Receptor-activating peptides for PAR-1 and PAR-2 relax rat gastric artery via multiple mechanisms.

Receptor-activating peptides for protease-activated receptors (PARs) 1 or 2 enhance gastric mucosal blood flow (GMBF) and protect against gastric mucosal injury in rats. We thus examined and characterized the effects of PAR-1 and PAR-2 agonists on the isometric tension in isolated rat gastric artery. The agonists for PAR-2 or PAR-1 produced vasodilation in the endothelium-intact arterial rings, which was abolished by removal of the endothelium. The mechanisms underlying the PAR-2- and PAR-1-mediated relaxation involved NO, endothelium-derived hyperpolarizing factor (EDHF) and prostanoids, to distinct extent, as evaluated by use of inhibitors of NO synthase, cyclo-oxygenase and Ca2+-activated K+ channels. The EDHF-dependent relaxation responses were significantly attenuated by gap junction inhibitors. These findings demonstrate that endothelial PAR-1 and PAR-2, upon activation, dilate the gastric artery via NO and prostanoid formation and also EDHF mechanisms including gap junctions, which would enhance GMBF.

Activation of trigeminal nociceptive neurons by parotid PAR-2 activation in rats.

To clarify involvement of protease-activated receptor-2 (PAR-2) in parotid pain, we examined whether PAR-2 activation in the parotid gland could activate trigeminal nociceptive neurons in anesthetized rats, by analyzing immunoreactive Fos as a nociceptive marker. Either the PAR-2 agonist SLIGRL-NH2 or capsaicin, injected into the parotid duct, caused expression of Fos in the trigeminal subnucleus caudalis, although the PAR-2-inactive reversed peptide had no such effect. The Fos expression caused by PAR-2 activation was inhibited by ablation of capsaicin-sensitive sensory neurons. Intraductal SLIGRL-NH2 did not increase vascular permeability in the parotid gland. Our data thus reveal that activation of PAR-2 in the parotid gland can cause activation of trigeminal nociceptive neurons via capsaicin-sensitive sensory nerves most probably by a non-inflammatory mechanism.

Proteinase-activated receptor-2-mediated relaxation in mouse tracheal and bronchial smooth muscle: signal transduction mechanisms and distinct agonist sensitivity.

We characterized the tracheal and bronchial relaxation caused by proteinase-activated receptor-2 (PAR-2) activation in ddY mice and/or in wild-type and PAR-2-knockout mice of C57BL/6 background. Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-NH(2)) and Thr-Phe-Leu-Leu-Arg-amide, PAR-2- and PAR-1-activating peptides, respectively, caused relaxation in the isolated ddY mouse trachea and main bronchus. The relaxation was abolished by specific inhibitors of cyclooxygenase (COX)-1, COX-2, mitogen-activated protein kinase kinase (MEK), and p38 MAP kinase. The MEK and p38 MAP kinase inhibitors did not affect prostaglandin E(2)-induced relaxation. Inhibitors of cytosolic Ca(2+)-dependent phospholipase A(2) (PLA), Ca(2+)-independent PLA(2), diacylglycerol lipase, tyrosine kinase, and protein kinase C exhibited no or only minor inhibitory effects on the PAR-mediated relaxation. Trypsin, a PAR-2 activator, and 2-furoyl-Leu-Ile-Gly-Arg-Leu-amide, a potent PAR-2-activating peptide, in addition to SLIGRL-NH(2), caused airway relaxation in wild-type C57BL/6 mice, as in ddY mice. In PAR-2-knockout mice, the peptide effects were absent and the potency of trypsin decreased. Desensitization of PAR-2 and/or PAR-1 greatly suppressed the relaxant effect of trypsin. The bronchial and tracheal tissues displayed distinct sensitivities toward trypsin and the PAR-2-activating peptides. Our data indicate an involvement of both COX-1 and COX-2, and the MEK-extracellular signal-regulated kinase and p38 MAP kinase signaling pathways in the PAR-2- and PAR-1-triggered relaxation of mouse airway tissue, and substantiate a role for PAR-2 in regulating both the trachea and bronchial responsiveness in the mouse lung.

Modulation of capsaicin-evoked visceral pain and referred hyperalgesia by protease-activated receptors 1 and 2.

Protease-activated receptors (PARs) 1 and 2 are expressed in capsaicin-sensitive sensory neurons, being anti- and pro-nociceptive, respectively. Given the possible cross talk between PAR-2 and capsaicin receptors, we investigated if PAR-2 activation could facilitate capsaicin-evoked visceral pain and referred hyperalgesia in the mouse and also examined the effect of PAR-1 activation in this model. Intracolonic (i.col.) administration of capsaicin triggered visceral pain-related nociceptive behavior, followed by referred hyperalgesia. The capsaicin-evoked visceral nociception was suppressed by intraperitoneal (i.p.) TFLLR-NH2, a PAR-1-activating peptide, but not FTLLR-NH2, a control peptide, and unaffected by i.col. TFLLR-NH2. SLIGRL-NH2, a PAR-2-activating peptide, but not LRGILS-NH2, a control peptide, administered i.col., facilitated the capsaicin-evoked visceral nociception 6-18 h after administration, while i.p. SLIGRL-NH2 had no effect. The capsaicin-evoked referred hyperalgesia was augmented by i.col. SLIGRL-NH2, but not LRGILS-NH2, 6-18 h after administration, and unaffected by i.p. SLIGRL-NH2, and i.p. or i.col. TFLLR-NH2. Our data suggest that PAR-1 is antinociceptive in processing of visceral pain, whereas PAR-2 expressed in the colonic luminal surface, upon activation, produces delayed sensitization of capsaicin receptors, resulting in facilitation of visceral pain and referred hyperalgesia.

Potent and metabolically stable agonists for protease-activated receptor-2: evaluation of activity in multiple assay systems in vitro and in vivo.

To develop potent and metabolically stable agonists for protease-activated receptor-2 (PAR-2), we prepared 2-furoylated (2f) derivatives of native PAR-2-activating peptides, 2f-LIGKV-OH, 2f-LIGRL-OH, 2f-LIGKV-NH(2), and 2f-LIGRL-NH(2), and systematically evaluated their activity in PAR-2-responsive cell lines and tissues. In both HCT-15 cells and NCTC2544 cells overexpressing PAR-2, all furoylated peptides increased cytosolic Ca(2+) levels with a greater potency than the corresponding native peptides, although a similar maximum response was recorded. The absolute potency of each peptide was greater in NCTC2544, possibly due to a higher level of receptor expression. Furthermore, the difference in potency between the 2-furoylated peptides and the native peptides was enhanced when evaluated in the rat superior mesenteric artery and further increased when measuring PAR-2-mediated salivation in ddY mice in vivo. The potency of 2f-LIGRL-NH(2), the most powerful peptide, relative to SLIGKV-OH, was about 100 in the cultured cell Ca(2+) signaling assays, 517 in the vasorelaxation assay, and 1100 in the salivation assay. Amastatin, an aminopeptidase inhibitor, augmented salivation caused by native peptides, but not furoylated peptides. The PAR-2-activating peptides, including the furoylated derivatives, also produced salivation in the wild-type C57BL/6 mice, but not the PAR-2-deficient mice. Our data thus demonstrate that substitution of the N-terminal serine with a furoyl group in native PAR-2-activating peptides dramatically enhances the agonistic activity and decreases degradation by aminopeptidase, leading to development of 2f-LIGRL-NH(2), the most potent peptide. Furthermore, the data from PAR-2-deficient mice provide ultimate evidence for involvement of PAR-2 in salivation and the selective nature of the 2-furoylated peptides.

Distinct roles for protease-activated receptors 1 and 2 in vasomotor modulation in rat superior mesenteric artery.

OBJECTIVE: Protease-activated receptors (PARs) 1 and 2 are expressed in various blood vessels including rat aorta, modulating vascular tone. We investigated the roles of PAR-1 and PAR-2 in vasomotor modulation in rat superior mesenteric artery. METHODS AND RESULTS: Effects of the PAR-2-activating peptide Ser-Leu-Ile-Gly-Arg-Leu-amide (SLIGRL-amide) and the PAR-1-activating peptide Thr-Phe-Leu-Leu-Arg-amide (TFLLR-amide) on isometric tension were examined in isolated rat superior mesenteric artery or aorta. Both SLIGRL-amide and TFLLR-amide caused relaxation in the precontracted rat aortic rings. The latter peptide, but not the former, produced contraction in the resting rings. NG-nitro-L-arginine methyl ester (L-NAME), but not apamin/charybdotoxin known to block the endothelium-derived hyperpolarizing factor (EDHF) pathway, abolished the relaxation and facilitated the contraction. In the precontracted rat superior mesenteric artery, SLIGRL-amide, but not TFLLR-amide, elicited endothelium-dependent relaxation, which was only partially inhibited by L-NAME with and without indomethacin. The residual relaxation was abolished by apamin/charybdotoxin. Carbenoxolone, a gap junction inhibitor, significantly attenuated the SLIGRL-amide-evoked, EDHF-dependent relaxation, although neither 17-octadecynoic acid, a P450 epoxygenase inhibitor, nor catalase, a hydrogen peroxide scavenger, revealed inhibitory effects. The residual response resistant to carbenoxolone was unaffected by ouabain/BaCl2. In the resting artery, TFLLR-amide, but not SLIGRL-amide, produced only slight contraction, which was dramatically facilitated by combination of L-NAME and apamin/charybdotoxin or by removal of the endothelium. CONCLUSIONS: Our data suggest that, in rat superior mesenteric artery, endothelial PAR-2, upon activation, causes relaxation via both NO and EDHF pathways, and that activation of muscular PAR-1 exhibits potential contractile activity that is largely masked by NO and EDHFs pathways triggered by endothelial PAR-1. Gap junctions might be involved in the EDHF mechanisms in this artery.

A protective role of protease-activated receptor 1 in rat gastric mucosa.

BACKGROUND AND AIMS: On activation, protease-activated receptor (PAR)-2 modulates multiple gastric functions and exerts mucosal protection via activation of sensory neurons. The role of PAR-1, a thrombin receptor, in the stomach remains unknown. We thus examined if the PAR-1 agonist could protect against gastric mucosal injury in rats. METHODS: Gastric mucosal injury was created by oral administration of ethanol/HCl or absolute ethanol in conscious rats. Gastric mucosal blood flow and acid secretion were determined in anesthetized rats. Immunohistochemical analyses of PAR-1 and cyclooxygenase (COX)-1 were also performed in rat and human stomach. RESULTS: The PAR-1 agonist TFLLR-NH(2), administered intravenously in combination with amastatin, protected against the gastric mucosal injury induced by ethanol/HCl or absolute ethanol. The protective effect of TFLLR-NH(2) was abolished by indomethacin or a COX-1 inhibitor but not by ablation of sensory neurons with capsaicin. TFLLR-NH(2) produced an NO-independent increase in gastric mucosal blood flow that was partially inhibited by blockade of the endothelium-derived hyperpolarizing factor pathway. This inhibitory effect was promoted by indomethacin. TFLLR-NH(2) suppressed carbachol-evoked acid secretion in an indomethacin-reversible manner. Immunoreactive PAR-1 and COX-1 were expressed abundantly in rat gastric muscularis mucosae and smooth muscle, and the former protein was also detectable in blood vessels. Similar staining was observed in human gastric muscularis mucosae. CONCLUSIONS: The PAR-1 agonist, given systemically, protects against gastric mucosal injury via COX-1-dependent formation of prostanoids, modulating multiple gastric functions. Our data identify a novel protective role for PAR-1 in gastric mucosa, and the underlying mechanism is entirely different from that for PAR-2.

Involvement of EDHF in the hypotension and increased gastric mucosal blood flow caused by PAR-2 activation in rats.

1. Agonists for protease-activated receptor-2 (PAR-2) cause hypotension and an increase in gastric mucosal blood flow (GMBF) in vivo. We thus studied the mechanisms underlying the circulatory modulation by PAR-2 activation in vivo, especially with respect to involvement of endothelium-derived hyperpolarizing factor (EDHF). 2. Arterial blood pressure and GMBF were measured in anesthetized rats in vivo. Vascular relaxation was assessed in the precontracted rat gastric arterial rings in vitro. 3. The PAR-2-activating peptide SLIGRL-NH2 and/or trypsin, administered i.v., produced largely NO-independent hypotension and increase in GMBF accompanied by decreased gastric mucosal vascular resistance (GMVR) in rats. 4. Combined administration of apamin and charybdotoxin, but not each of them, specifically abolished the hypotension, increased GMBF and decreased GMVR caused by the PAR-2 agonists. 5. In the isolated rat gastric artery, SLIGRL-NH2 elicited endothelium-dependent relaxation even in the presence of an NO synthase inhibitor and indomethacin, which was abolished by apamin plus charybdotoxin. 6. Our data suggest involvement of apamin/charybdotoxin-sensitive K+ channels in the PAR-2-triggered hypotension and increased GMBF, predicting a role of EDHF-like factors.

[Pain information pathways from the periphery to the cerebral cortex].

A recent PET study revealed that the first and second somatosensory cortices (SI, SII), and the anterior cingulate cortex are activated by painful peripheral stimulation in humans. It has become clear that painful signals (nociceptive information) evoked at the periphery are transmitted via various circuits to the multiple cerebral cortices where pain signals are processed and perceived. Human or clinical pain is not merely a modality of somatic sensation, but associated with the affect that accompanies sensation. Consequently, pain has a somatosensory-discriminative aspect and an affective-cognitive aspect that are processed in different but correlated brain structures in the ascending circuits. Considering the physiologic characteristics and fiber connections, the SI and SII cortices appear to be involved in somatosensory-discriminative pain, and the anterior cingulate cortex (area 24) in the affective-cognitive aspect of pain. This paper deals with the ascending pain pathways from the periphery to these cortices and their interconnections. Our recent findings on the protease-activated receptors 1 and 2 (PAR-1, and -2), which are confirmed to exist in the dorsal root ganglion cells, are also described. Activation of PAR-2 during inflammation or tissue injury at the periphery is pronociceptive, while PAR-1 appears to be antinociceptive. Based on the these findings, PAR-1 and PAR-2 are attracting interest as target molecules for new drug development.

The PAR-1-activating peptide facilitates pepsinogen secretion in rats.

Protease-activated receptor-2 (PAR-2) is abundantly expressed in gastric mucosal chief cells, facilitating pepsinogen secretion. In the present study, we investigated whether PAR-1, a thrombin receptor, could modulate pepsinogen secretion in rats. The PAR-1-activating peptide TFLLR-NH(2) as well as the PAR-2-activating peptide SLIGRL-NH(2), administered i.v. repeatedly at 1-h intervals, significantly increased gastric pepsinogen secretion over 2-4 h (after two to four doses). In contrast, the control peptide FTLLR-NH(2), given in the same manner, had no such effect. Thus, PAR-1, like PAR-2, might function to facilitate pepsinogen secretion, suggesting a novel role of the thrombin-PAR-1-pathway in the stomach.

[PAR (protease-activated receptor) as a novel target for development of gastric mucosal cytoprotective drugs].

Protease-activated receptor-2 (PAR-2), a G protein-coupled seven trans-membrane domain receptor, is distributed throughout the gastrointestinal tract, modulating various functions. In gastric mucosa, PAR-2 present in sensory neurons, upon activation, triggers mucus secretion by stimulating release of CGRP and tachykinins, resulting mucosal cytoprotection. PAR-2 activation also suppresses acid secretion and increase mucosal blood flow, contributing to the protective mechanisms. In contrast, PAR-2 is also present in chief cells, facilitating pepsinogen secretion. PAR-2 would thus appear to be primarily protective in gastric mucosa, but may also have an aggressive property in certain conditions. Finally, functions of PARs other than PAR-2 in gastric mucosa are also discussed.

Protease-activated receptor-2 (PAR-2) in the pancreas and parotid gland: Immunolocalization and involvement of nitric oxide in the evoked amylase secretion.

Protease-activated receptor-2, a G protein-coupled receptor activated by serine proteases such as trypsin, tryptase and coagulation factors VIIa and Xa, modulates pancreatic and salivary exocrine secretion. In the present study, we examined the distribution of PAR-2 in the pancreas and parotid gland, and characterized the PAR-2-mediated secretion of amylase by these tissues in vivo. Immunohistochemical analyses using the polyclonal antibody against rat PAR-2 clearly showed abundant expression of PAR-2 in rat pancreatic and parotid acini. The PAR-2 agonist SLIGRL-NH2, administered intraperitoneally (i.p.) at 1-10 micromol/kg and 1.5-15 micromol/kg, in combination with amastatin, an aminopeptidase inhibitor, facilitated in vivo secretion of pancreatic and salivary amylase in a dose-dependent manner, respectively, in the mouse. The PAR-2-mediated secretion of pancreatic amylase was abolished by pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor. The secretion of salivary amylase in response to the PAR-2 agonist at a large dose, 15 micromol/kg, but not at a smaller dose, 5 micromol/kg, was partially reduced by L-NAME. Pretreatment with capsaicin for ablation of the sensory neurons did not modify the PAR-2-mediated secretion of pancreatic and salivary amylase in the mouse. In conclusion, our study demonstrates expression of PAR-2 in rat pancreatic acini as well as parotid acini and indicates that nitric oxide participates in the PAR-2-mediated in vivo secretion of pancreatic amylase, and, to a certain extent, of salivary amylase, although capsaicin-sensitive sensory neurons, known to be activated by PAR-2, are not involved in the evoked pancreatic or salivary amylase secretion.

Role of N-methyl-D-aspartate receptors and the nitric oxide pathway in nociception/hyperalgesia elicited by protease-activated receptor-2 activation in mice and rats.

Activation of the peripheral protease-activated receptor-2 (PAR-2) triggers nociceptive behaviour and thermal hyperalgesia in rats. The present study created a novel mouse model for PAR-2-triggered nociception, and then examined the roles of NMDA receptors and the nitric oxide (NO) pathway in nociceptive processing by PAR-2. Intraplantar administration of the PAR-2 agonist SLIGRL-NH(2) elicited nociceptive responses in mice, an effect being more specific in mast cell-depleted mice. This PAR-2-triggered nociception was abolished by the NMDA receptor antagonist MK-801, but not the neuronal NO synthase inhibitor 7-nitro indazole. In contrast, the PAR-2-triggered thermal hyperalgesia in rats was blocked by both agents. Our study thus provides a novel mouse model for PAR-2-mediated nociception, and suggests that NMDA receptors are involved in PAR-2-triggered nociception and hyperalgesia, while NO contributes only to the latter.

Capsazepine inhibits thermal hyperalgesia but not nociception triggered by protease-activated receptor-2 in rats.

Protease-activated receptor-2 (PAR-2), expressed in sensory neurons, triggers thermal hyperalgesia, nociceptive behavior and spinal Fos expression in rats. In the present study, we examined if the nociceptive processing by PAR-2 is mediated by trans-activation of capsaicin receptors. The thermal hyperalgesia following an intraplantar (i.pl.) administration of the PAR-2-activating peptide SLIGRL-NH2 was completely abolished by the capsaicin receptor antagonist capsazepine. In contrast, neither the nociceptive behavior nor spinal Fos expression in response to i.pl. SLIGRL-NH2 were attenuated by capsazepine. Our data imply that trans-activation of capsaicin receptors by PAR-2 might be involved in the PAR-2-triggered thermal hyperalgesia, but not nociception.

Suppression by protease-activated receptor-2 activation of gastric acid secretion in rats.

Activation of protease-activated receptor-2 (PAR-2), a receptor activated by trypsin/tryptase, induces neurally mediated gastric mucus secretion accompanied by mucosal cytoprotection. In the present study, we investigated whether PAR-2 could modulate gastric acid secretion in rats. Messenger RNAs for PAR-2 and PAR-1 were detected in the gastric mucosa and smooth muscle. The PAR-2-activating peptide SLIGRL-NH(2), but not the inactive control peptide, when administered i.v., strongly suppressed gastric acid secretion in response to carbachol, pentagastrin or 2-deoxy-D-glucose in the rats with a pylorus ligation. The PAR-2-mediated suppression of acid secretion was resistant to cyclooxygenase inhibition or ablation of sensory neurons by capsaicin. Our results provide novel evidence that in addition to stimulating neurally mediated mucus secretion, activation of PAR-2 suppresses gastric acid secretion independently of prostanoid production or sensory neurons. These dual actions of PAR-2 would result in gastric mucosal cytoprotection.

The PAR-1-activating peptide attenuates carrageenan-induced hyperalgesia in rats.

We examined if thrombin or a receptor-activating peptide for protease-activated receptor-1 (PAR-1), a thrombin receptor, could modulate nociception at peripheral levels. Intraplantar administration of PAR-1 activators, thrombin or TFLLR-NH(2), but not its inactive control FTLLR-NH(2) or a PAR-2 activator SLIGRL-NH(2), significantly attenuated the hyperalgesia in rats treated with carrageenan, although they had no effect on nociception in naïve rats. The thrombin-PAR-1 system might thus act to attenuate nociception during inflammatory hyperalgesia.

Capsazepine partially inhibits neurally mediated gastric mucus secretion following activation of protease-activated receptor 2.

1. Protease-activated receptor 2 (PAR2), present in capsaicin-sensitive sensory neurons, induces gastric mucus secretion and mucosal cytoprotection. 2. We studied the possible cross-talk between PAR2 and vanilloid receptor 1 (VR1). The VR1 antagonist capsazepine partially inhibited the PAR2-mediated increase in gastric mucus secretion. 3. Thus, activation of VR1 is responsible, at least in part, for the neurally mediated mucosal cytoprotection following activation of PAR2.

Effects of somatosensory cortical stimulation on expression of c-Fos in rat medullary dorsal horn in response to formalin-induced noxious stimulation.

We examined the effects of epidural electrical stimulation of primary (SI) and secondary (SII) somatosensory cortex on expression of c-Fos protein in rat medullary dorsal horn neurons (Vc; trigeminal nucleus caudalis) in response to formalin-induced noxious stimulation. Epidural electrical stimulation (single pulse, 0.2 msec duration at 10 Hz) was applied to the left facial region SI or SII at three different stimulus intensities, 0.1, 0.5, and 1.0 mA for 60 min 0 or 2 hr after bilateral injection of formalin into the lower lip. SII stimulation at 1.0 mA immediately after injection of formalin, significantly decreased the number of Fos-positive cells in the right VcI/II by 32.4%. There was no significant change in the number of Fos-positive cells in the VcIII/IV. SII stimulation at 0.5 and 1.0 mA 2 hr after injection of formalin, significantly decreased the number of Fos-positive cells in the right VcI/II by 47.9% and 40.8%, but significantly increased the number of Fos-positive cells in the right VcIII/IV by 178.8% and 324.3%, respectively. In contrast, SI stimulation had no effect on expression of c-Fos in Vc. Possible direct corticotrigeminal projections were labeled anterogradely by injection of WGA-HRP into the SI and SII. In the Vc, labeled terminals were distributed mostly in the contralateral medial half of VcIII/IV and medullary reticular nucleus dorsalis but rarely in VcI/II. These results suggest that activation of SII-medullary fibers suppress nociceptive information from the oro-facial regions.

Specific expression of spinal Fos after PAR-2 stimulation in mast cell-depleted rats.

Protease-activated receptor-2 (PAR-2) in the sensory neurons may be involved in nociceptive processing. We attempted to detect and characterize specific expression of spinal Fos, a marker of nociception, in mast cell-depleted rats. Intraplantar (i.pl.) administration of not only the PAR-2 agonist SLIGRL-NH2, but also the control peptide LSIGRL-NH2, induced Fos expression in naive rats, whereas only the former specifically produced Fos expression in mast cell-depleted rats. This Fos expression was blocked by intrathecal DAMGO, a mu-opioid agonist, and, in part, by i.pl. calphostin C, a protein kinase C (PKC) inhibitor. Thus, specific expression of spinal Fos following peripheral PAR-2 activation is detectable in mast cell-depleted rats, suggesting activation of spinal nociceptive neurons, which is partially mediated by activation of PKC.

Protease-activated receptor-2 (PAR-2) in the rat gastric mucosa: immunolocalization and facilitation of pepsin/pepsinogen secretion.

1. Agonists of protease-activated receptor-2 (PAR-2) trigger neurally mediated mucus secretion accompanied by mucosal cytoprotection in the stomach. The present study immunolocalized PAR-2 in the rat gastric mucosa and examined if PAR-2 could modulate pepsin/pepsinogen secretion in rats. 2. PAR-2-like immunoreactivity was abundant in the deep regions of gastric mucosa, especially in chief cells. 3. The PAR-2 agonist SLIGRL-NH(2), but not the control peptide LSIGRL-NH(2), administered i.v. repeatedly at 0.3 - 1 micromol kg(-1), four times in total, significantly facilitated gastric pepsin secretion, although a single dose produced no significant effect. 4. The PAR-2-mediated gastric pepsin secretion was resistant to omeprazole, N(G)-nitro-L-arginine methyl ester (L-NAME) or atropine, and also to ablation of sensory neurons by capsaicin. 5. Our study thus provides novel evidence that PAR-2 is localized in mucosal chief cells and facilitates gastric pepsin secretion in the rats, most probably by a direct mechanism.