Effect of Endothelin-Converting Enzyme Inhibitors on big Endothelin-1 Induced Contraction in Isolated rat Basilar Artery

Summary.

 Introduction: The aim of this study was to investigate whether blocking functional endothelin-converting enzyme (ECE) activity may offer a new approach to inhibit the development of cerebral vasopasm after subarachnoid hemorrhage (SAH) by preventing transformation of big Endothelin-1 (big ET-1) to vasoactive Endothelin-1 (ET-1).

 Methods: In vitro, the effect of potential ECE inhibitors was determined by measurement of isometric contractions, induced by big ET-1, in isolated rat basilar arteries. Endothelium intact (E+) and de-endothelialized (E−) segments were examined after pre-incubated with the putative ECE inhibitors: Phosphoramidon (10⁻⁴ M), Captopril (10⁻³ M and 10⁻⁴ M) and [²²D-Val] big ET-1 (16–38) (10⁻⁵ M and 10⁻⁶ M).

 Results: Application of 10⁻⁴ M Phosphoramidon resulted in a statistically significant decrease in big ET-1 induced contraction in endothelium intact (E+) and de-endothelialized (E−) segments; 10⁻³ M Captopril in E− segments caused a statistically significant inhibitory effect; 10⁻⁴ M and 10⁻³ M Captopril in E+ segments showed no statistically significant effect; 10⁻⁵ M and 10⁻⁶ M [²²D-Val] big ET-1 (16–38) in E− segments produced no statistically significant effect. The application of 10⁻⁶ M [²²D-Val] big ET-1 (16–38) in E+ segments caused increased contractions as shown by the shift to the left of the concentration-effect curve (CEC).

 Conclusion: The present study indicates the existence of functional ECE activity in rat basilar artery, which is different in the endothelium and the smooth muscle layer. This ECE-activity could be inhibited by Captopril and Phosporamidon, suggesting a potency for prevention and therapy of cerebral vasospasm. However, the structural analogue of big ET-1, [²²D-Val] big ET-1 (16–38), was ineffective in reducing big ET-1 induced vasoconstriction and rather increased contraction in E+ vessels. Therefore further studies of the biochemical nature of the functional relevant cerebrovascular ECE activity are required for better understanding and development of other efficient ECE inhibitors.