Dual action of prostaglandin E2 in allergic inflammation.

The findings reported here demonstrate that PGE2 can exert both anti- and pro-inflammatory activities in one and the same tissue, as exemplified by inhibition of mediator release and enhancement of mediator action. Furthermore, the complete reversal of indomethacin potentiation of allergic inflammation by addition of PGE2 in low concentration advocates a regulatory function of the endogenous and locally formed PGE2. In the present in vivo model for mast cell-dependent inflammation the influence of PGE2 was mainly on the release of mediators. However, factors such as the degree of local blood flow, or the state of the tissue and the site of prostaglandin production, may in other instances shift the Yin-Yang balance in favour of PGE2 action at the target level for released mediators. Finally, it was noted that the cheek pouch mast cells, in addition to their pivotal role in the initiation of inflammatory reactions, have a predominant periarteriolar distribution that promotes oriented and, in terms of covered area, efficient migration of recruited leukocytes. Whether this previously unrecognized organization is specific for the hamster cheek pouch or exemplifies a more general phenomenon is presently not known.