Necessity of dual blockade of endothelin ETA and ETB receptor subtypes for antagonism of endothelin-1-induced contraction in human bronchi.
1. Endothelin (ET)-1 has been postulated to be involved in the development of obstructive airway diseases in man. In the present study, we attempted to characterize ET receptor subtypes mediating ET-1-induced contraction in human isolated bronchi. The ET receptor antagonists used in the present study were BQ-123 (ETA receptor-selective), BQ-788 (ETB receptor-selective) and BQ-928 (ETA/ETB dual). Sarafotoxin S6c (S6c) was also used as an ETB receptor-selective agonist. 2. In human bronchi, ET-1 and S6c (10(-12)M to 10(-7) M) produced concentration-dependent contraction with almost equal potency (pD2: 8.88 +/- 0.16 for ET-1 and 9.42 +/- 0.15 for S6c). The contraction induced by S6c was competitively antagonized by BQ-788 alone (1 and 10 microM) with a pKB value of 7.49 +/- 0.21, suggesting that the stimulation of ETB receptors causes a contraction of human bronchi. However, contrary to expectation, the concentration-response curves for ET-1 were not affected by BQ-788. The ET-1- and S6c-induced contractions were not affected by BQ-123 (10 microM). Thus, ET-1-induced contraction of human bronchi is not antagonized by BQ-123 alone or by BQ-788 alone. 3. Combined treatment with 10 microM BQ-123 and 10 microM BQ-788 significantly antagonized the contraction induced by ET-1 with a dose-ratio of 11. BQ-928 also significantly antagonized ET-1-induced contraction with a pKB value of 6.32 +/- 0.24. 4. The specific binding of [125I]-ET-1 to human bronchial membrane preparations was inhibited by BQ-123 (100 pM to 1 microM) by approximately 40%. Combination treatment with BQ-788 (100 pM to 1 microM) completely inhibited the BQ-123-resistant component of [125I]-ET-1 specific binding. 5. In conclusion, the present study demonstrates that BQ-788 alone cannot inhibit ET-1-induced contractions in human bronchi, although human bronchial ETB receptors are BQ-788-sensitive. Furthermore, it was shown that blockade of both receptor subtypes antagonizes ET-1-induced contraction, and that both receptor subtypes co-exist in human bronchial smooth muscles. These findings suggest that ETA receptors as well as ETB receptors are involved in ET-1-induced contraction in human bronchi. If ET-1 is involved in human airway diseases, dual blockade of ETA and ETB receptors may be necessary to treat the diseases.
Fukuroda
T
T
Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd, Ibaraki, Japan.
Ozaki
S
S
Ihara
M
M
Ishikawa
K
K
Yano
M
M
Miyauchi
T
T
Ishikawa
S
S
Onizuka
M
M
Goto
K
K
Nishikibe
M
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001980:Bronchi / Q000187:drug effects* / Q000378:metabolism; D016084:Bronchoconstriction / Q000187:drug effects*; D016232:Endothelins / Q000378:metabolism / Q000494:pharmacology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000378:metabolism / Q000494:pharmacology; D010880:Piperidines / Q000378:metabolism / Q000494:pharmacology; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin / Q000187:drug effects*
D016232:Endothelins; D009842:Oligopeptides; D010456:Peptides, Cyclic; D010880:Piperidines; D044022:Receptor, Endothelin A; D044023:Receptor, Endothelin B; D017466:Receptors, Endothelin; C086539:BQ 788; C072247:cyclo(Trp-Asp-Pro-Val-Leu)