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 incubated with sodium orthovanadate (vanadate) was increased in a time- and dose-dependent manner. The increasing effect of vanadate was reduced in the presence of tyrosine kinase inhibitors. Under the inhibition 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, suppressed the stimulatory release of lipoprotein lipase (LPL) activity from the fat pads by vanadate. Moreover, the vanadate-stimulated release of LPL activity was decreased by the cyclooxygenase and thromboxane synthetase inhibitors, and a thromboxane A(2) receptor antagonist, but was never suppressed by a lipoxygenase inhibitor. The stimulatory release of LPL activity by vanadate was also decreased in the presence of tyrosine kinase inhibitors. These results suggest that vanadate increases PL A(2) activity, and the increase in PL A(2) activity is partly involved in the vanadate-stimulated release of LPL activity with an association to the membrane tyrosine kinase.