Pharmacologic profile of endothelinA/B antagonist, [Thr18, gamma methyl Leu19]endothelin-1

The pharmacologic profile of [Thr18,gamma methyl Leu19]endothelin-1 (TM ET-1) was investigated in several in vitro and in vivo studies. We found that TM ET-1 inhibited 125I-ET-1 binding in porcine cardiac membrane (ETA receptor) and in bovine brain membrane (ETB receptor), with IC50 values of 0.7 and 0.25 nM, respectively. These values were almost comparable to those for ET-1. TM ET-1 had no effect on intracellular Ca2+ concentration ([Ca]i) in A10 cells mediated by ETA receptors, even at 10(-5) M, or in mouse peritoneal macrophages (MPMs) mediated by ETB receptors, even at 10(-6) M. Increases in [CA]i in A10 cells by ET-1 and in MPMs by ET-3 were completely blocked by pretreatment with 10(-7) M of TM ET-1. In porcine right coronary arteries (PCAs) and in great cardiac veins (PCVs), TM ET-1 caused no contraction at concentrations < or = 10(-6) and 10(-7) M, respectively, although it competitively inhibited ET-1-induced contraction of PCAs and Ala1,3,11,15-ET-1-induced constriction of PCVs with pA2 values of 7.0 and 9.2, respectively. Furthermore, TM ET-1 was more potent than BQ123, an ETA-specific antagonist, in inhibiting the rise in perfusion pressure in a hind-limb preparation in vitro and the increase in blood pressure in rats. These results suggest that TM ET-1 is a potent ETA and ETB antagonist without agonistic effects and can be used in future studies to help clarify the physiological role of ET.