Effects of an antral mucosectomy, L-364,718 and atropine on cephalic phase of gastric and pancreatic secretion in dogs

Food anticipatory hormonal responses: A systematic review of animal and human studies

Food anticipatory hormonal responses (cephalic responses) are proactive physiological processes, that allow animals to prepare for food ingestion by modulating their hormonal levels in response to food cues. This process is important for digesting food, metabolizing nutrients and maintaining glucose levels within homeostasis. In this systematic review, we summarize the evidence from animal and human research on cephalic responses. Thirty-six animal and fifty-three human studies were included. The majority (88 %) of studies demonstrated that hormonal levels are changed in response to cues previously associated with food intake, such as feeding time, smell, and sight of food. Most evidence comes from studies on insulin, ghrelin, pancreatic polypeptide, glucagon, and c-peptide. Moreover, impaired cephalic responses were found in disorders related to metabolism and food intake such as diabetes, pancreatic insufficiency, obesity, and eating disorders, which opens discussions about the etiological mechanisms of these disorders as well as on potential therapeutic opportunities.

GABAA receptor currents in the dorsal motor nucleus of the vagus in females: influence of ovarian cycle and 5α-reductase inhibition

The dorsal motor nucleus of the vagus (DMV) contains the preganglionic motor neurons important in the regulation of glucose homeostasis and gastrointestinal function. Despite the role of sex in the regulation of these processes, few studies examine the role of sex and/or ovarian cycle in the regulation of synaptic neurotransmission to the DMV. Since GABAergic neurotransmission is critical to normal DMV function, the present study used in vitro whole cell patch-clamping to investigate whether sex differences exist in GABAergic neurotransmission to DMV neurons. It additionally investigated whether the ovarian cycle plays a role in those sex differences. The frequency of phasic GABAA receptor-mediated inhibitory postsynaptic currents in DMV neurons from females was lower compared with males, and this effect was TTX sensitive and abolished by ovariectomy (OVX). Amplitudes of GABAergic currents (both phasic and tonic) were not different. However, females demonstrated significantly more variability in the amplitude of both phasic and tonic GABAA receptor currents. This difference was eliminated by OVX in females, suggesting that these differences were related to reproductive hormone levels. This was confirmed for GABAergic tonic currents by comparing females in two ovarian stages, estrus versus diestrus. Female mice in diestrus had larger tonic current amplitudes compared with those in estrus, and this increase was abolished after administration of a 5α-reductase inhibitor but not modulation of estrogen. Taken together, these findings demonstrate that DMV neurons undergo GABAA receptor activity plasticity as a function of sex and/or sex steroids.NEW & NOTEWORTHY Results show that GABAergic signaling in dorsal vagal motor neurons (DMV) demonstrates sex differences and fluctuates across the ovarian cycle in females. These findings are the first to demonstrate that female GABAA receptor activity in this brain region is modulated by 5α-reductase-dependent hormones. Since DMV activity is critical to both glucose and gastrointestinal homeostasis, these results suggest that sex hormones, including those synthesized by 5α-reductase, contribute to visceral, autonomic function related to these physiological processes.

Varying postprandial abdominovagal and cardiovagal activity in normal subjects

BACKGROUND

Several studies have supported the hypothesis of different presentations in the autonomic nervous system (ANS) between cardiac and gastric vagal activity. Due to the regionality of the ANS, different responses among different organ systems to the same stimulation (such as a meal) are quite possible.

METHODS

In this study we monitored the postprandial changes of heart rate variability (HRV) and gastrointestinal (GI) hormones to determine whether both responded in a similar pattern. Twenty-two healthy volunteers (6 males and 16 females) were enrolled. After recording a baseline ECG rhythm, further recordings were made at 20 min intervals for 120 min after a test meal. Serum human pancreatic polypeptide (PP), leptin, and total and active ghrelin levels were measured.

KEY RESULTS

After the meal, HR increased significantly from baseline at each time point, except for 20 min after the meal. The high frequency (HF) power decreased significantly from 40 min to 120 min after the meal. In addition, the low frequency (LF) power also decreased significantly from 60 min to 120 min. However, the LF:HF ratio increased significantly from 20 min to 120 min. There was a marked increase (>2 fold) of PP at 20 min after the meal, and the increase was sustained throughout the test period.

CONCLUSIONS & INFERENCES

These findings suggest that HRV reflects cardiac, but not equivalently, abdominovagal activity. Therefore, HRV as an abdominovagal activity measurement in patients with GI functional problems should be used with caution, and other markers such as PP should be included.

Neuroendocrinology of gastric H+ and duodenal HCO3- secretion: the role of brain-gut axis

Gastric H+ and duodenal HCO3- secretions are precisely regulated by neuro-hormonal mechanisms at central and peripheral levels to match the rate of these secretions with the type of stimulation of sensory receptors in the head area (sight, smell, taste, etc.) and in the gastro-intestinal system. Two-way communication pathways operate between the brain and the gut, each comprising afferent fibers signaling sensory information from the gut to the brain and efferent fibers transmitting signals in opposite direction. Short intramural and long extramural reflexes are triggered as well as various gut hormones are released by feeding that "cooperate" with the "brain-gut axis" in the alteration of exocrine and endocrine gastro-duodenal secretion, motility and blood circulation. The malfunction of gastric or duodenal secretory mechanisms may lead to disturbances of gastric H+-pepsin or duodenal mucus-HCO3- secretion and to gastro-duodenal disorders and diseases. This review presents recent advances in pathophysiological mechanisms underlying gastro-duodenal secretory disorders.

The role of the pancreatic renin-angiotensin system in acinar digestive enzyme secretion and in acute pancreatitis

The pancreas contains a local renin-angiotensin system (RAS), which is subject to activation by experimental pancreatitis. In the exocrine pancreas, angiotensin II receptor subtypes AT1 and AT2 have been localized in the pancreatic ducts, blood vessels and acinar cells. We hypothesize that local RAS activities may have a potential role in regulating pancreatic acinar digestive enzyme secretion. The present study was designed to elucidate firstly the existence of RAS components in pancreatic acinar cells and their regulation by acute pancreatitis. Secondly, the differential roles of AT1 and AT2 receptors in controlling digestive enzyme secretion from dispersed functional pancreatic acini were also investigated. The mRNA levels of RAS components were assessed by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). Acinar secretions were assayed by the measurement of alpha-amylase and lipase activities. Induction of acute pancreatitis was achieved by hyperstimulation of two intraperitoneal (i.p.) injections of cerulein (50 microg/kg/h). Results from RT-PCR showed that the mRNA levels of the major RAS components (angiotensinogen, AT1 and AT2 receptors) were expressed in isolated rat pancreatic acinar cells, and they were upregulated during pancreatitis. Exogenous addition of angiotensin II could stimulate a dose-dependent release of digestive enzymes from the acinar cells. Administration of the selective AT1 receptor antagonist losartan significantly inhibited the acinar digestion enzyme secretion in both normal and pancreatitis-induced acini. However, a specific AT2 receptor blocker PD123319 did not exhibit such a suppressive effect. These data indicate the existence of an acinar RAS in the pancreas of potential importance in the physiological regulation of digestive enzyme secretion. The differential actions of AT1 and AT2 receptors and their upregulation may have clinical relevance to the pathogenesis and management of acute pancreatitis.

Cephalic phase of acid secretion involves activation of medullary TRH receptor subtype 1 in rats

Mechanisms involved in the cephalic phase of gastric acid secretion were studied in awake fasted rats with chronic gastric fistula and exposed to the sight and smell of chow for 30 min. Acid secretion was monitored using constant intragastric perfusion and automatic titration. Sham feeding induced a peak acid response reaching 82 +/- 7 micromol/10 min within 20 min compared with the average 22 +/- 2 micromol/10 min in controls. The sham-feeding response was abolished by intracisternal pretreatment with the TRH(1)-receptor antisense oligodeoxynucleotides or subcutaneous injection of atropine, whereas TRH(1) mismatch oligodeoxynucleotides had no effect. Serum gastrin was not altered by the sham feeding and increased by refeeding. Gastrin antibody did not block the rise in acid during sham feeding, although the net acid response was reduced by 47% compared with the control group. Glycine-gastrin antibody, indomethacin and nitro-l-arginine methyl ester had no effect. Atropine and gastrin antibody decreased basal acid secretion by 98 and 75%, respectively, whereas all other pretreatments did not. These results indicate that the cholinergic-dependent acid response to sham feeding is mediated by brain medullary TRH(1) receptors in rats.

Neuronal activation of brain vagal-regulatory pathways and upper gut enteric plexuses by insulin hypoglycemia

Neuronal activation of brain vagal-regulatory nuclei and gastric/duodenal enteric plexuses in response to insulin (2 U/kg, 2 h) hypoglycemia was studied in rats. Insulin hypoglycemia significantly induced Fos expression in the paraventricular nucleus of the hypothalamus, locus coeruleus, dorsal motor nucleus of the vagus (DMN), and nucleus tractus solitarii (NTS), as well as in the gastric/duodenal myenteric/submucosal plexuses. A substantial number of insulin hypoglycemia-activated DMN and NTS neurons were choline acetyltransferase and tyrosine hydroxylase positive, respectively, whereas the activated enteric neurons included NADPH- and vasoactive intestinal peptide neurons. The numbers of Fos-positive cells in each above-named brain nucleus or in the gastric/duodenal myenteric plexus of insulin-treated rats were negatively correlated with serum glucose levels and significantly increased when glucose levels were lower than 80 mg/dl. Acute bilateral cervical vagotomy did not influence insulin hypoglycemia-induced Fos induction in the brain vagal-regulatory nuclei but completely and partially prevented this response in the gastric and duodenal enteric plexuses, respectively. These results revealed that brain-gut neurons regulating vagal outflow to the stomach/duodenum are sensitively responsive to insulin hypoglycemia.

Implication of gastrin in cyclooxygenase-2 expression in Helicobacter pylori infected gastric ulceration

Gastroduodenal ulcerations have worldwide distribution and the infection with Helicobacter pylori (HP) has been implicated in pathogenesis of this disease. The HP infection is usually accompanied by hypergastrinemia and enhanced generation of prostaglandins (PG), both implicated in the pathogenesis of peptic ulcerations but no study has been undertaken to assess the relationship between the HP infection and coexpression of gastrin and cyclooxygenases (COX), the rate limiting enzymes in the PG production. Since HP infection, usually accompanying peptic ulcerations, results in increased release of gastrin, a potent gastric mitogen that might be capable to induce COX-2 and to generate PG, we decided 1) to compare the seroprevalence of HP and its cytotoxic protein, CagA, in gastric ulcer patients with those in age- and gender-matched controls; 2) to determine the gene expression of gastrin and its receptors (CCK(B)-R) at the margin of gastric ulcer and in the mucosa of antrum and corpus before and after successful eradication of HP, 3) to assess the plasma levels and gastric luminal contents of gastrin before and after HP eradication and 4) to examine the mRNA and enzyme protein expression of COX-1 and COX-2 as well as the PGE2 generation in ulcer margin tissue and gastric antral and fundic mucosa before and after the HP eradication. The trial material included 20 patients with gastric ulcer and 40 age- and gender-matched controls. Anti-HP and anti-CagA IgG seroprevalence was estimated by specific antisera using ELISA tests. Gene expressions of gastrin, CCK(B)-R, COX-1 and COX-2 were examined using RT-PCR with beta-actin as a reference and employing Western blotting for COX-2 expression, while gastrin and PGE2 were measured by RIA. All gastric ulcers were located at smaller curvature within the antral mucosal area. The seroprevalence of HP, especially that expressing CagA, was significantly higher in gastric ulcers (85%) than in controls (62.5%). Both gastrin and CCK(B)-R mRNA were detected by RT-PCR in ulcer margin and gastrin mRNA was overexpressed in remaining antral mucosa, while CCK(B)-R mRNA was overexpressed in fundic mucosa of HP infected patients. Similarly, COX-2 mRNA and protein were found in margin of gastric ulcer and in the HP infected antral and fundic mucosa but not in the mucosa of HP eradicated patients in whom ulcers completely healed and gastrin was expressed only in antrum, CCK(B)-R only in corpus, while COX-1 was detected both in antrum and corpus. HP positive gastric ulcer patients showed about three times higher levels of plasma immunoreactive gastrin and about 50% higher luminal gastrin contents than the HP negative controls and this increased plasma and luminal gastrin was normalized following the HP eradication. A significant fall in gastrin and CCK(B)-R mRNA expression was noticed six weeks after HP eradication in gastric antral and fundic mucosa, while COX-2 mRNA completely disappeared after this treatment. We conclude that 1) HP infected gastric ulcer margin coexpresses gastrin, its receptors (CCK(B)-R), and COX-2; 2) HP infection may be implicated in gastric ulceration via increased release of gastrin that could be responsible for the overexpression of COX-2 that in turn could help ulcer healing through the stimulation of mucosal cell growth, restoration of the glandular structure and angiogenesis in the ulcer area and 3) gastrin produced in HP infected antral mucosa seems to be involved in the induction of COX-2 and PG production by this enzyme and this may contribute to the ulcer healing.

Luminal Nalpha-methyl histamine stimulates gastric acid secretion in duodenal ulcer patients via releasing gastrin

Nalpha-methyl histamine is an unusual histamine metabolite which is produced in the stomach infected by Helicobacter pylori and which was shown in animals to stimulate gastric acid secretion and to release gastrin in vitro isolated G-cells, but no information is available regarding its influence on gastric secretion and gastrin release in duodenal ulcer patients before and after H. pylori eradication. In this study, we compared the effects of intragastric administration of single or graded doses of Nalpha-methyl histamine on gastric acid secretion and plasma gastrin levels in 16 male duodenal ulcer patients (aging from 35 to 48 years and weighing 65-82 kg) before and after the eradication of H. pylori. Furthermore, the gastric luminal histamine and gastrin contents were determined before and after H. pylori eradication. In H. pylori-infected duodenal ulcer patients, the intragastric application of Nalpha-methyl histamine failed to affect gastric acid secretion or plasma gastrin levels. Following eradication of H. pylori, gastric luminal histamine and gastrin, and both basal gastric acid secretion and plasma gastrin levels, were significantly reduced. Nalpha-methyl histamine given intragastrically in graded doses to such H. pylori-eradicated duodenal ulcer patients was found to increase dose-dependently gastric acid output reaching at a dose of 5 mg, about 80% of histamine maximum induced by i.v. infusion of 25 microg/kg h of histamine dihydrochloride. We conclude that Nalpha-methyl histamine is a potent luminally active stimulant of gastrin release and gastric acid secretion in H. pylori-eradicated patients when luminal histamine is low but is not effective in H. pylori infected patients when luminal histamine is enhanced, possibly due to desensitization of gastrin (G-cells) and acid-producing (parietal) cells by Nalpha-methyl histamine produced excessively in H. pylori-infected stomach.

Helicobacter pylori-gastrin link in MALT lymphoma

BACKGROUND

There is accumulating evidence for the role of Helicobacter pylori in the development of gastric cancer as well as of lymphomas that arise in mucosa-associated lymphoid tissue (MALT). We reported recently that gastric cancer patients show high prevalence of cagA-positive H. pylori and express gastrin and gastrin receptors enabling them to stimulate tumour growth in autocrine fashion.

AIMS

Since the H. pylori infection is considered to be more strongly associated with MALT lymphoma than with gastric cancer, we decided to determine the gastrin and its receptors' mRNA expression and gastrin content in this tumour as well as the release of this hormone both into plasma and gastric lumen. Twenty MALT lymphoma patients were compared with 100 age- and gender-matched controls with similar dyspeptic symptoms.

RESULTS

The overall H. pylori seropositivity in MALT lymphoma was about 90% and CagA positivity was 70%, compared to 56% and 33%, respectively, in controls. The serum gastrin in MALT lymphoma was about sixfold higher than in controls while gastric luminal gastrin in these patients was over 70 times higher than in controls. Gastrin content in tumour was about 10-fold higher than in antral mucosa. Gastrin and gastrin-receptor (CCKB-receptor) mRNA were detected by reverse transcriptase-polymerase chain reaction in cancer tissue whilst in the fundic and antral mucosa, only enhanced expression of CCKB-receptor mRNA and gastrin mRNA was detected, respectively. Histamine stimulation in MALT lymphoma induced acid secretion that was only about 30% of control value due to atrophic gastritis. This study confirms an important role of CagA-positive H. pylori in the pathogenesis of MALT lymphoma and shows that this lymphoma is capable of synthesizing and releasing potent growth promoting gastrin, possibly due to the action on G-cells of H. pylori-originated Nalpha-methyl histamine and cytokines (tumour necrosis factor alpha and interleukin-8).

CONCLUSIONS

Gastric MALT lymphoma is closely linked to CagA-positive H. pylori infection. Gastrin and its receptors may be implicated in the pathogenesis of gastric lymphoma.

Canine vagus nerve stores cholecystokinin-58 and -8 but releases only cholecystokinin-8 upon electrical vagal stimulation

Cholecystokinin-58 has been shown to be the major form of cholecystokinin (CCK) released to the circulation upon lumenal stimulation of the small intestine in humans and dogs. In anesthetized dogs, electrical vagal stimulation evokes pancreatic exocrine secretion that is in part mediated through the release of CCK. We studied the molecular form of CCK stored in canine vagus nerves and that released into circulation upon electrical vagal stimulation. Gel filtration and radioimmunoassay of the water and acid extracts of canine vagus nerves indicated CCK-8 (35%) and CCK-58 (65%) as the major molecular forms in the vagus nerve. Both forms of CCK isolated from the vagal extracts were equally bioactive as the standard CCK-8 and CCK-58, respectively, in stimulation of amylase release from isolated rat pancreatic acini. Analysis of plasma collected after electrical vagal stimulation indicated that CCK-8 is the only form released into the circulation. The release of CCK-8 upon electrical vagal stimulation was not affected by application of lidocaine to the upper small intestinal mucosa, suggesting that it was released from vagal nerve terminals.

Intestinal fat-induced inhibition of meal-stimulated gastric acid secretion depends on CCK but not peptide YY

Fat in small intestine decreases meal-stimulated gastric acid secretion and slows gastric emptying. CCK is a mediator of this inhibitory effect (an enterogastrone). Because intravenously administered peptide YY (PYY) inhibits acid secretion, endogenous PYY released by fat may also be an enterogastrone. Four dogs were equipped with gastric, duodenal, and midgut fistulas. PYY antibody (anti-PYY) at a dose of 0.5 mg/kg or CCK-A receptor antagonist (devazepide) at a dose of 0.1 mg/kg was administered alone or in combination 10 min before the proximal half of the gut was perfused with 60 mM oleate or buffer. Acid secretion and gastric emptying were measured. We found that 1) peptone-induced gastric acid secretion was inhibited by intestinal fat (P < 0.0001), 2) inhibition of acid secretion by intestinal fat was reversed by CCK-A receptor antagonist (P < 0.0001) but not by anti-PYY, and 3) slowing of gastric emptying by fat was reversed by CCK-A antagonist (P < 0. 05) but not by anti-PYY. We concluded that inhibition of peptone meal-induced gastric acid secretion and slowing of gastric emptying by intestinal fat depended on CCK but not on circulating PYY.

Gastrin partially mediates insulin-induced acid secretion in dogs

A monoclonal antibody to gastrin was used to study the role of circulating gastrin in mediating insulin-stimulated acid output. On separate days, seven adult dogs with chronic gastric fistulas were pretreated i.v. with either 1) 7 mg of a gastrin monoclonal antibody (mAb 28.2); 2) 12.5 micrograms/kg atropine; 3) mAb 28.2 and atropine together; or 4) vehicle (0.1% canine serum albumin in 0.15 M NaCl). Thirty minutes later, acid secretion was stimulated by insulin (0.5 U/kg, i.v.), followed in 2 h by a 1-h infusion of histamine (40 micrograms/kg/h, i.v.). Acid output (mmol/15 min) in gastric effluent collected through the gastric fistula was determined by titration with 0.2 N NaOH to pH 7.0. Plasma gastrin was measured by radioimmunoassay. Plasma glucose was measured by a glucose oxidase method on an auto analyzer. Insulin induced a profound hypoglycemia (55 +/- 8 mg/dl) that coincided with a marked increase in acid output to 7.1 +/- 0.6 mmol/30 min by 45 min after injection. MAb 28.2 pretreatment and atropine pretreatment reduced insulin-stimulated acid outputs to 2.7 +/- 0.7 mmol/30 min and to 0.6 +/- 0.2 mmol/ 30 min, respectively. Acid output after combined pretreatment (0.5 +/- 0.2 mmol/30 min) was not significantly different than after atropine alone. Histamine-stimulated acid output (15.8 +/- 2.5 mmol/30 min) was not significantly reduced by any pretreatment. Insulin injection increased circulating gastrin concentrations to 32 +/- 7 fmol/ml, which was not significantly affected by atropine (39 +/- 9 fmol/ml). This study demonstrates that, in dogs, a significant part of insulin-stimulated acid secretion is mediated by circulating gastrin.

Advantages and disadvantages of current diagnostic tests for the detection of Helicobacter pylori

Current tests used to detect Helicobacter pylori are either invasive (histological detection, culture, the polymerase chain reaction (PCR), smear examination) or non-invasive (serology, 13C-urea breath test). These tests vary in their sensitivity and specificity, and the choice of test will depend on the situation, for example, whether the test is to detect infection or the success of eradication treatment. The accuracy of histological tests depends, to a large degree, on the expertise of the pathologist, while the accuracy of culture can depend on the conditions in which the specimen is transported and processed. When performed under optimal conditions, both techniques give very good results. The PCR test has similar sensitivity and specificity to histological and culture tests but a strict protocol must be followed to avoid contamination with H. pylori DNA. The rapid urease test (with a reading taken 1 hour later) is suitable for diagnosis before treatment but its sensitivity decreases after treatment. Smear examination has limited sensitivity. The urea breath test and serology (specific IgG detected by enzyme-linked immunosorbent assay with purified antigens) have sensitivities close to those using the best of the biopsy methods. Other points to consider when selecting a test are its availability, the rapidity of the results (which can range from a few minutes to 2 weeks), possibilities for retrospective analysis, quantification and the detection of pathogenic properties, the globality of certain tests that present an overall picture of the stomach, thus avoiding errors in sampling, and the cost of the test. Important added value can be gained from certain tests: histology allows evaluation of the status of the mucosa, culture allows strain typing and tests for antibiotic susceptibility, and the breath test can confirm successful eradication without endoscopy. When the diagnostic tests are performed correctly, most of them are highly accurate.

The involvement of endogenous nitric oxide in vagal-cholinergic stimulation of exocrine and endocrine pancreas in dogs

Previous studies showed that nitric oxide (NO), synthesized from L-arginine (L-arg) by NO synthase (NOS) in vascular epithelium and nerve terminals, affects exocrine pancreatic secretion, but its role in control of endocrine pancreas has not been studied. In this study, the role of NO in the control of pancreatic secretion in response to vagal-cholinergic stimulation and duodenal infusion of nutrients was determined in conscious dogs with chronic pancreatic fistulas. Sham feeding (SF), urecholine iv infusion, and duodenal perfusion with nutrients were used to stimulate the pancreatic protein secretion, and insulin and glucagon release in tests without and with iv infusion of NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase, L-arg, a substrate of NOS, or their combination was used. SF, urecholine, and duodenal nutrient resulted in the stimulation of pancreatic protein secretion reaching, respectively, 50, 20, and 42% of cerulein maximum. Infusion of L-arg almost doubled the basal protein secretion and tended to increase the secretory response to SF and duodenal nutrient. After infusion of L-NNA, the pancreatic secretory responses to SF, urecholine, and duodenal nutrient were inhibited by about 70, 30, and 75%, respectively. When L-arg was combined with L-NNA, the reduction in pancreatic secretion by L-NNA was significantly attenuated. SF resulted in a significant rise in plasma insulin and glucagon, and this response was completely abolished by L-NNA infusion. Urecholine and duodenal nutrient also resulted in a marked increment in plasma insulin and glucagon, the insulin (but not glucagon) increment being abolished by the pretreatment with L-NNA and reversed by the addition of L-arg.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of endogenous nitric oxide in the control of gastric acid secretion, blood flow and gastrin release in conscious dogs

Nitric oxide (NO) was shown to mediate gastric hyperemia following secretory stimulation but its role in the control of gastric secretion has not been clarified. Secretory studies were carried out on conscious dogs with chronic gastric fistula, Heidenhain pouch and esophageal fistula, while changes in gastric blood flow were measured in the mucosa of Heidenhain pouuch by laser Doppler flowmetry. Plasma gastrin was determined by radioimmunoassay. Infusion of NG-nitro-L-arginine (L-NNA) (bolus i.v. injection of 2.5 mg/kg followed by infusion of 0.5 mg/kg/h), a potent inhibitor of nitric oxide synthase, failed to affect basal gastric secretion or plasma gastrin level but suppressed an increase of this secretion induced by sham-feeding, ordinary meat feeding or i.v. infusion of bombesin (0.5 microgram/kg/h), pentagastrin (4 micrograms/kg/h) or histamine (40 micrograms/kg/h). In tests with feeding and bombesin infusion, L-NNA caused a significant and dose-dependent reduction in plasma gastrin levels. The inhibition by L-NNA of gastric acid secretory response to pentagastrin, histamine or feeding was accompanied by a decline in blood flow. Addition of L-arginine (bolus i.v. dose of 50 mg/kg followed by infusion of 5 mg/kg/h) significantly attenuated the L-NNA induced inhibition of gastric secretion and the reduction in plasma gastrin response as well as in the fall of gastric blood flow. We conclude that endogenous nitric oxide affects the gastric secretion and that this effect is mediated, at least in part, by the changes in the gastrin release and gastric blood flow.

Cholecystokinin in the control of gastric acid secretion in man

This study was designed to determine the role of cholecystokinin in the control gastric acid secretion in men using loxiglumide, a specific cholecystokinin receptor blocker. Three groups of healthy subjects (A, B, and C) were used; group A--for studies with postprandial gastric secretion, group B--for studies with exogenous gastric secretagogues and group C--for 12 hour intragastric pH-metry. Cephalic phase stimulated by modified sham feeding in group A subjects increased gastric acid secretion to about 50% of pentagastrin maximum and the treatment with loxiglumide in a standard dose (20 mumol/kg iv loading dose plus infusion of 20 mumol/kg/h afterwards) failed to affect this secretion. Gastric acid response to a 5% peptone meal instilled intragastrically greatly enhanced gastric acid secretion and plasma gastrin concentration but the addition of loxiglumide in the standard dose resulted in further increase in both gastric acid and plasma gastrin responses to peptone meal. Infusion of caerulein in gradually increasing doses (15-120 pmol/kg/h) and gastrin releasing peptide (25-200 pmol/kg/h) resulted in a dose dependent stimulation of gastric acid secretion reaching about 35% and 25% of maximum attained with pentagastrin. When loxiglumide was added in a standard dose, the acid responses to caerulein and gastrin releasing peptide were further increased two to three fold attaining the peak reaching, respectively, about 100% and 50% of pentagastrin maximum. In group C subjects, 12 hour pH-metry revealed the usual increase in gastric pH after each meal in tests with placebo. Loxiglumide (1200 mg tablets tid, po) resulted in significantly lower pH after each meal and this was accompanied by significantly higher gastrin responses than in placebo tests. We conclude that cholecystokinin released by peptone meal, ordinary meals or gastrin releasing peptide exerts a potent inhibitory influence on gastric acid secretion and gastrin release in men and this inhibition involves subtype A cholecystokinin receptors.

Role of endogenous nitric oxide in the control of canine pancreatic secretion and blood flow

BACKGROUND

Endogenous nitric oxide has been implicated in the control of mesenteric circulation, but its role in the control of pancreatic blood flow and exocrine pancreatic secretion has not been studied.

METHODS

Secretory studies were performed on conscious dogs with chronic pancreatic fistulas, and changes in pancreatic blood flow were measured by laser Doppler flowmetry in anesthetized animals.

RESULTS

Infusion of NG-nitro-L-arginine did not affect basal pancreatic protein secretion but suppressed an increase of this secretion induced by L-arginine but not that induced by glyceryl trinitrate. Sham-feeding, meal feeding, and infusion of secretin plus cholecystokinin induced pancreatic protein outputs reaching, respectively, 30%, 74%, and 50% of cerulein maximum in these dogs. Infusion of NG-nitro-L-arginine caused a profound inhibition of these secretions, whereas the addition of L-arginine reversed this inhibition in part. NG-nitro-L-arginine or L-arginine added to the incubation medium of isolated canine pancreatic acini did not affect basal or cholecystokinin-induced amylase release. In anesthetized dogs, infusion of NG-nitro-L-arginine caused a significant reduction in the pancreatic blood flow both while resting and following stimulation with secretin plus cholecystokinin but did not affect this flow in animals treated with glyceryl trinitrate. Addition of L-arginine attenuated the decrease in pancreatic blood flow and the increase in systemic blood pressure caused by NG-L-nitro-arginine.

CONCLUSIONS

Endogenous NO affects pancreatic secretion probably through the changes in the vascular bed.

Octreotide, a long-acting somatostatin analog, in the management of postoperative dumping syndrome. An update

Severe long-term complaints of dumping occur in a small number of patients after gastric surgery. Dietary modification, fiber preparations, and medical therapy are often ineffective. In these severely affected patients administration of the somatostatin analog octreotide before meals appears to be a promising new strategy. The effects of octreotide on both gastrointestinal transit time and hormonal changes appear to contribute to the benefits seen in dumping syndrome. However, as the majority of studies conducted have employed only a single dose of octreotide, careful long-term assessment of the nutritional and metabolic effects will be required. Recent results suggest that octreotide may be administered up to 2 hr before a meal and therefore has a sufficiently long duration of action to be of practical long-term use. Moreover, general improvements in life-style, as well as beneficial effects on symptoms, have been reported with long-term treatment, although the potential development of diarrhea will require careful monitoring. The development of an oral or nasal formulation should further improve the practical application of octreotide as a treatment for dumping syndrome.

Slow gastric emptying induced by high fat content of meal accelerated by cisapride administered rectally

The evaluation of agents potentially accelerating gastric emptying in gastric stasis syndromes is time-consuming. Since a previous study showed that emptying is slowed after antecedent fat ingestion and intravenous cisapride abolishes this effect, we investigated whether emptying delayed by fat incorporated into a meal is reversed by cisapride and thus could serve as a model for such evaluations. Twelve healthy males received, under double-blind conditions, 30 mg cisapride rectally or placebo, and 3 hr thereafter a semisolid meal of low (9.2 g) or high (37.9 g) fat content. The sequence of combinations placebo/low-fat meal, placebo/high-fat meal, and cisapride/high-fat meal was randomized. Gastric emptying and antral motility were recorded scintigraphically. After placebo/high-fat, emptying was significantly slower (P less than 0.05) than after placebo/low-fat. After cisapride/high-fat, emptying was significantly faster (P less than 0.01) than after placebo/high-fat and similar to that after placebo/low-fat. Antral motility was little affected. The slow emptying of a high-fat meal thus seems a suitable model for the evaluation of prokinetic drug effects.

Gastric protection by nocloprost against aspirin damage in humans. Possible role of epidermal growth factor

Ten healthy young male subjects took part in a double-blind, placebo-controlled crossover study to assess the effects of nocloprost on gastric microbleeding and endoscopic mucosal injury induced by the administration of aspirin (2.5 g). In addition, basal and pentagastrin-induced gastric acid and pepsin secretion and salivary and plasma contents of epidermal growth factor (EGF) were measured after placebo plus aspirin or nocloprost plus aspirin treatment in these subjects. Nocloprost (100 micrograms/dose) significantly reduced spontaneous gastric microbleeding and almost completely prevented gastric mucosal injury induced by aspirin. Nocloprost failed to affect basal and pentagastrin-stimulated gastric acid and pepsin secretion but increased significantly the salivary outputs and plasma concentrations of EGF. In conclusion, nocloprost is effective in preventing gastric injury by aspirin even at a non-antisecretory dose, and this protection may involve an excessive release of EGF.