Effect of latanoprost, prostaglandin F(2)alpha and nipradilol on isolated bovine ciliary muscle.

PURPOSE: Ciliary muscle tone is considered to be an important factor for control of uveoscleral outflow. In an attempt to clarify the functional roles of the ciliary muscle in uveoscleral outflow, the effects of latanoprost, prostaglandin (PG)F(2)alpha or nipradilol, all of which are known to increase uveoscleral outflow, were investigated, using the bovine ciliary muscle. METHODS: We isolated longitudinal ciliary muscle from bovine eyes and investigated the effects of these three agents on the mechanical properties of this muscle using isometric tension recording methods. RESULTS: Latanoprost and PGF(2)alpha evoked small but discrete contractions at a concentration of 0.1 microM even during the sustained contraction evoked by 10 mM acetylcholine (ACh). However, nipradilol did not evoke any response at concentrations up to 0.1 mM. None of these agents had an effect on the amplitude of the ciliary muscle twitch contraction evoked by electrical field stimulation. CONCLUSIONS: Our findings indicate that these three agents have no relaxant effect on isolated bovine ciliary muscle even during the sustained contraction evoked by ACh. Further, these agents had no effect on the contraction evoked by field stimulation, which indicates that the drugs have no presynaptic effects. These results are inconsistent with the hypothesis that drugs that increase uveoscleral outflow relax the ciliary muscle with a consequent increase in uveoscleral outflow. Further investigation of the role of ciliary muscle contractility on uveoscleral outflow is warranted.