Effect of nicotine on basal and bombesin stimulated canine plasma levels of gastrin, cholecystokinin and pancreatic polypeptide

The influence of nicotine on the basal and bombesin (BBS) stimulated plasma levels of gastrin, cholecystokinin (CCK) and pancreatic polypeptide (PP) was investigated in conscious dogs. Plasma levels of nicotine and gastrointestinal (GI) hormones were measured by employing gas liquid chromatography and specific radioimmunoassay (RIA). The basal levels of gastrin, CCK and PP were found to be in pg/ml (pmol/l) (mean +/- S.E.), 28 +/- 5 (13 +/- 3), 252 +/- 32 (66 +/- 8) and 347 +/- 136 (83 +/- 32), respectively and these values remained unchanged with nicotine. Significant increases in levels of gastrin, CCK and PP were, however, found with infusions of BBS alone or with BBS in combination with nicotine. Gastrin levels were higher whereas CCK and PP levels were lower with BBS alone than with BBS plus nicotine. The peak values for CCK and PP, but not gastrin, were less during second BBS infusion. These results indicate that nicotine, in presence of bombesin, has an inhibitory effect on the release of gastrin and a stimulatory effect on the release of PP and CCK.     

The effect of neurotensin and secretin on gastric acid secretion and mucosal blood flow in man

Neurotensin stimulates pancreatic secretion directly and by potentiating the effect of secretin. Neurotensin also inhibits gastric secretion. Secretin inhibits gastric secretion as well, but whether it also interacts with neurotensin is not known. Secretin is known to inhibit gastric mucosal blood flow (GMBF). The effect of neurotensin on GMBF is not known. Acid secretion (triple lumen perfused orogastric tube) and GMBF ([14C]aminopyrine clearance) were therefore measured in 6 subjects during neurotensin, secretin and neurotensin plus secretin infusions. Neurotensin plus secretin reduced acid secretion by a median 130 (range 34-394) mumol/min which was significantly greater than either neurotensin at 36 (7-67) mumol/min or secretin 54 (20-347) mumol/min alone (P less than 0.05). This effect appeared independent of GMBF. Neurotensin plus secretin reduced GMBF by 14 (12-27) ml/min but not significantly more than neurotensin at 11 (3-20) ml/min or secretin 18 (2-27) ml/min alone. Further, there was no correlation between changes in acid output and GMBF during infusion of the peptides. We conclude that the inhibitory effects of neurotensin and secretin on gastric secretion are at least additive and together they may function as an 'enterogastrone'.     

Effect of atropine and somatostatin on bombesin-stimulated plasma gastrin,cholecystokinin and pancreatic polypeptide in man

Infusion of the neuropeptide bombesin stimulates the secretion of several gastrointestinal hormones by an unknown mechanism. We have investigated the effects of atropine (15 ng/kg as bolus followed by 2.5 ng/kg · 30 min) and somatostatin (125 μg as i.v. bolus followed by 62.5 μg/30 min) on the stimulation of 3 hormones (gastrin, cholecystokinin and pancreatic polypeptide) by 60 pmol/kg · 20 min bombesin in 6 healthy volunteers. Plasma samples for measurement of hormones by sensitive and specific radioimmunoassays were obtained at − 5, 0, 2.5, 5, 7.5, 10, 15, 20, 25 and 30 min. Bombesin induced significant increases in plasma gastrin (12 ± 2 to 34 ± 3 pM; P < 0.0005), cholecystokinin (1.2 ± 0.2 to 8.9 ± 0.7 pM; P < 0.0001) and pancreatic polypeptide (22 ± 4 to 72 ± 19 pM; P < 0.05). There were great differences between the effects of atropine and somatostatin on the hormonal responses to bombesin. Atropine slightly increased the response of gastrin by 19% and that of cholecystokinin by 15%, but strongly inhibited the bombesin-stimulated pancreatic polypeptide secretion by 97%. On the other hand, somatostatin inhibited the bombesin-induced secretion of gastrin by 48%, cholecystokinin by 82% and pancreatic polypeptide by 107%. These results point to considerable qualitative and quantitative differences in the stimulatory mechanisms of bombesin on the hormones studied.     

Characterization of the murine pancreatic receptor for gastrin releasing peptide and bombesin.

The murine pancreatic receptor for bombesin and gastrin releasing peptide (GRP) has been characterized. Analysis of the binding of 125I-GRP to membranes indicates a single class of sites (10(-13) mol/mg protein) with Kd of 43 pM. A 70 kDa membrane protein was cross-linked to 125I-GRP by bis(sulfosuccinimidyl) suberate; labeling was blocked by GRP, GRP (14-27), AcGRP(20-27), GRP(18-27), bombesin and ranatensin, was partially blocked by [Leu13 psi (CH2NH)Leu14]bombesin and was unaffected by GRP(21-27) and GRP(1-16). The IC50 values for the competitive displacement of 125I-GRP from intact membranes by these peptides were similar to those obtained by the cross-linking experiments showing that the 70 kDa protein is the GRP receptor. The GRP receptor is G-protein coupled; divalent cations are required for high-affinity binding and nonhydrolyzable GTP analogs decrease receptor affinity. In minced pancreas, GRP caused a dose-dependent increase in inositol phosphates implicating phospholipase C in signal transduction. We suggest that the murine pancreatic receptor for bombesin/GRP is a 70 kDa membrane protein, is associated with a G-protein and stimulates phosphatidylinositol turnover.     

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.     

Comparison of enkephalin and atropine in the inhibition of vagally stimulated gastric and pancreatic secretion and gastrin and pancreatic polypeptide release in dogs

Enkephalins have been detected in vagal nerves and myenteric plexus neurons but no study has been performed to determine their action on vagally stimulated gastric and pancreatic secretion. In this study we infused IV methionine-enkephalin (Met-enk) alone, naloxone (a pure opiate antagonist) alone, or their combination before, during and after vagal stimulation in 4 dogs with esophageal, gastric and pancreatic fistulas. For the comparison, atropine was given before, during and after vagal stimulation in the same animals. Vagal stimulation was obtained by 15 min sham-feeding, which produced an increase in gastric H⁺ output to a peak of about 75% of the maximal response to pentagastrin and pancreatic protein secretion amounting to about 71% of the maximal response to caerulein. It was accompanied by a significant rise in serum gastrin and pancreatic polypeptide (PP) levels. Met-enk inhibited significantly both gastric H⁺ and pancreatic protein secretion and reduced plasma PP but not gastrin levels. Similar effects were obtained after the administration of atropine. The effects of Met-enk were partly reversed by the addition of naloxone. We conclude that (1) enkephalin suppresses vagally stimulated gastric and pancreatic secretion and plasma PP release; (2) these secretory effects of enkephalin seem to be mediated by opiate receptors and could be explained by its inhibitory action on acetylcholine release (“anticholinergic” action) in the stomach and the pancreas.     

The effect of somatostatin and 16,16-dimethyl-prostaglandin E2 on bombesin-stimulated canine gastric acid, plasma gastrin and pancreatic polypeptide secretion

We studied the effect of the intravenous infusion of 16,16-dimethylprostaglandin E2 methyl ester (di-M-PGE2) and somatostatin on bombesin-stimulated gastric acid secretion, plasma gastrin and plasma pancreatic polypeptide in four chronic gastric fistula dogs. Bombesin-stimulated gastric acid secretion was significantly inhibited by somatostatin and virtually abolished by di-M-PGE2. Both agents caused significant, but indistinguishable inhibition of gastrin release (P less than 0.05). Bombesin-stimulated pancreatic polypeptide release was also significantly inhibited by both somatostatin and di-M-PGE2; the inhibitory effect of somatostatin was significantly greater than that of di-M-PGE2 (P less than 0.05). This study provides further evidence in support of the complex interrelationships between agents responsible for the modulation of gastrointestinal physiology.     

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

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

Effects of bombesin and gastrin releasing peptide on catecholamine secretion from rat adrenal gland, in vitro

The effects of bombesin and gastrin releasing peptide (GRP) on the release of catecholamine were investigated by using isolated rat adrenal gland. Bombesin and GRP stimulated an epinephrine (E) release with dose-dependency. A half maximal effect of bombesin was observed at 1.2 X 10(-9) M, and a maximal release of E occurred at 1 X 10(-6) M of bombesin. The stimulatory effect of GRP on the E release was very similar to that of bombesin. Although both these peptides also stimulated a norepinephrine (NE) release, a significant effect was detected at concentrations of bombesin and GRP above 1 X 10(-7) M. Nicotine and pilocarpine stimulated both E and NE releases dose dependently, but the effect of pilocarpine on E and NE release was 1/100 or less potent than that of nicotine. Bombesin-induced catecholamine releases were not inhibited by hexamethonium or atropine that fully impeded the stimulatory effects of nicotine or pilocarpine. In addition, bombesin had additive effects on the nicotine- or pilocarpine-induced E and NE releases. These data strongly suggest that bombesin or GRP plays a physiological role as one of the important regulators in catecholamine secretion in the adrenal gland.     

Effects of ketamine on the cholecystokinin,somatostatin, substance P,and thyrotropin releasing hormone in discrete regions of rat brain

Intraperitoneal injection of ketamine (100 mg/kg body weight) significantly reduces the levels of cholecystokinin (CCK) somatostatin (SRIF), and substance P (SP)-like immunoreactivity in various regions of rat brain. No significant change in thyrotropin releasing hormone (TRH)-like immunoreactivity was observed. Neuropeptide systems may be involved in the neuropharmacologic effects of ketamine.     

Effect of medium-chain triglycerides and long-chain triglycerides on plasma pancreatic polypeptide secretion in man

Since it has been shown that stimulation of pancreatic enzyme secretion by triglycerides is dependent on the chain length of the fatty acids, we have studied whether the secretion of pancreatic polypeptide (PP) in response to triglycerides is also related to the chain length of the fatty acids. Therefore, the effect of equimolar amounts (60 mmol) of medium-chain triglycerides (MCT) and long-chain triglycerides (LCT) on plasma PP was studied in 6 normal subjects. In the control study the subjects ingested 60 ml of 0.15 mol/l saline. Ingestion of LCT resulted in significant increases in plasma PP from 33 +/- 7 to 55 +/- 7 pmol/l (P less than 0.01), whereas both MCT and saline did not significantly increase plasma PP concentrations. Similarly, the integrated plasma PP secretion after LCT (1022 +/- 392 pmol/l per 90 min) was significantly greater than that after MCT (-690 +/- 358 pmol/l per 90 min; P less than 0.001) and that after saline (-462 +/- 205 pmol/l per 90 min; P less than 0.01). It is concluded that the secretion of PP in response to triglycerides is dependent on the chain length of the fatty acids.     

Effect of adding albumin to solutions of cholecystokinin on pancreatic protein output and pancreatic polypeptide release

In four conscious dogs with chronic gastric and pancreatic Thomas fistulas we studied the effect of 99% pure cholecystokinin-33 (CCK-33) solutions on pancreatic secretion and PP release. CCK-33 was dissolved in 0.154 M NaCl alone or in the same solution containing 1 g per 100 ml dog albumin. The response of pancreatic protein output to increasing doses of CCK-33 (0.5, 1, 2, 4 IDU/kg per h) was significantly $\text{(P < 0.05)}$ higher when CCK was dissolved in NaCl with albumin than in NaCl alone. These results were confirmed by measuring CCK immunoreactivity in samples from tips of infusion lines by a gastrin radioimmunoassay. Release of pancreatic polypeptide (PP) following increasing doses of CCK-33 was also significantly $\text{(P < 0.05)}$ elevated when CCK was dissolved in an albumin-containing solution. There was a significant $\text{(P < 0.02)}$ correlation between plasma concentrations of PP and pancreatic protein output.This study suggests that albumin should be added to CCK-33 solutions to preserve biological activity. The biological effect of CCK-33 may be substantially underestimated if albumin is omitted.     

Influence of caloric intake on gastric inhibitory polypeptide,VIP and gastrin release in man

Blood glucose, gastric inhibitory polypeptide (GIP), vasoactive intestinal polypeptide (VIP) and gastrin secretions were measured over a three-hour period following the ingestion by normal subjects of a mixed meal with two different caloric levels (1055 Kcal and 1192 Kcal). No VIP secretion was observed after either meal. Gastrin release was not modified by the increase of caloric intake (mainly carbohydrates and lipids), whereas GIP secretion was significantly more important after the meal with the highest caloric value (peak at 30 mn: $\text{499.5±250.4}$ vs. $\text{273.4±128.7}\text{pg/ml}$ and integrated response $\text{53.3±20.5}$ vs. $\text{28.2±9.9}\text{ng}\text{×}\text{ml}{}^{\mathrm{?1}}\text{×180}\text{min}{}^{\mathrm{?1}}\text{?p<0.05}$). This difference could not be attributed to glucose since the blood glucose levels were not significantly different. It is more probably related to the total amount of ingested food. This suggests the existence of rapid mechanisms of adaptation to the incoming load of the GIP-producing cells.     

Effects of porcine gastrin releasing peptide (GRP) on canine antral motility and gastrin release in vivo

The effect of GRP on the vivo canine antrum was investigated. GRP caused a dose-dependent increase in antral gastrin output which was not significantly altered by administration of tetrodotoxin. The higher doses of GRP administered also caused excitation of antral motility which was abolished by tetrodotoxin, a finding in contrast to previous in vitro results demonstrating bombesin-induced antral smooth muscle contraction to be tetrodotoxin-resistant. These data suggest that in the vivo canine model GRP causes antral gastrin release via non-reurally mediated mechanisms (probably by acting directly on the G-cell) and excites antral motility via neurally-mediated mechanisms.     

Motor effects of gastrin releasing peptide (GRP) and bombesin in the canine stomach and small intestine

Close intraarterial injections of synthetic porcine gastrin releasing peptide (GRP) or bombesin stimulated contractions in the stomach and inhibited ongoing contractile activity in the small intestine of anaesthetized dogs. Contractile activity of the circular muscle was recorded by serosal strain gauges and phasic activity when desired was elicited by local field stimulation or intraarterial motilin injections. In the stomach (corpus and antrum) following tetrodotoxin blockade of field-stimulated contractions, the contractile response to either peptide was not present, suggesting that stimulation of receptors on nerves initiated contractions in the stomach. Similarly, in the small intestine, the inhibitory response was eliminated by tetrodotoxin suggesting a neural receptor. Pre-treatment with reserpine did not alter the inhibitory response, either in the presence or absence of atropine, therefore, adrenergic inhibitory mechanisms did not appear to be involved. The concentration of bombesin producing 50% inhibition of field stimulation (ED50) was increased following treatment with the putative M1 muscarinic antagonist, pirenzipine suggesting activation of M1 cholinergic inhibitory receptors by bombesin. After blockade by atropine of field-stimulated contractions and the contractile response to intraarterial acetylcholine, the ED50 for bombesin inhibition of motilin contractions was increased. After muscarinic blockade, the residual inhibitory response of GRP/bombesin may involve activation of a neural non-cholinergic non-adrenergic inhibitory mechanism. These results suggest that GRP and bombesin act to alter motility in the dog in vivo by affecting neural activity.     

Stimulation of canine pancreatic polypeptide, gastrin, and gastric acid secretion by ranatensin, litorin, bombesin nonapeptide and substance P

Four dogs with chronic gastric fistulas were give intravenous bombesin nonapeptide (B9), ranatensin, and litorin by constant infusion for 90 min at 1.2 micrograms x kg-1 on separate days. A dose response study with substance P (1.5, 3.0, 60, 18 and 54 micrograms x kg-1 x h-1) was also carried out and all tests compared to a standard protein meal (10g x kg-1). Plasma gastrin and PP were measured by radioimmunoassay and gastric acid by autobiuret titration. Substance P failed to stimulate gastric acid secretion or release either pancreatic polypeptide (PP) or gastrin. Basal gastrin levels were 8 +/-2 fmol/ml. The peak increment of gastrin released by bombesin was 95 +/- 16, ranatensin 22 +/- 6, litorin 18 +/- 4, and meal 39 +/- 5 fmol/ml. Bombesin caused significantly greater release of gastrin than a meal, litorin or ranatensin (P less than 0.01). Basal gastric secretion was 23 +/- 4 microequiv./min. B9 produced a peak acid secretion of 356 +/- 124 muequiv./min. There was no significant difference between the bombesin-like peptides (P less than 0.01). Basal plasma PP was 38 +/- 12 fmol/ml. B9 produced a peak PP increment of 600 +/- 50, litorin 137 +/- 36, ranatensin 98 +/- 11, and a meal 305 +/- 58 fmol/ml. B9 released significantly more PP than either litorin of ranatensin (P less than 0.01). The different amino acid sequences of the peptides are probably responsible for their potency. The substitution of a penultimate phenylalanine residue in litorin and ranatensin for leucine in bombesin does not prevent PP or gastrin release by bombesin-like peptides. Since bombesin-like peptides are widely distributed in the gastrointestinal tract of man and stimulate both acid and gut hormone secretion, it is possible that they might play a physiological role in the modulation of gastrointestinal function.     

Effect of the specific cholecystokinin-receptor antagonist loxiglumide on bombesin stimulated pancreatic enzyme secretion in man.

We have investigated the effects of the specific cholecystokinin (CCK) receptor antagonist loxiglumide on basal and bombesin stimulated pancreatic enzyme secretion, bilirubin output and plasma CCK release in six healthy subjects. The data were compared with those obtained in control experiments where saline was infused instead of loxiglumide. Basal amylase output (4.7 +/- 0.8 kU/45 min), trypsin output (2.9 +/- 0.8 kU/45 min) and bilirubin output (7.7 +/- 2.8 mmol/45 min) gradually declined during infusion of loxiglumide to values of 1.3 +/- 0.3 kU/45 min, 0.5 +/- 0.1 kU/45 min and 0.4 +/- 0.0 mmol/45 min, respectively, reaching statistical significance (P less than 0.05) in the 30 to 45-min period after the start of the loxiglumide infusion. In the control experiments saline infusion failed to influence basal amylase, trypsin and bilirubin output, while bombesin stimulated amylase output from 4.7 +/- 0.8 kU/45 min to 25.1 +/- 5.1 kU/45 min (P less than 0.05), trypsin output from 2.9 +/- 0.8 kU/45 min to 11.6 +/- 2.0 kU/45 min (P less than 0.05) and bilirubin output from 7.7 +/- 2.8 mmol/45 min to 68.0 +/- 16.0 mmol/45 min (P less than 0.05). Loxiglumide failed to significantly influence bombesin stimulated amylase output (36.7 +/- 9.0 kU/45 min) and trypsin output (8.3 +/- 2.9 kU/45 min), but almost abolished bilirubin output (9.7 +/- 3.6 mmol/45 min) (P less than 0.05). Basal plasma CCK (2.4 +/- 0.1 pM) was not significantly influenced by loxiglumide (2.4 +/- 0.2 pM).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of bombesin and gastrin-releasing peptide on the release of gastric inhibitory polypeptide and insulin in rats

The objective of this study was to determine whether bombesin- or gastrin-releasing peptide-induced release of insulin occurs before or after the release of gastric inhibitory polypeptide (GIP) in rats. The present results demonstrate that GIP release occurs before insulin release and suggest that bombesin-like peptides and GIP interact to stimulate insulin secretion.     

The effect of atropine and vagal stimulation on the release of neurotensin-like immunoreactivity in man

This study investigated the food stimulated release of neurotensin-like immunoreactivity (NTLI) in man with and without the administration of atropine, and the influence of vagal stimulation by modified sham feeding and insulin hypoglycaemia. NTLI was measured, after ethanol extraction, by specific C- and N-terminally directed antisera. With both a liquid fat meal and a mixed meal an early peak of NTLI occurred. The mixed meal also produced a second sustained rise in plasma NTLI. An intramuscular injection of 0.6 mg atropine sulphate abolished the early peak, but had no effect on the late peak. Modified sham feeding and insulin hypoglycaemia did not release NTLI. We conclude that it is possible that a cholinergic non-vagal mechanism is responsible for the early phase of food stimulated release of NTLI in man, and that the second sustained rise may be cholinergically independent.     

Stimulatory effect of intravenous calcium on pancreatic polypeptide secretion in man

In the present work we have examined the effect of i.v. calcium administration on the secretion of human pancreatic polypeptide (hPP) in normal subjects. The infusion of calcium glucono-galactono-gluconate, as to deliver 10 mg of calcium element per kilogram of body weight in two hours, was followed by a progressive elevation of plasma hPP which attained values two-fold those of the basal levels. This finding demonstrates that calcium behaves as a pancreatic polypeptide secretagogue in man.