SODIUM ORTHOVANADATE INCREASES PHOSPHOLIPASE A(2) ACTIVITY IN ISOLATED RAT FAT PADS - A ROLE OF PHOSPHOLIPASE A(2) IN THE VANADATE-STIMULATED RELEASE OF LIPOPROTEIN-LIPASE ACTIVITY

Phospholipase (PL) A(2) activity prepared from isolated rat fat pads i ncubated with sodium orthovanadate (vanadate) was increased in a time- and dose-dependent manner. The increasing effect of vanadate was redu ced in the presence of tyrosine kinase inhibitors. Under the inhibitio n of protein synthesis by cycloheximide, vanadate still showed a full effect on the increase in PL A(2) activity. Various PL A(2) inhibitors , such as manoalide, quinacrine and p-bromophenacyl bromide, suppresse d the stimulatory release of lipoprotein lipase (LPL) activity from th e fat pads by vanadate. Moreover, the vanadate-stimulated release of L PL activity was decreased by the cyclooxygenase and thromboxane synthe tase inhibitors, and a thromboxane A(2) receptor antagonist, but was n ever suppressed by a lipoxygenase inhibitor. The stimulatory release o f LPL activity by vanadate was also decreased in the presence of tyros ine kinase inhibitors. These results suggest that vanadate increases P L A(2) activity, and the increase in PL A(2) activity is partly involv ed in the vanadate-stimulated release of LPL activity with an associat ion to the membrane tyrosine kinase.