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H F Helander

Publications and source records attributed to H F Helander.

At least 19 recordsLinked to original sources
PubMed1996

Localization of mRNA for the muscarinic M1 receptor in rat stomach.

Cholinergic stimulation of receptors in the oxyntic mucosa results in secretion of mucus, pepsinogen and hydrochloric acid. There has been speculation as to the cellular localization of these receptors in the mucosa and as to which subtype is present in the different cell types. In the present study, utilizing radioactive riboprobes for the M1 muscarinic receptor subtype, we carried out in situ hybridization to determine which cells of the gastric corpus transcribe mRNA for this receptor. The antisense M1 probe hybridized strongly on the zymogen cells and, to a lesser extent, on the surface mucous cells and the muscle layers. Control sections from brain also displayed specific hybridization.

Animals↗
PubMed1996

The expression of pepsinogen c mRNA in normal gastroduodenal mucosa and the gastric ulcer margin of the rat.

During the healing of experimental gastric ulcers in the oxyntic mucosa, there is a dedifferentiation of the glands in the ulcer margin: previous studies have shown that the parietal cells lose their capacity to produce HCl, and mucous cells replace the zymogen cells. Primarily, we wished to investigate whether or not the glands of the ulcer margin transcribe mRNA for pepsinogen; secondly we also wanted to locate such transcription in other parts of the gastroduodenal epithelium. For this purpose, we first established the baseline for distribution of pepsinogen mRNA in normal rats. We then studied its location in the margin of ulcers in the corpus region after 1-15 days of healing. Formaldehyde-fixed paraffin sections were used for in situ hybridization of mRNA for pepsinogen C, utilizing radioactive riboprobes. The normal gastroduodenal mucosa showed widespread hybridization: the signal was particularly strong in the zymogen cells; weaker signals were obtained from the mucous neck cells, and the cells of the cardiac, antral, and Brunner glands. Specific hybridization was weak or absent in the ulcer margin during the entire period studied. It is concluded that the capacity to produce pepsinogen C is significantly reduced or absent in the gastric ulcer margin during the first 15 days of healing; this should reduce the risks of peptic attack on the delicate scar and margin tissues during ulcer healing.

Animals↗
PubMed1996

Hypergastrinemia increases proliferation of gastroduodenal epithelium during gastric ulcer healing in rats.

We investigated if hypergastrinemia exerted any influence on the proliferation of gastroduodenal epithelium during the healing of ulcers in rats. A mucosal ulcer was induced in the corpus region of the stomach in three groups of rats, which were then given vehicle, omeprazole (400 mumol/kg/day), or gastrin-17 (60 nmol/kg/day) for three or six days. A fourth group of unoperated rats served as controls. One hour before killing, [3H]thymidine was injected. The ulcer margin and corresponding control tissues were excised and processed for light microscopic determination of epithelial labeling index (LI), mitotic index, and apoptotic index. LI was also determined in other parts of the gastroduodenal mucosa. Three and six days after the ulcer operation, the LI in the vehicle-treated ulcer rats was significantly increased in the ulcer margin and in the duodenum, in comparison with the intact controls. In the ulcer margin, the mitotic index was significantly increased, in parallel with the LI; the apoptotic index remained at the control level. The LI in the ulcer margin was increased further after administration of omeprazole or gastrin-17, which elevated the plasma gastrin levels by 5-15 times. It is concluded that hypergastrinemia may increase cell proliferation in the ulcer margin, which may accelerate the rate of healing.

Animals↗
PubMed1996

Selective ligand-induced intracellular calcium changes in a population of rat isolated gastric endocrine cells.

BACKGROUND & AIMS: Peripheral regulation of acid secretion depends mainly on stimulation or inhibition of the three major gastric endocrine cells (enterochromaffin-like, gastrin, and somatostatin). The aim of this paper was to define physiological responses of enterochromaffin-like, gastrin, and somatostatin cells in a mixed endocrine cell population by measuring ligand-selective changes of intracellular calcium ([Ca2+]i) in individual cells. METHODS: Endocrine cells were enriched from a rat gastric cell suspension by elutriation, a density-gradient fractionation, and a 48-hour short-term culture. [Ca2+]i responses of individual cells to various ligands such as gastrin/carboxy-terminal cholecystokinin octapeptide and selective cholecystokinin antagonists, carbachol, and gastrin-releasing peptide were monitored using video imaging in a perfusion chamber. Characteristic [Ca2+]i changes distinguished the three cell types, confirmed by immunostaining. RESULTS: All enterochromaffin-like cells respond to cholecystokinin-B receptor stimulation, but only a few respond to carbachol. Gastrin cells respond to both gastrin-releasing peptide and carbachol but not to cholecystokinin-receptor agonists. Somatostatin cells have both stimulatory cholecystokinin-A and cholecystokinin-B receptors and inhibitory muscarinic receptors. All cells have inhibitory somatostatin receptors. CONCLUSIONS: Calcium-signaling responses of gastric endocrine cells are distinctive. This allows individual cell types in a mixed population to be characterized and permits an analysis of the hormones and transmitters that act directly on a specific cell type.

Animals↗
PubMed1995

Parietal cell kinetics after administration of omeprazole and ranitidine in the rat.

BACKGROUND: This study aimed at determining the turnover rate of parietal cells after inhibition of acid secretion. METHODS: Rats were given omeprazole (80 mumol/kg) by gavage once daily or ranitidine (1200 mumol/kg) by osmotic minipump for 5 days. Control rats received saline only. All rats were also given 3H-thymidine by osmotic minipumps. The animals were killed, 5, 14, 28, or 56 days after the start of the 3H-thymidine infusion. After formaldehyde fixation by perfusion through the aorta, light microscopic autoradiography was carried out on plastic sections of the oxyntic mucosa to determine the labeling index of the parietal cells. RESULTS: The average turnover rate in the control rats was calculated to be 0.61% per day, corresponding to a mean turnover time of 164 days. In the rats given inhibitors of acid secretion, the turnover rates did not differ significantly from those of the control group. CONCLUSION: Inhibition of gastric acid secretion did not significantly change the turnover rate of the parietal cells.

Animals↗
PubMed1994

In situ hybridization of mRNA for the gastric H+,K(+)-ATPase in rat oxyntic mucosa.

The H+,K(+)-ATPase member of the phosphorylating ion motive ATPases is composed of two subunits, a large alpha-subunit composed of about 1030 amino acids and a smaller beta-subunit consisting of about 290 amino acids. By biochemical and immunological methods both subunits have been found in high abundance in the gastric parietal cell. In the present study in situ hybridization was used for localizing and comparing concentrations of the mRNA for the two subunits in the gastric epithelium. For this purpose 3H-labelled probes were preferred. Hybridization was detected only in the parietal cells. The older parietal cells in the bottom of the mucosa gave a weaker hybridization signal than the younger parietal cells closer to the surface. The margin of experimental ulcers, where the parietal cells are of low differentiation, showed very weak, if any, hybridization. The differences observed in hybridization densities may reflect differences in mRNA synthesis or stability. It is conceivable that older parietal cells, as well as parietal cells of low differentiation, produce relatively small amounts of H+,K(+)-ATPase.

Animals↗
PubMed1994

Depletion of secretory granules from the feline parotid gland: action of NANC transmitters per se.

A parotid acinar degranulation of approximately 60 and 40% was observed in cats under pentobarbitone anaesthesia after a 90-min period of continuous stimulation of the parasympathetic auriculo-temporal nerve at 10 Hz in the absence and presence of atropine, respectively. Atropine completely abolished the large fluid response of the gland to the nerve stimulation. In the non-atropinized cats, bethanechol, infused into the carotid artery at a dose rate evoking a salivary flow similar to that in response to parasympathetic nerve stimulation, caused an acinar degranulation of approximately 25% and acinar vacuolation. Vasoactive intestinal peptide (VIP; 0.5 microgram kg-1 min-1 also infused into the carotid artery for 90 min) caused an acinar degranulation of the same magnitude as the parasympathomimetic drug but the peptide did not give rise to any fluid secretion or vacuole formation. The experiments were performed in the presence of alpha- and beta-adrenoceptor blockers. Thus, in parotid glands of the cat, producing no overt secretion of fluid, non-adrenergic, non-cholinergic (NANC) mechanisms may be at work causing exocytosis of the acinar granules. These mechanisms are also likely to contribute to the secretion of granules in response to parasympathetic nerve activity in the absence of blockade of the classical autonomic receptors.

Adrenergic alpha-Antagonists↗
PubMed1994

Gastrin effects on isolated rat enterochromaffin-like cells in primary culture.

The hormone gastrin stimulates acid secretion by releasing histamine from gastric enterochromaffin-like (ECL) cells and induces ECL cell proliferation in vivo. This study uses a > 90% pure ECL cell preparation in culture to compare gastrin effects on histamine release, histidine decarboxylase (HDC) activity, and DNA synthesis. Gastrin and the cholecystokinin octapeptide (CCK-8, nonsulfated) induced histamine release from ECL cells (24-96 h of primary culture) within 5 min of incubation [concentration eliciting 50% of maximal response (EC50), 4 and 2 x 10(-11) M, respectively]. The CCK-B antagonist L-365,260 inhibited this effect [concentration inhibiting 50% of maximal response (IC50), 2 x 10(-8) M], whereas the CCK-A antagonist L-364,718 (10(-8) M) and the tyrosine kinase inhibitor genistein (10(-4) M) had no effect. Histamine release was associated with a biphasic elevation of intracellular Ca2+. Gastrin stimulated HDC activity two- to threefold after 60 min of incubation (EC50, 10(-10) M). Gastrin also increased DNA synthesis in ECL cells, with an EC50 of 1.7 x 10(-12) M as measured by the incorporation of 5-bromo-2'-deoxyuridine (BrdU). Positive nuclear immunostaining increased two- to threefold in up to 20% of ECL cells after 48-96 h of incubation. This effect was inhibited by L-365,260 (IC50, 5 x 10(-9) M) and by genistein (10(-4) M) but was not altered by L-364,718 (10(-8) M). The antisecretory drugs omeprazole, lansoprazole, and pantoprazole did not affect BrdU incorporation in isolated ECL cells. In conclusion, acute and chronic gastrin effects on the ECL cell are mediated via CCK-B receptors but differ in apparent receptor affinity and signal transduction pathways.

Animals↗
PubMed1993

The site of acid secretion in the mammalian parietal cell.

Initiation of acid secretion in the gastric mucosa is accompanied by a morphological transformation in which the acid pump, the H+/K(+)-ATPase, translocates from a cytoplasmic vesicular location to the secretory surface lining the canaliculi. Associated with the morphological changes, activation of K+ and Cl- pathways are necessary to supply K+ to the extracytoplasmic face of the pump. Although the pump in the secretory membrane is known to secrete acid, it is not known whether activation of the KCl pathway occurs in the tubulovesicular membrane prior to the formation of the canaliculus, or when the pump is in the secretory membrane. The cellular site of activation of acid secretion in the rabbit gastric parietal cell was investigated using the covalent binding of [3H]omeprazole as a probe of acid secretion in rabbit gastric glands that were undergoing stimulation in vitro. This compound depends on an acidic environment for activation and covalent binding to the H+/K(+)-ATPase. Electron microscopic autoradiography showed that activation of the enzyme occurred only when it was present in the canalicular membrane and not when it was present in the cytoplasmic tubulovesicular membrane. Hence there is likely to be a physical separation of K+ and/or Cl- pathways from the ATPase in the resting cell, and stimulation of acid secretion is dependent on colocalization of these pathways in the canalicular membrane.

Aminopyrine↗
PubMed1993

Histamine secretion from rat enterochromaffinlike cells.

BACKGROUND: In vivo studies have suggested an important role for gastric enterochromaffinlike (ECL) cells in mediating acid secretion. Direct evidence for this function is lacking and requires a preparation of highly purified ECL cells. This work investigates the possible role and mechanism of histamine release from the ECL cell in the peripheral regulation of acid secretion, using purified ECL cells from rat fundic mucosa. METHODS: A combination of elutriation and density-gradient centrifugation was used to purify rat fundic ECL cells. Enrichment was determined by the presence of acidic vacuoles containing a V type adenosine triphosphatase, electron microscopy, immunostaining, and histamine content and release. RESULTS: ECL cells were enriched at least 65-fold with respect to the fundic epithelium. Gastrin (EC50 0.2 nmol/L) and cholecystokinin octapeptide (nonsulfated, EC50 0.04 nmol/L) stimulated histamine release in a time- and dose-dependent manner, suggesting a CCK-B receptor subtype, confirmed by the inhibition of gastrin/CCK stimulation with the CCK-B antagonist L365,260. Somatostatin also inhibited gastrin-mediated histamine release. Single cell imaging showed that gastrin elevated intracellular cytosolic calcium concentration biphasically. Carbachol and the C kinase activator 120-tetradecanoylphorbol-13-acetate also stimulated histamine release. Epinephrine (blocked by propranolol), forskolin, and dibutyryl-5'-cyclic adenosine monophosphate were also effective, implicating a beta-adrenergic pathway. The H3 agonist R-alpha-methyl-histamine inhibited, whereas the H3-antagonist thioperamide potentiated gastrin/CCK stimulated histamine release. CONCLUSIONS: These in vitro results support a central role for the ECL cell in the peripheral regulation of gastric acid secretion.

Animals↗
PubMed1993

Cell biology of gastric acid secretion.

The parietal cells, which are responsible for the production of gastric HCl acid, are uniquely equipped for high-gradient ion transport. Adequate energy is supplied by oxidative metabolism in the mitochondria, which occupy an exceptionally high proportion of the cytoplasmic volume. Another characteristic feature is the secretory canaliculi. These are tortuous small channels lined by microvilli which penetrate all parts of the cytoplasm and which expand during stimulation of secretion. The activity of the parietal cell is controlled by receptors for acetylcholine, histamine and gastrin on the basolateral cell membrane. Stimulation of these receptors modulates the levels of protein kinases in the cell and brings about the changes from resting to stimulated structure. A key role in the production of acid is played by the gastric acid pump, also known as the H+, K(+)-ATPase, which exports hydrogen ions in 1:1 exchange for potassium ions. This protein is a member of the P-type ATP-driven ion pumps and appears to be uniquely located in the parietal cell. The gastric acid pump is found in the tubulovesicular membranes of the resting cell and moves to the membrane lining the secretory canaliculus when acid secretion is stimulated. Functional acid secretion also requires the presence of KCl pathways in the secretory membrane in order to supply the acid pump with a source of potassium ions. For each hydrogen ion secreted across the secretory membrane, one bicarbonate ion is generated in the cytoplasm and is transported across the basolateral membrane in exchange for chloride. The movement of ions across the apical membrane is followed osmotically by water, resulting in the secretion of 160 mM HCl from the parietal cell.

Animals↗
PubMed1993

Effects of chloride transport inhibitors on intestinal fluid and ion transport in vivo and in vitro.

The hypothesis that intestinal fluid secretion is driven by Cl- has been tested by investigating the effects of NPPB (5-nitro-2-(3-phenyl-propylamino)-benzoate), a blocker of Cl- channels in nephrons, and the loop diuretic bumetanide, an inhibitor of the Na+, K+, 2Cl(-)-co-transporter. Both NPPB (IC50 (inhibitory concentration) approximately 100 microM) and bumetanide (IC50 approximately 2 microM) inhibited stimulated short-circuit current (Isc) in monolayers of a colonic cell line T84. NPPB also inhibited 36Cl- uptake by these cells, indicating that NPPB acts as a Cl- channel blocker in the T84 cells. NPPB (300 microM) and bumetanide (10 microM) abolished both stimulated Isc and Cl- secretion in isolated rat colonic mucosa. As judged by autoradiography, [3H]NPPB was found both in the crypts and at the surface after exposure of either side to the compound. In line with these results, NPPB and bumetanide reduced stimulated fluid secretion in everted colon sacs from the rat. In the anaesthetized rat model, neither bumetanide nor NPPB affected the net fluid transport. After luminal administration of [3H]NPPB to the rat, radioactivity was found mainly in the villus tips, whereas no labelling was found in the crypts. NPPB was bound to plasma protein (99%), and the inhibitory effects of both NPPB and bumetanide on Isc in T84 cells and fluid secretion in the colonic sacs decreased in the presence of albumin, again indicating that the compounds might not reach the in vivo target, or that the mechanism for fluid secretion in vivo may not be explained solely by the secretion of Cl-.

Animals↗
PubMed1993

Parasympathetic non-adrenergic, non-cholinergic mechanisms in reflex secretion of parotid acinar granules in conscious rats.

1. Female adult rats were subjected to sympathetic denervation of the parotid glands by bilateral removal of the superior cervical ganglion 10-12 days before acute experiments. The sympathectomy was in some of the experimental groups combined with either bilateral adrenal medullectomy, treatment with the sensory neurotoxin capsaicin or parasympathetic denervation of the gland by cutting the auriculotemporal nerve. 2. Food but not water was withheld for 29-32 h before acute experiments. All animals were given an intraperitoneal injection of phentolamine (2 mg kg-1) and propranolol (1 mg kg-1) and, when appropriate, also atropine (1 mg kg-1). Then the experimental animals were fed their ordinary food of hard chow for 60-90 min. Thereafter, these animals and their non-fed controls were killed, and the parotid glands were removed and used for either morphometric assessment or measurement of amylase activity. 3. In the atropinized rats subjected to sympathectomy alone, eating reduced the numerical density of acinar secretory granules by 50% and the total activity of amylase by 55%; the corresponding figures were, when sympathectomy was combined with adrenal medullectomy, 51 and 63%. Also, in atropinized animals subjected to sympathectomy and capsaicin pretreatment, eating reduced the numerical density of acinar granules and the total amylase activity, in this case by 45 and 35%, respectively. 4. In the atropinized rats subjected to sympathectomy and parasympathectomy, eating caused no change in the numerical density of acinar granules but reduced the total amylase activity by 35%. 5. In the non-atropinized rats subjected to sympathectomy alone, eating reduced the numerical density of acinar granules by 22%, while there was no change in the total amylase activity. 6. In conclusion, eating evoked a reflex activation of the sympathectomized parotid gland that engaged non-adrenergic non-cholinergic receptors of the acinar cells. The present results give weight to a physiological role for non-adrenergic non-cholinergic parasympathetic mechanisms in salivary secretion under reflex conditions.

Adrenal Medulla↗
PubMed1992

Omeprazole does not cause unscheduled DNA synthesis in rabbit parietal cells in vitro.

Parietal cells from rabbit gastric mucosa, enriched to greater than 90% purity, were used to study the effect of the H+,K(+)-ATPase inhibitor omeprazole on DNA in vitro. In this preparation, omeprazole undergoes acid-catalyzed conversion to its active form, the sulfenamide, which subsequently binds to luminal SH groups of the H+,K(+)-ATPase and thereby inhibits acid secretion. In the parietal cell fraction the S-phase inhibitor hydroxyurea (HU) decreased [3H]thymidine uptake by 40% as measured by liquid scintillation counting (LSC), presumably due to inhibition of scheduled DNA synthesis in contaminating stem cells. In the presence of HU, irradiation with ultraviolet light (UV) or treatment with the gastric carcinogen, 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) increased [3H]thymidine uptake by a factor of 5. Autoradiography of isolated, stimulated parietal cells showed that UV irradiation and MNNG treatment increased the average number of silver grains over the nuclei 18-fold and 4-fold, respectively. In contrast, treatment of histamine-stimulated parietal cells with omeprazole or ranitidine in concentrations 100 times the IC50 value for inhibition of acid secretion in the parietal cells did not increase [3H]thymidine incorporation above the control levels, measured either by LSC or by autoradiography. Extracted DNA from stimulated parietal cells treated with [3H]omeprazole or [3H]MNNG showed no binding of [3H]omeprazole but considerable binding of [3H]MNNG. It is concluded that parietal cells can undergo DNA repair, but there is no indication that omeprazole, or its acid-derived metabolites, should cause any damage to DNA, nor does it bind to DNA in its target cell, where the highest concentrations of omeprazole and its acid-derived products are found.

Animals↗
PubMed1992

Stereologic investigations of human gastric mucosa. II. Oxyntic mucosa from patients with Zollinger-Ellison syndrome.

Biopsy specimens from the oxyntic mucosa were obtained on 210 occasions from 76 patients with the Zollinger-Ellison syndrome (ZES) before and during omeprazole treatment. One-micrometer sections were examined by light microscopy, and in 5% linear hyperplasia of endocrine cells was observed. Morphometry was carried out in 91 of the specimens and showed a significant increase of the mean endocrine cell density in comparison with both young, healthy subjects and patients suffering from active peptic ulcer disease (PUD). No metaplasia, dysplasia, or neoplasia was detected in patients with ZES, and the mean mucosal thickness and parietal cell density remained normal. The parietal cells often displayed endosome-like structures, and occasionally there were lingulate cytoplasmic projections into the gland lumen. Electron microscopic morphometry was carried out in specimens from nine patients with ZES and did not show any significant differences in the parietal cells in comparison with healthy subjects.

Adolescent↗
PubMed1991

Immunoreactivities for epidermal growth factor (EGF) and for EGF receptors in rats with gastric ulcers.

The present study was aimed at assessing whether epidermal growth factor (EGF) and its receptors are present in the gastric mucosa during the healing of gastric ulcers. Immunohistochemical, immunochemical and functional studies were performed in rats after induction of ulcers in the oxyntic mucosa. Controls, which included non-operated and sham-operated animals, displayed only rare cells in the bottom of the oxyntic glands showing EGF-like immunoreactivity. Within one day after ulcer induction, a markedly increased number of chief cells in undamaged mucosa showed intense staining. Concomitantly, there was an increased immunoreactivity for EGF receptors in the mucous neck cells. Maximal immunostaining for both compounds was observed at 3 days after ulcer induction; augmented staining was still demonstrable after 3 weeks. RIA revealed significantly increased EGF concentration in the oxyntic mucosa three days after ulcer induction, and at this stage stimulated gastric acid secretion, measured in a parallel group of chronic fistula rats, indicated significant inhibition. The transient increases in EGF-like and EGF receptor immunoreactivities may stimulate gland cell proliferation. The local release of EGF-like substances may also serve to reduce gastric acidity and thereby promote ulcer healing.

Animals↗
PubMed1991

Partial pronase digestion of rat gastric mucosa isolates cells undergoing replicative DNA synthesis.

A pronase digestion procedure for the isolation of gastric mucosal cells was evaluated for its usefulness in measuring unscheduled DNA synthesis (UDS). The method has been claimed to be suited for assessing the genotoxicity potential of compounds. Compounds were given orally to rats. After 13 h [3H]thymidine was injected and after another hour the animals were killed. The dissected stomachs were treated with pronase for 45 min and the incorporation of radioactivity into DNA was determined. Autoradiography was also performed both on the mucosa and on the isolated cell suspension. The cell suspensions were found to include cells undergoing normal replicative (S phase) DNA synthesis. Of all cells isolated, 4.8 +/- 0.6% consisted of S phase cells. The total amount of DNA recovered (corresponding to the number of cells isolated) was variable and ranged from 20 to 671 micrograms DNA, i.e. approximately 30-fold variation. Neither omeprazole (10, 30 and 80 mg/kg) nor ranitidine (215 mg/kg) had any effect on [3H]thymidine incorporation. The known carcinogen 1-methyl-3-nitro-1-nitrosoguanidine (MNNG) increased incorporation. Refeeding of fasted animals increased incorporation of [3H]thymidine almost 4-fold, showing that animal feeding status influences incorporation. Hydroxyurea, the selective inhibitor of S phase DNA synthesis, inhibited [3H]thymidine incorporation in control and omeprazole-treated animals as well as that induced by MNNG by 92-98%. The results clearly show that the pronase digestion procedure used releases cells undergoing normal, replicative DNA synthesis and can therefore neither be used for measurements of UDS nor for the assessment of the genotoxic potential of drugs.

Administration, Oral↗