The penetration of exogenous prostaglandin and arachidonic acid into, and their distribution within, the mammalian eye

Abstract

The distribution of ³H and ¹⁴C activities in intraocular fluids and tissues was studied after topical application of ³H-prostaglandin F₂α (³H-PGF_2α) and/or ¹⁴C-arachidonic acid (¹⁴C-AA) to rabbit eyes; intravenous (i.v.) infusion of ³H-PGF₂α into rats; and after incubation of rat or rabbit globes in media containing these and other tracers. Thirty min after topical application of ¹⁴C-AA, the order of distribution of ¹⁴C per unit of tissue weight was cornea>>sclera>ciliary body>iris>aqueous>retina-choroid>vitreous>lens. The distribution of ³H was sclera>cornea>retinachoroid>ciliary body>aqueous>vitreous (lens > 0; iris > 0). After i.v. infusion of ¹⁴C-sucrose and ³H-PGF₂α into rats for 1 to 5 min, the globe/blood ratio of ³H was significantly lower than that of ¹⁴C. When isolated rat globes were incubated, the order of tracer uptake into the whole globe was AA>thiourea P`F₂α>sucrose, while the order of entry into the aqueous was thiourea>sucrose Á>-PGF₂α. The isolated rabbit cornea accumulated large amounts of ¹⁴C-AA which was not readily elutable and much smaller amounts of ³H-PGF₂α which was readily elutable. It is concluded that the sclera is highly permeable to PGF₂α, but that the cornea is an effective permeability barrier to this, and presumably all other PGs. The passage of AA through the outer coats of the globe is limited by its chemical incorporation into the cornea, sclera and conjunctiva. Thus, inhibition of the adverse intraocular effects of topically applied AA by topically applied drugs may only reflect the ability of these drugs to inhibit the synthesizing capacity of the superficial layers of the globe rather than that of the anterior uvea and other intraocular tissues.