Release of prostaglandins E and F in an algogenic reaction and its inhibition

E and F prostaglandins were measured by radioimmunoassay in the peritoneal fluid of rats which had been injected with an irritant, acetic acid. The considerable increase recorded 5 min after the injection virtually disappeared in 90 min. For the first 15 min the PGE2 level was twice that of PGF2 alpha, the levels then equalized and after 90 min the PGE2 level was less than that of PGF2 alpha. This balance between PGEs, which are hyperalgesic, and PGF2 alpha, which has often been shown to be a PGE antagonist, could regulate defence mechanisms. An examination of cells collected by washing the peritoneum revealed a large decrease between 15 and 30 min after injection of the irritant and suggested that the prostaglandins could be produced by neutrophil polynuclear cells but also by destruction of macrophages. Various types of prostaglandin biosynthesis inhibitors (non-steroid anti-inflammatory agents, non-narcotic analgesics and some monoamino-oxidase inhibitors and antioxidants) prevented prostaglandin release. Their activity on release paralleled their activity on acetic acid-induced writhing.