Nitric oxide pathway-mediated relaxant effect of bradykinin in the guinea-pig isolated trachea.
1. The effects of two nitric oxide (NO) biosynthesis-inhibitors NG-nitro-L-arginine (L-NOARG) and NG-monomethyl-L-arginine (L-NMMA) on the relaxation induced by bradykinin (BK, 100 nM), isoprenaline (Iso, 1 microM) and sodium nitroprusside (SNP, 1 microM) were investigated in epithelium-intact strips of guinea-pig isolated trachea. 2. Relaxations induced by BK (100 nM) in guinea-pig tracheal strips under spontaneous tone were inhibited in a concentration-related manner by L-NOARG and L-NMMA (1 to 100 microM), with IC50s (and 95% confidence limits) of 9.1 (6.9-11.6) microM and 7.0 (4.2-12.3) microM, respectively. However, at the maximal concentration (100 microM) used, neither of these drugs inhibited completely BK-induced relaxation (maximal inhibition of 74 +/- 7 and 67 +/- 7%, respectively). On the other hand, D-NMMA, the D-enantiomer of L-NMMA, up to 100 microM failed to inhibit BK-induced relaxation. The relaxation induced by Iso (1 microM) and SNP (1 microM) were not affected by either L-NOARG or L-NMMA (30 microM). 3. The inhibition of BK-induced relaxation caused by L-NOARG and L-NMMA was partially reversed by addition of excess of L-arginine but not D-arginine (1 mM). 4. Like L-NOARG and L-NMMA, methylene blue (10 microM), an agent that inhibits the activation of soluble guanylate cyclase by NO, also significantly inhibited BK-induced relaxation, leaving responses to Iso unaffected. 5. Indomethacin (0.3 nM to 10 nM), a cyclo-oxygenase inhibitor, concentration-dependently inhibited BK-mediated relaxation, with an IC50 of 2.6 (1.7-3.8) nM, without affecting Iso and SNP-mediated relaxant responses. 6. A combination of a very low concentration of indomethacin (1 nM) and either L-NOARG or L-NMMA (100 microM) changed the response of tracheal preparations to BK (100 nM) from a relaxation to a sustained contraction. 7. These findings indicate that BK-induced relaxation in guinea-pig trachea is mediated jointly by the release of NO or a NO-related substance and a prostanoid, probably prostaglandin E2.
Department of Pharmacology, Universidade Federal de Santa Catarina, Florianópolis, Brazil.
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Calixto
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology*; D015232:Dinoprostone / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D009569:Nitric Oxide / Q000037:antagonists & inhibitors / Q000502:physiology*; D019335:Nitroarginine; D014132:Trachea / Q000187:drug effects* / Q000502:physiology; D019323:omega-N-Methylarginine
D019335:Nitroarginine; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D001120:Arginine; D015232:Dinoprostone; D001920:Bradykinin; D008751:Methylene Blue; D007213:Indomethacin