Thromboxane increase in irradiated animals is caused by stimulation of cyclooxygenase activity

The irradiation of whole body of rabbits with a dose <»l' 6.0 Gy causes an increase in thromboxane synthesis from exogenous arachidonic acid. The uptake of |l4C]arachidonic acid and the total amount of radioac- tivity released during collagen stimulated aggregation of platelets are not changed following the exposure of animals. The irradiation changes the relation between released arachidonic acid and synthesized throm­boxane. 1'he amount of 12-hydroxyeicosatetraenoic acid remains un­changed. The results indicate that the increase in thromboxane synthesis is not associated with the activation of phospholipase but is caused by stimulation of cyclooxygenase activity.