Induced Biosynthesis of Cutaneous Prostaglandins by Ionizing Irradiation 1

Abstract

Abstract

This study has demonstrated that exposure of white domestic pig skin to a single treatment of X-ray irradiation (300-1000 rad) results in a rapid release of epidermal arachidonic acid followed by its transformation via the cyclooxygenase pathway into prostaglandin E₂ (PGE₂). Beyond 24 hr the epidermal PGE₂ decreased steadily. The time-dependent biosynthesis of epidermal PGE₂ can be blocked by the immediate topical application of 2.5% indomethacin in ethanol to the irradiated skin area. In order to seek an explanation for the progressive decrease of epidermal PGE₂ beyond 24 hr we assayed for the activity of the NADPH-dependent PGE₂-9-ketoreductase (an enzyme which catalyzes the transformation of PGE₂ into PGF_2α in the 105,000g supernatant fractions prepared from the irradiated and nonirradiated epidermal specimens. Our data revealed that the activity of this interconverting enzyme increased steadily beyond 24 hr. These results indicate that PGE₂ formed as a result of exposure of skin to X-rays is metabolized into PGF_2α. The biological significance of this interconversion and the role of PGF_2a in X-ray-induced injury to the skin remains to be determined.