Role of peptidase and cyclooxygenase inhibitors in the guinea-pig bronchial response to the synthetic endothelin ET(B) agonist IRL 1620 and antagonist BQ-788.
In isolated guinea-pig bronchial preparations the selective endothelin ETB agonist, IRL 1620 caused a concentration-dependent contraction. The pD2 value (7.16 +/- 0.09, n = 6) was significantly increased in the presence of peptidase inhibitors (thiorfan 1 microM, captopril 1 microM, bestatin 1 microM) (pD2 = 7.75 +/- 0.09, n = 6). Indomethacin (5 microM) did not appear to influence the ETB-agonist pD2 value (6.92 + 0.11, n = 6) but potentiated its maximal response significantly (67.23 +/- 4.81% vs. 53.37 +/- 4.80%). The concentration-response curve for the contractile response to IRL 1620 (pD2=7.83 +/- 0.01, n=16); was reproducible, although not completely, since the second curve to this selective ETB agonist was shifted significantly to the right (pD2 = 7.34 +/- 0.09, n = 16) and a decrease in the maximal response was observed (20.0 +/- 2.0%). BQ 788, a selective antagonist for ETB receptors, employed in concentrations ranging from 1.5 to 150 nM, caused a dose-dependent shift to the right of the concentration-response curve to IRL 1620, with a pIC50 value of 8.11 +/- 0.03; this action was not influenced by adding enzyme inhibitors (pIC50 = 8.17 +/- 0.29). Our data show that IRL 1620 undergoes a hydrolytic metabolism in guinea-pig bronchial preparations, which could influence the calculation of the pD2. Pretreatment of the tissue with peptidase inhibitors and indomethacin is consequently significant in the evaluation of IRL 1620 activity, while it does not influence the action of the antagonist, BQ 788.
Lazzeri
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Department of Psychiatry, Neurobiology, Pharmacology and Biotechnology, University of Pisa, Italy.
Nieri
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Lenzi
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Ratti
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C
Breschi
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MC
D000818:Animals; D001980:Bronchi / Q000187:drug effects*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000494:pharmacology*; D006168:Guinea Pigs; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010880:Piperidines / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology*; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000819:agonists*
D016861:Cyclooxygenase Inhibitors; D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D009842:Oligopeptides; D010446:Peptide Fragments; D010880:Piperidines; D011480:Protease Inhibitors; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; C074308:sovateltide; C086539:BQ 788; D011189:Potassium Chloride; D007213:Indomethacin