The high yield of prostacyclin biosynthesis by the iris and its effects on the intraocular muscles.

Iris, and to a lesser extent ciliary body, from cat and rabbit produce considerable amounts of prostacyclin (PGI2) after incubation of the tissue with 1-14C arachidonic acid. These tissues also generate PGI2-like material after gentle squeezing. It is likely that major metabolites found previously in iris and aqueous humor actually were 6-keto-PGF1alpha. It is concluded that PGH2 and PGI2 are synthetized at the same location. PGI2 induces a contraction of the sphincter and dilator and a relaxation of the ciliary muscle if the tissues had been previously exposed to indomethacin. Thromboxane A2 (TxA2) has either no effect or may cause a slight relaxation of the sphincter.