Release of different prostaglandins from vascular tissue by different stimulators

The prelabelling technique (incorporation of (1-14C)-arachidonic acid) was used to investigate the influence of bradykinin, the divalent cation ionophore A 23187, acetylcholine and phospholipase A2 (PLA2) on release and metabolism of arachidonic acid (AA) in peripheral vessels. Bradykinin stimulated the release of PGI2 and PGE2, both to the same extent. The main metabolite released by A 23187 was PGE2 which far exceeded the release of PGI2. PGD2 was released to the same degree as PGI2. Stimulation by acetylcholine released mainly PGI2. In contrast, the main metabolite of AA released by PLA2 was PGE2. Although the substances used were injected i.a. into the same tissue (isolated perfused rabbit ear) they produced a different pattern of PG release. The underlying reason may be different "microkinetics" of the substances due to a different lipophilia or different resistance to metabolizing enzymes. Thus, several cell types may have been reached which have different components of the various enzymes of the PG biosynthesis system.