Peptone stimulates CCK-releasing peptide secretion by activating intestinal submucosal cholinergic neurons

Chronic Intestinal Pseudo-Obstruction: Is There a Connection with Gut Microbiota?

Chronic intestinal pseudo-obstruction (CIPO) is a rare clinical syndrome characterized by severe impairment of gastrointestinal (GI) motility, and its symptoms are suggestive of partial or complete intestinal obstruction in the absence of any lesion restricting the intestinal lumen. Diagnosis and therapy of CIPO patients still represent a significant challenge for clinicians, despite their efforts to improve diagnostic workup and treatment strategies for this disease. The purpose of this review is to better understand what is currently known about the relationship between CIPO patients and intestinal microbiota, with a focus on the role of the enteric nervous system (ENS) and the intestinal endocrine system (IES) in intestinal motility, underling the importance of further studies to deeply understand the causes of gut motility dysfunction in these patients.

Synaptic Plasticity and Synchrony in the Anterior Cingulate Cortex Circuitry: A Neural Network Approach to Causality of Chronic Visceral Pain and Associated Cognitive Deficits

Human brain imaging studies have demonstrated the importance of cortical neuronal networks in the perception of pain in patients with functional bowel disease such as irritable bowel syndrome (IBS).Studies have identified an enhanced response in the anterior cingulate cortex (ACC) to colorectal distension in viscerally hypersensitive (VH) rats. Electrophysiological recordings show long-lasting potentiation of local field potential (LFP) in the medial thalamus (MT)-ACC synapses in VH rats. Theta burst stimulation in the MT reliably induced long-term potentiation (LTP) in the MT-ACC pathway in normal rats, but was occluded in the VH state. Further, repeated tetanization of MT increased ACC neuronal activity and visceral pain responses of normal rats, mimicking VH rats. These data provide conclusive evidence that chronic visceral pain is associated with alterations of synaptic plasticity in the ACC circuitry. The ACC synaptic strengthening may engage signal transduction pathways that are in common with those activated by electrical stimulation, and serve as an attractive cellular model of functional visceral pain.Evidences have shown that most patients with IBS have psychiatric comorbidity. Using rat gambling task (RGT), we discovered an impairment of decision-making behavior in VH rats. Electrophysiological study showed a reduction of LTP in the basolateral amygdala (BLA)-ACC synapses in VH rats. Multiple-electrode array recordings of local field potential (LFP) in freely behaving rats revealed that chronic visceral pain led to disruption of ACC spike timing and BLA local theta oscillation. Finally, cross-correlation analysis revealed that VH was associated with suppressed synchronization of theta oscillation between the BLA and ACC, indicating reduced neuronal communications between these two regions. These data suggest that functional disturbances in BLA-ACC neural circuitry may be relevant causes for the deficits in decision-making in chronic pain state.The viscero-sensation is a faculty of perception that does not depend upon any outward sense, but acts to influence the elicited behavioral response. Clinically, vagus nerve stimulation (VNS) has shown several beneficial effects for mood enhancement. Our recent study characterized that VNS facilitates decision-making and unveiled several important roles for VNS in regulating LFP and spike phases, as well as enhancing spike-phase coherence between key brain areas involved in cognitive performance.It is conceivable that the visceral pain experience may be better explained as a biopsychosocial model of pain and reflected in a matrix of neuronal structures. Understanding of desynchrony in the ACC network and cognitive deficits is likely to provide exciting and powerful future treatment for chronic visceral pain related debilitating mood, anxiety, and cognitive disorders.

The Diverse Metabolic Roles of Peripheral Serotonin

Serotonin (5-hydroxytryptamine or 5-HT) is a multifunctional bioamine with important signaling roles in a range of physiological pathways. Almost all of the 5-HT in our bodies is synthesized in specialized enteroendocrine cells within the gastrointestinal (GI) mucosa called enterochromaffin (EC) cells. These cells provide all of our circulating 5-HT. We have long appreciated the important contributions of 5-HT within the gut, including its role in modulating GI motility. However, evidence of the physiological and clinical significance of gut-derived 5-HT outside of the gut has recently emerged, implicating 5-HT in regulation of glucose homeostasis, lipid metabolism, bone density, and diseases associated with metabolic syndrome, such as obesity and type 2 diabetes. Although a new picture has developed in the last decade regarding the various metabolic roles of peripheral serotonin, so too has our understanding of the physiology of EC cells. Given that they are scattered throughout the lining of the GI tract within the epithelial cell layer, these cells are typically difficult to study. Advances in isolation procedures now allow the study of pure EC-cell cultures and single cells, enabling studies of EC-cell physiology to occur. EC cells are sensory cells that are capable of integrating cues from ingested nutrients, the enteric nervous system, and the gut microbiome. Thus, levels of peripheral 5-HT can be modulated by a multitude of factors, resulting in both local and systemic effects for the regulation of a raft of physiological pathways related to metabolism and obesity.

Vagus Nerve Stimulation Alters Phase Synchrony of the Anterior Cingulate Cortex and Facilitates Decision Making in Rats

Vagus nerve stimulation (VNS) can enhance memory and cognitive functions in both rats and humans. Studies have shown that VNS influenced decision-making in epileptic patients. However, the sites of action involved in the cognitive-enhancement are poorly understood. By employing a conscious rat model equipped with vagus nerve cuff electrode, we assess the role of chronic VNS on decision-making in rat gambling task (RGT). Simultaneous multichannel-recordings offer an ideal setup to test the hypothesis that VNS may induce alterations of in both spike-field-coherence and synchronization of theta oscillations across brain areas in the anterior cingulate cortex (ACC) and basolateral amygdala (BLA). Daily VNS, administered immediately following training sessions of RGT, caused an increase in 'good decision-maker' rats. Neural spikes in the ACC became synchronized with the ongoing theta oscillations of local field potential (LFP) in BLA following VNS. Moreover, cross-correlation analysis revealed synchronization between the ACC and BLA. Our results provide specific evidence that VNS facilitates decision-making and unveils several important roles for VNS in regulating LFP and spike phases, as well as enhancing spike-phase coherence between key brain areas involved in cognitive performance. These data may serve to provide fundamental notions regarding neurophysiological biomarkers for therapeutic VNS in cognitive impairment.

Hyperosmolarity in the small intestine contributes to postprandial ghrelin suppression

Plasma levels of the orexigenic hormone ghrelin are suppressed by meals with an efficacy dependent on their macronutrient composition. We hypothesized that heterogeneity in osmolarity among macronutrient classes contributes to these differences. In three studies, the impact of small intestinal hyperosmolarity was examined in Sprague-Dawley rats. In study 1, isotonic, 2.5×, and 5× hypertonic solutions of several agents with diverse absorption and metabolism properties were infused duodenally at a physiological rate (3 ml/10 min). Jugular vein blood was sampled before and at 30, 60, 90, 120, 180, 240, and 300 min after infusion. Plasma ghrelin was suppressed dose dependently and most strongly by glucose. Hyperosmolar infusions of lactulose, which transits the small intestine unabsorbed, and 3-O-methylglucose (3-O-MG), which is absorbed like glucose but remains unmetabolized, also suppressed ghrelin. Glucose, but not lactulose or 3-O-MG, infusions increased plasma insulin. In study 2, intestinal infusions of hyperosmolar NaCl suppressed ghrelin, a response that was not attenuated by coinfusion with the neural blocker lidocaine. In study 3, we reconfirmed that the low-osmolar lipid emulsion Intralipid suppresses ghrelin more weakly than isocaloric (but hypertonic) glucose. Importantly, raising Intralipid's osmolarity to that of the glucose solution by nonabsorbable lactulose supplementation enhanced ghrelin suppression to that seen after glucose. Hyperosmolar ghrelin occurred particularly during the initial 3 postinfusion hours. We conclude that small intestinal hyperosmolarity 1) is sufficient to suppress ghrelin, 2) may combine with other postprandial mechanisms to suppress ghrelin, 3) might contribute to altered ghrelin regulation after gastric bypass surgery, and 4) may inform dietary modifications for metabolic health.

Nutrient sensing in the gut: new roads to therapeutics?

The release of gut hormones involved in the control of food intake is dependent on the acute nutritional status of the body, suggesting that chemosensory mechanisms are involved in the control of their release. G protein-coupled taste receptors similar to those in the lingual system, that respond to sweet, bitter, umami, and fatty acids, are expressed in endocrine cells within the gut mucosa, and coordinate, together with other chemosensory signaling elements, the release of hormones that regulate energy and glucose homeostasis. In health, these nutrient sensors are likely to function as inhibitors to excessive nutrient exposure, and their malfunction may be responsible for a variety of metabolic dysfunctions associated with obesity; they may thus be considered as new therapeutic targets.

Cholecystokinin enhances visceral pain-related affective memory via vagal afferent pathway in rats

Background

Pain contains both sensory and affective dimensions. Using a rodent visceral pain assay that combines the colorectal distension (CRD) model with the conditioned place avoidance (CPA) paradigms, we measured a learned behavior that directly reflects the affective component of visceral pain, and showed that perigenual anterior cingulate cortex (pACC) activation is critical for memory processing involved in long-term visceral affective state and prediction of aversive stimuli by contextual cue. Progress has been made and suggested that activation of vagal afferents plays a role in the behavioral control nociception and memory storage processes.

In human patients, electrical vagus nerve stimulation enhanced retention of verbal learning performance. Cholecystokinin-octapeptide (CCK), which is a gastrointestinal hormone released during feeding, has been shown to enhance memory retention. Mice access to food immediately after training session enhanced memory retention. It has been well demonstrated that CCK acting on vagal afferent fibers mediates various physiological functions. We hypothesize that CCK activation of vagal afferent enhances visceral pain-related affective memory.

Results

In the presented study, infusion of CCK-8 at physiological concentration combining with conditional training significantly increased the CRD-induced CPA scores, and enhanced the pain affective memory retention. In contrast, CCK had no effect on CPA induced by non-nociceptive aversive stimulus (U69,593). The physiological implications were further strengthened by the similar effects observed in the rats with duodenal infusion of 5% peptone, which has been shown to induce increases in plasma CCK levels. CCK-8 receptor antagonist CR-1409 or perivagal application of capsaicin abolished the effect of CCK on aversive visceral pain memory, which was consistent with the notion that vagal afferent modulates affective aspects of visceral pain. CCK does not change the nociceptive response (visceral pain sensitivity) and anterior cingulate cortex neuronal responses to CRD.

Conclusion

CCK activating vagal afferent C fibers enhances memory consolidation and retention involved in long-term visceral negative affective state. Thus, in a number of gastrointestinal disorders, such as irritable bowel syndrome, nutrient content may contribute to painful visceral perception by enhancing visceral aversive memory via acts on vagal afferent pathway.

Detecting sweet and umami tastes in the gastrointestinal tract

Information about nutrients is a critical part of food selection in living creatures. Each animal species has developed its own way to safely seek and obtain the foods necessary for them to survive and propagate. Necessarily, humans and other vertebrates have developed special chemosensory organs such as taste and olfactory organs. Much attention, recently, has been given to the gastrointestinal (GI) tract as another chemosensory organ. Although the GI tract had been considered to be solely for digestion and absorption of foods and nutrients, researchers have recently found taste-signalling elements, including receptors, in this tissue. Further studies have revealed that taste cells in the oral cavity and taste-like cells in the GI tract appear to share common characteristics. Major receptors to detect umami, sweet and bitter are found in the GI tract, and it is now proposed that taste-like cells reside in the GI tract to sense nutrients and help maintain homeostasis. In this review, we summarize recent findings of chemoreception especially through sweet and umami sensors in the GI tract. In addition, the possibility of purinergic transmission from taste-like cells in the GI tract to vagus nerves is discussed.

Duodenal diazepam‐binding protein expression and plasma cholecystokinin after alcoholic pancreatitis

OBJECTIVE

After the first acute alcohol-induced pancreatitis (AAIP) episode 46 % of patients will have a recurrent attack, but the pathophysiology is unclear. The hyperstimulation of the pancreas with cholecystokinin (CCK) induces acute pancreatitis. Alcohol induces temporary stimulation of the pancreas and CCK could be a mediator. CCK is regulated by releasing peptides - diazepam-binding protein (DBI) being a possible candidate. The aim of this study was to investigate the possible association between CCK plasma levels and DBI expression in patients with AAIP or its recurrence.

MATERIAL AND METHODS

The study comprised 44 subjects (mean age 42 years): A) Patients with a first episode of AAIP (n = 9); B) patients with three or more episodes of AAIP (n = 11); C) patients with a heavy alcohol consumption, with no detected AAIP (n = 11) and D) healthy controls (n = 13). CCK levels were measured by radioimmunoassay (RIA). Duodenal biopsies were analyzed for DBI mRNA and histology.

RESULTS

There was no significant difference in CCK plasma levels, DBI expression or CCK/DBI ratio between the groups.

CONCLUSIONS

There were no changes in fasting CCK plasma levels or DBI expression. This may suggest that they do not play a major role as risk factors for alcohol-induced pancreatitis.

Identification of a protein hydrolysate responsive G protein-coupled receptor in enterocytes

G protein-coupled receptors (GPCRs) have the potential to play a role as molecular sensors responsive to luminal dietary contents. Although such a role for GPCRs has been implicated in the intestinal response to protein hydrolysate, no GPCR directly involved in this process has been previously identified. In the present study, for the first time, we identified GPR93 expression in enterocytes and demonstrated its activation in these cells by protein hydrolysate with EC50 of 10.6 mg/ml as determined by the induction of intracellular free Ca2+. In enterocytes, GPR93 was synergistically activated by protein hydrolysate in combination with an agonist, oleoyl-l-alpha-lysophosphatidic acid (LPA), which activated the receptor in these enterocytes with EC50 of 7.9 nM. The increased intracellular Ca2+ by GPR93 activation was observed without the addition of a promiscuous Galpha protein and was pertussis toxin sensitive, which suggests Galpha(q)- and Galpha(i)-mediated pathways. Activated GPR93 also induced pertussis toxin-sensitive ERK1/2 phosphorylation. Both nuclear factor of activated T cells and 12-O-tetradecanoylphorbol 13-acetate responsive elements reporter activities were induced by protein hydrolysate in cells exogenously expressing GPR93. The peptidomimetic cefaclor by itself did not activate GPR93 but potentiated the protein hydrolysate response and further amplified the synergistic enhancement of GPR93 activation by protein hydrolysate and LPA. These data suggest that, physiologically, the composition of stimuli might determine GPR93 activity or its sensitivity toward a given activator and suggest a new mechanism of the regulation of mucosal cell proliferation and differentiation and hormonal secretion by dietary products in the lumen.

CCK inhibits the orexigenic effect of peripheral ghrelin

CCK and ghrelin exert antagonistic effects on ingestive behavior. The aim of the present study was to investigate the interaction between ghrelin and CCK administered peripherally on food intake and neuronal activity in specific hypothalamic and brain stem nuclei, as assessed by c-Fos-like immunoreactivity (c-FLI) in nonfasted rats. Ghrelin (13 μg/kg body wt) injected intraperitoneally significantly increased the cumulative food intake when measured at 30 min and 1 h after injection, compared with the vehicle group (2.9 ± 1.0 g/kg body wt vs. 1.2 ± 0.5 g/kg body wt, P < 0.028). Sulfated CCK octapeptide (CCK-8S) (2 or 25 μg/kg body wt) injected simultaneously blocked the orexigenic effect of ghrelin (0.22 ± 0.13 g/kg body wt, P < 0.001 and 0.33 ± 0.23 g/kg body wt, P < 0.0008), while injected alone, both doses of CCK-8S exerted a nonsignificant trend to reduce food intake. Ghrelin (13 μg/kg body wt ip) markedly increased the number of c-FLI-positive neurons per section in the arcuate nucleus (ARC) compared with vehicle (median: 31.35 vs. 9.86, P < 0.0001). CCK-8S (2 or 25 μg/kg body wt ip) had no effect on neuronal activity in the ARC, as assessed by c-FLI (median: 5.33 and 11.21 cells per section), but blocked the ghrelin-induced increase of c- fos expression in this area when both peptides were administered simultaneously (median: 13.33 and 12.86 cells per section, respectively). Ghrelin at this dose had no effect on CCK-induced stimulation of c- fos expression in the paraventricular nucleus of the hypothalamus and the nucleus of the solitary tract. These results suggest that CCK abolishes ghrelin-induced food intake through dampening increased ARC neuronal activity.

Hypothalamic regulation of pancreatic secretion is mediated by central cholinergic pathways in the rat

The vago-vagal reflex plays an important role in mediating pancreatic secretion evoked by cholecystokinin and non-cholecystokinin-dependent luminal factors. We hypothesize that the vago-vagal reflex mediating pancreatic secretion in the rat is under central control and regulated by cholinergic pathways in the hypothalamus. To test this hypothesis, we demonstrated that chronic decerebration decreased basal pancreatic enzyme secretion from 318 +/- 12 to 233 +/- 9 mg h-1 and reduced the net increase in pancreatic secretion stimulated by intraduodenal infusion of 5 % peptone and hypertonic NaCl by 54 % and 45 %, respectively. Intracerebroventricular administration of methscopolamine (MSCP, 50 nmol (5 mul)-1), a blood-brain barrier-impermeant cholinergic muscarinic receptor antagonist, evoked results similar to those achieved by chronic decerebration. To localize the sites of action, we demonstrated that microinjection of MSCP (20 nmol) into the lateral hypothalamic nucleus or the paraventricular nucleus resulted in inhibition of both basal pancreatic protein secretion and luminally stimulated pancreatic secretion by 48 % and 52 %, respectively. Intracerebroventricular injection of hemicholinium-3 at doses known to deplete the endogenous ACh store produced similar inhibitory results. In addition, microinjection of ACh (5 pmol) or the muscarinic M1 receptor agonist McN-A-343 (30 ng) into the lateral hypothalamic nucleus increased pancreatic secretion over basal levels by 46 % and 40 %, respectively. Selective lesions of lateral septal cholinergic neurons decreased basal pancreatic secretion and inhibited peptone-induced pancreatic secretion by 30 %. Destruction of the lateral parabrachial nucleus produced a 44 % inhibition of peptone-induced pancreatic section. Finally, microinjection of glutamate into the lateral septum or the lateral parabrachial nucleus stimulated vagal pancreatic efferent nerve firings from a basal level of 0 +/- 0.5 impulses (30 s)-1 to 4.5 +/- 0.5 and 14 +/- 2 impulses (30 s)-1, respectively, and pancreatic protein output increased 50 % and 84 % over basal levels. Administration of MSCP to the paraventricular nucleus eliminated these effects. These observations suggest that cholinergic neurons of the lateral septum and lateral parabrachial nucleus regulate pancreatic secretion. Further, cholinergic input from the lateral parabrachial nucleus to the hypothalamus plays a major role in the modulation of vagal pancreatic efferent nerve activity and pancreatic secretion evoked by the vago-vagal reflex.

Secretagogue activities in cod (Gadus morhua) and shrimp (Penaeus aztecus) extracts and alcalase hydrolysates determined in AR4-2J pancreatic tumour cells

Peptides with gastrin immunoreactivity were measured in cod muscle (Gadus morhua) and shrimp heads (Penaeus aztecus) extracts and alcalase hydrolysates and separated by two chromatographic steps. Secretagogue activities present in crude extracts fractions were examined with or without specific antagonists of CCK receptors in AR4-2J cells. Several sub-fractions significantly stimulate amylase release, up to 110%. These stimulatory effects could be completely inhibited by the presence of L 365, 260 specific antagonist of CCKB receptors. After hydrolysis of the raw material, the samples were partially fractionated by two chromatographic steps and potential active fractions detected by a gastrin-CCK radioimmunoassay. The molecular masses of the active fractions were lower than for the extracts. Stimulation of amylase release was higher than with extracts, and the inhibition by L 365, 260, less pronounced. These results show that some peptides remaining after hydrolysis or extraction still exert biological activities and have to be tested in nutritional studies.

Soybean beta-conglycinin peptone suppresses food intake and gastric emptying by increasing plasma cholecystokinin levels in rats

Cholecystokinin (CCK) is an important physiologic mediator that regulates satiety and gastric emptying. We demonstrated previously that soybean peptone acts directly on rat small intestinal mucosal cells to stimulate CCK release. In the present study, we examined the effects of beta-conglycinin, a major component of soy protein, and its peptone on food intake and gastric emptying after an intraduodenal infusion of beta-conglycinin peptone in relation to CCK release and interaction with the mucosal cell membrane. Intraduodenal infusion of beta-conglycinin peptone inhibited food intake in a dose-dependent manner, but that of whole soy peptone or camostat did not. The suppression of food intake by beta-conglycinin peptone was abolished by an intravenous injection of devazepide, a selective peripheral CCK receptor antagonist. The beta-conglycinin peptone infusion strongly suppressed gastric emptying with marked increases in portal CCK levels. We also observed that the beta-conglycinin peptone dose dependently and more potently stimulated CCK release from isolated dispersed mucosal cells of the rat jejunum than did beta-conglycinin itself. This stimulation corresponded to the binding activity of the peptide or protein to solubilized components of the rat jejunum membrane as evaluated by surface plasmon biosensor. These results indicate that beta-conglycinin peptone suppresses food intake, and this effect may be due to beta-conglycinin peptone in the lumen stimulating endogenous CCK release with direct acceptance to the intestinal cells.

Neural hormonal regulation of exocrine pancreatic secretion

Exocrine pancreatic secretion is regulated by hormone-hormonal and neural-hormonal interactions involving several regulatory peptides and neurotransmitter from the gut, the pancreas and the vagus nerve. The roles of the gastrointestinal peptides including secretin, CCK, neurotensin, motilin, PYY and pancreatic islet hormones including insulin, pancreatic polypeptide and somatostatin have been established. Interactions among secretin, CCK and neurotensin produce synergistic stimulatory effect. Motilin modulates the cyclic pattern of pancreatic secretion while local insulin provides a permissive role for the action of secretin and CCK at physiological concentration. Somatostatin, PYY and pancreatic polypeptide are inhibitory regulators, acting either on the release of secretin and CCK or on the action of the two stimulatory hormones. The vagal afferent-efferent pathway mediates the actions of many of these regulatory peptides, particularly of secretin and CCK. Acetylcholine and nitric oxide are the neurotransmitters known to mediate the actions of secretin and CCK. Serotonin (5-HT) released from enterochromaffin cells in the intestinal mucosa and nerve terminals of the enteric nervous system and intrapancreatic nerves may be involved in both stimulatory and inhibitory mechanism through its various receptor subtypes. 5-HT also mediates the action of secretin and CCK. The regulatory roles of neuropeptides, PACP and GRP, are now established, whereas those of others are being uncovered. Pancreatic juice provides both positive and negative feedback regulation of pancreatic secretion through mediation of both secretin- and CCK-releasing peptides. Three CCK-releasing peptides have been purified: monitor peptide from pancreatic juice, diazepam-binding inhibitor from porcine intestine, and luminal CCK-releasing factor from rat intestinal secretion. All have been shown to stimulate CCK release and pancreatic enzyme secretion. Pancreatic phospholipase A2 from pancreatic juice and intestinal secretion appears to function as a secretin-releasing peptide. However, the detailed map of neurohormonal regulatory pathways of exocrine pancreatic secretion is yet to be constructed.

Neuroendocrine control of intestinal mucosal mast cells under physiological conditions

Mast cells are involved in the pathogenesis of both allergies to food and inflammatory bowel disorders. In addition, there are several lines of evidence suggesting that mucosal mast cells also respond to intraluminal stimuli. Our aim was to identify neuroendocrine stimuli that could modify mucosal mast cell activity in the rat. Anaesthetized rats were prepared for duodenal perfusion and mast cell activation was measured by analysis of RMCP II concentration in the duodenal perfusate. Either buffered saline solution or a 5% ovalbumin hydrolysate (OVH) solution was infused into the duodenum. Subdiaphragmatic vagotomy or afferent ablation by intraluminal treatment with capsaicin diminished RMCP II concentration in basal conditions and significantly reduced the response to OVH, which in control animals induced a three-fold increase of the protease. The noradrenergic blockers phentholamine and propranolol significantly diminished RMCP II concentration in basal conditions and completely blocked the response to OVH. Intravenous infusion of cholecystokinin-related peptides also induced a response of mast cells. However, the response was different depending on the peptide. CCK-8 induced a slight increase of RMCP II, whereas both CCK-33 and gastrin induced a significant decrease in mast cell activity. These results show that intraluminal content modulates mucosal mast cell activity by complex mechanisms involving both nervous and endocrine pathway.

Intestinal serotonin acts as paracrine substance to mediate pancreatic secretion stimulated by luminal factors

We recently demonstrated that luminal factors such as osmolality, disaccharides, and mechanical stimulation evoke pancreatic secretion by activating 5-hydroxytryptamine subtype 3 (serotonin-3, 5-HT3) receptors on mucosal vagal afferent fibers in the intestine. We hypothesized that 5-HT released by luminal stimuli acts as a paracrine substance, activating the mucosal vagal afferent fibers to stimulate pancreatic secretion. In the in vivo rat model, luminal perfusion of maltose or hypertonic NaCl increased 5-HT level threefold in intestinal effluent perfusates. Similar levels were observed after intraluminal 10(-5) M 5-HT perfusion. These treatments did not affect 5-HT blood levels. In a separate study, intraduodenal, but not intraileal, 5-HT application induced a dose-dependent increase in pancreatic protein secretion, which was not blocked by the CCK-A antagonist CR-1409. Acute vagotomy, methscopolamine, or perivagal or intestinal mucosal application of capsaicin abolished 5-HT-induced pancreatic secretion. In conscious rats, luminal 10(-5) M 5-HT administration produced a 90% increase in pancreatic protein output, which was markedly inhibited by the 5-HT3 antagonist ondansetron. In conclusion, luminal stimuli induce 5-HT release, which in turn activates 5-HT3 receptors on mucosal vagal afferent terminals. In this manner, 5-HT acts as a paracrine substance to stimulate pancreatic secretion via a vagal cholinergic pathway.

Vagal afferent responses to fatty acids of different chain length in the rat

The role of cholecystokinin (CCK) in the effect of dietary lipid on proximal gastrointestinal function and satiety is controversial. Recent work suggests that fatty acid chain length may be a determining factor. We investigated the mechanism by which long- and short-chain fatty acids activate jejunal afferent nerves in rats. Whole mesenteric afferent nerve discharge was recorded in anaesthetized male Wistar rats during luminal perfusion of saline, sodium oleate, and sodium butyrate (both 10 mM). Both fatty acids evoked characteristic afferent nerve responses, distinct from the mechanical response to saline, that were abolished in rats following chronic subdiaphragmatic vagotomy. The effect of oleate was abolished by the CCK-A receptor antagonist Devazepide (0.5 mg/kg), whereas the effect of butyrate persisted despite pretreatment with either Devazepide or a combination of the calcium channel inhibitors nifedipine (1 mg/kg) and the omega-conotoxins GVIA and SVIB (each 25 microg/kg). In summary, long- and short-chain fatty acids activate intestinal vagal afferents by different mechanisms; oleate acts via a CCK-mediated mechanism and butyrate appears to have a direct effect on afferent terminals.

Roles of 5-HT receptors in the release and action of secretin on pancreatic secretion in rats

5-Hydroxytryptamine (serotonin, 5-HT) is a hormone and neurotransmitter regulating gastrointestinal functions. 5-HT receptors are widely distributed in gastrointestinal mucosa and the enteric nervous system. Duodenal acidification stimulates not only the release of both 5-HT and secretin but also pancreatic exocrine secretion. We investigated the effect of 5-HT receptor antagonists on the release of secretin and pancreatic secretion of water and bicarbonate induced by duodenal acidification in anesthetized rats. Both the 5-HT(2) receptor antagonist ketanserin and the 5-HT(3) receptor antagonist ondansetron at 1-100 microg/kg dose-dependently inhibited acid-induced increases in plasma secretin concentration and pancreatic exocrine secretion. Neither the 5-HT(1) receptor antagonists pindolol and 5-HTP-DP nor the 5-HT(4) receptor antagonist SDZ-205,557 affected acid-evoked release of secretin or pancreatic secretion. None of the 5-HT receptor antagonists affected basal pancreatic secretion or plasma secretin concentration. Ketanserin or ondansetron at 10 microg/kg or a combination of both suppressed the pancreatic secretion in response to intravenous secretin at 2.5 and 5 pmol x kg(-1) x h(-1) by 55-75%, but not at 10 pmol x kg(-1) x h(-1). Atropine (50 microg/kg) significantly attenuated the inhibitory effect of ketanserin on pancreatic secretion but not on the release of secretin. These observations suggest that 5-HT(2) and 5-HT(3) receptors mediate duodenal acidification-induced release of secretin and pancreatic secretion of fluid and bicarbonate. Also, regulation of pancreatic exocrine secretion through 5-HT(2) receptors may involve a cholinergic pathway in the rat.

Peptones stimulate intestinal cholecystokinin gene transcription via cyclic adenosine monophosphate response element-binding factors

Cholecystokinin (CCK) is a potent intestinal hormone that regulates several digestive functions. Despite the physiological importance of CCK, the cellular and molecular mechanisms that govern its synthesis and secretion are not completely identified. Peptones, which are fair counterparts of the protein fraction in the intestinal lumen, are good stimulants of CCK secretion. We have previously shown that peptones activate CCK gene transcription in STC-1 enteroendocrine cells. The DNA element(s) necessary to induce the transcriptional stimulation was preliminary, localized in the first 800 bp of the CCK gene promoter. In the present study, we identify a DNA element [peptone-response element (PepRE)] essential to confer peptone-responsiveness to the CCK promoter, and we characterize the transcription factors implicated. Localization of the PepRE between -93 and -70 bp of the promoter was established using serial 5'-3'deletions. Systematic site-directed mutagenesis demonstrated that the core PepRE sequence, spanning from nucleotide -72 to -83, overlapped with the putative AP-1/CRE site. Mutations in the core sequence dramatically decreased peptone-responsiveness of CCK promoter fragments. The PepRE functioned as a low-affinity CRE consensus site, binding only transcription factors of the CREB family. Overexpression, in STC-1 cells, of a dominant-negative protein (A-CREB), that prevented the binding of CREB factors to DNA, completely abolished the peptone-induced transcriptional stimulation. Peptone treatment did not modify the nature and the abundance of proteins bound to the PepRE but led to increased phosphorylation of the CREB factors. In conclusion, the present study first demonstrates that CCK gene expression is under the control of protein-derived nutrients in the STC-1 enteroendocrine cell line.

Intestinal serotonin acts as a paracrine substance to mediate vagal signal transmission evoked by luminal factors in the rat

The vagus nerve conveys primary afferent information produced by a meal to the brainstem. Serotonin (5-HT), which abounds in intestinal enterochromaffin cells, is released in response to various stimuli. We have recently demonstrated that 5-HT released from intestinal enterochromaffin cells activates 5-HT3 receptors on vagal afferent fibres to mediate luminal non-cholecystokinin-stimulated pancreatic secretion. The present study was designed to evaluate the responses of vagal sensory neurons to intraluminal osmotic stimulation and luminal infusion of maltose, glucose or 5-HT. We investigated the role of endogenous 5-HT in signal transmission evoked by luminal stimuli to activate vagal sensory neurons. The discharges of vagal primary afferent neurons innervating the intestine were recorded from rat nodose ganglia. Luminal factors such as intestinal osmotic stimuli and perfusion of carbohydrates elicited powerful vagal nodose responses. Electrical subdiaphragmatic vagal stimulation activated 364 single units; 40 of these responded to intestinal mucosal stimuli. Of these 40, 30 responded to intraduodenal perfusion of hyperosmolar NaCl (500 mosmol l(-1)), 27 responded to tap water (5 mosmol l(-1)) and 20 and 19 responded to maltose (300 mM) and glucose (277.5 mM), respectively. The 5-HT3/4 antagonist tropisetron (ICS 205-930) or 5-HT3 antagonist granisetron abolished luminal stimuli-evoked nodose neuronal responses. Intraluminal infusion of 10(-5) and 10(-4) M 5-HT elicited increases in vagal afferent discharge in 25 and 31 units, respectively, by activating the 5-HT3 receptors. Acute subdiaphragmatic vagotomy, intestinal mucosal application of the local anaesthetic lidocaine (lignocaine) or administration of 5-HT3 antagonist each abolished the luminal 5-HT-induced nodose neuronal responses. In contrast, distension-sensitive neurons did not respond to duodenal infusion of 5-HT. Pharmacological depletion of 5-HT stores using p-chlorophenylalanine (PCPA), a 5-HT-synthesis inhibitor, abolished luminal factor-stimulated nodose neuronal responses. In contrast, pretreatment with 5,7-dihydroxytryptamine (5,7-DHT), a specific 5-HT neurotoxin that destroys 5-HT-containing neurons without affecting 5-HT-containing mucosal cells, had no effect on these responses. These results suggested that the nodose neuronal responses to luminal osmolarity and to the digestion products of carbohydrates are dependent on the release of endogenous 5-HT from the mucosal enterochromaffin cells, which acts on the 5-HT3 receptors on vagal afferent fibres to stimulate vagal sensory neurons.

Modulation of gastric distension-induced sensations by small intestinal receptors

Duodenal lipid exacerbates gastrointestinal sensations during gastric distension. Using luminal application of the local anesthetic benzocaine, we investigated the role of intestinal receptors in the induction of these sensations. Nine healthy subjects were studied on five occasions, during which isotonic saline or 20% lipid (2 kcal/min), combined with (duodenal or jejunal) 0.75% benzocaine or vehicle at 2.5 ml/min, was infused intraduodenally before and during gastric distension. Intragastric pressures and volumes, gastrointestinal sensations, and plasma CCK levels were determined. Duodenal lipid combined with vehicle increased gastric volume (in ml: saline, -10 +/- 18; lipid/vehicle, 237 +/- 30) and plasma CCK [mean levels (pmol/l): saline, 2.0 +/- 0. 2; lipid/vehicle, 8.0 +/- 1.6] and, during distensions, induced nausea (scores: saline, 3 +/- 2: lipid/vehicle, 58 +/- 19) and decreased pressures at which fullness and discomfort occurred. Duodenal but not jejunal benzocaine attenuated the effect of lipid on gastric volume, plasma CCK, and nausea during distension (135 +/- 38 and 216 +/- 40 ml, 4.6 +/- 0.6 pmol/l and not assessed, and 37 +/- 12 and 64 +/- 21 for lipid + duodenal benzocaine and lipid + jejunal benzocaine, respectively) and on pressures for sensations. In conclusion, intestinal receptors modulate gastrointestinal sensations associated with duodenal lipid and gastric distension. There is also the potential for local neural mechanisms to regulate CCK release and thereby reduce afferent activation indirectly.

Cefaclor, a cephalosporin antibiotic, delays gastric emptying rate by a CCK-A receptor-mediated mechanism in the rat

Studies in vitro suggest that cephalosporin antibiotics release the gut hormone cholecystokinin. Cholecystokinin is known to inhibit gastric emptying. Here we examine the effects of cefaclor on gastric emptying and intestinal motility. Male Sprague-Dawley rats were fitted with gastric cannulas. Following a 3-week recovery, the rate of gastric emptying of saline, peptone (4.5%) or cefaclor was determined after instillation into the gastric cannula, while intestinal transit was measured by using the propagation of arabic gum + charcoal mixture given intraduodenally. Gastric emptying of saline was significantly delayed by the addition of cefaclor (3, 10, 30 or 100 mM). The CCK-A antagonist SR-27897B (1 mg kg(-1), i.p.) reversed the delay induced by 10 mM cefaclor, whereas the CCK-B antagonist CI-988 (1 mg kg(-1), i.p.) had no significant effect. In capsaicin-treated rats, 10 mM cefaclor emptied more rapidly than in vehicle-treated animals. Thirty-minute intestinal transit was increased at 30 and 100 mM of cefaclor, while the gastric acid secretion following cefaclor instillation was no different than the group which received saline. The cephalosporin antibiotic cefaclor appears to be a potent stimulant of CCK release from gut endocrine cells, resembling the effects of peptone. Cefaclor delays gastric emptying via capsaicin-sensitive afferent pathways, which involve CCK-A receptor interaction.

Serotonin released from intestinal enterochromaffin cells mediates luminal non-cholecystokinin-stimulated pancreatic secretion in rats

BACKGROUND & AIMS

Similar to cholecystokinin (CCK), non-CCK-dependent duodenal factors stimulate vagal mucosal afferent fibers to mediate pancreatic enzyme secretion via a common cholinergic pathway. We tested the hypothesis that 5-hydroxytryptamine (5-HT) released from enterochromaffin (EC) cells plays an important role in the transduction of luminal information to the central nervous system via vagal afferent fibers to mediate pancreatic secretion.

METHODS

Pancreatic secretions were examined in conscious rats after intragastric administration of chopped rodent chow in the presence and absence of CCK or 5-HT(3) and 5-HT(2) antagonists. Pancreatic responses to intraduodenal administration of maltose, hyperosmolar NaCl, and light mucosal stroking were examined in rats pretreated with various pharmacological antagonists or after surgical or chemical ablation of vagal and 5-HT neural pathways.

RESULTS

Administration of L364, 718 inhibited 54% of pancreatic protein secretion evoked by intragastric administration of rodent chow. L364,714 and ICS 205-930, a 5-HT(3) antagonist, combined produced a 94% inhibition. Vagal afferent rootlet section eliminated pancreatic secretions evoked by intraduodenal stimuli. p-Chlorophenylalanine, a 5-HT synthesis inhibitor, but not 5,7-hydroxytryptamine, a 5-HT neurotoxin, also eliminated the pancreatic response to these luminal stimuli. The 5-HT(3) antagonist markedly inhibited pancreatic secretion induced by maltose and hyperosmolar NaCl. 5-HT(2) and 5-HT(3) antagonists combined inhibited the pancreatic response to light stroking of the mucosa.

CONCLUSIONS

Luminal factors such as osmolality, disaccharides, and mechanical stimulation stimulated pancreatic secretion via intestinal vagal mucosal afferent fibers. It is likely that 5-HT originating from intestinal EC cells activated 5-HT(3) and 5-HT(2) receptors on vagal afferent fibers to mediate luminal factor-stimulated pancreatic secretion.

Inhibition by CCK of ascending contraction elicited by mucosal stimulation in the duodenum of the rat

CCK released by intraluminal stimuli modifies duodenal activity contributing to a decrease in gastric emptying. However, the neural mechanisms by which CCK controls motility are not well known. The aim of this study was to investigate the interaction between CCK and the enteric nervous system through the study of the effects of CCK-8 on ascending excitation. Anaesthetized Sprague-Dawley rats were prepared with a strain-gauge sutured to the duodenum wall. An electrode holder was placed in the duodenum lumen to elicit ascending contraction. Electrical field stimulation of the duodenal mucosa (4 Hz, 0.6 ms, 30 V) induced an ascending excitation which was blocked by hexamethonium (10 mg kg-1; n=5) and atropine (0.3 mg kg-1; n=5), but enlarged by L-NNA (10(-5) mol kg-1; n=5). CCK-8 (3 ¿ 10(-9) mol kg-1 10 min-1) blocked ascending excitation and an inhibition of the induced phasic activity was observed instead (n=18). Individually, none of the CCK receptor antagonists (L-364 718 and L-365 260) (3 ¿ 10(-7) mol kg-1; n=6 each) blocked the inhibition of ascending excitation induced by CCK-8. However, simultaneous infusion of both antagonists abolished CCK-8 effect on electrical stimulation (n=5). Similarly, none of the CCK-8 agonists (A-71623, A-71378, gastrin) modified the ascending excitation. In contrast, the simultaneous infusion of A-71623 and CCK-4 (n=4) induced an effect similar to CCK-8. In conclusion, CCK-8 blocked ascending contraction elicited by electrical field stimulation of duodenal mucosa by means of simultaneous activation of CCK-A and CCK-B receptors.

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.

Diazepam-binding inhibitor mediates feedback regulation of pancreatic secretion and postprandial release of cholecystokinin

Recently, we isolated a trypsin-sensitive cholecystokinin-releasing peptide (CCK-RP) from porcine and rat intestinal mucosa. The amino acid sequence of this peptide was determined to be identical to that of the diazepam-binding inhibitor (DBI). To test the role of DBI in pancreatic secretion and responses to feeding, we used pancreaticobiliary and intestinal cannula to divert bile-pancreatic juice from anesthetized rats. Within 2 hours, this treatment caused a 2-fold increase in pancreatic protein output and a >10-fold increase in plasma CCK. Luminal DBI levels increased 4-fold. At 5 hours after diversion of bile-pancreatic juice, each of these measures returned to basal levels. Intraduodenal infusion of peptone evoked a 5-fold increase in the concentration of luminal DBI. In separate studies, we demonstrated that intraduodenal administration of antiserum to a DBI peptide specifically abolished pancreatic secretion and the increase in plasma CCK levels after diversion of bile-pancreatic juice. To demonstrate that DBI mediates the postprandial rise in plasma CCK levels, we showed that intraduodenal administration of 5% peptone induced dramatic increases in pancreatic secretion and plasma CCK, effects that could be blocked by intraduodenal administration of anti-DBI antiserum. Hence, DBI, a trypsin-sensitive CCK-RP secreted from the proximal small bowel, mediates the feedback regulation of pancreatic secretion and the postprandial release of CCK.

Secretion of the intestinotropic hormone glucagon-like peptide 2 is differentially regulated by nutrients in humans

BACKGROUND & AIMS

Glucagon-like peptide 2(1-33) (GLP-2(1-33)), an intestinally derived hormone, stimulates growth in rodent small and large bowel. To explore the physiology of GLP-2(1-33) secretion, we measured plasma GLP-2 levels in 6 healthy male volunteers, before and after test meals.

METHODS

Blood samples were collected over 24 hours with the subjects consuming a normal, solid mixed diet (2500 kcal) and for 4 hours after liquid test meals (400 kcal/300 mL) composed of carbohydrate, fat, or protein. All studies commenced at 9 AM. Plasma was extracted and analyzed in radioimmunoassays for N-terminal immunoreactive GLP-2 (N-IR-GLP-2; measures bioactive GLP-2(1-33)) as well as total IR-GLP-2 (T-IR-GLP-2), which includes GLP-2(1-33), GLP-2(3-33) (an inactive degradation product of GLP-2(1-33)), and the pancreatic major proglucagon fragment (an inactive precursor that contains GLP-2). Basal and nutrient-stimulated plasma samples were also analyzed by high-performance liquid chromatography to determine the levels of GLP-2(1-33) and GLP-2(3-33).

RESULTS

N-IR-GLP-2 levels were increased 2.0 +/- 0.2- to 2.8 +/- 0.5-fold 40 minutes after each mixed meal (P < 0.05-0.01) and returned to basal overnight, whereas T-IR-GLP-2 levels were increased 1.3 +/- 0.1-fold 40 minutes after breakfast only (P < 0.05). After ingestion of carbohydrate or fat alone, plasma N-IR-GLP-2 concentrations increased by 5.6 +/- 2.0- and 2.7 +/- 0.6-fold within 1 hour (P < 0.05). High-performance liquid chromatography analysis showed a relative increase in the levels of GLP-2(1-33) compared with GLP-2(3-33) (P < 0.05). Ingestion of the protein meal did not alter N-IR-GLP-2 levels, whereas T-IR-GLP-2 was increased by fat and protein (by 1.7 +/- 0. 2-fold for each, P < 0.01) but not by carbohydrate.

CONCLUSIONS

These results show that secretion of GLP-2(1-33) from the intestine is regulated in a nutrient-dependent manner in normal humans.

Both afferent and efferent nerves are implicated in cholecytokinin motor actions in the small intestine of the rat

Cholecystokinin (CCK) regulates intestinal motility after being released by several luminal nutrients. However the mechanism of action of CCK is still not well known. The aim of our study was to establish the mechanism of action of CCK in the rat intestine using an in vivo model and focusing on the nervous pathways involved in the response as well as type of receptors. Anesthetized rats were prepared with two strain-gauges, in duodenum and jejunum, to record circular muscle motor activity. A group of animals was also prepared with a catheter to infuse capsaicin inside the duodenum. Responses to CCK-octapeptide (CCK-8) as well as to CCK agonists were studied. CCK-8 was also infused after CCK antagonists, atropine, hexamethonium or L-nitroarginine. Results show that duodenal response to CCK-8 is excitatory although inhibitory responses can be induced by gastrin. In the jejunum, CCK-8 induces an inhibitory response that is mediated by both CCK-A and -B receptors. Excitatory responses to CCK-8 are due to stimulation of preganglionic receptors while inhibitory responses are NO mediated through stimulation of postganglionic CCK-B receptors. Capsaicin locally applied in duodenal mucosa significantly decreased CCK-8 response, whereas mucosal exposure to lidocaine completely blocked CCK-8 response. In conclusion our results show that CCK response varies along the intestine according to the predominance of excitatory or inhibitory efferent innervation. Moreover, CCK-8 actions are mediated through both extrinsic and intrinsic afferent fibres.

Diazepam-binding inhibitor33-50 elicits Ca2+ oscillation and CCK secretion in STC-1 cells via L-type Ca2+ channels

We recently isolated and characterized 86-amino acid CCK-releasing peptide from porcine intestinal mucosa. The sequence of this peptide is identical to that of porcine diazepam-binding inhibitor (DBI). Intraduodenal administration of DBI stimulates the CCK release and elicits pancreatic secretion in rats. In this study we utilized a murine tumor cell line (STC-1 cells) that contains CCK to examine if DBI directly acts on these cells to stimulate CCK release. We investigated the cellular mechanisms responsible for this action. We showed that DBI33-50, a biologically active fragment of DBI1-86, significantly stimulated CCK secretion in STC-1 cells. This action was abolished by Ca2+-free medium. The mean basal intracellular Ca2+ concentration ([Ca2+]i) was 52 nM in fura 2-loaded STC-1 cells. DBI33-50 (1-1,000 nM) elicited Ca2+ oscillations; DBI33-50 (10 nM) increased the oscillation frequency to 5 cycles/10 min and elicited a net [Ca2+]i increase (peak - basal) to 157 nM. In contrast, bombesin and forskolin caused an initial transient [Ca2+]i followed by a small sustained [Ca2+]i plateau. Withdrawal of extracellular Ca2+ abolished Ca2+ oscillations stimulated by DBI33-50. L-type Ca2+ channel blockers nifedipine and diltiazem (3-10 microM) markedly attenuated DBI-stimulated Ca2+ oscillations. In other cell types L-type Ca2+ channels are activated by cAMP-protein kinase A. DBI33-50 failed to stimulate cAMP formation in STC-1 cells. Similarly, DBI33-50 had no effect on myo-inositol 1,4, 5-trisphosphate concentration ([IP3]), whereas bombesin caused an eightfold increase in [IP3] over basal. In addition, inhibitors of phospholipase C (U-73122), phospholipase A2 (ONO-RS-082), and protein tyrosine kinase (genistein) did not alter the Ca2+ oscillations elicited by DBI33-50. It appears that DBI33-50 acts directly on STC-1 cells to elicit Ca2+ oscillations via the voltage-dependent L-type Ca2+ channels, resulting in the secretion of CCK. Mediation of this action is by intracellular mechanisms independent of the traditional signal transduction pathways, including phospholipase C, phospholipase A2, protein tyrosine kinase, and cAMP systems.

Effect of deramciclane, a new 5-HT receptor antagonist, on cholecystokinin-induced changes in rat gastrointestinal function

Recent studies suggested that serotonin receptors may be involved in modulating the actions of cholecystokinin (CCK) in the gastrointestinal tract. The present work was designed to compare the effects of deramciclane, a recently developed serotonin-2 (5-HT2A/2C) receptor antagonist, and lorglumide, a CCK(A) receptor antagonist, on exogenous and endogenous CCK-induced pancreatic enzyme secretion and pancreatic growth, as well as on the emptying of the stomach and the gallbladder. Pancreatic secretory function was tested while CCK release was evoked by diversion of bile-pancreatic juice in rats. Adaptive growth of the pancreas was induced by chronic intragastric administration of camostate, a potent synthetic trypsin inhibitor in rats. Gastric emptying of a noncaloric test meal was investigated in response to intraduodenal intralipid infusion, also in rats. In fasted mice, gallbladder emptying was examined in response to intragastric egg yolk administration. In rats, diversion of bile-pancreatic juice from the duodenum stimulated pancreatic amylase secretion. This action was blocked by deramciclane and by lorglumide. Pancreatic hypertrophy and hyperplasia induced by chronic camostate administration was also suppressed by both the serotonin- and the CCK-receptor antagonists. Intraduodenal administration of intralipid induced a significant delay in gastric emptying. This effect was inhibited by both deramciclane and lorglumide in rats. In mice, intragastric administration of egg yolk elicited an accelerated release of bile from the gallbladder. Prior treatment with either deramciclane or lorglumide abolished this response. Lorglumide was able to inhibit the functional responses elicited by exogenous CCK administration in both pancreas, stomach and gallbladder, while deramciclane was not effective under such circumstances. Our data show that deramciclane inhibited the effects of CCK on pancreatic, gastric and gallbladder function when its endogenous release was stimulated, but did not alter the effects of exogenously administered peptide. These results suggest that serotonin, primarily via 5-HT2A receptors, may modulate CCK-mediated gastrointestinal functions in rats.

Mucosal mast cells are involved in CCK disruption of MMC in the rat intestine

Our aim was to determine if mucosal mast cells could be activated by endogenous CCK and, as a consequence, mediate CCK actions in the small intestine. Rats were prepared for electromyography to record electrical activity in the small intestine. In another group of animals, the duodenum was perfused to measure rat mast cell protease II (RMCP II) as indicative of mast cell degranulation. Endogenous CCK release was induced by administration of soybean trypsin inhibitor (SBTI) in conscious rats or by intraduodenal perfusion of ovalbumin hydrolysate (OVH) in anesthetized rats. CCK concentration was measured by bioassay on pancreatic acini. SBTI in control rats disrupted migrating motor complexes (MMC) for >40 min. In rats treated with the mast cell stabilizer ketotifen, SBTI did not induce any change in the MMC pattern. RMCP II concentration in the duodenal perfusate significantly increased after OVH. Perfusate from ketotifen-treated animals did not show any significant increase in RMCP II values during OVH perfusion, although CCK plasma concentration was not different from the control group. Furthermore, infusion of the CCK-B receptor antagonist L-365,260 significantly blocked the increase of RMCP II concentration after OVH. Our results indicate that mucosal mast cells are degranulated by endogenous CCK release through stimulation of CCK-B receptors. Therefore mucosal mast cells participate in CCK intestinal actions.

The tachykinin NK1 receptor. Part II: Distribution and pathophysiological roles

The tachykinin NK1 receptor is widely distributed in both the central and peripheral nervous system. In the CNS, NK1 receptors have been implicated in various behavioural responses and in regulating neuronal survival and degeneration. Moreover, central NK1 receptors regulate cardiovascular and respiratory function and are involved in activating the emetic reflex. At the spinal cord level, NK1 receptors are activated during the synaptic transmission, especially in response to noxious stimuli applied at the receptive field of primary afferent neurons. Both neurophysiological and behavioural evidences support a role of spinal NK1 receptors in pain transmission. Spinal NK1 receptors also modulate autonomic reflexes, including the micturition reflex. In the peripheral nervous system, tachykinin NK1 receptors are widely expressed in the respiratory, genitourinary and gastrointestinal tracts and are also expressed by several types of inflammatory and immune cells. In the cardiovascular system, NK1 receptors mediate endothelium-dependent vasodilation and plasma protein extravasation. At respiratory level, NK1 receptors mediate neurogenic inflammation which is especially evident upon exposure of the airways to irritants. In the carotid body, NK1 receptors mediate the ventilatory response to hypoxia. In the gastrointestinal system, NK1 receptors mediate smooth muscle contraction, regulate water and ion secretion and mediate neuro-neuronal communication. In the genitourinary tract, NK1 receptors are widely distributed in the renal pelvis, ureter, urinary bladder and urethra and mediate smooth muscle contraction and inflammation in response to noxious stimuli. Based on the knowledge of distribution and pathophysiological roles of NK1 receptors, it has been anticipated that NK1 receptor antagonists may have several therapeutic applications at central and peripheral level. At central level, it is speculated that NK1 receptor antagonists could be used to produce analgesia, as antiemetics and for treatment of certain forms of urinary incontinence due to detrusor hyperreflexia. In the peripheral nervous system, tachykinin NK1 receptor antagonists could be used in several inflammatory diseases including arthritis, inflammatory bowel diseases and cystitis. Several potent tachykinin NK1 receptor antagonists are now under evaluation in the clinical setting, and more information on their usefulness in treatment of human diseases will be available in the next few years.

CCK-, secretin-, and cholinergic-independent pancreatic fluid hypersecretion in protease inhibitor-treated rats

Plasma cholecystokinin (CCK) levels in fed rats increased from 2.59 +/- 0.13 pmol/l to the peak of 27.6 +/- 4.1 pmol/l at 1 h after a single oral administration of synthetic protease inhibitor (PI; ethyl N-allyl-N-[(E)-2-methyl-3-[4-(4-amidino-phenoxycarbonyl)phenyl] propenoyl] amino acetate methansulfonate; 20 mg/kg body wt), but then returned to the preloading value at 12 h after administration. The pancreatic fluid secretion, rich in chloride but poor in bicarbonate, was significantly elevated at 6-12 h postfeeding (100.9 +/- 8.2 vs. 27.3 +/- 2.3 microliters/30 min in control rats, P < 0.01). Loxiglumide (50 mg.kg body wt-1.h-1), atropine (100 micrograms.kg body wt-1.h-1), or antisecretin serum (100 microliters/rat) at 12 h postfeeding did not modify the fluid hypersecretion. Loxiglumide, when given together with PI, completely abolished fluid hypersecretion, but it could not inhibit hypersecretion when applied 3 h after PI treatment. Labeling with 5-bromo-2'-deoxyuridine showed active proliferation of acinar cells at 3 h after PI treatment (3.56 +/- 0.29% vs. 0.46 +/- 0.08% in control, P < 0.001), but not in rats given loxiglumide together with PI. In rats that fasted from 12 h before to 12 h after PI feeding, neither pancreatic fluid hypersecretion nor active proliferation of acinar cells was observed. These results suggest that pancreatic fluid hypersecretion in fed rats at 6-12 h after PI treatment is caused not by CCK-, secretin-, or cholinergic-dependent mechanisms but probably by acinar cell proliferation.

Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

The preprotachykinin-A gene-derived peptides substance (substance P; SP) and neurokinin (NK) A are expressed in intrinsic enteric neurons, which supply all layers of the gut, and extrinsic primary afferent nerve fibers, which innervate primarily the arterial vascular system. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Within the enteric nervous system, SP and NKA are likely to mediate, or comediate, slow synaptic transmission and to modulate neuronal excitability via stimulation of NK3 and NK1 receptors. In the intestinal mucosa, tachykinins cause net secretion of fluid and electrolytes, and it appears as if SP and NKA play a messenger role in intramural secretory reflex pathways. Secretory processes in the salivary glands and pancreas are likewise influenced by tachykinins. The gastrointestinal arterial system may be dilated or constricted by tachykinins, whereas constriction and an increase in the vascular permeability are the only effects seen in the venous system. Various gastrointestinal disorders are associated with distinct changes in the tachykinin system, and there is increasing evidence that tachykinins participate in the hypersecretory, vascular and immunological disturbances associated with infection and inflammatory bowel disease. In a therapeutic perspective, it would seem conceivable that tachykinin antagonists could be exploited as antidiarrheal, antiinflammatory and antinociceptive drugs.