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 [H-3]leucine into the protein pool in the heart of consci ous rabbits. At 2 h after ischemic preconditioning (PC) with six 4-min occl usion/4-min reperfusion (O/R) cycles (group II), the [H-3]leucine content i n 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 stunni ng 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. Ingroup VI, pretreatment with CH. 24 h before th e 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 ascri bed to delayed toxicity of CH. Taken together, these results demonstrate th at, in the conscious rabbit, ischemic PC causes a rapid increase in myocard ial protein synthesis and that this increased protein synthesis (or at leas t a fraction of it) is necessary for the development of the protection agai nst myocardial stunning 24 h later. The late phase of ischemic PC is theref ore dependent on the formation of new proteins in intact animals.