title: Myocardial infarct size-Limiting effect of ischemic preconditioning: Its natural decay and the effect of repetitive preconditioning.
abstract: To characterize the cardioprotective effect of ischemic preconditioning, its natural decay and the effect of repetitive preconditioning were studied in the rabbit. Control rabbits underwent simple 30-minute coronary occlusion and 72 h reperfusion. In four groups, hearts were preconditioned with 5 minutes of ischemia and then allowed to "recover" for 5, 15, 25, or 35 minutes prior to the 30-minute coronary occlusion. In another two groups of rabbits, the preconditioning (PC) was performed by two or four cycles of 5 minutes ischemia separated by 5 minutes reperfusion. Infarct size was 43.9% ± 5.0% of area at risk in control rabbits. With recovery periods of 5 and 15 minutes, PC limited infarct size to 20.7% ± 2.9% and 26.7% ± 4.3% of the area at risk, respectively. As the recovery period increased, the infarct sizes progressively approached the control value, though PC still tended to be beneficial with a recovery time of 35 minutes. After two or four repetitions of 5-minute PC, infarct size was 16.4% ± 4.2% and 13.7% ± 2.6% of the area at risk, respectively, which were not significantly different from that after a single 5-minute PC (20.7% ± 2.9%). In another series of experiments, alteration of regional systolic thickening fraction (TF) after PC was assessed by an epicardial Doppler probe. Post-PC recovery of TF was 64.9% ± 8.9% of baseline value at 5 minutes and 73.2 ± 7.2% at 35 minutes after reperfusion, showing the persistence of modest stunning. These results suggest that in the rabbit heart, 5 minutes ischemia affords the myocardium a marked resistance against ischemic necrosis and that this resistance, which is unrelated to myocardial stunning, decays over a period of 30 minutes. Furthermore, the data imply that the resistance to ischemic injury is almost maximally induced by a single episode of 5 minutes ischemia and is not markedly enhanced by its repetition.
authors.affiliation: From the Second Department of Internal Medicine, Sapporo Medical College, Sapporo, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Miura
authors.forename: T
authors.initials: T
authors.lastname: Adachi
authors.forename: T
authors.initials: T
authors.lastname: Ogawa
authors.forename: T
authors.initials: T
authors.lastname: Iwamoto
authors.forename: A
authors.initials: A
authors.lastname: Tsuchida
authors.forename: O
authors.initials: O
authors.lastname: Iimur