Pharmacological characterization of pre- and postsynaptic prostanoid receptors in pig gastric fundus
Introduction
Five different prostanoid receptor classes, i.e. DP, EP, FP, IP and TP receptors (for review, see Coleman et al., 1994) are known, where the naturally occurring prostanoids PGD2, PGE2, PGF2α, PGI2 (prostacyclin) and tromboxane A2 (TXA2), respectively, are the most potent agonists. The EP receptor can further be divided into four subtypes: EP1, EP2, EP3 and EP4, and four EP3-receptor isoforms are known (Coleman et al., 1994). The release of acetylcholine from peripheral autonomic cholinergic neurones is modified by a number of different presynaptic receptors, and prostanoid receptors were previously described on cholinergic neurones, whereby activation of these receptors increases or decreases the release of acetylcholine depending on the tissue and species. The cyclooxygenase inhibitor indomethacin had no effect on electrically induced [3H]-acetylcholine release in human bronchi, but stimulation of EP3-receptors inhibited it (Reinheimer et al., 1998). Also in guinea-pig trachea and canine bronchial tissue, evidence for the presence of inhibitory EP-receptors on the cholinergic neurones was obtained (Deckers et al., 1989, Spicuzza et al., 1998). In human urinary bladder, there is evidence for the presence of stimulatory TP- and FP-receptors on cholinergic neurones (Palea et al., 1998). In the longitudinal muscle-myenteric plexus (LMMP) preparation from guinea-pig ileum, indomethacin was found to inhibit contractions and acetylcholine release induced by nicotine (Yagasaki et al., 1984, Okpako and Taiwo, 1984), and the inhibitory effect of indomethacin was partially prevented by PGE2 (Yagasaki et al., 1984, Takeuchi et al., 1991) and completely by PGI2 (Fukunaga et al., 1993). This suggests the presence of stimulatory IP- and EP-receptors on the cholinergic nerve endings, although PGE2 might have its effect via the IP-receptors.
Prostanoid receptors are also described on smooth muscle cells, causing contraction or relaxation depending on the prostanoid receptor subtype. Functionally, three groups of prostanoid receptors can be recognized: EP1-, TP- and FP-receptors are contractile receptors; the EP3-receptor is an inhibitory receptor inhibiting smooth muscle relaxation, although it is suggested that activation of EP3-receptors causes contraction of uterine and gastrointestinal smooth muscles via calcium mobilization in these tissues; IP-, DP-, EP2- and EP4-receptors are relaxant receptors (Coleman et al., 1994). In mouse ileum and gastric fundus, muscular contractile EP1-, EP3-, TP- and FP-receptors were found (Okada et al., 2000).
Circularly oriented muscle strips of pig gastric fundus, mounted in classic organ baths, show a progressive increase in basal muscle tone during the course of the experiment despite regular rinsing (Mandrek and Kreis, 1992, Leclere and Lefebvre, 1998). This effect was prevented by the addition of indomethacin (Leclere and Lefebvre, 2002), indicating that prostanoids are released and have a contractile influence. The aim of the present study was to investigate the effect of prostanoids on electrically induced [3H]-acetylcholine release from cholinergic neurones innervating the circular muscle of pig gastric fundus and to characterize the involved receptor subtype. In these experiments, the influence of the substances studied on muscle tone was also assessed in an attempt to characterize the contractile prostanoid receptor(s) on the circular muscle cells of the pig gastric fundus.
A preliminary account of these findings has been presented at the 11th European Symposium of the European Society for Neurogastroenterology and Motility (De Backer et al., 2002).
Section snippets
Tissue preparation
Experiments were carried out on isolated circular smooth muscle strips of the pig gastric fundus. The stomach was removed from healthy castrated male pigs, slaughtered at a local abattoir, and transported to the laboratory in ice-chilled physiological salt solution (PSS). After the mucosa was removed, strips of approximately 1.5 cm in length and 0.3 cm in width were cut in the direction of the circular muscle; the tissues thus also contained a narrow band of longitudinal muscle. All strips were
Control experiments and effect of indomethacin
In the first set of experiments, tissues were only stimulated twice (S1 and S2) and indomethacin (n=6) or its solvent (parallel control tissues, n=6) was added before S2. In the control tissues, the release of tritium before S1 (sample 3) was 610±70 Bq per g tissue (n=6). Electrical stimulation caused a marked increase above basal release of radioactivity. The amount of tritium released due to S1 (samples 4, 5, 6 and 7) above basal release was 1950±320 Bq per g tissue (n=6), and the evoked
Discussion
The aim of this study was to identify whether prejunctional prostanoid receptors modulate acetylcholine release from cholinergic nerve endings innervating the circular muscle layer of pig gastric fundus; an attempt was also made to characterize the muscular prostanoid receptor responsible for the contraction of the circular muscle strips under basal conditions. It should be kept in mind that the circularly oriented muscle strips also contained a narrow band of longitudinal muscle. In view of
Acknowledgements
This study was financially supported by grant G.0053.02 of the Fund for Scientific Research (Flanders) and by Interuniversity Pole of Attraction Programme P5/20 (Federal Services for Scientific, Technical and Cultural Affairs).
References (24)
- et al.
Evidence for the involvement of prostaglandins in modulation of acetylcholine release from canine bronchial tissue
European Journal of Pharmacology
(1989) - et al.
Role of prostacyclin in acetylcholine release from myenteric plexus of guinea-pig ileum
European Journal of Pharmacology
(1993) - et al.
Influence of nitric donors and of the α2-agonist UK-14,304 on acetylcholine release in the pig gastric fundus
Neuropharmacology
(2001) - et al.
Contractile responses of longitudinal and circular smooth muscle of the canine stomach to prostaglandins E and F2 alpha
Prostaglandins Leukotrienes and Medicine
(1982) - et al.
A comparison in vitro of human and rabbit distal colonic muscle responses to inflammatory mediators
Gastroenterology
(1990) - et al.
6-Isopropoxy-9-oxoxanthene-2-carboxylic acid (AH 6809), a human EP2 receptor antagonist
Biochemical Pharmacology
(1995) - et al.
Contribution of endogenous prostaglandins to excitation of the myenteric plexus of guinea-pig ileum: are adrenergic factors involved?
European Journal of Pharmacology
(1984) - et al.
Metabolites of arachidonic acid formed by human gastrointestinal tissues and their actions on the muscle layers
British Journal of Pharmacology
(1981) - et al.
New evidence with selective agonists and antagonists for the subclassification of PGE2-sensitive (EP) receptors
Advances in Prostaglandin, Thromboxane and Leukotriene Research
(1987) - et al.
VIII. International Union of Pharmacology. Classification of prostanoid receptors: properties, distribution, and structure of the receptors and their subtypes
Pharmacological Reviews
(1994)
Pharmacological characterization of prostanoid receptors on circular smooth muscle cells and on cholinergic neurones innervating the circular muscle layer of pig gastric fundus
Neurogastroenterology and Motility
AH 6809, a prostaglandin DP-receptor blocking drug on human platelets
British Journal of Pharmacology
Cited by (11)
Effect of central and peripheral injection of prostaglandin E2 and F2α on feeding and the crop-emptying rate in chicks
2017, Prostaglandins and Other Lipid MediatorsCitation Excerpt :These results suggest that PGs affect the activity of the vagus nerve and then alter the crop emptying rate in chicks. It is also possible that IP-injected PGs directly affect intestinal smooth muscle because PGE2 and PGF2α contracts the circular muscle strips o pig gastric fundus in vitro [35]. On the other hand, there is a paucity of knowledge how central PGE2 affect food passage in the digestive tract.
Neurogenic contraction of mouse rectum via the cyclooxygenase pathway: Changes of PGE<inf>2</inf>-induced contraction with dextran sulfate sodium-induced colitis
2010, Pharmacological ResearchCitation Excerpt :In addition, prostanoid receptors exist on cholinergic neurons in the GI tract, where their activation increases or decreases the release of acetylcholine (ACh) depending on the tissue and species. In longitudinal preparations of muscle-myenteric plexus from guinea-pig ileum, treatment with indomethacin inhibited contractions and the release of ACh induced by nicotine, and the inhibitory effects were prevented by PGE2 and PGI2 [6,7]. These reports suggest a role for PGs in contractile responses regulated by neuronal- and non-neuronal pathways in GI tissues.
Emerging role of cyclooxygenase isoforms in the control of gastrointestinal neuromuscular functions
2010, Pharmacology and TherapeuticsCardiovascular effect of peripheral injected melittin in normotensive conscious rats: Mediation of the central cholinergic system
2009, Prostaglandins Leukotrienes and Essential Fatty AcidsCharacterization of prostanoid receptors present on adrenergic neurons innervating the porcine uterine longitudinal muscle
2008, Prostaglandins and Other Lipid MediatorsAlterations in spontaneous contractions of rat ileum and jejunum after peritonitis
2008, European Journal of Pharmacology