AIM: To study dose-effect and time-effect changes of endothelin (ET) in myocardium and plasma during myocardial ischemia and its mechanism. METHODS:After inducing myocardial ischemia of rats in vivo with different dose of pituitrin(Pit) and the optimal dosage in the Pit at different time point, ET concentration in the myocardium and plasma was measured.Moreover, immunohistochemical study and RT-PCR were also applied in this study. RESULTS:ET concentration in myocardium increased gradually with the increase of Pit dose. ET concentration elevated significantly ( P