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

Abstract

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 1a concentrations in the aqueous humor were quantified by radioimmunoassay. The capacity of ICB tissue homogenates to generate eicosanoids from exogenously supplied [1- 14 C]-arachidonic acid was assessed radiometrically by HPLC. Paracentesis resulted in a rapid and dramatic increase in aqueous humor PGE 2 concentrations. Within 10 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 PGE 2 and protein levels gradually declined to near baseline levels 48 hours after trauma. ICB homogenates from naive animals produced significant amounts of eicosanoids (total PG=2.95 nmol/10 min/100 mg tissue). HHT (12 hydroxy-heptadecatrienoic acid) was produced in the greatest quantity, followed by PGE 2 , PGI 2 , and TXB 2 /PGF 2a. Notably, following paracentesis, eicosanoid synthesis by the isolated ICB was observed to diminish abruptly. Formation of all eicosanoids was uniformly reduced by ˜ 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 ICB PG synthetic activity that may impact on the selection of an optimal dosing paradigm for efficacy testing of topically administered NSAIDs.