Irradiation decreases vascular prostacyclin formation with no concomitant effect on platelet thromboxane production.

Effects of irradiation on vascular tissue include endothelial cell degeneration, vasoconstriction, and thrombus formation. The effect of irradiation on the in-vitro production of prostacyclin (PGI2) was evaluated, since it is a potent antithrombotic metabolite and vasodilator. After a single dose of 200 rad, umbilical artery PGI2 levels were much decreased when estimated both be bioassay and by evaluation of the stable end-product of PGI2, 6-keto-prostaglandin in Fl alpha. The mean PGI2 production in control tissue was 0.94 +/- 0.14 (1SEM) ng/mg vascular tissue compared with 0.18 +/- 0.07 ng/mg in paired irradiated vessels (p less than 0.001). However, irradiation had no effect on platelet thromboxane formation in a dose rage of 200-2000 rad. Since radiotherapy is routinely administered for the whole period of therapy in daily dose fractions similar to the in-vitro experimental dose used in this study, recovery of vascular PGI2 production may be inhibited for the total period of radiotherapy.