Pharmacologic characterization of intrinsic mechanisms controlling tone and relaxation of porcine lower esophageal sphincter.
The neurotransmitters mediating relaxation of lower esophageal sphincter (LES) were studied using circular LES strips from adult pigs in organ baths. LES relaxation by sodium nitroprusside (1 nM-3 microM), vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP; 1 nM-1 microM), ATP (10 microM-30 mM), and tricarbonyldichlororuthenum dimer (1 microM-1 mM) was unaffected by tetrodotoxin (1 microM) or l-N(G)-nitroarginine methyl ester (l-NAME; 100 microM). Calcitonin gene-related peptide (CGRP; 1 nM-1 microM) did not affect LES tone. ATP relaxation was blocked by 1 microM apamin and the P2Y(1) antagonist MRS 2179 (N6-methyl 2'-deoxyadenosine 3',5'-bisphosphate; 10 microM). Apamin inhibited PACAP relaxation. VIP and PACAP relaxation was blocked by 10 U/ml alpha-chymotrypsin. L-NAME (-62.52 +/- 13.13%) and 1H-[1,2,4]oxadiazole-[4,3-alpha]quinoxalin-1-one (ODQ; 10 microM, -67.67 +/- 6.80%) similarly inhibited electrical LES relaxation, and apamin blocked non-nitrergic relaxation. Nicotine relaxation (100 microM) was inhibited by L-NAME (-60.37 +/- 10.8%) and ODQ (-41.90 +/- 7.89%), and apamin also blocked non-nitrergic relaxation. Non-nitrergic and apamin-sensitive LES relaxation by electrical stimulation or nicotine was strongly inhibited by MRS 2179, slightly inhibited by alpha-chymotrypsin and the P2X(1,2,3) receptor antagonist NF 279 (8,8 cent-[carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino)]bis-1,3,5-naphthalenetrisulfonic acid hexasodium salt; 10 microM), and unaffected by tin protoporphyrin IX (100 microM). Porcine LES relaxation after stimulation of intrinsic inhibitory motor neurons is mediated by two main neuromuscular pathways: nitric oxide through guanylate cyclase signaling and apamin-insensitive mechanisms and by non-nitrergic apamin-sensitive neurotransmission mainly mediated by ATP, ADP, or a related purine acting on P2Y1 receptors and a minor contribution of purinergic P2X1,2,3 receptors and PACAP. Nitrergic and purinergic co-transmitters show parallel effects of similar magnitude without major interplay. Our study shows no role for CGRP and only a minor one for VIP and carbon monoxide in porcine LES relaxation.
Farré
Ricard
R
Fundació de Gastroenterologia Dr. Francisco Vilardell, Barcelona, Spain.
Aulí
Mariona
M
Lecea
Begoña
B
Martínez
Emma
E
Clavé
Pere
P
D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D004558:Electric Stimulation; D049630:Esophageal Sphincter, Lower / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009433:Neural Inhibition; D018377:Neurotransmitter Agents / Q000502:physiology; D009538:Nicotine / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000494:pharmacology; D013552:Swine; D013873:Thionucleotides / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
D018377:Neurotransmitter Agents; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D013873:Thionucleotides; D009599:Nitroprusside; C030812:adenosine 5'-O-(2-thiodiphosphate); D014660:Vasoactive Intestinal Peptide; D000244:Adenosine Diphosphate; D009538:Nicotine; D000255:Adenosine Triphosphate; D015740:Calcitonin Gene-Related Peptide; D019331:NG-Nitroarginine Methyl Ester