EDN1 and neoplasm: In our previous studies investigating the blood flow-modifying effects of endothelin receptor ligands, such as ET-1 itself, sarafotoxin and IRL 1620 in the HSN tumour model, IRL 1620 was the most promising for selective reduction in tumour blood flow with minimal effects on systemic blood pressure and blood flow in the majority of normal tissues (Bell et al, 1995, 1999).