Heterogeneity of endothelin ETA receptor-mediated contractions in the rabbit saphenous vein.

The involvement of endothelin ETA receptors in endothelin-1-induced contractions of the rabbit saphenous vein was studied. After desensitization of endothelin ETB receptors by pretreatment with sarafotoxin S6c, endothelin-1 and sarafotoxin S6b and a high concentration of endothelin-3 caused dose-dependent contractions. However, endothelin-1-induced contractions were much less sensitive to an endothelin ETA receptor antagonist, BQ-123 (cyclo (-D-Asp-L-Pro-D-Val-L-Leu-D-Trp-)), than sarafotoxin S6b-induced responses. The pA2 values of BQ-123 for endothelin-1- and sarafotoxin S6b-induced contractions were 5.69 and 7.65, respectively. These results suggest pharmacological heterogeneity of endothelin ETA receptors in the rabbit saphenous vein.