Evidence for the use of a pool of the free arachidonic acid in rat cerebral cortex tissue for prostaglandin F2alpha synthesis in vitro.

To determine if the arachidonic acid which is released post-mortem in rat cerebral cortex is directly available for the in vitro synthesis of prostaglandin F2 alpha, cerebral cortex slices or homogenates were incubated in the presence of [2H8]arachidonic acid. The deuterium to protium ratios in the prostaglandin F2 alpha were compared to those in the free arachidonic acid and other lipids of the tissue after 5 and 60 min of incubation. In the slice, the prostaglandin F2 alpha reached maximum labelling before any of the lipids examined except for a pool of rapidly labelled free arachidonic acid located at the damaged surfaces of the tissue. The prostaglandin F2 alpha recovered in the medium after 60 min of incubation had a deuterium to protium ratio twice that of the prostaglandin F2 alpha found in the tissue. Norepinephrine doubled the labelling of the prostaglandin produced by the slice. The labelling of the prostaglandin F2 alpha in homogenates was 10 times higher than in tissue slices and the deuterium to protium ratio of the total free arachidonic acid was similar to that of prostaglandin F2 alpha. The results indicate that exogenous and endogenous arachidonic acid do not mix appreciably in the intact slice and that the prostaglandin synthetase is present on the damaged surface as well as the intact interior of the slice.