Sodium Orthovanadate Increases Phospholipase A2 Activity in Isolated Rat Fat Pads: a Role of Phospholipase A2 in the Vanadate-Stimulated Release of Lipoprotein Lipase Activity.

Phospholipase (PL) A2 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 A2 activity. Various PL A2 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 A2 receptor antagonist, but was never suppressed by a lipooxygenase 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 A2 activity, and the increase in PL A2 activity is partly involved in the vanadate-stimulated release of LPL activity with an association to the membrane tyrosine kinase.