FROZEN STORAGE OF OVINE AND RAT-TISSUES ADVERSELY AFFECTS LIPOPROTEIN-LIPASE ACTIVITY

The purpose of this study was to determine effects of frozen storage ( frozen in liquid N, stored for 6 weeks at -80 degrees C) of ovine adip ose, and skeletal and cardiac muscle tissues on dietary induced change s in total (intra- and extracellular) lipoprotein lipase (LPL) activit y previously determined in fresh tissue. Ewes were grown on either a l ow- (LE) or high-energy (HE) diet for 120 days (six per diet). In fres h tissue of HE ewes, LPL activity was higher (P < 0.05) for adipose ti ssue, and lower (P < 0.05) for skeletal and cardiac muscles than fresh tissues of LE ewes. Frozen storage altered these dietary effects and decreased (P < 0.01) LPL activity in adipose and cardiac tissues; trea tment differences were maintained in skeletal muscle, and LPL activity was similar for fresh and frozen skeletal muscle of LE ewes. In subse quent experiments, ovine adipose and cardiac tissues were subjected to frozen storage and LPL activity assayed with either a protease inhibi tor (aprotinin, 2 mu g/mL), or with 1 mM/L EGTA and without Ca2+ in th e medium. Either treatment inhibited loss of LPL activity in frozen ti ssues. Frozen storage of hearts from five male, Sprague-Dawley rats de creased (P < 0.01) LPL activity; no decrease in activity was observed when protease inhibitor was used. However, it is not certain whether i nclusion of protease inhibitor and (or) elimination of Ca2+ in frozen- thawed tissue prevents loss of effects on LPL activity that would be o bserved in fresh tissue in response to dietary changes or other physio logical perturbations. In conclusion, frozen storage causes loss of LP L activity in ovine and rat tissues. Thus, frozen storage of tissue ma y be inappropriate when subsequent analysis of LPL activity is of inte rest. (C) Elsevier Science Inc. 1996