Prostaglandin E2 suppression of acetylcholine release from parasympathetic nerves innervating guinea-pig trachea by interacting with prostanoid receptors of the EP3-subtype.
1. We have demonstrated recently that exogenous prostaglandin E2 (PGE2) inhibits electrical field stimulation (EFS)-induced acetylcholine (ACh) release from parasympathetic nerve terminals innervating guinea-pig trachea. In the present study, we have attempted to characterize the pre-junctional prostanoid receptor(s) responsible for the inhibitory action of PGE2 and to assess whether other prostanoids modulate, at a prejunctional level, cholinergic neurotransmission in guinea-pig trachea. To this end, we have investigated the effect of a range of both natural and synthetic prostanoid agonists and antagonists on EFS-evoked [3H]-ACh release. 2. In epithelium-denuded tracheal strips pretreated with indomethacin (10 microM), PGE2 (0.1 nM-1 microM) inhibited EFS-evoked [3H]-ACh release in a concentration-dependent manner with an EC50 and maximal effect of 7.62 nM and 74% inhibition, respectively. Cicaprost, an IP-receptor agonist, PGF2alpha and the stable thromboxane mimetic, U46619 (each at 1 microM), also inhibited [3H]-ACh release by 48%, 41% and 35%, respectively. PGD2 (1 microM) had no significant effect on [3H]-ACh release. 3. The selective TP-receptor antagonist, ICI 192,605 (0.1 microM), completely reversed the inhibition of cholinergic neurotransmission induced by U-46619, but had no significant effect on similar responses effected by PGE2 and PGF2alpha. 4. A number of EP-receptor agonists mimicked the ability of PGE2 to inhibit [3H]-ACh release with a rank order of potency: GR63799X (EP3-selective) > PGE2 > M&B 28,767 (EP3 selective) > 17-phenyl-omega-trinor PGE2 (EP1-selective). The EP2-selective agonist, AH 13205 (1 microM), did not affect EFS-induced [3H]-ACh release. 5. AH6809 (10 microM), at a concentration 10 to 100 times greater than its pA2 at DP-, EP1- and EP2-receptors, failed to reverse the inhibitory effect of PGE2 or 17-phenyl-omega-trinor PGE2 on [3H]-ACh release. 6. These results suggest that PGE2 inhibits [3H]-ACh release from parasympathetic nerves supplying guinea-pig trachea via an interaction with prejunctional prostanoid receptors of the EP3-receptor subtype. Evidence for inhibitory prejunctional TP- and, possibly, IP-receptors was also obtained although these receptors may play only a minor role in suppressing [3H]-ACh release when compared to receptors of the EP3-subtype. However, the relative importance of the different receptors will depend not only on the sensitivity of guinea-pig trachea to prostanoids but on the nature of the endogenous ligands released locally that have activity on parasympathetic nerves.
Spicuzza
L
L
Thoracic Medicine, Imperial College School of Medicine at the National Heart & Lung Institute, London.
Giembycz
M A
MA
Barnes
P J
PJ
Belvisi
M G
MG
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000109:Acetylcholine / Q000378:metabolism*; D000368:Aged; D015237:Dinoprost / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology*; D004146:Dioxanes / Q000494:pharmacology; D004558:Electric Stimulation; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D010275:Parasympathetic Nervous System / Q000187:drug effects* / Q000378:metabolism; D018078:Receptors, Prostaglandin E / Q000819:agonists / Q000187:drug effects* / Q000378:metabolism; D058308:Receptors, Prostaglandin E, EP3 Subtype; D014132:Trachea / Q000294:innervation* / Q000378:metabolism
D004146:Dioxanes; C545647:PTGER3 protein, human; D018078:Receptors, Prostaglandin E; D058308:Receptors, Prostaglandin E, EP3 Subtype; C057498:ICI 192605; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D015237:Dinoprost; D015232:Dinoprostone; D000109:Acetylcholine