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.
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