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Biomedical subjects

R Håkanson

Publications and source records attributed to R Håkanson.

At least 19 recordsLinked to original sources
PubMed2005

Ghrelin treatment reverses the reduction in weight gain and body fat in gastrectomised mice.

BACKGROUND AND AIMS: The gastric hormone ghrelin has been reported to stimulate food intake, increase weight gain, and cause obesity but its precise physiological role remains unclear. We investigated the long term effects of gastrectomy evoked ghrelin deficiency and of daily ghrelin injections on daily food intake, body weight, fat mass, lean body mass, and bone mass in mice. METHODS: Ghrelin was given by subcutaneous injections (12 nmol/mouse once daily) for eight weeks to young female mice subjected to gastrectomy or sham operation one week previously. RESULTS: Gastrectomy reduced plasma concentrations of total ghrelin (octanoylated and des-octanoylated) and active (octanoylated) ghrelin by approximately 80%. Immediately after injection of ghrelin, the plasma concentration was supraphysiological and was still elevated 16 hours later. Daily food intake was not affected by either gastrectomy or ghrelin treatment. The effect of ghrelin on meal initiation was not studied. At the end point of the study, mean body weight was 15% lower in gastrectomised mice than in sham operated mice (p<0.001); daily ghrelin injections for eight weeks partially prevented this weight loss. In sham operated mice, ghrelin had no effect on body weight. The weight of fat was reduced in gastrectomised mice (-30%; p<0.01). This effect was reversed by ghrelin, enhancing the weight of fat in sham operated mice also (+20%; p<0.05). Gastrectomy reduced lean body mass (-10%; p<0.01) and bone mass (-20%; p<0.001) compared with sham operated mice. Ghrelin replacement prevented the gastrectomy induced decrease in lean body mass but did not affect bone. In sham operated mice, ghrelin affected neither of these two parameters. CONCLUSIONS: Ghrelin replacement partially reversed the gastrectomy induced reduction in body weight, lean body mass, and body fat but not in bone mass. In sham operated mice, ghrelin only increased fat mass. Our results suggest that ghrelin is mainly concerned with the control of fat metabolism and that ghrelin replacement therapy may alleviate the weight loss associated with gastrectomy.

Adipose Tissue↗
PubMed2005

The vagus regulates histamine mobilization from rat stomach ECL cells by controlling their sensitivity to gastrin.

The ECL cells in the oxyntic mucosa secrete histamine in response to gastrin, stimulating parietal cells to produce acid. Do they also operate under nervous control? The present study examines histamine mobilization from rat stomach ECL cells in situ in response to acute vagal excitation and to food or gastrin following vagal or sympathetic denervation. Applying the technique of microdialysis, we monitored the release of histamine by radioimmunoassay. Microdialysis probes were placed in the submucosa on either side of the stomach, 3 days before experiments. The rats were awake during microdialysis except when subjected to electrical vagal stimulation. One-sided electrical vagal stimulation raised serum gastrin and mobilized gastric histamine. However, gastrin receptor blockade prevented the histamine mobilization, indicating that circulating gastrin accounts for the response. Vagal excitation by hypoglycaemia (insulin) or pylorus ligation did not mobilize either gastrin or histamine. The histamine response to food was almost abolished by gastrin receptor blockade, and it was halved on the denervated side after unilateral subdiaphragmatic vagotomy. While the histamine response to a near-maximally effective dose of gastrin was unaffected by vagotomy, the response to low gastrin doses was reduced significantly. Abdominal ganglionic sympathectomy failed to affect the histamine response to either food or gastrin. In conclusion, gastrin is responsible for most of the food-evoked mobilization of ECL-cell histamine. The histamine response to electrical vagal stimulation reflects the effect of circulating gastrin rather than a direct action of the vagus on the ECL cells. Vagal denervation was accompanied by an impaired histamine response to food intake, probably reflecting the right-ward shift of the serum gastrin concentration-histamine response curve. The results suggest that the vagus controls the sensitivity of the ECL cells to gastrin.

Animals↗
PubMed2004

Histamine and histidine decarboxylase are hallmark features of ECL cells but not G cells in rat stomach.

The oxyntic mucosa of the rat stomach is rich in ECL cells which produce and secrete histamine in response to gastrin. Histamine and the histamine-forming enzyme histidine decarboxylase (HDC) have been claimed to occur also in the gastrin-secreting G cells in the antrum. In the present study, we used a panel of five HDC antisera and one histamine antiserum to investigate whether histamine and HDC are exclusive to the ECL cells. By immunocytochemistry, we could show that the ECL cells were stained with the histamine antiserum and all five HDC antisera. The G cells, however, were not stained with the histamine antiserum, but with three of the five HDC antisera. Thus, histamine and HDC coexist in the ECL cells (oxyntic mucosa) but not in G cells (antral mucosa). Western blot analysis revealed a typical pattern of HDC-immunoreactive bands (74, 63 and 54 kDa) in oxyntic mucosa extracts with all five antisera. In antral extracts, immunoreactive bands were detected with three of the five HDC antisera (same as above); the pattern of immunoreactivity differed from that in oxyntic mucosa. Food intake of fasted rats or treatment with the proton pump inhibitor omeprazole raised the HDC activity and the HDC protein content of the oxyntic mucosa but not of the antral mucosa; the HDC activity in the antrum was barely detectable. We suggest that the HDC-like immunoreactivity in the antrum represents a cross-reaction with non-HDC proteins and conclude that histamine and HDC are hallmark features of ECL cells but not of G cells.

Animals↗
PubMed2003

Rat stomach ECL cells: mode of activation of histidine decarboxylase.

Histidine decarboxylase (HDC) occurs in ECL cells in the oxyntic mucosa of rat stomach. It is activated by gastrin. Refeeding of fasted rats or treatment with the proton pump inhibitor omeprazole promptly raised the serum gastrin concentration and consequently the HDC activity and the HDC protein content of the oxyntic mucosa. The food- and omeprazole-induced increase in HDC mRNA expression in the oxyntic mucosa was modest by comparison. Blockade of translation (cycloheximide) but not transcription (actinomycin D) prevented the postprandial rise in HDC activity. The half-life of HDC activity (after blockade of translation) was 94 min in omeprazole-treated rats and 55 min in fasted controls. The rate of enzyme synthesis was estimated to be 15 times higher in omeprazole-treated rats than in fasted controls. Inhibition of histamine uptake into ECL-cell granules by reserpine, a blocker of the vesicular monoamine transporter type-2, lowered the HDC activity and prevented the gastrin-induced HDC activation. We suggest that HDC activation reflects enhanced transcription, translation and/or posttranslational enzyme activation as well as stabilization, and that a high cytosolic histamine concentration suppresses HDC activation.

Animals↗
PubMed2002

Effects of calcium deficiency and calcium supplementation on gastrectomy-induced osteopenia in the young male rat.

BACKGROUND: Surgical removal of the stomach (gastrectomy, Gx) induces osteopenia. In this study we compared the osteopenic effect of Gx with that induced by calcium (Ca) deficiency. METHODS: Young male rats were subjected to Gx and/or low Ca diet (-Ca). A group of Gx rats received standard diet + oral Ca supplementation (+Ca). The rats were killed at various times after the operation/start of treatment (longest time 12 weeks). After 8 weeks on low Ca diet, the blood Ca2+ concentration was lowered slightly in both Sham-operated and Gx rats. The calvariae were subjected to transillumination analysis and quantitative histomorphometry. Also the tibiae were subjected to histomorphometry. RESULTS: Transillumination of the calvariae revealed extensive bone loss in the rats that had been subjected to Gx and/or low Ca diet. Gx + Ca induced the same bone loss as Gx alone. These observations were later confirmed in quantitative terms by histomorphometry (Sham-Ca 56%, Gx 35%, Gx + Ca 32%, Gx - Ca 58% less bone area than in Sham). The osteopenia induced by Gx + low Ca diet seetned more rapid in onset than that induced by Gx or low Ca diet alone. Tibiae from Gx rats and rats given a low Ca diet displayed a reduced trabecular bone volume (Sham-Ca 27% remaining, Gx 36%, Gx + Ca 44%, Gx - Ca 17%) and reduced trabecular number (Sham-Ca 44% remaining, Gx 41%, Gx + Ca 56%, Gx - Ca 33%). The trabecular thickness was reduced in the Gx rats and Gx - Ca rats (Gx 78% remaining, Gx - Ca 63%) but not in Sham-operated rats receiving a low Ca-diet (95% remaining). CONCLUSION: Although the pattern of osteopenia was qualitatively quite similar in Gx rats and Ca-deficient rats, in quantitative terms the low Ca diet was more detrimental to bone than Gx. Ca deficiency induced a similar degree of osteopenia in both Sham and Gx rats. Ca supplementation failed to prevent the Gx-induced osteopenia.

Analysis of Variance↗
PubMed2002

Post-gastrectomy osteopenia in the rat: bone structure is preserved by retaining 10%-30% of the oxyntic gland area.

BACKGROUND: The acid-producing part of the rat stomach (fundus) is rich in endocrine cells, i.e. ECL cells and A-like cells. The ECL cells operate under gastrin control and manufacture histamine, the chromogranin-derived peptide pancreastatin and an unidentified peptide hormone. The A-like cells produce ghrelin, a newly discovered growth hormone-releasing hormone. Surgical removal of the entire glandular stomach (gastrectomy, Gx) or the acid-producing part (fundectomy, Fx) causes osteopenia, which is striking in the calvaria. We speculate that the osteopenia develops after surgical removal of the fundus, because the fundus hosts agents that preserve bone. This study examines how much of the fundus is needed to preserve normal skull bone. METHODS: Increasing portions of the fundus were resected surgically. The serum gastrin, ghrelin and pancreastatin concentrations were measured. The rats were killed after 10 weeks and the calvariae were subjected to transillumination analysis and quantitative histomorphometry. RESULTS: Fx elevated serum gastrin in proportion to the amount of fundus resected, i.e., the more fundus that was resected, the higher the serum gastrin concentration. Serum ghrelin and pancreastatin concentrations were reduced proportionally to the amount of fundus resected. In rats subjected to 90% or 100% Fx, the calvariae displayed the anticipated pattern of bone loss. No bone loss was seen when 70% or less of the fundus was resected. CONCLUSIONS: The results of the present study indicate that 10%-30% of the fundic mucosa is needed to preserve bone. The Gx/Fx-evoked osteopenia may be explained by hormonal deficiency caused by surgically eliminating or diminishing one of the endocrine cell populations in the fundic mucosa.

Animals↗
PubMed2002

Gastrectomized rats respond with exaggerated hypercalcemia to oral and intravenous calcium loads because of impaired ability of bone to take up Ca2+.

BACKGROUND: Gastrectomy (Gx) causes osteopenia. The hypothesis tested in the present study is that Gx affects Ca homeostasis and that an impaired ability to handle Ca contributes to the Gx-evoked osteopenia. METHODS: SHAM-operated and Gx rats were compared with respect to changes in blood Ca2+ after oral or intravenous loads of CaCl2 1-2 weeks or 2-4 months after the operations. RESULTS: Different doses of oral CaCl2 raised blood Ca2+ more in Gx than in SHAM rats, more so after 2-4 months than after 1-2 weeks. The rise was greater in fasted (48 h) rats than in fed rats regardless of whether they were SHAM or Gx. While SHAM rats tolerated high doses of CaCl2 well, Gx rats died when exposed to quite modest doses, particularly 2-4 months after Gx. Intravenous infusion of CaCl2 (2,500 micromol/kg/h) induced a greater and steeper rise in blood Ca2+ in Gx rats than in SHAM rats. Kinetic analysis of the blood Ca2+ data showed Gx rats to display: 1) a decreased Ca2+ elimination clearance from the central distribution compartment (blood), 2) a reduced size of the peripheral distribution compartment (the so-called bone fluid compartment). and 3) a spectacular decrease in the intercompartmental clearance (transfer of Ca2+ from blood to bone). These effects were notably apparent after 2-4 months. At sacrifice, the Gx-evoked osteopenia was confirmed by planimetric analysis of the calvariae. revealing 40% reduction of bone tissue after 2-4 months. CONCLUSIONS: Based on the present data we argue that Gx rats respond with exaggerated hypercalcemia to oral and intravenous CaCl2 loads because of a greatly impaired transfer of Ca+ from blood to bone. We suggest that with time this impairment results in osteopenia.

Administration, Oral↗
PubMed2002

Gastrectomy has no effect on bone regeneration in rats despite a decrease in bone mass.

BACKGROUND: Gastrectomy, specifically the removal of the acid-producing part of the stomach (fundectomy), is known to cause osteopenia. This effect has been ascribed to the elimination of a hypothetical osteotropic peptide hormone, presumably produced in the oxyntic mucosa. Since osteopenia is due to a disturbed balance between bone formation and resorption, we assessed the effect of gastrectomy on osteogenesis, more specifically mandibular orthotopic bone regeneration. METHODS: Adult rats were either gastrectomized or sham-operated. Two weeks later, unilateral 5-mm transosseous defects were made in the mandibles and covered with microporous barrier membranes (GORE-TEX Membrane). After 6 weeks of healing. bone-bridging of the defects was analyzed by computerized light microscopic image analysis. Furthermore, bone mass was analyzed in the contralateral untreated mandibular side, in calvarial bone, and in femora by morphometry and dry/ash weights. RESULTS: While gastrectomy resulted in a clearly decreased bone mass, manifested as increased marrow spaces in all bones and as decreased dry and ash weights in femora, no difference in mandibular bone healing rate was found between the groups. CONCLUSIONS: Since secluding of the defect space by membrane barriers implies that osteogenic cells have to be recruited primarily from intra-osseous stem cells by their proliferation and differentiation into actively bone-forming osteoblasts, the results indicate that gastrectomy has no effect on these processes. The findings thus imply that the disturbed balance in bone remodeling caused by gastrectomy, resulting in osteopenia, may be due to stimulated bone resorption rather than to reduced bone formation.

Animals↗
PubMed2002

Drug-induced prevention of gastrectomy- and ovariectomy-induced osteopaenia in the young female rat.

Both ovariectomy (Ovx) and gastrectomy (Gx) induce osteopaenia in rats and humans. While the effect of Ovx has been ascribed to oestrogen deficiency, the underlying mechanism behind Gx is poorly understood. Alendronate, oestrogen and parathyroid hormone (PTH) are known to prevent the osteopaenia induced by Ovx in rats. The purpose of the present study was to determine whether alendronate, oestrogen or PTH could also prevent Gx-evoked osteopaenia. Rats were Ovx-, Gx-, or were sham-operated (Sham) and were then treated with alendronate (50 micro g/kg/day), oestrogen (10 micro g/kg/day) or PTH(1-84) (75 micro g/kg/day) for eight weeks. At sacrifice, serum PTH was unaffected by surgery (Ovx, 64+/-8 pg/ml; Gx, 75+/-13 pg/ml; Sham, 58+/-11 pg/ml). The bone mineral density (BMD) of the fifth lumbar vertebra (L5) was analysed. Ovx and Gx reduced the BMD (ash weight/Volume) of the L5 by 15+/-4% and 22+/-3% respectively. Trabecular BMD and the cortical bone mineral content (BMC) of the femur were assessed using peripheral computed tomography. Both Ovx and Gx markedly reduced trabecular BMD in the metaphyseal area of the distal femur (Ovx, -37+/-7%; Gx, -49+/-7%). The cortical BMC of the femur was only slightly reduced. Alendronate prevented trabecular bone loss after both Ovx and Gx, while oestrogen and PTH prevented trabecular bone loss after Ovx but not after Gx. In conclusion, the bisphosphonate alendronate prevented both Ovx- and Gx-induced trabecular bone loss. In contrast, PTH and oestrogen prevented Ovx-induced but not Gx-induced trabecular bone loss, suggesting that the mechanism behind the trabecular bone loss in Ovx rats differs from that in Gx rats. The results support the notion that the mechanism of action for the bone-sparing effect of these drugs differs. The ability of alendronate, and probably also other bisphosphonates, to prevent Gx-evoked osteopaenia in the rat might be of potential clinical interest when dealing with post-Gx osteopaenia in humans.

Alendronate↗
PubMed2001

Gastrin and the neuropeptide PACAP evoke secretion from rat stomach histamine-containing (ECL) cells by stimulating influx of Ca2+ through different Ca2+ channels.

1. Gastrin and PACAP stimulate secretion of histamine and pancreastatin from isolated rat stomach ECL cells. We have examined whether or not secretion depends on the free cytosolic Ca2+ concentration ([Ca2+]i) and the pathways by which gastrin and PACAP elevate [Ca2+]i. Secretion was monitored by radioimmunoassay of pancreastatin and changes in [Ca2+]i by video imaging. The patch clamp technique was used to record whole-cell currents and membrane capacitance (reflecting exocytosis). 2. In the presence of 2 mM extracellular Ca2+, gastrin and PACAP induced secretion and raised [Ca2+]i. Without extracellular Ca2+ (or in the presence of La3+) no secretion occurred. The extracellular Ca2+ concentration required to stimulate secretion was 10 times higher for gastrin than for PACAP. Depletion of intracellular Ca2+ pools by thapsigargin had no effect on the capacity of gastrin and PACAP to stimulate secretion. 3. Gastrin-evoked secretion was inhibited 60-80 % by L-type channel blockers and 40 % by the N-type channel blocker omega-conotoxin GVIA. Combining L-type and N-type channel blockers did not result in greater inhibition than L-type channel blockers alone. Whole-cell patch clamp measurements confirmed that the ECL cells are equipped with voltage-dependent inward Ca2+ currents. A 500 ms depolarising pulse from -60 mV to +10 mV which maximally opened these channels resulted in an increase in membrane capacitance of 100 fF reflecting exocytosis of secretory vesicles. 4. PACAP-evoked secretion was reduced 40 % by L-type channel blockers but was not influenced by inhibition of N-type channels. SKF 96365, a blocker of both L-type and receptor-operated Ca2+ channels, inhibited PACAP-evoked secretion by 85 %. Combining L-type channel blockade with SKF 96365 abolished PACAP-evoked secretion. 5. The results indicate that gastrin- and PACAP-evoked secretion depends on Ca2+ entry and not on mobilisation of intracellular Ca2+. While gastrin stimulates secretion via voltage-dependent L-type and N-type Ca2+ channels, PACAP acts via L-type and receptor-operated Ca2+ channels.

Animals↗
PubMed2001

A-like cells in the rat stomach contain ghrelin and do not operate under gastrin control.

Ghrelin is a 28 a.a. gastric peptide, recently identified as a natural ligand of the growth hormone secretagogue receptor (orphan receptor distinct from the receptor for growth hormone releasing hormone). In the present study, radioimmunoassay demonstrated ghrelin-like material in the rat oxyntic mucosa with moderate amounts also in antrum and duodenum. Small amounts were found in the distal intestines and pancreas. Northern blot analysis revealed abundant ghrelin mRNA in the oxyntic mucosa. Immunocytochemistry demonstrated ghrelin-immunoreactivity in endocrine-like cells in the oxyntic mucosa. Such cells occurred in low numbers also in the antrum and duodenum. The rat oxyntic mucosa is rich in endocrine (chromogranin A/pancreastatin-immunoreactive) cells, such as the histamine-rich ECL cells (65-75% of the endocrine cells), the A-like cells (20-25%) and the D cells (somatostatin cells) (10%). The ghrelin-immunoreactive (IR) cells contained pancreastatin but differed from ECL cells and D cells by being devoid of histamine-forming enzyme (ECL cell constituent) and somatostatin (D cell constituent). Hence, ghrelin seems to occur in the A-like cells. The ghrelin-IR cells in the antrum were distinct from the gastrin cells, the serotonin-containing enterochromaffin cells and the D cells. Conceivably, ghrelin cells in the antrum and distally in the intestines also belong to the A-like cell population. The concentration of ghrelin in the circulation was lowered by about 80% following the surgical removal of the acid-producing part of the stomach in line with the view that the oxyntic mucosa is the major source of ghrelin. The serum ghrelin concentration was higher in fasted rats than in fed rats; it was reduced upon re-feeding and seemed unaffected by 1-week treatment with the proton pump inhibitor omeprazole, resulting in elevated serum gastrin concentration. Infusion of gastrin-17 for 2 days failed to raise the serum ghrelin concentration. Omeprazole treatment for 10 weeks raised the level of HDC mRNA but not that of ghrelin mRNA or somatostatin mRNA in the oxyntic mucosa. Hence, unlike the ECL cells, ghrelin-containing A-like cells do not seem to operate under gastrin control.

Animals↗
PubMed2001

Isolated rat stomach ECL cells generate prostaglandin E(2) in response to interleukin-1 beta, tumor necrosis factor-alpha and bradykinin.

The ECL cells control parietal cells by releasing histamine in their immediate vicinity. Gastrin and pituitary adenylate cyclase-activating peptide (PACAP) stimulate histamine secretion from isolated ECL cells, while somatostatin and galanin inhibit stimulated secretion. Prostaglandin E2 and related prostaglandins likewise suppress ECL-cell histamine secretion. Conceivably, that is how they inhibit acid secretion. In the present study, we examined if prostaglandin E2 can be generated by isolated ECL cells. Rat stomach ECL cells were purified (>90% purity) by counterflow elutriation and gradient centrifugation and cultured for 48 h. ECL cell stimulants (gastrin and PACAP) and inflammatory agents (interleukin-1 beta, tumor necrosis factor-alpha and bradykinin) were tested for their ability to induce prostaglandin E2 accumulation (24-h incubation), measured by radioimmunoassay. Gastrin and PACAP did not affect prostaglandin E2 accumulation but interleukin-1 beta (300 pg/ml), tumor necrosis factor-alpha (10 ng/ml) and bradykinin (1 microM) induced a 2- to 3-fold increase in the amount of prostaglandin E2 accumulated. While the combination of interleukin-1 beta and bradykinin induced a 9-fold increase, the combination interleukin-1 beta+tumor necrosis factor-alpha and bradykinin + tumor necrosis factor-alpha induced additive effects only. The combination of interleukin-1 beta + tumor necrosis factor-alpha + bradykinin did not induce a greater effect than interleukin-1 beta + bradykinin. The effect of interleukin-1 beta + bradykinin was abolished by adding 10 nM hydrocortisone (suppressing phospholipase A2 and cyclooxygenase) or 1 microM indomethacin (inhibiting cyclooxygenase). Incubating ECL cells in the presence of interleukin-1 beta+bradykinin for 24 h reduced their ability to secrete histamine in response to gastrin. The inhibitory effect was reversed by 1 microM indomethacin. Also, increasing the concentrations of hydrocortisone in the medium resulted in an enhanced gastrin-stimulated histamine secretion. Hence, the previously described acid-inhibiting effect of inflammatory agents may be explained by inhibition of ECL-cell histamine mobilization, consequent to enhanced formation of prostaglandin E2 by cells in the oxyntic mucosa, including the ECL cells themselves.

Animals↗
PubMed2001

Extracts of ECL-cell granules/vesicles and of isolated ECL cells from rat oxyntic mucosa evoke a Ca2+ second messenger response in osteoblastic cells.

Surgical removal of the acid-producing part of the stomach (oxyntic mucosa) reduces bone mass through mechanisms not yet fully understood. The existence of an osteotropic hormone produced by the so-called ECL cells has been suggested. These cells, which are numerous in the oxyntic mucosa, operate under the control of circulating gastrin. Both gastrin and an extract of the oxyntic mucosa decrease blood calcium and stimulate Ca2+ uptake into bone. Conceivably, gastrin lowers blood calcium indirectly by releasing a hypothetical hormone from the ECL cells. The present study investigated, by means of fura-2 fluorometry, the effect of extracts of preparations enriched in ECL cell granules/vesicles from rat oxyntic mucosa on mobilization of intracellular Ca2+ in three osteoblast-like cell lines, UMR-106.01, MC3T3-E1 and Saos-2, and of extracts of isolated ECL cells in UMR-106.01 cells. The extracts were found to induce a dose-related rapid increase in intracellular Ca2+ concentrations in the osteoblast-like cells. The response was not due to histamine or pancreastatin, known ECL cell constituents, and could be abolished by pre-digesting the extracts with exo-aminopeptidase. The results show that the increase in [Ca2+](i) reflects a mobilization of Ca2+ from the endoplasmic reticulum. The observation of an increase in [Ca2+](i) also in murine embryonic fibroblasts show that the response is not limited to osteoblastic cells. The finding that the extracts evoked a typical Ca2+ -mediated second messenger response in osteoblastic cells provides evidence for the existence of a novel osteotropic peptide hormone (gastrocalcin), produced in the ECL cells, and supports the view that gastrectomy-induced osteopathy may reflect a lack of this hormone.

3T3 Cells↗
PubMed2001

Neurohormonal regulation of secretion from isolated rat stomach ECL cells: a critical reappraisal.

ECL cells are endocrine/paracrine cells in the oxyntic mucosa. They produce, store and secrete histamine and chromogranin A-derived peptides such as pancreastatin. The regulation of ECL-cell secretion has been studied by several groups using purified ECL cells, isolated from rat stomachs. Reports from different laboratories often disagree. The purpose of the present study was to re-evaluate the discrepancies by studying histamine (or pancreastatin) secretion from standardized preparations of pure, well-functioning ECL cells. Cells from rat oxyntic mucosa were dispersed by pronase digestion, purified by repeated counter-flow elutriation and subjected to density gradient centrifugation. The final preparation consisted of more than 90% ECL cells (verified by histamine and/or histidine decarboxylase immunocytochemistry). They were maintained in primary culture for 48 h before they were exposed to candidate stimulants and inhibitors for 30 min after which the medium was collected for determination of mobilized histamine (or pancreastatin). Gastrin-17 and sulphated cholecystokinin octapeptide (CCK-8s) raised histamine secretion 4-fold, the EC(50) for both peptides being around 100 pM. The neuropeptide pituitary adenylate cyclase activating peptide (PACAP-27) (5-fold increase) and the related neuropeptides vasoactive intestinal peptide (VIP) and peptide histidine isoleucine (PHI) (3-fold increase) mobilized histamine with similar potency (EC(50) ranging from 80 to 140 pM). Adrenaline, isoprenaline and terbutaline stimulated secretion by activating a beta2 receptor subtype, while acetylcholine and carbachol were without effect. Secretion experiments were invariably run in parallel with a gastrin standard curve. Somatostatin, prostaglandin E2 (PGE2) and the PGE1 congener misoprostol inhibited PACAP- and gastrin-stimulated secretion by more than 90%, with IC(50) values ranging from 90-720 (somatostatin) to 40-200 (misoprostol) pM. The neuropeptide galanin inhibited secretion by 60-70% with a potency similar to that of somatostatin. Proposed inhibitors such as peptide YY, neuropeptide Y and the cytokines interleukin 1-beta and tumor necrosis factor alpha induced at best a moderate inhibition of gastrin- or PACAP-stimulated secretion at high concentrations, while calcitonin gene-related peptide, pancreatic polypeptide and histamine itself were without effect. Inhibition of gastrin- or PACAP-stimulated secretion was routinely compared to a somatostatin standard curve. In conclusion, gastrin, PACAP, VIP/PHI and adrenaline stimulated secretion. Somatostatin and PGE2 were powerful inhibitors of both gastrin- and PACAP-stimulated secretion; although equally potent, galanin was less effective than somatostatin and PGE2.

Animals↗
PubMed2001

Does combined gastrectomy and ovariectomy induce greater osteopenia in young female rats than gastrectomy alone?

Osteopenia develops in experimental animals following surgical removal of the ovaries (ovariectomy. Ovx) or the stomach (gastrectomy, Gx). Though the effect of Ovx has been ascribed to estrogen deficiency, the mechanism behind the Gx-evoked osteopenia remains unknown. In order to compare Gx- and Ovx-evoked osteopenia, young female rats were subjected to Ovx, gx, the combination of ovx and Gx, or sham operation (SHAM). Serum osteoclast-derived tartrate-resistant acid phosphatase 5b was measured as an index of bone resorption, and serum osteocalcin as an index of bone formation/turnover. Bone resorption predominated over bone formation during the first 4 days after Ovx but not later. Bone resorption predominated over bone formation throughout the first 4-week period after Gx. the changes were not additive in the ovx+Gx group. Transillumination and histomorphometry of the calvariae revealed extensive osteopenia in the Gx and the Ovx+Gx groups but not in the Ovx group. Peripheral quantitative computerized tomography of the femur metaphysis showed a decrease in the trabecular bone mineral density (BMD) in all three groups although Ovx+Gx seemed to induce greater trabecular bone loss than Gx alone. However, dual energy X-ray absorptiometry (DXA) of the intact femurs revealed reduced bone mineral content (BMC) in the Gx and Ovx+Gx groups but not in the Ovx group. Indeed, cortical bone was impaired by Gx and Ovx+Gx but not by Ovx. Hence, it seems clear that the Gx-evoked osteopenia differs from that induced by Ovx but that the osteopenia induced by Ovx+Gx is only marginally greater than that induced by Gx alone.

Animals↗
PubMed2001

Functionally impaired, hypertrophic ECL cells accumulate vacuoles and lipofuscin bodies. An ultrastructural study of ECL cells isolated from hypergastrinemic rats.

ECL cells in the oxyntic mucosa of stomach control gastric acid secretion by mobilizing histamine in response to gastrin. They respond to gastrin also with hypertrophy and hyperplasia. ECL cells exhibit functional impairment upon long-term gastrin stimulation. The impairment is manifested in a gradual decline of the activity of the histamine-forming enzyme per individual ECL cell and in a failure of gastrin to mobilize histamine. The mechanism behind this impairment is unknown. In the present study, rats were treated with the proton pump inhibitor pantoprazole for 45 days to induce sustained hypergastrinemia. The ECL cells were isolated from normogastrinemic and hypergastrinemic rats and size-separated from other mucosal cells by the elutriation technique. The total ECL cell number was twofold higher in hypergastrinemic rats than in normogastrinemic rats, and most of the cells appeared in elutriation fractions where large cells predominate. The ECL cells of the different fractions were analyzed by quantitative electron microscopy. Normal-sized ECL cells from hypergastrinemic rats displayed a reduced number of secretory vesicles (probably because of degranulation) compared with normal-sized ECL cells from normogastrinemic rats. Hypertrophic ECL cells from hypergastrinemic rats had an unchanged number of secretory vesicles, supporting the view that such cells fail to respond to gastrin with degranulation. Although both normal-sized and hypertrophic ECL cells from hypergastrinemic rats contained vacuoles, those in the hypertrophic ECL cells were larger and more numerous. In addition, hypertrophic ECL cells were found to contain numerous, prominent lipofuscin bodies which are the presumed end product of crinophagia. Conceivably therefore, large vacuoles and lipofuscin bodies cause functional impairment of the hypertrophic ECL cells.

2-Pyridinylmethylsulfinylbenzimidazoles↗
PubMed2001

Control of gastric acid secretion:the gastrin-ECL cell-parietal cell axis.

Gastric acid secretion is under nervous and hormonal control. Gastrin, the major circulating stimulus of acid secretion, probably does not stimulate the parietal cells directly but acts to mobilize histamine from the ECL cells in the oxyntic mucosa. Histamine stimulates the parietal cells to secrete HCl. The gastrin-ECL cell pathway has been investigated extensively in situ (gastric submucosal microdialysis), in vitro (isolated ECL cells) and in vivo (intact animals). Gastrin acts on CCK2 receptors to control the synthesis of ECL-cell histamine, accelerating the expression of the histamine-forming enzyme histidine decarboxylase (HDC) at both the transcription and the translation/posttranslation levels. Depletion of histamine by alpha-fluoromethylhistidine (an irreversible inhibitor of HDC) prevents gastrin-induced but not histamine-induced gastric acid secretion. Acute CCK2 receptor blockade inhibits gastrin-evoked but not histamine-induced acid secretion. Studies both in vivo/in situ and in vitro have suggested that while acetylcholine seems capable of activating parietal cells, it does not affect histamine secretion from ECL cells. Unlike acetylcholine, the neuropeptides pituitary adenylate cyclase-activating peptide and vasoactive intestinal peptide mobilize ECL-cell histamine. Whether vagally stimulated acid secretion reflects an effect of the enteric nervous system on the ECL cells (neuropeptides) and/or a direct one on the parietal cells needs to be further investigated.

Animals↗