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-l (0.1 nM-0.3 JIM) 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 JiM), a potent and selective ETA receptor antagonist, potently antagonized ET-1-induced contraction in human pulmonary artery (pKB = 6.8 with 1 JIM BQ-123, n = 7) but had no effect in human bronchus (n = 6). 3 Sarafotoxin S6c (0.1 nM-0. IliM), 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 1O JM carbachol; n = 5. BQ-123 (1-1 I1M) 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 (0.1-101M) antagonized ET-1-induced contractions in guinea-pig pulmonary artery (pKB = 6.7 with 1 JIM BQ-123, n = 6), aorta (pKB = 7.1 with 1 JIM BQ-123, n = 6) and trachea (pKB = 6.2 with 1 AIM BQ-123, n = 6) but was without marked effect in bronchus (n = 4). In contrast, sarafotoxin S6c (0.1 nM-0.l JIM) 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 ± 3.1% of 1O JIM carbachol, n = 4. Sarafotoxin S6c (0.1 nM-0. 1 JIM) 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 (IO IM, 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 1O JM carbachol, n = 6) or lower region of the trachea (48.5 ± 5.9% of 1OJIM carbachol, n = 6) than in the middle region of the trachea (14.4 ± 4.0% of 10 JiM carbachol, n = 6) or the upper region of the trachea (19.3 ± 2.7% of 1O JM carbachol, n = 6). There were minimal regional differences in either ET-1-induced contraction or the potency of BQ-123 (3 JIM) 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 JiM) was essentially abolished with 10 IM 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 trache...