Edema and cell infiltration in the phorbol ester-treated mouse ear are temporally separate and can be differentially modulated by pharmacologic agents

The temporal patterns of edema and accumulation of the PMN marker enzyme, myeloperoxidase (MPO), were examined following application of tetradecanoylphorbol acetate (TPA) to mouse ears. After application of 2.5 g TPA, edema peaked at 6 hr, while MPO activity peaked at 24 hr. Pharmacological agents with defined mechanisms of action, delivered orally or topically, were assessed for effects on these responses. For oral administration, compounds were delivered 1 hr before and 6 hr after TPA and for topical administration compounds were delivered at 15 min and 6 hr after TPA. Topical and oral corticosteroids inhibited both edema and MPO accumulation. Cyclooxygenase and lipoxygenase inhibitors were very effective against MPO accumulation but were either inactive or moderately active vs edema. Anti-histamine/anti-serotonin agents had little effect on edema, but could inhibit or exacerbate MPO accumulation depending on dose and route of administration. Topically applied histamine itself did not effect TPA-induced edema, but markedly suppressed MPO accumulation. Acetone, the vehicle, when topically applied between 0.5 and 2 hr after TPA inhibited MPO accumulation by 60–80%, but had little effect on edema. Acetone applied before 0.5 hr or after 2 hr had no effect on either parameter. These results indicate that in the TPA-induced ear inflammation model the MPO response at 24 hr may be a useful additional indicator of drug activity.