ANTAGONIST ACTIVITY OF [THR(18),GAMMA-METHYLLEUCINE(19)]ENDOTHELIN-1 IN HUMAN ENDOTHELIN RECEPTORS

Receptor binding and antagonist properties of endothelin-1 analogues, [Thr(18),gamma-methylleucine(19)]endothelin-1, [Thr(18),Leu(19)]endoth elin-1 and [Thr(18),cyclohexylalanine(19)]endothelin-1, were investiga ted using cloned human endothelin ETA and ETB receptors expressed in C hinese hamster ovary cells. Among them, [Thr(18),gamma-methylleucine(1 9)]endothelin-1 had a high affinity for endothelin ETA and ETB recepto rs with respective K-d values of 300 and 110 pM and had no agonist act ivity on the stimulation of arachidonic acid release in endothelin ETA and ETB receptor-expressing cells. [Thr(18),gamma-methylleucine(19)]E ndothelin-1 had potent antagonist activity in endothelin-1-induced ara chidonic acid release in endothelin ETA and ETB receptor-expressing ce lls with respective pA(2) values of 8.2 and 8.5. In an inositol phosph ate accumulation assay, [Thr(18),gamma-methylleucine(19)]endothelin-1 also exhibited potent antagonist activity for endothelin ETA and ETB r eceptors with respective pA(2) values of 8.0 and 8.4. In conclusion, [ Thr(18),gamma-methylleucine(19)]endothelin-1 acts as a potent and nons elective antagonist with no agonist activity for cloned human endothel in ETA and ETB receptors.