The endothelin receptors in rabbit isolated rings of saphenous artery and saphenous vein have been characterized using endothelin-1, endothelin-2, endothelin-3, sarafotoxin S6c, and BQ123. Although artery rings were more sensitive than those from vein to the contractile action of phenylephrine, endothelin-1 was about three times more potent as a contractile agonist on vein than on artery. In rings precontracted with phenylephrine, carbachol was 10 times more potent in vein than in artery rings to induce endothelium-dependent relaxation. However, in rings precontracted to a similar tone by endothelin-1, the relaxation elicited by carbachol was reduced in the vein but remained unchanged in the artery. In endothelium-denuded saphenous artery, endothelin-1 and endothelin-2 elicited contraction with equal potency, whereas endothelin-3 and sarafotoxin S6c were weak agonists. In saphenous vein, the rank order of sensitivity was sarafotoxin S6c > endothelin-2 > or = endothelin-1 = endothelin-3, whereas sarafotoxin S6c and, to a lesser extent, endothelin-3 act as partial agonists. The ETA receptor antagonist BQ123 shifted, to the right, the concentration-response curves of endothelin-1 on endothelium-denuded saphenous artery (pA2 = 7.25). In the endothelium-denuded saphenous vein, 10 microM BQ123 shifted to the right only the response to high concentrations of endothelin-1. In vein but not in artery, endothelin-1 and sarafotoxin S6c induced an endothelium-dependent relaxation, which was increased, in the case of endothelin-1, in the presence of BQ123.2+.