Decreased Myocardial Extracellular and Muscle Lipoprotein Lipase Activities in Endotoxin-Treated Rats

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Abstract
These studies were initiated to determine if skeletal muscle lipoprotein lipase (LPL) activities are decreased as is the case in the myocardium following endotoxin and to compare the distribution of LPL activities between intracellular and extracellular compartments of the heart in endotoxemic and normal rats. Rats were sacrificed 7 hr after an intravenous injection of saline (control) or 2 mg Escherichia coli endotoxin per 100 g. LPL activities were measured on homogenates of acetone—ether powders of heart ventricles, epididymal fat pads, and selected skeletal muscles including diaphragm, red gastrocnemius, white gastrocnemius, and soleus. The myocardium from endotoxin-treated rats contained 22% of the LPL activity measured in saline-treated rats. Likewise, red gastrocnemius, soleus and diaphragm muscles from endotoxemic rats had significantly less (P < 0.05) enzyme activity than was present in normal rats (42, 57, and 41% of control activity, respectively). Hearts from endotoxin- and saline-treated rats were perfused for 1 min with Krebs-Ringer bicarbonate buffer, pH 7.4, containing 1% BSA and 5 U heparin/ml to release extracellular LPL activity. Endotoxin administration resulted in significantly lower enzyme activities in both intra- and extracellular compartments, but the latter was decreased to a greater extent, being 7% of the corresponding control value. These results indicate that depressed LPL activity following endotoxin injection is widespread among tissues and suggest that the reduction may be most pronounced in the extracellular compartment. The findings support earlier studies implicating impaired triacylglycerol removal as a contributing factor in hypertriacylglycerolemia associated with endotoxicosis.