Carbachol-stimulated Acid Secretion Research Articles

Lack of cholinergic innervation in gastric mucosa does not affect gastrin secretion or basal acid output in neurturin receptor GFRα2 deficient mice

Efferent signals from the vagus nerve are thought to mediate both basal and meal-induced gastric acid secretion, and provide trophic support of the mucosa. However, the underlying mechanisms are incompletely understood. Neurturin, signalling via glial cell line-derived neurotrophic factor (GDNF)-family receptor α2 (GFRα2), is essential for parasympathetic innervation of many target tissues but its role in gastric innervation is unknown. Here we show that most nerve fibres in wild-type mouse gastric mucosa, including all positive for gastrin-releasing peptide, are cholinergic. GFRα2-deficient (KO) mice lacked virtually all cholinergic nerve fibres and associated glial cells in the gastric (oxyntic and pyloric) mucosa but not in the smooth muscle, consistent with the selective expression of neurturin mRNA in the gastric mucosa. 2-Deoxyglucose and hexamethonium failed to affect acid secretion in the GFRα2-KO mice indicating the lack of functional innervation in gastric mucosa. Interestingly, basal and maximal histamine-induced acid secretion did not differ between wild-type and GFRα2-KO mice. Moreover, circulating gastrin levels in both fasted and fed animals, thickness of gastric mucosa, and density of parietal and different endocrine cells were similar. Carbachol-stimulated acid secretion was higher in GFRα2-KO mice, while atropine reduced basal secretion similarly in both genotypes. We conclude that cholinergic innervation of gastric mucosa depends on neurturin-GFRα2 signalling but is dispensable for gastrin secretion and for basal and maximal acid output. Basal acid secretion in the KO mice appears to be, at least partly, facilitated by constitutive activity of muscarinic receptors.

Role of Rho in rabbit parietal cell.

Rho is known as an important regulator of actin microfilament formation. We were led to study it because a dynamic rearrangement of actin filaments occurs during activation of gastric acid secretion. In order to use specific probes, the rabbit gastric gland culture system was employed and the various genes were expressed using adenovirus vector. When the constitutive active mutant of Rho (RhoAV14) was expressed, histamine- or carbachol-stimulated acid secretion monitored by (14)C-aminopyrine accumulation was inhibited. Conversely, expression of C3 toxin, the specific inhibitor of Rho, and expression of G(12/13)-specific regulator of G-protein signaling domain, the specific inhibitor of G(12/13) which is considered to be an upstream mediator of Rho, both potentiated acid secretion stimulated by the agonists. F-actin staining of parietal cell expressing RhoAV14 revealed that the microfilament supporting the intracellular canaliculi (not on the basolateral membrane) almost disappeared. No clear changes in the intracellular localization of Rho were observed during stimulation of parietal cell. In resting glands, the endogenous active form of Rho was relatively high, and it decreased during histamine stimulation. The finding that any treatment which inhibit Rho augment acid secretion whereas those that activate Rho inhibit secretion strongly suggests that the Rho-pathway conducts a negatively regulating signal in parietal cell activation, possibly via site-specific regulation of actin microfilaments.

Protein kinase C-alpha attenuates cholinergically stimulated gastric acid secretion of rabbit parietal cells.

(1) The phorbolester 12-O-tetradecanoyl phorbol-13-acetate (TPA), an activator of protein kinase C (PKC), inhibits cholinergic stimulation of gastric acid secretion. We observed that this effect strongly correlated with the inhibition of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activity in rabbit parietal cells. (2) The aim of this study was to specify the function of PKC-alpha in cholinergically stimulated H(+) secretion. PKC-alpha represents the only calcium-dependent PKC isoenzyme that has been detected in rabbit parietal cells. (3) Gö 6976, an inhibitor of calcium-dependent PKC, concentration-dependently antagonized the inhibitory effect of TPA, and, therefore, revealed the action of PKC-alpha on carbachol-induced acid secretion in rabbit parietal cells. (4) TPA exerted no additive inhibition of carbachol-stimulated acid secretion if acid secretion was partially inhibited by the potent CaMKII inhibitor 1-[N,O-bis(5-isoquinolinsulfonyl)-N-methyl-L-tyrosyl]-4-phenyl-piperazine (KN-62). (5) Since both kinase modulators, TPA and KN-62, affected no divergent signal transduction pathways in the parietal cell, an in vitro model has been used to study if PKC directly targets CaMKII. CaMKII purified from parietal cell-containing gastric mucosa of pig, was transphosphorylated by purified cPKC containing PKC-alpha up to 1.8 mol P(i) per mol CaMKII in vitro. The autonomy site of CaMKII was not transphosphorylated by PKC. (6) The phosphotransferase activity of the purified CaMKII was in vitro inhibited after transphosphorylation by PKC if calmodulin was absent during transphosphorylation. Attenuation of CaMKII activity by PKC showed strong similarity to the downregulation of CaMKII by basal autophosphorylation. (7) Our results suggest that PKC-alpha and CaMKII are closely functionally linked in a cholinergically induced signalling pathway in rabbit parietal cells. We assume that in cholinergically stimulated parietal cells PKC-alpha transinhibits CaMKII activity, resulting in an attenuation of acid secretion.

Soluble Adenylyl Cyclase (sAC) is an important mediator for gastrin, histamine and carbachol stimulated acid secretion in rat parietal cells

Soluble Adenylyl Cyclase (sAC) is an important mediator for gastrin, histamine and carbachol stimulated acid secretion in rat parietal cells

Regulatory mechanism of gastric acid secretion and mucosal integrity--an analysis with various gene deficient mice

Mechanisms for gastric acid secretion have been elucidated through invention of new methods and new drugs. Current genetic technology have generated knockout (KO) mice lacking receptors such as CCK2, histamine H2, muscarinic M3 and M1, or enzymes such as histidine decarboxylase (HDC) and H+,K(+)-ATPase. Here, we review the functional and morphological changes in the gastric mucosa of such KO mice. In M3R-KO mice (intragastric pH 5.9), carbachol, histamine and gastrin stimulated acid secretion like they did in wild-type mice. Carbachol-stimulated acid secretion was significantly inhibited by famotidine and pirenzepine. The serum gastrin level in M3R-KO mice was increased, yet the stomach weight and the gastric mucosa remained unchanged. In H2R-KO mice (intragastric pH 3.0), serum gastrin and mucosal histamine levels significantly increased. Carbachol significantly stimulated acid secretion, yet histamine and gastrin had little or no effect on acid secretion. The stomach wet weight increased with time after birth and the serum albumin level was decreased. In the gastric mucosa with hyperplasia, numerous enlarged cysts and a marked expression of TGF-alpha were observed, indicating the occurrence of Menetrier's disease like mucosal changes. G/D cell ratio was greatly increased, providing evidence of the increased serum gastrin level. In HDC-KO mice (intragastric pH 4.5), the stomach weight was also increased 6 mo after birth, with no enlarged cysts in the gastric mucosa. The above results indicate that KO mice can be used to yield many important findings that selective antagonists cannot reveal.

Inhibition of carbachol stimulated acid secretion by interleukin 1β in rabbit parietal cells requires protein kinase C

BACKGROUNDInterleukin 1β (IL-1β) is a potent inhibitor of gastric acid secretion. Regulatory actions at several levels have previously been demonstrated, including direct inhibition of parietal cell acid secretion. Although IL-1β...

Effect of purified lipopolysaccharides from strains of Helicobacter pylori and Helicobacter felis on acid secretion in mouse gastric glands in vitro.

As a bacterial product, Helicobacter pylori lipopolysaccharide (LPS) can originate in close proximity to parietal cells, but the role of this uniquely structured endotoxin on acid secretion has not been fully investigated and remains unclear. The purpose of this study was to test the direct effect of purified LPS (tested range, 0.1 to 100 microg/ml) from various strains of H. pylori and from one Helicobacter felis strain on histamine- and carbachol-stimulated acid secretion in vitro using mouse gastric glands and the accumulation of [(14)C]aminopyrine. In addition, we investigated whether H. pylori LPS can interfere with two native antisecretory substances, prostaglandin E(2) (PGE(2)) and somatostatin, which may contribute to bacterial pathogenicity. Except for the LPS from H. pylori SS1 (Sydney strain), which gave a statistically significant increase in both histamine- and carbachol-stimulated acid output (38 and 24%, respectively; P < 0.05), no effect of the tested LPS was observed on acid secretion. H. pylori LPS purified from a patient isolate did not affect the potency or the efficacy of the inhibitory dose response curve to PGE(2) or somatostatin. Bacterial interstrain variation in the direct stimulatory effect of Helicobacter-derived LPS on acid secretion was observed, which probably reflects the molecular structure of LPS and the potential to contribute to virulence. Importantly, the data showed that H. pylori LPS did not have any direct antisecretory properties. It can be speculated that the acid stimulatory properties of LPS from H. pylori SS1 may contribute to the gastric damage observed in the mouse model of H. pylori infection.

Gastric acid secretion in aquaporin-4 knockout mice.

The aquaporin-4 (AQP4) water channel has been proposed to play a role in gastric acid secretion. Immunocytochemistry using anti-AQP4 antibodies showed strong AQP4 protein expression at the basolateral membrane of gastric parietal cells in wild-type (+/+) mice. AQP4 involvement in gastric acid secretion was studied using transgenic null (-/-) mice deficient in AQP4 protein. -/- Mice had grossly normal growth and appearance and showed no differences in gastric morphology by light microscopy. Gastric acid secretion was measured in anesthetized mice in which the stomach was luminally perfused (0. 3 ml/min) with 0.9% NaCl containing [(14)C]polyethylene glycol ([(14)C]PEG) as a volume marker. Collected effluent was assayed for titratable acid content and [(14)C]PEG radioactivity. After 45-min baseline perfusion, acid secretion was stimulated by pentagastrin (200 microg. kg(-1). h(-1) iv) for 1 h or histamine (0.23 mg/kg iv) + intraluminal carbachol (20 mg/l). Baseline gastric acid secretion (means +/- SE, n = 25) was 0.06 +/- 0.03 and 0.03 +/- 0.02 microeq/15 min in +/+ and -/- mice, respectively. Pentagastrin-stimulated acid secretion was 0.59 +/- 0.14 and 0.70 +/- 0.15 microeq/15 min in +/+ and -/- mice, respectively. Histamine plus carbachol-stimulated acid secretion was 7.0 +/- 1.9 and 8.0 +/- 1.8 microeq/15 min in +/+ and -/- mice, respectively. In addition, AQP4 deletion did not affect gastric fluid secretion, gastric pH, or fasting serum gastrin concentrations. These results provide direct evidence against a role of AQP4 in gastric acid secretion.

Selective action of a CCK-B/gastrin receptor antagonist, S-0509, on pentagastrin-, peptone meal- and beer-stimulated gastric acid secretion in dogs.

The pharmacological effects of a novel CCK-B/gastrin receptor antagonist, S-0509, on gastric acid secretion in dogs remain unknown. To evaluate the antisecretory effects of S-0509 on gastric acid secretion and to compare such effects with famotidine or atropine in dogs stimulated with various gastric stimulants. Ten beagle dogs with a denervated Heidenhain pouch and three beagle dogs with an innervated gastric fistula were used. Gastric acid secretion was stimulated by either continuous intravenous administration of pentagastrin, carbachol or histamine, or oral administration of a peptone meal or beer. In the Heidenhain pouch model, both intravenously administered and orally administered S-0509 significantly inhibited the gastric acid secretion stimulated by pentagastrin, peptone meal and beer. Nonetheless, the drug had little or no effect on carbachol-stimulated or histamine-stimulated acid secretion. Famotidine extensively inhibited all gastric acid secretion stimulated by the above stimulants in a non-selective manner. Atropine also significantly inhibited the acid secretion stimulated by pentagastrin, peptone meal, beer or carbachol, but was not able to inhibit stimulation due to histamine. Oral administration of peptone meal or beer significantly increased the plasma gastrin level. Similarly to the Heidenhain pouch model, even in the gastric fistula (GF) model, S-0509 significantly inhibited pentagastrin-stimulated gastric acid secretion, yet the drug had no effect on carbachol-stimulated secretion. S-0509 is a selective CCK-B/gastrin receptor antagonist in dogs that inhibits gastric acid secretion stimulated by pentagastrin and gastrin-releasing substances, but does not inhibit histamine-stimulated and carbachol-stimulated acid secretion.

Antisecretory and ulcer healing effects of S-0509, a novel CCK-B/gastrin receptor antagonist, in rats.

The effects of a novel CCK-B/gastrin receptor antagonist, S-0509, on gastric acid secretion and the healing of acetic acid ulcers in rats were examined. S-0509, orally administered 1, 6, and 12 hr prior to a 3-hr pylorus ligation, significantly inhibited basal gastric acid secretion in both normal rats and rats with gastric ulcers. The inhibition was nearly dose-related, persisted for more than 15 hr, and proved to be more potent in rats with ulcers than in normal rats. In addition, S-0509 markedly inhibited pentagastrin- and carbachol-stimulated acid secretion in both normal rats and rats with ulcers, but failed to inhibit histamine-stimulated secretions. In chronic gastric fistula rats, S-0509 also significantly inhibited pentagastrin- and carbachol-stimulated gastric acid secretion in a dose-related manner, but had no effect on histamine-stimulated secretion. These effects were largely similar to those observed with famotidine, although famotidine also inhibited histamine-stimulated secretion. A two-week treatment with S-0509 markedly enhanced the spontaneous healing of acetic acid ulcers and prevented the delay in ulcer healing caused by indomethacin. Gastric secretion was significantly inhibited and the plasma gastrin level was increased in the animals studied. It is concluded that S-0509 is a promising new antisecretory drug for the treatment of peptic ulcers.

Carbachol stimulation of gastric acid secretion and its effects on the parietal cell.

1. The acid secretagogue effect of gastrin is mainly mediated by the release of enterochromaffin-like (ECL) cell histamine, but the mechanism of muscarinic stimulation of acid secretion remains unclear. The results of studying aminopyrine uptake in isolated parietal cells, and histamine release in isolated ECL cells suggest that muscarinic agents may act both directly on the parietal cell and indirectly via histamine release from ECL cells. 2. We examined parietal and ECL cell responses to the muscarinic agent carbamylcholine (carbachol) in conscious rats and in rat isolated vascularly perfused stomachs. 3. Intravenous carbachol stimulated acid secretion in conscious gastric fistula rats and increased H+K+ ATPase mRNA abundance, indicating activation of parietal cells. In these experiments there was no increase in portal venous histamine, or in oxyntic mucosal histidine decarboxylase (HDC) enzyme activity and HDC mRNA abundance. 4. In rat isolated stomachs stimulated with carbachol in the dose range 10 nM(-1) mM only the 1 microM concentration increased venous histamine significantly. 5. We concluded that the muscarinic agent carbachol stimulates acid secretion and H+K+ ATPase mRNA in vivo by a direct effect on the parietal cell, that does not depend on the release of ECL cell histamine.

Pharmacology of JB-9315, a new selective histamine H 2-receptor antagonist

1. 1. The histamine H 2-receptor antagonistic activity and antisecretory and antiulcer effects of JB-9315 were studied in comparison with the standard H 2 blocker ranitidine. 2. 2. In vitro, JB-9315 is a competitive antagonist of histamine H 2 receptors in the isolated, spontaneously beating guinea-pig right atrium, with a pA 2 value of 7.30 relative to a value of 7.36 for ranitidine. JB-9315 was specific for the histamine H 2 receptor because, at high concentration, it did not affect histamine- or acetylcholine-induced contractions in guinea-pig isolated ileum or rat isolated duodenum, respectively. 3. 3. JB-9315 dose dependently inhibited histamine-, pentagastrin- or carbachol-stimulated acid secretion and basal secretion in the perfused stomach preparation of the anesthetized rat. In the pylorusligated rat after intraperitoneal administration, total acid output over 4 h was inhibited by JB-9315 with an ID 50 of 32.8 mg/kg, confirming its H 2-receptor antagonist properties. 4. 4. JB-9315 showed antiulcer activity against cold stress plus indomethacin-induced lesions with an ID 50 of 6.8 mg/kg. 5. 5. JB-9315, 50 and 100 mg/kg, inhibited macroscopic gastric hemorrhagic lesions induced by ethanol. In contrast, ranitidine (50 mg/kg) failed to reduce these lesions. 6. 6. These results indicate that JB-9315 is a new antiulcer drug that exerts a cytoprotective effect in addition to its gastric antisecretory activity.

Interleukin 1β and tumour necrosis factor α inhibit acid secretion in cultured rabbit parietal cells by multiple pathways

Background—The cytokines interleukin 1β (IL-1β) and tumour necrosis factor α (TNF-α) are inhibitors of gastric acid secretion when administered systemically.Aims—To investigate the inhibitory effect of IL-1β and TNF-α on cultured,...

Effect of N alpha-methyl-histamine on acid secretion in isolated cultured rabbit parietal cells: implications for Helicobacter pylori associated gastritis and gastric physiology.

Helicobacter pylori has been shown to produce the unusual metabolite N alpha-methyl-histamine. This compound is known to be a potent agonist at inhibitory histamine H3 receptors. There is increasing evidence implicating this receptor in the control of gastric acid secretion but the mechanism for this remains to be clarified. To investigate the effect of N alpha-methyl-histamine on the acid secretory activity of parietal cells and to determine the mechanism for such effects, thus helping to determine the role of this compound in the pathophysiology of H pylori infection. Rabbit parietal cells were isolated and enriched by collagenase-EDTA digestion and centrifugal elutriation. Following culture on Matrigel coated plates, acid secretion was assessed by 14C aminopyrine accumulation. N alpha-methyl-histamine (100 microM) was as potent as histamine (100 microM) in stimulating acid secretion. This effect was reversed by ranitidine indicating it was mediated via the H2 receptor. N alpha-methyl-histamine potentiated the effects of both carbachol (increased by 280%) and gastrin (by 350%) (p < 0.01). N alpha-methyl-histamine had no inhibitory actions on forskolin or carbachol stimulated acid secretion suggesting that there is not an inhibitory H3 receptor located directly on the parietal cell. Bacterially produced N alpha-methyl-histamine directly stimulates acid secretion by parietal cells and this may contribute to the increased acid secretion that contributes to duodenal ulceration.

Epidermal growth factor inhibits carbachol-stimulated canine parietal cell function via protein kinase C

BACKGROUND & AIMS: Epidermal growth factor (EGF) inhibits secretagogue- stimulated gastric acid secretion via an EGF receptor located on parietal cells. The aim of this study was to examine whether this growth factor inhibited carbachol-stimulated acid secretion through a protein kinase C-dependent mechanism. METHODS: The effect of EGF on carbachol-stimulated aminopyrine uptake, inositol trisphosphate formation, and intracellular Ca2+ ([Ca2+]i) in purified cultured parietal cells was studied. The ability of protein kinase A and C inhibitors to alter the inhibitory action of EGF was assessed. EGF- mediated translocation and activation of protein kinase C in parietal cells were determined. RESULTS: EGF dose dependently inhibited carbachol-stimulated aminopyrine uptake in a pertussis toxin- insensitive, genistein (tyrosine kinase inhibitor)--sensitive manner, with a maximal inhibitory effect (37.5% +/- 6.8%) achieved at 10(-7) mol/L. EGF did not significantly inhibit carbachol-stimulated inositol trisphosphate formation and did not alter the initial transient increase or sustained plateau in [Ca2+]i stimulated by this secretagogue. The protein kinase C inhibitors H-7 and staurosporine dose dependently reversed the inhibitory action of EGF, whereas H-89 (protein kinase A inhibitor) failed to alter the effect of EGF. EGF pretreatment increased the translocation of alpha and beta 1 isoforms of protein kinase C and stimulated kinase activity in parietal cells. EGF did not down-regulate the parietal cell muscarinic receptor. CONCLUSIONS: The inhibitory action of EGF on carbachol-stimulated parietal cell activity seems to involve protein kinase C. (Gastroenterology 1996 Feb;110(2):469-77)

Stimulus-Secretion Coupling in Rat Parietal-Cells Is Affected by Extracellular Magnesium

We investigated the effects of extracellular magnesium on stimulus-secretion coupling in isolated rat parietal cells. A high concentration of extracellular magnesium (10mM) decreased basal and carbachol-stimulated calcium levels, whereas low magnesium levels (0.2mM) had the opposite effect. The calcium-triggered acid secretion was influenced in the same manner. Basal and carbachol-stimulated acid secretion could be enhanced by incubation in a buffer of low magnesium concentration, whereas a high magnesium concentration totally suppressed the carbachol-induced acid secretion. These results demonstrate that magnesium plays a modulative role in calcium-dependent stimulus-secretion coupling in rat parietal cells.

Effects of Helicobacter pylori on histamine and carbachol stimulated acid secretion by human parietal cells.

Helicobacter pylori (H pylori) infection is associated with hypo, normal, and hypersecretory disorders of the gastric mucosa. Pathophysiological pathways by which H pylori interacts with acid secretion are still unclear. The effects of H pylori on (14C) aminopyrine uptake by human parietal cells were examined as an indirect assay for acid secretion. Isolated oxyntic glands were stimulated with submaximal concentrations of histamine or carbachol and incubated with sonicates of different H pylori strains. Omeprazole and sonicates of Campylobacter jejuni served as positive and negative controls, respectively. Two of four H pylori strains reduced hydrochloric acid sequestration within the parietal cells significantly and in a dose dependent manner in up to 80%. Interaction with acid secretion may therefore constitute a factor contributing to a distinct pathogenicity of H pylori strains.

Exocrine secretion and processing of pro-xenopsin in rat gastric lumen

This study examines the effects of acid, acid secretagogues, and pepstatin on gastric luminal concentrations of xenopsin-like immunoreactivity (XPLI) by in situ luminal perfusion of the stomach in anesthetized rats. During perfusion with saline over a 2-h period, the concentration of XPLI fell in parallel with acid output. Levels of XPLI fell more rapidly when the saline contained 20 micrograms/ml pepstatin A and when phosphate-buffered saline (pH 7.0) was used. These treatments did not, however, alter acid output. After a basal condition was established at 90 min, intravenous injection of carbachol, pentagastrin, or histamine stimulated acid and pepsin secretion and also led to an increase in XPLI concentration, which was pepstatin sensitive. Acid itself was also a stimulus for pepsin and XPLI output, which were correlated at various levels of acidity. Although pepstatin blocked the effect of acid on XPLI output, it did not lead to an accumulation of xenopsin (XP) precursor in the luminal fluid. However, the decrement in acid-stimulated XPLI output seen in the presence of pepstatin was matched by an increment in XP precursor associated with the mucosal surface. During high-pressure liquid chromatography, approximately 70% of the acid-generated XPLI eluted at the position of mammalian XP. These data support the notion that, during heightened acid output, XP is secreted by a pepsin-dependent process or generated by the action of pepsin on XP precursor present on the mucosal surface of the rat stomach.

A new potent and selective non-peptide gastrin antagonist and brain cholecystokinin receptor (CCK-B) ligand: L-365,260

L-365,260 (3R(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin-3-yl)-N′ -(3-methylphenyl)urea), interacted in a stereoselective and competitive manner with guinea pig stomach gastrin and brain cholecystokinin (CCK) receptors. The affinity of L-365,260 for both gastrin (K i = 1.9 nM) and brain CCK-B (K i = 2.0 nM) receptors was > 2 orders of magnitude higher than its affinity for peripheral pancreatic CCK-A receptors or various other receptors. L-365,260 exhibited a similar high affinity for brain CCK-B receptors of rats, mice and man. A somewhat lower affinity for gastrin and brain CCK-B (IC 50 = 20–40 nM) receptors was observed in dog tissues. In vivo, oral administration of L-365,260 antagonized gastrin-stimulated acid secretion in mice (ED 50 = 0.03 mg/kg), rats (ED 50 = 0.9 mg/kg) and guinea pigs (ED 50 = 5.1 mg/kg). L-365,260 did not affect basal acid secretion and did not antagonize histamine- or carbachol-stimulated acid secretion in mice. L-365,260 represents a potentially powerful new tool for investigating gastrin and brain CCK-B receptors, and possibly their role in physiology and disease.

Dissociation of pepsinogen and acid secretion in the guinea pig

In vivo observations have suggested that acid secretion may potentiate pepsinogen release. We measured pepsinogen and acid secretion by guinea pig fundic mucosal sheets stimulated by 10−4 M histamine, 10−8 and 10−9 M cholecystokinin, and 3 × 10−7 M carbamylcholine and then investigated the effects of 10−4 M omeprazole on basal, carbacholstimulated, and cholecystokinin-stimulated secretion. Histamine increased basal acid secretion fivefold (p < 0.01) without altering pepsinogen secretion. Cholecystokinin did not stimulate acid secretion but increased pepsinogen secretion by factors of 23.1 at 10−8 M and 9.1 at 10−9 M (both p < 0.01). The combination of 10−4 M histamine and 10−9 M cholecystokinin increased acid secretion 3.5-fold and pepsinogen secretion 6.4-fold, statistically equivalent to the sum of the effects of histamine and cholecystokinin alone. Carbachol increased acid secretion and pepsinogen secretion by factors of 4.0 and 10.9, respectively (both p < 0.01). Pretreatment with 10−4 M omeprazole abolished basal and carbachol-stimulated acid secretion. However, pepsinogen secretion was unaffected (p > 0.05). Furthermore, omeprazole-treated tissues increased pepsinogen secretion by factors of 10.0 with 3 × 10−7 M carbachol and 9.1 with 10−9 M cholecystokinin (both p < 0.01). Thus, basal and secretagogue-stimulated pepsinogen secretion appear independent of acid secretion in intact guinea pig mucosa.