Lysosomal changes in an animal model of myocardial ischemia. Treatment with methylprednisolone

In this work we have employed a new extraction buffer for isolation of cardiac lysosomes from control and ischemia canine tissue. Compared to previous techniques, this buffer (0.6 M KCl, 0.25 M sucrose) enabled a 300% increase in the yield of particulate cardiac lysosomes and allowed acceptable levels of specific activity to be maintained. It also permitted great enrichment of a membrane-bound enzyme localized to a microsomal fraction, rotenone-insensitive NADH-cytochrome c reductase (RINCR). Ischemia was produced by ligation of the left anterior descending coronary artery for 2 hr, and myocardial blood flow (MBF) was measured using 85Sr labeled microspheres (15 microns). Enzymatic changes were measured in endocardial tissue of the ischemic left ventricular wall for comparison with control nonischemic samples. N-Acetyl-beta-glucosaminidase (NAG) was the most reliable lysosomal marker enzyme; this was depleted significantly (P < 0.001) in particulate lysosomal fractions; significant increases in the supernatant (P < 0.001) were found in areas of ischemia that were less than 25% of the control MBF. Lysosomal latency also diminished significantly during ischemia. Loss of total activity of RINCR in the microsomal fraction was highly significant (P < 0.001) in the areas of profound ischemia. The above data were compared with those from animals in which methylprednisolone (30 mg/kg) was administered 30 min prior to ligation of the coronary artery. Between the two groups (untreated versus methylprednisolone-treated animals) no significant differences could be found in total losses of NAG and RINCR or the rate at which these enzymatic changes ocurred. Lysosomal latency studies also revealed lack of significant changes between both groups. Thus, no significant "protective" effects of methylprednisolone could be found after 2 hr of ischemia.