抄録
Thapsigargin, a hexaoxygenated tetraacylated sesquiterpene lactone isolated from the roots of Thapsia garganica L., is one of non-TPA type tumor promoters that stimulate prostaglandin E2 production at very low concentrations and induce inflammation when applied topically. Effects of thapsigar-gin on platelet activating factor (PAF) production by rat peritoneal macrophages were examined. Levels of PAF in the conditioned medium and in the cells were determined by radioimmunoassay after extraction of PAF using immunoaffinity mini-columns. It was demonstrated that thapsigargin at concentrations of 3 to 100 ng/ml stimulated production of cell-associated PAF when measured 10 min after incubation. Levels of PAF in the conditioned medium were less than the detectable amount.
The stimulative effect by thapsigargin reached a plateau at a concentration of 30 ng/ml. Time course experiments revealed that the levels of cell-associated PAF showed a peak 10 to 15 min after incubation with thapsigargin at a concentration of 30 ng/ml. The levels were then declined until 40 min after incubation. When macrophages were preincubated for 3 h with dexamethasone at concentra-tions of 0.01, 0.1 and l μg/ml, thapsigargin (30 ng/ ml) -stimulated PAF production in the cells at 10 min were decreased. However, the maximum inhibition was about 50% even at 1μg/ml of dexamethasone. These date suggest that by treatment with thapsigargin, PAF is partly produced through formation of lyso-PAF by activated phospholipase A2 since dexamethasone shows partial inhibition of thapsigargin-induced PAF production, and thap-sigargin-stimulated PAF production may partly account for proinflammatory activity of thapsigar-gin.
