Endothelin Receptor Subtypes in Human and Guinea-pig Pulmonary Tissues

1. In this study the endothelin (ET) receptor subtypes mediating contractions produced by ET-1 in human and guinea-pig pulmonary tissues were investigated. In addition the receptor responsible for ET-1-induced prostanoid release in human bronchus was determined. 2. In human bronchus and human pulmonary artery ET-1 (0.1 nM-0.3 microM) was a potent and effective contractile agent (pD2 = 7.58 +/- 0.15, n = 6, and 8.48 +/- 0.11, n = 7, respectively). BQ-123 (1-10 microM), a potent and selective ETA receptor antagonist, potently antagonized ET-1-induced contraction in human pulmonary artery (pKB = 6.8 with 1 microM BQ-123, n = 7) but had no effect in human bronchus (n = 6). 3. Sarafotoxin S6c (0.1 nM-0.1 microM), the ETB-selective agonist, did not contract human pulmonary artery (n = 5), but potently and effectively contracted human bronchus: pD2 = 8.41 +/- 0.17, maximum response = 74.4 +/- 3.1% of 10 microM carbachol; n = 5. BQ-123 (1-10 microM) did not antagonize sarafotoxin S6c-induced contraction in human bronchus (n = 5). 4. ET-1 potently contracted guinea-pig trachea, bronchus, pulmonary artery and aorta (pD2 = 8.15 +/- 0.14, 7.72 +/- 0.12, 8.52 +/- 0.12, and 8.18 +/- 0.12, respectively, n = 6-14). BQ-123 (0.1-10 microM)antagonized ET-1-induced contractions in guinea-pig pulmonary artery (pKB = 6.7 with 1 microM BQ-123,n = 6), aorta (pKB = 7.1 with 1 microM BQ-123, n = 6) and trachea (pKB = 6.2 with 1 microM BQ-123, n = 6) butwas without marked effect in bronchus (n = 4). In contrast, sarafotoxin S6c (0.1 nM-0.l microM) did not contract guinea-pig aorta (n = 4) or guinea-pig pulmonary artery (n = 6) but potently and effectively contracted guinea-pig bronchus: pD2= 8.55 +/- 0. 1; maximum contraction = 63.6 +/0 3.1% of 10 microM carbachol,n = 4. Sarafotoxin S6c (0.1 nM-0. 1 microM) was a much less effective agonist in guinea-pig trachea:maximum contraction = 13.9 +/- 2.5% of 10 JM carbachol, n = 4; P< 0.0001, compared to bronchus.Contractions produced by sarafotoxin S6c in guinea-pig bronchus or trachea were unaffected by BQ-123(IO microM, n=4).5. Significant differences were observed in the efficacy, relative to carbachol, but not the potency of sarafotoxin S6c in guinea-pig airways, with a much greater maximum contractile response in bronchus(69.6 +/- 2.4% of 10 microM carbachol, n = 6) or lower region of the trachea (48.5 +/- 5.9% of 10 microM carbachol,n = 6) than in the middle region of the trachea (14.4 +/- 4.0% of 10 microM carbachol, n = 6) or the upper region of the trachea (19.3 +/- 2.7% of 10 microM carbachol, n = 6). There were minimal regional differences in either ET-1-induced contraction or the potency of BQ-123 (3 microM) for inhibition of responses to ET-1 in guinea-pig airways.6. Release of various prostanoids in human bronchus induced by ET-1 (0.3 microM) was essentially abolished with 10 IM BQ-123.7. These data provide evidence that distinct ET receptors mediate ET-1-induced contraction in human pulmonary artery, guinea-pig pulmonary artery and guinea-pig aorta (ETA subtype) compared with human bronchus and guinea-pig bronchus (non-ETA, perhaps ETB subtype). Contractions to ET-1 in guinea-pig trachea appear to involve both ETA and non-ETA (ETB?) receptor subtypes. Furthermore,regional differences appear to exist in the relative distribution of ET receptor subtypes in guinea-pig airways. In human bronchus ET-1-induced prostanoid release, unlike the contractile response, appears to be mediated via ETA receptor activation.