Effect of prostaglandin E2 on the electrical activity of cat isolated stomach muscle

Regulation of pacemaker frequency in the murine gastric antrum

PGE(2) has been linked to the production of gastric arrhythmias such as tachygastria. The interstitial cells of Cajal (ICC) generate electrical rhythmicity in gastrointestinal muscles, and may therefore be a target for PGE(2) in gastric muscles. We cultured ICC from the murine gastric antrum, verified that cells were Kit immunoreactive, and measured spontaneous slow waves. These events were caused by spontaneous inward (pacemaker) currents that were not blocked by nifedipine. Forskolin and 8-bromoadenosine 3':5'-cyclic monophosphate (8-Br-cAMP) reduced the frequency of pacemaker currents in ICC and of slow waves in intact antral muscles. The effects of forskolin and 8-Br-cAMP were not blocked by inhibitors of protein kinase A, suggesting that cAMP has direct effects on pacemaker activity. PGE(2) mimicked the effects of forskolin and 8-Br-cAMP on ICC, but increased slow-wave frequency in intact muscles. Therefore, the chronotropic effects of specific prostaglandin EP receptor agonists were examined. Butaprost and ONO-AE1-329, EP(2) and EP(4) receptor agonists, mimicked the effects of forskolin and 8-Br-cAMP on ICC and intact muscles. Sulprostone (EP(3)>EP(1) agonist), GR63799, and ONO-AE-248 (EP(3) agonists) enhanced the frequencies of pacemaker currents in ICC and slow waves in intact muscles. The effects of sulprostone were not blocked by SC-19220, an EP(1) receptor antagonist. These observations suggest that the positive chronotropic effects of PGE(2) in intact muscles are mediated by EP(3) receptor stimulation. The effects of PGE(2) in intact muscles may be dependent upon the relative expression of EP receptors and/or proximity of receptors to sources of PGE(2).

Protective effect of amtolmetin guacyl versus placebo diclofenac and misoprostol in healthy volunteers evaluated as gastric electrical activity in alcohol-induced stomach damage

Amtolmetin guacyl (AMG) is a nonsteroidal antiinflammatory drug (NSAID) of high therapeutic activity and free of damaging effects on the gastrointestinal tract. Since acute ulcer and nausea have been found to be associated with gastric dysrhythmias, cutaneous electrogastrography and ultrasonographic study of the gastric emptying time were performed simultaneously in 24 healthy volunteers before and for 180 min after a liquid meal with 0.5 g/kg body weight of alcohol in double-blind, placebo-controlled, crossover studies. Before the recording session, each subject had taken placebo, AMG, a standard NSAID, or a gastric protective drug for four days. Alcohol administration increased the tachygastria percentage while diclofenac, AMG, and misoprostol alone did not induce gastrointestinal symptoms and gastric dysrhythmias. As regards alcohol-induced gastric dysrhythmia, placebo and diclofenac showed a clear increase in tachygastria while AMG and misoprostol did not. AMG is able to induce a normalization of gastric dysrhythmia induced by alcohol administration probably due to its peculiar mechanism of action, which involves capsaicin and CGRP pathways.

Effects of prostaglandins E1 and E2 on cultured smooth muscle cells and strips of rat aorta

Using patch-clamp and Indo-1AM techniques, we studied the effects of prostaglandins (PG) E1 and E2 on transmembrane ionic currents and cytosolic calcium concentration ([Ca2+]i) in cultured rat aortic smooth muscle cells (SMC) and on isotonic contraction-relaxation of strips of the rat thoracic aorta. In voltage-clamped at -70 mV single SMC PGE1 and PGE2 in concentration 100 nM evoked inward and outward currents. The inward current was unaffected by the Cl channel blocker DIDS (0.1 mM). The outward current was blocked by internal Cs+ and external Ba2+ and was likely due to increased Ca2+ activated K+ conductance. Application of PGE1 and PGE2 in the bath solution evoked relaxation of aortic strips in a concentration-dependent manner. In both cases indomethacin was ineffective. The rise in [Ca2]i evoked by PGEs was observed in single cells loaded with Indo-1AM. Whole-cell voltage-activated T- and L-type Ca2+ currents were reduced by both PGE1 and PGE2. The results obtained in this work indicate that in cultured rat aortic SMC PGE1 and PGE2 increase [Ca2+]i with subsequent activation of Ca(2+)-dependent K+ currents, block voltage-activated Ca2+ currents, and at the same time induce relaxation of aortic strips.

The action of histamine on the isolated stomach muscle of the cat

The effect of histamine on contractile and electric activity was studied in the isolated stomach muscle strips of 138 cats. Histamine dose-dependently produced tonic and phasic contractions of the muscle preparations from the fundus and the corpus but only phasic contraction of the antral muscle preparations. The frequency of gastric slow waves (SWs) was also increased dose-dependently by histamine. The responses of muscle contractions and gastric SW frequency to histamine were completely blocked by pretreatment with pyrilamine (10(-6) M) and were significantly inhibited by atropine (10(-5) M) but not by cimetidine (10(-5) M), hexamethonium (10(-5) M), phentolamine (10(-5) M), or propranolol (10(-5) M). The inhibition by pyrilamine was competitive. Although atropine inhibited the effect of histamine significantly, it could not completely block the effect of histamine even at a high concentration (3 x 10(-5) M). It is concluded that histamine may participate in the regulation of gastric motility in the cat by acting on the H1 receptor to cause the release of acetylcholine and also other contractile substance(s).

Effect of dopamine on electrical activity of isolated stomach muscle in cats

The effect of dopamine on electrical activity (gastric slow wave) of the stomach was studied in isolated stomach muscle strips of 145 cats. The gastric slow wave was recorded by four monopolar electrodes (Ag-AgCl) in Krebs-Ringer solution (pH 7.4, temperature 36 +/- 0.5 degrees C) bubbled with 5% CO2 in O2. Dopamine induced concentration-dependent alterations in frequency and propagation of slow waves. Development of irregular propagation was significantly suppressed by domperidone pretreatment. The variation of dopamine-induced slow-wave frequency was significantly inhibited by domperidone and phentolamine but not by propranolol, hexamethonium, and tetrodotoxin. The study indicates that a dopamine receptor exists in the stomach and plays a role in the genesis of gastric electrical abnormality.