Occlusion of the circumflex coronary artery induced a profound redistribution in ischemic rabbit myocardium of several lysosomal acid hydrolases, including cathepsin D, B-acetylglucosaminidase, and acid phosphatase. 30-45 min after ligation non-sedimentable cathepsin D activity rose from 36% of the total activity to 42-48% and in immunohistochemical preparations cathepsin D appeared to have diffused from lysosomes into the cytosol of injured cells. A pharmacologic dose of methylprednisolone (50 mg/kg) significantly delayed the subcellular redistribution of cathepsin D and the other hydrolases in ischemic heart. Thus, in treated hearts the nonsedimentable activity of cathepsin D rose to only 38% after 30 min of ischemia and 42% after 45 min (P<0.05 compared to untreated ischemia at each time). Similarly, unlike untreated hearts, no evidence of enzyme diffusion from lysosomes could be demonstrated immunohistochemically in corticosteroid-treated ischemic hearts for over 45 min. After 1-2 h of ischemia, however, steroid-protected myocytes deteriorated and the biochemical activity and anatomical distribution of cathepsin D were indistinguishable from untreated ischemic hearts. This study demonstrates that corticosteroid pretreatment does not prevent alterations in cardiac lysosomes during severe ischemia indefinitely, but does delay their development significantly.
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