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Increased protein synthesis is necessary for the development of late preconditioning against myocardial stunning.

In phase I of this study, the rate of protein synthesis was measured by the incorporation of [3H]leucine into the protein pool in the heart of conscious rabbits. At 2 h after ischemic preconditioning (PC) with six 4-min occlusion/4-min reperfusion (O/R) cycles ( group II), the [3H]leucine content in the ischemic-reperfused region was increased by 82% compared with that in controls ( group I), indicating increased protein synthesis. This increase was completely abrogated by pretreatment with cycloheximide (CH; group III). In phase II, rabbits underwent six O/R cycles for three consecutive days ( days 1-3). Controls ( group IV) exhibited late PC against myocardial stunning on days 2 and 3. In group V, which received CH 30 min before the 1st O/R cycle on day 1 (same dose as group III), late PC against stunning on day 2 was completely abrogated. In group VI, pretreatment with CH 24 h before the 1st sequence of O/R cycles had no effect on myocardial stunning on day 1, indicating that the absence of late PC on day 2 in group V cannot be ascribed to delayed toxicity of CH. Taken together, these results demonstrate that, in the conscious rabbit, ischemic PC causes a rapid increase in myocardial protein synthesis and that this increased protein synthesis (or at least a fraction of it) is necessary for the development of the protection against myocardial stunning 24 h later. The late phase of ischemic PC is therefore dependent on the formation of new proteins in intact animals.