 400 mg of cimetidine was given before the meal. Subjects were studied under three conditions: (1) during infusion of saline; (2) during continuous infusion of secretin, 6.6 pmol/kg.h; and (3) during three intermittent 10-min periods of secretin infusion, 7.6 pmol/kg.h during each period. Both continuous and intermittent infusion of secretin increased half-emptying time, by 133% and 55%, respectively. The plasma secretin concentration in condition 1 was 0.8 pM; plateau concentration in condition 2 was 9.8 pM; and integrated mean concentration in condition 3 was 4.8 pM. It is concluded that secretin at approximately physiologic plasma concentrations retards gastric emptying of solid food in humans.

Neuronal localization and motor effects of gastrin-releasing peptide (GRP) in rat uterus

All parts of the internal female reproductive tract of the rat contained nerve fibers with immunocytochemically visible gastrin-releasing peptide (GRP)-like material. GRP-like immunoreactivity was also seen in nerve cell bodies of the paracervical ganglion formation, which in addition, harboured GRP nerve fibers. Pharmacological experiments were performed on isolated uterine and cervical smooth muscle tissue from two groups of spayed animals, one of which received estradiol. Both GRP and its non-mammalian counterpart, bombesin, evoked concentration-dependent clonic contractions in uterus and cervix, most pronounced in the estrogen-treated animals. Bombesin induced a stronger contractile force than GRP. The responses were not affected by tetrodotoxin. The observations suggest that GRP may be one of several neural messengers involved in the control of uterine motor activity.

Interaction of [125I]-Tyr4-bombesin with specific receptors on normal human pancreatic membranes

The binding of bombesin to its receptors on normal human pancreatic membranes was investigated using high specific activity, radioiodinated bombesin ([125I]-Tyr4-bombesin), prepared by an oxidative method with chloramine-T. Binding was specific, temperature-dependent, saturable, reversible and linearly related to membranes protein concentration. After a 30 min period of incubation with membranes the degradation of the tracer has never been found superior to 20%. Scatchard analysis of binding data was compatible with a single class of binding sites with a high affinity (0.96 nM) and a Bmax of 753 fmol/mg protein. [125I]-Tyr4-bombesin binding to human pancreatic membranes was competitively inhibited by (1-Tyr4-)bombesin, GRP, the nonapeptide of bombesin and litorin but not by unrelated hormones such as somatostatin, CCK, human gastrin, etc. These results describe for the first time the presence of specific receptors for bombesin on human pancreatic membranes. The binding characteristics obtained are comparable with those found in other species.

Peptide-containing nerve fibers in the stomach wall of rat and mouse

Peptide-containing nerve fibers were found to be numerous in the glandular stomach of the rat and mouse. The immunoreactive neuropeptides demonstrated included vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), gastrin-releasing peptide (GRP), substance P (SP), enkephalin, somatostatin, cholecystokinin, and neuropeptide Y (NPY). The density and distribution of the various peptide-containing fibers did not differ overtly between the pyloric and oxyntic gland areas except for the GRP fibers, which were fewer in the pyloric than in the oxyntic mucosa. The entire VIP nerve fiber population was found to also contain PHI. Immunoreactive NPY was found to occur in the VIP/PHI fibers (VIP/PHI/NPY fibers) in the smooth muscle and intramural ganglia of both rat and mouse and in the mucosa of the mouse. Mucosal VIP/PHI fibers in the rat did not contain any NPY-like material. Perivascular NPY fibers in both species and mucosal NPY fibers in the rat did not contain VIP or PHI. The mucosa harbored numerous GRP fibers and VIP/PHI (rat) or VIP/PHI/NPY (mouse) fibers, and a modest number of NPY (rat) and SP fibers. In the submucosa the peptide-containing nerve fibers were found mainly in the ganglia and around blood vessels. Blood vessels received a rich supply of NPY fibers; the number of perivascular VIP/PHI, GRP, and SP fibers was much lower by comparison. The smooth muscle and myenteric ganglia harbored not only VIP/PHI/NPY, GRP, and SP fibers but also enkephalin, somatostatin, and cholecystokinin fibers. Gastrin-releasing peptide, VIP/PHI/NPY, SP, and enkephalin nerve cell bodies occurred in the myenteric ganglia. As studied in the rat, vagal denervation did not affect the density and distribution of the various peptide-containing nerve fibers. After sympathectomy, mucosal and perivascular NPY fibers disappeared. The other types of peptide-containing nerve fibers were not affected.

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

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

Glucose perfusion intragastric titration

A comparison was made between use of isotonic 0.15 M sodium chloride and 5.8 g/100 ml glucose solutions for measurement of gastric acid secretion by intragastric titration in normal and ulcer subjects. Glucose distention did not cause significantly different acid secretion than saline distention in either group. The total amounts of glucose entering the duodenum over the 3.5-hr study period were 99 g in normal subjects and 122 g in ulcer subjects. In normal subjects, circulating gastrin-related acid secretion curves were not significantly different during endogenous peptone and exogenous G-17 stimulation using either the glucose or the saline meals. This finding provides evidence that glucose meals of this size do not alter sensitivity to gastrin. With glucose meals, inhibition of gastric emptying caused retention of a sufficient volume in the stomach to permit accurate continuous intragastric titration. Saline meals caused pronounced diarrhea which was not seen after glucose meals. Glucose distention intragastric titration allows reliable comparisons of endogenously and exogenously stimulated gastric acid secretion without serious side effects and is especially suitable for studying acid secretion in duodenal ulcer subjects.

Molecular forms of cholecystokinin in human plasma during infusion of bombesin

Bombesin is a tetradecapeptide with stimulatory actions on several gastrointestinal functions. Infusion of bombesin (60 pmol/kg. 20 min) into 7 normal subjects induced significant increases in plasma cholecystokinin (CCK) as measured with 2 sequence-specific radioimmunoassays. Employing antibody 1703, specific for carboxyl-terminal CCK-peptides containing at least 14 amino acid residues, plasma CCK concentrations rose from 0.8 +/- 0.2 pmol/l to 9.9 +/- 1.7 pmol/l (p less than 0.005), while using antibody T204, specific for the sulfated tyrosine region of CCK, plasma CCK levels increased from 2.9 +/- 0.5 pmol/l to 12.4 +/- 1.3 pmol/l (p less than 0.005). Plasma samples obtained from 3 subjects during bombesin infusion were fractionated by Sephadex column chromatography. Fractionation revealed 4 molecular forms of CCK: peak I eluted in the void volume and comprised 0-7% of CCK-like immunoreactivity, peak II eluted at 35% and comprised 8-41% of CCK-like immunoreactivity, peak III eluted at 50% and comprised 44-61% of CCK-like immunoreactivity, and peak IV eluted at 75% and comprised 15-27% of CCK-like immunoreactivity. Radioimmunoassay with a carboxyl-terminal CCK-antibody fully cross-reacting with gastrin did not reveal additional molecular forms of CCK. Since both the carboxyl-terminus and the sulfated tyrosine region are required for biological activity of CCK, it is likely that all these molecular forms of CCK possess biological activity.

Neuronal gastrin-releasing peptide in the mammalian gut and pancreas

Immunoreactive gastrin releasing peptide (GRP) was demonstrated in neuronal elements in the porcine pancreas and in the gut of several mammals. Immunoreactive endocrine cells could not be detected. The results of radioimmunochemical analysis agreed well with those of immunocytochemistry. The occurrence of gastrin-releasing peptide-containing nerve cell bodies in the myenteric ganglia all along the gut indicates that gastrin-releasing peptide fibers are intramural in origin. The distribution of gastrin-releasing peptide fibers in all layers of the gut wall suggests multiple functions of gastrin-releasing peptide, including a role in the regulation of intramural neuronal activities, smooth muscle tone and in secretory and absorptive processes.

The effects of proglumide on cholecystokinin-, bombesin-, and glucagon-induced satiety in the rat

Intraperitoneal (IP) administration of the glutaramic acid derivative proglumide inhibited satiety induced by all IP doses of cholecystokinin octapeptide (CCK-OP) in 3-hour food-deprived intact rats. Proglumide did not influence satiety when administered alone and did not inhibit satiety induced by IP glucagon. While proglumide did not inhibit satiety induced by low doses of IP bombesin, it partially and significantly inhibited the satiety effects produced by high doses of this peptide. Since bombesin is a known secretagogue for CCK in several species, these results indicate that while bombesin and CCK act independently to induce satiety, the effect induced by high doses of bombesin is mediated, in part, by the release of endogenous CCK or a structurally related peptide. Furthermore, these results illustrate that proglumide is a specific antagonist of CCK-induced satiety and is, therefore, a potentially useful tool for investigating the physiologic role of this peptide in the control of food intake.