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W Schepp

Publications and source records attributed to W Schepp.

At least 73 records · Page 4Linked to original sources
PubMed1993

Effect of bombesin antagonist D-Phe6-BN(6-13)OMe on vagally induced gastrin release from perfused rat stomach.

The aim of the present study was to evaluate the effect of the bombesin antagonist D-Phe6-BN(6-13)OMe (BN-antagonist) on vagally stimulated gastrin release from the isolated rat stomach, which was perfused via the celiac artery with Krebs-Ringer buffer. Vagal stimulation was performed for 10 minutes with 1 ms, 10 V and 10 or 2 Hz, respectively. Gastrin secretion increased significantly during stimulation with 10 and 2 Hz. BN-antagonist was added to the perfusate at the concentration of 10(-6) M, which induced a significant reduction of vagally stimulated gastrin release at 10 Hz (619 +/- 65 vs. 252 +/- 62 pg/10 min, p < 0.05), but not at 2 Hz (564 +/- 117 vs. 493 +/- 113 pg/10 min, p > 0.05). In contrast, atropine (10(-7) M) reduced significantly the gastrin response at 2 Hz (270 +/- 78 pg/10 min, p < 0.01), but not at 10 Hz (446 +/- 87 pg/10 min, p > 0.05). The combination of BN-antagonist and atropine elicited an inhibition of vagally stimulated gastrin release similar to each substance when given alone. Basal gastrin release was not changed by the BN-antagonist. The present data suggest, that in the rat stomach endogenously released bombesin-related peptides contribute to the noncholinergic stimulation of gastrin release at higher stimulation frequencies (10 Hz), however, bombesin-related peptides are not involved, when lower stimulation frequencies (2 Hz) are employed. At both stimulation frequencies additional mechanisms are activated which are noncholinergic and not related to bombesin peptides.

Animals↗
PubMed1993

Leukotriene B4 and C4 production in isolated rat gastric mucosal cells.

Dispersed rat gastric mucosal cells (F0) were separated into five fractions (F1-F5) by counterflow elutriation, with F1 representing the smallest and F5 the largest cell diameters. In F0-F5, leukotriene B4 (LTB4) release in response to 10(-5) M calcium ionophore A-23187 was 7.68 +/- 1.26, 51.6 +/- 10.8, 72.4 +/- 10.4, 7.1 +/- 0.7, 5.7 +/- 0.6, and 11.6 +/- 3.4 pg.10(6) cells-1 x 30 min-1. In the identical fractions, sulfidopeptide release in response to A-23187 was 200.6 +/- 20.5, 1,116.0 +/- 166.6, 1,309.4 +/- 163.2, 189.8 +/- 25.8, 108.0 +/- 18.0, and 158.4 +/- 54.0 pg.10(6) cells-1 x 30 min-1. High-pressure liquid chromatography verified the radioimmunologically determined LTB4 and identified LTC4 as the only sulfidopeptide LT released. LT release from F2 cells in response to A-23187 was time and dose dependent, reaching maximal stimulation at 10(-5) M A-23187. This response was blocked by the dual inhibitor of cyclooxygenase and lipoxygenases, BW755C (2 x 10(-5)-2 x 10(-4) M), by the selective 5-lipoxygenase inhibitor L-651,392 (10(-7)-10(-5) M), and by MK-886 (10(-9)-10(-7) M), which blocks translocation of 5-lipoxygenase. The postreceptor stimuli dibutyryl adenosine 3',5'-cyclic monophosphate, forskolin, 12-O-tetradecanoyl-phorbol-13-acetate, and oleyl-acetyl-glycerol failed to induce LT release. However, 10(-4) M arachidonic acid increased basal LT release up to eightfold and increased A-23187-stimulated LT release by an additional 30%.(ABSTRACT TRUNCATED AT 250 WORDS)

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗
PubMed1992

Pertussis toxin reverses prostaglandin E2- and somatostatin-induced inhibition of rat parietal cell H(+)-production.

In enzymatically dispersed enriched rat parietal cells we studied the effect of pertussis toxin on prostaglandin E2 (PGE2)- or somatostatin-induced inhibition of H(+)-production. Parietal cells were incubated in parallel in the absence (control cells) and presence of pertussis toxin (250 ng/ml; 4 h). [14C]Aminopyrine accumulation by both pertussis toxin-treated and control cells was used as an indirect measure of H(+)-production after stimulation with either histamine, forskolin or dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP) alone and in the presence of PGE2 (10(-9)-10(-7) M) or somatostatin (10(-9)-10(-6) M). PGE2 inhibited histamine- and forskolin-stimulated [14C]aminopyrine accumulation but failed to alter the response to dbcAMP. Somatostatin was less effective and less potent than PGE2 in inhibiting stimulation by histamine or forskolin and reduced the response to dbcAMP. Pertussis toxin completely reversed inhibition by both PGE2 and somatostatin on histamine- and forskolin-stimulated H(+)-production but failed to affect inhibition by somatostatin of the response to dbcAMP. After incubation of crude control cell membranes with [32P]NAD+, pertussis toxin catalysed the incorporation of [32P]adenosine diphosphate (ADP)-ribose into a membrane protein of molecular weight of 41,000, the known molecular weight of the inhibitory subunit of adenylate cyclase (Gi alpha). Pertussis toxin treatment of parietal cells prior to the preparation of crude membranes almost completely prevented subsequent pertussis toxin-catalysed [32P]ADP ribosylation of the 41,000 molecular weight protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1992

Pertussis toxin-sensitive and pertussis toxin-insensitive inhibition of parietal cell response to GLP-1 and histamine.

We have recently shown that in rat parietal cells the glucagon-like peptide 1 (GLP-1) variants 7-36 amide, 1-37, and 1-36 amide stimulate H+ production as indirectly measured by [14C]aminopyrine (AP) accumulation. This response to the GLP-1 peptides was intracellularly mediated by activation of adenylate cyclase and by adenosine 3',5'-cyclic monophosphate (cAMP) as second messenger. In the present study, we compared prostaglandin (PG)E2, somatostatin, and the protein kinase A antagonist Rp-adenosine-3',5'-monophosphorothioate (Rp-cAMPS) with respect to their inhibitory effects on parietal cell function induced by GLP-1 or histamine. PGE2 and somatostatin noncompetitively inhibited AP accumulation and cAMP production in response to the GLP-1 variants and histamine (IC50): [mean inhibitory concn 5 x 10(-9) M PGE2; 3 x 10(-7) somatostatin]; at their maximal concentrations PGE2 (10(-7) M) and somatostatin (10(-6) M) caused 85 and 65% inhibition, respectively. Treatment with pertussis toxin (PT; 250 ng/ml; 4 h) reversed the inhibitory effect of PGE2 and somatostatin on AP accumulation and cAMP production. At 2 x 10(-3) M (IC50: 3 x 10(-4) M) Rp-cAMPS completely inhibited AP accumulation induced by the GLP-1 variants or histamine; this effect was insensitive to PT. Specificity of Rp-cAMPs as protein kinase A inhibitor is suggested by inhibition of AP accumulation in response to Sp-cAMPS and N6,O2-dibutyryl adenosine 3',5'-cyclic phosphate sodium, and forskolin, activators of protein kinase A and adenylate cyclase, respectively. We conclude that the parietal cell responses to GLP-1 and histamine are inhibited by identical mechanisms. Effects of PGE2 and somatostatin are mediated by the PT-sensitive subunit of adenylate cyclase Gi, whereas Rp-cAMPS interferes with cAMP-dependent mechanisms that are insensitive to PT.

Adenylate Cyclase Toxin↗
PubMed1991

Fish oil reduces ethanol-induced damage of the duodenal mucosa in humans.

Eight healthy volunteers were studied before and after 3 weeks of dietary supplementation with fish oil (10.5 g day-1, 18% (1.9 g) eicosapentaenoic acid). Duodenal mucosal lesions were induced by instillation of 40 ml ethanol (40%). Mean endoscopic lesion score was lower after fish oil treatment (1.62 +/- 0.32; mean +/- SEM) than before (3.25 +/- 0.31; P less than 0.01). Histologic lesion score fell from 22.75 +/- 1.98 before treatment to 13.50 +/- 1.51 after fish oil (P less than 0.01). Basal and pentagastrin-stimulated gastric acid output remained unaffected. Release of prostaglandin E2, 6-keto-prostaglandin F1 alpha, and thromboxane B2 from biopsy specimens of the duodenal mucosa in vitro was not significantly altered after fish oil ingestion. In the same in vitro system calcium ionophore A23187-induced release of total leukotriene C (LTC) increased from 10.6 +/- 1.5 ng g-1 mucosa 20 min before treatment to 30.4 +/- 3.2 ng after fish oil. High pressure liquid chromatography analysis showed that this increase was partly due to formation of LTC5 as after fish oil 28% of total LTC were identified as LTC5 whereas 72% were LTC4. We conclude that in humans fish oil reduces ethanol-induced damage of the duodenal mucosa without inhibiting gastric acid secretion or stimulating prostaglandin formation. It remains to be clarified if the changes in leukotriene formation are relevant for the mucosaprotective fish oil effect.

6-Ketoprostaglandin F1 alpha↗
PubMed1991

GLP-1-(7-36) amide, -(1-37), and -(1-36) amide: potent cAMP-dependent stimuli of rat parietal cell function.

We investigated the effect of glucagon-like peptide 1 (GLP-1)-(7-36) amide and its molecular variants GLP-1-(1-37) and GLP-1-(1-36) amide on enzymatically dispersed enriched rat parietal cells using [14C]aminopyrine accumulation as a measure of H+ production. GLP-1-(7-36) amide was 100 times more potent than GLP-1-(1-37) and GLP-1-(1-36) amide in stimulating [14C]aminopyrine accumulation. At their maximally effective concentrations, GLP-1-(7-36) amide (10(-8) M), GLP-1-(1-37) (10(-6) M), and GLP-1-(1-36) amide (10(-6) M) reached 80-90% of the response to 10(-4) M histamine. However, the peptides were 100-10,000 times more potent than histamine, which induced maximal [14C]aminopyrine accumulation at 10(-4) M. Stimulation by GLP-1 was dependent on the presence of a phosphodiesterase inhibitor and was not altered by pertussis toxin. Ranitidine failed to affect the response to the GLP-1 variants. Stimulation of H+ production by GLP-1 was accompanied by an increase in the formation of adenosine 3',5'-cyclic monophosphate (cAMP) but not by changes in phosphoinositol breakdown. In stimulating [14C]aminopyrine accumulation, the GLP-1 variants acted additively to threshold but not to maximal concentrations of histamine, suggesting that histamine and GLP-1 activate the same cAMP pool. In contrast, in anesthetized rats GLP-1-(7-36) amide (10-500 ng.kg-1.h-1) had no effect on basal and pentagastrin-stimulated acid secretion in vivo. We conclude that GLP-1 exerts a direct stimulatory effect on rat parietal cells. This potent effect is mediated by cAMP and is independent of H2 receptors. In vivo direct stimulation by GLP-1 of the parietal cells might be counterbalanced by indirect inhibitory mechanisms that are excluded in the in vitro cell system.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Bombesin-like peptides stimulate gastrin release from isolated rat G-cells.

Bombesin-like peptides as well as receptor-independent activators were tested for their effect on gastrin release from acutely dispersed rat gastric G-cells. The amphibian peptide bombesin as well as its mammalian analogues neuromedin B and neuromedin C stimulated gastrin release. Maximal responses were achieved with 10(-9) M bombesin (191.0 +/- 16.8% of basal release), 10(-8) M neuromedin C(205.9 +/- 17.6%) and 10(-7) M neuromedin B (162.2 +/- 10.4%), respectively. The phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate (TPA) and the synthetic diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol (OAG) are receptor-independent activators of the protein kinase C. Both TPA (10(-6) M) and OAG (10(-5) M) stimulated gastrin release to 214.0 +/- 29.3% and 198.2 +/- 20.8% of basal, respectively. Calcium ionophore A23187 (10(-5) M) was the most effective stimulant tested (364.7 +/- 39.6%). Its effect was reversed by the calmodulin antagonist W 7 (10(-6)-10(-5) M). Finally, forskolin (10(-5) M), a direct activator of cAMP-formation, as well as the cAMP-analogue dbcAMP (10(-3) M) induced gastrin release. IN conclusion, neuromedin B is less potent and less effective than neuromedin C and bombesin in stimulating rat gastric G-cells. In addition, gastrin release is activated by calcium- and phospholipid-dependent as well as by cAMP-induced cellular signal transduction mechanisms.

Amino Acid Sequence↗
PubMed1990

Galanin inhibits gastrin release from isolated rat gastric G-cells.

Enzymatically isolated rat gastric mucosal cells (0.25% G-cells) were separated by counterflow elutriation, yielding a fraction in which the G-cell content was relatively enriched to 1.4%. In this fraction, basal gastrin release (mean +/- SE) was 31.1 +/- 1.3 pg.10(6) cells-1.60 min-1 and was stimulated by 10(-8) M neuromedin C (222.3 +/- 18.1% of basal), 10(-4) M carbachol (227.5 +/- 25.9%), 10(-6) M 12-O-tetradecanoylphorbol-13-acetate (TPA) (196.3 +/- 14.7%), and 10(-3) M dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP) (193.9 +/- 6.8%), respectively. The neuropeptide galanin was tested at 10(-10) to 10(-7) M. Galanin had no effect on basal gastrin release but reduced the responses to neuromedin C, carbachol, TPA, and DBcAMP. IC50 ranged between 1 X 10(-10) and 8.6 X 10(-10) M galanin. Although in the relatively enriched G-cell fraction D-cells were not detectable by immunocytochemistry, a low rate of somatostatin release was still measured by radio-immunoassay (5.3 +/- 0.5 pg.10(6) cells-1.60 min-1). However, galanin failed to increase this rate under basal conditions or in response to any of the stimulants tested. These results favor the assumption that galanin might exert a direct inhibitory effect on rat gastric G-cells. Galanin seems to interfere at an intracellular mechanism(s), which is induced by neuromedin C and carbachol and which is commonly activated by protein kinase C- and cAMP-mediated stimulation.

Aminopyrine↗
PubMed1990

Dual modulation by adenosine of gastrin release from canine G-cells in primary culture.

The effects of adenosine on gastrin release were studied in enzymatically dispersed canine antral cells after 24-36 h in primary culture. We found two contrasting actions for adenosine: inhibition of forskolin-stimulated gastrin release and potentiation of bombesin-stimulated gastrin release. These actions appeared to be mediated by A1 and A2 receptors, respectively. Forskolin-stimulated gastrin release was reduced by adenosine and the A1-selective agonist N6-(L-2-phenylisopropyl)adenosine (L-PIA) but not by the A2-selective agonist 2-phenylaminoadenosine (CV 1808). This inhibition by adenosine was reversed by the preferential A1-receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) as well as by the nonselective adenosine receptor antagonist 8-phenyltheophylline (8-PT). Incubation of the cells with pertussis toxin (200 ng, 8 h) reversed the inhibition by adenosine. In contrast, bombesin stimulation of gastrin release was potentiated by adenosine and CV 1808 but not altered by L-PIA. This effect was enhanced by DPCPX and was not altered by treatment of cells with pertussis toxin. In the absence of exogenous adenosine, 8-PT and DPCPX produced a small increase in basal and stimulated gastrin release. These data suggest dual modulation by adenosine of G-cell function. A1 receptors inhibit adenosine 3,5'-cyclic monophosphate (cAMP)-mediated gastrin release via a pertussis toxin-sensitive mechanism, whereas A2 receptors potentiated the response to cAMP-independent stimuli of gastrin release. Enhancement of gastrin release by adenosine antagonists suggests functional restraint by endogenous adenosine.

Adenosine↗
PubMed1990

Effect of substance P and neurokinin A on rat parietal cell function.

In enzymatically dispersed enriched (76%) rat parietal cells we studied the effect of substance P on acid sequestration as indirectly measured by [14C]aminopyrine accumulation. Substance P (10(-8)-10(-5) M) had no effect on basal [14C]aminopyrine accumulation. Yet, the peptide reduced the response to histamine and to the postreceptor agonists forskolin and dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP). Inhibition by substance P followed noncompetitive kinetics and reduced stimulated parietal cell function by up to 45% at 10(-5) M. The antagonist [D-Pro2, D-Trp7,9]-substance P at 10(-5) M partly reversed the inhibitory effect of substance P. Cholinergic stimulation of [14C]aminopyrine accumulation was not reduced by substance P. Neurokinin A, another tachykinin that is structurally related to substance P, was of comparable potency and efficacy in reducing [14C]aminopyrine accumulation in response to histamine, forskolin, and DBcAMP. Inhibition of forskolin- or DBcAMP-induced [14C]aminopyrine accumulation persisted in the presence of 10(-5) M ranitidine. Inhibition by substance P and neurokinin A of the response to histamine was not sensitive to pertussis toxin. Both tachykinins failed to reduce histamine- and forskolin-stimulated cAMP production. Our data suggest that substance P and neurokinin A exert a direct effect on rat parietal cells. They attenuate histamine-stimulated acid sequestration at an intracellular step that is distal to the adenylate cyclase and that does not involve pertussis toxin-sensitive GTP-binding proteins.

Aminopyrine↗
PubMed1990

Potential mediation of prostaglandin E2 release from isolated human parietal cells by protein kinase C.

Parietal cells are a major source of gastric mucosal prostaglandins in various species. We examined cholinergic stimulation of prostaglandin E2 (PGE2) release from human parietal cells; using activators of the protein kinase C we attempted to get an indirect insight into cellular mechanisms which control PGE2 release. Gastric mucosal specimens were obtained at surgery and the cells were dispersed by collagenase and pronase E. Parietal cells were enriched to 65-80% by a Percoll gradient, and were incubated for 30 min. PGE2 release into the medium (radioimmunoassay) was 74-126 pg/10(6) cells/30 min under basal conditions and was 2.6-fold increased by carbachol (10(-5) and 10(-4) M). Similarly, PGE2 release was stimulated by phospholipase C (20-200 mU/ml, 364% above basal), 1-oleoyl-2-acetyl-sn-glycerol (10(-9)-10(-5) M, 229%), 12-O-tetradecanoylphorbol-13-acetate (TPA; 10(-9)-10(-5) M, 283%) and calcium ionophore A23187 (10(-7)-10(-5) M, 219%). Simultaneous presence of A23187 and TPA synergistically induced stimulation which was slightly higher than the sum of the individual responses. N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide W-7, a putative calmodulin antagonist, inhibited TPA-induced PGE2 release at concentrations regarded specific for blocking calmodulin (IC50 = 1.5 X 0(-6) M). We conclude that in human parietal cells PGE2 is released upon cholinergic stimulation and that phospholipase C and protein kinase C are involved in the control of PGE2 release. We speculate that calmodulin might interact with a protein phosphorylated by protein kinase C to cause PGE2 release.

Calcimycin↗