Effect of gastrin receptor blockade on gastrin and histidine decarboxylase gene expression in rats during achlorhydria.

BACKGROUND: Gastrin stimulates histidine decarboxylase (HDC) activity and proliferation of enterochromaffin-like (ECL) cells. Furthermore, it has been suggested that gastrin controls HDC gene expression. We therefore analysed the effect of gastrin receptor blockade by PD 136 450 (CAM 1189) on HDC gene expression. The influence of PD 136 450 on gastrin, somatostatin, and chromogranin A was also evaluated. METHODS: Gene expression of HDC, gastrin, somatostatin, and chromogranin A (CgA) was analysed by Northern blot analyses after 14 days' application of the proton pump inhibitor BY 308 and/or the gastrin/cholecystokinin B receptor antagonist PD 136 450. RESULTS: PD 136 450 had no significant effect on gastrin mRNA or somatostatin mRNA in controls and during proton pump inhibition. BY 308 treatment resulted in a marked induction of HDC and CgA mRNA, whereas concomitant PD 136 450 in a concentration previously shown to suppress maximal pentagastrin-induced gastric acid secretion and to prevent BY 308-induced ECL cell proliferation did not result in significant alteration. PD 136 450 increased HDC significantly and CgA mRNA to a lesser extent in normogastrinaemic rats, whereas previous work showed a decreased ECL cell labelling index. CONCLUSIONS: These data suggest that there are independent regulatory pathways for ECL cell proliferation and gene expression. Other factors besides gastrin may act through PD 136 450-insensitive pathways to control HDC and CgA gene expression.

Sodium butyrate induces neuroendocrine cytodifferentiation in the insulinoma cell line RINm5F.

The differentiating agent sodium butyrate inhibits proliferation and stimulates cell-specific hormone expression in rat insulinoma cells. In this study, we investigated the effect of sodium butyrate on neuroendocrine cytodifferentiation in the rat insulinoma subclone, RINm5F. The cells were cultured with 0.5, 1, or 1.5 mM sodium butyrate for up to 72 h. Ultrastructurally, cells cultured with 1 mM sodium butyrate revealed a more differentiated appearance with an induction of cellular compartments involved in regulated insulin secretion. Morphometric analysis showed a significant elevation of neuroendocrine granule density. The total area of the specific granules was increased after incubation with 1 mM sodium butyrate for 48 and 72 h. Proliferation of RINm5F cells was inhibited by sodium butyrate in a dose-dependent manner. DNA production ceased completely within 24 h at 1.5 mM sodium butyrate. This concentration of sodium butyrate increased the cellular insulin content 8.9-fold and the insulin production 2-fold after 72 h. The insulin release was reduced from 79 +/- 3.5% in controls to 37 +/- 5.6% of total in a 24-h incubation period after 3 days of culture with 1.5 mM sodium butyrate. Insulin mRNA levels increased to a maximum of 324% compared with controls after 48 h of culture with 1.5 mM sodium butyrate. Chromogranin A mRNA levels increased to a similar extent (368 +/- 26%), whereas sodium butyrate did not stimulate the expression of synaptophysin, a major membrane component of small neuroendocrine vesicles. In conclusion, our data suggest the selective induction of neuroendocrine cytodifferentiation by sodium butyrate in RINm5F cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the gastric H+/K(+)-ATPase and histidine decarboxylase during omeprazole treatment.

The gastric proton pump H+/K(+)-ATPase in the parietal cell is central to acid secretion into the stomach. We performed the following experiment to examine the pattern of expression of the alpha- and beta-subunits of the H+/K(+)-ATPase at the transcriptional level during 7 days' application of the proton pump inhibitor omeprazole, in relation to the expression of gastrin and histamine, two stimuli of gastric acid secretion. Serum gastrin concentrations and mRNA levels of antral gastrin, fundic histidine decarboxylase (HDC) and H+/K(+)-ATPase alpha- and beta-subunits were determined after 8 h, 1, 3 and 7 days. Omeprazole treatment rapidly caused an increase in the serum gastrin concentration and the antral gastrin mRNA level after 3 days. HDC mRNA expression showed a steady increase with a 5-fold induction after 1 week. However, mRNA levels of the alpha- and beta-subunits of the H+/K(+)-ATPase were unchanged during the course of omeprazole treatment. These results suggest that omeprazole inhibition of the gastric proton pump does not result in feedback activation of H+/K(+)-ATPase gene expression despite adaptive changes of the endocrine stomach.

Tamoxifen or cyproterone acetate in combination with buserelin are ineffective in patients with pancreatic adenocarcinoma.

Experimental evidence and preliminary clinical data suggest a responsiveness of pancreatic adenocarcinoma to sex hormones and LH-RH agonists. In this study, we investigated the effect of the antiestrogen tamoxifen and the antiandrogen cyproterone acetate in combination with the LH-RH agonist buserelin in 9 patients with unresectable pancreatic adenocarcinoma. In all patients the disease was progressive under this therapeutic regimen. In conclusion, complete androgen blockade and antiestrogens in combination with LH-RH agonist cannot be recommended in patients with widespread pancreatic adenocarcinoma.

Stimulation of insulin release is uncoupled from insulin biosynthesis in tumoral RINm5F cells.

RINm5F cells, an insulin-secreting subclone of a rat insulinoma cell line, were incubated in serum-free medium up to 24 hours in the presence or absence of glucagonlike peptide-1(7-36)amide in various concentrations, 3-isobutyl-1 methylxanthine (1 mM), choleratoxin (10 nM), carbachol (1 mM), and potassium (40 mM). Insulin release and biosynthesis were measured by the immunoreactive insulin content of the cells and the medium. Steady-state levels of insulin-specific mRNA were determined by Northern and slot blot analysis. Short-term insulin release is significantly stimulated by all secretagogues tested. A significant increase of insulin biosynthesis by any of the various secretagogues was not detectable on the peptide and mRNA level. Sodium butyrate (1 mM), a differentiating agent, increased insulin-specific mRNA levels in RINm5F cells after 72 hours. In conclusion, substances known to stimulate short-term insulin release in RINm5F cells do not stimulate insulin biosynthesis, indicating an uncoupling of insulin secretion and biosynthesis in these transformed beta cells.

Structure of the canine pancreatic lipase gene.

Identification of three overlapping clones in a canine genomic lambda phage library allowed us to determine a detailed restriction enzyme map of the primary transcriptional unit of the pancreatic lipase gene (15.5 kilobase pairs) as well as 15 and 6 kilobase pairs of 5'- and 3'-flanking regions, respectively. DNA sequence analysis provided the primary structure of (a) 1,345 nucleotides (nt) of 5'-flanking sequence including CAAT and TATA boxes at positions -112 and -35, respectively, and a class 2 glucocorticoid receptor binding sequence at position -97, (b) 13,127 out of approximately 15,500 nt of the transcriptional unit which is organized into 13 exon sequences, and (c) 1,270 nt of 3'-flanking sequence. Exon 1 encodes the entire 5'-nontranslated mRNA sequence; exon 2, the ATG initiation codon and the hydrophobic portion of the signal peptide; and exon 6, Ser154 which shows homology to the active Ser152 in the porcine enzyme. Comparison of the amino acid sequences of human lipoprotein lipase, rat hepatic lipase, and Drosophila yolk proteins 1, 2, and 3 with canine pancreatic lipase shows that the central region of highest homology (encoded by exons 6-8 in the dog gene) contains four highly conserved subregions which may play a critical role in enzyme-substrate and protein-ligand binding for lipases and yolk proteins, respectively. Comparison of the sequences of 10 lipases from prokaryotes and eukaryotes identifies a 9-residue consensus sequence surrounding the active serine which includes the previously identified sequence Gly-X-Ser-X-Gly. The hydrophobic nature of this sequence in the 10 lipases contrasts with the hydrophilic nature of the corresponding sequences in serine proteases and thus defines an active site serine consensus sequence specific for lipases. An analysis of 5'- and 3'-flanking and intron 1-4 sequences in transient expression studies with AR4-2J and 266-6 cells was unable to reveal tissue-specific promoter or enhancer sequences.

Coupled induction of exocrine proteins and intracellular compartments involved in the secretory pathway in AR4-2J cells by glucocorticoids.

Treatment of AR4-2J cells with dexamethasone at 10 nM for 96 h inhibited cell replication by 75% and increased cell size (30%), protein content (1.6-fold) and protein synthesis (2-fold). The increase in protein synthesis was largely due to a 5 to 10-fold increase in the synthesis of secretory proteins. Amylase activity increased 20 to 30-fold in cellular homogenates and 10 to 20-fold in culture medium. Both in the presence and absence of dexamethasone AR4-2J cells release their secretory proteins by constitutive secretion. The proportion of newly synthesized amylase retained by the cells over the 14 h labeling period increased from 15 to 30% with hormone treatment. As judged by comigration on polyacrylamide gels and Western blots analyzed by immunospecific sera, AR4-2J cells synthesize and secrete the majority of known pancreatic secretory proteins. Dexamethasone increased the synthesis of trypsinogen 12 to 16-fold, chymotrypsinogen 4.5 to 6-fold, the group of procarboxypeptidases 6-fold, and amylase 7 to 10-fold. Messenger RNA levels for trypsinogen, amylase and lipase were each increased 4 to 5-fold. At the ultrastructural level dexamethasone led to significant increases in rough endoplasmic reticulum (RER) (30-fold) and Golgi elements (1.5-fold) and to the de novo appearance of electron-opaque granules (0.1-0.5 microns) which were shown to contain amylase by immunolocalization techniques employing protein A-gold. Dexamethasone also led to the formation of gap junctions between AR4-2J cells. These findings indicate that AR4-2J cells provide a model for differentiation of pancreatic acinar cells which should also be studied for the differentiation markers for the regulated secretory pathway.

[Endocrine pancreas tumor as a cause of exocrine pancreas insufficiency: problems of immunologic tumor diagnosis and classification]. / Endokriner Pankreastumor als Ursache einer exokrinen Pankreasinsuffizienz: Probleme immunologischer Tumordiagnostik und -klassifikation.

The case of a 32-year old man with exocrine pancreatic insufficiency and progressive weight loss is reported. Ultrasound examination of the abdomen revealed a huge tumor of the pancreatic head. Smears obtained by a percutaneous fine-needle biopsy showed characteristics of a neuroendocrine tumor. Serum hormone levels and immunocytochemistry presented no evidence for a hormonal activity of the tumor. The exocrine pancreatic insufficiency was explained by an obstruction of the pancreatic duct system. In the present case report the problems of diagnostic approaches to endocrine pancreatic tumors are discussed.

[Effect of osmolality on the gastrointestinal permeation of various carbohydrates in healthy persons]. / Einfluss der Osmolalität auf die gastrointestinale Permeation verschiedener Kohlenhydrate am Gesunden.

The effect of a high osmotic solution on active and passive sugar permeation was investigated in 19 healthy volunteers. The reduced rate of active sugar absorption (3-O-MG and xylose) out of a high osmotic solution was interpreted as a consequence of an impaired emptying of the stomach. The increased passive permeation of intact disaccharides applied in hyperosmolar solution demonstrates an increased gastrointestinal permeability. Intubation studies suppose increased disaccharide absorption out of hyperosmolar solution in the stomach, i.e. high osmolar solutions increase gastric mucosal permeability.