Neurohormonal regulation of histamine release from isolated rabbit fundic mucosal cells

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

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.

Prostaglandins inhibit secretion of histamine and pancreastatin from isolated rat stomach ECL cells

1. The present study examines the effect of naturally occurring prostanoids and prostaglandin (PG) congeners on gastrin- and pituitary adenylate cyclase-activating peptide (PACAP)-evoked histamine and pancreastatin secretion from isolated rat stomach ECL cells. 2. ECL cells (75-85% purity) were isolated from rat stomach using pronase digestion followed by repeated counter-flow elutriation and cultured for 48 h before secretion experiments. The release of histamine and pancreastatin was determined by radioimmunoassay. 3. None of the PGs tested stimulated the release of either histamine or pancreastatin. 4. PGE1 and PGE2 inhibited both gastrin- and PACAP-evoked histamine and pancreastatin secretion (IC50 = 1-2 x 10(-10) M). Most other naturally occuring prostanoids and PG congeners had no or little inhibitory effect. The PGE analogues misoprostol and sulprostone were more potent (IC50 = 0.9 x 10(-11) M and 2 x 10(-11) M respectively) than PGE1 and PGE2. The rank order of potency was misoprostol > sulprostone > PGE1 = PGE2, suggesting the involvement of the so-called EP3 receptor. 5. The effects of PGs on the stomach ECL cells may be direct or indirect, for instance through the stimulated release of somatostatin from contaminating D cells (2-3%). However, the amount of somatostatin in the cell culture after 48 h was below the limit of detection, and somatostatin immunoneutralization did not prevent misoprostol from inhibiting secretion from the ECL cells. 6. The misoprostol-induced inhibition was reversed by pertussis toxin suggesting the involvement of G-protein subunits G alpha(0) and/or G alpha(i). 7. In view of the potency by which PGE1, PGE2, misoprostol and sulprostone inhibited the stimulated release of histamine and pancreastatin, we suggest that the ECL cells represent a primary target for prostaglandins acting via an EP3 receptor in the oxyntic mucosa. 8. The results suggest that the clinically useful effect of misoprostol as an anti-ulcer drug reflects its ability to inhibit stomach ECL-cell histamine secretion.

Neurohormonal stimulation of histamine release from neuroendocrine cells of the human adenomatous prostate

BACKGROUND

Neuroendocrine cells (NE) constitute a population of highly specialized cells in prostatic glands; histamine has never been described in these cells. This article shows the presence and the regulation of release of histamine in NE.

METHODS

In 21 prostatic adenomas, NE were identified by specific antisera against neuroendocrine markers (chromogranin-A, synaptophysin), histamine, and histidine decarboxylase (HDC); a rate HDC-cDNA probe was used to detect this enzyme by in situ hybridization.

RESULTS

Immunoreactive cells for chromogranin-A, histamine, and HDC were found among luminal epithelial glandular cells. Similar cells were also labeled with the HDC-cDNA probe. Glandular cells, isolated from prostatic adenomas, were shown to contain histamine (7-40 pmol/mg cellular protein). L(-) norepinephrine causes a time-dependent (t1/2 = 22 min) histamine release; the alpha 1-receptor antagonists WB-4101 and YM-617 specifically inhibited this release, in agreement with a mediation by alpha 1-adrenoreceptor subtype.

CONCLUSIONS

There is some evidence for the presence in prostatic adenomas of histamine-forming cells of neuroendocrine type; histamine release from these cells is under the control of alpha 1-adrenoreceptor subtype.

Neurohormonal regulation of histamine and pancreastatin secretion from isolated rat stomach ECL cells

ECL cells are numerous in the acid-producing part of the rat stomach. They are rich in histamine and pancreastatin, a chromogranin A-derived peptide, and they secrete these products in response to gastrin. We have examined how isolated ECL cells respond to a variety of neuromessengers and peptide hormones. Highly purified (85%) ECL cells were collected from rat stomach using repeated counter-flow elutriation and cultured for 48 h before experiments were conducted. The ECL cells responded to gastrin, sulphated cholecystokinin-8 and to high K+ and Ca2+ with the parallel secretion of histamine and pancreastatin. Glycine-extended gastrin was without effect. Forskolin, an activator of adenylate cyclase, induced secretion, whereas isobutylmethylxanthine, a phosphodiesterase inhibitor, raised the basal release without enhancing the gastrin-evoked stimulation. Maximum stimulation with gastrin resulted in the release of 30% of the secretory products. Numerous neuromessengers and peptide hormones were screened for their ability to stimulate secretion and to inhibit gastrin-stimulated secretion. Pituitary adenylate cyclase activating peptide (PACAP)-27 and -38 stimulated secretion of both histamine and pancreastatin with a potency greater than that of gastrin and with the same efficacy. Related peptides, such as vasoactive intestinal peptide, helodermin and helospectin, stimulated secretion with lower potency. The combination of EC100 gastrin and EC50 PACAP produced a greater response than gastrin alone. None of the other neuropeptides or peptide hormones tested stimulated secretion. Serotonin, adrenaline, noradrenaline and isoprenaline induced moderate secretion at high concentrations. Muscarinic receptor agonists did not stimulate secretion, and histamine and selective histamine receptor agonists and antagonists were without effect. This was the case also with GABA, aspartate and glutamate. Somatostatin and galanin, but none of the other agents tested, inhibited gastrin-stimulated secretion. Our results reveal that not only gastrin but also PACAP is a powerful excitant of the ECL cells, that not only somatostatin, but also galanin can suppress secretion, that muscarinic receptor agonists fail to evoke secretion, and that histamine (and pancreastatin) does not evoke autofeedback inhibition.

Short-term inhibitory effect of somatostatin on gastric histamine synthesis

In this study we investigated the short-term effect of somatostatin on histamine synthesis in a cell population isolated from rabbit gastric mucosa and enriched in enterochromaffin-like cells. Somatostatin inhibited basal and gastrin-stimulated histamine synthesis through a dual mechanism involving a decrease in the affinity of histidine decarboxylase (HDC) for its substrate (L-histidine) and a reduction in the number of functional HDC molecules. H-89 (an inhibitor of cAMP-dependent protein kinase) mimicked somatostatin-induced reduction of HDC affinity, which, on the contrary, was selectively reversed by pertussis toxin (PTX). Furthermore, forskolin was shown to reverse the inhibitory effect of H-89 and to prevent the somatostatin-induced reduction in HDC affinity for L-histidine. Thus, the somatostatin-induced reduction in affinity seems to involve a PTX-sensitive G protein and an inhibition of the cAMP-dependent pathway. On the other hand, the somatostatin-induced decrease in the number of functional HDC molecules seems to be PTX insensitive and independent from a modulation of the cAMP pathway, and does not seem to involve a significant change in HDC messenger RNA expression or a regulation of protein kinase C. The exact nature of this second mechanism will need further studies to be elucidated.

Dual inhibitory pathways link antral somatostatin and histamine secretion in human, dog, and rat stomach

BACKGROUND & AIMS

The secretion and function of antral histamine are not known. The aims of this study were to characterize the mechanisms of histamine release from the gastric antrum of humans, dogs, and rats and to determine whether histamine can influence the secretion of somatostatin and gastrin.

METHODS

Somatostatin, gastrin, and histamine secretion from superfused antral segments was measured using radioimmunoassay.

RESULTS

Superfusion with thioperamide (H3 antagonist) increased somatostatin and decreased gastrin and histamine secretion in all three species; superfusion with (r)-alpha-methylhistamine (H3 agonist) had the opposite effect. The pattern implied that endogenous histamine, acting via H3 receptors, exerts an inhibitory paracrine influence on somatostatin secretion, which in turn regulates gastrin secretion. Superfusion with somatostatin antibody increased histamine secretion; the increase was not affected by the gastrin antagonist L-365,260, implying that it was not mediated by the concurrent increase in gastrin but by suppression of an inhibitory pathway linking somatostatin and histamine. Superfusion with methacholine alone and in the presence of either the H3 agonist or antagonist confirmed the existence of reciprocal inhibitory pathways linking somatostatin and histamine.

CONCLUSIONS

Antral histamine in humans, dogs, and rats is linked to antral somatostatin via reciprocal inhibitory paracrine pathways that serve to amplify the regulatory influence of somatostatin.