Alternative pathway to endothelin-converting enzyme for the synthesis of endothelin in human blood vessels

We have investigated whether a chymostatin-sensitive Enzyme, such as chymase, contributes to the production of vasoconstrictor endothelin Peptides from exogenous big endothelin- 1 in endothelium-denuded human umbilical vein. Big endothelin-1 contracted veins with a pD2 = 7.75 +/- 0.08 (n = 23) and was five times less potent than endothelin-1 (pD2 = 8.43 +/- 0.11, n = 10). The selective endothelin-converting Enzyme inhibitor, PD159790, (30 microM, n = 17) produced a significant (P < 0.005), threefold rightward shift of the big endothelin-1 concentration-response curve with no reduction in maximum response. A further shift was obtained with 100 microM PD159790 (n = 6), with a significant decrease in the maximum response from 84.0 +/- 5.3%KCl to 34.2 +/- 6.7%KCl (P < 0.005). Chymostatin (30 microM) had no effect on the big endothelin-1 response, however, the inhibitory effect of 100 microM chymostatin was significant (P < 0.005). Unlike PD159790, chymostatin did not significantly modify the maximum response to big endothelin-1. The combination of 30 microM PD159790 and 100 microM chymostatin was more effective than either inhibitor alone. Our data suggest a role for both endothelin-converting Enzyme and a chymostatin-sensitive Enzyme, such as chymase, in the conversion of big endothelin-1 to constrictor endothelin Peptides in human umbilical vein smooth muscle. In cardiovascular diseases in which endothelin-converting Enzyme activity is increased, inhibition of both Enzymes may be required for effective therapeutic intervention.