BQ-123 is primarily used in research settings to study the endothelin system, which plays a critical role in regulating blood pressure and vascular function. It is a selective endothelin A (ETA) receptor antagonist, making it valuable for investigating conditions like hypertension, pulmonary arterial hypertension, and heart failure. By blocking ETA receptors, it helps researchers understand the mechanisms of vasoconstriction and vascular remodeling. Additionally, BQ-123 is utilized in preclinical studies to explore its potential therapeutic effects in diseases involving abnormal endothelin signaling. Its application is crucial for developing targeted treatments for cardiovascular and pulmonary disorders.