Functional evidence for the presence of a phosphoramidon-sensitive enzyme in rat brain that converts big endothelin-1 to endothelin-1.

Abstract Endothelin-1 (ET-1) is produced from its precursor, big endothelin-1 (BigET-1), by a putative endothelin-converting enzyme (ECE), but it is not known whether the nzyme is present in the brain. This study was conducted to examine the central hemodynamic effects of BigET-1 and to indirectly determine the presence of an ECE in rat brain. Cardiovascular efffects of centrally administered BigET-1 and ET-1 were examined in anesthetized, ventilated rats. BigET-1 (100 pmol) or ET-1 (10 pmol) applied to the IV ventricle produced similar prolonged decreases in mean arterial pressure (MAP) and renal blood flow (RBF). Thus, peak decreases with BigET-1 were (mean ± S.E.): MAP=−35 ± 4%; RBF=−27 ± 5%, while those with ET-1 were: MAP=−36 ± 5%; RBF=−29 ± 9%. Pretreatment with phosphoramidon, a metalloprotease inhibitor (90 nmol), abolished the hemodynamic responses elicited by BigET-1 (MAP=−9 ± 2%; RBF=−3 ±2%) but not those produced by ET-1. These data indicate that: i) conversion of BigET-1 to ET-1 in the brain is essential for the expression of hemodynamic actions and ii) a metalloprotease capable of converting BigET-1 to ET-1 is present in rat brain.