Role of Endothelin-A (ETA) and Endothelin-B (ETB) Receptors in the Vasodilatory Response to Endothelin-3 (ET-3)
Status:
Completed
Trial end date:
2010-01-01
Target enrollment:
Participant gender:
Summary
Endothelin-1 (ET-1) has been linked to a number of conditions including pulmonary arterial
hypertension (PAH). ET-1 acts via 2 receptors, ETA and ETB. The ET-1 receptor blockers
bosentan and sitaxsentan have been shown to be beneficial in patients with PAH. Bosentan
blocks both ETA and ETB receptors. Sitaxsentan selectively blocks ETA receptors.
Theoretically, selective ETA blockade may be associated with greater vasodilation and
clearance of ET-1 by leaving the ETB receptor unblocked. This has not been directly studied
in humans.
We aim to investigate the endothelial ETB-mediated vascular responses between bosentan and
sitaxsentan by using a ETB selective agonist (ET-3). We hypothesise that at clinically
relevant doses:
- Bosentan will show evidence of ETB receptor blockade compared to sitaxsentan and
placebo.
- These effects will be confirmed by 2 functional markers of ETB receptor antagonism:
plasma ET-1 (a very sensitive, but not necessarily clinically relevant marker), and the
forearm vasodilator response to ET-3.