title: Met-enkephalin-dependent nitrergically mediated relaxation in the guinea pig ileum.
abstract: Met-enkephalin-induced modulation of tetrodotoxin (0.1 microM)-sensitive nonadrenergic, noncholinergic (NANC) nerve-mediated responses of the longitudinal muscle layer of guinea pig ileum during electrical field stimulation (EFS, 0.8 ms, 40 V, 20 s, 1 Hz or 10 Hz) were studied. The response to EFS of untreated preparations was a twitch followed by a low-amplitude tonic contraction. The NANC nerve-mediated response revealed in the presence of phentolamine (5 microM), propranolol (5 microM) and atropine (3 microM) consisted of relaxation followed by a twitch and a tonic contraction. The relaxation was inhibited by NG-nitro-L-arginine (0.1-0.5 mM), a nitric oxide synthase inhibitor. L-arginine (0.5 mM), a substrate of nitric oxide synthase, restored the relaxation to the initial level indicating its nitrergic origin. After adenosine 5'-triphosphate-induced desensitization of purinoceptors the relaxation was enhanced while the contractions decreased. Met-enkephalin (1 nM-1 microM) abolished (J-Hz EFS) or reduced (10-Hz EFS) the relaxation in a frequency-dependent manner, suggesting an inhibitory prejunctional enkephalinergic mechanism modulating the nitrergically mediated relaxant events in the longitudinal muscle layer.
authors.affiliation: Laboratory of Peripheral Synapses, Bulgarian Academy of Sciences, Sofia, Bulgaria.
authors.forename: C
authors.initials: C
authors.lastname: Ivancheva
authors.forename: R
authors.initials: R
authors.lastname: Radomirov
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects* / Q000294:innervation; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000187:drug effects; D019335:Nitroarginine / Q000494:pharmacology
chemical_list: D019335:Nitroarginine; D004744:Enkephalin, Methionine; D001120:Arginine