Objective. In a model of rat cardiac hypertrophy

the changes in the distribution of ET- 1 receptors in two subcellular fractions

the sarcolemma and the light vesicles during myocardial hypertrophy were studied. Methods. Cardiac hypertrophy was produced by placing a constricting clip around the suprarenal abdominal aorta of rats

and ET- 1 receptor was assayed with radioactive analysis method. Results. It was found that plasma and ventricular ET- 1 levels increased significantly on week 2 and week 4 of pressure overload. ET- 1 binding studies showed that during myocardial hypertrophy

the maximum binding capacity （Bmax） was increased by 41％ （P< 0.01） and 65％ （P< 0.01） in sarcolemma in H- 2 week and H- 4 week groups

but was decreased by 24％ （P< 0.01） and 21％ （P< 0.01） in light vesicles. The sum of Bmax of sarcolemmal and light vesicle fractions was increased by 33％ （P< 0.01） and 57％ （P< 0.01） in group H- 2 week and H- 4 week

respectively. Conclusion. ET- 1 receptors in rat heart were externalized from light vesicles to sarcolemma

which may contribute to the development of myocardial hypertrophy.