Transient loss of prostaglandin synthetic capacity in rabbit iris-ciliary body following anterior chamber paracentesis

The trauma-induced acute ocular inflammatory response has been characterized by investigating the kinetics of blood-aqueous barrier (BAB) breakdown, prostaglandin (PG) accumulation in the aqueous humor, and cyclooxygenase (PGH synthase) activity of the iris-ciliary body (ICB) following paracentesis in the NZA rabbit. BAB breakdown was assessed by quantifying plasma protein extravasation into the anterior chamber. PGE(2) and 6-keto-PGF(1 alpha) concentrations in the aqueous humor were quantified by radioimmunoassay. The capacity of ICE tissue homogenates to generate eicosanoids from exogenously supplied [I-C-14]-arachidonic acid was assessed radiometrically by HPLC. Paracentesis resulted in a rapid and dramatic increase in aqueous humor PGE(2) concentrations, Within Io minutes, PGE(2) concentrations increased 937-fold, from 6.2+/-4.9 pg/ml to maximal concentrations of 5810+/-3829 pg/ml. PG synthesis was followed temporally by an increase in aqueous humor protein, with peak levels (53.1 mg/ml) achieved within 30 minutes post paracentesis. Both PGE2 and protein levels gradually declined to near baseline levels 48 hours after trauma. ICE homogenates from naive animals produced significant amounts of eicosanoids (total PG=2.95 nmol/10 min/100 mg tissue). HHT (Iz hydroxy-heptadecatrienoic acid) was produced in the greatest quantity, followed by PGE(2), PGI(2), and TXB2/PGF(2 alpha). Notably, following paracentesis, eicosanoid synthesis by the isolated ICE was observed to diminish abruptly. Formation of all eicosanoids was uniformly reduced by approximate to 40% five minutes following paracentesis, with an 81% decrease in synthetic activity at 15 minutes. Eicosanoid synthetic capacity was only restored to baseline 48 hours post paracentesis, These findings suggest that, following ocular trauma, temporal changes occur in ICE PG synthetic activity that may impact on the selection of an optimal dosing paradigm for efficacy testing of topically administered NSAIDs.