Calcitonin gene-related peptide mediates capsaicin-induced neuroendocrine responses in rat antrum

Proton Pump Inhibitors Prevent Gastric Antral Ulcers Induced by NSAIDs via Activation of Capsaicin-Sensitive Afferent Nerves in Mice

BACKGROUND/AIMS

We examined the effects of proton pump inhibitors (PPIs) on gastric antral ulcers induced by non-steroidal anti-inflammatory drugs in re-fed mice and the role of capsaicin-sensitive afferent nerves (CSANs) in the protective effects of PPIs on the antral mucosa.

METHODS

Male mice were administered indomethacin after 2 h of re-feeding of diet after a 24-h fast, and gastric lesions were examined 24 h after indomethacin dosing. The effects of PPIs (lansoprazole and omeprazole), histamine H₂-receptor antagonists (H₂-RAs, famotidine, ranitidine), capsaicin and misoprostol on the formation of antral ulcers induced by indomethacin were examined. Functional ablation of CSANs was caused by pretreatment of mice with a high dose of capsaicin.

RESULTS

Indomethacin produced lesions selectively in the gastric antrum in re-fed conditions. Formation of antral ulcers was not affected by H₂-RAs, but inhibited by PPIs, capsaicin and misoprostol. The anti-ulcer effect of lansoprazole was 30 times stronger than that of omeprazole. Antral ulcers induced by indomethacin were markedly aggravated in mice with ablated CSANs. The effects of PPIs and capsaicin on ulcer formation were inhibited by ablation of CSANs, pretreatment with a capsaicin receptor antagonist (capsazepine/ruthenium red) and an inhibitor of nitric oxide synthesis (L-NAME). However, the inhibitory effect of misoprostol was not prevented by the ablation of CSANs or drugs.

CONCLUSIONS

The results suggested that CSANs play an important role in protection of the antral mucosa and that both lansoprazole and omeprazole are capable of preventing NSAID-induced antral ulcers by activating CSANs.

Sensory nerves and pancreatitis

Sensory nerves are a kind of nerve that conduct afferent impulses from the periphery receptors to the central nervous system (CNS) and are able to release neuromediators from the activated peripheral endings. Sensory nerves are particularly important for microcirculatory response, and stimulation of pancreatic sensory nerves releases a variety of neuropeptides such as substance P (SP), calcitonin gene-related peptide (CGRP), etc., leading to neurogenic inflammation characterized as the local vasodilatation and plasma extravasation. Deactivation of sensory nerves often leads to the disturbances of pancreatic microcirculation. Pancreatitis is a common digestive disease that can lead to severe complications and even death if it goes untreated. Experimental studies in animals and tissue analysis in patients with pancreatitis have shown significant changes in sensory nerves supplying the pancreatic gland. Thus making clear the whole mechanism of pancreatitis is essential to treat and cure it. Sensory nerves may have a close correlation with the development of pancreatitis, and knowing more about the role of sensory nerve in pancreatitis is important for the treatment for pancreatitis. This review is aimed to summarize the relationship between sensory nerves and pancreatitis.

Stress-related alterations of acyl and desacyl ghrelin circulating levels: mechanisms and functional implications

Ghrelin is the only known peripherally produced and centrally acting peptide hormone that stimulates food intake and digestive functions. Ghrelin circulates as acylated and desacylated forms and recently the acylating enzyme, ghrelin-O-acyltransferase (GOAT) and the de-acylating enzyme, thioesterase 1/lysophospholipase 1 have been identified adding new layers of complexity to the regulation of ghrelin. Stress is known to alter gastrointestinal motility and food intake and was recently shown to modify circulating ghrelin and GOAT levels with differential responses related to the type of stressors including a reduction induced by physical stressors (abdominal surgery and immunological/endotoxin injection, exercise) and elevation by metabolic (cold exposure, acute fasting and caloric restriction) and psychological stressors. However, the pathways underlying the alterations of ghrelin under these various stress conditions are still largely to be defined and may relate to stress-associated autonomic changes. There is evidence that alterations of circulating ghrelin may contribute to the neuroendocrine and behavioral responses along with sustaining the energetic requirement needed upon repeated exposure to stressors. A better understanding of these mechanisms will allow targeting components of ghrelin signaling that may improve food intake and gastric motility alterations induced by stress.

Abdominal surgery inhibits circulating acyl ghrelin and ghrelin-O-acyltransferase levels in rats: role of the somatostatin receptor subtype 2

Clinical studies are evaluating the efficacy of synthetic ghrelin agonists in postoperative ileus management. However, the control of ghrelin secretion under conditions of postoperative gastric ileus is largely unknown. Peripheral somatostatin inhibits ghrelin secretion in animals and humans. We investigated the time course of ghrelin changes postsurgery in fasted rats and whether somatostatin receptor subtype 2 (sst(2)) signaling is involved. Abdominal surgery (laparotomy and 1-min cecal palpation) induced a rapid and long-lasting decrease in plasma acyl ghrelin levels as shown by the 64, 67, and 59% reduction at 0.5, 2, and 5 h postsurgery, respectively, compared with sham (anesthesia alone for 10 min, P < 0.05). Levels were partly recovered at 7 h and fully restored at 24 h. The percentage of acyl ghrelin reduction was significantly higher than that of desacyl ghrelin at 2 h postsurgery and not at any other time point. This was associated with a 48 and 23% decrease in gastric and plasma ghrelin-O-acyltransferase protein concentrations, respectively (P < 0.001). Ghrelin-positive cells in the oxyntic mucosa expressed sst(2a) receptor and the sst(2) agonist S-346-011 inhibited fasting acyl ghrelin levels by 64 and 77% at 0.5 and 2 h, respectively. The sst(2) antagonist S-406-028 prevented the abdominal surgery-induced decreased circulating acyl ghrelin but not the delayed gastric emptying assessed 0.5 h postinjection. These data show that activation of sst(2) receptor located on gastric X/A-like cells plays a key role in the rapid inhibition of circulating acyl ghrelin induced by abdominal surgery while not being primarily involved in the early phase of postoperative gastric ileus.

The effect and mechanism of action of capsaicin on gastric acid output

BACKGROUND

Capsaicin has beneficial pharmacological properties, such as the ability to improve appetite and digestion. However, capsaicin has been reported to suppress gastric acid output, but to increase secretion; no consensus as to its effects on gastric acid output has been reached, and the underlying mechanisms remain to be elucidated.

METHODS

Rat gastric lumen was perfused with capsaicin. Basal acid output and gastric acid secretion stimulated by vagal nerve activation and bethanecol, a muscarinic receptor agonist, were measured. After intravenous infusion of calcitonin gene-related peptide (CGRP), the measurements were repeated. The secretion of gastrin, somatostatin, and histamine was measured in isolated vascularly perfused rat stomach after vagal nerve and bethanecol stimulation, and under the influence of capsaicin.

RESULTS

Capsaicin administration had no effect on basal gastric acid output, but inhibited acid secretion resulting from vagal stimulation. Capsaicin had no effect on acid secretion resulting from stimulation with bethanecol. Administration of high-dose CGRP inhibited basal acid output and gastric acid secretion from both vagal nerve and bethanecol stimulation. Low-dose CGRP inhibited gastric acid secretion because of vagal stimulation, but had no effect on basal secretion or acid secretion following stimulation with bethanecol. Capsaicin administration inhibited the stimulated gastrin and histamine secretion and reversed the suppression of somatostatin secretion mediated by vagal stimulation. However, capsaicin had no effect on stimulated gastrin secretion, suppression of somatostatin secretion, or stimulated histamine secretion because of bethanecol.

CONCLUSIONS

Capsaicin inhibited gastric acid output, and the mechanism underlying this effect appears to involve vagal nerve inactivation.

Dual, time-dependent deleterious and protective effect of anandamide on the course of cerulein-induced acute pancreatitis. Role of sensory nerves

Some recent studies indicate that cannabis may induce acute pancreatitis in humans and administration of anandamide increases the severity of acute pancreatitis; whereas another study exhibits some therapeutic effects in acute pancreatitis. Aim of the present study was to discover what is the reason for these opposite confusing results and to determine the role of sensory nerves in this effect. Acute pancreatitis was induced in rats by cerulein. Anandamide, an endogenous cannabinoid, was administered i.p. (1.5 micromol/kg) before or 2 h after cerulein administration. Stimulation of sensory nerves was performed by capsaicin (0.5 mg/kg s.c.). In rats treated with combination of anandamide plus capsaicin, capsaicin was given 10 min after each dose of anandamide. After the last injection of cerulein or 4 h later, the study was terminated. In our study we observed that stimulation of sensory nerves by capsaicin, before administration of cerulein, reduced the severity of acute pancreatitis. Anandamide, administered alone before cerulein, increased pancreatic damage in acute pancreatitis. Anandamide administered in combination with capsaicin, before cerulein, abolished the capsaicin-induced protective effect on the pancreas. Opposite effects were observed when capsaicin and anandamide were administered after injection of cerulein. Capsaicin increased the severity of acute pancreatitis, whereas anandamide reduced pancreatic damage and reversed the deleterious effect of capsaicin. We conclude that the effect of anandamide on the severity of acute pancreatitis depends on the phase of this disease. Administration of anandamide, before induction of pancreatitis, aggravates pancreatic damage; whereas anandamide administered after induction of pancreatitis, reduces the severity of acute pancreatitis. Sensory nerves are involved in the mechanism of this biphasic effect of anandamide.

Capsaicin-sensitive nerves and neurokinins modulate non-neuronal nNOS expression in lung

We investigated the effects of substance P (SP) and neurokinin A (NKA) infusion and acute stimulation of capsaicin-sensitive sensory nerves fibers (CAP) on lung recruitment of neuronal nitric oxide synthase (nNOS)-positive inflammatory and respiratory epithelial (RE) cells in guinea-pigs. We evaluated if the effects of CAP stimulation were maintained until 14 days and had functional pulmonary repercussions. After 24h of CAP and 30 min after SP and NKA infusions there was an increase in nNOS-positive eosinophils and mononuclear cells compared to controls (P<0.05). SP group presented an increase in nNOS-positive RE (P<0.05). After 14 days of CAP stimulation, there was a reduction in resistance (R(rs)) and elastance (E(rs)) of respiratory system in capsaicin pre-treated animals. We noticed a correlation between nNOS-positive eosinophils (R=-0.644, P<0.05) and mononuclear cells (R=-0.88, P<0.001) and R(rs). Concluding, CAP and neurokinins increase nNOS expression by inflammatory and RE cells. The increase in nNOS expression induced by low and high doses stimulation of CAP is longstanding and correlated to pulmonary mechanical repercussions.

Effects of capsaicin on visceral smooth muscle: a valuable tool for sensory neurotransmitter identification

Studying the visceral effects of the sensory stimulant capsaicin is a useful and relatively simple tool of neurotransmitter identification and has been used for this purpose for approximately 25 years in the authors' and other laboratories. We believe that conclusions drawn from experiments on visceral preparations may have an impact on studies dealing with the central endings of primary afferent neurons, i.e. research on nociception at the spinal level. The present review concentrates on the effects of capsaicin--through the transient receptor potential vanilloid receptor type 1 (TRPV1) receptor--on innervated gastrointestinal, respiratory and genitourinary smooth muscle preparations. Tachykinins and calcitonin gene-related peptide (CGRP) are the most widely accepted transmitters to mediate "local efferent" effects of capsaicin-sensitive nerves in tissues taken from animals. Studies more and more frequently indicate a supra-additive interaction of various types of tachykinin receptors (tachykinin NK(1), NK(2), NK(3) receptors) in the excitatory effects of capsaicin. There is also evidence for a mediating role of ATP, acting on P(2) purinoceptors. Non-specific inhibitory actions of capsaicin-like drugs have to be taken into consideration while designing experiments with these drugs. Results obtained on human tissues may be sharply different from those of animal preparations. Capsaicin potently inhibits tone and movements of human intestinal preparations, an effect mediated by nitric oxide (NO) and/or vasoactive intestinal polypeptide.

Role of capsaicin-sensitive nerves and histamine H1, H2, and H3 receptors in the gastroprotective effect of histamine against stress ulcers in rats

It is assumed that an overproduction of gastric acid is the most important factor in the development of peptic ulcer. However, it has been also demonstrated that gastric defense mechanisms, which prevent mucosal injury, are enhanced by the same factors that increase acid secretion. The aim of this study was to examine the role of capsaicin-sensitive sensory nerves and histamine H1, H2, and H3 receptors in histamine-induced gastroprotection against stress ulcers. Studies were performed on rats with intact or ablated sensory nerves. Ablation of sensory nerves was induced by neurotoxic doses of capsaicin. Gastric ulcers were induced by water immersion and restrain stress. Before exposure to stress, rats were pretreated with saline (control), histamine (10 micromol/kg), histamine H1 receptor antagonist pyrilamine (100 micromol/kg), histamine H2 receptor antagonist ranitidine (100 micromol/kg), histamine H3 receptor antagonist thioperamide (100 micromol/kg), or a combination of histamine with these histamine receptor antagonists.

RESULTS

Histamine alone reduced ulcer area evoked by stress and this effect was accompanied by an increase in gastric mucosal blood flow and mucosal DNA synthesis, as well as a decrease in serum pro-inflammatory interleukin-1beta concentration. Treatment with combination of pyrilamine plus histamine caused an increase in gastric ulcer area and serum interleukin-1beta above the value observed in animals treated with saline, and this effect was accompanied by a decrease in gastric mucosal DNA synthesis. Ranitidine, in combination with histamine, reduced the ulcer area and serum interleukin-1beta to a minimal value, whereas gastric mucosal blood flow and DNA synthesis reached a maximal value. Pretreatment with thioperamide before histamine administration abolished the histamine-evoked reduction in gastric ulcer area. Ablation of sensory nerves increased the ulcer area in animals treated with saline or histamine, or histamine in combination with pyrilamine or ranitidine. In animals with sensory nerves ablation combined with administration of thioperamide plus histamine, the ulcer area was similar to that in saline-treated animals with intact sensory nerves. We conclude that: (1) histamine exhibits protective effect against stress-induced gastric ulcer and that this gastroprotection is related to stimulation of histamine H1 and H3 receptors; (2) blockade of histamine H2 receptors exhibited beneficial effect on gastric mucosa against stress-induced gastric ulcers; and (3) ablation of sensory nerves aggravates stress-induced gastric ulcer and reduces histamine-evoked gastroprotection related to stimulation of histamine H3 receptors.

Functional interaction between transforming growth factor α and capsaicin-sensitive sensory neurons in the rat stomach

BACKGROUND AND AIMS

Transforming growth alpha (TGFalpha) and sensory neurons have been shown to promote gastric mucosal protection and healing. Aims were to examine in vitro interactions between gastric sensory neurons, the sensory neuropeptide calcitonin gene-related peptide (CGRP), and TGFalpha.

METHODS

Gastric mucosal/submucosal tissue fragments from Sprague-Dawley (SD) rats were incubated in short-term (30 min) culture. Peptide release into media and TGFalpha tissue content were measured by radioimmunoassay.

RESULTS

TGFalpha (1 x 10(-8) to 1 x 10(-6) M) caused dose-dependent stimulation of CGRP release. Maximal CGRP release (+87%) was observed with 1 x 10(-6) M TGFalpha: 28.6+/-3.8 vs. control of 15.5+/-2.7 pg/g tissue; P<0.05. Both CGRP (1 x 10(-7) to 1 x 10(-5) M) and capsaicin (1 x 10-(8) to 1 x 10(-6)M) significantly inhibited basal TGFalpha release in a dose-dependent fashion that ranged from -20% to -39%. In contrast, capsaicin-induced sensory denervation caused significant increases in both basal TGFalpha release and TGFalpha tissue content.

CONCLUSION

Function interactions between TGFalpha and gastric sensory neurons are suggested by the observations that (1) TGFalpha stimulated CGRP release from gastric sensory neurons; (2) CGRP and acute capsaicin treatment inhibited TGFalpha release and; (3) capsaicin-induced sensory denervation caused significant increases in both gastric TGFalpha basal release and tissue content.

Transforming growth factor alpha-mediated gastroprotection against stress ulceration in the rat: involvement of capsaicin-sensitive sensory neurons

Exogenously administered TGF alpha has been shown to protect rodent gastric mucosa against injury caused by acid-dependent and acid-independent injury. The present study examined whether the gastroprotective effects of TGF alpha on stress-induced gastric ulceration in the rat involves activation of capsaicin-sensitive sensory neurons. Fasted male SD rats were subjected to water restraint stress (WRS) for four hours. Thereafter, rats were euthanized; the stomach opened and macroscopic areas of gastric ulceration quantitated (mm(2)). Gastric tissue contents of TGF alpha and the sensory neuropeptide, calcitonin gene-related peptide (CGRP) were determined by radioimmunoassay. Prior to stress rats received TGF alpha 50, 100 or 200 microg/kg by intraperitoneal injection. Sensory denervation was accomplished by high dose capsaicin treatment. WRS caused severe ulceration in the gastric corpus; 46.1 + 6.6 mm(2). Parenteral administration of TGF alpha caused dose-dependent reduction in gastric injury: 34.7 + 4.9 mm(2) with 50 microg/kg (p < 0.05); 25.4 + 3.6 mm(2) with 100 microg/kg (p < 0.001) and 9.4 + 0.8 mm(2) with 200 microg/kg (p < 0.001). The gastroprotective action of TGF alpha (200 microg/kg, i.p.) was abolished by capsaicin-induced sensory denervation. In addition, WRS ulceration was associated with significant reduction in gastric CGRP (-42%) and TGF alpha (-48%) content. Reduction in CGRP content was prevented by TGF alpha pretreatment. We conclude that: 1) TGF alpha caused dose-dependent gastroprotection against WRS ulceration, 2) TGF alpha-mediated gastric mucosal protection was prevented by capsaicin-induced sensory denervation and, 3) stress-induced injury was associated with significant reduction in gastric content of both TGF alpha and CGRP.

Delayed gastrointestinal transit in patients with hepatocellular carcinoma

BACKGROUND AND AIM

Disturbed gastrointestinal (GI) motility exists in cirrhotic patients; however, less is known about the character of GI transit in hepatocellular carcinoma (HCC) patients. It is interesting to study the GI transit in HCC patients and to explore the patient factors modulating GI transit.

METHODS

A non-invasive hydrogen breath test, which measured the orocecal transit time (OCTT), was used to study GI transit in 40 HCC patients, 20 cirrhotics and 40 age- and sex-matched healthy volunteers with normal bowel habits. Meanwhile, their clinical manifestations and various blood parameters, such as platelet count, prothrombin time, erythrocyte sedimentation rate etc. were collected. The plasma endothelin-1 and nitrate/nitrite levels were also measured.

RESULTS

The OCTT were delayed in HCC and cirrhotic patients compared with controls (116.3 +/- 7.8 and 104.5 +/- 10.6 vs 75.3 +/- 5.1 min, P < 0.05). Neither the severity of liver damage, presence of ascites, tumor size, portal hypertension, nor various blood parameters, such as nitrate/nitrite, endothelin-1, platelet count etc., had any influence on GI transit. Only serum alpha-fetoprotein levels exhibited a trend toward positive correlation with the OCTT (r = 0.271, P = 0.091).

CONCLUSIONS

Hepatocellular carcinoma patients have delayed GI transit. The confounding factor responsible for the disturbance of GI transit in HCC patients needs further exploration.

Amylin, released from the gastric fundus, stimulates somatostatin and thus inhibits histamine and acid secretion in mice

BACKGROUND & AIMS

Amylin, a peptide that displays 50% homology with calcitonin gene-related peptide (CGRP), is colocalized with somatostatin in endocrine cells of the gastric fundus. The present study was designed to determine the mechanism of action of amylin on gastric exocrine and endocrine secretion.

METHODS

Acid secretion was measured in the isolated mouse stomach by titration. Somatostatin and histamine secretion were measured in rat fundic segments by radioimmunoassay.

RESULTS

In isolated mouse stomach, amylin caused a concentration-dependent decrease in acid secretion. In rat fundic segments, amylin and CGRP each caused a concentration-dependent increase in somatostatin and a decrease in histamine secretion. Changes in histamine secretion induced by amylin reflected changes in somatostatin secretion and could be abolished by addition of somatostatin antibody. Both the somatostatin and the histamine responses to amylin were abolished by the selective amylin antagonist AC187 but were unaffected by the CGRP antagonist CGRP8-37. In contrast, the responses to CGRP were abolished by CGRP8-37 but were unaffected by AC187. AC187 alone decreased somatostatin and increased histamine in fundic segments and increased acid secretion in isolated stomach, indicating that endogenous amylin participates in the regulation of gastric endocrine (somatostatin and histamine) and exocrine (acid) secretion.

CONCLUSIONS

In gastric fundus, release of amylin from somatostatin cells interacts with distinct amylin receptors to enhance somatostatin secretion via an autocrine pathway that leads to inhibition of histamine and acid secretion.

Localization of calcitonin gene-related peptide receptors in rat gastric mucosa

The location of calcitonin gene-related peptide (CGRP) receptors in the rat stomach has not been elucidated. It was recently reported that the CGRP receptor is formed when a calcitonin-receptor-like receptor (CRLR) and receptor activity modifying protein (RAMP) 1 are co-expressed on the cell membrane. The aim of this study was to determine the location and the role of CGRP receptors in the rat gastric mucosa. Gene expressions of CRLR and RAMP1 were investigated by Northern blot analysis, reverse transcription-polymerase chain reaction (RT-PCR), and in situ hybridization. Immunohistochemical stainings for CGRP, somatostatin, gastrin, and chromogranin A were performed. Gastric endocrine cells were collected by counterflow-elutriation and their responses to CGRP were studied. CRLR and RAMP1 mRNA was expressed mainly in small gastric epithelial cells in the pyloric glands. The mRNA expression had a similar distribution to that of D cells. In cultured gastric endocrine cells, CGRP enhanced somatostatin production, while it inhibited the secretion of histamine and gastrin. Our results suggest that CGRP receptors are expressed in D cells in the rat gastric mucosa and control production and secretion of somatostatin.

Capsaicin-sensitive afferents and their role in gastroprotection: an update

The pivotal role of capsaicin-sensitive peptidergic sensory fibers in the maintenance of gastric mucosal integrity against injurious interventions was suggested by the authors 20 years ago. Since then substantial evidence has accumulated for the local sensory-efferent function of the released CGRP, tachykinins and NO in this gastroprotective mechanism. This overview outlines some recent achievements which shed light on new aspects and further horizons in this field. (1) Cloning the capsaicin VR-1 receptor (an ion channel-coupled receptor) and raising the VR-1 knockout mice provided a definite molecular background for the existence of capsaicin-sensitive afferents with both sensory and mediator releasing functions in the stomach. This cation channel is also sensitive to hydrogen ions. (2) VR-1 agonists (capsaicin, resiniferatoxin, piperine) protect against gastric ulcer of the rat parallel with their sensory stimulating potencies. (3) Antidromic stimulation of capsaicin-sensitive vagal and somatic afferents results in the release of CGRP, tachykinins, NO and somatostatin. Somatostatin with gastroprotective effect is released from D cells and sensory nerve endings. (4) The recent theory for the existence of spinal afferents without sensory function [P. Holzer, C.A. Maggi, Dissociation of dorsal root ganglion neurons into afferent and efferent-like neurons, Neuroscience 86 (1998) 389-398] is discussed. Data proposed to support this theory are interpreted here on the basis of a dual sensory-efferent function of VR-1 positive afferents, characterized by a frequency optimum of discharges for release vasodilatory neuropeptides below the nociceptive threshold. (5) Recent data on the effect of capsaicin in healthy human stomach are summarized. These results indicate that the gastroprotective effect of capsaicin in the human stomach involves additional mechanisms to those already revealed in the rat.

Calcitonin gene-related peptide regulates amino acid absorption across rat jejunum

The calcitonin gene related peptide (CGRP) is widely distributed in the enteric nervous system and gut afferents. Its role in normal digestion and absorption is not characterised. This study is conducted to elucidate whether CGRP regulates amino acid absorption in the small intestine. In in vivo experiments using the single-pass perfusion technique, intravenous infusion of CGRP (250-750 pmol/kg-min) reduced alanine absorption by 35-40%. The effects were completely blocked by the antagonist hCGRP (8-37). Moreover, intravenous infusion of CGRP antagonist blocked the inhibitory effect of intraluminal capsaicin perfusion on alanine absorption. Similarly, intracerebral injection of CGRP decreased alanine absorption, an effect which was reduced by vagotomy. In vitro experiments using isolated jejunal strips showed that CGRP reduced alanine absorption in a dose-dependent manner. At 6 pM, CGRP decreased alanine absorption by 33%. Similarly, CGRP reduced the absorption of proline and taurine by 20 and 11.5%, respectively. Kinetic studies revealed that CGRP reduces alanine influx into intestinal epithelial cells by inhibiting the affinity of the carriers. It is demonstrated that CGRP is involved in the regulation of jejunal amino acid absorption through intrinsic (enteric) and extrinsic (central) neural mechanisms.

The mechanism of action of amtolmetin guacyl, a new gastroprotective nonsteroidal anti-inflammatory drug

Amtolmetin guacyl (2-methoxyphenyl-1-methyl-5-p-methylbenzoyl-pyrrol-2-acetamido acetate) (MED15) is a new nonsteroidal anti-inflammatory drug (NSAID) with anti-inflammatory, analgesic and antipyretic properties similar to the traditional drugs, but with unexpected gastroprotective effects. In an in vivo rat model, amtolmetin guacyl administered orally demonstrates inhibition of gastric acid secretion following stimulation by various agonists, and up-regulation of gastric bicarbonate production. Pretreatment with MED15 also shows a significant reduction of indomethacin-induced gastric damage in the rat. The reason behind this behaviour appears to be bound to the presence in the MED15 molecule of a vanillic moiety known to stimulate capsaicin receptors. In fact, the antisecretive effect of MED15 is blocked by capsazepine (a specific capsaicin receptor antagonist). This effect is confirmed by the interference found with anti-histamine H(1) drugs. Owing to the connection between capsaicin and calcitonin gene-related peptide (CGRP), a possible effect of MED15 on CGRP receptors was hypothesized, considering the leading role played on gastric mucosa by the predominant sensory neuropeptide of the stomach wall, CGRP. In fact, the anti-secretive and gastroprotective effect of MED15 is abolished by CGRP-(8-37) (the specific CGRP receptor antagonist). The unmodified MED15 molecule is found throughout the gastroenteric tract for long periods of time following oral administration, as further confirmation of the mechanism of action being based on the presence of the vanillic moiety at receptor level.

Capsaicin inhibits the pentagastrin-stimulated gastric acid secretion in anaesthetized rats with acute gastric fistula

The effect of capsaicin on basal and pentagastrin-stimulated gastric acid secretion was investigated in the urethane anaesthetized acute gastric fistula rat. Gastric acid secretion was measured by flushing of the gastric lumen with saline every 15 min or by continuous gastric perfusion. Capsaicin given into the rat stomach at 120 ng x mL(-1) prior to pentagastrin (25 microg x kg(-1), iv) reduced gastric acid secretory response to pentagastrin by 24%. Intravenous (iv) capsaicin (0.5 microg x kg(-1)) did not reduce the pentagastrin-stimulated gastric acid secretion. After topical capsaicin desensitization (3 mg x mL(-1)), basal gastric acid secretion and that in response to pentagastrin (25 microg x kg(-1), intraperitonaeally) was unaltered compared with the control group. Data indicate that topical capsaicin inhibits gastric acid secretion stimulated with pentagastrin in anaesthetized rats.

Capsaicin-sensitive afferent sensory nerves in modulating gastric mucosal defense against noxious agents

In the rat stomach, evidence has been provided that capsaicin-sensitive sensory nerves (CSSN) are involved in a local defense mechanism against gastric ulcer. In the present study capsaicin or resiniferatoxin (RTX), a more potent capsaicin analogue, was used to elucidate the role of these sensory nerves in gastric mucosal protection, mucosal permeability, gastric acid secretion and gastrointestinal blood flow in the rat. In the rat stomach and jejunum, intravenous RTX or topical capsaicin or RTX effected a pronounced and long-lasting enhancement of the microcirculation at these sites, measured by laser Doppler flowmetry technique. Introduction of capsaicin into the rat stomach in very low concentrations of ng-microg x mL(-1) range protected the gastric mucosa against damage produced by topical acidified aspirin, indomethacin, ethanol or 0.6 N HCl. Resiniferatoxin exhibited acute gastroprotective effect similar to that of capsaicin and exerted marked protective action on the exogenous HCl, or the secretagogue-induced enhancement of the indomethacin injury. The ulcer preventive effect of both agents was not prevented by atropine or cimetidine treatment. Capsaicin given into the stomach in higher desensitizing concentrations of 6.5 mM markedly enhanced the susceptibility of the gastric mucosa and invariably aggravated gastric mucosal damage evoked by later noxious challenge. Such high desensitizing concentrations of capsaicin, however, did not reduce the cytoprotective effect of prostacyclin (PGI2) or beta-carotene. Capsaicin or RTX had an additive protective effect to that of atropine or cimetidine. In rats pretreated with cysteamine to deplete tissue somatostatin, capsaicin protected against the indomethacin-induced mucosal injury. Gastric acid secretion of the pylorus-ligated rats was inhibited with capsaicin or RTX given in low non-desensitizing concentrations, with the inhibition being most marked in the first hour following pylorus-ligation. Low intragastric concentrations of RTX reduced gastric hydrogen ion back-diffusion evoked by topical acidified salicylates. It is concluded that the gastropotective effect of capsaicin-type agents involves primarily an enhancement of the microcirculation effected through local release of mediator peptides from the sensory nerve terminals. A reduction in gastric acidity may contribute to some degree in the gastric protective action of capsaicin-type agents. The vasodilator and gastroprotective effects of capsaicin-type agents do not depend on vagal efferents or sympathetic neurons, involve prostanoids, histaminergic or cholinergic pathways.

Neural emergency system in the stomach

The maintenance of gastric mucosal integrity depends on the rapid alarm of protective mechanisms in the face of pending injury. Afferent neurons of extrinsic origin constitute an emergency system that is called into operation when the gastric mucosa is endangered by acid and other noxious chemicals. The function of these chemoceptive afferents can be manipulated selectively and explored with the excitotoxin capsaicin. Most of the homeostatic actions of capsaicin-sensitive afferents are brought about by peptides released from their peripheral endings in the gastric wall. When stimulated, chemoceptive afferents enhance gastric blood flow and activate hyperemia-dependent and hyperemia-independent mechanisms of protection and repair. In the rodent stomach, these local regulatory roles of sensory neurons are mediated by calcitonin gene-related peptide acting via calcitonin gene-related peptide 1 receptors and neurokinin A acting via neurokinin 2 receptors, with both peptides using nitric oxide as their common messenger. In addition, capsaicin-sensitive neurons form the afferent arc of autonomic reflexes that control secretory and motor functions of the stomach. The pathophysiological potential of the neural emergency system is best portrayed by the gastric hyperemic response to acid backdiffusion, which is signaled by afferent nerve fibers. This mechanism limits damage to the surface of the mucosa and creates favorable conditions for rapid restitution and healing of the wounded mucosa.

Effects of calcitonin gene-related peptide on somatostatin and gastrin gene expression in rat antrum

The ability of exogenous calcitonin gene-related peptide (CGRP) to regulate gastric somatostatin and gastrin messenger RNA was studied in vitro in rat antral mucosal/submucosal tissues. Somatostatin and gastrin mRNA were quantified by Northern and dot blot hybridization and regulatory peptides were measured by radioimmunoassay. Incubation of antral tissues in the presence of CGRP [1 x 10(-7) M] for 60 min resulted in a reciprocal increase in somatostatin and a decrease in gastrin release: 214.7+/-28.5 vs. control of 81.7+/-5.9 pg somatostatin per gram of tissue and 2.2+/-0.3 vs. control of 5.5+/-0.7 ng gastrin per gram of tissue (P < 0.001). CGRP caused parallel changes in somatostatin and gastrin mRNA levels: somatostatin mRNA increased by 212% from 0.40+/-0.02 to 1.25+/-0.09 absorbance units (AU) (P < 0.001) and gastrin mRNA decreased by 73% from 0.55+/-0.08 to 0.15+/-0.02 AU (P < 0.001). Somatostatin monoclonal antibody prevented CGRP-mediated inhibition of both gastrin release and gastrin mRNA levels. In conclusion, CGRP is capable of modulating both the secretion and gene expression of regulatory peptides from antral G and D cells. Somatostatin immunoneutralization studies suggest that the actions of CGRP on gastrin release and gene expression are indirect and mediated through the paracrine influences of somatostatin.

Capsaicin and the stomach. A review of experimental and clinical data

Capsaicin, the pungent principle of hot pepper, because of its ability to excite and later defunctionalize a subset of primary afferent neurons, has been extensively used as a probe to elucidate the function of these sensory neurons in a number of physiological processes. In the rat stomach, experimental data provided clear evidence that capsaicin-sensitive (CS) sensory nerves are involved in a local defense mechanism against gastric ulcer. Stimulation of CS sensory nerves with low intragastric concentrations of capsaicin protected the rat gastric mucosa against injury produced by different ulcerogenic agents. High local desensitizing concentrations of capsaicin or systemic neurotoxic doses of the agent markedly enhanced the susceptibility of the rat gastric mucosa to later noxious challenge. Resiniferatoxin, a potent analogue of capsaicin possesses an acute gastroprotective effect similar to that of capsaicin in the stomach. The gastroprotective effect of capsaicin-type agents involves an enhancement of the microcirculation effected through the release of mediator peptides from the sensory nerve terminals with calcitonin gene-related peptide being the most likely candidate implicated. They do not depend on vagal efferent or sympathetic neurons or involve prostanoids. The gastric mucosal protective effect of prostacyclin is retained after systemic or topical capsaicin desensitization. Capsaicin-sensitive fibers are involved in the repair mechanisms of the gastric mucosa. A protective role for CS sensory nerves has also been demonstrated in the colon. In most studies, capsaicin given into the stomach of rats or cats inhibited gastric acid secretion. In humans, although recent studies provide evidence in favor of a beneficial effect of capsaicin on the gastric mucosa, an exact concentration-related assessment of the effect of the agent is still lacking.

Capsaicin-induced calcitonin gene-related peptide release from isolated rat stomach measured with a new chemiluminescent enzyme immunoassay

The peripheral capsaicin-sensitive afferent nerve has been reported to play an important role in gastroprotection and to release a calcitonin gene-related peptide (CGRP). We developed a new chemiluminescent enzyme immunoassay (CLEIA) for CGRP and measured capsaicin-induced CGRP release from the isolated and inverted rat stomach. The basal CGRP release from the stomach was 0.40 +/- 0.02 pg/mg wet weight in a 30-min incubation. Capsaicin (1 x 10(-8)-1 x 10(-5) M) stimulated CGRP release in a concentration-dependent manner. In the stomach from rats with defunctionalization of afferent neurons, the levels of the basal and capsaicin-induced CGRP release were below the limit of detection. On the other hand, the capsaicin-induced CGRP release was not blocked by tetrodotoxin treatment. The gangliosym-pathectomy abolished the increase in the CGRP levels. However, the capsaicin-induced CGRP release was not affected by pretreatment with 6-hydroxydopamine, a neurotoxin that causes a complete degeneration of adrenergic nerve terminals. In conclusion, the CLEIA system may be useful for detecting the released CGRP and studying the activity of capsaicin-sensitive nerves, particularly the CGRP-containing nerves. Our results also confirmed that although the CGRP-containing nerve runs in the sympathetic nerve trunk, the activity of the nerve is not affected by adrenergic nerves, and the capsaicin-induced CGRP release may be attributable to the tetrodotoxin-resistant component.

Influence of capsaicin-sensitive afferent neurons and nitric oxide (NO) on cerulein-induced pancreatitis in rats

CONCLUSION

Stimulation of afferent neurons by capsaicin exerts protective activity against cerulein-induced pancreatitis. This action is dependent on endogenous release of nitric oxide (NO). Deactivation of afferent neurons by high doses of capsaicin contributes to the severity of pancreatitis. This action involves mainly decreased pancreatic blood flow (PBF). Afferent nerves and NO cooperate in the maintenance of the integrity of pancreatic tissue.

BACKGROUND

Stimulation of capsaicin-sensitive afferent fibers protects gastric mucosa against damage and causes changes in mucosal blood flow. The aim of the present study was to determine the role of stimulation or ablation of capsaicin-sensitive neurons and NO in the course of cerulein-induced pancreatitis in the rat.

METHODS

Low and high doses of capsaicin were administered to animals with pancreatitis and to those without pancreatitis. The effect of several parameters was assessed. NO activity was blocked by NG-nitro-L-arginine.

RESULTS

We found that a low dose of capsaicin administered intragastrically caused an increase in PBF. A neurotoxic dose of capsaicin caused a decrease in PBF, RNA content, and DNA synthesis. Pancreatitis led to a significant decrease in PBF and DNA synthesis, but an increase in pancreatic weight, protein content, plasma amylase concentration, and neutrophil adherence. Stimulatory doses of capsaicin attenuated the pancreatic tissue damage of pancreatitis, and alteration of PBF, DNA synthesis, and neutrophil adherence. Capsaicin-induced ablation of afferent neurons caused an increase in all indicators of pancreatic damage. Blocking NO enhanced pancreatic damage, and this was reversed by addition of L-arginine.

Differences in action of topical and systemic cysteamine on gastric blood flow, gastric acid secretion and gastric ulceration in the rat

The effect of cysteamine on gastric blood flow and on the indomethacin-induced gastric mucosal damage was studied. In anesthetized rats, cysteamine (280 mg/kg) given subcutaneously (s.c.) decreased gastric blood flow measured by the laser Doppler flowmetry technique. In contrast, cysteamine (1-60 mg/ml) applied topically to the serosal surface of the stomach evoked a concentration-dependent and long-lasting increase in gastric blood flow. At 60 mg/ml, cysteamine increased blood flow by 166.8 +/- 26.1% of predrug control value. Pretreatment with indomethacin (20 mg/kg, s.c.), intravenous (i.v.) atropine (1 mg/kg), propranolol (1 mg/kg, i.v.), combined H1 and H2-blockade or bilateral cervical vagotomy alone or combined with i.v. guanethidine (8 mg/kg), or pretreatment with the capsaicin analogue resiniferatoxin did not reduce the vasodilator response to cysteamine. The vasodilator response to topical capsaicin, was not reduced after s.c. cysteamine (280 mg/kg) pretreatment. In conscious pylonus-ligated rats, s.c. cysteamine (100 or 280 mg/kg) given simultaneously with indomethacin inhibited gastric acid output but had variable effects on the indomethacin-induced gastric mucosal damage. Cysteamine (100 or 280 mg/kg) administered s.c. 4 h prior to indomethacin enhanced gastric injury by s.c. indomethacin, but did not prevent the gastroprotective action of capsaicin. In contrast, orally administered cysteamine (60 mg/ml) reduced gastric injury induced by s.c. indomethacin plus intragastric HCl. These data provide the first evidence for the effect of cysteamine on gastric microcirculation in the rat and suggest a direct vasodilator effect for topical cysteamine. The microvascular effects of cysteamine are largely responsible for the different effects of this agent on experimental gastric injury.

Mechanisms of proton-induced stimulation of CGRP release from rat antrum

Mechanisms of acid-evoked CGRP release from gastric afferent nerves were investigated in rat antral mucosal/submucosal tissues. Low pH (pH 4.0, 5.0 and 6.0) stimulated antral CGRP release significantly and dose-dependently from rat antral fragments. Removal of extracellular calcium from the incubation medium resulted in significant inhibition (59%, P < 0.001) of acid (pH 4.0)-stimulated CGRP release. Conotoxin (1 x 10(-7) M), the selective blocker of N-type calcium channels, also significantly inhibited proton (pH 4.0)-induced CGRP release to values that were 74% below net stimulated levels. Neither nifedipine (1 x 10(-6) M), the L-type Ca(2+)-channel antagonist, nor indomethacin (1 x 10(-5) M), inhibitor of prostaglandin synthesis, altered acid-induced CGRP release. In contrast, ruthenium red (1 x 10(-5) M), capsaicin antagonist, almost completely prevented acid (pH 4.0)-stimulated CGRP release. Capsazepine (1 x 10(-4) M), a specific capsaicin receptor antagonist, also completely abolished acid-induced CGRP release. In conclusion, the results of these studies indicate that hydrogen ions are capable of evoking CGRP release from peripheral sensory neurons in rat antral mucosal/submucosal tissues. Proton-evoked CGRP release requires extracellular calcium and involves N-type calcium channels. Furthermore, acid appears to exert a capsaicin-like effect to evoke sensory neuropeptide release that is sensitive to capsazepine and ruthenium red. These data suggest that proton-induced antral CGRP release represents a direct action of hydrogen ions on mucosal/submucosal sensory dendritic nerve endings to effect local release of neuropeptide.

Calcitonin gene-related peptide modulates acid-mediated regulation of somatostatin and gastrin release from rat antrum

BACKGROUND & AIMS

Acid has been shown to stimulate calcitonin gene-related peptide (CGRP) release from peripheral sensory afferent nerve endings in the stomach. The aim of this study was to determine whether endogenous CGRP was involved, by a neurocrine mechanism, in acid-mediated stimulation of somatostatin and inhibition of gastrin release.

METHODS

A two-compartment sleeve of antral mucosal/submucosal tissue was perfused to determine sensory nerve and endocrine cell responses to luminal acid. CGRP receptor antagonist, CGRP8-37, was used to inhibit the actions of endogenously released CGRP.

RESULTS

Perfusion of the antral sleeve lumen with media of increasing hydrogen ion concentration caused pH-dependent increases in CGRP and somatostatin release and decrease in gastrin release. CGRP8-37 inhibited significantly basal somatostatin (-36%) and stimulated basal gastrin (+65%) release (P < 0.02). Furthermore, CGRP8-37 administration prevented luminal acid-mediated inhibition of gastrin release and stimulation of somatostatin release. These results indicate that CGRP8-37 prevented acid-mediated feedback inhibition of gastrin release and acid-induced feedforward somatostatin release.

CONCLUSION

These results suggest that CGRP plays an important role in the response of antral D and G cells to luminal acid and that local effector action of endogenous CGRP participates in regulation of antral regulatory peptide secretion.

Calcitonin gene-related peptide (CGRP)-enhanced non-adrenergic non-cholinergic contraction of guinea-pig proximal colon

1. We have investigated the effect of calcitonin gene-related peptide (CGRP) on non-adrenergic, non-cholinergic (NANC) excitatory transmission to the longitudinal muscle of the guinea-pig proximal colon. 2. In the presence of atropine (0.3 microM), guanethidine (5 microM), hexamethonium (100 microM) and indomethacin (3 microM), electrical field stimulation (EFS, 1 Hz, 0.3 ms for 10 s) produced tetrodotoxin-(300 nM)-sensitive contractions which were reduced by the combined administration of FK 888 (10 microM) and MEN 10,376 (0.3 microM), to block tachykinin NK1 and NK2 receptors, respectively. Thus, the EFS-induced NANC contractions are a tachykinin-mediated response. 3. CGRP, at concentrations higher than 0.1 nM, caused an increase in the electrically-evoked, NANC contractions in a concentration-dependent manner and at 10 nM produced a maximal effect (pEC50 = 9.20 +/- 0.17, n = 6). 4. 5-Hydroxytryptamine (5-HT, 1-100 nM) also caused an increase in the EFS-induced NANC contractions in a concentration-dependent manner and at 30 nM produced a maximal effect (pEC50 = 8.06 +/- 0.09, n = 4), but calcitonin (10-100 nM) failed to enhance the EFS-induced NANC responses. Moreover, a 5-HT4 receptor antagonist, DAU 6285 (3 microM) abolished the enhancing action of 5-HT (30 nM). 5. The combined administration of FK 888 (10 microM) plus MEN 10,376 (0.3 microM) abolished the enhancement of EFS-induced NANC contractions by CGRP (10 nM), but DAU 6285 (3 microM) had no effect on the enhancement. 6. Human CGRP8-37 (1 microM), a CGRP1 receptor antagonist had no effect on the submaximal enhancement of the electrically-evoked, NANC contractions by CGRP (1 nM).7. CGRP (30 nM) had no effect on contractions evoked by exogenous substance P (0.3-1 nM).8. These results indicate that in the guinea-pig proximal colon, CGRP produced an enhancement ofNANC contraction induced by EFS through prejunctional mechanisms and that the enhancement is mediated by the stimulation of non-CGRP1 receptors located on intramural tachykininergic neurones.Further, the possible contribution of 5-HT to the enhancing effect of CGRP appeared to be negligible.

CGRP antagonists enhance gastric acid secretion in 2-h pylorus-ligated rats

The influence of calcitonin gene-related peptide (CGRP) antagonists on gastric acid secretion was investigated in rats. Intravenous injection of the CGRP receptor antagonist, CGRP(8-37) (128 nmol/kg) or the CGRP antibody #4901 (4.8 mg/kg, IV) completely prevented alpha-CGRP (3.9 nmol/kg/h)-induced inhibition of acid response to pentagastrin in urethane-anesthetized rats with gastric fistula. CGRP antibody (4.8 mg/kg, IV) increased by 93% gastric acid secretion in conscious rats with pylorus ligation for 2 h. (CGRP(8-73) (128 nmol/kg, IV) also enhanced the acid response measured 2 h after pylorus ligation in conscious rats and in urethane-anesthetized rats infused with pentagastrin by 91% and 56%, respectively. These results suggest that endogenous CGRP attenuates the gastric acid response measured 2 h after pylorus ligation.