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Biomedical subjects

W E Schmidt

Publications and source records attributed to W E Schmidt.

At least 73 records · Page 4Linked to original sources
PubMed1998

Pituitary adenylate cyclase activating polypeptide induces degranulation of rat peritoneal mast cells via high-affinity PACAP receptor-independent activation of G proteins.

In this study, the secretory effects of PACAP and PACAP analogues on [3H]serotonin-loaded purified rat peritoneal mast cells (RPMCs) were investigated. PACAP(1-27) and PACAP(6-27) stimulated [3H]serotonin release with low potency (ED50: 2 x 10(-6) M) but high efficacy. The N-terminally truncated PACAP form, PACAP(6-27), stimulated tracer release with an ED50 of 0.2 x 10(-6) M, indicating a high-affinity PACAP receptor-independent mechanism of action. The secretory response to PACAP(1-27) could be inhibited by 60-min preincubation with pertussis toxin (ptx), which inhibits G proteins. U73122, a cell-permeable phospholipase C inhibitor, dose-dependently inhibited the secretory effect of 5 microM PACAP(1-27) with an IC50 value of 4 microM (N = 4; p < 0.006). We conclude that PACAP exerts a secretory effect in RPMCs by high-affinity PACAP receptor-independent direct activation of one or more G proteins, which may then activate the PLC-dependent signal-transduction pathway.

Adenylate Cyclase Toxin↗
PubMed1998

The promoter of human p22/PACAP response gene 1 (PRG1) contains functional binding sites for the p53 tumor suppressor and for NFkappaB.

We describe functional binding sites for the tumor suppressor p53 and for NFkappaB residing in the promoter of the novel human early response gene p22/PRG1 (IEX-1/DIF-2). Gel shift and supershift assays demonstrate binding of p53 and NFkappaB to their corresponding sites in vitro. CAT-reporter gene assays show transactivation of the human p22/PRG1 promoter by p53 in Hep3B cells stably transfected with a temperature-sensitive mutant p53, but not in p53-deficient Hep3B cells. TNF alpha induced NFkappaB dependent transactivation was shown in HepG2 cells or in 818-4 pancreatic cancer cells. These data imply that human p22/PRG1 is a target gene for p53 and NFkappaB involved in growth regulation and stress response.

Apoptosis Regulatory Proteins↗
PubMed1998

Pituitary adenylate cyclase activating polypeptide induces multiple signaling pathways in rat peritoneal mast cells.

Pituitary adenylate cyclase activating polypeptide (PACAP) is a high-affinity ligand for at least two types of G-protein coupled receptors, the PACAP type 1 and type 2 receptor. In this study it is demonstrated that the C-terminal PACAP-fragment PACAP(6-27) stimulates serotonin release from rat peritoneal mast cells with higher potency (EC50: 0.2 vs. 2.0 microM) than the PACAP receptor ligand PACAP(1-27). PACAP-induced degranulation of rat peritoneal mast cells was abolished by pertussis toxin and by benzalkonium chloride (IC50: 9.1 microg/ml) indicating the involvement of heterotrimeric G-proteins of the Gi-type. The PACAP effect was also reduced by inhibitors of the phosphatidylinositol specific phospholipase C ((U73122), IC50: 4 microM; (ET-18-O-CH3), IC50: 18 microM), by D609, a specific inhibitor of the phosphatidylcholine specific phospholipase C (IC50: 41 microM), by the protein kinase C-inhibitor staurosporine (IC50: 0.6 microM) and by the lipoxygenase inhibitor nordihydroguaiaretic acid (NGDA) but not by indomethacin. It is concluded that PACAP peptides stimulate secretion in rat peritoneal mast cells in a PACAP receptor-independent manner, probably via direct activation of heterotrimeric G-proteins of the Gi-type; these G-proteins may lead to a sequential activation of different signaling cascades (see above), which may converge at the level of one or more staurosporine-sensitive protein kinase.

Adenylate Cyclase Toxin↗
PubMed1998

The proliferation-associated early response gene p22/PRG1 is a novel p53 target gene.

The novel early response gene p22/PRG1 is linked to cell cycle entry and the induction of proliferation in various cell types although its exact function is still unknown. The p22/PRG1 promoter region contains a 20 bp sequence matching the consensus binding motif for the tumor suppressor protein p53. Gel shift assays demonstrated that p53 specifically binds to an oligonucleotide derived from the p53 binding site of the p22/PRG1 promoter. Chloramphenicol acetyltransferase (CAT) reporter gene assays confirmed that this site confers p53-dependent transcriptional activity to the p22/PRG1 promoter. In Hela cells, p22/PRG1 promoter constructs induced CAT expression only when cotransfected with an expression plasmid for wild-type, but not for mutant p53. Similarly, CAT expression was inducible at the permissive (31 degrees C) but not at the non-permissive temperature (39 degrees C) in the rat embryo fibroblast-derived cell line clone-6 that expresses a temperature-sensitive mutant p53. Conversion of this mutant p53 to a functional p53 at the permissive temperature was accompanied by a significant increase of endogenous p22/PRG1 mRNA level in this cell line. Gamma-irradiation of rat splenocytes or doxorubicin-treatment of Hela cells increased p53 levels followed by transcriptional activation of p22/PRG1 and p21/Waf1 in parallel. Our data demonstrate that p22/PRG1 transcription is induced by p53 during p53-dependent cell cycle arrest and apoptosis. Therefore, p22/PRG1 represents a novel target for transcriptional activation by p53.

Animals↗
PubMed1998

Effect of human pancreastatin peptide (hP-16) on oral glucose tolerance in man.

The gastrointestinal peptide, pancreastatin, has been shown to inhibit insulin release and exocrine pancreatic secretion in the rat. Human pancreastatin-like peptides first isolated from a carcinoid tumor, are expressed in human islets of Langerhans. To investigate the influence of human pancreastatin-16 (hP-16) on oral glucose tolerance (OGTT) in non-diabetic humans, we synthesized the C-terminally amidated human pancreastatin peptide. Healthy male volunteers (n = 6) received in a double-blind placebo-controlled study a 75 g standard OGTT during the i.v. infusion of hP-16 (10 pmol/kg/min) or saline over a time period of 3 h. Peak glucose levels (mg/dl) declined from 151.4 +/- 10.3 (control) to 122.5 +/- 9.7 (hP-16) (mean +/- SEM), peak insulin levels (microU/ml) from 46.3 +/- 2.9 (hP-16) to 32.2 +/- 4.0 (control) and peak C-peptide levels (pmol/ml) from 1.9 +/- 0.1 (hP-16) to 1.2 +/- 0.1 (control). Integrated incremental glucose, insulin and C-peptide responses were reduced by 47% (p < 0.001), 23% (p < 0.05) and 15% (p < 0.05), respectively. In conclusion, these findings indicate that hP-16 attenuates the elevation of blood glucose and insulin levels after an oral glucose load in non-diabetic humans.

Adult↗
PubMed1998

Severe ischemic-type biliary strictures due to hepatic artery occlusion seven years after liver transplantation--a rare cause of late cholestatic graft failure.

Although ischemic cholangitis is an important cause of early cholestatic graft failure in hepatic allografts, it rarely leads to biliary tract abnormalities in the late postoperative period. We describe a 54-year-old woman who underwent orthotopic liver transplantation for alcoholic liver cirrhosis in 1988 and presented in April of 1995 with malaise, jaundice, dark urine, clay-colored stools and cholestasis. An endoscopic retrograde cholangiopancreatography demonstrated a rapid progressive sclerosing cholangitis. Liver biopsy findings showed mild portal hepatitis, specimens were non-diagnostic with regard to cholangitis, and no infection was found. Duplex ultrasonography suggested obstruction of hepatic artery blood flow and celiac arteriogram confirmed complete hepatic arterial occlusion. Progressive destruction and irregular stricturing and dilatation of the intra- and extrahepatic biliary tree, complicating ascending infectious cholangitis, progressive cholestatic jaundice and insufficient endoscopic biliary drainage made a hepatic retransplantation in 1995 mandatory. Ischemic cholangitis is an important cause of cholestatic graft failure, but this type of cholangitis is difficult to diagnose because of its misleading biopsy manifestations. We conclude that liver transplant recipients who exhibit nonanastomotic strictures on cholangiography should be evaluated for occlusion of the hepatic artery as a possible cause.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1997

Relaxant effect of xenin on rat ileum is mediated by apamin-sensitive neurotensin-type receptors.

The action of xenin, a novel 25-residue peptide of the neurotensin (NT)/xenopsin family, was investigated in isolated rat ileal muscle strips and in dispersed longitudinal smooth muscle cells of rat small intestine in vitro. Xenin relaxes KCl-precontracted ileal strips dose dependently (1 nM-3 microM). The order of potency of the investigated peptides was as follows: xenopsin = NT = xenin > neuromedin N. Kinetensin was inactive. Tetrodotoxin, hexamethonium, tetraethylammonium, 4-aminopyridine, and NG-nitro-L-arginine did not influence the relaxant effects of xenin or NT, whereas the K+ channel blocker apamin nearly abolished their effects. Desensitization against one of the peptides or blockade of NT receptors by SR-48692 prevented the effect of xenin and NT. Structure-activity experiments revealed that the COOH-terminal part of the molecules of xenin and NT is essential for biological activity. Experiments with isolated dispersed smooth muscle cells and binding studies on intestinal smooth muscle cell membranes confirmed and extended the results obtained with muscle strips. In conclusion, xenin relaxes rat ileal smooth muscle via a muscular NT-type apamin-sensitive receptor.

Animals↗
PubMed1997

Cellular handling of unoccupied and agonist-stimulated cholecystokinin receptor determined by immunolocalization.

Cellular handling of receptor molecules is an important mechanism for the regulation of appropriately sensitive hormone-stimulated signaling. Until now, our understanding of the cellular handling of the cholecystokinin (CCK) receptor has been largely limited to following a tagged ligand through the cell. In the present work, we report the application of unique CCK receptor antisera directed toward intracellular domains, which permitted the immunolocalization of this molecule independently of its occupation with ligand. The CCK receptor antisera were also useful in Western blotting and immunoprecipitation of this receptor. Unstimulated CCK receptors remained on the surface of both recombinant stable rat CCK-A receptor-bearing Chinese hamster ovary cell line (CHO-CCKR) cells and native rat pancreatic acinar cells and did not constitutively internalize. Agonist stimulation of the CHO-CCKR cells resulted in the prompt internalization of a subset of surface receptors, representing those that were occupied with ligand. Unoccupied receptors remained on the surface, uninfluenced by the stimulated signaling pathways. Consistent with this, CCK receptor phosphorylation induced by 12-O-tetradecanoylphorbol-13-acetate treatment did not stimulate receptor internalization. After internalization, we observed substantial receptor recycling to the plasma membrane. These insights provide the first evidence that CCK receptor internalization occurs as a direct result of an induced conformational change and presumed bimolecular interaction, rather than as an effect of a signaling event.

Amino Acid Sequence↗
PubMed1997

An outbreak of hantavirus pulmonary syndrome in western Paraguay.

During an investigation of hantavirus pulmonary syndrome (HPS) in Paraguay in 1995, sera from persons with HPS-like illness, houshold contacts of confirmed HPS case-patients, and a sample of the area residents were analyzed by ELISA for antibodies to Sin Nombre virus (SNV). Rodent serosurveys and analysis of precipitation records were also conducted. Twenty-three of 24 available probable cases were SNV antibody-positive, 17 of whom were ill between July 1995 and January 1996. Four (14.8%) of 27 case-contacts and 44 (12.8%) of 345 community residents were also seropositive. Calomys laucha (vesper mouse) was the most common rodent species captured and the most frequently SNV-seropositive. Rainfall in May 1995 was 10-fold greater than that seen in May over the preceding 11 years. This 17 case-cluster represents the largest documented outbreak since HPS was first recognized in 1993. Calomys laucha is the likely primary rodent reservoir for a SNV-like hantavirus in western Paraguay. Fluctuations in monthly precipitation rates may have contributed to increased risk for HPS in this region.

Adult↗