| Cys–Val–Tyr–Phe–Cys–His–Leu–Asp–Ile–Ile–Trp, CVYFCHLDIIW, With a disulfide bridge between Cys¹ and Cys⁵, forming a constrained ring structure. IRL 1038 is an antagonist of the ETB receptor that is responsible for the release of relaxing factor from the vascular endothelium.
IRL-1038 acts as a selective ETB receptor antagonist: At 3 µM concentration, it inhibits ETB receptor–mediated contractions in guinea pig ileal and tracheal smooth muscle without exhibiting agonistic activity. Notably, it has no effect on ETA receptor–mediated contractions in rat aortic smooth muscle, indicating receptor subtype specificity. IRL-1038 serves as a valuable tool for investigating ETB receptor signaling and its role in vascular contractility and endothelial function. As an ETB antagonist, it opens avenues for therapies targeting conditions such as hypertension, vasoconstrictive disorders, or pulmonary hypertension, where modulation of ETB activity is therapeutically relevant.
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