Kick-starting the cancer-immunity cycle by targeting CD40.

Stimulation of CD40 on dendritic cells to expand and activate tumor-specific T cells and generate anticancer immunity is an attractive therapeutic approach. Since CD40 agonists exert their effects upstream of checkpoint inhibitors, including PD-1 or PD-L1 antagonists, they are ideal candidates for combination regimens.

Gastrin release: Antrum microdialysis reveals a complex neural control.

We used microdialysis to monitor local gastrin release in response to food, acid blockade and acute vagal excitation. For the first time, gastrin release has been monitored continuously in intact conscious rats in a physiologically relevant experimental setting in a fashion that minimizes confounding systemic effects. Microdialysis probes were placed in the submucosa on either side of the antrum, 3 days before the experiments. The concentration of gastrin in the antral submucosal compartment was about 20 times higher than in the microdialysate and estimated to be 5-10 times higher than in serum regardless of the prandial state. The rats were conscious during microdialysis except when subjected to electrical vagal stimulation. Acid blockade (omeprazole treatment of freely fed rats for 4 days), or bilateral sectioning of the abdominal vagal trunks (fasted, 3 days post-op.), raised the gastrin concentration in blood as well as microdialysate. The high gastrin concentration following omeprazole treatment was not affected by vagotomy. Vagal excitation stimulated the G cells: electrical vagal stimulation and pylorus ligation (fasted rats) raised the gastrin concentration transiently in both serum and microdialysate. Food intake induced a 2- to 3-fold increase in serum gastrin, while gastrin in antral microdialysate increased 10- to 15-fold. In unilaterally vagotomized rats (fasted, 3 days post-op.), food evoked a prompt peak gastrin release followed by a gradual decline on the intact side. On the vagotomized side of the antrum, the peak response seemed to be reduced while the microdialysate gastrin concentration remained elevated. Thus, unilateral vagotomy surprisingly raised the integrated gastrin response to food on the denervated side compared to the intact side, indicating that vagotomy suppresses an inhibitory as well as a stimulating effect on the G cells. While local infusion of atropine was without effect, infusion of the neuronal blocker tetrodotoxin (TTX) (which had no effect on basal gastrin) virtually abolished the food-evoked gastrin response and lowered the high microdialysate gastrin concentration in omeprazole-treated rats by 65%. We conclude that activated gastrin release, unlike basal gastrin release, is highly dependent on a neural input: 1) Vagal excitation has a transient stimulating effect on the G cells. The transient nature of the response suggests that the vagus has not only a prompt stimulatory but also a slow inhibitory effect on gastrin release. 2) Although vagal denervation did not affect the gastrin response to anacidity, the TTX experiments revealed that both food-evoked and anacidity-evoked gastrin release depends on neural input.

Tachyphylaxis of the ECL-cell response to PACAP: receptor desensitization and/or depletion of secretory products.

BACKGROUND AND PURPOSE: Rat stomach ECL cells secrete histamine and pancreastatin in response to gastrin and pituitary adenylate cyclase-activating peptide-27 (PACAP). This study applies microdialysis to explore how ECL cells in situ respond to PACAP and gastrin. EXPERIMENTAL APPROACH: Both peptides were administered by microinfusion into the gastric submucosa. The microdialysate was analysed for histamine and pancreastatin (ECL-cell markers) and for somatostatin (D-cell marker). KEY RESULTS: Microinfusion of PACAP (0.01-0.3 nmol microl(-1)) raised microdialysate histamine and pancreastatin dose-dependently. The response was powerful but short-lived. The response to gastrin was sustained at all doses tested. It is unlikely that the transient nature of the histamine response to PACAP reflects inadequate histamine synthesis, since the pancreastatin response to PACAP was short-lived too, and both gastrin and PACAP activated ECL-cell histidine decarboxylase. Unlike gastrin, PACAP mobilized somatostatin. Co-infusion of somatostatin abolished the histamine-mobilizing effect of PACAP. However, pretreatment with the somatostatin receptor type-2 antagonist (PRL-2903) did not prolong the histamine response to PACAP, suggesting that mobilization of somatostatin does not explain the transient nature of the response. Repeated administration of 0.1 nmol microl(-1) of PACAP (1 h infusions, 1 h intervals) failed to induce a second histamine response. Pretreatment with a low dose of PACAP (0.03 nmol microl(-1)) abolished the response to a subsequent near-maximal PACAP challenge (0.3 nmol microl(-1)). CONCLUSION: The transient nature of the histamine response to PACAP reflects desensitization of the PACAP receptor and/or exhaustion of a specific storage compartment that responds to PACAP but not to gastrin.

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.

Effect of reserpine on the generation of the chromogranin A-derived neuropeptide WE-14 in rat oxyntic mucosa.

WE-14, a post-translational product of the neuroendocrine protein chromogranin A (CgA), is generated in distinct subpopulations of endocrine cells. The objective of this study was to investigate the generation of WE-14 in the endocrine cell types of the oxyntic mucosa of the stomach, after treatment with reserpine, an irreversible inhibitor of vesicular monoamine uptake 2 (VMAT2). Reserpine (10 mg/kg) was administered subcutaneously and tissue analysed 1, 3, 5 and 18 h following treatment. The oxyntic mucosa was analysed immunohistochemically employing a site-specific WE-14 antiserum, a region-specific CgA antiserum and an antiserum against histidine decarboxylase (HDC), a marker of the histamine-producing ECL cells in the oxyntic mucosa. The number of oxyntic endocrine cells exhibiting WE-14 immunostaining increased more than 100-fold 18 h after reserpine administration relative to vehicle treated controls. Double immunostaining with HDC revealed that most, but not all, of the WE-14 positive cells were ECL cells. These results suggest that reserpine has the ability to influence the post-translational processing of CgA to generate WE-14 in rat stomach ECL cells, presumably as a consequence of reduced VMAT2-driven accumulation of histamine.

Masticatory and nutritional aspects on fixed and removable partial dentures.

The aim of the present study was to evaluate mastication, food selection and nutritional aspects in two groups of persons restored with fixed (FPD, N=44) and removable (RPD, N=40) partial dentures respectively. The subjects were part of a cohort study of 67-68-year-old men living in Malmö, Sweden. The two groups were very similar regarding social factors and the inclusion criteria were chosen so that the groups were very equal regarding oral factors, apart from the difference in fixed and removable partial dentures. The number of natural teeth, number of replaced teeth and occlusal contacts did not differ significantly between the two groups, nor did the distribution of maxillary and mandibular dentures. A comprehensive examination of several general health factors included a home interview of dietary habits. A clinical examination included a 20-minute oral examination with registration of number of teeth, FPDs, RPDs, and occlusal contacts. It also included masticatory tests: chewing gum colour mixing, chewing gum bolus shaping, and swallowing threshold (number of strokes to the first swallow of an almond). The consumption of hard and soft foods was revealed by the dietary interview as well as the intake of energy and some nutrients. There was a significant difference between the groups regarding the capacity to mix the two-coloured chewing gum, to shape the chewing gum bolus and in the consumption of hard foods. There was no difference in the swallowing threshold and the consumption of soft foods. The intake of energy and nutrients did not differ significantly between the groups. The differences in masticatory capacity found thus seem to have little, if any, effect on the factors of importance for general health. A reasonable explanation for the differences found is that artificial teeth that are well retained, such as FPDs, make more active chewing possible than do removable, and often somewhat loose-fitting partial dentures.

Submucosal microinfusion of endothelin and adrenaline mobilizes ECL-cell histamine in rat stomach, and causes mucosal damage: a microdialysis study.

Rat stomach ECL cells release histamine in response to gastrin. Submucosal microinfusion of endothelin or adrenaline, known to cause vasoconstriction and gastric lesions, mobilized striking amounts of histamine. While the histamine response to gastrin is sustainable for hours, that to endothelin and adrenaline was characteristically short-lasting (1-2 h). The aims of this study were to identify the cellular source of histamine mobilized by endothelin and adrenaline, and examine the differences between the histamine-mobilizing effects of gastrin, and of endothelin and adrenaline. Endothelin, adrenaline or gastrin were administered by submucosal microinfusion. Gastric histamine mobilization was monitored by microdialysis. Local pretreatment with the H1-receptor antagonist mepyramine and the H2-receptor antagonist ranitidine did not prevent endothelin- or adrenaline-induced mucosal damage. Submucosal microinfusion of histamine did not cause damage. Acid blockade by ranitidine or omeprazole prevented the damage, suggesting that acid back diffusion contributes. Gastrin raised histidine decarboxylase (HDC) activity close to the probe, without affecting the histamine concentration. Endothelin and adrenaline lowered histamine by 50-70%, without activating HDC. Histamine mobilization declined upon repeated administration. Endothelin reduced the number of histamine-immunoreactive ECL cells locally, and reduced the number of secretory vesicles. Thus, unlike gastrin, endothelin (and adrenaline) is capable of exhausting ECL-cell histamine. Microinfusion of alpha-fluoromethylhistidine (known to deplete ECL cells but not mast cells of histamine) reduced the histamine-mobilizing effect of endothelin by 80%, while 1-week pretreatment with omeprazole enhanced it, supporting the involvement of ECL cells. Somatostatin or the prostanoid misoprostol inhibited gastrin-, but not endothelin-stimulated histamine release, suggesting that endothelin and gastrin mobilize histamine via different mechanisms. While gastrin effectively mobilized histamine from ECL cells in primary culture, endothelin had no effect, and adrenaline, a modest effect. Hence, the striking effects of endothelin and adrenaline on ECL cells in situ are probably indirect, possibly a consequence of ischemia.

WE-14, a chromogranin a-derived neuropeptide.

The neuropeptide WE-14 is derived from the posttranslational processing of chromogranin A (CgA). While CgA is expressed in a preponderance of neuroendocrine cells, WE-14 is generated in a distinct subpopulation of CgA-immunopositive cells, most notably in the adrenal, pituitary, and parathyroid glands. Physiological and pharmacological studies have demonstrated that CgA is cleaved to generate WE-14 in the adrenal chromaffin cell population and in the enterochromaffin-like (ECL) cells of the oxyntic mucosa. Pathological analyses of neuroendocrine tumors have revealed a heterogeneous pattern of WE-14 immunostaining, with variable concentrations quantified and chromatographically resolved in tissue extracts. Phylogenetic surveys have demonstrated that WE-14 exhibits an ancient lineage, while ontogenetic examination has shown that it is generated at an early stage during fetal development. Putative WE-14 receptor binding sites have been identified in several tissues; however, the physiological role of WE-14 remains enigmatic.

ECL-cell histamine mobilization in conscious rats: effects of locally applied regulatory peptides, candidate neurotransmitters and inflammatory mediators.

1. The ECL cells control gastric acid secretion by mobilizing histamine in response to circulating gastrin. In addition, the ECL cells are thought to operate under nervous control and to be influenced by local inflammatory processes. 2. The purpose of the present study was to monitor histamine mobilization from ECL cells in conscious rats in response to locally applied regulatory peptides, candidate neurotransmitters and inflammatory mediators. 3. Microdialysis probes were implanted in the submucosa of the acid-producing part of the rat stomach. Three days later, the agents to be tested were administered via the microdialysis probe and their effects on basal (48 h fast) and stimulated (intravenous infusion of gastrin-17, 3 nmol kg(-1) h(-1)) mobilization of ECL-cell histamine was monitored by continuous measurement of histamine in the perfusate (radioimmunoassay). 4. Locally administered gastrin-17 and sulfated cholecystokinin-8 mobilized histamine as did pituitary adenylate cyclase-activating peptide-27, vasoactive intestinal peptide, peptide YY, met-enkephalin, endothelin and noradrenaline, adrenaline and isoprenaline. 5. While gastrin, sulfated-cholecystokinin-8, met-enkephalin and isoprenaline induced a sustained elevation of the submucosal histamine concentration, endothelin, peptide YY, pituitary adenylate cyclase activating peptide, vasoactive intestinal peptide, noradrenaline and adrenaline induced a transient elevation. 6. Calcitonin gene-related peptide, galanin, somatostatin and the prostanoid misoprostol inhibited gastrin-stimulated histamine mobilization. 7. The gut hormones neurotensin and secretin and the neuropeptides gastrin-releasing peptide, neuropeptide Y and substance P failed to affect ECL-cell histamine mobilization, while motilin and neuromedin U-25 had weak stimulatory effects. Also acetylcholine, carbachol, serotonin and the amino acid neurotransmitters aspartate, gamma-aminobutyric acid, glutamate and glycine were inactive or weakly active as was bradykinin. 8. In summary, a range of circulating hormones, local hormones, catecholamines, neuropeptides and inflammatory mediators participate in controlling the activity of rat stomach ECL cells in situ.

Control of secretion from rat stomach ECL cells in situ and in primary culture.

The acid-producing part of the stomach is rich in peptide-hormone-producing endocrine/paracrine cells of different types. In birds and all mammals studied, ECL cells constitute the quantitatively predominant endocrine cell population in this location. They produce histamine and an as yet unidentified peptide hormone. The paracrine action of the ECL cells is to provide histamine to mediate the stimulating effect of gastrin on the acid-secreting parietal cells: the gastrin-ECL cell-parietal cell axis. Secretion of histamine from the ECL cells was studied in intact conscious rats subjected to gastric submucosal microdialysis and using isolated cells in primary culture. The microdialysis experiments revealed that ECL-cell histamine can be mobilized by the local infusion of gastrin, pituitary adenylate cyclase-activating peptide (PACAP), vasoactive intestinal peptide (VIP), peptide YY (PYY), met-enkephalin, endothelin and noradrenaline/adrenaline. While gastrin and met-enkephalin induced a sustained elevation of the submucosal histamine concentration, endothelin, PYY, PACAP, VIP, and noradrenaline/adrenaline induced a transient elevation. Somatostatin, galanin and the prostanoid, misoprostol, inhibited gastrin-stimulated histamine mobilization. Studies of isolated ECL cells (80-90% purity) showed gastrin, PACAP and VIP to stimulate histamine secretion and somatostatin, galanin and misoprostol to inhibit gastrin-stimulated secretion. At present, it seems unlikely that metenkephalin, endothelin, adrenaline and PYY act directly on the ECL cells in situ since the effects could not be reproduced with isolated ECL cells. Clearly, the ECL cells operate under the multifactorial control of circulating hormones, local hormones, catecholamines, neuropeptides and inflammatory mediators.

Mobilization of rat stomach ECL-cell histamine in response to short- or long-term treatment with omeprazole and/or YF 476 studied by gastric submucosal microdialysis in conscious rats.

1. Mobilization of histamine from the ECL cells was monitored by gastric submucosal microdialysis in conscious rats. The ECL cells are known to operate under gastrin control and the purpose of the present study was to examine their in situ response to short-term (12 h) as well as long-term (28 days) hypergastrinaemia, induced by treatment with the proton pump inhibitor omeprazole. 2. Hypergastrinaemia promptly raised the histamine concentration in the microdialysate. The effect was prevented by CCK(2) receptor blockade (YF476). On day 7 of omeprazole treatment the microdialysate histamine concentration reached a peak, five times higher than before treatment. Subsequently (14 and 28 days), less histamine was mobilized. 3. Gastrin infusion (4 h) raised the microdialysate histamine concentration in a dose-dependent manner in fasted rats and freely fed rats and in rats treated with omeprazole for a week. However, while fasted and fed rats responded to low doses of gastrin, the omeprazole-treated rats required large doses of gastrin to respond. 4. When the amount of histamine mobilized was related to the serum gastrin concentration the following EC(50) values could be calculated: fasted rats 2.3 x 10(-10) M, freely fed rats 2.5 x 10(-10) M, omeprazole-treated rats 8.7 x 10(-10) M. The maximal histamine responses in the three groups were 18.4 pmol 4 h(-1)+/-0.8, 21.9 pmol 4 h(-1)+/-1.2 and 68.0 pmol 4 h(-1)+/-3.5, respectively. 5. The results suggest that ECL cells, exposed to a high gastrin concentration for a week, respond with a shift in the receptor-ligand binding affinity from high to low. Apparently, CCK(2) receptors of the ECL cells are subject to dynamic changes with respect to ligand-binding affinity.

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.

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.

Effects of CCK2 receptor blockade on growth parameters in gastrointestinal tract and pancreas in rats.

Gastrin has a growth-promoting effect on the oxyntic mucosa of the stomach but has been claimed also to affect other parts of the gastrointestinal tract and pancreas. This report describes the effects of the cholecystokinin, (CCK2) receptor antagonists YM022 and YF476 on various growth parameters in the gastrointestinal tract and pancreas of the rat. YM022 and YF476 were given subcutaneously in doses known to produce maximum and sustained CCK2 receptor blockade. The body weight was not affected. However, the oxyntic mucosal weight, thickness and protein and DNA contents were reduced by 15-20% already within 1-2 days and by about 30% after 4-8 weeks of CCK2 receptor blockade. Hence, the response of the oxyntic mucosa to CCK2 receptor blockade was in the form of hypotrophy (reduced protein content) and hypoplasia (reduced DNA content). There were no obvious effects of CCK2 receptor blockade on the intestine or pancreas (nor on liver, kidney or thyroid). The proton pump inhibitor omeprazole was used to induce hypergastrinaemia and was given with or without YM022. Omeprazole treatment for 4 weeks increased the oxyntic mucosal weight and thickness by 15-20%. YM022 prevented these effects. We conclude that while elevated circulating gastrin levels, acting on CCK2 receptors, exert a growth-promoting effect on the oxyntic mucosa (but not elsewhere), normal serum gastrin levels exert a mucosa-preserving effect.

Cell-specific processing of chromogranin A in endocrine cells of the rat stomach.

The rat stomach is rich in endocrine cells. The acid-producing (oxyntic) mucosa contains ECL cells, A-like cells, and somatostatin (D) cells, and the antrum harbours gastrin (G) cells, enterochromaffin (EC) cells and D cells. Although chromogranin A (CgA) occurs in all these cells, its processing appears to differ from one cell type to another. Eleven antisera generated to different regions of rat CgA, two antisera generated to a human (h) CgA sequences, and one to a bovine (b) CgA sequence, respectively, were employed together with antisera directed towards cell-specific markers such as gastrin (G cells), serotonin (EC cells), histidine decarboxylase (ECL cells) and somatostatin (D cells) to characterize the expression of CgA and CgA-derived peptides in the various endocrine cell populations of the rat stomach. In the oxyntic mucosa, antisera raised against CgA(291-319) and CGA(316-321) immunostained D cells exclusively, whereas antisera raised against bCgA(82-91) and CgA(121-128) immunostained A-like cells and D cells. Antisera raised against CgA(318-349) and CgA(437-448) immunostained ECL cells and A-like cells, but not D cells. In the antrum, antisera against CgA(291-319) immunostained D cells, and antisera against CgA(351-356) immunostained G cells. Our observations suggest that each individual endocrine cell type in the rat stomach generates a unique mixture of CgA-derived peptides, probably reflecting cell-specific differences in the post-translational processing of CgA and its peptide products. A panel of antisera that recognize specific domains of CgA may help to identify individual endocrine cell populations.

alpha-fluoromethylhistidine depletes histamine from secreting but not from non-secreting rat stomach ECL cells.

Histamine in the oxyntic mucosa of the rat stomach occurs in mast cells (10%) and ECL cells (90%). Unlike the mast cells, the ECL cells operate under the control of gastrin. alpha-Fluoromethylhistidine, an irreversible inhibitor of the histamine-forming enzyme, histidine decarboxylase depletes ECL-cell but not mast-cell histamine. This report shows that the effectiveness by which histidine decarboxylase inhibition depletes ECL-cell histamine depends on the rate of histamine secretion. Rats received alpha-fluoromethylhistidine by continuous subcutaneous infusion for 24 h. Maximally effective doses (>/=3 mg/kg/h) inhibited histidine decarboxylase and reduced oxyntic mucosal histamine in fed rats by 80-90%. In fasted rats, the reduction was 50%. alpha-Fluoromethylhistidine greatly reduced the number of histamine-immunoreactive ECL cells (immunocytochemistry) and of secretory vesicles in the ECL cells (electron microscopy) in fed but not in fasted rats. The half-life of oxyntic mucosal histamine (determined upon histidine decarboxylase inhibition) was 2.6 h in fed rats and 19.4 h in fasted rats. The amount of histamine secreted in response to gastrin (monitored by gastric submucosal microdialysis) was greatly reduced by alpha-fluoromethylhistidine in fed rats but not in fasted rats. ECL cells were isolated from rat stomach by elutriation (80% purity). Their histamine content was determined after culture, with or without alpha-fluoromethylhistidine, in the presence of varying concentrations of gastrin. In a medium containing 10 nM gastrin, ECL cells responded to a maximally effective concentration of alpha-fluoromethylhistidine (0.1 nM) with 80% reduction in histamine content. In the absence of gastrin, ECL cells responded to alpha-fluoromethylhistidine with 45% reduction of histamine; the releasable histamine pool was unaffected. In conclusion, the combination of histidine decarboxylase inhibition and a high rate of histamine secretion will promptly exhaust the ECL-cell histamine pool, while histidine decarboxylase inhibition and a low secretion rate will affect the histamine pool much less.

Anaesthetic agents inhibit gastrin-stimulated but not basal histamine release from rat stomach ECL cells.

By mobilizing histamine in response to gastrin, the ECL cells in the oxyntic mucosa play a key role in the control of the parietal cells and hence of gastric acid secretion. General anaesthesia suppresses basal and gastrin- and histamine-stimulated acid secretion. The present study examines if the effect of anaesthesia on basal and gastrin-stimulated acid secretion is associated with suppressed ECL-cell histamine secretion. A microdialysis probe was implanted in the submucosa of the ventral aspect of the acid-producing part of the stomach (32 rats). Three days later, ECL-cell histamine mobilization was monitored 2 h before and 4 h after the start of intravenous infusion of gastrin (5 nmol kg(-1) h(-1)). The rats were either conscious or anaesthetized. Four commonly used anaesthetic agents were given 1 h before the start of the experiments by intraperitoneal injection: chloral hydrate (300 mg kg(-1)), pentobarbitone (40 mg kg(-1)), urethane (1.5 g kg(-1)) and a mixture of fluanisone/fentanyl/midazolam (15/0.5/7.5 mg kg(-1)). In a parallel series of experiments, basal- and gastrin-induced acid secretion was monitored in six conscious and 25 anaesthetized (see above) chronic gastric fistula rats. All anaesthetic agents lowered gastrin-stimulated acid secretion; also the basal acid output was reduced (fluanisone/fentanyl/midazolam was an exception). Anaesthesia reduced gastrin-stimulated but not basal histamine release by 55 - 80%. The reduction in gastrin-induced acid response (70 - 95%) was strongly correlated to the reduction in gastrin-induced histamine mobilization. The correlation is in line with the view that the reduced acid response to gastrin reflects impaired histamine mobilization. Rat stomach ECL cells were purified by counter-flow elutriation. Gastrin-evoked histamine mobilization from the isolated ECL cells was determined in the absence or presence of anaesthetic agents in the medium. With the exception of urethane, they inhibited gastrin-evoked histamine secretion dose-dependently, indicating a direct effect on the ECL cells. Anaesthetized rats are widely used to study acid secretion and ECL-cell histamine release. The present results illustrate the short-comings of such an approach in that a number of anaesthetic agents were found to impair not only acid secretion but also the secretion of ECL-cell histamine - some acting in a direct manner.

Long-lasting cholecystokinin(2) receptor blockade after a single subcutaneous injection of YF476 or YM022.

Histamine-forming ECL cells in the rat stomach operate under the control of gastrin. They represent a convenient target for studying cholecystokinin-B/gastrin (CCK(2)) receptor antagonists in vivo. We examined the effectiveness and duration of action of two CCK(2) antagonists, YM022 and YF476, with respect to their effect on ECL-cell histidine decarboxylase (HDC) activity in the rat. Oral administration of subcutaneous deposition of YF476 or YM022 reduced the HDC activity. The maximum/near-maximum dose for both drugs and for both modes of administration was 300 micromol kg(-1) (effects measured 24 h after dose). At this dose and time the serum concentration of YF476 was 20 - 40 nmol l(-1). The dose 300 micromol kg(-1) was used in all subsequent studies. A single subcutaneous injection of YF476 inhibited the HDC activity for 8 weeks. The circulating concentration of YF476 remained high for the same period of time (>/=15 nmol l(-1)). Subcutaneous YM022 suppressed the HDC activity for 4 weeks. A single oral dose of YF476 or YM022 inhibited the HDC activity for 2 - 3 days. Chronic gastric fistula rats were used to study the effect of subcutaneous YF476 on gastrin-stimulated acid secretion. A single injection of YF476 prevented gastrin from causing an acid response for at least 4 weeks (the longest time studied). We conclude that a single subcutaneous injection of 300 micromol kg(-1) YF476 causes blockade of CCK(2) receptors in the stomach of the rat for 8 weeks thus providing a convenient method for studies of the consequences of long-term CCK(2) receptor inhibition.

Gastric submucosal microdialysis: a method to study gastrin- and food-evoked mobilization of ECL-cell histamine in conscious rats.

Rat stomach ECL cells are rich in histamine and chromogranin A-derived peptides, such as pancreastatin. Gastrin causes the parietal cells to secrete acid by flooding them with histamine from the ECL cells. In the past, gastric histamine release has been studied using anaesthetized, surgically manipulated animals or isolated gastric mucosa, glands or ECL cells. We monitored gastric histamine mobilization in intact conscious rats by subjecting them to gastric submucosal microdialysis. A microdialysis probe was implanted into the submucosa of the acid-producing part of the stomach (day 1). The rats had access to food and water or were deprived of food (48 h), starting on day 2 after implantation of the probe. On day 4, the rats received food or gastrin (intravenous infusion), and sampling of microdialysate commenced. Samples (flow rate 1.2 microl min(-1)) were collected every 20 or 60 min, and the histamine and pancreastatin concentrations were determined. The serum gastrin concentration was determined in tail vein blood. Exogenous gastrin (4-h infusion) raised microdialysate histamine and pancreastatin dose-dependently. This effect was prevented by gastrin receptor blockade (YM022). Depletion of ECL-cell histamine by alpha-fluoromethylhistidine, an irreversible inhibitor of the histamine-forming enzyme, suppressed the gastrin-evoked release of histamine but not that of pancreastatin. Fasting lowered serum gastrin and microdialysate histamine by 50%, while refeeding raised serum gastrin and microdialysate histamine and pancreastatin 3-fold. We conclude that histamine mobilized by gastrin and food intake derives from ECL cells because: 1) Histamine and pancreastatin were released concomitantly, 2) histamine mobilization following gastrin or food intake was prevented by gastrin receptor blockade, and 3) mobilization of histamine (but not pancreastatin) was abolished by alpha-fluoromethylhistidine. Hence, gastric submucosal microdialysis allows us to monitor the mobilization of ECL-cell histamine in intact conscious rats under various experimental conditions not previously accessible to study. While gastrin receptor blockade lowered post-prandial release of ECL-cell histamine by about 80%, unilateral vagotomy reduced post-prandial mobilization of ECL-cell histamine by about 50%. Hence, both gastrin and vagal excitation contribute to the post-prandial release of ECL-cell histamine.