Prolonged corticosteroid treatment exerts transient inhibitory effect on prostaglandin E₂ release from rabbits' eyes

In humans, the retina and choroid (the photoreceptor and its vascular layers, respectively), are affected by an immunogenic inflammatory reaction - uveitis, associated with excessive levels of prostaglandin E₂ (PGE₂), and treated for prolonged periods with corticosteroids, known for their inhibitory effect on prostaglandins (PGs) production. In order to assess whether this drug retains its inhibitory effect during chronic use, we investigated the effect of long-term systemic administration of corticosteroids on PGE₂ release by the choroid and retina of rabbits' eyes. We used eyes traumatized by laser irradiation, in which the inflammatory reaction is associated with an enhanced PGE₂ in vitro release by the choroid-retina throughout a 2-week period; levels peaked on days 1 and 7 to values 2.2- and 5.5-fold, respectively, greater than baseline. Systemic corticosteroid administration to laser-exposed rabbits curtailed the excessive PGE₂ release during the first post-laser week; later the amounts released progressively increased to levels 5.5-fold higher than baseline (day 14), whereas in the corresponding untreated laser group, levels were significantly lower. PGE₂ tissue content on days 7 and 14 in steroid-treated and untreated laser groups were similarly elevated. We conclude that during prolonged systemic corticosteroids treatment the steroidal inhibitory effect on enhanced PGE₂ formation by the retina-choroid of laser injured eyes is transient; it is evident during the early phase following drug administration, whereas later excessive PGE₂ release is resumed.