The effect of different calcium antagonists on histamine- and carbachol-induced acid secretion in the isolated mouse stomach

Effect of caffeic acid phenethyl ester on gastric acid secretion in vitro

Caffeic acid phenethyl ester (CAPE), one of the major components of propolis (honeybee resin), has demonstrated a wide spectrum of activities including suppression of eicosanoids by inhibition of cyclooxygenase-1 and cyclooxygenase-2 enzyme activities. The aim of this study was to investigate the effect of CAPE on basal and secretagogues-stimulated gastric acid secretion in vitro. In the isolated, lumen-perfused, stomach preparation of mouse, CAPE (10-100 microM) did not affect the basal gastric acid secretion nor the secretion stimulated by histamine, pentagastrin, isobutyl methylxanthine and high levels of K+. By contrast, CAPE increased the gastric acid secretion induced by the muscarinic receptor agonist, 5-methylfurmethide (5-MEF). CAPE also inhibited the acetylcholinesterase activity in an in vitro colorimetric assay. Eserine (10 microM), a well known acetylcholinesterase inhibitor, also increased 5-MEF-stimulated acid secretion. Our results show that CAPE increases gastric acid secretion stimulated by an acetylcholine agonist receptor likely through inhibition of acetylcholinesterase activity.

Role of neuropeptide-sensitive L-type Ca(2+) channels in histamine release in gastric enterochromaffin-like cells

Peptides release histamine from enterochromaffin-like (ECL) cells because of elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) by either receptor-operated or voltage-dependent Ca(2+) channels (VDCC). To determine whether VDCCs contribute to histamine release stimulated by gastrin or pituitary adenylate cyclase-activating polypeptide (PACAP), the presence of VDCCs and their possible modulation by peptides was investigated in a 48-h cultured rat gastric cell population containing 85% ECL cells. Video imaging of fura 2-loaded cells was used to measure [Ca(2+)](i), and histamine was assayed by RIA. Cells were depolarized by increasing extracellular K(+) concentrations or by 20 mM tetraethylammonium (TEA(+)). Cell depolarization increased transient and steady-state [Ca(2+)](i) and resulted in histamine release, dependent on extracellular Ca(2+). These K(+)- or TEA(+)-dependent effects on histamine release from ECL cells were coupled to activation of parietal cells in intact rabbit gastric glands, and L-type channel blockade by 2 microM nifedipine inhibited 50% of [Ca(2+)](i) elevation and histamine release. N-type channel blockade by 1 microM omega-conotoxin GVIA inhibited 25% of [Ca(2+)](i) elevation and 14% of histamine release. Inhibition was additive. The effects of 20 mM TEA(+) were fully inhibited by 2 microM nifedipine. Both classes of Ca(2+) channels were found in ECL cells, but not in parietal cells, by RT-PCR. Nifedipine reduced PACAP-induced (but not gastrin-stimulated) Ca(2+) entry and histamine release by 40%. Somatostatin, peptide YY (PYY), and galanin dose dependently inhibited L-type Ca(2+) channels via a pertussis toxin-sensitive pathway. L-type VDCCs play a role in PACAP but not gastrin stimulation of histamine release from ECL cells, and the channel opening is inhibited by somatostatin, PYY, and galanin by interaction with a G(i) or G(o) protein.

Roles of in vitro- and in vivo-administered histamine and serotonin in compound 48/80-induced gastric acid secretion in isolated, perfused rat stomach

In this investigation, an isolated, perfused rat stomach system was used to elucidate the roles of histamine, serotonin, and the action of cimetidine, methysergide, and propranolol in relation to the in vivo and in vitro administration of compound 48/80. While histamine administered both in vivo and in vitro stimulated acid secretion in the perfused rat stomach, serotonin, added in vitro, inhibited histamine-induced gastric acid secretion. Cimetidine, given either in vivo or in vitro, blocked histamine-induced acid secretion, and methysergide, but not propranolol, reversed the serotonin-induced inhibition of histamine-stimulated acid secretion. Compound 48/80, given in vitro, caused gastric acid secretion that was blocked by pretreatment with cimetidine. Administered in vivo, however, compound 48/80 inhibited both basal and histamine-stimulated acid secretion. This inhibition was partially reversed by pretreatment with methysergide. The absence of inhibition of acid secretion by in vitro-administered compound 48/80 may be related to the timing of the serotonin effect. When serotonin was given prior to histamine, it blocked acid secretion, whereas no inhibition occurred when serotonin was administered together with histamine. None of the other agents investigated affected basal acid secretion.