Contraction to big endothelin‐1, big endothelin‐2 and big endothelin‐3, and endothelin‐converting enzyme inhibition in human isolated bronchi

All three endothelin precursor peptides, i.e. big endothelin-1 (big ET-1), big endothelin-2 (big ET-2) and big endothelin-3 (big ET-3), produced contractile responses in human isolated bronchi, demonstrating the presence of functional endothelin-converting enzyme (ECE) in this tissue. The maximal contractile responses were equal to 108.4+/-8.0% (0.1 microM big ET-1; n=4), 85.2+/-11.8% (0.1 microM big ET-2; n=7) and 43.0+/-7.2% (0.1 microM big ET-3; n=5) of the reference response to acetylcholine (1 mM). The response to big ET-1 (0.1 microM), but not endothelin-1 (ET-1, 0.1 microM), was diminished after overnight storage of the tissue at 4 degrees C, demonstrating instability of the enzyme. The responses to all three big-endothelins were significantly inhibited, by the ECE inhibitors CGS 26393 and CGS 26303, in a concentration-related manner. The responses to the mature peptides ET-1, endothelin-2 (ET-2), and endothelin-3 (ET-3) were unaffected by CGS 26393 and CGS 26303. Phosphoramidon (10 microM) also produced an inhibition of the response to big ET-1 that was equivalent to that produced by CGS 26393 (10 microM). Combination of CGS 26393 (10 microM) and phosphoramidon (10 microM) did not produce an additive inhibition. These results demonstrate the presence of functional ECE for all three big endothelins in human bronchus and inhibition of the enzyme by newly developed orally active ECE inhibitors, as well as phosphoramidon. British Journal of Pharmacology (2000) 129, 170 - 176