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 p ancreastatin. The regulation of ECL-cell secretion has been studied by seve ral groups using purified ECL cells, isolated from rat stomachs. Reports fr om different laboratories often disagree. The purpose of the present study was to re-evaluate the discrepancies by studying histamine (or pancreastati n) secretion from standardized preparations of pure, well-functioning ECL c ells. Cells from rat oxyntic mucosa were dispersed by pronase digestion, pu rified by repeated counter-flow elutriation and subjected to density gradie nt centrifugation. The final preparation consisted of more than 90% ECL cel ls (verified by histamine and/or histidine decarboxylase immunocytochemistr y). They were maintained in primary culture for 48 h before they were expos ed 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 hista mine secretion 4-fold, the EC50 for both peptides being around 100 pM. The neuropeptide pituitary adenylate cyclase activating peptide (PACAP-27) (5-f old increase) and the related neuropeptides vasoactive intestinal peptide ( VIP) and peptide histidine isoleucine (PHI) (3-fold increase) mobilized his tamine with similar potency (EC50 ranging from 80 to 140 pM). Adrenaline, i soprenaline and terbutaline stimulated secretion by activating a beta (2) r eceptor subtype, while acetylcholine and carbachol were without effect. Sec retion experiments were invariably run in parallel with a gastrin standard curve. Somatostatin, prostaglandin E-2 (PGE(2)) and the PGE(1) congener mis oprostol inhibited PACAP- and gastrin-stimulated secretion by more than 90% , with IC50 values ranging from 90-720 (somatostatin) to 40-200 (misoprosto l) pM. The neuropeptide galanin inhibited secretion by 60-70% with a potenc y similar to that of somatostatin. Proposed inhibitors such as peptide YY, neuropeptide Y and the cytokines interleukin 1-beta and tumor necrosis fact or cr induced at best a moderate inhibition of gastrin- or PACAP-stimulated secretion at high concentrations, while calcitonin gene-related peptide, p ancreatic polypeptide and histamine itself were without effect. Inhibition of gastrin- or PACAP-stimulated secretion was routinely compared to a somat ostatin standard curve. In conclusion, gastrin, PACAP, VIP/PHI and adrenali ne stimulated secretion. Somatostatin and PGE(2) were powerful inhibitors o f both gastrin- and PACAP-stimulated secretion; although equally potent, ga lanin was less effective than somatostatin and PGE(2). (C) 2001 Elsevier Sc ience B.V. All rights reserved.