Abstract: Aim To observe the changes of endothelin receptors and their subtypes of left ventricules in normal SD rats and dilated cardiomyopathy rats.Methods To establish the best condi tions of the binding experiment, different protein concent rations, incubation temperature and incubating time were tested with 1 25I-ET-1 ligand respectively.With the selected condi tions, saturation binding experiment s were performed to determine the amount of endothelin receptor and its subtypes in normal SD rats and in dilated cardiomyopathy ones.Results (1) The opt imal incubating temperature was 37 ℃.Under this condition, the binding amount of 1 25 I-ET-1 increased rapidly in 0～30 minutes, and reached to saturation point at 60 minutes, and there was alinear correlation between 1 25I-ET-1 binding amount and cell membrane protein concentration. (2) Endo thelin-1, bosentan, BQ123, BQ788 etc.could competit ively suppress the bound of 1 25 I-ET-1 to endothelin receptors.(3) The amount of endothelin receptor in left vent ricle of dilated cardiomy opathy rats was (92.21±34.34) nmol·kg^-1 protein, which was significantly low than that in normal SD ones.There was no change on the ratio of endothelin receptor subty pes A and B.Conclusion 125I-ET-1 can be used to determine the amount of endo thelin receptor and its subty pes in varied tissues specifically.The amount of endothelin receptor in left ventricle of dilated cardiomyopathy rats is down regulated, but the ratio of endothelin receptor subtype A vs B remains to be 2:1.

Key words: endo thelinre, dilated cardiomyopathy, radioligand binding assay