Abstract
Human and porcine big ET-1 and big ET-2 are similarly potent in contracting parenchymal strips of the guinea-pig lung while big ET-3 is inactive,suggesting that the endothelin-converting enzyme (ECE) which converts big ET-3 is not present and that at least two distinct ECE activities exist, one selective for big ET-1 and big ET-2 and one for big ET-3. Metalloendoprotease inhibitors (phosphoramidon and DL-thiorphan), but not captopril, inhibited the contractions elicited by human big ET-1 and big ET-2 but DL-thiorphan was less active, suggesting that a non-selective enzymatic process is involved in conversion of big ET-1 and big ET-2 in addition to a phosphoramidon-sensitive ECE. Big ET-1 and big ET-2 induced much higher contractions than their corresponding mature peptides. Both metalloendoprotease inhibitors, but not captopril, similarly potentiated contractions induced by ET-1, ET-2 or ET-3 to the level of those evoked by big ET-1 and big ET-2, indicating that only mature ET isopeptides and not their precursors are suceptible to degradation by metalloendoproteases.
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