In addition to its potent vasocontractile effects, endothelin-1 (ET-1) has potent positive inotropic and chronotropic effects on isolated heart muscles in vitro. However, it is not known whether the production of ET-1 in the heart is altered by exercise. In this study we investigated the production of ET-1 in the heart during exercise. Rats performed treadmill running of 45-min duration. Sedentary rats served as controls. Immediately after exercise, the heart was quickly removed. The peptide level of ET-1 in the heart was measured by a sandwich-enzyme immunoassay. The peptide level of ET-1 in the heart was significantly higher in the exercise group than in the control sedentary group. Therefore, we have demonstrated that production of ET-1 in the heart is increased by exercise. The present study suggests that myocardial ET-1 participates in the modulation of cardiac function during exercise.
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