Suc-[Glu9,Ala11,15]-endothelin-1 (8-21), IRL 1620, identifies two populations of ET(B) receptors in guinea-pig bronchus.
The pharmacological properties of endothelin receptors (ETR) were investigated in guinea-pig bronchus by comparing binding and functional results. In binding assays, both the ET(B) agonists, endothelin-3 (ET-3) and N-suc-[Glu9,Ala11,15]ET-1(8-21) (IRL 1620), and the antagonist, N-cis-2,6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D- 1-methoxycarbonyltryptophanyl-D-norleucine (BQ 788), showed biphasic inhibition curves of [125I]-endothelin-1 (ET-1) binding to bronchus membranes prepared from intact or epithelium-deprived tissue. IRL 1620 did not completely displace specifically [125I]-ET-1 bound to these tissue preparations. In the presence of the ET(A)-selective antagonist, cyclo(-D-Trp-D-Asp-L-Pro-D-Val-L-Leu) (BQ 123, 1 microM), IRL 1620 displacement curves were shallow but a complete inhibition was reached at a concentration of 1 microM. Both curves were better represented by two-site models. In addition, BQ 788 competition curves became monophasic when binding experiments were performed in the presence of 1 microM BQ 123. The non-selective agonist, ET-1, and BQ 123 inhibited [125I]-ET binding to bronchus membranes in dose-dependent fashions with monophasic curves. The contracting activity of IRL 1620 (0.55 nM- 1.6 microM) was tested on multiple-ring bronchial preparations pretreated with peptidase and cyclo-oxygenase inhibitors. BQ 788 shifted IRL1620 concentration-response curves to the right while BQ 123 did not influence bronchial responsiveness. In addition, a potentiation of the maximal response to the agonist was observed in BQ 788 treated bronchial rings. This effect was abolished by tissue pretreatment with Nomega-nitro-L-argininemethylester (L-NAME) or epithelium removal but not by pretreatment with atropine or iberiotoxin. Our results demonstrate that guinea-pig bronchus contains two populations of ET(B) receptors with different affinities for the ET(B)-selective agonist, IRL 1620. One ET(B) receptor population appears to activate bronchial muscle contraction while another on epithelial cells causes muscle relaxation through the release of nitric oxide (NO).
Mazzoni
M R
MR
Department of Psychiatry, Neurobiology, Pharmacology and Biotechnology, University of Pisa, Italy. mariarm@farm.unipi.it
Breschi
M C
MC
Ceccarelli
F
F
Lazzeri
N
N
Giusti
L
L
Nieri
P
P
Lucacchini
A
A
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001980:Bronchi / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D019332:Endothelin-1 / Q000378:metabolism / Q000494:pharmacology; D016232:Endothelins / Q000378:metabolism* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism* / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D011869:Radioligand Assay; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000187:drug effects / Q000378:metabolism*
D019332:Endothelin-1; D016232:Endothelins; D004791:Enzyme Inhibitors; D007457:Iodine Radioisotopes; D009842:Oligopeptides; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D010880:Piperidines; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; C074308:sovateltide; C086539:BQ 788; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D019331:NG-Nitroarginine Methyl Ester