Signal transduction systems for prostaglandins in the iris and ciliary body.

The limited information now available suggests that PGE2 receptors of intraocular muscles (the iris and ciliary muscles) can mobilize Ca2+, causing contraction, and can raise the cAMP level, which is generally associated with relaxation in smooth muscle. It is tempting to speculate that these two PGE2 effects might be localized to the iris sphincter and to the ciliary muscle fibers, respectively. This hypothesis could account for PGE-induced miosis and for increased uveoscleral outflow due to a decrease in resistance to the passage of fluid, which could occur when ciliary muscle fibers are in a relaxed state.